55 The Effects of Dietary Net Energy Levels on Grow-Finish Performance and Carcass Characteristics of Market Gilts Managed with Improvest

Abstract

Abstract Improvest is a gonadotropin releasing factor (GnRF) analogue-diphtheria toxoid conjugate injection approved for temporary suppression of ovarian function and estrus in market gilts (Zoetis Canada Inc.). Study objectives were to determine the effects of three different net energy levels (LOW – 2.216 Mcal/kg, MID – 2.341 Mcal/kg, or HIGH – 2.466 Mcal/kg) during the grow-finish period on live performance and carcass characteristics of market gilts managed with Improvest (IMP) compared with market gilts not managed with Improvest (CON). The study consisted of 1,008 market gilts (average starting weight of 30.8 kg) in 48 pens (21 pigs/pen) with experimental treatments arranged as a 2 × 3 factorial design with main effects of Improvest (IMP or CON) and net energy level (LOW, MID, or HIGH). An equal number of pigs were marketed from each of the six treatment groups on day-83 (21.9% of the population), day-90 (21.9% of the population), day-97 (21.9% of the population), and day-104 (34.3% of the population) of the experiment. The weighted average for time post-second Improvest injection to marketing was 39.8 days. Data were analyzed with PROC MIXED of SAS, with pen serving as the experimental unit, fixed effects of Improvest (IMP or CON), net energy level (LOW, MID, or HIGH) and their interaction, and a random effect of pen location. There were no significant interactions (P ≥ 0.20) for average daily feed intake (ADFI), average daily gain (ADG), Feed:Gain (F:G), hot carcass weight (HCW), dressing percentage, backfat thickness, or predicted lean yield. However, IMP gilts consumed more feed (6.8% greater ADFI; P < 0.01), grew faster (5.0% greater ADG; P < 0.01), were less efficient (1.5% greater F:G; P < 0.01), were heavier (3.5 kg HCW; P < 0.01), and were fatter (1.9 mm greater backfat thickness and 0.9% less predicted lean yield; P < 0.01) than CON gilts. No difference (P = 0.21) in carcass dressing percentage between IMP and CON gilts was detected (Table 1). There were significant effects (P < 0.05) of net energy level for ADFI, ADG, F:G, HCW, and dressing percentage. Pigs fed LOW diets had the greatest ADFI, slightly less ADG, the least efficient F:G ratio, the lightest HCW, and reduced dressing percentage compared with HIGH (P < 0.01). There were no differences (P > 0.05) for backfat thickness or predicted lean yield among dietary energy level treatments. Overall, these data indicate that typical Improvest response levels were sustained at each of the net energy levels evaluated in this study (response levels for HCW of 2.6 kg for LOW, 3.4 kg for MID, and 4.5 kg for HIGH); however, consideration should still be provided to the known production impacts of low net energy diets when market gilts are managed with Improvest.