Research breakthrough in dairy heifer reproduction

Synchrony programs allow groups of dairy heifers to be put up for artificial insemination (AI) on a single day. Producing AI bred calves from heifers increases the rate of genetic gain in dairy herds by breeding replacements from the highest genetic merit animals, as well as improving performance in the current heifer group. Synchronised heifers calve more quickly, meaning more days in milk during their first season and more time to recover before the next mating season.

International researchers identified differences between heifers and milking cows in how heifers respond to synchrony drugs, then used this knowledge to design synchrony programs specifically for heifers. However, these programs had never been tested in New Zealand so Peter and his team wanted to explore whether these findings would also apply to NZ’s pasture based seasonal dairy industry.

In the 2023 spring mating season, 565 heifers from 4 Manawatu dairy farms were randomly treated with either the current CIDR® heifer synchrony program or a new CIDR heifer synchrony program (known as a modified 5-day Cosynch program). Both programs used the same drugs, but the new program design altered the treatment timings and used some additional injections to align better with the activity of heifer ovaries.

After AI the heifers were mated for the rest of the spring mating season as normal, then reproductive performance was evaluated via aged pregnancy testing. The heifers treated with the new modified 5-day Cosynch program showed significantly higher in calf rates, both for AI and for the entire first 6 weeks of the mating season.

If a mob of 100 heifers were synchronised with the new modified 5-day Cosynch program, compared to the current NZ standard heifer program, this would, on average, result in:

• 17 additional heifers in calf to AI.
• 13 additional heifers in calf after 6 weeks of mating.
• 10 days extra days in milk for the heifer mob during their 1st season.

Once both the costs (drugs, yarding, feed, etc) and benefits (extra milk, higher value calves) of the new program were calculated, this improved reproductive performance was worth around an extra $70 per heifer compared to the NZ standard program.

If you are already using synchrony programs for your heifers, please talk to your vet about the benefits of using a modified 5-day Cosynch. Heifer synchrony programs are a great option to improve your heifer performance, so get in touch with your vet if you would like to explore how they can work for your farm.

Thank you very much to the farmers who allowed their heifer groups to be included in this study, to Zoetis for their support with study design and supplying CIDR devices, and to Parnell Animal Health for supplying injectable hormones.