Abstract #251

# 251
Effects of late-gestation heat stress on immunity and performance of calves.
Geoffrey Dahl*1, Ana Monteiro2, Sha Tao2, 1University of Florida, Gainesville, FL, 2University of Georgia, Tifton, GA.

Heat stress effects during lactation are well characterized and include reductions in dry matter intake, milk yield and metabolic shifts that reduce the efficiency of milk production. Similarly, when dry cows are heat stressed they experience lower intake, reduced mammary growth and compromised immune function that ultimately results in a poorer transition into lactation and lower milk yield. Recently, we have focused on the effects of late gestation heat stress on calf survival and performance, with a series of studies examining preweaning growth and health, and later reproductive and productive responses, in an attempt to quantify acute and persistent effects of in utero stress. Calves born to dams heat stressed when dry have lower body weight at birth, are shorter at weaning, and do not achieve the same level of weight or height accumulation to 12 mo of age observed in calves from dams that are cooled when dry. Some of the reduced growth may result from the lower immune status observed in calves heat stressed in utero, which begins with poorer apparent efficiency of immunoglobulin absorption and extends to lower survival rates through puberty. However, heat stressed calves also have permanent shifts in metabolism that may lead to greater peripheral accumulation of energy and less lean growth relative to those from cooled dams. Comparing reproductive performance in calves heat stressed versus those cooled in utero, we observe that the cooled heifers require fewer services to attain pregnancy and become pregnant at an earlier age. Tracking the milk production in calves that were heat stressed in utero versus those cooled in late gestation revealed a significant reduction of yield in the first lactation, approximately 5 kg/d through 35 weeks of lactation, despite similar bodyweight and condition score at calving. These observations indicate that a relatively brief period of heat stress in late gestation dramatically alters the health, growth, and ultimate performance of dairy calves. Thus, it is critical to effectively manage heat stress of dry cows to avoid negative effects on the calf.

Key Words: in utero heat stress, growth, health

Speaker Bio
Dr. Dahl is Professor & Chair of the Department of Animal Sciences at the University of Florida.  In addition to his administrative responsibilities, Dr. Dahl conducts applied and basic research with direct impact on animal production and health. Specifically, his program focuses on understanding the physiological impact of management interventions, notably photoperiod and heat stress abatement, at various stages of the lactation cycle, in an attempt to harness that knowledge to optimize cow health and performance.  The fundamental aspects of Geoff’s research has led to application in other agriculturally important species including sheep, goats and pigs.