23 The effects of dietary net energy level on grow-finish performance and carcass characteristics of intact male market pigs managed with Improvest

Abstract

Abstract Improvest is a gonadotropin releasing factor (GnRF) analogue-diphtheria toxoid conjugate product approved for temporary suppression of testicular function and reduction of boar taint in intact male pigs (Zoetis Canada Inc.). Objectives for this study were to determine the effects of dietary net energy (NE) level during the grow-finish period on live performance and carcass characteristics of intact male pigs managed with Improvest/immunological castration (IC) when compared with physically castrated (PC) male pigs. The 101-d study began when 1,008 pigs (504 intact male pigs and 504 PC male pigs; 10 wk old) were allocated by body weight to 48 pens with 21 intact males or 21 PC males per pen. Three dietary NE treatments were fed to pigs using five dietary phases to provide an average of 2,212 kcal/kg (Low NE), 2,337 kcal/kg (Medium NE), or 2,462 kcal/kg (High NE). Dietary programs were formulated according to standardized ileal digestible lysine requirements of IC males or PC males. The experiment was designed and analyzed as a 2 × 3 factorial with main effects of Improvest management and NE. For the overall study period, there were no significant interactions between Improvest management and NE (P ≥ 0.19) for average daily feed intake (ADFI), average daily gain (ADG), or gain to feed ratio (G:F; Table). There were also no significant interactions between Improvest management and NE (P ≥ 0.06) for carcass characteristics. Immunologically castrated male pigs consumed less feed (5.3% less ADFI; P < 0.01), grew faster (5.1% greater ADG; P < 0.01), and were more efficient (11.2% greater G:F; P < 0.01) compared with PC male pigs. Hot carcass weight (HCW) did not differ (P = 0.16) between IC males and PC males (attributed to 1.6 percentage unit less dressing percentage for IC males; P < 0.01); however, IC males were leaner (0.9 mm less backfat and 0.65% greater predicted lean yield; P < 0.01) compared with PC males. For the overall study period, pigs fed Low NE and Medium NE diets consumed more feed than pigs fed High NE diets, and pigs fed Low NE diets grew slower than pigs fed Medium NE and High NE diets. This resulted in pigs fed Low NE diets having 4.4% less G:F than pigs fed Medium NE and 8.6% less G:F than pigs fed High NE diets (P < 0.01). Pigs fed Low NE had 3.0 kg lighter (P < 0.01) HCW compared with Medium NE, while High NE had intermediate HCW that did not differ from the other two treatments. Overall, typical Improvest response levels were sustained for each of the NE treatments in this study; however, consideration should be provided to the known production impacts of low NE diets when male market pigs are managed with Improvest.