Effect of plane of nutrition on feedlot performance and carcass traits of desert sheep
AbstractSeventy Barki lambs were used in this study. Five prefattening levels of nutrition were used during the period from 7 to 20 months of age included high (H), medium (M), low l (L1), low 2 (L2) and low 3 (L3) representing 100, 75, 50, 40, and 30 per cent of Morrison feeding standards, respectively. Dry feeding (D) was provided throughout the prefattening period for all lambs except in the first three levels, where nearly half of the lambs in each group were allowed to graze (G) during a period of 13 weeks without supplementation. All animals were slaughtered at the end of a 70 day fattening period during which they were given the same fattening ration according to Morrison’s fattening standards. Prefattening plane of nutrition significantly affected initial and slaughter weights, average daily gain, dressing percentage and chilled carcass weight. Higher planes of nutrition resulted in a relatively higher value for these traits except daily gain, which was relatively higher in lower planes. In the lower fed groups the shoulder was relatively heavier while the neck was relatively lighter in the higher fed groups. The higher planes resulted in heavier muscles, greater fat thickness over longissimus dorsi, larger l. dorsi area and lower percentages for the lean and bone of the 9-10-11 rib cut. Fat percentage of the 9-10-11 rib cut was relatively higher for the lambs on higher planes of nutrition. There was no statistically significant difference in the chemical composition of the 9-10-11 rib cut of lambs fed different planes of nutrition. Males had significantly higher initial slaughter weight, daily gain, dressing percentage based on empty body weight, chilled carcass weight, percentage of neck, weights of muscles, eye-muscle area and percentage of lean and bone in 9-10-11 rib cut than females. Females however, had significantly higher percentages of loins, legs, racks, tail, more fat thickness over l. dorsi and percentage of fat in the 9-10-11 rib cut as compared with males. Judging from the results of carcass traits and relative costs for each plane of nutrition, the MG plane was recommended for lambs living under such prevailing conditions.