Effects of sex and year on growth and live assessment of carcass characteristics of lambs grazing annual pastures

Abstract

Lambs from the Poll Dorset x (Border Leicester x Merino) cross were raised from a late lambing in 1983 (a year when pastures grew unchecked and had high clover content) and 1984 (a year with intermittent dry periods and a low clover content in pastures). Multivariate repeated measures analyses were used to compare growth rates for rams, wethers and ewes within 2 periods of growth in 1983, and 4 in 1984. In all stages rams grew significantly faster than wethers and ewes, whereas wether growth rate exceeded that of ewes in only 3 stages. In general, when pasture availability and quality was high, rams grew faster than wethers by 0.3 kg/week and ewes by 0.5 kg/week. The rams grew 0.16 kg/week faster when pasture availability was limiting for a period in winter but lost significant (P<0.01) body condition, whilst ewes maintained both weight and condition. When good quality feed was again available, rams gained more weight than wethers, as did wethers compared with ewes, while rams and wethers gained more condition than ewes. Carcass weight and fatness, measured either as indicators of fat (GR measurement or fat score) or as total subcutaneous fat, could be predicted from assessments made on live lambs. Full liveweight, sex and year explained 41% of variation in GR, 48% in fat score and 79% in subcutaneous fat. Condition score, sex and year explained 45% of variation in GR, 52% in fat score and 57% in subcutaneous fat. Full liveweight, condition score, sex and year explained 80% of the variation in subcutaneous fat, 47% in GR and 57% in fat score. An interaction of sex with full liveweight in predicting carcass weight and subcutaneous fat indicated that as carcass size increased, the sex of the lamb became an increasingly important consideration when assessing characteristics important in describing lamb carcasses. Dressing percentage decreased by 0.08/kg as liveweight increased. This result was consistent over the 2 years, with opportunities for error being assessed and eliminated in the second year. Notwithstanding that this was an unimportant loss in real terms, published information showed an increase in dressing percentage with liveweight.

Sire Breed, Litter Size, and Environment Influence Genetic Potential for Lamb Growth When Using Sire Breeding Values

“…Male lambs were heavier and grew faster at all times measured, and this has been demonstrated in previous studies [ 3 , 20 , 21 ]. Despite male lambs being castrated in this study, this effect is consistent with the impact of testosterone, a potent muscle growth stimulant [ 22 ].…”

“…Despite male lambs being castrated in this study, this effect is consistent with the impact of testosterone, a potent muscle growth stimulant [ 22 ]. Thatcher, Warren, and Nicholls [ 21 ] demonstrated significantly faster growth in rams compared to wethers ( p < 0.05), thus the differential in growth between wethers and ewe lambs in this study is likely to have been further increased if the male lambs were left entire. Producers can utilise these growth differentials to predict puberty in ewe lambs or slaughter dates in wether lambs based on the focus of the enterprise.…”

Influence of breed and feeding on the main quality characteristics of sheep carcass and meat: A review

“…All of these factors have been studied to determine if they can be influenced by sex (Thatcher et al, 1991), breed (Kremer et al, 2004), genotype (SantosSilva et al, 2002), age (Leymaster and Jenkins, 1993), weight at slaughter (Pérez et al, 2007), type of feed (Díaz et al, 2002) and productive year (Thatcher et al, 1991). The presence of contusions, which are characterized by degree, location and extension, are also important because they reduce the value of meat cuts and carcasses (Tarumán and Gallo, 2008).…”