Carry-over effects of dry period heat stress on the mammary gland proteome and phosphoproteome in the subsequent lactation of dairy cows

Abstract

Exposure to heat stress during a cow’s dry period disrupts mammary gland remodeling, impairing mammary function and milk production during the subsequent lactation. Yet, proteomic changes in the mammary gland underlying these effects are not yet known. We investigated alterations in the mammary proteome and phosphoproteome during lactation as a result of dry period heat stress using an isobaric tag for relative and absolute quantitation (iTRAQ)-based approach. Cows were cooled (CL; n = 12) with fans and water soakers in a free stall setting or were heat stressed through lack of access to cooling devices (HT; n = 12) during the entire dry period (approximately 46 days). All cows were cooled postpartum. Mammary biopsies were harvested from a subset of cows (n = 4 per treatment) at 14, 42, and 84 days in milk. Overall, 251 proteins and 224 phosphorylated proteins were differentially abundant in the lactating mammary gland of HT compared to CL cows. Top functions of differentially abundant proteins and phosphoproteins affected were related to immune function and inflammation, amino acid metabolism, reactive oxygen species production and metabolism, tissue remodeling, and cell stress response. Patterns of protein expression and phosphorylation are indicative of increased oxidative stress, mammary gland restructuring, and immune dysregulation due to prior exposure to dry period heat stress. This study provides insights into the molecular underpinnings of disrupted mammary function and health during lactation arising from prior exposure to dry period heat stress, which might have led to lower milk yields.

Impact of close-up dry period heat stress on performance, fertility, and immunometabolic blood indices of dairy cows – prospective cohort study

“…Dry cows are not only susceptible to thermal stress during lactation but also during the dry period that precedes lactation. Cows exposed to HS during the dry period have been found to exhibit altered postabsorptive metabolism and produce signi cantly less milk during the subsequent lactation, with reductions ranging from 3 to 7.5 kg/d [8,38,39].…”

A review of dairy cattle heat stress mitigation in Indonesia

“…Because lactating dairy cows are more thermolabile than non-lactating cows. Skibiel et al [26] observed that the rectal temperature of lactating cows was 0.9°C higher than that of prepartum cows under similar environmental conditions. According to Thornton et al [30], a cow's rectal temperature is 38.5°C under normal conditions and 39.5°C under heat stress conditions.…”

“…Rectal temperature can be used as an indicator to identify the beginning of heat stress in animals produced by the microenvironment and nutrition [25]. Calves' and adult dairy cows' normal respiratory rates vary from 20-40 to 15-35 breaths/min, respectively [26]. As air temperature rises, changes in respiratory rate occur, causing the animals to breathe more frequently to dissipate heat [25].…”

“…The ability of livestock to withstand heat in the environment is known as heat tolerance. Animals under heat stress will display changes in body temperature and respiratory frequency [26]. When the heat tolerance coefficient (HTC) = 2, cattle are considered to have a high level of heat resistance; the higher the HTC value, the lower the resistance.…”

“…Rectal temperature is one indicator to measure heat stress in dairy cattle. Skibiel et al [26] stated that cattle's rectal temperature varies dramatically from spring (38.36°C) through summer (38.86°C). Rectal temperature is a marker of thermal equilibrium.…”