Cellular and mitochondrial adaptation mechanisms in the colon of lactating dairy cows during hyperthermia.

Heat stress causes barrier dysfunction and inflammation of the small intestine of several species. However, less is known about the molecular and cellular mechanisms underlying the response of the bovine large intestine to hyperthermia. We aimed to identify changes in the colon of dairy cows in response to constant heat stress using a proteomic approach. Eighteen lactating Holstein dairy cows were kept under constant thermoneutral conditions (16°C and 68% relative humidity [RH]; temperature-humidity index [THI] = 60) for 6 d (period 1) with free access to feed and water. Thereafter, 6 cows were equally allocated to (1) thermoneutral condition with ad libitum feeding (TNAL; 16°C, RH = 68%, THI = 60), (2) heat stress condition (HS; 28°C, RH = 50%, THI = 76) with ad libitum feeding, or (3) pair-feeding at thermoneutrality (TNPF; 16°C, RH = 68%, THI = 60) for another 7 d (period 2). Rectal temperature, milk yield, dry matter and water intake were monitored daily. Then, cows were slaughtered and colon mucosa samples were taken for proteomic analysis. Physiological data were analyzed by ANOVA and colon proteome data were processed using DESeq2 package in R. Rectal temperature was significantly higher in HS than in TNPF and TNAL cows in period 2. Proteomic analysis revealed an enrichment of activated pathways related to colonic barrier function and inflammation, heat shock proteins, AA metabolism, reduced overall protein synthesis rate, and post-transcriptional regulation induced by heat stress. Further regulations were found for enzymes of the tricarboxylic acid cycle and components of the mitochondrial electron transport chain, presumably to reduce the generation of reactive oxygen species, maintain cellular ATP levels, and prevent apoptosis in the colon of HS cows. These results highlight the cellular, extracellular, and mitochondrial adaptations of the colon during heat stress and suggest a dysfunction of the hindgut barrier integrity potentially resulting in a "leaky" colon.

The effect of chronic, mild heat stress on metabolic changes of nutrition and adaptations in rumen papillae of lactating dairy cows.

Global warming and accompanying high ambient temperatures reduce feed intake of dairy cows and shift the blood flow from the core of the body to the periphery. As a result, hypoxia may occur in the digestive tract accompanied by disruption of the intestinal barrier, local endotoxemia and inflammation, and altered nutrient absorption. However, whether the barrier of the rumen, like the intestine, is affected by ambient heat has not been studied so far. Lactating Holstein dairy cows were subjected to heat stress at 28°C (temperature-humidity index = 76; n = 5) with ad libitum feed intake or to thermoneutral conditions at 15°C (temperature-humidity index = 60; n = 5) and pair-feeding to heat-stressed animals for a total of 4 d. Gas exchange and feed intake behavior were measured in a respiration chamber, and rumen epithelia were taken after slaughter. Heat stress significantly reduced meal size and whole-body fat oxidation but increased meal frequency and carbohydrate oxidation. The mRNA expression of toll-like receptor 4 (TLR4) and tight junction proteins and the phosphorylation of TLR4 downstream targets (interleukin-1 receptor-associated kinase 4, stress-activated protein kinase, p38 mitogen-activated protein kinase, and nuclear factor k-B) in the rumen epithelium were not affected by heat. The proteomics approach revealed increased expression of rumen epithelium proteins involved in the AMP-activated protein kinase (AMPK) and insulin signaling pathways in heat-stressed cows. Also, proteins involved in chaperone-mediated folding of proteins were upregulated, whereas those involved in antioxidant defense system were downregulated. Further, we found evidence for increased carbohydrate phosphorylation accompanied with an increased flux of carbohydrates through the hexosamine biosynthetic pathway, providing substrates for protein glycosylation. In conclusion, the mild heat stress did not induce barrier dysfunction or inflammatory responses in the rumen epithelium of dairy cows, probably because of adaptations in feed intake behavior and defense mechanisms at the tissue level.

Effects of intensified or conventional milk feeding on pre-weaning health and feeding behavior of Holstein female calves around weaning.

Health, inflammatory, and stress indices as well as feeding behavior around weaning were measured for Holstein female calves fed intensified milk or conventionally during the pre-weaning period. Calves (n ꞊ 48) were randomly assigned to one of two experimental treatments including a conventional (CF) or an intensified feeding (IF) groups. In CF group, calves (n ꞊ 24) received 0.52 kg of dry matter (DM) per day from pasteurized whole milk (23.00% crude protein (CP) and 27.00% fat) until day 50 of age. In IF group, calves (n = 24) fed 0.97 kg of DM per day on average for the first three weeks, and then, milk allowance decreased gradually to reach 0.52 kg DM per day and continued until day 50. All calves were gradually weaned from day 51 to 56. Blood samples were taken on days 14, 28, and 57 at 06:30 AM for serum amyloid A (SAA), cortisol, alanine aminotransferase (ALT), and iron analyses. Conventionally fed calves had more days with fever during the pre-weaning period. Blood SAA and cortisol levels were higher in CF calves on day 14. However, SAA levels were higher for IF calves on day 57. Intensified milk-fed calves spent more time for standing than CF calves. A trend to be significant was observed for non-nutritive oral behavior in IF calves. In summary, dairy calf health can be improved by intensified milk feeding during the pre-weaning period; however, this method has the potential to reduce calves welfare around weaning transition.

TECHNICAL NOTE: Development of a pressure sensor-based system for measuring rumination time in pre-weaned dairy calves.

The pressure-based noseband sensor system (RWS: RumiWatch System; ITIN + HOCH GmbH Feeding Technology, Liestal, Switzerland) has recently been validated for the measurement of rumination time in mature cows. We aimed in this study at developing a similar pressure-based system for monitoring rumination in young dairy calves. To this end, a vegetable oil-filled silicon tube with a built-in pressure sensor (outer diameter 5.7 mm, length 38 cm) was attached to the noseband of a calf halter. In contrast to the RWS developed for mature cows, the accelerometer, the battery, the data logger, and the SD card of the RWS were integrated into 1 box to reduce the weight of the RWS to 0.35 kg. The box was attached to the halter so that it was located behind the right ear of the calf. Ten pre-weaned German Holstein calves (49-106 kg BW and 33-63 days of age) were equipped with the RWS. Calves were milk-fed thrice a day and offered hay and commercial starter for ad libitum intake. In parallel, animals were monitored by a video camera connected to a video recorder for 12 h. Two independent observers assessed the video records to obtain a reliable gold standard for the evaluation of the newly developed RWS. Data obtained by either RWS or visual video observation were processed as min rumination per h, yielding a total of 120 pairs of values (12 pairs per animal) for regression analysis. Assessment of 2 independent observers were highly correlated (r = 0.99). Results indicated relatively low random error between results obtained from the RWS (on y-axis) and video observations (on x-axis) (R2 = 0.82). However, the intercept of the regression line (y = 7.70 + 0.64 x) was significantly different from zero (P < 0.01) and the 95% confidence interval of the slope (0.79-0.94) did not include the value of 1. This translates to a significant systemic error resulting in overestimation of rumination time which is attributable to nutritive and nonnutritive oral activities that almost exclusively lasted for up to 10 min. Exclusion of false positive rumination signals lasting less than 10 or 5 consecutive min from the analysis reduced the random and systemic errors of the model (R2 = 0.86 and 0.93, respectively). We conclude that the newly developed RWS can be used to provide accurate measurement of rumination time in young calves. However, an extra programmed algorithm in the evaluation software is recommended to make the system more user-friendly for measurements on calves.

Metabolic Response to Heat Stress in Late-Pregnant and Early Lactation Dairy Cows: Implications to Liver-Muscle Crosstalk.

Climate changes lead to rising temperatures during summer periods and dramatic economic losses in dairy production. Modern high-yielding dairy cows experience severe metabolic stress during the transition period between late gestation and early lactation to meet the high energy and nutrient requirements of the fetus or the mammary gland, and additional thermal stress during this time has adverse implications on metabolism and welfare. The mechanisms enabling metabolic adaptation to heat apart from the decline in feed intake and milk yield are not fully elucidated yet. To distinguish between feed intake and heat stress related effects, German Holstein dairy cows were first kept at thermoneutral conditions at 15°C followed by exposure to heat-stressed (HS) at 28°C or pair-feeding (PF) at 15°C for 6 days; in late-pregnancy and again in early lactation. Liver and muscle biopsies and plasma samples were taken to assess major metabolic pathway regulation using real-time PCR and Western Blot. The results indicate that during heat stress, late pregnant cows activate Cahill but reduce Cori cycling, prevent increase in skeletal muscle fatty acid oxidation, and utilize increased amounts of pyruvate for gluconeogenesis, without altering ureagenesis despite reduced plane of nutrition. These homeorhetic adaptations are employed to reduce endogenous heat production while diverting amino acids to the growing fetus. Metabolic adaptation to heat stress in early lactation involves increased long-chain fatty acid degradation in muscle peroxisomes, allowance for muscle glucose utilization but diminished hepatic use of amino acid-derived pyruvate for gluconeogenesis and reduced peroxisomal fatty acid oxidation and ATP production in liver of HS compared to PF cows in early lactation. Consequently, metabolic adaptation to heat stress and reduced feed intake differ between late pregnancy and early lactation of dairy cows to maintain energy supply for fetus development or milk production simultaneously reducing endogenous heat production.

The control of short-term feed intake by metabolic oxidation in late-pregnant and early lactating dairy cows exposed to high ambient temperatures.

The objective of the present study was to integrate the dynamics of feed intake and metabolic oxidation in late pregnant and early lactating Holstein cows under heat stress conditions. On day 21 before parturition and again on day 20 after parturition, seven Holstein cows were kept for 7days at thermoneutral (TN) conditions (15°C; temperature-humidity-index (THI)=60) followed by a 7day heat stress (HS) period at 28°C (THI=76). On the last day of each temperature condition, gas exchange, feed intake and water intake were recorded every 6min in a respiration chamber. Pre- and post-partum cows responded to HS by decreasing feed intake. The reduction in feed intake in pre-partum cows was achieved through decreased meal size, meal duration, eating rate and daily eating time with no change in meal frequency, while post-partum cows kept under HS conditions showed variable responses in feeding behavior. In both pre- and post-partum cows exposed to heat stress, daily and resting metabolic heat production decreased while the periprandial respiratory quotient (RQ) increased. The prolonged time between meal and the postprandial minimum in fat oxidation and the postprandial RQ maximum, respectively, revealed that HS as compared to TN early-lactating cows have slower postprandial fat oxidation, longer feed digestion, and thereby showing a shift from fat to glucose utilization.