Inheritance of horns and occurrence of cryptorchism in indigenous, Rambouillet and crossbred sheep in India

Abstract

Observations were made on the horn growth and on the testicles of the offspring of Rambouillet, Malpura, and Chokla ewes joined to Rambouillet rams at the Central Sheep and Wool Research Institute, Malpura (Rajasthan) in western India. No cryptorchids were observed among these sheep and it was concluded there is no risk of introducing cryptorchism from Chokla and Malpura to sheep in the breeding program at the Institute. The observations were consistent with polledness resulting from the action of a gene P which is dominant in ewes and incompletely dominant in rams. Both Malpura and Chokla sheep consist almost exclusively of sheep that are PP. Among the Rambouillet sheep observed, both P and the recessive p were present, the former in low frequency. In addition, an allele of intermediate dominance P' was present. In the absence of P, P' initiates the growth of horns in ewes. Observations made on the Mandya (or Bannur) sheep were consistent with the same mode of inheritance of polledness existing in the breed as in Malpura and Chokla. Among the Gaddi sheep observed there were many ewes with horns. The genes P' and p were segregating in this breed. The Madras Red sheep observed all had horn sites consistent with the sheep being pp.