Two key issues should be considered in selecting and conditioning gilts before they enter the breeding herd, according to Canadian researcher George Foxcroft.
First, consider their genetic merit for reproductive traits, says Foxcroft with the Swine Research and Technology Center, Edmonton, Alberta.
Second, consider environmental influences that might affect gilt development and future reproductive performance.
Development of specific dam line females has addressed the first issue, despite ongoing selection pressure for growth and carcass traits and the negative effect they often have on breeding performance. The increases in lean growth in offspring make the performance of contemporary dam line females even more impressive, adds Foxcroft.
Litter of origin has a major impact on subsequent reproductive performance. The physiological basis for these reproductive differences seem to be as diverse as those reported for genotypes with differences in embryonic survival. The uterine environment in which the gilt develops, as much as genetic merit of littermate females, may influence sexual maturation and subsequent fertility.
Postnatal nutrition and interactions between growth, onset of puberty and lifetime reproductive performance have been extensively studied. A minimum growth threshold exists, below which growth and metabolic state will delay the onset of boar-induced puberty.
More limited data suggest an upper threshold, above which very high growth rates may also delay the onset of puberty. Within these growth thresholds, there is no consistent evidence that any particular age or weight at breeding confers a production advantage in terms of lifetime reproductive performance.
Foxcroft offers a few tips in gilt management:
Select gilts earlier in the nursery.
Expose gilts to boars at 135 days of age (75% of gilts cycle within 30 days of boar contact); stimulating early does not mean breeding early.
Growth rate does not affect response to boars.
Allow gilts to cycle three to four times before breeding.
Breed at about 300-lb.
Feed gilts slower-growing diets.
The well-documented benefits of identifying and capitalizing on early sexual maturation to enhance lifetime performance provide a convincing case for important refinements in gilt management.
University of Missouri researcher A.M. Gaines reported results of a three-part trial studying performance of pigs injected with dexamethasone (Dex) either one hour or 24 hours after birth. His report was presented at the Midwest sectional meeting of the American Society of Animal Science (ASAS).
In the first phase, 225 pigs from a 1,800-head commercial sow unit were divided according to birth weight and sex and given one of three treatments: saline, Dex-1 (2 mg/kg body weight injection within one hour of birth) or Dex-24 (same injection within 24 hours after birth).
Birth weights did not differ among treatments or between sexes. However, weaning weights at 15 days did show a treatment by sex interaction. Dex-treated males were 12% heavier than saline males and Dex-treated females were lighter than saline females.
In the second phase, 186 pigs from the first experiment were shipped to a nursery facility and fed fortified corn-soybean meal diets in a three-phase feeding program. After 49 days, again there appeared to be a treatment by sex interaction for weight, with Dex-treated barrows 8% heavier than saline barrows. Gilts showed no difference and there were no differences in feed efficiency with either sex.
In the third phase of the experiment, the nursery pigs were moved to a finishing unit with a four-phase feeding program and split-sex feeding. Real-time ultrasound was used to measure 10th rib backfat depth and loineye area. After 83 days, Dex-treated barrows were 11 lb. heavier than saline barrows with no difference in gilts. No treatment differences were noted for backfat, loineye or feed efficiency.
The researchers concluded that Dex, given within 24 hours of birth, significantly improves both pre-weaning and post-weaning performance of barrows with no beneficial effects on gilts.
Gaines and his co-authors received the National Pork Board Innovation Award for Research at the Midwest ASAS meeting for the Dex study.
Research briefs from the Midwest section American Society of Animal Science.