|dc.description.abstract||Over recent years sheep numbers in New Zealand have steadily declined due to increased expansion of dairying. This has caused not only reduced ewe breeding flock numbers but also pushed lamb production to less productive areas. New Zealand lamb exports were worth $3 billion in 2016 (MIA, 2016) therefore a significant contributor to the red meat industry which is the second highest export earner behind dairy products. Another challenge to the industry is to meet expectations of the consumer who want leaner carcasses with less fat. Lean meat makes up 50-60% of total carcass weight, therefore selecting for increases in lean muscle is of benefit to increase carcass value and financial return. Birth weight has been observed to influence lean meat production through muscle mass and growth rates, but little is known about its effect on lamb final weight and carcass traits such as lean meat production. Could emphasising the importance of ewe nutrition be of financial gain to farmers if resulting lambs have production benefits over and above improved survival rates due to increased lamb birth weights.
2521 NZ Romney ram lambs from 2009-2016 were investigated for an association between birth weight and subsequent weaning weight and final weight with carcass traits (lean meat, leg, loin and shoulder yield). SPSS v24.0 was used for calculating correlations between birth weight, weaning weight and final lamb weight with carcass yield traits and between subject effects (sire, birth weight, weaning weight and final lamb weight). Excel 2013 was used for basic statistical analysis (means and standard deviations).
Birth weight was found to have a positive correlation with weaning weight and final lamb weight (0.467 and 0.152 respectively) and this was highly significant (p<0.001). Furthermore birth weight also greatly influenced lamb growth rates with the heavier the birth weight, the greater the growth rate. Low birth weight (2.75 kg) grew at 81.25 g/day, medium birth weight (5.88 kg) at 241.28 g/day and high birth weight (9.50 kg) at 366.66 g/day respectively. Birth weight also was correlated positively with leg, loin, shoulder and total yield (lean meat) with 0.018, 0.055, 0.147 and 0.078 respectively. Only shoulder and total yield were significant (p<0.001). Weaning weight was found to be positively correlated with final lamb weight (0.413) and this was highly significant (p<0.001) it was also correlated positively with carcass yield traits (loin, shoulder, total yield) which were highly significant (p<0.001) however leg yield was found not to have a significant correlated (p> 0.005). Final lamb weight was positively correlated with loin, shoulder and total yield (0.189, 0.151 and 0.055 respectively) and these were all highly significant (p<0.001). Leg yield was found to have a negative correlation (-0.120) and this was also highly significant (p<0.001). Birth weight was found to be significantly affected by sire (p<0.001), while lean meat was significantly affected by both sire and weaning weight (p<0.001), leg yield was sire and final lamb weight (p<0.001), shoulder yield year was sire and lamb final weight (p<0.001) and finally loin yield, sire, weaning and final lamb weight (p<0.001).
These results suggest that birth weight is important for maximising yield as it influences growth rates of lambs and is strongly correlated with lamb weaning weight. Weaning weight is strongly correlated with lamb final weight which had the greatest influence on carcass yield traits, as expected due to a strong genetic correlation with live weight and carcass weight. Overall these results reemphasise the importance of maximising lamb birth weight and reducing the factors which influence it negatively such as inadequate ewe nutrition in order to have lambs which have high yielding carcasses.||en