Many causes of repeat breeder cows
DAIRY cows served two or three times without becoming pregnant are difficult to treat because there are so many possible causes of infertility.
Speaking at the Sanofi conference, Peter Vos of Utrect Universitys faculty of vet medicine, Holland, said that repeat breeders were economically important to milk producers and presented a frustrating situation for vets.
These cows have normal oestrous cycles with no clinical abnormalities but fail to get in calf after two or three inseminations. Vets know treatment with hormones alone is not always successful, he added.
Factors which may be involved include hormonal abnormalities before ovulation, failure of the dam to recognise pregnancy or of the embryo to produce a strong signal, genetic abnormalities of the embryo and fertility failure.
Reasons for fertility failure include low semen fertility, ovulation failure, blocked oviducts, malformation of the genetic tract and whites, said Dr Vos.
In a herd achieving a normal pregnancy rate of 55% to AI, Dr Vos estimated that 12% of pregnancy failure is caused by fertility failure, 25% by early embryonic death, 6% by later embryonic death and 3% by foetal death. Many repeat breeders could result from these normal causes of non-pregnancy.
Errors in cow management and poor heat detection also cause low conception rates resulting in the appearance of repeat breeders.
Treatment to induce ovulation during oestrous and to overcome early embryonic death should come before culling repeat breeders, providing cows with genetic abnormalities have been identified. But success with hormonal treatment is limited, he warned.