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 fac tor (GRFi; n = 5) or human serum albumin (HSAi; n = 4) were used to de termine the effects of reduced serum somatotropin (ST) and IGF-I on me tabolism and production in gestating and lactating sows. Sows farrowed , pigs were weaned at 28 d of lactation, and sows were observed for es trus after weaning. Blood samples were collected at 15-min intervals f or 5 to 6 h on d 110 of gestation and d 21 of lactation. Mean ST (nano grams/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 concent rations 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 great er (P < .05) in GRFi than in HSAi sows during gestation and lactation. Sows actively immunized against GRF weighed less (P < .01) and had mo re backfat (P < .01) at d 110 of gestation than HSAi sows; in vitro gl ucose oxidation and lipogenic rate of adipose tissue were greater (P < .05 for treatment x day interaction) in GRFi than in HSAi sows at d 1 10 of gestation. Across treatment, mammary gland oxidation of glucose and glucose clearance rates increased (P < .05), whereas adipose tissu e utilization of glucose decreased ( P < .05) during lactation. During lactation, GRFi sows mobilized more (P < .05) backfat than did contro ls. Total number of pigs farrowed, number born alive, birth weight, pi g body composition, milk composition at beginning and end of lactation , survival rate during lactation, weaning weight, feed disappearance d uring lactation, and weaning to estrus interval were not different bet ween treatment groups. Milk consumption on d 20 of lactation was great er (P < .05) in pigs on HSAi than sows on GRFi. Active immunization ag ainst GRF abolished pulsatile release of ST, reduced IGF-I, and increa sed thyroxine during lactation. These data indicate that ST may play a facilatory rather than essential role in support of lactation in sows .