Frequency of monozygotes and sex ratio for twin born in Sahiwal, Karan Swiss and Karan Fries cattle

Present study was carried out on 18,608 calving records of both singleton and twin born occurs during 42 years from January 1969 to December 2011 in Sahiwal, Karan Swiss and Karan Fries cattle at National Dairy Research Institute, Karnal, India.Pregnancies in pure and crossbred cattle resulted from artificial insemination and natural services have been included but not by harmonal treatment or embryo transfer techniques.These calving have 143 twin births out of this six in Sahiwal, 55 in Karan Swiss and 82 in Karan Fries occurred.The sex ratio for isosexual males: heterosexual: isosexual females in Sahiwal, Karan Swiss and Karan Fries was 00:80: 20, 18.60:46.51:34.88 and 36.21:32.76:31.03,respectively.The significant deviation from 1:2:1 ratio was observed in Karan Fries and, it was not found in Karan Swiss cattle.Bonnier method was used for mathematically calculating the frequency of monozygous twin in present study.The observed frequency for monozygous twin was 1.76 for all twin cases.However, only live birth considered then it was 1.8.It inferred that the frequency of monozygous twin was lower in twins born and breedwise variation was observed in the sex ratio.