Invited review: Heat stress effects during late gestation on dry cows and their calves

• Published in: Journal of dairy science Vol. 96; no. 7; pp. 4079 - 4093
• Main Authors: Tao, S., Dahl, G.E.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.07.2013
• Subjects: Animals; Animals, Newborn - growth & development; Animals, Newborn - metabolism; Body Temperature Regulation; calves; Cattle; Cattle Diseases - embryology; Cattle Diseases - physiopathology; cooling; cows; dairy cattle; early lactation; environmental factors; Female; fetal development; Fetal Growth Retardation - etiology; Fetal Growth Retardation - veterinary; Fetal Hypoxia - etiology; Fetal Hypoxia - veterinary; fetus; Gestational Age; growth retardation; heat; heat stress; Heat Stress Disorders - embryology; Heat Stress Disorders - physiopathology; Heat Stress Disorders - veterinary; Hot Temperature; hypoxia; Immunity; lactation; Lactation - physiology; late gestation; malnutrition; Mammary Glands, Animal - physiopathology; metabolism; milk synthesis; milk yield; parturition; passive immunity; Placenta - physiopathology; Postpartum Period - physiology; Pregnancy; progeny; prolactin; temperature; heat stress; late gestation; lactation; fetus
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.2012-6278

In dairy cattle, late gestation is a critical period for fetal growth and physiological transition into the next lactation. Environmental factors, such as temperature and light, exert dramatic effects on the production, health, and well-being of animals during this period and after parturition. The aim of this review was to introduce effects of heat stress during late gestation on dairy cattle, and discuss the biological mechanisms that underlie the observed production and health responses in the dam and her fetus. Relative to cooled cows, cows that are heat stressed during late gestation have impaired mammary growth before parturition and decreased milk production in the subsequent lactation. In response to higher milk yield, cows cooled prepartum undergo a series of homeorhetic adaptations in early lactation to meet higher demand for milk synthesis compared with heat-stressed cows, but no direct effect of environmental heat stress on metabolism exists during the dry period. Prepartum cooling improves immune status of transition cows and evidence suggests that altered prolactin signaling in immune cells mediates the effects of heat stress on immune function. Late-gestation heat stress compromises placental development, which results in fetal hypoxia, malnutrition, and eventually fetal growth retardation. Maternal heat stress may also have carryover effects on the postnatal growth of offspring, but direct evidence is still lacking. Emerging evidence suggests that offspring from prepartum heat-stressed cows have compromised passive immunity and impaired cell-mediated immune function compared with those from cooled cows.