The effect of dose timing schedule on live performance, carcass cutting yields, and fat quality of market gilts...

The objective of this study was to evaluate the effects of dose timing on live performance, carcass cutting yields, and fat quality of gilts managed using GnRF immunization. The 15-week study began when 1056 gilts (11 weeks old; average starting weight of 31.7 kg) were allocated by weight to 48 pens, with 22 gilts per pen. Experimental treatments were arranged as a 2 × 2 factorial, with main effects of the interval between dose 1 and dose 2 of the GnRF immunization (4 or 6 weeks; interval between doses) and the interval between dose 2 and marketing [weighted averages of 49 days (long) or 35 days (short); marketing interval]. Age and days on feed were consistent among treatment groups, and pigs were marketed using a similar strategy, in which the heaviest 3-5 pigs from each pen were marketed during study week 12, the next heaviest 3-5 pigs from each pen were marketed during study week 14, and the remaining pigs in each pen were marketed during study week 15. Hot carcass weight and optical probe readings were collected at slaughter. Following slaughter, 283 carcasses (target of 24 per treatment for each marketing event) were selected for evaluation of carcass cutting yields and meat quality. There were limited interactions between interval between doses and marketing interval, with nonsignificant interactions (P ≥ 0.07) observed for average daily feed intake (ADFI), average daily gain (ADG), and gain: feed (G: F) ratio during the grow-finish period, as well as for hot carcass weight, backfat thickness, and carcass primal weights. Overall, this study illustrated the trade-offs associated with altering the time from dose 2 to marketing. From a live production standpoint, there were significant differences (P < 0.01) in time from dose 2 to marketing for ADFI and feed efficiency (F: G ratio), with the short marketing interval resulting in lower ADFI (2.47 vs. 2.53 kg) and improved F: G (2.69 vs. 2.74) compared with the long marketing interval. From a meat processing standpoint, differences in fat deposition were observed for marketing interval. The long marketing interval resulted in 0.78 mm greater backfat thickness, 0.15 kg heavier trimmed bellies, a 1.30-unit lower iodine value, and firmer bellies compared with the short marketing interval. Thus, producers utilizing GnRF immunization for gilts should closely monitor the interval between dose 2 and marketing to optimize live performance and carcass quality.