RELATIVE SIZE OF CALF AND DAM AND FREQUENCY OF CALVING DIFFICULTIES

The frequencies of calving difficulties were computed for 458 calvings of first and second parity Friesian, Ayrshire and Jersey dams with pure and crossbred progeny in all possible combinations. It was found that heavier breeds of dams have higher frequency of difficult calvings. For each breed of dam there is also a direct relationship between the mean birth weight of the calves and the frequency of calving difficulties associated with the breed or cross of calf. An index of calving difficulties calculated in the form of a discriminant function which combined both the birth weight of the calf and the calving weight and parity of the dam was: Z = log BW−0· log DW−0·10 P, where Z is the index of calving difficulties, BW and DW are respectively the birth and dam weight and P the parity variable withthe values of one for second parity and zero for the first. © 1969, British Society of Animal Science. All rights reserved.