CONCENTRATIONS OF HORMONES AND METABOLITES, ESTIMATES OF METABOLISM, PERFORMANCE, AND REPRODUCTIVE-PERFORMANCE OF SOWS ACTIVELY IMMUNIZED AGAINST GROWTH HORMONE-RELEASING FACTOR

Cyclic females actively immunized against growth hormone-releasing factor (GRFi; n = 5) or human serum albumin (HSAi; n = 4) were used to determine the effects of reduced serum somatotropin (ST) and IGF-I on metabolism and production in gestating and lactating sows. Sows farrowed, pigs were weaned at 28 d of lactation, and sows were observed for estrus after weaning. Blood samples were collected at 15-min intervals for 5 to 6 h on d 110 of gestation and d 21 of lactation. Mean ST (nanograms/milliliter) was less (P < .05) in GRFi than in HSAi sows at d 21 of lactation, but it was similar at d 110 of gestation. Serum concentrations of IGF-I were less (P < .05) in GRFi than in HSAi sows at d 21 of lactation but not at d 110 of gestation. Serum thyroxine was greater (P < .05) in GRFi than in HSAi sows during gestation and lactation. Sows actively immunized against GRF weighed less (P < .01) and had more backfat (P < .01) at d 110 of gestation than HSAi sows; in vitro glucose oxidation and lipogenic rate of adipose tissue were greater (P < .05 for treatment x day interaction) in GRFi than in HSAi sows at d 110 of gestation. Across treatment, mammary gland oxidation of glucose and glucose clearance rates increased (P < .05), whereas adipose tissue utilization of glucose decreased ( P < .05) during lactation. During lactation, GRFi sows mobilized more (P < .05) backfat than did controls. Total number of pigs farrowed, number born alive, birth weight, pig body composition, milk composition at beginning and end of lactation, survival rate during lactation, weaning weight, feed disappearance during lactation, and weaning to estrus interval were not different between treatment groups. Milk consumption on d 20 of lactation was greater (P < .05) in pigs on HSAi than sows on GRFi. Active immunization against GRF abolished pulsatile release of ST, reduced IGF-I, and increased thyroxine during lactation. These data indicate that ST may play a facilatory rather than essential role in support of lactation in sows.