Validating a heat stress model: The effects of an electric heat blanket and nutritional plane on lactating dairy cows

Heat Stress Mitigation: Impact of Increased Cooling Sessions on Milk Yield and Welfare of Dairy Buffaloes in a Semiarid Summer

The current study aimed to evaluate the impact of increasing cooling sessions from three to five times a day on milk yield and the welfare of dairy buffaloes during a semiarid summer in Pakistan. Eighteen Nili Ravi buffaloes were randomly assigned to three cooling strategies: (1) CTL, where buffaloes were cooled with a handheld hosepipe twice daily for 5 min each; (2) 3CS, where buffaloes were cooled using sprinklers three times daily; and (3) 5CS, where buffaloes were cooled using sprinklers five times daily. Each sprinkler cooling session lasted 1 h, with a 6 min cycle of 3 min of water on and 3 min off. Results showed that the 5CS group produced 1.6 and 3.2 kg more milk per day compared to the 3CS and CTL groups, respectively (p < 0.001). Both the 5CS and 3CS groups had consistently lower core body temperatures and respiration rates than the CTL group. Buffaloes in the 5CS group spent significantly more time eating (p < 0.001). Additionally, the 5CS group exhibited lower cortisol and blood urea nitrogen levels (p = 0.001) and higher glucose levels than the CTL group (p = 0.006). In conclusion, increasing cooling sessions to five times daily improved milk yield and welfare compared to the traditional cooling strategy (CTL) in dairy buffaloes during semiarid summers, highlighting the benefits of optimized cooling practices.

Impacts of dietary betaine on rectal temperature, laying performance, metabolism, intestinal morphology, and follicular development in heat-exposed laying hens

This experiment assessed the influences of betaine (BET; 2000 mg/kg) on rectal temperature (Tr), laying performance, metabolism, intestinal morphology, and follicular development in heat-stressed hens. One-hundred and twenty-eight Hisex white hens (42wks) were housed in 4 battery cages (8 pens/cage; 4 hens/pen) and divided into 4 treatments: 1) thermoneutral (TN) environments and a control diet (TNCON), 2) TN and a diet accompanied with BET (TNBET), 3) heat stress (HS) environments and a control diet (HSCON), or 4) HS and a diet accompanied with BET (HSBET). Following acclimation (15d), hens of TNCON and TNBET remained in TN, while HSCON and HSBET hens were subjected to cyclical HS (5d; 16.9-37.5 °C). Cyclical HS increased Tr compared with TN hens (1.6 °C; P < 0.01), but supplemental BET decreased Tr (0.4 °C; P < 0.01). Relative to TN treatments, HS declined egg production, weight, and mass (18, 4.2, and 26%, respectively; P < 0.01), but BET ameliorated the egg production and mass (13.1 and 16.2%, respectively; P < 0.01). Compared with HSCON, feed conversion ratio and survival rate were improved in HSBET hens (12.3 and 6.25%, respectively; P ≥ 0.03). Relative to TN hens, HS elevated glucose and blood urea nitrogen (BUN) levels (15 and 4%, respectively; P ≤ 0.04). Supplemental BET decreased BUN levels (6.6%; P < 0.01) relative to HSCON hens. Furthermore, HS diminished jejunal villus height and villus surface area (∼27 and 35%, respectively; P < 0.01) relative to TN hens but were unaltered by BET supplementation. Relative to TN hens, HS decreased oviduct's weight, ovary's length, and ovarian primordial and primary follicles count (18, 23, 34 and 44%, respectively; P < 0.01) and caused fibrosis in shell gland (3-fold; P = 0.05). Collectively, HS impaired productivity, metabolism, intestinal architecture, and reproductive efficiency. Feeding BET reduced Tr, improved laying performance, and slightly altered metabolism but did not affect intestinal and follicular measurements in heat-stressed hens.

Effects of heat stress on markers of skeletal muscle proteolysis in dairy cattle

Heat stress (HS) markedly affects postabsorptive energetics and protein metabolism. Circulating urea nitrogen increases in multiple species during HS and it has been traditionally presumed to stem from increased skeletal muscle proteolysis; however, this has not been empirically established. We hypothesized HS would increase activation of the calpain and proteasome systems as well as increase degradation of autophagosomes in skeletal muscle. To test this hypothesis, lactating dairy cows (∼139 d in milk; parity ∼2.4) were exposed to thermal neutral (TN) or HS conditions for 7 d (8 cows/environment). To induce HS, cattle were fitted with electric blankets for the duration of the heating period and the semitendinosus was biopsied on d 7. Heat stress increased rectal temperature (1.3°C) and respiratory rate (38 breaths per minute) while it decreased dry matter intake (34%) and milk yield (32%). Plasma urea nitrogen (PUN) peaked following 3 d (46%) and milk urea nitrogen (MUN) peaked following 4 d of environmental treatment and while both decreased thereafter, PUN and MUN remained elevated compared with TN (PUN: 20%; MUN: 27%) on d 7 of HS. Contrary to expectations, calpain I and II abundance and activation and calpain activity were similar between groups. Likewise, relative protein abundance of E3 ligases, muscle atrophy F-box protein/atrogin-1 and muscle ring-finger protein-1, total ubiquitinated proteins, and proteasome activity were similar between environmental treatments. Finally, autophagosome degradation was also unaltered by HS. Counter to our hypothesis, these results suggest skeletal muscle proteolysis is not increased following 7 d of HS and call into question the presumed dogma that elevated skeletal muscle proteolysis, per se, drives increased AA mobilization.

Effect of feeding a Saccharomyces cerevisiae fermentation product to Holstein cows exposed to high temperature and humidity conditions on milk production performance and efficiency-A pen-level trial

The objective of this study was to evaluate the effect of feeding a Saccharomyces cerevisiae fermentation product (SCFP) on milk production efficiency of Holstein cows naturally exposed to high temperature and humidity conditions. The study was conducted in 2 commercial farms in Mexico from July to October 2020 and included 1 wk covariate period, 3 wk adaptation, and 12 wk data collection. Cows [n = 1,843; ≥21 d in milk (DIM) and <100 d carried calf] were enrolled and assigned to the study pens (n = 10) balanced for parity, milk yield, and DIM. Pens were fed a total mixed ration diet either without (CTRL) or with SCFP (19 g/d, NutriTek, Diamond V). Milk yield, energy-corrected milk (ECM), milk components, linear somatic cell score, dry matter intake (DMI), feed efficiency (FE; Milk/DMI and ECM/DMI), body condition score, and the incidence of clinical mastitis, pneumonia, and culling were monitored. Statistical analyses included mixed linear and logistic models accounting for repeated measures (when applicable; multiple measurements per cow within treated pens) with pen as the experimental unit and treatment, time (week of study), parity (1 vs. 2+), and their interactions as fixed and pen nested within farm and treatment as random effect. Parity 2+ cows within pens fed SCFP produced more milk than cows within CTRL pens (42.1 vs. 41.2 kg/d); there were no production differences between groups of primiparous groups. Cows within SCFP pens had lower DMI (25.2 vs. 26.0 kg/d) and greater FE (1.59 vs. 1.53) and ECM FE (1.73 vs. 1.68) than cows within CTRL pens. Milk components, linear somatic cell score, health events, and culling were not different between groups. At the end of the study (245 ± 54 DIM), SCFP cows had greater body condition score than CTRL (3.33 vs. 3.23 in the first parity; 3.11 vs. 3.04 in 2+ parity cows). Feeding Saccharomyces cerevisiae fermentation products to lactating cows exposed to high temperature and humidity conditions improved FE.

Effects of dietary antioxidant supplementation on metabolism and inflammatory biomarkers in heat-stressed dairy cows

Heat-stress-induced inflammation may be ameliorated by antioxidant supplementation due to the purported effects of increased production of reactive oxygen species or oxidative stress on the gastrointestinal tract barrier. Thus, study objectives were to evaluate whether antioxidant supplementation [AGRADO Plus 2.0 (AP); EW Nutrition] affects metabolism and inflammatory biomarkers in heat-stressed lactating dairy cows. Thirty-two mid-lactation multiparous Holstein cows were assigned to 1 of 4 dietary-environmental treatments: (1) thermoneutral (TN) conditions and fed a control diet (TN-CON; n = 8), (2) TN and fed a diet with AP (10 g antioxidant; n = 8), (3) heat stress (HS) and fed a control diet (HS-CON; n = 8), or (4) HS and fed a diet with AP (HS-AP; n = 8). The trial consisted of a 23-d prefeeding phase and 2 experimental periods (P). Respective dietary treatments were top-dressed starting on d 1 of the prefeeding period and continued daily throughout the duration of the experiment. During P1 (4 d), baseline data were collected. During P2 (7 d), HS was artificially induced using an electric heat blanket (Thermotex Therapy Systems Ltd.). During P2, the effects of treatment, day, and treatment-by-day interaction were assessed using PROC MIXED of SAS (SAS Institute Inc.). Heat stress (treatments 3 and 4) increased rectal, vaginal, and skin temperatures (1.2°C, 1.1°C, and 2.0°C, respectively) and respiration rate (33 breaths per minute) relative to TN cows. As expected, HS decreased dry matter intake, milk yield, and energy-corrected milk yield (32%, 28%, and 28% from d 4 to 7, respectively) relative to TN. There were no effects of AP on body temperature indices or production. Milk fat, protein, and lactose concentrations remained unaltered by HS or AP; however, milk urea nitrogen was increased during HS regardless of AP supplementation (26% relative to TN). Circulating glucose remained unchanged by HS, AP, or time. Additionally, HS decreased circulating glucagon (29% from d 3 to 7 relative to TN), but there was no additional effect of AP. There was a tendency for nonesterified fatty acid concentrations to be increased in HS-AP cows throughout P2 (60% relative to TN-CON), whereas it remained similar in all other treatments. Blood urea nitrogen increased for both HS treatments from d 1 to 3 before steadily decreasing from d 5 to 7, with the overall increase being most pronounced in HS-CON cows (27% relative to TN-CON). Further, supplementing AP decreased blood urea nitrogen in HS-AP on d 3 relative to HS-CON (15%). Circulating serum amyloid A tended to be and lipopolysaccharide binding protein was increased by HS, but neither acute-phase protein was affected by AP. Overall, AP supplementation appeared to marginally alter metabolism but did not meaningfully alter inflammation during HS.

Epigenomics of rats' liver and its cross-species functional annotation reveals key regulatory genes underlying short term heat-stress response

Molecular responses to heat stress are multifaceted and under a complex cellular post-transcriptional control. This study explores the epigenetic and transcriptional alterations induced by heat stress (42 °C for 120 min) in the liver of rats, by integrating ATAC-seq, RNA-Seq, and WGBS information. Out of 2586 differential ATAC-seq peaks induced by heat stress, 36 up-regulated and 22 down-regulated transcript factors (TFs) are predicted, such as Cebpα, Foxa2, Foxo4, Nfya and Sp3. Furthermore, 150,189 differentially methylated regions represent 2571 differentially expressed genes (DEGs). By integrating all data, 45 DEGs are concluded as potential heat stress response markers in rats. To comprehensively annotate and narrow down predicted markers, they are integrated with GWAS results of heat stress parameters in cows, and PheWAS data in humans. Besides better understanding of heat stress responses in mammals, INSR, MAPK8, RHPN2 and BTBD7 are proposed as candidate markers for heat stress in mammals.

Effects of dietary betaine on body temperature indices, performance, metabolism, and hematological variables of dairy heifer calves during hot summer conditions

Background and Aim: Heat stress (HS) can negatively impact farm animal productivity and adversely affect animal welfare worldwide, placing a major financial burden on global livestock producers. Dietary betaine (trimethylglycine) has been known to have several biological functions, which may aid in offering beneficial effects on livestock productivity during HS conditions. However, information on the role of dietary betaine in heat-stressed dairy heifer calves is yet to be documented. Therefore, this study aimed to assess the effects of supplementing dietary betaine on body temperature indices, blood metabolites, productive performance, and complete blood count (CBC) (hematological indices) in hyperthermic dairy heifer calves. Materials and Methods: In total, 14 Holstein heifer calves (4.0 ± 0.9 months old) were individually housed and randomly allocated to one of two dietary treatments: (1) a control diet (CON; n = 7) and (2) a control diet complemented with 21 g/d of natural betaine (BET; n = 7) top-dressed once daily. The experiment lasted for 28 d, during which all animals were subjected to natural cyclic HS conditions (26.1–39.2°C; 73.2–84.0 temperature–humidity index). Rectal temperature (RT) and respiration rate (RR) were measured twice daily (0700 and 1500 h), whereas dry matter intake (DMI) was measured once daily (0800 h). In addition, blood samples (collected from the jugular vein) were analyzed for metabolites and CBC on days 7, 14, 21, and 28. Results: Relative to CON, BET supplementation was able to decrease RT on day 23 of the experiment (p = 0.04). Alternatively, RR was similar between the dietary treatments (p = 0.73). Feeding BET did not affect DMI compared with CON during HS conditions (p = 0.48). Furthermore, compared with CON, BET supplementation did not change leukocytes, neutrophils, lymphocytes, and hematocrit levels during HS conditions (p ≥ 0.17). However, a post hoc analysis indicated that hematocrit levels were decreased in BET-fed calves on day 7 of the study compared with CON calves during HS conditions (p = 0.05). Moreover, circulating glucose, albumin, and triglycerides were found to be similar between dietary treatments (p ≥ 0.55). Conclusion: BET supplementation slightly reduced RT and circulating hematocrit but did not affect other metrics in this HS experiment. More research into the effects of different doses of dietary BET on dairy heifer calves is needed.

Performance and welfare of dairy buffaloes subjected to different cooling strategies during subtropical summer

This study aimed to evaluate the effects of different cooling strategies on milk yield and physiological and behavioral responses of Nili Ravi buffaloes during subtropical summer in Pakistan. Thirty Nili Ravi buffaloes were randomly assigned to three treatments: (1) CNT buffaloes cooled with the application of water using handheld hosepipe twice daily, 3 min each with a water flow rate of 40 L/min; (2) 2SS, buffaloes cooled with sprinklers twice daily; (3) 3SS, buffaloes cooled with sprinklers thrice daily. Each of the sprinkler sessions lasted for 1 h with a 12-min cycle (3 min water on, 9 min off). The trial was carried out from mid-July until the end of September 2019. The average ambient afternoon temperature humidity index was 86.9. The results indicated that the buffaloes in the 3SS group had lower respiration rate and rectal temperature than those in the CNT and the 2SS groups (P < 0.01). The 3SS group had more daily milk yield (P = 0.019) and milk fat % (P < 0.01) than the CNT and 2SS groups. The lying time and the lying bout length were significantly longer in the 3SS than in the CNT and 2SS groups. The blood cortisol levels tended to be lower in the 3SS group than in the CNT and 2SS groups (P = 0.051). In conclusion, the 3SS cooling strategy had more milk yield, more milk fat, and better welfare than the CNT strategy using less groundwater and both performed better than the 2SS strategy.

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.

Changes in Blood Metabolites and Immune Cells in Holstein and Jersey Dairy Cows by Heat Stress

Simple Summary

As global temperatures rise, thermal stress can be a major problem affecting cows. If they are subjected to heat stress, they are likely to exhibit abnormal metabolic reactions and affect their immune system. However, the relationship between metabolism and immunity during thermal stress and these crosstalk mechanisms remain unclear. Therefore, the aim of this study was to understand the changes in blood immune cell response with the physiological metabolism changes of Holstein and Jersey cows through the biochemistry and flow cytometry branches under thermal stress conditions. We found that various blood metabolites were reduced in both Holsteins and Jerseys by heat stress conditions. There were breed-specific variations in the immune cell population in Holstein and Jersey cows under different environmental conditions. The main findings of this study provide information on the metabolism and immunity changes of two types of cow under heat stress, broadening the potential relationship of these changes.

Abstract

Owing to increasing global temperatures, heat stress is a major problem affecting dairy cows, and abnormal metabolic responses during heat stress likely influence dairy cow immunity. However, the mechanism of this crosstalk between metabolism and immunity during heat stress remains unclear. We used two representative dairy cow breeds, Holstein and Jersey, with distinct heat-resistance characteristics. To understand metabolic and immune responses to seasonal changes, normal environmental and high-heat environmental conditions, we assessed blood metabolites and immune cell populations. In biochemistry analysis from sera, we found that variety blood metabolites were decreased in both Holstein and Jersey cows by heat stress. We assessed changes in immune cell populations in peripheral blood mononuclear cells (PBMCs) using flow cytometry. There were breed-specific differences in immune-cell population changes. Heat stress only increased the proportion of B cells (CD4–CD21+) and heat stress tended to decrease the proportion of monocytes (CD11b+CD172a+) in Holstein cows. Our findings expand the understanding of the common and specific changes in metabolism and immune response of two dairy cow breeds under heat stress conditions.

Common and Differential Dynamics of the Function of Peripheral Blood Mononuclear Cells between Holstein and Jersey Cows in Heat-Stress Environment

Simple Summary

Seasonal change, particularly changing to hot and humid season, has a negative effect on dairy cows in various ways, including productivity, reproduction, metabolism, and immunity. In high-temperature and humid weather, dairy cows are vulnerable to diseases by weakened immune system. However, the cause of this has not been fully described. Therefore, this study aims to understand changes of specific gene expression and immune pathways based on transcriptome analysis from peripheral blood mononuclear cells of Holstein and Jersey dairy cows between normal and heat-stress environmental conditions. We observed that the two breeds of dairy cow have common and different immune shifts according to the changes of temperature and humidity condition. Overall, the findings of this study improve the understanding of the underlying mechanisms by which seasonal changes affect dairy cow immunity.

Abstract

Heat stress has been reported to affect the immunity of dairy cows. However, the mechanisms through which this occurs are not fully understood. Two breeds of dairy cow, Holstein and Jersey, have distinct characteristics, including productivity, heat resistance, and disease in high-temperature environments. The objective of this study is to understand the dynamics of the immune response of two breeds of dairy cow to environmental change. Ribonucleic acid sequencing (RNA-seq) results were analyzed to characterize the gene expression change of peripheral blood mononuclear cells (PBMCs) in Holstein and Jersey cows between moderate temperature-humidity index (THI) and high THI environmental conditions. Many of the differentially expressed genes (DEGs) identified are associated with critical immunological functions, particularly phagocytosis, chemokines, and cytokine response. Among the DEGs, CXCL3 and IL1A were the top down-regulated genes in both breeds of dairy cow, and many DEGs were related to antimicrobial immunity. Functional analysis revealed that cytokine and chemokine response-associated pathways in both Holstein and Jersey PBMCs were the most important pathways affected by the THI environmental condition. However, there were also breed-specific genes and pathways that altered according to THI environmental condition. Collectively, there were both common and breed-specific altered genes and pathways in Holstein and Jersey cows. The findings of this study expand our understanding of the dynamics of immunity in different breeds of dairy cow between moderate THI and high THI environmental conditions.

The effects of zinc amino acid complex on biomarkers of gut integrity, inflammation, and metabolism in heat-stressed ruminants

Study objectives were to evaluate the effects of replacing 40 mg/kg of dietary Zn from Zn sulfate (ZS) with Zn amino acid complex (ZA; Zinpro Corporation, Eden Prairie, MN) on inflammation and intestinal integrity in heat-stressed and pair-fed (PF) ruminants. Forty Holstein steers (173.6 ± 4.9 kg) were randomly assigned to 1 of 5 dietary-environmental treatments: (1) thermoneutral (TN) ad libitum with 75 mg/kg of dry matter (DM) ZS (ZSCON); (2) TN pair-fed with 75 mg/kg DM ZS (ZSPF); (3) TN pair-fed with 40 mg/kg DM ZA and 35 mg/kg DM ZS (ZAPF); (4) heat stress (HS) ad libitum with 75 mg/kg DM ZS (ZSHS); and (5) HS ad libitum 40 mg/kg DM ZA and 35 mg/kg DM ZS (ZAHS). Before study initiation, calves were fed their respective diets for 21 d. Following the pre-feeding phase, steers were transferred into environmental chambers and were subjected to 2 successive experimental periods. During period 1 (5 d), all steers were fed their respective diets ad libitum and housed in TN conditions (20.2 ± 1.4°C, 30.4 ± 4.3% relative humidity). During period 2 (6 d), ZSHS and ZAHS steers were exposed to cyclical HS conditions (27.1 ± 1.5°C to 35.0 ± 2.9°C, 19.3 ± 3.5% relative humidity), whereas the ZSCON, ZSPF, and ZAPF steers remained in TN conditions and were fed ad libitum or pair-fed relative to their ZSHS and ZAHS counterparts. Overall, steers exposed to HS had markedly increased rectal temperature (0.83°C), respiration rate (26 breaths per min), and skin temperature (8.00°C) relative to TN treatments. Rectal temperature from ZAHS steers was decreased (0.24°C) on d 4 to 6 of HS relative to ZSHS steers. Regardless of diet, HS decreased DMI (18%) relative to ZSCON steers. Circulating glucose from HS and PF steers decreased (16%) relative to ZSCON steers. Heat stress and nutrient restriction increased circulating nonesterified fatty acids 2- and 3-fold, respectively, compared with ZSCON steers. Serum amyloid A increased ~2-fold in PF relative to ZSCON and HS steers. We detected no treatment effect on blood pH; however, ZAHS steers had increased HCO₃ relative to ZSHS. Relative to ZSHS, ZAHS steers had increased jejunum villi height (25%), a tendency for increased ileum villi height (9%), and decreased duodenal villi width (16%). In summary, ZA supplementation has some beneficial effects on thermal indices, intestinal architecture characteristics, and biomarkers of leaky gut in heat-stressed steers, indicative of an ameliorated heat load, and thus may be a nutritional strategy to minimize negative consequences of HS.

Effects of a Saccharomyces cerevisiae fermentation product on heat-stressed dairy cows

The objective of this study was to evaluate the effects of supplementing a Saccharomyces cerevisiae fermentation product (SCFP) on body temperature indices, metabolism, acute phase protein response, and production variables during heat stress (HS). Twenty multiparous lactating Holstein cows (body weight = 675 ± 12 kg; days in milk = 144 ± 5; and parity = 2.3 ± 0.1) were used in an experiment conducted in 2 replicates (10 cows/replicate). Cows were randomly assigned to 1 of 2 dietary treatments: control diet (CON; n = 10) or the CON diet supplemented with 19 g/d of SCFP (n = 10; NutriTek, Diamond V, Cedar Rapids, IA). Cows were fed their respective diets for 21 d before initiation of the study. The experiment consisted of 2 periods: thermoneutral (period 1; P1) and heat stress (period 2; P2). During P1 (4 d), cows were fed ad libitum and housed in thermoneutral conditions for collecting baseline data. During P2 (7 d), HS was artificially induced using an electric heat blanket (EHB; Thermotex Therapy Systems Ltd., Calgary, AB, Canada). Cows were fitted with the EHB for the entirety of P2. Rectal temperature, respiration rate, and skin temperature were obtained twice daily (0600 and 1800 h) during both periods. Overall, HS increased rectal temperature, skin temperature, and respiration rate (1.4°C, 4.8°C, and 54 breaths/min, respectively) relative to P1, but no dietary treatment differences were detected. Compared with P1, HS decreased dry matter intake and milk yield (36 and 26%, respectively), and the reductions were similar between dietary treatments. Relative to P1, HS increased milk fat content and milk urea nitrogen (17 and 30%, respectively) and decreased milk protein and lactose contents (7 and 1.4%, respectively). Overall, HS increased (52%) plasma cortisol concentrations of CON, but circulating cortisol did not change in SCFP-fed cows. Heat stress increased circulating lipopolysaccharide binding protein and serum amyloid A (SAA; 2- and 4-fold, respectively), and SCFP supplementation tended to decrease peak SAA (∼33%) relative to CON cows. Overall, although HS did not influence circulating white blood cells and neutrophils, SCFP increased circulating white blood cells and neutrophils by 9 and 26%, respectively, over CON in P2. In conclusion, HS initiated an acute phase protein response and feeding SCFP blunted the cortisol and SAA concentrations and altered some key leukocyte dynamics during HS.

Effects of dietary electrolytes, osmolytes, and energetic compounds on body temperature indices in heat-stressed lactating cows

Objectives were to determine the effects of a product containing electrolytes, osmolytes, and energetic compounds (EOEC) on body temperature indices in heat-stressed (HS) Holstein cows. Lactating cows were assigned to 1 of 2 treatments: 1) a control diet (n = 10) or 2) a control diet supplemented with 113 g/d of EOEC (n = 10; Bovine BlueLite® Pellets; TechMix LLC, Stewart, MN). The trial consisted of 2 experimental periods (P). During P1 (4 d), cows were fed their respective treatments and housed in thermoneutral conditions. During P2 (4 d), HS was artificially induced using an electric heat blanket (EHB). Overall, HS markedly increased vaginal temperature (Tv), rectal temperature (Tr), skin temperature (Ts), and respiration rate (RR) (P < .01). There were no dietary treatment differences in Tv, Tr, or RR; however, during P2 EOEC-supplemented cows had increased Ts (0.8 °C; P = .04). Compared to P1, HS decreased DMI and milk yield (45 and 27%, respectively, P < .01) similarly amongst treatments. Relative to P1, circulating insulin decreased (41%; P = .04) in CON cows, whereas it remained unaffected in EOEC-supplemented cows, resulting in a 2-fold increase in EOEC compared with CON-fed cows (P < .01) during P2. Relative to P1, HS increased circulating non-esterified fatty acids (NEFA; 63%; P < .01). During P2, there tended to be a treatment by day interaction on circulating NEFA, as concentrations decreased from d 2 to 4 of P2 in EOEC-fed cows but continued to increase in CON cows. In summary, feeding EOEC altered some key aspects of energetic metabolism and increased Ts.