Comparison of Four Perennial Forage Finishing Systems and a Limit-Fed Corn-Based Finishing System on Lamb Growth and Carcass Characteristics

Abstract Text:

The objective for the study was to compare four perennial forage finishing systems and a limit-fed corn-based finishing system on lamb growth and carcass characteristics. Each treatment consisted of 3 replicate fields/pens of 6 lambs per field/pen blocked by gender and initial starting weight.  The finishing systems were grazed alfalfa (ALF), grazed ryegrass (RG), grazed alfalfa for 56 d followed by grazed ryegrass for the remainder of the finishing period (ALF/RG), grazed ryegrass for 56 d followed by grazed alfalfa for the remainder of the finishing period (RG/ALF), and limit-fed, corn-based diet fed to achieve a similar rate of gain as the grazed alfalfa treatment (CONC). Lambs were slaughtered when the field/pen average reached the target BW of 58 kg or if forage became limiting.  It was hypothesized that lamb growth and carcass characteristics would be similar for concentrate feeding and alfalfa but greater than alfalfa/ryegrass combinations and ryegrass. Predetermined contrasts between ALF and the other treatments were conducted using LSMESTIMATE in PROC MIXED. Lamb ADG LSM was not different between ALF (0.22 kg/d) and CONC (0.21 kg/d) (P > 0.05), but ALF was greater than RG/ALF (0.18 kg/d), ALF/RG (0.17 kg/d), and RG (0.14 kg/d) (P < 0.05).  Carcass weight was lower for ALF (27.33 kg) than CONC (30.89 kg) but ALF was heavier than RG (21.96 kg) (P < 0.05) and not different from ALF/RG (24.87 kg) and RG/ALF (25.72 kg) (P > 0.05).  Loin eye area was smaller for ALF (14.07 cm²) than CONC (16.96 cm²), but ALF was larger than ALF/RG (12.07 cm²) and RG (12.41 cm²) (P < 0.05) and not different than RG/ALG (13.07 cm²) (P >0.05).  Back fat was less for ALF (0.44 cm) than CONC (0.57 cm) (P < 0.05), but ALF was not different than RG (0.33 cm), ALF/RG (0.35 cm) or RG/ALF (0.39 cm) (P > 0.05).  Body wall was thinner for ALF (1.59 cm) than CONC (2.17 cm) (P < 0.05), but ALF was not different than RG (1.31 cm), ALF/RG (1.53 cm) or RG/ALF (1.49 cm) (P > 0.05). Limit-fed corn resulted in heavier carcasses, with greater muscling and back fat than grazing alfalfa.  Grazing alfalfa produced heavier carcasses, with greater loin eye muscle than grazing ryegrass alone. Leaner carcasses were produced from the grazing programs.

Keywords: lambs grazing alfalfa