اثر سن شیرگیری و نوع پرورش بر عملکرد رشد بره های لری بختیاری

Introduction: Sheep and goat meat is considered as one of the main sources of red meat in Iran. Lori-Bakhtiari sheep is one of the most important breeds among the native sheep breeds in Iran with a large population and acceptable meat quality and also adaptability to poor ranges. Weaning lambs is the removal of a milk-based diet, either provided by the ewe or milk replacement in a hand-rearing system, onto forage or grain-based diet. As with any management practice such as a change of diet or significant social change for the animal, the period may be stressful and careful management is essential. The time of weaning is very important in lambs since it affects feed consumption; growth performance and carcass characteristics of lambs. Range sheep operations traditionally have allowed lambs to graze with their dams until late spring or early summer. This poses a problem when severe drought conditions and forage availability is limited. Early weaning can provide some very appealing benefits: More pasture will be available to maintain the retained ewe flock if lambs and cull ewes are removed earlier in the year; The ewe’s nutrient requirements are reduced after weaning, which will cause ewes on pasture to eat less and lose less weight; Lambs use supplemental feed more efficiently for growth than ewes use it for milk production; Placing lambs in a feedlot will reduce predator losses. This study was conducted to investigate the effects of weaning age and rearing type on the growth performance of Lori-Bakhtiari male and female lambs.
Materials and Methods: 150 Lori-Bakhtiari ewes were synchronized during the mating season and then randomly mated with Lori Bakhtiari rams. A total of 110 ewes gave birth in the lambing season with a range of 10 days, of which 113 healthy lambs (59 male lambs and 54 female lambs) were selected and studied at two months of age. The experiment was conducted in a completely randomized design. Male lambs were divided into six treatments including early-weaned fattening lambs (10 heads), early-weaned non-fattening lambs (10 heads), traditional weaned fattening lambs (10 heads), traditional weaned non-fattening lambs (8 heads), late weaned fattening lambs (10 heads) and late weaned non-fattening lambs (11 heads), and Female lambs were studied in three treatments including early weaning (17 heads), traditional weaning (20 heads) and late weaning (17 heads). Weaning of lambs in early weaning, normal weaning, and late weaning was performed at the mean age of two months, three months, and four months, respectively. The fattening of male lambs continued until the age of six months. Other non-fattened weaned lambs (male and female) were raised with their dams up to six months of age without access to the mother's breast. Lambs had access to dry forage (in winter) and wet forage (in spring and summer) in addition to milk before weaning. At birth, the weight of all lambs was measured and the sex and type of birth (single and twin) of lambs were recorded. The weight of all lambs was measured and recorded at two months and then monthly up to six months. Daily weight gain in monthly periods and final weight gain in lambs of different treatments were calculated. Data were statistically analyzed by SAS software and MIXED procedure.
Results: At three months of age, early-weaned fattening lambs were heavier than the lambs of other treatments (P<0.05). At four months of age, early-weaned fattening lambs weighed more than traditional weaned fattening lambs and traditionally weaned fattening lambs weighed more than male lambs in other treatments (P<0.05). At this age, the weight of male lambs in traditionally weaned non-fattening, late-weaned fattening, and late weaned non-fattening treatments was not statistically significant. Also, in five-month-old male lambs, the weight of early-weaned fattening lambs was higher than the lambs of other treatments (P<0.05). The five-month weight difference of lambs was not significant in non-fattening treatments. At six months of age, early-weaned fattening lambs weighed more than traditional weaned fattening lambs, and traditionally weaned fattening lambs weighed more than male lambs in other treatments (P<0.05). In general, at six months of age, fattening lambs weighed more than non-fattening lambs (P<0.05). There was no statistically significant difference in the weights of lambs of non-fattening treatments at the age of six months.
In male lambs, early-weaned fattening lambs from two to three months of age gained 293 g / day, which was significantly higher than the lambs of other treatments in the same period (P<0.01). The average daily weight gain in male lambs from three to four months of age was higher in early-weaned and traditional weaned fattening treatments than in other treatments (P<0.01). In males and from two to six months of age, the mean daily weight gain in early-weaned fattening, traditionally weaned fattening, and late weaned fattening treatments was 242, 226, and 212 g / day, respectively, and the difference between early-weaned fattening and late weaned fattening treatments was significant (P<0.01). During these four months, the average daily weight gain was equal in the non-fattening treatments. During the same period, the mean daily weight gain in fattening lambs was higher than the average daily weight gain in non-fattening lambs (P<0.01).
There was no statistically significant difference between female lambs in different treatments for weight at the same age. Also, there were no significant differences in terms of average daily gain in the rearing period between female lambs in different treatments.
Conclusion: Data obtained in this study indicated that weaning of male lambs at two months of age and fattening them until six months of age had positive effects on their growth and final weight and weaning of female lambs at two months of age hadn’t a negative effect on their weight gain until six months of age.