Kvet Forum
Well-known member
A repeat breeder cow is a cow that has failed to become pregnant following three or more consecutive serves at normal inter-estrus intervals. An incidence of 10–18% is reported, but these figures depend on the herd pregnancy rate. For example, in a 100-cow herd with a 40% pregnancy rate, 22 cows will need four or more serves compared to six in a herd with a pregnancy rate of 60%.
Aetiology
The statistical chance is as outlined above. Failure of fertilization or early embryo death may result from a hostile uterine environment, blocked oviducts/salpingitis, delayed ovulation, bursal adhesions and anatomical abnormalities (e.g. segmental aplasia in maiden heifers).
Diagnosis
A vaginal examination should be undertaken on the day of estrus to check for clear mucus and a normal cervix. The cervix, uterus, oviducts and ovaries/bursae should be examined rectally and by ultrasound.
Management
If there is a cloudy/purulent mucus, the cow should not be served. An antibiotic uterine wash-out should be carried out and the cow served at the next estrus or short-cycled by PGF2α injection in 10 days.
If adhesions, salpingitis or other physical abnormalities are found, the cow should be culled unless the genetic value of the animal warrants oocyte collection and in-vitro fertilization to produce embryos for transfer into recipients.
If no abnormalities are found on examination of repeat breeder cows, a GnRH injection can be given on the day of service (holding injection). Treatment with an injection of GnRH around the time of insemination has been shown to improve fertility in repeat breeder cows by inducing an LH surge and ensuring ovulation occurs synchronously with the insemination. This treatment is likely to be most effective in cows that suffer from ‘delayed ovulation’.
Treatment with GnRH on day 11 after service has been shown to increase the pregnancy rate in cows by up to 10% compared with untreated controls. The treatment induces LH release and luteinization or ovulation of large second-wave follicles, reducing oestradiol secretion and possibly increasing luteal progesterone concentrations. This reduces the risk of premature luteolysis and leads to a reduction in early embryonic loss. This treatment can be given to all cows or targeted on cows returning to estrus for a second or third service (repeat breeders).