Effects of feeding beef females supplemental fat during gestation on cold tolerance in newborn calves

Effects of prepartum fat supplementation of the dam on cold tolerance of ca lves were determined in two studies. In Exp. 1, 22 F1, crossbred heifers ge stating F2 calves received diets containing either 1.7 or 4.7% dietary fat starting at d 250 +/- 2 d of gestation. Safflower seeds (Carthamus tinctori us) containing 37% oil with 79% linoleic acid were the supplemental fat sou rce in isocaloric-isonitrogenous diets. Calves were separated fl om their d arns at birth, fed pooled dairy-cow colostrum, muzzled to prevent sucking, and returned to their dams in a heated (22 degrees C) barn for 3.5 h. At 4 h of age, a jugular catheter was inserted. At 5 h of age, calves were place d in a 0 degrees C room for 140 min and rectal temperatures and blood sampl es were obtained at 10- and 20-min intervals. Blood was; assayed for glucos e, cortisol, and cholesterol. In Exp. 2, 18 multiparous, crossbred beef cow s bred to Murray Grey sires were;randomly assigned to receive diets contain ing either 1.7 or 3.1% dietary fat starting at 235 +/- 2 d gestation. Saffl ower seeds were used as the supplemental fat source ill isocaloric-isonitro genous diets. At d 260 of gestation, premature parturition was induced in o ne-half of the cows from each diet group by feeding Ponderosa pine (Pinus p onderosa) needles. Experimental protocols were the same as in Exp. 1, excep t that cold exposure was at 9 degrees C for 200 min. Rectal temperatures we re affected in Exp. 1 by time and diet x time (both P < .01) and diet x cal f sex (P < .05) and in Exp. 2 by calf age (P < .05), time, and calf age x t ime (both P < .01). Plasma cortisol concentrations were affected by time (P < .01) and calf sex x time (P < .05) in Exp. 1 and by time (P < .01) in Ex p. 2. Cholesterol concentrations in Exp. 1 were affected by diet x time (P < .05) and in Exp. 2 by time (P < .05). Plasma glucose concentrations were affected in Exp. 1 by diet (P < .05) and in Exp. 2 by calf age, time, and c alf age x time (all P < .01). We conclude from Exp. 1 that feeding heifers supplemental fat during late gestation increased glucose concentrations in the newborn calf, resulting in favorable responses in body temperature in t he cold-stressed newborns. This increase in substrate availability suggests a potential positive effect on heat generation in newborns during sustaine d periods of cold stress. In Exp. 2, premature calves had compromised cold tolerance possibly due to impaired shivering or brown adipose tissue thermo genesis.