Objectives: This experiment was designed to re-evaluate the efficiency of two different methods of puberty induction based on exposure of pre-pubertal gilts to a variety of boar stimuli. Associations among pubertal response characteristics and 1) birth weight phenotype, and 2) sow lifetime productivity, were also explored.
How research was conducted: Gilts (n = 307) were selected and assigned to receive Fenceline (FBE) or Physical (PBE) Boar Exposure in a boar exposure area (BEAR). Starting at 185 days of age, gilts were exposed for 15 min to boar stimuli each day for three weeks. At the start of week 3, half the non-pubertal gilts in each treatment were assigned to receive PG600 or to act as non-treated Controls. At their detected first estrus (Heat-No-Serve: HNS), gilts were relocated into stalls for additional measurements of ovarian activity and hormonal status and inseminated at second estrus. Responses to treatment and subsequent fertility were assessed for all gilts that expressed estrus in Weeks 1 to 3, and for gilts (n=264) with birth, puberty and first service records.
Research findings: The results of this experiment confirm significant advantages for use of physical boar exposure in a BEAR system, measured as the proportion of HNS events during each successive week of exposure to boars, and in the overall response over the full three-week period. PG600 treatment of non-pubertal gilts at the start of week 3, improved the induction (HNS) response by 30% compared to the Controls and the overall estrus induction rate, including use of PG600 in half of the gilts still not pubertal by week 3, was 94% for the PBE protocol and 15% greater than for the FBE protocol. The week at which pubertal estrus induction was recorded was associated with subsequent fertility. Clear advantages in the percentage of females served for at parities 1 through 4 indicated that pubertal sensitivity to boar exposure was an indicator of breeding success. Age at removal from the breeding herd was also associated with the timing of pubertal estrus: Gilts in estrus in weeks 1 and 2 remained in the breeding herd for more than 100 additional days compared to those recorded in estrus in week 3, and for more than an additional 250 days compared to gilts recorded in pubertal estrus in weeks 4 to 7. The subset of data from the present study also suggest advantages to selection of replacement gilts weighing more than 1 kg at birth and from birth litters with more than 12 total born.
What these findings mean to the industry: These results confirm that, in a population of contemporary replacement gilts managed in a commercial farm environment, the protocol used to expose gilts to boar stimuli has a major impact on the efficiency of inducing a pubertal estrus (HNS) response. Direct contact with mature, high libido boars, maximizes the HNS response and also sensitizes non-pubertal gilts to PG600 treatment. Collectively, full physical contact with boars in a designated BEAR system, linked with PG600 treatment of gilts not recorded in estrus after 14 days, triggered a HNS event in over 90% of gilts in this study within a 28-day period. The efficiency of this puberty induction program provides the best guarantee that gilts will meet target weights for breeding at second estrous (135 – 150 kg) and earlier responding gilts had better lifetime productivity. Irrespective of any “litter of origin” effects on the efficiency of replacement gilt production, this study confirms that efficient gilt selection programs can be major drivers of improved sow lifetime productivity.
Contact information: Robert V. Knox, Ph.D, 360 ASL 1207 West Gregory Drive, MC-630, Urbana, IL 61801 USA Phone: 217-244-5177. firstname.lastname@example.org