This study investigated the effect of feedlot production on lamb growth characteristics of three common South African breeds: Merino, South African Mutton Merino (SAMM) and Dorper. Lambs were supplied with a balanced diet (16% crude protein, 9.41 MJ ME/kg feed) ad libitum and had free access to water. Lambs from each breed were divided into six groups. One group of each breed was slaughtered every three weeks until 105 days under feedlot production were reached. The weights of the lambs were recorded weekly, along with feed intake, to obtain the individual daily intake, average daily gain (ADG) and feed conversion ratio ( The results confirm that the Merino is a late maturing breed that is recognised for its wool rather than meat production, and therefore exhibits weaker growth characteristics. The SAMM is a dual-purpose breed that has also been selected for growth and meat production, and therefore exhibits desirable production characteristics, while the Dorper is an early maturing breed that deposits localized fat at an earlier age as it grows, thereby producing fatter carcasses than SAMM and Merino lambs. Therefore, Dorper lambs should be slaughtered at lower live weights so that carcasses are not graded as over-fat. ______________________________________________________________________________________
The objective of this study was to determine the effect of time spent in a feedlot on the size of the various fat depots and the distribution of the main tissues (muscle, bone, and fat) of three common South African sheep breeds. Lambs were supplied with a balanced diet (16% protein, 10 MJ ME/kg feed) ad libitum and had free access to water. Lambs from each breed were divided into six groups, which were slaughtered at 21-day intervals until a production period of 105 days had been reached. During carcass dressing, visceral and renal fat was removed and expressed as a percentage of carcass weight. The subcutaneous fat (SCF) depth was measured on the longissimus lumborum at the 13th rib position using an electronic calliper. The proportion of muscle, bone and fat was determined by dissecting a three-rib cut made on the prime rib between the 9th and 11th ribs. The percentage of visceral and renal fat increased throughout the production period for all breeds. The percentage of renal fat was up to 2.9% higher than the percentage visceral fat in both SAMM production groups. Dorper lambs tended to have high SCF levels (5.6 mm fat after 42 days) due to the early maturing nature of the breed. They reached a maximum fat depth of 20.4 mm fat after 105 days. The SAMM lambs tended to deposit SCF at a slower rate and the late maturing Merino breed was found to be much leaner, and did not reach the high fat levels of the SAMM or Dorper lambs. The percentage of muscle and bone in all carcasses decreased with an increase in the number of days in the feedlot, while the percentage of carcass fat increased during this period. The increase in late maturing adipose tissue in all breeds as they become older is amplified by the restricted movement in the feedlot and high energy diet that the lambs receive.
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