Abstract Objectives of this study were to determine the effects of standardized ileal digestible (SID) lysine on growth performance and economical outcomes of immunologically-castrated male pigs weighing 81 to 111 kg. The experiment consisted of 1, 008 pigs (PIC 800 sire line × PIC Camborough F1 sows) randomly assigned to one of 48 pens (21 pigs/pen). Six dietary treatments were designed in a titration manner with equidistant treatments. Treatments for SID lysine levels (as-fed) were 0. 60%, 0. 66%, 0. 72%, 0. 79%, 0. 85%, or 0. 91%. Net energy was formulated to equivalent levels of 2. 41 Mcal/kg. Minimum ratios of 30% Met: Lys, 60% Met+Cys: Lys, 66% Thr: Lys, 21% Trp: Lys, 70% Val: Lys, 56% Ile: Lys, and 102% Leu: Lys on a SID basis were used for all diets. Diets were formulated to meet or exceed other nutrient requirements established by NRC (2012). Diet costs were estimated using commercial costs in Canada during 2024 (i. e. , where and when the experiment took place) and were CAD424 for the 0. 60% SID lysine diet, CAD429 for the 0. 66% SID lysine diet, CAD433 for the 0. 72% SID lysine diet, CAD446 for the 0. 79% SID lysine diet, CAD459 for the 0. 85% SID lysine diet, and CAD473 for the 0. 91% SID lysine diet. Pigs were administered the second dose of the GnRF analogue on d 17 of the 23 d of the experiment. Data were analyzed with pen as the experimental unit. Dietary SID lysine level served as the fixed effect and pen replicate served as a random effect. Two single-degree of freedom orthogonal contrasts were used to test the linear or quadratic effects of increasing SID-lysine level. Linear effects (P 0. 01) were observed for average daily gain (ADG) and gain: feed (G: F) while a quadratic effect (P = 0. 04) was observed for estimated income over feed costs. Average daily feed intake was affected (P = 0. 03) by treatment but not in a consistent manner across the equidistant treatments. Average daily gain increased linearly from 1. 22 kg/d to 1. 29 kg/d as SID lysine level increased from 0. 60% to 0. 91%. Gain: feed increased linearly from 0. 372 to 0. 404 as SID lysine level increased from 0. 60% to 0. 85% and was not different between SID lysine levels of 0. 85% and 0. 91%. Estimated income over feed costs showed a weak quadratic response with the greatest numerical levels occurring at the SID lysine level of 0. 66% but were unaffected by treatment (P = 0. 16). In conclusion, the greatest levels of performance were achieved at SID lysine levels of 0. 85% for immunologically castrated male pigs weighing 81 to 111 kg, while estimated income over feed costs were unaffected by the different levels of SID lysine tested in this experiment.
Bohrer et al. (2026) studied this question.