US research shows new heifer calves' advantage; COWS.
USING sexed female semen has gained significant momentum across the UK's dairy herds where the prospect of a valuable replacement heifer and the likelihood of an easy calving have attracted many dairy farmers to this practice.
But researchers from the USA have just uncovered a further advantage to producing a heifer calf and revealed that the female calf's mother will produce significantly more milk than the cow producing a bull.
The trend is most pronounced of all in a first-calf heifer which will give more milk in both her first and second lactations if her first calf is female. If her second calf is also a heifer, the benefit accumulates, and is worth 446kg of milk over the two lactations.
This is 2.7% more production than a cow which produced two bulls, and there is no difference between the two in the quality of the milk.
And while the researchers - from Harvard and Kansas State Universities and from Dairy Records Management Systems - knew that the generally easier calving of a heifer calf was likely to have a positive effect on subsequent production, they were able to prove unequivocally that there was an additional cause.
Beginning their research with 2.39 million lactation records from 1.49 million Holsteins, they subsequently cut this dataset down to eliminate lactations which began with difficult calvings, and even among this easy calving group, there was a positive effect on milk production of a female calf.
The mechanisms involved were not specifically identified but there was circumstantial evidence to suggest the female foetus was exerting a hormonal influence on her dam.
Relating the group's findings to the farm situation, Professor Katie Hinde said there were more compelling reasons than before to use sexed female semen.
She added: "Often in the USA, dairy farmers use sexed semen on heifers and one of the reasons for doing this is to avoid dystocia.
"But now we know there's also a production advantage to be gained, I'd say that if a heifer's first calf is a bull, it's worth considering sexed semen for her second lactation."
Here in the UK, cattle breeding company, Cogent, which pioneered the use of sexed semen and now has one of the largest sexing facilities in the world at its Cheshire HQ, is delighted with the findings.
The company's reproduction technologies manager Innes Drummond said: "Dairy farmers have been using sexed semen produced in Cheshire since 2000. Every year since the facility opened, we have accumulated customers, fine-tuned the sexing procedures and improved outcomes.
"Now we have a product from which at least 90% of pregnancies will be female, and our customers are increasingly benefitting from the sexed female advantage.
"These benefits include the production of a valuable heifer calf to become a herd replacement, the easier calving of a generally smaller female calf and the chance of assisting with cash flow by breeding the lower end of the dairy herd to a beef sire.
"But now we know the mother of the heifer calf will also give more milk, there's an even more compelling reason to use sexed semen."
Tom Woof from Cogent carries out an insemination using sexed semen