Effect of seasonal variations during dry and wet seasons on reproductive performance and biological and economic criteria of hair sheep under Halaieb rangeland conditions

摘要

This study was conducted to evaluate the impact of seasonal variations (wet and dry season) on the reproductive and productive performance and to do an economic evaluation of hair sheep under Halaieb rangeland conditions and determine which season is the best in grazing areas. A total of 64 multiparous AbouDelik ewes were bred in two different seasons. During the first season (dry season), a total of 35 ewes, 2-4 years of age and 32.02 +/- 0.52 kg weight, were bred during May and June, while lambing and lactation took place in the months of November, December and January. On the other hand, during the wet season, 29 ewes, 2-4 years age and 31.06 +/- 0.57 kg weight, were bred during November and December, whereas lambing and lactation took place in the months of May, June and July. Sheep grazed 8 h daily in the same pastures during the study and then moved back to the barns to receive a sorghum vulgare supplement with a dosage of 250 g per head per day. The results revealed that there were no significant effects of breeding season on conception, lambing and abortion rates. However, the wet season had higher (P<0.05) prolificacy, mortality rates, lambs' weight and lambs born to ewes serviced. Contrariwise, dry-season lambs had a higher (P<0.05) weaning weight. Also, milk yield (mL d (1)) and number of lambs weaned per lambs born (LW/LB) increased (P<0.05) in the dry season compared to the wet season. No significant differences between the two seasons regarding the biological criteria studied were observed. On the other hand, the flock bred in the dry season generated a higher gross margin than that bred in the wet season. In this context, variable costs of the wet breeding season flock were recorded to be close to the value of the dry breeding season. Hence, it is concluded that the reproductive and productive performance of hair sheep raised in grazing areas in the Halaieb triangle is affected when lambs are born during the dry season because of the higher lamb mortality rate during this period which eliminates any comparative advantage for the good reproductive performance of ewes during the period of feed availability in the wet season. The high lamb mortality rates and low weaning weights in the wet breeding season lessen the economical merits of higher reproductive performance during the seasonal availability of feed in the wet season.