Feed intake–dependent and –independent effects of heat stress on lactation and mammary gland development

Abstract

With a growing population, a reliable food supply is increasingly important. Heat stress reduces livestock meat and milk production. Genetic selection of highproducing animals increases endogenous heat production, while climate change increases exogenous heat exposure. Both sources of heat exacerbate the risk of heat-induced depression of production. Rodents are valuable models to understand mechanisms conserved across species. Heat exposure suppresses feed intake across homeothermic species including rodents and production animal species. We assessed the response to early-mid lactation or late-gestation heat exposure on milk production and mammary gland development/ function, respectively. Using pair-fed controls we experimentally isolated the feed intake-dependent and -independent effects of heat stress on mammary function and mass. Heat exposure (35°C, relative humidity 50%) decreased daily feed intake. When heat exposure occurred during lactation, hypophagia accounted for approximately 50% of the heat stress-induced hypogalactia. Heat exposure during middle to late gestation suppressed feed intake, which was fully responsible for the lowered mammary gland weight of dams at parturition. However, the impaired mammary gland function in heat-exposed dams measured by metabolic rate and lactogenesis could not be explained by depressed feed consumption. In conclusion, mice recapitulate the depressed milk production and mammary gland development observed in dairy species while providing insight regarding the role of feed intake. This opens the potential to apply genetic, experimental, and pharmacological models unique to mice to identify the mechanism by which heat is limiting animal production.

Genomic insights into local adaptation and phenotypic diversity of Wenchang chickens

“…SEMA3A encodes a secreted guidance protein that functions as an extracellular negative regulator of the integrity and function of the glomerular filtration barrier ( Tufro, 2014 ). Heat stress affects feed intake and adipogenesis ( Belhadj Slimen et al., 2016 ; Xiao et al., 2020 ). SUGCT encodes a mitochondrial enzyme that synthesizes glutaryl-CoA from glutarate in tryptophan and lysine catabolism ( Niska-Blakie et al., 2020 ).…”

Late-Gestation in utero Heat Stress Limits Dairy Heifer Early-Life Growth and Organ Development

“…Additionally, alterations in maternal feed intake are reported to decrease slightly under late-gestation heat stress, on average by 13% (Ouellet et al, 2020), which could influence offspring growth outcomes. Yet, when accounting for the confounding effect of dissimilar feed intakes, pair-fed studies assessing late-gestation heat stress in both rodents and dairy cattle still identify reductions in offspring size (i.e., birth weight and stature) and passive immune transfer relative to both thermoneutral pair-fed and ad libitum fed counterparts (Almoosavi et al, 2020;Xiao et al, 2020).…”

Inflammatory Mediation of Heat Stress-Induced Growth Deficits in Livestock and Its Potential Role as a Target for Nutritional Interventions: A Review

“…These intake-independent changes may vary with the intensity and duration of the heat stress but are typically associated with disruptions in metabolic processes [ 56 , 57 , 58 ]. Large-scale pair-feeding studies in feedlot cattle are rare due to their high costs and logistical difficulties, but a study performed in pair-fed mice estimated that around 50% of heat stress effects were due to intake-independent factors [ 59 ]. Such mechanisms alter endocrine and metabolic aspects of growth regulation, which helps to explain poor growth performance observed in heat-stressed feedlot lambs, even when thermoneutral counterparts were pair-fed [ 31 , 54 ].…”