We encounter a significant percentage of maiden heifers in a prepubertal state when presented for a pre-breed scan. These heifers are not fit for breeding.
We recommend identifying this group of animals to get them out to grass with supplementation of 3kg of heifer growing ration. This approach results in normal fertile heat cycles within three weeks.
Some farmers use the pre-breed scan to group heifers that can be synchronised with a prostaglandin injection either immediately or six days later. The pre-breed scan will also identify those heifers for breeding over the following three days without the need for injection.
Alternative synchronisation approaches include 'watch and inject', 'double inject' and 'Rolls Royce', listed here in order of increasing cost.
However, the time required for heat detection decreases, there is less risk of missed heats, and some of the prepubertal animals will establish pregnancy with the 'Rolls Royce' treatment.
In the 'watch and inject' regimen, heat detection and AI continue for six days from the onset of the breeding programme. On the sixth day, heifers not bred are injected with prostaglandin. All heifers should be bred by the tenth day of your breeding programme.
This approach works well when heifers are managed close to home. Remember that prepubertal heifers will not respond to this treatment.
The 'double inject' approach entails injecting all heifers both 14 days before and two days prior to the start of the breeding season. All cycling heifers should be detected in heat over a three day period.
Prepubertal heifers will not respond to this treatment either. The cost of this approach will range from €10 to €15 per animal, excluding veterinary fees.
The 'Rolls Royce' entails the injection of a Progesterone-releasing Intravaginal Device (PRID) or Controlled Internal Drug Release (CIDR) device per vaginum for eight days with a prostaglandin injection on the day prior to removing the PRID or CIDR.
Please note that the new PRID devices are easier to insert in maiden heifers and do not have the high device loss rates experienced with the old PRID device. All heifers should present in heat over a one day period. This facilitates AI and indeed a fixed time AI on outside farms.
Some farmers might also consider inserting the PRID or CIDR devices 15 days after breeding for a five day period. This results in tight synchrony of repeats and reduces the risk of missing heats.
This should be given consideration if heifers are managed on outside farms where you want to use AI to breed future replacements and reduce the risks of using stock bulls.
Stock bulls are an option for breeding maiden heifers. Genomic testing has increased the probability of breeding replacements with desired production potential traits.
Please ensure that your stock bull is fertility tested as over 10pc of stock bulls are either infertile or sub fertile. Any injury to a bull will impair spermatogenesis, which will reduce his fertility six weeks later, even if he might appear fit for purpose.
Dr Dan Ryan is a bovine reproductive physiologist and can be contacted at www.reprodoc.ie