You see a bull described as a ‘curve bender’, so what does this mean? In essence it means that, although the bull has above average growth in his calves, they have below average birthweights. In other words his calves are born small but grow fast – the Holy Grail of bull breeding!

Our wonderful old sire, Willalooka Arthur, was a classic curve bender, low birth weight and high calving ease coupled with above average growth. This is easily seen on his Breedplan graph.


Sometimes bulls have progeny which bend the curve the opposite way! The bull below has heavy calves that grow slower than average.


If you are looking at Breedplan figures, not graphs, it is not so obvious to pick the curve benders. A recent Hereford sale introduced an interesting concept. They gave a star rating based on various criteria. One criterion was that the bull should have a birthweight EBV less than 10% of his 400 day weight EBV. This ratio takes into account that a bigger bull could be expected to have a comparable increase in the size of his calves.

I had a good look at Murray Grey figures and this ratio seems to work pretty well in our breed as a predictor of calving ease.The average birthweight EBV is 3.3 and the average 200 day EBV is 32 so the average ratio would be about 10%. If you are looking for a bull that will have better than average calving ease it is worth checking the ratio of BW to 400 day weight.

We select our bulls to have moderate or low birthweights and it was interesting to see that our resident bulls have BW EBVs less than 10% of their 400 day EBV.