Growth performance and carcass responses of TN70 × Tempo grower-finisher pigs to graded indispensable amino acid concentration expressed relative to SID lysine

Abstract

Modern pig genotypes require periodic re-evaluation of dietary indispensable amino acid specifications to support their genetic potential for lean growth. This study evaluated the effects of graded levels of a balanced indispensable amino acid profile on the growth performance and carcass characteristics of TN70 × Tempo grower-finisher pigs and estimated the dietary amino acid level associated with optimum biological responses. A total of 1,056 pigs (528 boars and 528 gilts) were evaluated during two production periods (late summer/autumn and winter). Within each period, pigs were allocated to six isoenergetic dietary treatments providing 70, 80, 90, 100, 110 or 120% of the prevailing commercial SID lysine specification. Each dietary treatment × sex combination comprised four pens of 11 pigs per period, with the pen as the experimental unit. SID lysine was used as the reference amino acid according to the ideal protein concept, and the ratios of the other indispensable amino acids to SID lysine were maintained across treatments. The treatments, therefore, represented graded dietary amino acid levels within a balanced profile rather than a titration of lysine in isolation. Significant dietary amino acid level × sex interactions were observed for final body weight (FBW), total weight gain (TWG), average daily gain (ADG), feed conversion ratio (FCR) and cold carcass weight (CCW) (P < 0.05), with boars generally exhibiting a greater response to increasing dietary amino acid level than gilts. No dietary amino acid level × production period interactions were detected for any measured variable (P > 0.05), providing no clear evidence that the response to increasing dietary amino acid level differed between production periods. Dietary amino acid level affected dressing percentage (DP) and lean percentage (LP) (P < 0.05), but not average daily feed intake (ADFI; P > 0.05). Overall performance differed between production periods, although these differences could not be attributed specifically to season. Quadratic regression estimated optima of 110.1% for FBW, TWG and ADG, 107.9% for FCR, 110.2% for CCW and 110.1% for DP. These results indicate that the commercial balanced amino acid specification used at the time of the study may have been slightly below the level required to maximise biological performance in TN70 × Tempo grower-finisher pigs.