2 April 1999

Concentrates affect fertility

HIGH merit cows on a low concentrate diet for a number of lactations suffer more infertility than those fed high concentrate diets.

According to Jennie Pryce, Edinburgh-based SAC geneticist, results from its Langhill Herd show that although yield increases with genetic merit, yields are lower on the low concentrate diet.

For each extra unit of pedigree index for fat and protein, cows produced 0.17kg of milk on the high concentrate diet and 0.12kg of milk on the low concentrate diet.

"Production on the low concentrate diet is constrained as genetic merit increases. That could be because they are incapable of eating as much." Yield results are consistent across lactations, said Dr Pryce.

"But in first lactation, increasing genetic merit tends to reduce days to first heat for those on the high concentrate diet, compared with those on a low concentrate diet. It could be that heifers yield so much on a high concentrate diet that they do not start cycling as quickly as those yielding less.

"But when animals are kept on a low concentrate diet the reverse happens, so high merit animals have longer days to first service on a low concentrate diet."