PS9-15. Effect of Direct-fed Microbial Additives on Days on Feed to Slaughter Weight, Carcass, and Wholesale Cut Yields from Light or Heavy Body Weight, Intact or Castrated Crossbred Lambs.

Abstract Improving the productivity of finishing lambs raised under heat stress conditions is an important challenge for sheep production in tropical regions. Nutritional strategies, including the use of microbial feed additives (DFM), may enhance animal performance and carcass characteristics. In addition, animal type (AT) and initial body weight (IBW) at the beginning of the finishing phase may influence growth rate and carcass yield. The objective of this study was to evaluate the effect of two DFM on days on feed (DOF) required to reach slaughter body weight (SBW) and on carcass and wholesale cut yields of light or heavy intact or castrated crossbred lambs. Thirty-two crossbred lambs (< 6 mo of age) were housed in pairs and fed a finishing diet consisting of 70% commercial concentrate and 30% chopped tropical grass hay. Lambs were classified by AT (intact or castrated) and IBW (heavy = 33 kg or light = 28 kg) and assigned to four dietary treatments: control (CON), DFM1, DFM2, and a mixture of DFM1 and DFM2. The additives, containing different blends of bacteria and yeast, were manually mixed into the diet throughout the finishing phase until lambs reached SBW (41 kg). To evaluate carcass characteristics, lambs were slaughtered at a commercial slaughterhouse. Hot carcass weight was recorded at slaughter, and cold carcass weight was determined after 24 h of chilling. Each carcass was processed into primary cuts, including neck, shoulder/rib plate, loin, and hind leg. Primary cut weights were expressed as a percentage of cold carcass weight. Data were analyzed using a completely randomized design with a factorial arrangement of treatments (4 DFM × 2 AT × 2 IBW). Means were separated using Tukey’s test. Days on feed to reach SBW were similar among dietary treatments (CON = 59 d, DFM1 = 80 d, DFM2 = 68 d, DFM1–2 = 65 d) but were lower (P < 0.05) for intact (43 d) or heavy weight (56 d) lambs compared with castrated (93 d) or light weight (80 d) lambs. Hot carcass yield (CON = 45.45%, DFM1 = 45.02%, DFM2 = 44.93%, DFM1 + 2 = 44.38%) and cold carcass yield (CON = 45.25%, DFM1 = 44.91%, DFM2 = 43.13%, DFM1 + 2 = 44.25%) were not affected (P > 0.05) by dietary treatment, AT, or IBW. Similarly, the yields of neck, shoulder/rib plate, loin, and hind leg were not influenced (P > 0.05) by DFM, AT, or IBW. In summary, castration and lower initial body weight increased the number of days required for crossbred lambs to reach slaughter weight. However, DFM, animal type, and initial body weight did not influence carcass yield or wholesale cut proportions.