Lifetime productivity of crossbred cows. 2. Age and weight at first oestrus, calf birth weight, assisted calvings, calving interval and reproduction rate

Abstract

Crossbred heifers were born in 1974 from 7 breeds of cattle by mating Hereford bulls to Shorthorn cows, Hereford bulls to Friesian cows (calves double-suckled), Hereford bulls to Jersey cows (and Jersey bulls to Hereford cows), and using semen or natural service of Sahiwal, Charolais, Simmental and Brahman bulls on Hereford cows. Breed differences were important sources of variability for age and weight at first oestrus. The heifers were joined with Hereford bulls to produce backcross progeny during the years 1976-84 in a semi-arid environment. Parity (confounded with year and age of dam) and its interaction with breed had significant effects on frequency of assisted calvings, birth weight, calving rate and weaning rate. On average, over all parities, European cross dams (Charolais, Simmental) had calves of higher birth weight than other types but also had more assisted calvings, a lower calving rate and longer calving interval. Dairy cross dams (Friesian, Jersey) had early puberty, short calving intervals, few assisted calvings and higher calving rates. Zebu cross cows (Brahman, Sahiwal) had poor early reproductive performance due to late onset of oestrus, but similar or better subsequent calving rates and calving intervals. Their calves had lower birth weights but required similar assistance to Europeans. Shorthorn cross cows had similar calving intervals and more assisted calvings than other types in spite of their calves having average birth weights.