Browsing by Author "Perez-Hernandez, G."

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    Cyclical heat stress during lactation influences the microstructure of the bovine mammary gland
    Perez-Hernandez, G.; Ellett, Mark D.; Banda, L. J.; Dougherty, D.; Parsons, Catherine L. M.; Lengi, A. J.; Daniels, Kristy M.; Corl, Benjamin A. (Elsevier, 2024-05-31)
    This study aimed to evaluate the effect of heat stress on mammary epithelial cell (MEC) losses into milk, secretory mammary tissue structure, and mammary epithelial cell activity. Sixteen multiparous Holstein cows (632 ± 12 kg BW) approximately 100 DIM housed in climate-controlled rooms were paired by BW and randomly allocated to one of 2 treatments, heat stress (HS) or pair-feeding thermoneutral (PFTN) using 2 cohorts. Each cohort was subjected to 2 periods of 4 d each. In period 1, both treatments had ad libitum access to a common TMR and were exposed to a controlled daily temperature-humidity index (THI) of 64. In period 2, HS cows were exposed to controlled cyclical heat stress (THI: 74–80), while PFTN cows remained at 64 THI and daily DMI was matched to that of the HS cows. Cows were milked twice daily, and milk yield was recorded at each milking. Individual milk samples on the last day of each period were used to quantify MEC losses by flow cytometry using butyrophilin as a cell surface marker. On the final day of period 2, individual bovine mammary tissue samples were obtained for histomorphology analysis, assessment of protein abundance, and evaluation of gene expression of targets associated with cellular capacity for milk and milk component synthesis, heat response, cellular proliferation, and autophagy. Statistical analysis was performed using the GLIMMIX procedure of SAS. Milk yield was reduced by 4.3 kg by HS (n = 7) compared with PFTN (n = 8). Independent of treatment, MEC in milk averaged 174 cells/mL (2.9% of total cells). There was no difference between HS and PFTN cows for MEC shed or concentration in milk. Alveolar area was reduced 25% by HS, and HS had 4.1 more alveoli than PFTN. The total number of nucleated MEC per area was greater in HS cows (389 ± 1.05; mean ± SE) compared with PFTN (321 ± 1.05); however, cell number per alveolus was similar between groups (25 ± 1.5 vs. 26 ± 1.4). There were no differences in relative fold expression for GLUT1, GLUT8, CSN2, CSN3, LALBA, FASN, HSPA5, and HSPA8 in HS cows compared with PFTN cows. Immunoblotting analyses showed a decrease in abundance for phosphorylated STAT5 and S6K1, and an increase in LC3 II in HS cows compared with PFTN cows. These results suggest that even if milk yield differences and histological changes occur in the bovine mammary gland after 4 d of heat exposure, MEC loss into milk, nucleated MEC number per alveolus, and gene expression of nutrient transport, milk component synthesis, and heat-stress-related targets are unaffected. In contrast, the abundance of proteins related to protein synthesis and cell survival decreased significantly, whereas proteins associated with autophagy were upregulated in HS cows compared with PFTN cows.
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    Tissue-specific responses to oxidative fuel source preference during heat stress in lactating dairy cows
    Ellett, Mark D.; Daniels, Kristy M.; Hanigan, Mark D.; Corl, Benjamin A.; Perez-Hernandez, G.; Parsons, Catherine L. M.; Melvin, J. A.; Fausnacht, D. W.; McMillan, R. P.; Baumgard, L. H.; Rhoads, Robert P. (American Dairy Science Association, 2024-09-18)
    Prolonged exposure to high environmental temperatures results in an accumulated heat load that induces a heat stress (HS) response in dairy cattle. Heat stress compromises dairy farm profitability by reducing milk yield, altering milk composition, and hindering reproductive performance. The ability to alternate between carbohydrate and lipid sources for energy production is termed metabolic flexibility (Met Flex). The objective of this study was to evaluate the Met Flex of mammary, muscle, and liver tissue in lactating dairy cows under HS and thermoneutral (TN) conditions. Sixteen Holstein cows were assigned to 1 of 2 treatment groups: pair-feeding in TN conditions (PFTN) or HS conditions. All cows experienced a 4-d TN period with ad libitum intake followed by a 4-d treatment period. Heat stress cows were exposed to a temperature-humidity index (THI) ranging from 76 to 80 and the PFTN cows were exposed to a THI of 64. Milk production and health data were recorded twice daily. Semitendinosus biopsies were obtained on d 4 of each period and postmortem mammary and liver samples were obtained on d 4 of period 2. All tissue samples were assayed for Met Flex. Activity of mitochondrial (Mit) enzymes were assessed in skeletal muscle only. Four days of HS decreased milk yield, altered milk composition, and increased respiration rate and rectal temperatures. No differences in Met Flex were observed in mammary or liver tissue during period 2. However, HS, but not PFTN conditions, lowered Met Flex of skeletal muscle by 18.3% when compared with TN ad libitum feed intake conditions of period 1. No treatment differences were observed in skeletal muscle Mit enzyme activity indicating the decrease in Met Flex occurred independently of changes in Mit function. The reduction in Met Flex of skeletal muscle during HS may contribute to reduced milk yield and warrants further investigation.