189 The Effects of Dose Timing / Intervals on Grow-Finish Performance, Carcass Characteristics, Carcass Cutting Yields, and Meat Quality of Market Gilts Managed with Improvest
Authors: Wang Yifei , Hansen Blaine , Pollmann Steve , Bohrer Benjamin M 
Published: October 2023

Abstract
Improvest (Zoetis Canada Inc.) immunization provides temporary suppression of ovarian function and estrus in market gilts. The product requires two sequential injections administered at least 4 weeks apart, with full suppression of ovarian function demonstrated 4 to 10 weeks after the second injection. Recent research has shown the importance of closely monitoring the durations between the injections and between the second injection and slaughter. The objective was to determine the effects of dose timing and interval on grow-finish performance, carcass cutting yields, and meat quality of market gilts managed with Improvest when days on feed remained constant. The study consisted of 1,056 market gilts (average starting body weight of 31.7 kg) in 48 pens (22 pigs/pen) with experimental treatments arranged as a 2 × 2 factorial design with main effects of interval between the first and second Improvest injection (D1-D2; 4-week interval or 6-week interval) and time between the second Improvest injection and slaughter [D2-slaughter; weighted average of 34 to 35 days post-second injection (SHORT) or weighted average of 48 to 49 days post-second injection (LONG)]. Pigs were marketed using a similar strategy where the heaviest 3 to 5 pigs from each pen were marketed during study week 12, the next heaviest 3 to 5 pigs from each pen were marketed during study week 14, and the remaining pigs in the pen were marketed during study week 15. Hot carcass weight and optical probe readings (Destron PG-203; Anitech Identification System Inc.) were collected during slaughter. Following slaughter, 288 carcasses (24/treatment for each marketing event; pigs near the population average) were selected for evaluation of carcass cutting yields and meat quality. Data were analyzed with PROC MIXED of SAS, with pen serving as the experimental unit. There were limited interactions between D1-D2 and D2-slaughter, with nonsignificant interactions (P ≥ 0.07) for average daily feed intake (ADFI), average daily gain (ADG), and feed:gain (F:G) ratio during the grow-finish period, hot carcass weight, backfat thickness, or carcass primal weights. Overall, this study illustrated the trade-offs associated with altering the duration of time between D2-slaughter. From a live production standpoint, there were significant differences (P &lt; 0.01) for D2-slaughter for ADFI and F:G ratio, with SHORT having reduced ADFI (2.47 kg versus 2.53 kg) and more efficient F:G (2.69 versus 2.74) compared with LONG (Table 1). From a meat processing standpoint, there were meaningful differences observed in fat deposition for D2-slaughter. In terms of fat quantity, backfat thickness and belly primal weight were affected (P &lt; 0.01) by D2-slaughter (LONG had 0.78 mm greater backfat thickness and 0.15 kg heavier trimmed bellies). In terms of fat quality, iodine value and belly firmness were affected (P &lt; 0.01) by D2-slaughter (LONG had 1.30 units lower iodine value and superior belly flop scores).