Improved reproductive performance and economic outcomes from use of a modified 5-day Cosynch program in pasture-based dairy heifers

Abstract

The primary objective of this study was to evaluate reproductive performance in dairy heifers submitted to fixed-time artificial insemination (FTAI) following a modified 5-day Cosynch program (m5dC) compared to a 7-day Cosynch program (7dC). Additionally, the study examined the economic impacts of treating heifers with the m5dC program compared to the 7dC program, and the effect of pre-synchronization with prostaglandin (PG) on serum progesterone (P4) concentration.

At the start of the breeding season, maiden heifers (n = 565) from four New Zealand dairy farms were randomly allocated to one of two synchronization programs: 1) m5dC (n = 283), 500 μg cloprostenol administered on Study Day −10, 100 μg gonadotrophin-releasing hormone (GnRH) on Study Day −8, 500 μg cloprostenol on Study Day −3, 500 μg cloprostenol on Study Day −2, 100 μg GnRH concurrent with FTAI on Study Day 0, and insertion of an intravaginal P4-releasing insert (CIDR) for 5 days commencing on Study Day −8; 2) 7dC (n = 282), 100 μg GnRH administered on Study Day −10, 500 μg cloprostenol on Study Day −3, 100 μg GnRH concurrent with FTAI on Study Day −1 and insertion of a CIDR for 7 days commencing on Study Day −10. Heifers were then mated either by a combination of insemination to observed heat and natural mating or by natural mating alone, depending on farm management policy, for a total mating period of up to 10 weeks.

Serum P4 concentration was measured in a subset of heifers (n = 34) selected randomly from both treatment groups at the time of CIDR insertion; geometric mean values were lower for m5dC heifers (1.35 ng/ml (95 % CI 1.04–1.76)) than 7dC heifers (2.95 ng/ml (95 % CI 1.79–4.84)). Conception rate (CR) to FTAI and subsequent reproductive performance were evaluated based on ultrasound pregnancy diagnosis carried out between Study Days 95 and 123. Performance was significantly improved for m5dC heifers compared to 7dC heifers for both CR to FTAI (62.0 % vs. 45.4 %, p = 0.0007) and 6-week pregnancy rate (87.6 % vs. 74.4 %, p = 0.0002). Mean interval from FTAI to conception was shorter for m5dC heifers (15.1 days) compared to 7dC heifers (25.0 days). A difference in final pregnancy rate was not detected between treatment groups (p = 0.18). A partial budget was constructed to estimate the economic return of synchronizing heifers with the m5dC program compared to the 7dC program, producing a net return of NZ$72.29 per heifer. Synchronization of dairy heifers with an m5dC program resulted in superior reproductive performance at FTAI and following 6 weeks of mating compared to the 7dC program.