Comparison of the lysine requirement of immunologically versus physically castrated male pigs

Abstract Text: Replacement of physical castrates (PC) with immunological castrates (IC) requires review of feeding programs for male pigs, especially amino acid requirements.  The objective of this study was to compare the SID lysine requirement of IC versus PC during three growth phases.  One hundred and fifty IC and PC (PIC 359 x C29) were allotted based on initial BW to one of six blocks. Initial BW for each phase were 30.0 ± 0.8, 64.7 ± 1.4 and 111.9 ± 1.9 kg for IC and 32.4 ± 0.6, 69.8 ± 1.0 and 114.5 ± 1.3 kg for PC. Phase performance was monitored during a 5 week period for phases 1 and 3 and a 4 week period for phase 2. Pens always remained at the same SID lysine treatment percentage throughout each of the three phases. Injections of a GnRF analog (Improvest®, Zoetis Inc., Florham Park, NJ) were administered at 11.5 and 19 weeks of age; phase 3 commenced 2 weeks after the second injection to avoid the period of rapidly changing feed intake. Diets were based on corn, soybean meal and synthetic amino acids to meet the projected lysine requirement and 5% above requirement of other essential amino acids. Treatment SID lysine levels were set at 80, 90, 100, 110 and 120% of the projected requirement for each gender, based on previous performance and the NRC (2012) modeling program. The relative lysine contributions of lysine from soybean meal and synthetic lysine were held constant within each dietary phase for each gender.  A one slope broken line regression model was used to determine lysine requirement, based on breakpoint analyses. The SID lysine requirement of IC for phases 1, 2 and 3 based on ADG were 1.03, 0.89, and 0.55% and based on GF were 0.99, 0.72, and 0.55%.  The SID lysine requirement of PC for phases 1, 2 and 3 based on ADG were 0.85, 0.62 and 0.47% and based on GF were 0.86, 0.58 and 0.47%.  Averaging these data, the SID lysine requirement of IC are 1.01, 0.81 and 0.55% and of PC 0.86, 0.60 and 0.47%, for phases 1, 2 and 3, respectively. In conclusion, the lysine requirements of IC are greater than PC (117%, 135% and 117% for phases 1, 2 and 3, respectively), even after the second injection, when IC pigs are believed to become physiologically similar to PC pigs.

Keywords: pigs, lysine, immunological castration