Dry Period Heat Stress Impacts Mammary Protein Metabolism in the Subsequent Lactation

Abstract

Dry period heat stress impairs subsequent milk production, but its impact on milk protein content and yield is inconsistent. We hypothesize that dairy cow exposure to dry period heat stress will reduce milk protein synthesis in the next lactation, potentially through modified amino acid (AA) transport and compromised mTOR signaling in the mammary gland. Cows were enrolled into heat-stressed (dry-HT, n = 12) or cooled (dry-CL, n = 12) treatments for a 46-day dry period then cooled after calving. Milk yield and composition and dry matter intake were recorded, and milk, blood, and mammary tissue samples were collected at 14, 42, and 84 days in milk (DIM) to determine free AA concentrations, milk protein fractions, and mammary AA transporter and mTOR pathway gene and protein expression. Dry matter intake did not significantly differ between treatments pre- or postpartum. Compared with dry-CL cows, milk yield was decreased (32.3 vs. 37.7 ± 1.6 kg/day) and milk protein yield and content were reduced in dry-HT cows by 0.18 kg/day and 0.1%. Further, dry-HT cows had higher plasma concentrations of glutamic acid, phenylalanine, and taurine. Gene expression of key AA transporters was upregulated at 14 and 42 DIM in dry-HT cows. Despite minor changes in mTOR pathway gene expression, the protein 4E-BP1 was upregulated in dry-HT cows at 42 DIM whereas Akt and p70 S6K1 were downregulated. These results indicate major mammary metabolic adaptations during lactation after prior exposure to dry period heat stress.

Increased dietary methionine, lysine and histidine supply modulated the heat stress-induced metabolic remodeling of dairy cows

“…In contrast, our metabolic pathway analysis found the Phe and Tyr metabolism differed only in the multiparous cows. Dado-Senn et al (2021) observed increased plasma concentrations of Phe after heat stress pointing to links with immune and heat shock response. Phe metabolism interacts with T-cell immune response suppression (Yang et al, 2012) and its supplementation increased HSP70 expression (Plakidou-Dymock and McGivan, 1994).…”

“…master regulator of protein synthesis stimulated by BCAA and Lys (Doelman et al, 2015;Lin et al, 2018), were suggested to explain the decreased protein synthesis in the mammary gland during heat stress (Rıús, 2019). Heat stress downregulated the expression of genes involved in AA utilization, AA transport, and mTOR kinase activity in bovine mammary epithelial cells (Kaufman et al, 2018;Dado-Senn et al, 2021). Through a different pathway, insulin also activates downstream mTOR pathways but it is dependent on BCAA availability (Shimobayashi and Hall, 2016;Keneź et al, 2019).…”

Abundance of Amino Acid Transporters and mTOR Pathway Components in the Gastrointestinal Tract of Lactating Holstein Cows

“…It is located in the plasma membrane in MDCKII cells and the apical membrane of human kidney tubules and proximal tubules [ 65 ]. SLC1A1 was also detected in mammary tissue [ 67 ] and placentomes [ 6 ] from dairy cows. SLC6A6 is a Na+- and Cl−-dependent, high-affinity, low-capacity transporter of taurine and β-alanine on the membrane surface [ 68 ].…”

Udder Health Monitoring for Prevention of Bovine Mastitis and Improvement of Milk Quality

“…Moreover, the impact of heat stress extends beyond milk production, influencing its quality simultaneously as well, with considerable modifications being reported in the case of certain physical-chemical parameters, such as lipid, lactose, protein, casein, and urea content [ 27 , 33 , 34 , 35 ]. According to studies carried out by Hill and Wall (2014) [ 36 ], Liu et al (2017) [ 37 ], as well as Dado-Senn et al (2021) [ 38 ], a reduction in lactose, casein and/or fat content was observed in cows exposed to heat stress.…”