Female fertility and body composition

I participated in a Webinar on Fertility and Body Composition run by Southern Beef Technology Services. The bottom line was that heifers need to have at least 5 mm of fat to have the best chance of going in calf. That has been our experience too.

The table below gives the conception rates at various rib fat thickness and body weights at 400 days of age.

The recommendation in this area is that heifers should be at 60% of their mature body weight at joining. We reckon that our cows might average 700 kg so we like to see them about 420 kg at joining.

Furthermore our females need some fat on their backs to cope with our cold cold winters. The above picture shows our autumn calving mob in snow. Our experience is that some of the larger framed, leaner, heavy milkers do find it hard to go back in calf within a limited joining period. The progeny of Lindsay Starbright, being very lean, found their first few winters pretty tough.

This spring the cow whose last calf had the best growth rate has just calved 49 days after the first cow calved which means that her calf is the only one not within the Breedpan contemporary group. She was synchronised and probably conceived on the 2nd return after unsuccessful AI.

Our approach has been not the penalise the heavy producers but provide better feed. At the same time we are seeking bulls with positive fat EBVs that will be easy doing in our climate. Willalooka Arthur has been superb in that regard. In time our herd will be more moderate framed, better muscled but with better fat coverage. The challenge is to breed for more muscle without losing the fat coverage.