Don’t forget your HEIFER SYNCHRONY

Now is the time to plan your heifer AI mating! Various programmes exist to synchronise heifers for artificial insemination (AI).

There are several reasons to AI your yearling heifers: rearing extra AI replacements to increase herd size more rapidly, getting the same number of AI replacements with a shorter AI period in the milking herd, and increasing the rate of genetic gain of your herd. Some programmes synchronise heifers to one day of AI (CIDR/DIB), others to a few days requiring heat detection (PG). Plan what to use for heat detection (e.g. check the detectors you choose actually stay on yearling heifers!).

Prostaglandin (PG) programmes only work in animals that are cycling (i.e. have the relevant structures on their ovaries). If heifers are in poor condition, or not well grown (<60% of mature liveweight at 15 months old when mating starts), poor submission rates can be expected from PG programmes. A CIDR/DIB synchronisation programme is necessary in these pre-pubertal heifers.

Ideally heifers should be mated to start calving 1-2 weeks earlier than the milking herd. This will help them achieve calving pattern targets and good reproductive performance at their next mating (heifers take longer to start cycling post-calving). This means you will need your yearling heifers at the required target mating weight 1-2 weeks earlier. You will also need to plan the labour required to calve heifers down earlier than the main herd.

After an AI programme, you will normally still need natural mating bulls. These should be of a breed that is a low risk for assisted calvings (essentially as close to Jersey bulls as possible). Calving difficulty breeding values (BVs) should be as close as possible to -2.5% (typical Jersey figure).

Sires for AI should also be picked paying particular attention to the calving difficulty BV. For example, Holstein-Friesian sires have calving difficulty BVs typically positive (e.g. +1.4%). Cross breeds will be intermediate. The yearling bulls used with these heifers should be around 14-15 months of age, the same as the heifers. Libido and fertility are lower in very young bulls, so care should be taken to try to ensure bulls used are at the 14-15 months of age at the heifer planned start of mating (PSM).

A study based in NZ over 10 pasture-based herds with 1137 heifers was conducted by S. McDougall. It compared different heifer synchronisation programmes – double PG (on days -13 and -2), and CIDR/DIB programmes (with set time AI on day 1 or day 0). The day 0 CIDR/DIB programme had a higher conception rate to AI (57%) than the double PG programme (48%). The study concluded that the CIDR/DIB programme resulted in the highest fertility and economic benefit.

Get in touch with your primary vet through mating consults EARLY to sort out heifer programmes!