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sur le développement des zones arides et semi-arides

Titre : Effect of feed composition and sex on feedlot performance, carcass characteristics and profitability of Dorper lambs

Auteur : Hanel, Emma Claire

Université de soutenance : Stellenbosch University

Grade : Master of Science (MScAgric) 2022

Résumé partiel
The Dorper is the most numerous of the meat sheep breeds in South Africa. However, the early maturity of the breed and its tendency to deposit localised fat at an earlier age, typically requires them to be slaughtered at a lower live weight when compared to later maturing breeds. These characteristics tend to be enhanced under favourable environmental conditions, such as intensive feeding systems. Most feedlot operators discriminate against Dorper’s and are reluctant to finishing them owing to their slaughtering at a lower live weight or having their grade negatively affected, thereby reducing the income potential. There is limited literature describing the effect of diet and sex on the performance and profitability of feedlot finished Dorper lambs. The objectives of this two-part study were to determine the effect of treatment (diet) and sex on overall feedlot production parameters of Dorper lambs. Part two considered the effect of diet and sex on carcass characteristics and overall profitability parameters. Eighty-four Dorper lambs were randomly allocated to one of seven treatment groups (1=control, 2=low-energy, 3=high-protein, 4=high-protein + low-energy, 5=high-fat + low- starch, 6=high-fat + low-starch + high-protein, 7=control + β antagonist), comprising 12 animals each- 6 ram and 6 ewe lambs in a 2 x 7 factorial design. Treatment yielded a significant (P ≤ 0.05) effect on performance for most of the measured parameters (dry matter intake, number of feedings, final weight, liveweight gain, average daily gain and feed conversion ratio), while the effect of sex was limited, and the interaction of treatment and sex was significant for feed conversion ratio (P = 0.01) only. Findings of this study show the lambs final weight was significantly the highest for Treatment 4. Moreover, these animals yielded superior performance for liveweight gain and ADG across all groups in both ram and ewe lambs (P ≤ 0.05). Although, not significant, rams on average yielded numerically slightly superior performance compared to ewe lambs across the measured parameters. Treatment 1 yielded the best feed conversion in both rams and ewes, suggesting that the standard feedlot diet resulted in the most efficient growth, while Treatment 7 was shown not effective in improving feedlot performance for all the recorded parameters. Findings of Part two, investigating the main effects on carcass characteristics, show that Diet yielded a significant (P ≤ 0.05) effect on most of the measured parameters (final weight, warm and cold carcass weights, warm and cold slaughter percentage, feed cost, carcass value and margin above specified costs) while the effect of sex was limited.

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