Effects of cooling dry cows under heat load conditions on mammary gland enzymatic activity, intake of food and water, and performance during the dry period and after parturition

Effect of heat stress during the dry period on milk yield and reproductive performance of Holstein cows

This study aimed to determine the influence of heat stress during the dry period on milk yield and reproductive performance of Holstein cows in a hot environment. Breeding and milk production records of cows, as well as meteorological data between 2017 and 2020 from a commercial dairy herd (n = 12,102 lactations), were used to determine the relationship between climatic conditions during the dry period (average of the temperature-humidity index (THI) at the beginning, middle, and end of the dry period) and reproductive efficiency and milk yield traits. THI was divided into < 70 (no heat stress), 70-80 (moderate heat stress), and > 80 (severe heat stress). First-service pregnancy rate of cows decreased (P < 0.01) with increasing hyperthermia during the dry period (9.5, 7.3, and 3.4% for THI < 70, 70-80, and > 80, respectively). All-service pregnancy rate was highest (P < 0.01) for cows not undergoing heat stress during the dry period (60.2%) and lowest (42.6%) for cows with severe heat stress during the dry period. Cows not experiencing heat stress during the dry period required a mean ± SD of 5.6 ± 3.8 services per pregnancy compared with 6.5 ± 3.6 (P < 0.01) for cows subjected to THI > 80 during the dry period. Cows not suffering heat stress during the dry period produced more (P < 0.01) 305-day milk (10,926 ± 1206 kg) than cows subjected to moderate (10,799 ± 1254 kg) or severe (10,691 ± 1297 kg) heat stress during the dry period. Total milk yield did not differ (P > 0.10) between cows not undergoing heat stress (13,337 ± 3346 kg) and cows subjected to severe heat stress during the dry period (13,911 ± 4018 kg). It was concluded that environmental management of dry cows during hot months is warranted to maximize reproductive performance and milk yield in the following lactation.

Effects of prenatal heat stress on birth weight and birth weight genetic parameters in German Holstein calves

The aim of this study was to infer the effects of heat stress (HS) during late gestation of dams on phenotypes and on direct and maternal genetic parameters for birth weight (BiW). We considered 171,221 Holstein calves kept in 56 large-scale co-operator herds. For a clear separation of maternal effects, only calves from dams with at least 3 offspring were included in the analyses. The genotype data set comprised 41,143 SNPs from 1,883 Holstein bulls. Temperature-humidity indices (THI) during the last 8 wk of gestation were calculated in each herd to reflect prenatal HS. A further prenatal HS descriptor was the first principal component (PC1) from principal component analysis considering the daily THI during the last 56 d of gestation. Regression coefficients of BiW on prenatal THI during the last 12 wk of gestation and PC1 were estimated in 13 consecutive phenotypic analyses. The strongest BiW decline was -0.63 kg per standardized THI, identified during 50 to 56 d before birth. A reaction norm model with weekly prenatal THI or PC1 nested within maternal genetic and maternal permanent environmental effects was defined to infer maternal sensitivity in response to prenatal THI alterations. Direct BiW heritabilities were close to 0.33 in the course of prenatal THI. Maternal BiW heritabilities marginally increased from 0.07 to 0.08 with increasing THI. Genetic correlations between maternal genetic effects at maximum HS levels and remaining THI were larger than 0.95, indicating the absence of genotype by time-lagged HS interactions. In contrast, maternal permanent environmental correlations between BiW at prenatal THI indicating HS with BiW at remaining THI substantially declined with increasing THI distances. Hence, from a herd management perspective, avoiding HS during the dry period of the dams will contribute to a slight increase in fetus growth.

The Impact of Heat Stress on Immune Status of Dairy Cattle and Strategies to Ameliorate the Negative Effects

Heat stress (HS) is well known to influence animal health and livestock productivity negatively. Heat stress is a multi-billion-dollar global problem. It impairs animal performance during summer when animals are exposed to high ambient temperatures, direct and indirect solar radiations, and humidity. While significant developments have been achieved over the last few decades to mitigate the negative impact of HS, such as physical modification of the environment to protect the animals from direct heat, HS remains a significant challenge for the dairy industry compromising dairy cattle health and welfare. In such a scenario, it is essential to have a thorough understanding of how the immune system of dairy cattle responds to HS and identify the variable responses among the animals. This understanding could help to identify heat-resilient dairy animals for breeding and may lead to the development of climate resilient breeds in the future to support sustainable dairy cattle production. There are sufficient data demonstrating the impact of increased temperature and humidity on endocrine responses to HS in dairy cattle, especially changes in concentration of hormones like prolactin and cortisol, which also provide an indication of the likely im-pact on the immune system. In this paper, we review the recent research on the impact of HS on immunity of calves during early life to adult lactating and dry cows. Additionally, different strategies for amelioration of negative effects of HS have been presented.

Programming effects of late gestation heat stress in dairy cattle

The final weeks of gestation represent a critical period for dairy cows that can determine the success of the subsequent lactation. Many physiological changes take place and additional exogenous stressors can alter the success of the transition into lactation. Moreover, this phase is pivotal for the final stage of intrauterine development of the fetus, which can have negative long-lasting postnatal effects. Heat stress is widely recognised as a threat to dairy cattle welfare, health, and productivity. Specifically, late gestation heat stress impairs the dam's productivity by undermining mammary gland remodelling during the dry period and altering metabolic and immune responses in early lactation. Heat stress also affects placental development and function, with relevant consequences on fetal development and programming. In utero heat stressed newborns have reduced birth weight, growth, and compromised passive immune transfer. Moreover, the liver and mammary DNA of in utero heat stressed calves show a clear divergence in the pattern of methylation relative to that of in utero cooled calves. These alterations in gene regulation might result in depressed immune function, as well as altered thermoregulation, hepatic metabolism, and mammary development jeopardising their survival in the herd and productivity. Furthermore, late gestation heat stress appears to exert multigenerational effects, influencing milk yield and survival up to the third generation.

Effects of Selenium as a Dietary Source on Performance, Inflammation, Cell Damage, and Reproduction of Livestock Induced by Heat Stress: A Review

Heat stress as a result of global warming has harmful consequences for livestock and is thus becoming an urgent issue for animal husbandry worldwide. Ruminants, growing pigs, and poultry are very susceptible to heat stress because of their fast growth, rapid metabolism, high production levels, and sensitivity to temperature. Heat stress compromises the efficiency of animal husbandry by affecting performance, gastrointestinal health, reproductive physiology, and causing cell damage. Selenium (Se) is an essential nutritional trace element for livestock production, which acts as a structural component in at least 25 selenoproteins (SELs); it is involved in thyroid hormone synthesis, and plays a key role in the antioxidant defense system. Dietary Se supplementation has been confirmed to support gastrointestinal health, production performance, and reproductive physiology under conditions of heat stress. The underlying mechanisms include the regulation of nutrient digestibility influenced by gastrointestinal microorganisms, antioxidant status, and immunocompetence. Moreover, heat stress damage to the gastrointestinal and mammary barrier is closely related to cell physiological functions, such as the fluidity and stability of cellular membranes, and the inhibition of receptors as well as transmembrane transport protein function. Se also plays an important role in inhibiting cell apoptosis and reducing cell inflammatory response induced by heat stress. This review highlights the progress of research regarding the dietary supplementation of Se in the mitigation of heat stress, addressing its mechanism and explaining the effect of Se on cell damage caused by heat stress, in order to provide a theoretical reference for the use of Se to mitigate heat stress in livestock.

Long-term heat stress at final gestation: physiological and heat shock responses of Saanen goats

The long exposure to heat negatively changes performance and productivity of animals, particularly when heat stress is associated with gestation. Indeed, little is known about the negative effects of long-term heat stress on the final gestation of dairy goats. In this context, the physiological and cellular responses of Saanen goats submitted to heat stress (37°C from 10:00 to 16:00 h) were investigated from day 60th pre-partum to day 60th post-partum. At final gestation, 46 pregnant Saanen goats were randomly assigned to the treatments: control (CT; thermal neutral conditions) and heat stress (HS; climatic chamber). After partum, all experimental goats were maintained in thermal neutral conditions. The rectal, dorsal, mammary temperatures and respiratory frequency, cortisol release, milk yield, milk quality, and the genes HSP60, HSP70, HSP90, Glucocorticoid receptor and ACTHR. Goats subjected to HS showed significantly (P < 0.05) higher rectal, dorsal, and mammary temperatures and significantly mobilized the increase of respiratory frequency to lose heat as compared to CT goats. The HS challenge significantly increased cortisol release from day 15th pre-partum to day 15th post-partum. CT goats produced more milk than HS from weeks 4 to 10 of lactation (P <0.001), with no difference in milk quality. However, on day 15th post-partum, there was a significant effect of HS treatment on the expression of HSP70 and ACTHR genes as compared to CT treatment, confirming the long-term effect of HS on Saanen goats. In conclusion, the physiological parameters studied increased pre-partum in the hottest hour, and cortisol peaked on day 15 pre-partum for heat-stressed goats. Although on the 15th day post-partum, all goats were in thermal comfort, and the physiological parameters were within the normal range, the concentration of cortisol continued to be significantly higher for goats submitted to thermal stress. Indeed, milk yield was greater for goats subjected to pre-partum thermal comfort. Furthermore, the expression of HSP70 and ACTHR genes on peripheral blood mononuclear cells are interesting biomarkers for studying the long-term effect of heat stress on Saanen goats.

Effect of injectable trace mineral supplementation on peripheral polymorphonuclear leukocyte function, antioxidant enzymes, health, and performance in dairy cows in semi-arid conditions

The objective of this study was to evaluate the effect of subcutaneous injections of 15 mg/mL Cu, 5 mg/mL Se, 60 mg/mL Zn, and 10 mg/mL Mn on health, performance, polymorphonuclear leukocyte (PMNL) function, circulating glutathione peroxidase (GPx) and superoxide dismutase (SOD) concentrations, and inflammation of dairy cows undergoing the transition period in high temperature-humidity index. A total of 923 multiparous cows from 2 commercial dairy farms were randomly allocated into 1 of 2 treatment groups as follows: control and injectable trace mineral supplementation (ITMS). Cows in the ITMS group received 7 mL of subcutaneous injections at dry-off (208 ± 3 d of gestation), 260 ± 3 d of gestation, and at 35 ± 3 d in milk (DIM). Data regarding health traits, reproductive performance, milk yield, and survivability were extracted from farm database software, and animals were followed-up until 300 DIM. For a subset of 142 cows from one herd, blood samples were collected at enrollment, and at 3 ± 1, 7 ± 1, 10 ± 1, and 35 ± 3 DIM to evaluate hematology, PMNL function, GPx and SOD concentrations, and circulating haptoglobin. Logistic regression was used to assess health and pregnancy per artificial insemination at first service. Cox proportional hazards models were used to evaluate hazard of pregnancy and culling. Mixed linear regression models accounting for repeated measures were used to assess all continuous variables collected over time. Parity, twinning, and previous gestation length were considered as potential confounders. Farm was included as a random effect. The ITMS cows tended to have lower incidence of metritis and stillbirth compared with control group. However, ITMS treatment did not influence the incidence of other diseases (e.g., mastitis, retained placenta), milk yield, reproductive performance, culling, and leukocyte count. Neutrophil-to-lymphocyte ratio, PMNL phagocytosis, and oxidative burst as well as intensity of the oxidative burst were greater for ITMS-treated cows in comparison to control cows. The ITMS cows had decreased expression of the adhesion molecule L-selectin on PMNL surface. The serum concentration of GPx and SOD were not affected by ITMS treatment. In conclusion, ITMS tended to reduce the incidence of metritis and stillbirth parturition, improved PMNL function, and improved the inflammatory status of dairy cows undergoing the transition period in high temperature-humidity index conditions. However, these findings did not translate into improved milk yield, reproductive performance, and survivability.

Dry Period Heat Stress Impacts Mammary Protein Metabolism in the Subsequent Lactation

Simple Summary

Heat stress during the dry period of dairy cows reduces milk yield in the following lactation. Factors such as altered mammary metabolism could impact yields and alter milk composition, including milk protein. We sought to determine if exposure to dry period heat stress would influence mammary milk protein metabolism during the subsequent lactation. Objectives were to first determine the impact of dry period heat stress on milk protein yields and secondly characterize the amino acid and protein profiles in the mammary tissue, milk, and blood to elucidate potential carry-over impact of dry period heat stress on systems that participate directly in milk protein metabolism (i.e., mTOR). We found that heat stress during the dry period reduces milk yield, protein content, and protein yield in the subsequent lactation. The plasma amino acid profile and mammary amino acid transporters are altered in dry period heat-stressed cows, and mammary mTOR signaling proteins are differentially expressed as well. It appears that dry period heat stress impacts mammary metabolism with consequences on milk yield and protein content. The continuous production of high-quality and -quantity milk is vital as a sustainable source of protein in the face of rising global temperatures.

Abstract

Dry period heat stress impairs subsequent milk production, but its impact on milk protein content and yield is inconsistent. We hypothesize that dairy cow exposure to dry period heat stress will reduce milk protein synthesis in the next lactation, potentially through modified amino acid (AA) transport and compromised mTOR signaling in the mammary gland. Cows were enrolled into heat-stressed (dry-HT, n = 12) or cooled (dry-CL, n = 12) treatments for a 46-day dry period then cooled after calving. Milk yield and composition and dry matter intake were recorded, and milk, blood, and mammary tissue samples were collected at 14, 42, and 84 days in milk (DIM) to determine free AA concentrations, milk protein fractions, and mammary AA transporter and mTOR pathway gene and protein expression. Dry matter intake did not significantly differ between treatments pre- or postpartum. Compared with dry-CL cows, milk yield was decreased (32.3 vs. 37.7 ± 1.6 kg/day) and milk protein yield and content were reduced in dry-HT cows by 0.18 kg/day and 0.1%. Further, dry-HT cows had higher plasma concentrations of glutamic acid, phenylalanine, and taurine. Gene expression of key AA transporters was upregulated at 14 and 42 DIM in dry-HT cows. Despite minor changes in mTOR pathway gene expression, the protein 4E-BP1 was upregulated in dry-HT cows at 42 DIM whereas Akt and p70 S6K1 were downregulated. These results indicate major mammary metabolic adaptations during lactation after prior exposure to dry period heat stress.

Cooling ameliorates decreased milk protein metrics in heat-stressed lactating Holstein cows

Cooling can alleviate the negative consequences of heat stress on multiple milk production metrics in dairy cows. However, it is still controversial whether cooling can increase milk protein content compared with heat-stressed cows. The objective of the present study was to evaluate the relief effect of cooling on the decrease in milk protein concentration during heat stress and elucidate the potential metabolic mechanisms. Thirty lactating multiparous Holstein cows (days in milk = 175 ± 25 d, milk yield = 27.5 ± 2.5 kg/d; mean ± SD) were assigned to 1 of 3 treatments: heat stress (HS; n = 10), cooling (CL; n = 10), and cooling with pair-feeding (PFCL; n = 10). The barns for PFCL and CL cows were equipped with sprinklers and fans, whereas the barn for HS cows were not. The average temperature-humidity index during the experiment ranged from 74 to 83. The spraying was activated automatically 2 times per day (1130-1330 h and 1500-1600 h) with 3 min on and 6 min off during the first 2 wk, and 1.5 min on and 3 min off during the last 2 wk, whereas the fans operated 24 h/d. The experiment lasted for 4 wk in total. Milk, urine, feces, total mixed ration, blood, and rumen fluid samples were collected weekly. Compared with HS, feed efficiency (1.24 and 1.49), milk protein yield (0.82 and 0.94 kg/d), and milk fat yield (0.98 and 1.26 kg/d) were increased in PFCL, whereas the differences between CL and HS were not significant. Compared with HS cows, PFCL and CL cows had a lower respiratory rate (70.6, 59.1, and 60.3 breaths per minute, respectively), rectal temperature (38.95, 38.61, and 38.51°C), and shoulder skin temperature (33.95, 33.25, 33.40°C), and had greater milk protein content (3.41, 3.72, and 3.69%) and milk fat percent (4.08, 4.97, 4.65%). Both the blood activity of catalase (increased by 12.8 and 41.0%) and glutathione peroxidase (12.6 and 40.4%) of PFCL and CL cows were greater than the HS cows. Compared with HS, cooling increased the blood content of glucose, methionine, threonine, and cystathionine by 10.7% and 10.3%, 19.0% and 9.5%, 15.8% and 12.0%, and 9.5% and 23.8% in PFCL and CL, respectively. In conclusion, the results indicated that cooling partially rescued milk protein synthesis induced by heat stress, and the potential mechanism may have been due to increased antioxidant ability, blood glucose, and key AA. Consequently, in addition to modifying the environment, nutritional and physiological strategies designed to influence carbohydrate, AA, and oxidative homeostasis may be an opportunity to maintain or correct low milk protein content during the warm summer months.

Critical Temperature-Humidity Index Thresholds for Dry Cows in a Subtropical Climate

The effects of heat stress on dry cows are profound and significantly contribute to lower overall welfare, productivity, and profitability of the dairy sector. Although dry cows are more thermotolerant than lactating cows due to their non-lactating state, similar environmental thresholds are currently used to estimate the degree of heat strain and cooling requirements. Records of dry cow studies conducted over 5 years in Gainesville, Florida, USA were pooled and analyzed to determine environmental thresholds at which dry cows exhibit signs of heat stress in a subtropical climate. Dry-pregnant multiparous dams were actively cooled (CL; shade of a freestall barn, fans and water soakers, n = 107) or not (HT; shade only, n = 111) during the last 7 weeks of gestation, concurrent with the entire dry period. Heat stress environmental indices, including ambient temperature, relative humidity, and temperature-humidity index (THI), and animal-based indices, including respiration rate, rectal temperature and daily dry matter intake were recorded in all studies. Simple correlations were performed between temperature-humidity index and each animal-based indicator. Differences in respiration rate, rectal temperature and dry matter intake between treatments were analyzed by multiple regression. Using segmented regression, temperature-humidity thresholds for significant changes in animal-based indicators of heat stress were estimated. Stronger significant correlations were found between the temperature-humidity index and all animal-based indices measured in HT dry cows (−0.22 ≤ r ≤ 0.35) relative to CL dry cows (−0.13 ≤ r ≤ 0.19). Although exposed to similar temperature-humidity index, rectal temperature (+0.3°C; P &lt; 0.001) and respiration rate (+23 breaths/min; P &lt; 0.001) were elevated in HT dry cows compared with CL cows whereas dry matter intake (−0.4 kg of dry matter/d; P = 0.003) was reduced. Temperature-humidity index thresholds at which respiration rate and rectal temperature began to change were both determined at a THI of 77 in HT dry cows. No significant temperature-humidity threshold was detected for dry matter intake. At a practical level, our results demonstrate that dry cow respiration rate and rectal temperature increased abruptly at a THI of 77 when provided only shade and managed in a subtropical climate. Therefore, in the absence of active cooling, dry cows should be closely monitored when or before THI reaches 77 to avoid further heat-stress related impairments during the dry period and the subsequent lactation and to mitigate potential carry-over effects on the offspring.

Use of the Comprehensive Climate Index to estimate heat stress response of grazing dairy cows in a temperate climate region

The aim of the study was to assess the effect of the summer thermal environment on physiological responses, behaviour, milk production and its composition on grazing dairy cows in a temperate climate region, according to the stage of lactation. Twenty-nine Holstein Friesian multiparous cows were randomly selected and divided into two groups, according to the days in milk, as mid-lactation (99 to 170 d in milk, n = 15) and late lactation (225 to 311 d in milk, n = 14). The comprehensive climate index (CCI) was used to classify the hour of each day as thermoneutral or heat stress, considering a threshold value of CCI of 20°C. Data were collected for 16 d (summer 2017) and analysed as a completely randomized 2 × 2 factorial arrangement with repeated measurements over time. Vaginal temperature increased with CCI ≥ 20°C. Respiration rates were dependent on the thermal condition, regardless of days in milk. There was an interaction between the time of day and the CCI category for activity and rumination. Grazing activity decreased by 17.6% but lying down, standing, and shaded animals increased by 1.6, 9.8, and 6.3% respectively when CCI ≥ 20°C. Over 80% of cows presented a panting score ≥1. However, milk production and composition (fat, protein, and lactose concentrations as well as somatic cell count) were not affected by the thermal condition, although there was a numerical (non-significant) decrease in afternoon milk protein concentration on days with CCI ≥ 20°C, while urea in milk increased. In conclusion, thermal condition challenged grazing dairy cows' behaviour and physiology independent of the stage of lactation but had little or no effect on milk production.

Access to shade during the dry period improves the performance of multiparous Holstein cows

Context Heat stress (HS) has a negative effect on milk production and on the final period of gestation. There is almost no information of HS effect on dairy cows with temperature–humidity index (THI) less than 72 and more than 68. Aim Determine the effect of voluntary access to shade during the dry period on physiological parameters and subsequent postpartum performance of Holstein cows. Methods Twenty-six multiparous cows were used in a randomised complete-block design to evaluate two treatments: without access to shade (CON) and with voluntary access to shade (SHA) for 62 ± 5.3 days before calving. During the dry period, cows were housed in two yards. After calving, cows were managed all together. The THI was used to characterise environmental conditions. During the dry period, rectal temperature (7:00 am and 5:00 pm), respiration rate (7:00 am, 1:00 pm and 5:00 pm) and animal behaviour (feed intake, rumination and standing) were measured. Dry matter (DMI) and water intake, bodyweight, body condition score, and serum insulin and non-esterified fatty acid concentrations were measured during dry and lactation periods. At calving, calf weight, composition of colostrum, placenta weight, cotyledon number and weight were recorded. During the lactation period, production and composition of milk and resumption of ovarian activity were measured. Key results Average THI during dry and lactation periods were 70.7 ± 4.88 and 57.2 ± 6.53 respectively. During the dry period, SHA cows had a lower respiration rate at 1:00 p.m. (56 ± 0.8 vs 67 ± 0.8 breath per minute (b.p.m), P &lt; 0.0001) and at 5:00 p.m. (48 ± 0.8 vs 55 ± 0.8 b.p.m, P = 0.04), and higher DMI (12.0 ± 0.07 vs 11.4 ± 0.07 kgDM/cow.day, P &lt; 0.0001) than did CON cows. Shaded cows produced more solid-corrected milk (30.4 ± 0.31 vs 29.5 ± 0.31 kg/cow.day, P = 0.04), fat (1.48 ± 0.040 vs 1.33 ± 0.040 kg/cow.day, P = 0.01) and protein (1.12 vs 1.03 ± 0.015 kg/cow.day, P = 0.01). Conclusion There was no effect of access to shade on calf weight, colostrum composition, placenta characteristics, serum non-esterified fatty acid and insulin concentrations, body condition score evolution, lactation DMI and days to first ovulation postpartum. Implications HS during the last 60 days of gestation negatively affected solid-corrected milk, daily fat and protein production.

Feed intake-dependent and -independent effects of heat stress on lactation and mammary gland development

With a growing population, a reliable food supply is increasingly important. Heat stress reduces livestock meat and milk production. Genetic selection of high-producing animals increases endogenous heat production, while climate change increases exogenous heat exposure. Both sources of heat exacerbate the risk of heat-induced depression of production. Rodents are valuable models to understand mechanisms conserved across species. Heat exposure suppresses feed intake across homeothermic species including rodents and production animal species. We assessed the response to early-mid lactation or late-gestation heat exposure on milk production and mammary gland development/function, respectively. Using pair-fed controls we experimentally isolated the feed intake-dependent and -independent effects of heat stress on mammary function and mass. Heat exposure (35°C, relative humidity 50%) decreased daily feed intake. When heat exposure occurred during lactation, hypophagia accounted for approximately 50% of the heat stress-induced hypogalactia. Heat exposure during middle to late gestation suppressed feed intake, which was fully responsible for the lowered mammary gland weight of dams at parturition. However, the impaired mammary gland function in heat-exposed dams measured by metabolic rate and lactogenesis could not be explained by depressed feed consumption. In conclusion, mice recapitulate the depressed milk production and mammary gland development observed in dairy species while providing insight regarding the role of feed intake. This opens the potential to apply genetic, experimental, and pharmacological models unique to mice to identify the mechanism by which heat is limiting animal production.

Impact of Maternal High Stocking Density during the Dry Period on Dairy Calf Health, Behaviour, and Welfare

Simple Summary

Negative impacts of stressful maternal experience during pregnancy on offspring health and behaviour have been reported in various mammalian species including humans, laboratory animals, and farm animals. This study investigated the effect of limited space allowance for dairy cows during late gestation on the growth and behaviour of their offspring during the pre-weaning period. Our results indicated associations between maternal high stocking density and a higher frequency of social behaviours and increased behavioural reactivity to weaning in offspring. Maternal high stocking density also reduced behavioural reactions of healthy offspring to a painful procedure. However, there was no association between maternal high stocking density and offspring growth or behaviour in the first week of life. To our knowledge, this study is the first to attempt to demonstrate associations between maternal stocking density during late pregnancy and offspring behaviour in dairy cattle.

Abstract

This study aimed to investigate the effect of maternal stocking density during late pregnancy (approximately 60 ± 4 days before calving) on offspring performance during the pre-weaning period. Forty-five dairy calves were born to cows that went through either industry minimum standards (H: n = 24, high stocking density) or more extensive space allowances (L: n = 21, low stocking density) during the dry period. Body weight and average daily gain during the pre-weaning period (day 1–49) were measured. Observations were made of: (i) activity levels (day 2–6); ii) the level of training required to use an automatic feeder, and behavioural reactions to the group environment (d7); (iii) feeding and social behaviour in the group pen (day 7–21); and (iv) responses to weaning (day 40–49) and disbudding (day 28+). Compared to L calves, H calves made more frequent social contacts with pen mates in the group pen (p = 0.003) and decreased their lying time around weaning (p = 0.045). Among the healthy calves, L calves displayed more severe behavioural reactions to the disbudding procedure (p < 0.001), a significant increase in salivary cortisol concentrations (p = 0.013), and more frequent pain-related behaviour (p = 0.036). This study indicated associations between maternal stocking density during late pregnancy and some welfare-relevant offspring outcomes during the pre-weaning period; these effects were found to be modulated by offspring health status.

Genotype by environment interaction due to heat stress during gestation and postpartum for milk production of Holstein cattle

Remarkable increases in the production of dairy animals have negatively impacted their tolerance to heat stress (HS). The evaluation of the effect of HS on milk yield is based on the direct impact of HS on performance. However, in practical terms, HS also exerts its influence during gestation (indirect effect). The main purpose of this study was to identify and characterize the genotype by environment interaction (G × E) due to HS during the last 60 days of gestation (THI_g) and also the HS postpartum (THI_m) over first lactation milk production of Brazilian Holstein cattle. A total of 389 127 test day milk yield (TD) records from 1572 first lactation Holstein cows born in Brazil (daughters of 1248 dams and 70 sires) and the corresponding temperature-humidity index (THI) obtained between December 2007 and January 2013 were analyzed using different random regression models. Cows in the cold environment (THI_g = 64 to 73) during the last 60 days of gestation produced more milk than those cows in a hot environment (THI_g = 74 to 84), particularly during the first 150 days of lactation (DIM). The heritabilities (h2) of TD were similar throughout DIM for cows in THI_g hot (0.11 to 0.20) or (0.10 to 0.22), while the genetic correlations (rg) for TD between these two environments ranged from 0.11 to 0.52 along the first 250 DIM. The h2 estimates for TD across THI_m were similar for cows in THI_g hot (0.07 to 0.25) and THI_g cold (0.08 to 0.19). The rg estimates ranged from 0.17 to 0.42 along THI_m between TD of cows in cold and hot THI_g. The results were consistent in demonstrating the existence of an additional source of G × E for TD due to THI_g and THI_m. The present study is probably the first to provide evidence of this source of G × E; further research is needed because of its importance when the breeding objective is to select animals that are more tolerant to HS.

Carry over effects of late-gestational heat stress on dairy cattle progeny

The impacts of late gestation heat stress on the dam and her subsequent lactation are well-recognized. However, more recent research has demonstrated the long-lasting and severe negative consequences on the in-utero heat-stressed progeny. Dairy calves born to late gestation heat-stressed dams weigh less at birth and up to one year of age and have compromised metabolism and immune function. In-utero programming of these offspring may coordinate alterations in thermoregulation, mammary development, and milk synthetic capacity at different developmental windows. Thus, prenatally heat-stressed dairy heifers will produce less milk across multiple lactations and have a lower herd survival rate, potentially negatively impacting the U.S. dairy economy. Dry period heat stress abatement strategies should be considered not only for the productivity and welfare of the pregnant dam but also for the developing calf.

Late gestation heat stress in dairy cows: Effects on dam and daughter

In dairy cattle, the final weeks before parturition are physiologically challenging and an important determinant of subsequent production performance. External stressors should be carefully managed during this period to avoid adding strain on the animals. Late-gestation heat stress impairs productivity in the dam and exerts transgenerational effects on progeny. Physiological responses are complex and detriments to performance are multifaceted. Late-gestation heat stress blunts mammary gland involution in the first half of the dry period and impairs cell proliferation as calving approaches. Moreover, cows that were exposed to prepartum heat-stress exhibit reduced adipose tissue mobilization and a lower degree of insulin resistance during early lactation. Prepartum heat exposure also depresses immune function and evidence links this decrease to altered prolactin signaling under heat stress. Placental functions are also impaired as reflected in a higher cotyledon mass but lower maternal circulating estrone sulfate concentrations, potentially resulting in lower nutrient supply and reduced calf birth weight. In addition, calves born to heat-stressed dams show impaired immune function and therefore higher disease susceptibly. Novel evidence reported that intrauterine heat stress alters the methylation profile of liver and mammary DNA, which may also contribute to the poorer performance during adulthood of calves exposed to heat stress in utero. Understanding the contribution of all altered biological systems during late-gestation heat stress can be used as a basis for improving cow management during the dry period. This article provides a review of the impacts of late-gestation heat stress and of the emerging understanding of the biological mechanisms that underlie the observed impairments of performance.

Physiological, health, lactation, and reproductive traits of cooled dairy cows classified as having high or low core body temperature during the dry period1

Primary objectives of this study were to compare concentrations of pregnancy-associated glycoprotein (PAG) before calving, prolactin (PRL) after calving, and energy balance indicators before and after calving in cooled cows classified as having high (HT) or low (LT) core body temperature (CBT) during the dry period. Secondary objectives were to investigate associations between dry-period CBT and likelihood of cows developing health disorders, and compare health, productive and reproductive traits of HT and LT cows. Dry Holstein cows (n = 260) with 250 to 260 d of gestation from three herds were enrolled in the study during summer. Cows were provided evaporative cooling during the dry and lactating period. The vaginal temperature was recorded in 5-min intervals during 7 consecutive days and cows were classified as HT or LT. Blood samples were collected weekly from enrollment until 14 ± 3 d in milk (DIM). Additional blood samples were collected within 12 h postpartum from a subgroup of cows (n = 25) to determine PRL concentration. Cows were monitored for health disorders, productive, and reproductive performance until 13 wk of the subsequent lactation. High temperature cows had shorter (P < 0.01) gestation length (273.9 ± 0.9 vs. 278.2 ± 0.9 d) and greater (P < 0.01) incidence of twinning (19.7 vs. 4.2%) than LT cows. Cows classified as HT had greater (P = 0.02) PAG concentration (134.1 ± 4.9 vs. 117.4 ± 4.9 ng/mL), but postpartum PRL concentration did not (P = 0.55) differ between HT and LT cows. Primiparous HT cows had greater (P = 0.05) prepartum nonesterified fatty acids concentration (135, 95% CI = 102 to 178 vs. 104, 95% CI = 75 to 144 mmol/dL) than primiparous LT cows, but no differences (P = 0.72) were observed between CBT group in multiparous cows. The concentration of β-hydroxybutyrate was greater (P = 0.04) for LT compared with HT cows at 7 ± 3 DIM. The quadratic effect of CBT tended (P = 0.09) to be associated with risk of health disorders within 60 DIM. Milk yield tended (P = 0.10) to be greater for LT compared with HT cows (49.3 ± 1.9 vs. 46.2 ± 1.6 kg). Pregnancy per AI at first service did not (P = 0.64) differ between HT and LT cows. In conclusion, HT cows have distinct concentrations of PAG in late gestation and energy balance indicators during the transition period. In addition, CBT assessment during the dry period may be a useful tool to identify cows expected to have impaired health and milk yield in the subsequent lactation.

Heat Stress Impacts Immune Status in Cows Across the Life Cycle

Heat stress has a myriad of effects on dairy cattle across the life cycle. Whereas, the most commonly recognized impacts are associated with production responses, emerging evidence indicates that heat stress profoundly alters the immune response of calves and cows, from the prenatal stage through lactation. For example, in utero heat stress reduces passive immune transfer regardless of colostrum source, relative to normothermic conditions in late gestation. Dry cows exposed to heat stress have lower immunoglobulin responses to ovalbumin vaccination, but this effect dissipates with cooling following parturition. Conversely, cows under heat stress when dry exhibit carryover effects on the innate arm of the immune system in early lactation. In this paper we review the effects of heat stress throughout the life cycle of the dairy cow, with particular emphasis on the impact of heat stress during late gestation on the cow and the developing fetus, both before and after parturition. In addition, the impact of altered immune status under heat stress on other physiological systems, especially those supporting milk production, are considered. Finally, management interventions to prevent and reverse the effect of heat stress are presented.

Dry period heat stress induces microstructural changes in the lactating mammary gland

The bovine dry period is a non-lactating period between consecutive lactations characterized by mammary gland involution and redevelopment phases to replace senescent mammary epithelial cells with active cells primed for the next lactation. Dairy cows exposed to heat stress during the dry period experience milk yield reductions between 3–7.5 kg/d in the next lactation, partially attributed to processes associated with mammary cell growth and turnover during the dry period. However, the carry-over impact of dry period heat stress on mammary morphology during lactation has yet to be determined. In the current study, we hypothesized that exposure to heat stress during the dry period would alter alveolar microstructure and cellular turnover (i.e. proliferation and apoptosis) during lactation. Cows were either subjected to heat stress (HT, access to shade; n = 12) or cooling (CL, access to shade, fans, and soakers; n = 12) for a 46 d dry period. Upon calving, all cows were treated similarly with access to cooling for their entire lactation. Six cows per treatment were randomly selected for mammary gland biopsies at 14, 42, and 84 days in milk. Tissues were sectioned and stained for histological analysis. During lactation, HT cows produced 4 kg less colostrum and 3.7 kg less milk compared with CL cows. Lactating mammary gland microstructure was impacted after exposure to dry period heat stress; HT cows had fewer alveoli and a higher proportion of connective tissue in the mammary gland relative to CL cows, however alveolar area was similar between treatments. Rates of mammary epithelial cell proliferation and apoptosis were similar between treatment groups. This suggests that heat stress exposure during the dry period leads to reductions in milk yield that could be caused, in part, by a reduction in alveoli number in the lactating mammary gland but not to dynamic alterations in cellular turnover once lactation is established.

The impact of heat stress on the immune system in dairy cattle: A review

Heat stress is well documented to have a negative influence on livestock productivity and these impacts may be exacerbated by climate change. Dairy cattle can be more vulnerable to the negative effects of heat stress as these adverse impacts may be more profound during pregnancy and lactation. New emerging diseases are usually linked to a positive relationship with climate change and the survival of microrganisms and/or their vectors. These diseases may exaggerate the immune suppression associated with the immune suppressive effect of heat stress that is mediated by the hypothalamic-pituitary-adrenal (HPA) and the sympathetic-adrenal-medullary (SAM) axes. It has been established that heat stress has a negative impact on the immune system via cell mediated and humoral immune responses. Heat stress activates the HPA axis and increases peripheral levels of glucocorticoids subsequently suppressing the synthesis and release of cytokines. Heat stress has been reported to induce increased blood cortisol concentrations which have been shown to inhibit the production of cytokines such as interleukin-4 (IL-4), IL-5, IL-6, IL-12, interferon γ (IFNγ), and tumor necrosis factor-α (TNF- α). The impact of heat stress on the immune responses of dairy cows could be mediated by developing appropriate amelioration strategies through nutritional interventions and cooling management. In addition, improving current animal selection methods and the development of climate resilient breeds may support the sustainability of livestock production systems into the future.

Short communication: Effect of barn climate and management-related factors on bovine colostrum quality

Several factors have been reported to influence colostrum quality (immunoglobulin concentration). To date, knowledge of the influence of climatic factors in association with other potential influencing factors on colostrum quality is scarce. Associated influential factors are parity, body condition score, length of dry period, ration fed ante partum (AP), β-hydroxybutyrate postpartum (PP), milk yield, milk fat and protein, as well as somatic cell counts from previous and current lactation. The objective of the present study was to examine the effect of barn climate and the aforementioned factors on colostrum quality. Data were collected from 1,381 multiparous Holstein Friesian cows kept on one dairy farm over a period of one year (August 2014 to August 2015). Colostrum was harvested on farm within 1 h PP. The quantity and quality of first colostrum (estimated by Brix refractometry) were recorded for each cow. Additional data recorded were parity, body condition score at drying off, length of dry period, ration fed AP, milk yield data from previous and current lactation, milk somatic cell counts, and β-hydroxybutyrate PP. During the study period, temperature and humidity were recorded in the barn every hour, and temperature-humidity-index (THI) was calculated. Linear regression was performed with colostrum quality as the dependent variable. In the final model, colostrum quantity (L), length of dry period, parity, and climatic factors (specifically, median humidity in the 3rd week AP and hours with THI ≥72 in the last 14 and 21 d AP, respectively) were significant. Colostrum quality improved with parity and length of dry period and decreased with colostrum quantity, humidity, and hours with a THI ≥72. A classification and regression tree analysis revealed that colostrum quantity was the most important factor in this model [normalized importance (NI) 100%]. Parity (NI 42.7%), length of dry period (NI 37.1%), and climatic factors (NI 0.4 to 1.9%) followed with decreasing importance. These results indicate that the most important factors for colostrum quality (i.e., colostrum quantity and parity) may not be influenced by management. The 2 factors that can be influenced by management [i.e., length of dry period and THI (e.g., by cooling)], were quantitatively of minor importance compared with the other 2 factors. Further studies are necessary to determine whether changing these factors can improve colostrum quality significantly.

PHYSIOLOGY SYMPOSIUM: Effects of heat stress during late gestation on the dam and its calf12

Heat stress during late gestation in cattle negatively affects the performance of the dam and its calf. This brief exposure to an adverse environment before parturition affects the physiological responses, tissue development, metabolism, and immune function of the dam and her offspring, thereby limiting their productivity. During the dry period of a dairy cow, heat stress blunts mammary involution by attenuating mammary apoptosis and autophagic activity and reduces subsequent mammary cell proliferation, leading to impaired milk production in the next lactation. Dairy cows in early lactation that experience prepartum heat stress display reduced adipose tissue mobilization and lower degree of insulin resistance in peripheral tissues. Similar to mammary gland development, placental function is impaired by heat stress as evidenced by reduced secretion of placental hormones (e.g., estrone sulfate) in late gestation cows, which partly explains the reduced fetal growth rate and lighter birth weight of the calves. Compared with dairy calves born to dams that are exposed to evaporative cooling during summer, calves born to noncooled dry cows maintain lower BW until 1 yr of age, but display a stronger ability to absorb glucose during metabolic challenges postnatally. Immunity of the calves, both passive and cell-mediated immune function, is also impaired by prenatal heat stress, resulting in increased susceptibility of the calves to diseases in their postnatal life. In fact, dairy heifers born to heat-stressed dry cows without evaporative cooling have a greater chance leaving the herd before puberty compared with heifers born to dry cows provided with evaporative cooling (12.2% vs. 22.7%). Dairy heifers born to late-gestation heat-stressed dry cows have lower milk yield at maturity during their first and second lactations. Emerging evidence suggests that late-gestation heat stress alters the mammary gland microstructure of the heifers during the first lactation and exerts epigenetic alterations that might explain, in part, their impaired productivity.

Effect of heat stress during early, late, and entire dry period on dairy cattle

Cooling during the entire dry period abates the negative effects of heat stress postpartum, yet the temporal relationship of cooling (i.e., early or late dry period) to performance is unknown. We evaluated the effect of heat stress early, late, and for the entire dry period on subsequent performance. Cows were selected based on mature-equivalent milk yield and dried off 45 d before expected calving. Cows were blocked by parity, previous 305-d mature equivalent milk yield, and body weight (BW) and randomly assigned to cooling (shade, fans, and soakers; CL) or heat stress (shade; HT). Treatments included CL (n = 20) or HT (n = 18) during the entire dry period, HT during the first 3 wk dry and then CL until calving (HTCL, n = 21), or CL during the first 3 wk dry period and then HT until calving (CLHT, n = 19). Heat stress increased rectal temperature (RT; CL, 38.8; HT, 39.1 ± 0.04°C) and respiration rate (RR; CL, 52.9; HT, 70.5 ± 1.9 breaths/min) during the early dry period. In the late dry period, HT increased RT and RR relative to CL cows (RT = CL, 38.7; HT, 39.1; CLHT, 39.1; HTCL, 38.9 ± 0.05°C; RR = CL, 47; HT, 64; CLHT, 66; HTCL, 53 ± 2.1 breaths/min). During the early dry period, HT decreased dry matter intake (CL, 11.8; HT, 10.5 ± 0.35 kg/d) but dry matter intake did not differ among treatments during late dry period (HT, 10.7; HTCL, 11.1; CL, 11.2; CLHT, 10.1 ± 0.55 kg/d). Cows exposed to prepartum cooling during the entire dry period had increased dry matter intake compared with cows exposed to heat stress during the late dry period (CL vs. CLHT, 11.2 ± 0.55 and 10.1 ± 0.55 kg/d, respectively). Heat stress at any time reduced gestation length compared with cows under prepartum cooling during the entire dry period (CL, 277 vs. HT, 274; CLHT, 273; and HTCL, 274 ± 1.17 d). Dry period length decreased by approximately 4 d if cows were exposed to HT at any time. During the early dry period, HT decreased BW, whereas CL increased BW relative to that at dry-off (CL, 6.9; HT, -9.4 ± 3.7 kg). In the late dry period, we detected no differences in BW gain among treatments, but cows exposed to prepartum cooling for the entire dry period tended to have increased BW gain compared with HT and HTCL. Prepartum cooling during the early or late dry period alone partially rescued milk yield only in the first 3 wk of lactation (CL, 32.9; HT, 26.6; CLHT, 29.7; HTCL, 30.7 ± 1.37 kg/d). Cooling for the entire dry period increased milk yield up to 30 wk into lactation compared with all other treatments. Thus, HT at any time during the dry period compromises performance of cows after calving.

Animal factors associated with core body temperature of nonlactating dairy cows during summer

The primary objectives of the current study were to investigate animal factors associated with core body temperature (CBT) and to determine the time of the day in which CBT assessment best describes the magnitude of hyperthermia throughout the day of heat-stressed dry cows. The secondary objective was to develop a predictive model for CBT of dry cows. Nonlactating Holstein cows (n = 105) with 250 to 260 d of gestation from 2 commercial dairies were enrolled in the study during summer. During 4 consecutive days, CBT from all cows was recorded in 5-min intervals and average CBT was calculated for each cow. In addition, mean, maximum, minimum, and standard deviation of daily CBT were calculated and using these measures cows were categorized as having high temperature (HT) or low temperature (LT) based on the median values. Cows carrying twins had greater (P < 0.01) CBT than cows bearing singletons (39.07 ± 0.07 vs. 38.84 ± 0.03 °C). Average CBT decreased (P < 0.01) 0.015 ± 0.004 °C for each 1-d increase in gestation length. Cows in Dairy A tended (P = 0.09) to have lower CBT than cows in Dairy B (38.91 ± 0.04 vs. 39.00 ± 0.06 °C). Season of birth, lactation number, body condition score category, previous projected 305-d mature equivalent milk yield, days in milk at dry-off, days after dry-off at enrollment, days of gestation at enrollment, and calf sex were not associated (P > 0.12) with CBT. Principal component analyses showed that 71% of the variance of CBT was explained by the first principal component alone, which was correlated with mean CBT (r = 0.99). Among all time points assessed, CBT recorded at 2215 h had the highest correlation with the first principal component (r = 0.93). The best agreement for classifying cows as HT or LT was between mean daily CBT and assessment at 2215 h (k = 0.73). The model that resulted in best predictivity (0.56) of average CBT included the following variables: dairy, gestation length, and twinning. In conclusion, findings from the present study suggest that CBT assessed between 250 and 260 d of gestation is negatively associated with gestation length and cows bearing twins have greater CBT than singletons. Our results indicate that the best time of the day to evaluate severity of heat stress in dry cows is 2215 h. Predictive models for CBT of dry cows should include dairy, twinning, and gestation length.

TRIENNIAL LACTATION SYMPOSIUM/BOLFA: Late gestation heat stress of dairy cattle programs dam and daughter milk production

Anticipated increases in the world population to 9 billion people will lead to increased demand for food. Dairy products represent one of the most sustainable animal sources of food protein because ruminants can utilize byproduct and forage feeds unsuitable for human consumption. Continued improvements in productivity will depend on deeper understanding of the biology of lactation, including developmental programming of tissues critical to that process. Although prenatal programming of postnatal phenotype is well documented for growth, behavior, and disease, there may also be instances of "programming" that last for a specific physiological stage (e.g., lactation). We distinguish between these 2 terms by the use of developmental programming to describe a permanent effect, whereas the more general term is used to describe nonpermanent impacts on the mammary gland. Despite this complexity, here we review the evidence that exposure to elevated temperature and humidity during late gestation can program reduced yields in the subsequent lactation, largely through effects at the mammary gland. Furthermore, we provide emerging evidence that adult capacity for milk synthesis can be programmed in the calf that dam is carrying by events during fetal life occurring 2 yr before. Specifically, calves born to dams that are heat stressed for the final 6 wk of gestation produce 19% less milk in lactation relative to calves from dams provided with evaporative cooling. Importantly, the increased milk yield in animals derived from dams under evaporative cooling occurred without a greater decline in BW that accompanies negative energy balance during early lactation. Therefore, the increase in milk production suggests an increase in the efficiency of conversion of feed to milk. These data indicate that a brief period of heat stress late in development reduces the physiological efficiency of the cow in a coordinated manner to result in a substantial decline in productivity. It is likely that this programming effect would be observed across genetic lines and result in poor sustainability of milk production. Milk will continue to be an important source of high-quality, human-edible food and technologies that improve the efficiency of production will be critical to enhance sustainability. These data provide compelling support for the concept that programming impacts on the dam and the developing fetus will play a role in optimizing the efficiency of production.

Evaporative cooling in late gestation heat-stressed Murrah buffaloes increases efficiency of next reproductive cycle

Evaporative cooling during late gestation period improves post-partum reproductive performance in Murrah buffaloes. To prove this hypothesis, sixteen pregnant dry Murrah buffaloes at sixty days pre-partum were selected and divided into two groups of eight animals each. Group 1 of buffaloes (Cooled/CL) was managed under fan and mist cooling during dry period, whereas second group of buffaloes (non-cooled/NCL) remained without the provision of cooling. After parturition, all the animals were managed under evaporative cooling till the end of experimental period. Reproductive performance in cooled (CL) and non-cooled (NCL) groups, respectively, viz. 1st and 2nd ovulation from calving (48.63 ± 2.41, 69.25 ± 2.34 days and 57.75 ± 3.35, 93.63 ± 2.84 days); calving to conception interval (117.88 ± 4.21 days and 117.88± 4.21 days); conception rate (87.5% ± 2.16% and 57% ± 2.26%); and follicular diameter at the time of 1st and 2nd ovulation (14.84 ± 0.16, 15.75 ± 0.13 mm and 12.65 ± 0.13, 13.35 ± 0.11 mm) varied significantly (p < .05). Total peak oestrogen concentration was significantly (p < .05) higher in cooled (26.7 ± 1.32 pg/ml) relative to non-cooled (20.7 ± 1.22 pg/ml) buffaloes. Time from onset of oestrus to ovulation varied significantly (p < .05) in cooled (32 ± 2.22 hr) and non-cooled (40 ± 2.86 hr) buffaloes. The peak progesterone concentration reached to (4.25 ng/ml) in cooled group and (4.16 ng/ml) in non-cooled group after first ovulation.

Economic feasibility of cooling dry cows across the United States

Heat stress during the dry period reduces milk yield in the subsequent lactation of dairy cows. Our objectives were to quantify the economic losses due to heat stress if dry cows are not cooled and to evaluate the economic feasibility of dry cow cooling. We used weather data from the National Oceanic and Atmospheric Administration to calculate the number of heat stress days for each of the 50 US states. A heat stress day was declared when the daily average temperature-humidity index was ≥68. The number of dairy cows in each state in 2015 was obtained from the USDA-National Agricultural Statistics Service. We assumed that 15% of the cows were dry at any time, a 60-d dry period, and a calving interval of 400d. Only cows in their second or greater parity (65%) benefitted from cooling during the dry period of the previous parity. Milk yield decreased by 5kg in the subsequent lactation (340d) if the cow experienced heat stress during the dry period based on a review of the literature. The default marginal value of milk minus feed cost was $0.33/kg of milk. The investment analysis included purchases of fans and soakers and use of water and electricity. Investment in a dry cow barn was considered separately. The average US dairy cow would experience 96 (26%) heat stress days during the year if not cooled and loses 447kg of milk in the subsequent lactation if not cooled when dry. Annual losses would be $810 million if dry cows were not cooled ($87/cow per yr). For the top 3 milk-producing states (California, Wisconsin, New York), and Florida and Texas, the average milk losses in the subsequent lactation were 522, 349, 387, 1,197, and 904kg, and reduced profit per cow per year would be $101, $68, $75, $233, and $176, respectively. The average benefit-cost ratio and payback periods of cooling dry cows in the United States were 3.15 and 0.27 yr (dry cow barn already present) and 1.45 and 5.68 yr (if investing in a dry cow barn) in the default scenario. To reach positive net present values, 6d (barn is present) and 55d (barn investment necessary) of heat stress annually were necessary (default assumptions). Other benefits of cooling, such as increased health and more productive offspring, were not considered. In conclusion, cooling of dry cows was profitable for 89% of the cows in the United States when building a new barn is required (under default assumptions) and very profitable when construction of a dry cow barn is not required (except for Alaska).

A Case Study of Behaviour and Performance of Confined or Pastured Cows During the Dry Period

The objectives of this study were to determine the effect of the dry cow management system (pasture or confined) on: (1) lying behaviour and activity; (2) feeding and heat stress behaviours; (3) intramammary infections, postpartum. Non-lactating Holstein cows were assigned to either deep-bedded, sand freestalls ( n = 14) or pasture ( n = 14) using rolling enrollment. At dry-off, cows were equipped with an accelerometer to determine daily lying time (h/d), lying bouts (bouts/d), steps (steps/d) and divided into periods: far-off (60 to 15 d prepartum), close-up (14 to 1 d prepartum), calving (calving date) and postpartum (1 to 14 d postpartum). Respiration rates were recorded once weekly from dry off to calving from 1300 to 1500 h. Feeding displacements were defined as one cow successfully displacing another from the feed bunk and were recorded once per week during the 2 h period, immediately after feeding at 800 h. Pastured cows were fed a commercial dry cow pellet during far-off and total mixed ration during close-up, with free access to hay and grazing. Freestall housed cows were fed a total mixed ration at far-off and close-up. Cows housed in freestalls were moved to a maternity pen with a mattress at commencement of labour. Pastured cows calved in pasture. After calving, all cows were commingled in a pen identical to the freestall housing treatment. Cows housed in freestalls laid down for longer during far-off and close-up periods, had fewer lying bouts during the calving period and took fewer steps throughout the study period when compared to pastured cows. Freestall housed cows experienced more displacements after feeding than did pastured cows. Respiration rates increased with an increasing temperature humidity index, more in pastured cows than in freestall housed cows. Pastured cows altered their lying behaviour and activity, suggesting a shift in time budget priorities between pastured and confined dry cows. Pastured cows also experienced less aggression around feeding but may be more susceptible to heat stress.

Climatic conditions, twining and frequency of milking as factors affecting the risk of fetal losses in high-yielding Holstein cows in a hot environment

An epidemiological study of risk factors for fetal losses was carried out on 62,403 high-yielding Holstein cows in 29 large highly technified dairy herds in northern Mexico (25° N; 23.5 °C mean annual temperature). Multivariate multiple-group response model indicated that fetal losses between 43 and 260 days of pregnancy were 23 %. Heat-stressed cows at conception (temperature-humidity index, THI >82) were 14 times more likely (P < 0.01) to present fetal losses than not heat-stressed cows (27 vs. 18 %). Heat-stressed cows at 60 days of pregnancy (THI >82) were 4.5 times more likely (P < 0.01) to present fetal losses than cows suffering heat stress in early gestation (29.1 vs. 17.7 %). The proportion of cows experiencing fetal loss was lower for multiparous than primiparous cows (odds ratio; OR = 0.7). Cows with twin pregnancies had significantly increased chances of losing their fetuses than cows with a single fetus (33.6 vs. 20.7 %; P < 0.01). Cows with three milkings per day were 30 % more likely (P < 0.01) to lose their fetuses than cows milked twice daily. Cows calving in winter and spring had significantly increased chances of losing their fetuses than cows calving in summer and fall (30-35 vs. 4-5 %; P < 0.01). It was concluded that, in this particular environment, heat stress exert a great influence on fetal losses in high producing Holstein cows.

Dry period cooling ameliorates physiological variables and blood acid base balance, improving milk production in murrah buffaloes

This study aimed to evaluate the impact of evaporative cooling during late gestation on physiological responses, blood gas and acid base balance and subsequent milk production of Murrah buffaloes. To investigate this study sixteen healthy pregnant dry Murrah buffaloes (second to fourth parity) at sixty days prepartum were selected in the months of May to June and divided into two groups of eight animals each. One group of buffaloes (Cooled/CL) was managed under fan and mist cooling system during dry period. Group second buffaloes (Noncooled/NCL) remained as control without provision of cooling during dry period. The physiological responses viz. Rectal temperature (RT), Respiratory rate (RR) and Pulse rate were significantly (P < 0.05) lower in group 2, with the provision of cooling. Skin surface temperature at thorax was significantly lower in cooled group relative to noncooled group. Blood pH and pO2 were significantly (P < 0.05) higher in heat stressed group as compared to the cooled group. pCO2, TCO2, HCO3, SBC, base excess in extracellular fluid (BEecf), base excess in blood (BEb), PCV and Hb were significantly (P < 0.05) higher in cooled group as compared to noncooled group. DMI was significantly (P < 0.05) higher in cooled relative to noncooled animals. Milk yield, FCM, fat yield, lactose yield and total solid yield was significantly higher (P < 0.05) in cooled group of Murrah buffaloes.

Acute brief heat stress in late gestation alters neonatal calf innate immune functions

Heat stress, as one of the environmental stressors affecting the dairy industry, compromises the cow milk production, immune function, and reproductive system. However, few studies have looked at how prenatal heat stress (HS) affects the offspring. The objective of this study was to evaluate the effect of HS during late gestation on calf immunity. Calves were born to cows exposed to evaporative cooling (CT) or HS (cyclic 23-35°C) for 1 wk at 3 wk before calving. Both bull and heifer calves (CT, n=10; HS, n=10) were housed in similar environmental temperatures after birth. Both CT and HS calves received 3.78 L of pooled colostrum within 12 h after birth and were fed the same diet throughout the study. In addition to tumor necrosis factor α, IL-1β, IL-1 receptor antagonist (IL-1RA), and toll-like receptor (TLR)2, and TLR4 mRNA expression, the expression of CD14(+) and CD18(+) cells, and DEC205(+) dendritic cells were determined in whole blood samples at d 0, 3, 7, 14, 21, and 28. The neutrophil to lymphocyte ratio, differential cell counts, and the hematocrit were also determined. During late gestation, the HS cows had greater respiration rates, rectal temperatures, and tended to spend more time standing compared with the CT cows. The HS calves had less expression of tumor necrosis factor-α and TLR2 and greater levels of IL-1β, IL-1RA, and TLR4 compared with CT calves. The HS calves also had a greater percentage of CD18(+) cells compared with the CT calves. Additionally, a greater percentage of neutrophils and lesser percentage of lymphocytes were in the HS calves compared with the CT calves. The results indicate that biomarkers of calves' immunity are affected in the first several weeks after birth by HS in the dam during late gestation.

Late-gestation heat stress abatement on performance and behavior of Holstein dairy cows

The objective of this study was to evaluate cooling to lessen the effects of heat stress during the last 3 wk of gestation on performance and behavior of multiparous Holstein cows. Twenty nonlactating cows were randomly assigned to treatments approximately 21 d before their expected calving date based on mature equivalent milk production and parity. Treatments were only imposed during the last 3 wk of gestation and included heat stress (HT; n=10) and cooling (CL; n=10), both under a similar photoperiod (14 h of light and 10 h of dark). Dry cows were housed in a sand-bedded stall with the stall areas for CL cows equipped with sprinklers and fans that were on from 0700 to 1900 h, whereas those for the HT cows were not. After parturition, all cows were housed in a barn with cooling devices. Rectal temperatures were measured daily at 1400 h and respiration rates were recorded by counting the flank movements for 1 min at 1500 h on odd days over the last 3 wk of gestation to calving. Daily dry matter intake was measured from -21 d relative to expected calving to 21 d after calving and milk production was recorded daily up to 180 d in milk. Behavioral changes of dry cows were studied continuously for 24 h at -10 d relative to expected calving. The average temperature-humidity index during the last 3 wk of gestation was 69.7 and was not significantly different between treatments. Heat-stressed cows exhibited greater rectal temperatures (39.5 vs. 39.2°C), greater respiration rates (70.4 vs. 63.3 breaths/min), and decreased dry matter intake (13.7 vs. 15.5 kg/d) compared with CL cows. Compared with HT cows, CL cows produced more milk during 180 d in milk (40.5 vs. 44.6 kg/d). Heat stress decreased ruminating (243.2 vs. 282.5 min/d) and chewing times (390.6 vs. 448.7 min/d) at -10 d before calving. The CL cows had shorter standing times than their HT counterparts (390.4 vs. 474.0 min/d). These results confirm that heat stress abatement in the late gestation period improves performance of dairy cows in subsequent lactation.

Effect of heat stress during late gestation on immune function and growth performance of calves: isolation of altered colostral and calf factors

Calves born to cows exposed to heat stress during the dry period and fed their dams' colostrum have compromised passive and cell-mediated immunity compared with calves born to cows cooled during heat stress. However, it is unknown if this compromised immune response is caused by calf or colostrum intrinsic factors. Two studies were designed to elucidate the effects of colostrum from those innate to the calf. The objective of the first study was to evaluate the effect of maternal heat stress during the dry period on calf-specific factors related to immune response and growth performance. Cows were dried off 46 d before expected calving and randomly assigned to 1 of 2 treatments: heat stress (HT; n=18) or cooling (CL; n=18). Cows of the CL group were housed with sprinklers, fans and shade, whereas cows of HT group had only shade. After calving, the cows were milked and their colostrum was frozen for the subsequent study. Colostrum from cows exposed to a thermoneutral environment during the dry period was pooled and stored frozen (-20 °C). Within 4h of birth, 3.8L of the pooled colostrum from thermoneutral cows was fed to calves born to both HT and CL cows. Day of birth was considered study d 0. All calves were exposed to the same management and weaned at d 49. Blood samples were collected before colostrum feeding, 24h after birth and twice weekly up to d 28. Total serum IgG concentrations were determined. Body weight was recorded at birth and at d 15, 30, 45, and 60. Relative to CL calves, HT calves were lighter at birth (38.3 vs. 43.1 kg), but no difference in weight gain was observed at d 60. Additionally, HT calves had lower apparent efficiency of IgG absorption (26.0 vs. 30.2%), but no differences were observed for total IgG concentration. The objective of the second study was to evaluate the isolated effect of the colostrum from HT cows on calf immune response and growth performance. The experimental design was identical to the first study, but all calves were born to cows under thermoneutral conditions during the dry period. At birth, calves were blocked by sex and birth weight and then randomly assigned to 1 of 2 treatments, which meant they received pooled colostrum from HT cows or CL cows. No treatment effect was observed on passive immune transfer or on postnatal growth. Thus, heat stress during the last 6 wk of gestation negatively affects the ability of the calf to acquire passive immunity, regardless of colostrum source.

Effect of heat stress during the dry period on mammary gland development

Heat stress during the dry period negatively affects hepatic metabolism and cellular immune function during the transition period, and milk production in the subsequent lactation. However, the cellular mechanisms involved in the depressed mammary gland function remain unknown. The objective of the present study was to determine the effect of heat stress during the dry period on various indices of mammary gland development of multiparous cows. Cows were dried off approximately 46 d before expected calving and randomly assigned to 2 treatments, heat stress (HT, n=15) or cooling (CL, n=14), based on mature equivalent milk production. Cows in the CL treatment were provided with sprinklers and fans that came on when ambient temperatures reached 21.1°C, whereas HT cows were housed in the same barn without fans and sprinklers. After parturition, all cows were housed in a freestall barn with cooling. Rectal temperatures were measured twice daily (0730 and 1430 h) and respiration rates recorded at 1500 h on a Monday-Wednesday-Friday schedule from dry off to calving. Milk yield and composition were recorded daily up to 280 d in milk. Daily dry matter intake was measured from dry off to 42 d relative to calving. Mammary biopsies were collected at dry off, -20, 2, and 20 d relative to calving from a subset of cows (HT, n=7; CL, n=7). Labeling with Ki67 antigen and terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling were used to evaluate mammary cell proliferation and apoptosis, respectively. The average temperature-humidity index during the dry period was 76.6 and not different between treatments. Heat-stressed cows had higher rectal temperatures in the morning (38.8 vs. 38.6°C) and afternoon (39.4 vs. 39.0°C), greater respiration rates (78.4 vs. 45.6 breath/min), and decreased dry matter intake (8.9 vs. 10.6 kg/d) when dry compared with CL cows. Relative to HT cows, CL cows had greater milk production (28.9 vs. 33.9 kg/d), lower milk protein concentration (3.01 vs. 2.87%), and tended to have lower somatic cell score (3.35 vs. 2.94) through 280 d in milk. Heat stress during the dry period decreased mammary cell proliferation rate (1.0 vs. 3.3%) at -20 d relative to calving compared with CL cows. Mammary cell apoptosis was not affected by prepartum heat stress. We conclude that heat stress during the dry period compromises mammary gland development before parturition, which decreases milk yield in the next lactation.