Interpretive Summary: In utero heat stress alters calf phenotype: the role of programming

By: G. E. Dahl, J. Laporta (University of Florida)

Whereas negative impacts of heat stress on production and health outcomes of dairy cattle are well described during lactation, recent studies support the concept that even dry cows are negatively impacted by heat stress in late gestation.  Indeed, heat stress in the dry period programs a reduction in milk yield and immune status that persists for the next lactation. More critically, in utero heat stress shifts the trajectory of calf development to a lower productivity and health phenotype, which cannot be recovered from after birth. Mechanistically, altered patterns of genomic methylation underlie the changes in organ development in the in utero heat stressed calf, particularly at the level of the mammary gland, ovaries and adrenal glands. Furthermore, in utero heat stress accelerates gut closure which results in a lower health phenotype. Fetal programming as a result of in utero heat stress impacts that calf and the offspring of that calf, supporting the concept that heat stress in utero drives epigenetic changes that decrease the achievement of genetic potential of the offspring.