Comparison of production-related responses to hyperinsulinemia and hypoglycemia induced by clamp procedures or heat stress of lactating dairy cattle

Abstract

Hyperinsulinemia concurrent with hypoglycemia is one of a myriad of physiological changes typically experienced by lactating dairy cows exposed to heat stress, the consequences of which are not yet well defined or understood. Therefore, the objective of this experiment was to separate the production-related effects of hyperinsulinemia with hypoglycemia from those of a hyperthermic environment. Multiparous lactating Holstein cows (n = 23; 58 ± 4 d in milk, 3.1 ± 0.3 lactations) were housed in temperature-controlled rooms and all were subjected to 4 experimental periods as follows: (1) thermoneutral (TN; temperature-humidity index of 65.1 ± 0.2; d 1-5), (2) TN + hyperinsulinemichypoglycemic clamp (HHC; insulin infused at 0.3 µg/ kg of BW per h, glucose infused to maintain 90 ± 10% of baseline blood glucose for 96 h; d 6-10), (3) heat stress (HS; temperature-humidity index of 72.5 ± 0.2; d 16-20), and (4) HS + euglycemic clamp (EC; glucose infused to reach 100 ± 10% of TN baseline blood glucose for 96 h; d 21-25). Cows were fed and milked twice daily. Feed refusals were collected once daily for calculation of daily dry matter intake, and milk samples were collected at the beginning and end of each period for component analyses. Circulating insulin concentrations were measured in daily blood samples, whereas glucose concentrations were measured more frequently and variably in association with clamp procedures. Rectal temperatures and respiration rates were greater during HS than TN, as expected, and states of hyperinsulinemia and hypoglycemia were successfully induced by the HHC and high ambient temperatures (HS and EC). Feed intake differed based upon thermal environment as it was similar during TN and HHC periods, and declined for HS and EC. Milk production was not entirely reflective of feed intake as it was greatest during TN, intermediate during HHC, and lowest during HS and EC. All milk components differed with the experimental period, primarily in response to the thermal environment. Interestingly, TN baseline glucose concentrations were highly correlated with the change in glucose from TN to HS, and were related to glycemic status during HS. Furthermore, although few in number, those cows that failed to become hypoglycemic during HS tended to have a greater reduction in milk yield. The work presented here addresses a critical knowledge gap by broadening our understanding of the physiological response to heat stress and the related changes in glycemic state. This broadened understanding is fundamental for the development of novel, innovative management strategies as the dairy industry is compelled to become increasingly efficient in spite of global warming.

Heat Stress Increases Mammary Epithelial Cells and Reduces Viable Immune Cells in Milk of Dairy Cows

“…Cow respiration rates and rectal temperatures are reported in a previous paper, and were both significantly increased during HS periods compared to TN periods [ 17 ]. Milk yield, components, and somatic cell count in cows maintained under thermoneutral and heat stress conditions are presented Table 2 .…”

“…This experiment utilized a subset of samples from a previous study [ 17 ] and complete experimental details can be found in that paper. All procedures involving animals were approved by the Virginia Tech Institutional Animal Care and Use Committee.…”

“…Twelve Holstein dairy cows at 55 ± 13 days in milk (DIM, mean ± SD) and of 3.0 ± 1.2 parity in three replicates from the six replicates of the full experiment were sampled. Only 12 cows were sampled due to unavailability of a fully functional flow cytometer during three of the six replicate experiments reported in [ 17 ]. Two cows of 12 were removed from one replicate experiment due to respiratory disease leaving incomplete data and their data were not included in analyses (n = 10).…”

“…The clamp periods had no impact on somatic cell counts. Feed intake, milk yield, and milk component data as well as additional details on temperature programs can be found in Stewart et al, 2022 [ 17 ].…”

Reproductive and lactational responses of multiparous dairy cattle to short-term postpartum chromium supplementation during the summer months

“…Likewise, blood glucose concentrations in the current experiment did not differ between treatment groups ( Table 1 ). Previous work from our laboratory and others suggests that insulin-stimulated glucose uptake is already maximized in heat-stressed dairy cattle ( Rhoads et al, 2009 ; Xie et al, 2016 ; Stewart et al, 2022 ). Consequently, it is likely that Cr is unable to further increase glucose uptake under these conditions.…”