At an individual cow BV level, figures from over 2.3 million cows with early aged pregnancy testing results support the research herd findings.
Figure 1 shows a significant difference in performance at the extremes of cow fertility; BVs of +5 and – 5. It appears
from this dataset that the relationship is not linear. Gains in 6 week-in-calf rate appear to taper off as BVs increase, particularly at BV +3 and beyond.
It is important to keep things in context as well. Few cows have extreme +/-5 BVs in the NZ national herd, as illustrated in Figure 2 which plots the Fertility BV distribution of the 2.38 M cows analysed.
The majority of cow Fertility BVs sit between -1 and + 2. The figure also shows the average fertility BVs of balanced index LIC bull teams marketed in the same year. This illustrates, at a national level, the potential scope for improvement of cow genetic fertility while keeping focus on other important traits. The scope within individual herds will depend on the herd’ own spread of BVs. While creating and maintaining a high herd level of genetic fertility is important, the impacts of increasing BV may eventually taper off.