There is a decline in dairy cow fertility across the world and no-one is sure why, a dairy researcher says.
Tom Brownlie, a veterinarian for Cognosco, a private research company based in Waikato, told about 40 farmers, farm advisers, and academics at a Rongotea seminar, that cows and heifers needed to be in good body condition to make sure they got in-calf each year.
He said if cows were too thin, they often didn't get in-calf, or had calves late, losing milk production and failing to get in-calf next time around.
Brownlie said reports suggested dairy cows had not been as fertile (as good as getting in-calf), with information coming from Britain, mainland Europe and Australia.
"Arguably there's a genetic component. There is an element of the concentration on production, and fertility might have slipped. If you imagine all the factors that make up fertility as a cake, then the focus on production is one of the slices."
There are other factors, such as body weight and condition and breed which have an impact on cow fertility, as well as recognising when a cow is in season.
Brownlie said in New Zealand, losses due to fertility could now be quantified.
He said research funded by DairyNZ, the Ministry for Primary Industries, Agmardt, and LIC showed about 65 per cent of dairy cows did not reach an optimal weight before mating.
"We might not have been raising our heifers as well as we need to."
Brownlie said each dairy farmer brought up to 20 per cent of new heifers into the research herd, culling old, late calvers and low performance cows.
It made heifers the single biggest group in a herd.
A well grown heifer not only got in-calf earlier than a lighter heifer, but produced more milk in her first and subsequent lactations.
"What's much more exciting is we can actually measure reproductive performance of cows. Traditionally we couldn't, we only had empty rates to go on and they're affected by herd management."
Brownlie said the national target was that 78 per cent were in-calf in the first six weeks of mating.
He said that was the average of the top quarter of herds and had remained the same for years.
"So the optimist would say fertility is not in decline any further, but it hasn't turned the corner and improved either. We do need it to be up. The dairy industry set a target of 78 per cent in-calf in six weeks for the average herd by 2020.
"Breed does have an impact at an individual cow level. So if you are a kiwi cross cow, then you are the most fertile and more likely to conceive than if you're a jersey. And lastly come friesians.
"It's a positive for the dairy industry. Everyone wins from this if we can just get our heifers coming in at target weights. The bonus is there are about 80 kilograms of milk a heifer produces if she is up to weight, rather than a skinny heifer."
Brownlie said the extra milk produced and an early calving heifer meant a dairy farmer could pay a grazier to get the heifers up to target.
Less than a quarter of dairy farmers weighed their heifers if they raised them on their farm, and few had their herd body score conditioned (BCS) by another.
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