INFLUENCE OF DOCKING AND CASTRATION ON GROWTH AND CARCASS TRAITS OF FAT-TAIL KARAKUL, RAMBOUILLET AND CROSSBRED LAMBS

Growth and carcass data were obtained on 312 lambs derived from two breeds, Rambouillet, Karakul, and two crosses, Suffolk X Rambouillet and Karakul X Rambouillet. Other factors included docked vs undocked, sex (males, females and castrates) and type of birth (litter size). The traits studied were birth weight, pre- and post-weaning growth and carcass scores and measurements. Breed, sex and type of birth significantly affected birth weight and preweaning gains. Karakul ewes produced larger lambs at birth which had higher preweaning gains. Effects of sex and type of birth followed expected patterns for birth weight and preweaning gains. Postweaning gains tended to be greater for male and crossbred type lambs. Pure Rambouillet and female lambs gained significantly slower than other types. Karakul and Karakul-cross lambs were fatter in all measures (tail fat, rib and back cover, kidney and pelvic fat). Tail fat trim was an important item of waste in undocked Karakul types; for female lambs fat trim was 1151 g (4.5% of the carcass), for males 915 g (3.6%). In crossbred docked males, females and castrates, tail fat trim was 233 g (0.94%), 318 g (1.29%) and 247 g (1.00%, respectively. It is concluded that crossing with a non fat-tail breed and docking reduced tail fat trim to 1% of carcass or less in male or castrate lambs.