When do dry cows get heat stressed? Correlations of rectal temperature, respiration rate, and performance

A comprehensive study of respiration rates in dairy cattle in a Mediterranean climate

Respiration rate (RR) is often used to assess health and heat stress in cattle, influencing decisions that affect their welfare (e.g., medical treatment and cooling). Despite its importance, systematic information on how RR responds to various intrinsic and extrinsic factors is limited. This study recorded RR and behavior in 406 female Holstein and Jersey cattle (newborn to sixth-lactation cows) in California over a year to (1) describe RR across different life stages (calf, heifer, lactating, and dry), (2) evaluate how different weather or thermal load indexes predict RR using linear regression and mixed models, and (3) assess the effects of individual characteristics (life stage, breed, milk production, and lactation state) and behavior (posture and location) on RR in a Mediterranean climate. A total of 11,210 RR and behavior records were obtained over 39 d between October 2016 and August 2017. Each record was paired with individual characteristics and 25 different weather parameters within 5 min of collection. Data analysis involved descriptive statistics, mixed models, and linear and multinomial logistic regressions. Across all life stages, RR ranged from 16 to 185 breaths/min, with first and third quartiles at 37 and 59 breaths/min, respectively. The likelihood of upper normal RR values (30-50 breaths/min, according to some textbooks) was highest when air temperatures (AT) were below 20 to 25°C, depending on the life stage. During observations, AT ranged from 1.8 to 43.9°C and was the sole most reliable RR predictor, accounting for 35% of the observed variation. Although most individual characteristics and behaviors influenced RR, the biological significance was sometimes unclear. Calves showed the highest RR increase (+17 breaths/min per 10°C increase in AT), whereas dry cows showed the lowest (+11 breaths/min). Increases in RR for heifers and lactating cows were 13 and 14 breaths/min per 10°C increase in AT, respectively. We suspect differences in cooling provisions and metabolic rates across categories drove these results. In general, Jersey cattle had higher RR than Holsteins (∼3 breaths/min every 10°C), except in calves. Respiration rates were the lowest when heifers, lactating, and dry animals were near the feed bunk, likely due to soakers' provisions for mature cattle. Respiration rates averaged 52 and 49 ± 3 breaths/min for lying and standing postures, respectively, with <1 breath/min change per 10°C increase in AT. For lactating cows, RR increased by ∼2 breaths/min for every 10 kg of milk produced but decreased by ∼1 breath/min for every 50 d of pregnancy. No relationship of RR with DIM or lactation number was found. Our study systematically collected RR data from a relatively large number of dairy cattle across different life stages and weather conditions, suggesting that current textbook RR thresholds may underestimate upper values for cattle and demonstrating that AT was the most reliable predictor of RR changes in a Mediterranean climate. Respiration rates varied with life stage, breed, posture, location, milk yield, and gestation length, with more pronounced changes in calves, suggesting a need for further research to understand these variations and their welfare implications.

Effect of a nutritional immunomodulator in dry cows heat stressed with an electric blanket model

Heat stress in the dry period reduces yield and health in the next lactation. Previous work indicates that feeding OmniGen AF (OMN; Phibro Animal Health) mitigates the detrimental effects of heat stress. Electric blankets (EB) can induce heat stress in lactating cows, but EB have not been used with dry cows. The objectives of this study were to explore efficacy of the EB on cows during the dry period, as well as to examine the effect of feeding OMN to heat-stressed cows. We hypothesized that EB would increase body temperature in dry cows and OMN would ameliorate the effects of heat stress. Fifty Holstein cows were housed individually in a tie-stall barn upon dry-off ∼48 d before expected calving (223.7 ± 5 d carried calf) and cows were fitted with EB or no blanket (NB). Within EB and NB, cows were fed OMN (OMN; 56 g/d) or did not receive OMN (CON), which resulted in a 2 × 2 factorial of 4 treatments: NB-CON, EB-CON, NB-OMN, and EB-OMN. Throughout the dry period, DMI, water intake, and respiration rate (breaths/min) were measured daily, and rectal temperature was measured twice daily. After calving, all the cows were cooled and managed identically, and milk yield and composition were measured at each milking. Use of EB increased rectal temperature and respiration rate relative to NB regardless of diet; OMN treatment did not affect rectal temperature or respiration rate. Dry matter intake was reduced by over 1 kg/d with EB, and OMN feeding reversed this effect. Water intake increased with EB relative to NB, but OMN was without effect. Treatment did not affect gestation length. In early lactation, EB cows produced 6 kg/d less ECM relative to NB, and OMN reversed the effect on milk yield in EB cows. These data support the hypotheses that EB induce heat stress in dry cows and that OMN effectively mitigates the detrimental effects of heat stress in the dry period.

Stage-specific milk yield losses and associated sweating, respiration, and rectal temperature responses under varying temperature-humidity index thresholds in lactating and dry cows

Heat stress (HS) may result in changes in the behavior, endocrine system, and physiological characteristics of dairy cows, and it may even lead to death in severe cases. As the effects of global warming have become more notable, the prevalence of HS has increased among dairy cows. Therefore, comprehensive strategies, including not only cooling measures but also dietary adjustments and genetic improvements for heat tolerance, are required to help these animals regulate their body temperature and avoid HS. In addition, detecting HS signs is essential for both lactating and dry cows to ensure appropriate interventions. The temperature-humidity index (THI) is a widely used tool for evaluating the effects of HS on livestock. Because the physiological state of cattle significantly influences their responses to HS, it is imperative to establish specific THI thresholds for both lactating and dry cows to implement appropriate cooling regimens and optimize animal welfare. In this study, we used the THI to investigate the relationship between rectal temperature (RT), respiration rate (RR), and sweating rate (SR) in lactating and dry cows. We also explored the relationships between milk yield at different lactation stages and THI thresholds. The results indicated that lactating and dry cows had different THI thresholds based on their immediate physiological responses. Compared with lactating cows, dry cows had higher THI thresholds for RT, RR, and SR. In addition, cows in early-, intermediate-, and late-lactation stages under thermoneutral conditions produced significantly more milk than did those under mild, moderate, and severe HS conditions, indicating that milk yield losses occur under HS conditions. Taken together, these findings provide valuable insights into how HS can be mitigated in subtropical dairy farms. For lactating cows, implementing cooling measures is recommended when the THI reaches 66 to 67, whereas for dry cows, waiting until the THI reaches 73 is recommended. Milk yield losses may occur when lactating cows are under HS conditions. Therefore, appropriate cooling measures should be implemented at accurate THI thresholds to ensure optimal animal welfare for both lactating and dry cows.

A Framework for Comprehensive Dairy Calf Health Investigations

The objective of this narrative review is to provide a systematic framework for veterinarians to investigate dairy calf health, focusing on critical control points and key performance indicators (KPIs) to address morbidity and mortality challenges in preweaned calves. Recommendations target prenatal maternal nutrition, heat stress abatement, and optimal calving management to minimize risks associated with perinatal mortality and preweaning morbidity. Further, comprehensive colostrum management is discussed to ensure excellent transfer of passive immunity, which includes prompt collection and feeding within two hours of birth at a volume of 8.5-10% of calf body weight. Nutritional guidance emphasizes the importance of transition milk and feeding higher planes of nutrition to support immunity, with recommendations that milk total solids exceed 10% to meet energy needs. Environmental management recommendations include a minimum of 3.3 m2 of space per calf, the use of low-dust bedding, and air quality controls to reduce respiratory disease. Lastly, regular health data collection and KPI monitoring, such as average daily gain and morbidity rates, are essential for data-driven improvements. By implementing these evidence-based recommendations, veterinarians can support dairy farmers in reducing calf morbidity and mortality, ultimately enhancing calf welfare and lifetime productivity.

Impact of Heat Stress on Oocyte Developmental Competence and Pre-Implantation Embryo Viability in Cattle

Rectal and vaginal temperatures are utilised in both in vivo and in vitro models to study the effects of heat stress on oocyte competence and embryo viability in cattle. However, uterine temperature increases by only 0.5 °C in heat-stressed cows, significantly lower than simulated increases in in vitro models. Temperature variations within oviducts and ovarian follicles during heat stress are poorly understood or unavailable, and evidence is lacking that oocytes and pre-implantation embryos experience mild (40 °C) or severe (41 °C) heat stress inside the ovarian follicle and the oviduct and uterus, respectively. Gathering detailed temperature data from the reproductive tract and follicles is crucial to accurately assess oocyte competence and embryo viability under realistic heat stress conditions. Potential harm from heat stress on oocytes and embryos may result from reduced nutrient availability (e.g., diminished blood flow to the reproductive tract) or other unidentified mechanisms affecting tissue function rather than direct thermal effects. Refining in vivo stress models in cattle is essential to accurately identify animals truly experiencing heat stress, rather than assuming heat stress exposure as done in most studies. This will improve model reliability and aid in the selection of heat-tolerant animals.

Influence of Heat Stress on Body Surface Temperature and Blood Metabolic, Endocrine, and Inflammatory Parameters and Their Correlation in Cows

This study aimed to determine whether heat stress affected the values and correlations of metabolic, endocrinological, and inflammatory parameters as well as the rectal and body surface temperature of cows in the early and middle stages of lactation. This experiment was conducted in May (thermoneutral period), June (mild heat stress), and July (moderate to severe heat stress). In each period we included 15 cows in early lactation and 15 in mid-lactation. The increase in rectal and body surface temperatures (°C) in moderate to severe heat stress compared to the thermoneutral period in different regions was significant (p < 0.01) and the results are presented as mean and [95%CI]: rectal + 0.9 [0.81-1.02], eye + 6 [5.74-6.25], ear + 13 [11.9-14.0], nose + 3.5 [3.22-3.71], forehead + 6.6 [6.43-6.75], whole head + 7.5 [7.36-7.68], abdomen + 8.5 [8.25-8.77], udder + 7.5 [7.38-7.65], front limb + 6 [5.89-6.12], hind limb + 3.6 [3.46-3.72], and whole body + 9 [8.80-9.21]. During heat stress (in both mild and moderate to severe stress compared to a thermoneutral period), an increase in the values of extracellular heat shock protein 70 (eHsp70), tumor necrosis factor α (TNFα), cortisol (CORT), insulin (INS), revised quantitative insulin sensitivity check index (RQUICKI), urea, creatinine, total bilirubin, aspartate transpaminase (AST), gamma-glutamyl transferase (GGT), lactate dehydrogenase (LDH), and creatin kinase (CK) occurred, as well as a decrease in the values of triiodothyronine (T3), thyroxine (T4), non-esterified fatty acids (NEFA), glucose (GLU), β-Hydroxybutyrate (BHB), calcium, phosphorus, total protein (TPROT), albumin (ALB), triglycerides (TGCs), and cholesterol (CHOL). In cows in early lactation compared to cows in mid-lactation, there was a significantly larger increase (p < 0.01) in the values of eHsp70, TNFα, GLU, RQUICKI, and GGT, while the INS increase was smaller during the three experimental periods. The decrease in the values of Ca, CHOL, and TGC was more pronounced in cows in early lactation compared to cows in mid-lactation during the three experimental periods. Rectal temperature was related to eHsp70 (r = 0.38, p < 0.001) and TNFα (r = 0.36, p < 0.01) and showed non-significant poor correlations with other blood parameters. Blood parameters correlate with body surface temperature, with the following most common results: eHsp70 and TNFα showed a moderately to strongly significant positive correlation (r = 0.79-0.96, p < 0.001); CORT, INS, and Creat showed fairly to moderately significant positive correlations; T3, T4, NEFA and GLU showed fairly to moderately significant negative correlations (r = 0.3-0.79; p < 0.01); RQUICKI, urea, AST, and GGT showed fairly and significantly positive correlations; and TGC, CHOL, TPROT, and ALB showed fairly and significantly negative correlations (r = 0.3-0.59; p < 0.01). Measuring the surface temperature of the whole body or head can be a useful tool in evaluating the metabolic response of cows because it has demonstrated an association with inflammation (TNFα, eHsp70), endocrine response (CORT, T3, T4), the increased use of glucose and decreased use of lipids for energy purposes (INS, NEFA, GLU, and RQUICKI), and protein catabolism (ALB, TPROT, urea, Creat), which underlies thermolysis and thermogenesis in cows under heat stress. In future research, it is necessary to examine the causality between body surface area and metabolic parameters.

Modeling the relationship between heat stress, feed intake, and day relative to calving in nonlactating dairy cows

Heat stress (HS) during the dry period can affect animal welfare, health, dry matter intake (DMI), and milk production in the subsequent lactation, which will negatively affect the profitability of dairy farms. In this study, the objective was to model the changes in DMI in pregnant nonlactating heat-stressed dairy cows with or without access to evaporative cooling systems. A database was built, composed of individual DMI records from 244 pregnant nonlactating dairy cows from an average -29.3 d (range: -42 to -21 d; SD: ±7.54 d) to -1 d relative to calving (DRC) and housed in environmental conditions in which temperature-humidity index (THI) ranged from 58.4 to 83.3, with or without access to evaporative cooling systems. Generalized additive mixed-effects models were used to describe the relationships of DMI with HS and DRC. Changes in DMI with the increase in THI and the progression of pregnancy in cows with or without evaporative cooling systems were estimated using differential equations. On average, cows housed in barns without evaporative cooling systems had a reduction in DMI of 1.30 kg/d and increased rectal temperature in 0.22°C in relation to those housed in barns with evaporative cooling systems. Dry matter intake decreased as THI increased, but the reduction was greater for noncooled cows as THI values increased. In addition, regardless of the THI, DMI started to decrease at -14 DRC for cooled cows, whereas for noncooled cows it already started at -30 DRC, relative to the previous days evaluated. The intensity of the reduction was lesser for cows that had access to evaporative cooling systems or were in the dry period in May to June as compared with those that were in the dry period in July to August or September to October. The models generated in this study, which include environmental variables, should lead to more accurate predictions of DMI during HS that can be used to formulate diets to meet the needs of the late pregnant cow because it is possible to predict changes in DMI as the heat load and DRC change. Such models are also expected to help dairy nutritionists to decide when and how to apply the dietary strategies available to attenuate the reductions in DMI with the intensity of HS and progression of pregnancy.

Precision Detection of Real-Time Conditions of Dairy Cows Using an Advanced Artificial Intelligence Hub

One of the main challenges in the adoption of artificial intelligence-based tools, such as integrated decision support systems, is the complexities of their application. This study aimed to define the relevant parameters that can be used as indicators for real-time detection of heat stress and subclinical mastitis in dairy cows. Moreover, this study aimed to demonstrate the use of a developed data-mining hub as an artificial intelligence-based tool that integrates the defined relevant information (parameters or traits) in accurately identifying the condition of the cow. A comprehensive theoretical framework of the data-mining hub is demonstrated, the selection of the parameters that were used for the data-mining hub is listed, and the relevance of the traits is discussed. The practical application of the data-mining hub has shown that using 21 parameters instead of 13 and 8 parameters resulted in a high overall accuracy of detecting heat stress and subclinical mastitis in dairy cows with a high precision effect reflecting a low percentage of misclassifying the conditions of the dairy cows. This study has developed an innovative approach in which combined information from different independent data was used to accurately detect the health and wellness status of the dairy cows. It can also be implied that an artificial intelligence-based tool such as the proposed theoretical data-mining hub of dairy cows could maximize the use of continuously generated and underutilized data in farms, thus ultimately simplifying repetitive and difficult decision-making tasks in dairy farming.

Late-Gestation in utero Heat Stress Limits Dairy Heifer Early-Life Growth and Organ Development

Dairy calves exposed to late-gestation heat stress weigh less, have impaired immunity, produce less milk across multiple lactations, and have reduced productive life. However, less is known about the relationship between in utero heat stress and organ morphology and development. Herein, we characterized the consequences of late-gestation in utero heat stress on body and organ growth trajectories during early-life development. Holstein heifers were either in utero heat-stressed (IU-HT, n = 36, dams exposed to THI &gt; 68) or cooled (IU-CL, n = 37, dams exposed to THI &gt; 68 with access to active cooling) during late gestation (54 ± 5 d prepartum). All heifers were reared identically from birth to weaning. Upon birth, calves were weighed and fed 3.78 L of colostrum followed by 0.87 kg DM/d milk replacer (MR) over two feedings and ad libitum starter concentrate daily. Weaning began at 49 d and ended at 56 d of age. Feed intake was recorded daily, and body weight (BW) and other growth measures were recorded at 0, 28, 56, and 63 d. Blood was collected at d 1 then weekly. Subsets of heifers were selected for euthanasia at birth and 7 d after complete weaning (n = 8 per group each) to harvest and weigh major organs. Reduced BW and stature measures persisted in IU-HT heifers from 0 to 63 d of age with a 7% lower average daily gain and reduced starter consumption relative to IU-CL heifers. IU-HT heifers had lower hematocrit percentages and reduced apparent efficiency of absorption of IgG relative to IU-CL heifers. Additionally, IU-HT heifers had reduced gross thymus, spleen, thyroid gland, and heart weight at birth and larger adrenal glands and kidneys but smaller ovaries relative to BW at 63 d. The mammary gland of IU-HT heifers was smaller relative to IU-CL heifers at birth and 63 d adjusted for BW, suggesting mechanisms leading to impaired milk yield in mature IU-HT cows are initiated early in development. In summary, in utero heat stress reduces whole-body size and limits development of key organs with potential repercussions on dairy calf metabolic adaptation, immune function, and future productivity.

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.

Effects of rumen-protected choline supplementation in Holstein dairy cows during electric heat blanket-induced heat stress

Dairy cows experiencing heat stress (HS) attempt to thermoregulate through multiple mechanisms, such as reducing feed intake and milk production and altering blood flow to increase heat dissipation. Effects of choline on energy metabolism and immune function may yield it a viable nutritional intervention to mitigate negative effects of HS. The primary objective of this experiment was to determine if supplementation of rumen-protected choline during, or before and during, an increased heat load would ameliorate the negative effects of HS on production and immune status. Heat stress was induced via an electric heat blanket model with a 3-d baseline period and 7-d HS period for all cows. Multiparous mid-lactation (208 ± 31 days in milk) Holstein cows were fed the same basal herd diet, blocked by pre-experiment milk yield, and randomly assigned to receive one of the following: (1) no rumen-protected (RP) choline (n = 7); (2) RP choline (60 g/d) via top-dress during the HS period (n = 8); or (3) RP choline (60 g/d) via top-dress during the baseline and HS periods (n = 8). Imposing HS via electric heat blanket raised respiration rate with all cows surpassing the HS threshold of 60 breaths/min. The increase in respiration rate tended to be ameliorated with either schedule of RP choline supplementation. Milk yield tended to increase when RP choline was supplemented in both the baseline period and during HS. Supplementation of RP choline tended to reduce blood fatty acid and triglyceride and tended to increase the revised quantitative insulin sensitivity check index. The role of RP choline supplementation to partially ameliorate the effects of HS should be further explored as a potential nutritional strategy to mitigate the negative consequences of HS on health and production.

Recent Advances on Early Detection of Heat Strain in Dairy Cows Using Animal-Based Indicators: A Review

In pursuit of precision livestock farming, the real-time measurement for heat strain-related data has been more and more valued. Efforts have been made recently to use more sensitive physiological indicators with the hope to better inform decision-making in heat abatement in dairy farms. To get an insight into the early detection of heat strain in dairy cows, the present review focuses on the recent efforts developing early detection methods of heat strain in dairy cows based on body temperatures and respiratory dynamics. For every candidate animal-based indicator, state-of-the-art measurement methods and existing thresholds were summarized. Body surface temperature and respiration rate were concluded to be the best early indicators of heat strain due to their high feasibility of measurement and sensitivity to heat stress. Future studies should customize heat strain thresholds according to different internal and external factors that have an impact on the sensitivity to heat stress. Wearable devices are most promising to achieve real-time measurement in practical dairy farms. Combined with internet of things technologies, a comprehensive strategy based on both animal- and environment-based indicators is expected to increase the precision of early detection of heat strain in dairy cows.

Late-gestation heat stress abatement in dairy heifers promotes thermoregulation and improves productivity

Multiparous, nonlactating pregnant cows are negatively affected by heat stress, but the effect of heat stress on more thermotolerant pregnant heifers has received less attention. Our objective was to characterize the effect of late-gestation heat abatement on thermoregulatory responses and subsequent milk production of nulliparous Holstein heifers. Pregnant heifers, blocked by body condition score (BCS) and predicted transmitting ability (PTA) for milk, were enrolled in either heat stress (HT, shade of freestall barn; n = 16) or cooling (CL, shade of freestall barn, water soakers, and fans; n = 15) environments during the last 60 d of pregnancy (~8 weeks). Rectal temperature (RT; thermometer), respiration rate (RR; breaths/min), sweating rate (SR; VapoMeter, Delfin Technologies, Kuopio, Finland), and skin temperature (ST; infrared thermometer) were measured thrice weekly from enrollment to calving. Vaginal temperature (VT; i-button intravaginal device) was measured every 10 min for 7 consecutive days at wk -8, -6, -4, and -2 relative to calving and averaged hourly. Daily thermoregulatory patterns assessed by SR and ST, were measured every 4 h over a 36-h time interval at wk -6, -4, and -2 relative to calving. Upon calving, milk, protein, and fat yields were recorded twice daily for 15 wk. The average temperature-humidity index (Hobo Pro temperature probe, Onset Computer Corporation, Pocasset, MA) in the barn during the precalving period was 77 (minimum of 72, maximum of 82). Only heifers that gave birth to a female calf (CL = 12, HT = 14) were included in the statistical analysis. In the precalving period, CL heifers had lower RR (44.3 vs. 60.0 ± 1.6 breaths/min), RT (38.7 vs. 38.8 ± 0.04°C), unshaved ST (34.7 vs. 35.3 ± 0.17°C), and unshaved SR (19.0 vs. 35.2 ± 1.9 g/m²h), relative to HT heifers. Additionally, VT was lower in CL heifers during wk -4, and -2, specifically during early morning and early afternoon hours. When measured over a 36-h time interval, ST and SR were lower in CL heifers, when compared with HT heifers for all weeks. Notably, ST was reduced overnight and SR was reduced during the daytime. Cooled heifers had higher milk yield (35.8 vs. 31.9 ± 1.4 kg/d), when compared with HT heifers. Similar to multiparous cows, our data indicate that actively cooling heifers in late pregnancy is effective in promoting thermoregulation and results in elevated milk production postcalving.