AGE is likely to be one of the biggest factors contributing to lower dairy herd fertility.
This was one of the key messages from the Fleurieu Dairy Fertility Investigation Project, in which four dairy herds around the area were studied to try and find the cause behind reduced fertility.
Willunga Vet Services veterinarian and Dairy Australia InCalf adviser Simon Edwards, who headed the project, said where 10 to 15 years ago farmers were getting between a 60 per cent and 70pc in-calf rate in the first six weeks of mating, figures were now down to 50pc or less.
He was speaking at a recent field day held at the property of Chris and Bev Williams.
"This is making it really difficult to get enough heifer replacements in the system to then have enough young animals in the herd," he said.
"The average conception rate in heifers is now 55pc, but the conception rate drops dramatically after their second lactation.
"If you have an older herd, it is going to be less fertile based on these results."
Dr Edwards said there were lower numbers of replacement heifers on the four study farms, meaning the herds were older.
"In theory, you want to make sure the best-quality heifers are coming through the system and that those replacement heifers are coming into the herd nice and early on in the mating season," he said.
"In these herds, there were a large number of carryover cows and repeat breeders that might take four or five matings to get in-calf, as well as cows that weren't getting in-calf but hanging on to them because there weren't enough replacements to get rid of them, based on fertility."
The four herds studied in the project had conception rates between 30pc and 35pc - about three matings per pregnancy - which had a big impact on farm costs.
Submission rates - the number of cows that have calved and available to mate at the start of the mating period - were above 80pc on most of the farms. Dr Edwards said this meant the vast majority of cows that should have been mated in those first three weeks of mating were actually mated and given a better opportunity to get in-calf.
*Full report in Stock Journal, February 16 issue, 2012.
