Direct, maternal and heterosis effects for slaughter and carcass characteristics in three breeds of fat tailed sheep

Abstract

Direct, maternal and heterosis effects for slaughter and carcass characteristics of 162 lambs of three fat-tailed Iranian breeds of sheep, Karakul (K), Mehraban (M) and Baluchi (B), and their reciprocal crosses were estimated. The lambs were kept in a feedlot for 120 days after weaning and were slaughtered at 195 days of age. Offals, internal fat, and carcass cuts were individually weighed, and testicular weight, volume and dimensions, backfat thickness, and rib-eye muscle area and dimensions were measured. The large-size M was superior to the small-size B for maternal environment effects on weight and percentage of omental and mesenteric (OM) fat and tail-fat, whereas B ranked highest among the breeds for maternal effects on proportion of offals and prime cuts. Baluchi, which are adapted to the desert conditions, had a higher direct genetic effect compared with other breeds for fat production, as is indicated by its thicker ( P < 0.05) backfat and higher weight and percentage of tail fat and body-cavity fat ( P > 0.10). For K direct genetic effects resulted in leaner carcasses of their progeny. A small degree of positive overall heterosis was observed for weight or size of each trait measured, but heterosis virtually disappeared when the traits were expressed as a percentage of slaughter or carcass weight. Exceptions were significant heterosis exhibited by testis weight (6.6%) and volume (7.9%) as a percentage of slaughter weight, and by percentage of OM fat (10.1%) which showed largest estimates of overall heterosis. It was concluded that the magnitude of heterosis depends, in part, on the rate of development of a tissue. Tissues that had their greatest growth at a specific point in the developmental process showed the highest heterosis at that point.