Effect of breed and castration on production and carcass traits of male lambs following an intensive finishing period

Abstract

The practice of crossbreeding using a terminal sire and the use of intact rather than castrated animals has the potential to increase the productivity of lambs produced from the hill sheep sector. The objective of this study was to compare the production and carcass characteristics of purebred Scottish Blackface (SB) and Texel cross Scottish Blackface (TXSB) ram and wether lambs fed on a concentrate diet and slaughtered at different ages. Two hundred spring born male lambs (average birth age ± SD 9.53 d) were assigned to a 2 × 2 factorial arrangement with two breeds SB (n = 100) and TXSB (n = 100) and two sexes (wether: n = 100 and ram: n = 100). Lambs were harvested following a 36 d ad libitum concentrate indoor finishing period. The study was carried out over five harvest batches between October and April. The mean ages of the lambs at harvest (n = 40; 20 TXSB and 20 SB lambs) in October, November, January, March, and April were 196, 242, 293, 344, and 385 days, respectively The TXSB lambs were heavier at slaughter than SB lambs (P < 0.001), and ram lambs were heavier at slaughter than wether lambs (P < 0.01). Improved ADG (P < 0.001), lower feed conversion ratio (FCR) (which was calculated by dividing total feed intake by total weight gain; P < 0.001), and higher feed intake (P < 0.05) were recorded in TXSB lambs with consistency across the five harvest time points. Rams had greater ADG (P < 0.001) and FCR (P < 0.05) compared with wether lambs, and no differences were observed between sexes for feed intake. The TXSB (P < 0.001) lambs had higher (P < 0.001) dressing percentages compared with SB, while wether lambs had greater dressing percentages compared with rams. The TXSB lambs had heavier carcass weights (P < 0.001) with higher conformation grades (P < 0.001) and less fat cover (P < 0.001) than SB lambs, while ram lambs had heavier (P < 0.001) carcasses than wether lambs. There was greater fat cover on the loin muscles of SB (P < 0.001) and wether (P < 0.001) lambs compared with TXSB and ram lambs, respectively. The results from this study suggest that TXSB lamb's offer hill sheep farmers a potential strategy for improved lamb production efficiency, while ram lambs offer lamb finishers increased growth rates, higher FCR, and produce a more desirable carcass than do wether lambs.