عنوان مقاله [English]
نویسنده [English]چکیده [English]
Introduction: A large volume of literature describes the biological roles of vitamin E and its application to preventing disease and improving health and productive performances of farm animals. It is widely documented that vitamin E play an important role in the reproductive performance. The vitamin E requirement may be defined as the amount required preventing peroxidation in the particular subcellular membrane which is most susceptible to peroxidation (Koyunku and Yerlikaya 2007). Little is known about the effects of vitamin E supplementation on specific reproductive events in sheep. Most nutritionists assume that reproductive performance will not be limited when domestic animals are fed diets that meet the NRC levels. However, little is known about the effects of vitamin E supplementation on specific reproductive events in sheep and goats. Because fertilization in this animals is an all or none phenomenon (i.e., either all ovulated eggs are fertilized or none of them are fertilized), the three major variables that contribute to litter size are ovulation rates, embryonic survival and foetal survival rate (Koyunku and Yerlikaya 2007). The present experiment has been conducted in the two flocks with a history of relatively moderate fertility (90 %). The objective was to examine the effect of vitamin E supplementation on the number of lambs weaned and total lamb weaned weight.
Materials and Methods: The experiment was conducted using 200 Lori Bakhtiarii ewes (100 ewes per flock), with an average live body weight 57.5±6.7 kg and between two to seven years of age. The ewes in each flock were randomly divided into two groups, consisting of 50 ewes per group. Each group of ewes assigned to consume one of the two diets. Diets contained basal diet plus 250 gram per ewe barley grains (control) or basal diet plus 250 gram per ewe barley grains plus 500 IU vitamin E. The basal diet was based on local feeds; pasture herbage and the salt stone as free. The experiment started with the natural mating period in late summer. The feeding regimens started from 2 weeks before lasted to 3 weeks after ram introduction. The ewes from all groups were kept in the same shed and consisted as one flock while grazing. Ewes were placed in individual pens once daily to receive supplemental treatments. Ewes remained in individual pens until all trial supplements had been consumed. Ewes in each flock were mated to 10 fertile Lori Bakhtiari rams during the breeding seasons of 34 days in late summer and early autumn. Weight and body condition score of ewes at mating were measured. Body condition scoring (BCS=1 for emaciated ewes to BCS=5 for obese ewes at 0.5 interval) has been described by Russel et al. (1969). The body condition score of the ewes in this method based on touching of the tips of both the spinous and the transverse processes of the vertebrae, and the fullness of fat and muscle cover over and around the vertebrae in the loin region. The animals were general kept indoors from December to May and lambed indoors. Date of lambing, the number of lambs born, lambs birth weight, survival rate of lambs from birth to weaning and lambs weaning weight were measured. Some combination traits as total lamb birth weight and total lamb weaning weight per exposed ewe were calculated. Data were analyzed using General Linear Models (GLM) procedure of SAS.
Results: There were no significance difference among the flocks and treatments on the ewe's body weight and body condition score of ewes at mating. Difference between control and vitamin E treatments with respect to the number of lambs born per ewe exposed to the rams was tended to be significant (p=0.06). The number of lambs born per ewe exposed to the rams was not affected by flock, and body condition score of ewes at mating. Yearling ewes produced fewer lambs than older ewes but differences were not statistically significant. Mean of birth weight of lambs were not statistically differing between flocks, treatments, ewes body condition scores and ewes parity. Total birth weight of lambs per ewe exposed to the rams and per ewe lambing was differ between treatments (p < 0.01) and was higher in vitamin E treatment. Total birth weight of lambs per ewe exposed to the rams was not affected by flock or ewe parity but, total birth weight of lambs per ewe lambing was differing between flocks (p < 0.01). Effects of body condition score on the total birth weight of lambs per ewe exposed to the rams and per ewe lambing were statistically significance (p < 0.05). The number of weaned lambs (p < 0.01), total lambs weaned weight per ewe exposed to the rams (p < 0.01) and total lambs weaned weight per ewe lambing (p < 0.05) were higher in vitamin E treatment than control group. There were not significance difference among different flocks and different ewe parity on the number of lamb's weaned and total lambs weaning weight per ewe exposed to the rams and per ewe lambing. Body condition scores was influenced the number of lambs weaned and total lambs weaning weight per ewe exposed to the rams (p < 0.05).
Conclusion: Data obtained in this study indicated that in the Lori Bakhtiatri sheep, using supplemental vitamin E in the diet of ewes given before mating, significantly increased the number of weaned lambs and total weight of weaning lambs per ewe exposed to the rams. These findings should be useful in further exploring the frequency and amount of vitamin E supplementation that may improve reproductive performance of ewes.