406 EFFECTS OF SUCKLING INTENSITY ON MILK YIELD AND PIGLET GROWTH IN LACTATION-ENHANCED ALPHA-LACTALBUMIN TRANSGENIC GILTS

Abstract

The objective of the present study was to determine the effects of suckling intensity on milk yield and piglet growth. Lactation capacity of the gilts was enhanced through over-expression of a mammary-specific transgene, bovine alpha-lactalbumin. Lactational response to increased suckling stimulation was determined by fostering litters of either the same age (day 1) or 7 days older (day 7) than the day of lactation to gilts either non-transgenic (C) or transgenic (T) for bovine alpha-lactalbumin. Twenty first-parity gilts were allocated between 4 treatments depending on gilt genotype and age of litter fostered (CDay1, CDay7, TDay1, TDay7). Litters were standardized to 10 piglets within 24 h postpartum, and non-birth piglets were fostered to subject gilts with an equal litter weight within age groups at 36 h postpartum. Milk yield was determined by the weigh-suckle-weigh method on Days 6, 9, 12, 15, and 18 of lactation. Mean daily milk yield was greater (P = 0.031) for T gilts compared with C gilts, and tended to be greater (P = 0.056) for all gilts with Day 7 piglets compared to those with Day 1 piglets. Daily milk yield of TDay7 gilts increased rapidly to peak at Day 9 and was greater than the milk yield of all C gilts at Days 9 (P < 0.01), 12 (P < 0.02), and 15 (P < 0.02). Mean daily milk yield of TDay7 gilts was 2.1 kg greater (P = 0.002) than for CDay7 gilts and 2.0 kg greater (P = 0.004) than for TDay1 gilts. Daily milk yield of TDay1 gilts was not different (P = 0.491) from that of CDay1 gilts. Daily milk yield of CDay7 gilts did not differ (P = 0.630) from that of CDay1 gilts. Piglet weight gain between Days 3 and 6 was greater (P < 0.01) in the TDay7 group than in all other groups, and was greater (P < 0.05) than in the C groups from Days 6 through 9. No difference was found in comparing accumulated weight gain of the piglets between the day of age at foster (Day 1 vs. Day 7; P = 0.606) or between the CDay1 and CDay7 groups (P = 0.759). Accumulated weight gain of piglets suckling TDay7 gilts from Days 3 through 6 and from Days 3 through 9 was greater (P < 0.02) than in the other groups, and continued to be greater (P < 0.05) than in either of the C groups through Day 15. However, by Day 15, accumulated weight gain of the piglets suckling TDay1 gilts was not different (P = 0.395) from that of the TDay7 group and was greater (P = 0.049) than that of the CDay1 group by Day 15. The enhanced lactation potential of the transgenic gilts synergizes with suckling intensity to stimulate increased milk production during early lactation, and also stimulates piglet growth. This synergy may help regulate milk yield during lactation in bovine alpha-lactalbumin transgenic swine.