Reproduction Rate and Viability of Nilagiri and Nilagiri Synthetic Breeds of Sheep

Abstract Reproduction data of 4648 Nilagiri and 6542 Nilagiri Synthetic ewe records spreads over 27 years (from 1989 to 2015) representing 4530 Nilagiri and 5950 Nilagiri Synthetic breeding ewes were used in this study. Flocks belonged to the Sheep Breeding Research Station, Sandynallah, India. Flock dynamics of six age groups (1.5–7.5 yrs) were assessed. Ultimate objective of this research work was to evaluate the replacement rate, reproduction rate, flock structure and dynamics of Nilagiri and Nilagiri Synthetic sheep breeds. Three parameters were used to evaluate flock dynamics, age specific replacement rate, net reproduction rate and intrinsic rate of increase or innate capacity for increase of population. The replacement rate estimated was significantly higher (P value < 0.002) in Nilagiri (0.289) than Nilagiri Synthetic sheep (0.260). The age-specific death rates ranged from 0.026 (3.5–4.5 years) to 0.191 (6.5–7.5 years) with highest 0.191 and 0.134 in Nilagiri and Nilagiri Synthetic sheep from 1.5 to 7.5 years of age, respectively. The replacement requirements will be met if the ewes are kept in the flock until five years of age with a net reproduction rate of 1.024 in Nilagiri and if the ewes are kept in the flock until six years of age with a net reproduction rate of 1.196 in Nilagiri Synthetic. Nilagiri ewes in intermediate ages had more multiple births and older ewes weaned more lambs. The flock strength was not maintained unless the ewes were kept till the fifth lambing Nilagiri, third lambing in Nilagiri Synthetic sheep. All estimates tended to increase with dams age up to six years and decreased thereafter. The results of Ro and rm showed that the studied flock must consist of 6 age groups to maintain its size and replace itself. It may be recommended to cull the breeding ewe at the age of 6 years to accelerate genetic improvement. Based on the findings it is concluded that suitable breeding policy of selection and culling of such flock should be formulated.