Dairy cows2

Improving cow fertility

As part of the Pillars of a Sustainable Dairy System research programme, AbacusBio consultants are working with DairyNZ and breeding companies to assess how well the fertility breeding value can improve herd reproductive performance.

Over three or more decades, there has been a decline in cow fertility – resulting from a negative genetic correlation between fertility and production, meaning intensive selection for production traits has eroded the fertility performance of cows over this time.

Since the inclusion of fertility in the National Breeding Objective in 2001, there has been an improvement in the genetic merit for fertility in New Zealand cows.

“However, there is a long way to go before the industry reaches its target to improve fertility to levels observed a number of decades ago,” AbacusBio consultant Hadyn Craig says.

Therefore, it is opportune that a validation study of the fertility Breeding Value (BV) be undertaken and an analysis of how fertility genetic merit impacts herd performance across varying environments, which could identify ways to target different selection strategies and increase the rate of improvement of fertility.

Based on our findings, DairyNZ genetic evaluation developer Melissa Stephen says that, a cow’s genetic merit for fertility clearly does make a difference.

“The results suggest that herds with a fertility problem can benefit more from the selection of sires with higher fertility estimated breeding values (EBVs), compared to the benefits that should be expected in high fertility herds,” Hadyn explains.

The magnitude of the impact of fertility EBV increases in proportion to the magnitude of the fertility problem. This provides an opportunity to use these differences in impact to make greater progress depending on how a farmer’s herd is performing.

An example would be through the creation of a specific index, such as low fertility herd breeding worth (BW), which farmers could use to place greater selection weighting to fertility.

A simpler alternative would be to provide a message to farmers to favour high BW bulls that also have a high fertility BV, if they wish to address a long-term fertility problem in their herds via genetics.