The effect of gilt age at first estrus and breeding on third estrus on sow body weight changes and long-term reproductive performance

The objective of this trial was to determine the effect of age at first estrus on BW changes and long-term reproductive performance of sows. At approximately 100 d of age, prepubertal C22 gilts (n = 431) were allocated to trial. At a pen average of 140 d of age, gilts began daily direct contact with mature boars to stimulate onset of puberty. Gilts (n = 317, 73%) were recorded as cyclic by 180 d of age (select) and were classified on the basis of age at puberty into 3 puberty groups: 1) early puberty (EP; <153 d of age; n = 85); 2) intermediate puberty (IP; 154 to 167 d of age; n = 140); or 3) late puberty (LP; 168 to 180 d of age; n = 90). Gilts not exhibiting the standing reflex by 180 d of age were considered nonselect (NS; n = 91). Mean day to puberty and age at puberty attainment in each of the classifications were EP: 9.6 +/- 0.5 d and 147.4 +/- 0.5 d; IP: 19.3 +/- 0.5 d and 159.9 +/- 0.3 d; LP: 33.8 +/- 0.7 and 175.7 +/- 0.6 d, respectively. Fewer NS gilts (73.0%) were bred than were EP (97.7%), IP (93.2%), or LP (93.0%) gilts (P < 0.05). Total number of piglets born and born alive were not different between classifications and increased (P < 0.05) over successive parities in EP, IP, and NS gilts. For gilts initially served, there was no effect of puberty group classification on retention in the herd to farrow a third litter, but the rate of fallout per parity tended to be greatest for NS (17.2%) compared with EP (12.4%), IP (15.6%), and LP (14.2%) gilts (P < 0.08). Taken together, these data suggest that the response to a standardized protocol of boar stimulation can identify 50 to 75% of gilts that will have greatest lifetime productivity in the breeding herd. In the known cyclic (select) gilts, BW increased over the productive life of the sow, and EP gilts were lighter than LP gilts at every measured event (P < 0.05). Plasma IGF-1 only differed between puberty groups at d 100 of age (EP: 169.0 +/- 4.4; IP: 157.2 +/- 3.5; LP: 144.0 +/- 4.4 ng/mL), suggesting a mechanism linking IGF-1 status and age at puberty in the present study.