PSXIV-26 Evaluation of restricted maximum intake on visceral organ mass and carcass characteristics of finishing lambs fed a concentrate-based diet.

Abstract We previously reported that limiting feed intake in growing wethers to 92% of ad libitum intake for 28 or 56 d of the 56-d finishing period reduced DMI (P < 0.01) but did not affect gain to feed ratio or final body weight (BW; P ≥ 0.11). Backfat, longissimus area, bodywall thickness, empty body weight (EBW) as a percent of final BW, and dressing percent were also unaffected (P ≥ 0.12). However, hot and cold carcass weights were greatest in the ad libitum group (P ≤ 0.04) and EBW in kg tended to differ (P = 0.06). The objective of this study was to determine the effect of limiting feed intake in growing wethers to 92% of ad libitum intake for 28 or 56 d of the 56-d finishing period on the mass of visceral organs and carcass cutouts. Thirty Polypay wethers (initial BW = 25.6 ± 5.27 kg) were blocked by BW, sorted into 15 pens (2 lambs/pen), and then randomly allotted to one of three treatments: CON (fed ad libitum for 56 d), 28L (restricted to 92% of ad libitum intake for 28 d, then ad libitum for 28 d), or 56L (restricted to 92% of ad libitum intake for 56 d). The restricted groups were fed 92% of the feed intake of the CON group within their block. Data were analyzed using the MIXED procedure of SAS 9.4 with treatment as fixed effect and block as the random effect. Tukey’s adjustment was used for mean separation. Shoulder muscle weight was greatest in CON and 56L (P = 0.02), while shoulder fat and bone weights tended to differ (P ≤ 0.07). Carcass muscle and bone weight were greater in CON and 56L, while carcass fat weight was greatest in CON and least in 28L (P ≤ 0.04). However, when expressed as percentages of the carcass, muscle, fat, and bone did not differ by treatment (P ≥ 0.16). Among visceral organs, only heart and liver weights differed (P = 0.02), with the heart heaviest in CON and 56L, and liver heaviest in CON but lightest in 56L. When expressed as g/kg of EBW, liver mass was greatest in 28L and least in 56L (P = 0.03). Among whole meat cuts, only the breast differed, which was heaviest in CON and 56L (P < 0.01). Limit feeding wethers for a portion of the finishing period decreased carcass weight and tissue mass, but limit feeding for the entire period had minimal effects on carcass weight and composition. Liver mass responded strongly to feed restriction and may reflect a reduction in maintenance energy demands, potentially improving growth efficiency.