This study examined the performance of lambs offered one of six diet types; ad-libitum concentrates (ALC), forage rape (Brassica napus L. FR), hybrid brassica (Brassica napus L. HB), kale (Brassica oleracea L. K), permanent pasture (predominantly Lolium perenne. PP) or reseeded perennial ryegrass (Lolium perenne. RS). Lamb grazing days (LGD) were higher for FR, HB and K compared to PP and RS (P < 0.05). Lambs offered ALC had higher average daily gain (ADG) compared to lambs offered FR, HB and K (P < 0.001). Lambs offered PP and RS had the lowest ADG (P < 0.05). Texel x Scottish Blackface (TXSB) lambs achieved a higher ADG compared to Scottish Blackface (SBF) entire males or SBF castrate males offered ALC, FR, HB, K and RS (P < 0.01). SBF entire males achieved a higher ADG compared to SBF castrate males offered ALC, FR and PP (P < 0.01). Lambs, slaughtered at ≥40 kg live weight, offered ALC had higher slaughter and carcass weights compared to lambs offered FR, HB and K (P < 0.0001). TXSB lambs had lower carcass fat and superior carcass conformation than SBF entire males and SBF castrate males (P < 0.001). The results indicate that ALC diet maximises ADG, but lambs offered FR, HB and K outperform those offered PP and RS during autumn/winter grazing. PP and RS swards were inadequate for finishing lambs in the autumn/winter period due to the decline in nutritive quality and lower LGD compared to FR, HB and K.
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