117 A Low Litter Birth Weight Phenotype Reduces the Retention Rate of Potential Replacement Gilts. (10th April 2018) - Patterson, J
Abstract: Decades of selection for increased litter size has resulted in a population of sows with an extreme low (L) average litter birth weight phenotype (BWP), irrespective of litter size. We hypothesize that this phenotype is the result of poor placental development driven by extreme intra-uterine crowding of embryos in early gestation and involves an interaction of hard to measure reproductive traits that are not responsive to current selection practices. However, measuring and managing this sow-dependent phenotype at production nucleus level would improve overall breeding herd efficiency and the number of quality weaned pigs per sow lifetime. In a NPB-funded project designed to test this concept, individual piglet weights (n = 47, 338) were recorded in litters born to parity 1 - 7 multiplication sows producing Camborough replacement gilts (n = 1097; PIC). BWP was determined over at least two successive parities for litters with >9 total born. Sows (n = 651: overall mean BWP = 1.36 kg) were then classified as having a low (L, < 1.15 kg, n=63), low-medium (LM, ≥1.16 to ≤ 1.36 kg, n=281), medium-high (MH, > 1.36 and ≤ 1.6 kg, n=254) or high (H, > 1.6 kg, n=53) BWP based on their successive litter records. Within 12 h after birth, live gilts born to these sows (n = 7552) received a unique ear ID tag and retention rate (RR) was determined from birth until pre-selection to enter the breeding herd (pre-pubertal gilts at 190 d of age) having applied the standardized selection criteria. RR was analyzed as a Chi square using the PROC FREQ procedure of SAS. RR was lower (P ≤ 0.05) for L than for LM, MH and H sows within 4 d after birth (91.4, 94.1, 95.4, and 95.6 %, respectively), at 24 d of age (81.4, 84.5, 87.2, and 86.9 %, respectively), at 70 d of age (66.7, 75.4, 78.7, and 79.2 %, respectively) and at pre-selection (42.6, 52.3, 55.3, and 56.2 %, respectively). As has been reported for low individual pig birth weights, retention of gilts born to sows with the low BWP was compromised. Effects of a low BWP on final selection and on sow lifetime productivity will be determined. At the level of the production multiplication unit, the ability to predict a low BWP can be directed at strategic culling decisions and protocols for pre-weaning management of potential replacement gilts to improve retention in the gilt pool.