Most dairy farmers chase milk yields in a bid to bolster end margins, but a new report has found that improved herd fertility not only brings with it higher levels of welfare, efficiency, milk yields and profits, but also reduced methane emissions.

According to Professor Phil Garnsworthy, the optimum lifetime of cows is four lactations, which provides the best balance between lifetime milk yield, spreading rearing costs, and genetic improvement. However, he pointed out that majority of cows, are culled before their third lactation, with failure to conceive being the main reason for their departure from the herd.

"Poor fertility in dairy herds results in premature culling of cows, lower lifetime performance, less opportunity for genetic selection, and increased replacement rate, said Professor Garnsworthy, who was speaking at the British Cattle Breeders' Club conference, which is celebrating it's 75th anniversary this year.

An increased replacement rate means that more heifers have to be kept on the farm, consuming feed and contributing to environmental impacts.

Feed required for replacement heifers also increases if age at first calving is greater than the target of 24 months. He added that trials had shown that herds with a range of 20 to 45% replacement rate and 24 to 36 months age at first calving, feed energy required for replacement heifers varied from 16 to 44% of total feed energy required for the whole herd.

"Improving fertility is a win-win strategy that increases resource efficiency, feed efficiency, and all aspects of sustainability," added the professor of dairy science from the University of Nottingham School of Biosciences.

He told a packed audience in a Telford hotel that premature culling following a second calving due to infertility means such cows do not reach their potential milk yield and profitability thereby leading to low efficiency.

"Annual milk yield per cow increases over the first three lactations and then reaches a plateau. In their first lactation, cows typically yield 70 to 80% of their mature milk yield because they divert some nutrients towards growth rather than milk. Furthermore, economic costs of rearing are not repaid from milk income minus fed costs until approximately half way through the second lactation."

Low fertility can also affect efficiency as a cow with good fertility can have four lactations in the first four years of life in the milking herd, while a female with average or low fertility will only have three lactations in four years.

As a result, the professor said the cow with good fertility will produce 27% more milk in her lifetime for an increase in energy intake of only 12%, therefore feed efficiency is increased by 8%. Furthermore, methane emissions per litre of milk are reduced by 13%.

"Basically, the cow with good fertility spreads feed inputs and methane outputs incurred during the rearing period over more litres of milk in her lifetime," he said.

Interestingly, average whole farm feed efficiency (WFFE) increases as grazing time decreases. Figures from a project conducted by the Research Partnership Nottingham University and AHDB Dairy, whereby WFFE was defined as annual milk production divided by total feed dry matter produced or purchased for all dairy animals, including milking cows, dry cows and youngstock, showed that figures ranged from 0.99 for farms grazing cows for more than nine months of the year compared to 1.13 for cows housed all year. This is due to less control over feed supply when cows are grazing.

According to Professor Garnsworthy, the main driver of WFFE was milk output per hectare, which was a function of stocking rate, milk yield per cow and grass/forage quality. Feed wastage or feed underutilisation was another important driver.

Of the animal management and health factors, the biggest single driver was proportion of cows culled for fertility, followed by age at first calving. Reducing fertility culls from 40% to 20% would improve WFFE by 15%, he said.

By improving fertility, and thereby reducing replacement rate and increasing feed efficiency, GHG emissions are also reduced from all sources, with the possible exception of farm energy use (e.g. electricity for milking and refrigeration, fuel for machinery).

Overall sustainability of dairy plus beef production is likely to be improved by using sexed semen too when its use would result in 1.95 heifers per cow produced in three lactations instead of 1.08 with conventional semen. Sexed semen allows producers to breed replacements from the best heifers and cows, and to produce dairy cross beef calves from inferior cows. According to AHDB statistics, sexed semen was used for 70% of dairy inseminations in 2021/22.