The objective of this study was to evaluate relationships between measurements of temperature-humidity index (THI) and rectal, vaginal, and udder surface temperatures in lactating cows exposed to heat stress (HS). In experiment 1, 12 multiparous and 8 primiparous Holstein cows experienced a THI ranging from 69 to 76 at 2000 to 1000 h and THI from 74 to 82 at 1000 to 2000 h (peaked at 82 from 1400 to 1800 h). Cows were exposed to HS 10 h daily for 21 d. Measurements of rectal temperature (RT) and udder surface temperature were collected at 1000 and 1500 h (±30 min). Vaginal temperature was monitored every 10 min using digital loggers, averaged over 1 h, and paired with corresponding rectal and udder surface temperature data. In experiment 2, 12 multiparous Holstein cows experienced a THI ranging from 60 to 76 at 2000 to 1000 h and THI from 69 to 83 at 1000 to 2000 h (peaked at 83 from 1600 and 1900 h), eliciting 10 h/d of HS for 7 d. Rectal and udder surface temperatures were analyzed at 0700 and 1500 h (±30 min). Vaginal temperature was recorded and analyzed as indicated in experiment 1. Afternoon THI showed weak correlations with surface temperature (r = 0.19, n = 420 in experiment 1; r = 0.23, n = 84 in experiment 2), weak to moderate correlations with RT (r = 0.34, n = 366 in experiment 1; r = 0.26, n = 84 in experiment 2), and moderate correlations with vaginal temperature (r = 0.34, n = 175 in experiment 1; r = 0.35, n = 40 in experiment 2). Moreover, vaginal temperature increased 0.10 and 0.22°C per unit of THI (R = 0.15 in experiment 1; R = 0.40 in experiment 2). Afternoon vaginal temperature strongly correlated with RT (r = 0.69, n = 131 in experiment 1; r = 0.63, n = 37 in experiment 2) and explained 57 (experiment 1) and 68% (experiment 2) of variation in RT. Surface temperature showed moderate to strong correlations with RT (r = 0.57, n = 84) and vaginal temperature (r = 0.74, n = 37) in experiment 2. In conclusion, THI showed a weak to moderate relationship with core body temperatures and explained the increase in rectal and vaginal temperatures experienced by HS cows. Compared with rectal temperature, vaginal temperature showed stronger relationships with THI and can be used to determine thermal load. Udder surface temperature showed a moderate to strong relationship with core body temperature, and this relationship may support the use of surface temperature data to manage thermal load in HS cows.

Poor utilization of amino acids contributes to losses of milk protein yield in dairy cows exposed to heat stress (HS). Our objective was to test the effect of essential amino acids on milk production in lactating dairy cows exposed to short-term HS conditions. To achieve this objective, 12 multiparous, lactating Holstein cows were assigned to two environments (thermoneutral (THN) or HS) from days 1 to 14 in a split-plot type cross-over design. All cows received 0 g/day of essential amino acids from days 1 to 7 (negative control (NC)) followed by an intravenous infusion of l-methionine (12 g/day), l-lysine (21 g/day), l-leucine (35 g/day), l-isoleucine (15 g/day) and l-valine (15 g/day, methionine, lysine and branched-chain amino acids (ML+BCAA)) from days 8 to 14. The basal diet was composed of ryegrass silage and hay, and a concentrate mix. This diet supplied 44 g of methionine, 125 g of lysine, 167 g of leucine, 98 g of isoleucine and 109 g of valine per day to the small intestine of THN cows. Temperature-humidity index was maintained below 66 for the THN environment, whereas the index was maintained above 68, peaking at 76, for 14 continuous h/day for the HS environment. Heat stress conditioning increased the udder temperature from 37.0°C to 39.6°C. Cows that received the ML+BCAA treatment had greater p.m. rectal and vaginal temperatures (0.50°C and 0.40°C, respectively), and respiration rate (8 breaths/min) compared with those on the NC treatment and exposed to a HS environment. However, neither NC nor ML+BCAA affected rectal or vaginal temperatures and respiration rates in the THN environment. Compared with THN, the HS environment reduced dry matter intake (1.48 kg/day), milk yield (2.82 kg/day) and milk protein yield (0.11 kg/day). However, compared with NC, the ML+BCAA treatment increased milk protein percent by 0.07 points. For the THN environment, the ML+BCAA treatment increased concentrations of milk urea nitrogen. For the HS environment, the ML+BCAA treatment decreased plasma concentrations of arginine, ornithine and citrulline; however, differences were not observed for the THN environment. In summary, HS elicited expected changes in production; however, infusions of ML+BCAA failed to increase milk protein yield. Lower dry matter intake and greater heat load in response to ML+BCAA contributed to the lack of response in milk production in HS cows. The ML+BCAA treatment may have reduced the breakdown of muscle protein in heat-stressed cows.

Heat stress is detrimental to food-producing animals and animal productivity remains suboptimal despite the use of heat abatement strategies during summer. Global warming and the increase of frequency and intensity of heatwaves are likely to continue and, thus, exacerbate the problem of heat stress. Heat stress leads to the impairment of physiological and cellular functions of ectothermic and endothermic animals. Therefore, it is critical to conceive ways of protecting animals against the pathological effects of heat stress. In experiments with endothermic animals highly sensitive to heat (Bos taurus), we have previously reported that heat-induced systemic inflammation can be ameliorated in part by nutritional interventions. The experiments conducted in this report described molecular and physiological adaptations to heat stress using Drosophila melanogaster and dairy cow models. In this report, we expand previous work by first demonstrating that the addition of a postbiotic from Aspergillus oryzae (AO) into the culture medium of ectothermic animals (Drosophila melanogaster) improved survival to heat stress from 30 to 58%. This response was associated with downregulation of genes involved in the modulation of oxidative stress and immunity, most notably metallothionein B, C, and D. In line with these results, we subsequently showed that the supplementation with the AO postbiotic to lactating dairy cows experiencing heat stress decreased plasma concentrations of serum amyloid A and lipopolysaccharide-binding protein, and the expression of interleukin-6 in white blood cells. These alterations were paralleled by increased synthesis of energy-corrected milk and milk components, suggesting enhanced nutrient partitioning to lactogenesis and increased metabolic efficiency. In summary, this work provides evidence that a postbiotic from AO enhances thermal tolerance likely through a mechanism that entails reduced inflammation.

Hyperthermia alters utilization of AA in protein synthesis and cell-signaling activity in bovine mammary cells. Essential AA and insulin regulate translation of proteins by controlling the activity of mammalian target of rapamycin (mTOR) signaling pathway. The objectives of this study were to evaluate (1) the effects of incubation temperature on the mTOR signaling pathway and transcription of AA transporters in a bovine mammary alveolar cell line (MAC-T) and (2) the combined effects of incubation temperature and insulin on the mTOR signaling pathway in this cell line. Cells were cultured in medium with 10% fetal bovine serum at 37°C and 5% CO. In experiment 1, cells were subjected to 37°C (control) or 41.5°C (high incubation temperature; HT) for 12 h. In experiment 2, cells were assigned to 1 of 4 treatments as a 2 × 2 factorial arrangement, including 2 cell culture temperatures (control and HT) and absence or presence of 1.0 μg/mL of insulin. Proteins were harvested and separated by gel electrophoresis. In experiment 1, gene expression of AA transporters (SLC1A1, SLC1A5, SLC3A2, SLC7A1, SLC7A5, and SLC36A1) were evaluated, and changes of ≥2 fold were deemed significantly different. In experiments 1 and 2, immunoblotting was used to identify total and site-specific phosphorylated forms of protein kinase B (Akt1; Ser473), p70 S6 kinase (S6K1; Thr389), ribosomal protein S6 (rpS6; Ser235/236), and eukaryotic elongation factor 2 (eEF2; Thr56). Phosphorylated and total forms of Akt1, S6K1, rpS6, and eEF2 were quantified and expressed as the ratio of phosphorylated to total protein. In experiment 1, HT resulted in a ≥2-fold increase expression of SLC1A1 and SLC3A2. High incubation temperature reduced the phosphorylated to total ratio of Akt1 and rpS6 and increased the phosphorylated to total ratio of eEF2. In experiment 2, we found no temperature by insulin interactions on phosphorylation state of the protein factors of interest. High incubation temperature reduced the phosphorylated to total ratio of Akt1. The addition of insulin increased the phosphorylated to total ratio of Akt1, S6K1, and rpS6. In summary, HT reduced the activity of the mTOR signaling pathway and increased the expression of AA transporters. High incubation temperature possibly reduced protein translation by reducing the mTOR signaling pathway activity in an effort to adapt to thermal stress. These results may help explain the direct effect of elevated temperature on AA metabolism and protein translation in heat-stressed animals.

The objective of this study was to examine the effect of reducing rumen-degradable protein (RDP) and rumen-undegradable protein (RUP) proportions on feed intake, milk production, and N-use efficiency in primiparous and multiparous cows exposed to warm climates. Eighteen primiparous and 30 multiparous mid-lactation Holstein cows were used in a completely randomized design with a 2 × 2 factorial arrangement of treatments. Cows were randomly assigned to 1 of 4 dietary treatments formulated to contain 2 proportions of RDP (10 and 8%) and 2 proportions RUP (8 and 6%) of dry matter (DM) indicated as follows: (1) 10% RDP, 8% RUP; (2) 8% RDP, 8% RUP; (3) 10% RDP, 6% RUP; and (4) 8% RDP, 6% RUP. Protein sources were manipulated to obtain desired RDP and RUP proportions. Diets were isoenergetic and contained 50% forage and 50% concentrate (DM basis). Cows were individually fed the 10% RDP, 8% RUP diet 3 wk before treatment allocation. Cows were exposed to the prevailing Tennessee July and August temperature and humidity in a freestall barn with no supplemental cooling. Main effects and their interaction were tested using the Mixed procedure of SAS (least squares means ± standard error of the mean; SAS Institute Inc., Cary, NC). Observed values of nutrient intake and milk production were used to obtain NRC (2001) model predictions. Cows showed signs of heat stress throughout the study. Reducing from 10 to 8% RDP decreased dry matter intake (DMI; 0.9 kg/d) at 8% RUP, but increased DMI (2.6 kg/d) at 6% RUP in primiparous cows. Reducing from 10 to 8% RDP decreased milk yield (10%) at 8% RUP, but increased yield (14%) at 6% RUP. Treatments did not affect yield of energy-corrected milk. For multiparous cows, treatments did not affect DMI. Reducing from 10 to 8% RDP decreased yield of energy-corrected milk (3.4%) at 8% RUP, but increased yield (8.8%) at 6% RUP. Reducing from 10 to 8% RDP and 8 to 6% RUP both increased N-use efficiency for primiparous and multiparous cows. The NRC model underestimated metabolizable protein and RUP supply, and overestimated RUP requirements, resulting in predictive losses of milk yield 1.4 to 5.8 times greater than observed values. In summary, the reduction of RDP and RUP proportions did not affect DMI, whereas the RUP reduction at 10% RDP had a small negative effect on energy-corrected milk yield. However, reduction of RDP and RUP consistently improved N-use efficiency of heat-stressed multiparous cows. The reduction of RDP and RUP proportions reduced DMI and milk yield but did not affect energy-corrected milk yield in primiparous cows, indicating a limited supply of nutrients.