Growth and carcass characteristics of crossbred lambs in various production systems

Abstract

Lamb growth, carcass and pelt measurements are reported from 5775 lambs born to Border Leicester × Merino (BLM) and Hyfer (Dorset × Merino composite) ewes joined to Dorset, Suffolk and Hyfer rams in three lamb-production systems at Cowra and Wagga Wagga over 5 years. The production systems involved lambings at different seasons of the year and increasing levels of intensification from autumn annual joining, spring joining with a backup mating for non-pregnant ewes, to an accelerated 8-monthly lambing system. Lambs from BLM ewes were 0.7 kg heavier at birth and grew 3% faster and reached slaughter, at 18 kg carcass weight, 1–2 weeks earlier than did lambs from Hyfer ewes (P < 0.01). The advantage in growth rate of lambs from BLM compared with Hyfer ewes was greater for lambs born in November. These lambs had poorer growing conditions over the summer months, with 22% lower growth rate and taking 5 weeks longer to reach slaughter than did lambs born in March or August. There was no difference between Dorset and Suffolk sire breeds for any lamb growth traits, with lambs from Hyfer sires growing 7% slower. Ram and cryptorchid lambs reached slaughter 1 week earlier than did wethers, with ewes a further 9 days later (P < 0.01). Sex differences were maximised when lamb growth was greatest. There were no differences in carcass fat measurements between ram and cryptorchid lambs, although both were considerably leaner than wethers (2.2–3.0 mm fat at the GR site), which were 1.3–2.1 mm leaner than ewes at 18-kg carcass weight. The range in average growth rate of progeny of the BLM ewes from the 12 different source flocks at Cowra and Wagga Wagga was 10–14% of the mean which was twice the difference in average growth rate of progeny from the BLM and Hyfer dams. There was also significant variation among the BLM source flocks for carcass fat measurements. Lamb progeny from the different sire- and dam-breed combinations had varying levels of heterozygosity. There appears to be little loss of heterosis or hybrid vigour for lamb growth, although the sire breed × dam breed interaction was significant (P < 0.01) for age at slaughter at Wagga Wagga, in which the ranking of the lamb types was consistent with the levels of heterozygosity. The estimates of between-lambing repeatability for the ewes were highest for birthweight (0.35 Cowra and 0.27 Wagga Wagga) and declined at later ages (0.26–0.17), with lower estimates for carcass traits.

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

“…The higher growth rates in ram lambs observed in the present study agree with the growth rates found by Lee (1986a) . The 15% higher ADG for ram compared with wether lambs is in close agreement with the results of the studies of Fogarty and Mulholland (2012) and Fogarty et al (2000) but lower than the 39% higher ADG reported for Border Leicester ram compared with wether lambs by Lee (1986b) . Increased gains in ram lambs are associated with male sex hormones such as testosterone ( Kiyma et al, 2000 ) which stimulates increased dietary nitrogen utilization efficiency, an action that is also accompanied by decreased fat deposition ( Judge, 1989 ; Lawrence and Fowler, 1997 ).…”

<b>Time on feedlot and sexual effects on animal performance and characteristics of lamb’s meat

“…According to Haddad, Husein, and Swedan (2006), there was no effect of castration in lambs for HCW, CCW, dressing percentage, or LMA. Fogarty and Mulholland (2012) observed higher for BFT (3.9 mm) in wether lambs when compared with ram animals (2.9 mm). Sales (2014) found that wether lambs had greater dressing percentage and BFT, but LMA was lower when compared with rams.…”

“…Lambs fed for a longer period, as expected, had higher carcass weight when compared with animals that spent less time in the feedlot however, with lower feed efficiency ( Table 2). Fogarty and Mulholland (2012) observed that rams had higher body weight at 70 and 170 days of life when compared with females. That resulted in heavier and leaner carcasses.…”

“…Among them, castration facilitates the management, decreases aggressive behavior, and improve carcass characteristics, mainly through greater fat deposition and carcass yield, which can influence the commercial value of meat (Fisher, Bray, & Johnstone, 2010;Fogarty & Mulholland, 2012).Castration also reduces sheep aroma and flavor, but non-castrated fed intensively for short time should also produce meat without bad taste and with enough fat deposition. Animals that remain less time on feed and are harvested earlier might have less influence of sexual condition in carcass and meat characteristics.…”

“…Animals that remain less time on feed and are harvested earlier might have less influence of sexual condition in carcass and meat characteristics. In some studies no statistical difference between males not castrated and castrated based on performance, carcass characteristics, and meat quality (Fogarty & Mulholland, 2012;Vargas Junior et al, 2014 This trial was proposed to verify as far as noncastrated intensively fed lambs may produce high quality meat, with the same acceptability by the consumer of the meat from castrated animals. The Dorper x Santa Inês cross, commonly used by Brazilian farmers, show good fat deposition which can be increased by castration and age and this can accentuate the characteristic sheep flavor.…”