Factors affecting reproduction rates in a commercial Brahman crossbred herd

Abstract

Data were collected from a commercial herd in central Queensland to compare the effect of genotype on reproductive performance. Brahman back cross (B6H2), and Santa Gertrudis cross (SG4B2H2) cows had lower pregnancy rates and conceived later in the mating season than first cross (H5B3) COWS. The age of cow by breed of cow interaction on pregnancy rates indicated that phenotypically fertile cows can be selected from subfertile genotypes. Age of cow had a significant effect on reproductive performance. There was an increase in pregnancy rates and tendency for earlier conception in the mating season as age and selection intensity increased. Two-year-old cows had lower foetal survival rates than older cows. Year effects were consistently significant for time of conception within the mating season, but this effect was variable on pregnancy rates. The regression on cow weight was significant for pregnancy rates and usually significant for month of conception. The slope of the line was positive indicating that higher cow weight increased the probability of conception earlier in the mating season.