Fertility of zero-grazed dairy cattle following hormone treatment and fixed-time artificial insemination

Abstract

Reproduction is important to dairy herds and achievement of economically optimal performance still remains a substantial multi-factorial challenge in many herds. Poor estrus expression and detection, repeat breeding, prolonged postpartum anestrus and delayed onset of puberty are some of the limiting factors to attainment of optimum reproductive efficiency in zero-grazed herds. This study investigated the fertility of anestrous and repeat breeder zero grazed dairy animals following induction of ovarian cyclicity, synchronization of ovulation, and fixed time insemination. The following three categories of animals were recruited into the study: 1) Delayed puberty or anestrus in heifers (n=26), 2) Prolonged postpartum anestrus (n=23), and 3) Repeat breeding cows and heifers (n=28). The seventy seven animals (69 Friesians, 7 Ayrshires and 1 Guernsey) were all zero-grazed and had a median age and parity of 5.0 years and 2.5 respectively, and a body condition score of at least 2.5 on a scale of 1 to 5. All study animals were intramuscularly injected with Gonadotropin Releasing Hormone (GnRH) on Day 0, Prostaglandin F2α (PGF2α) on Day 7, and GnRH on Day 9. Treated animals had timed artificial insemination (AI) 8-24 hours after the last injection. Pregnancy diagnosis was performed by rectal palpation 60 days post-AI. The pregnancy rate for anestrous cows (6/23) was 26.1%, repeat breeder cows (5/14) 35.7%, anestrous heifers (16/26) 61.5% and repeat breeder heifers (5/14) 35.7%. This treatment protocol may improve fertility outcomes in zero-grazed units where anestrus is a problem, reproductive skills are deficient, there is scarcity of labor or where there is an inability to commit the required time for estrus detection.