As we draw nearer to the onset of mating, talk is turning to when and how the maiden heifers will be mated.
Farmers are especially mindful of this year's maiden heifers because it is their progeny that will be the first heifers to be milking in a quota-free era. A lot of discussion focuses around the use of either AI or bulls for natural mating the maiden heifers.
The main positives of using AI on heifers are to:
• Increase the rate of genetic gain in your herd;
• Increase the number of AI replacements;
• Get a chance to increase herd size more rapidly;
• Be able to achieve the required number of AI replacement heifers with a short AI period in the milking herd.
Clearly, the use of AI on the maiden heifers has benefits. However, using AI on heifers also requires consideration. The number one priority is to get the maiden heifers in-calf on time.
Any system that results in a compromise on the submission of heifers and conception of pregnancy will cost you money. This loss occurs in terms of fewer days in milk and less time between calving and mating, which would result in lower reproductive performance.
Aim to at least start mating the maiden heifers no later than the cows and possibly 7-10 days before the cows. Before attempting AI on heifers, farmers should ask themselves several questions:
• Do you have easy access to the heifers and what handling facilities are available? Many farmers bring the heifers back to the milking platform for three weeks to make this easier, but you will need to consider whether you have enough pasture/feed to cope with the increase in feed demand.
• How will heifers be drafted and held for insemination? Consider the time that this will take and when it will be done. This will substantially increase the workload at a busy time of year.
• What type of heat detection should be used? The big risk here is the potential to miss a heifer that is actually on heat or misinterpret signs and think a heifer is on heat when she is not. Many farmers suggest the use of scratch cards, Kamars (heat mount detectors) or crayons above tailpaint for heifers, while others value the use of vasectomised bulls. Regular paddock checks are often important to get good results.
• Have you selected the sires to be used? Mating heifers to Holstein-Friesian AI sires can result in serious calving difficulties that can negate the benefits of AI. Jersey sires typically don't cause a problem and crossbred sires are intermediate for risk of calving difficulty.
• Will you use DIY AI or an AI technician? Heifers can be more difficult to inseminate, and have you considered the extra time this will take?
• What bulls will you need? Run one bull per 30 yearling heifers. Make sure there are always at least two sexually active bulls running with the heifers from the start of the mating period and leave bulls with the heifers for at least seven weeks after first insemination. AI may be a preferable option if you are short of bull power.
• Will you heat synchronise your heifers? Remember, returns to synchrony will occur when the bulls are running (18-24 days after main insemination date) so you will need to increase the bull:heifer ratio to one bull per 15 non-pregnant heifers or use AI.
Heat synchronisation can be very time-efficient as the work of heat detection and AI is shortened into planned intensive periods.
This can be ideal for management of the maiden heifers. Note, however, that most synchronisation programmes will have minimal effect on the six-week in-calf rate and are unlikely to reduce the empty rate.
A range of synchronisation programmes are available using prostaglandin (PG) and these are usually the least expensive.
Treatment with PG does not work on heifers that have not started cycling (prepubertal), and a single PG injection will not work on any heifer that has been on heat in the past six days. Heifers that respond to PG are usually on heat within two to five days of treatment, but some may take up to seven days to respond. There are several variations in PG programmes. However, one common method used is where heifers are heat detected and mated normally for the first six days. Any heifer not seen bulling is given a single injection of PG on day six or seven of mating, which results in most heifers coming in heat during the first 12 days of mating.
Intravaginal devices are a second option for synchrony, and are more preferable than PG if heifers are below live-weight target at mating and a number are not cycling.
Heifers are treated nine days before mating, with treated heifers showing signs of heat from days 10-12 -- more than three days from the start of mating. Options are available to use fixed time insemination or insemination following heat detection.
Dr Mary Kinston is an agricultural consultant based in Kerry. Email: email@example.com