Pub stories of successful heifer calvings can result from doing the small things well, vet Andrew Cochrane writes.

Andrew Cochrane

I write about this topic with slight trepidation as there is a wealth of information on this subject. However, I’m sure some of you will have been recently disappointed with heifer scanning results or have recurring nightmares about last season’s heifer calving. Equally as a vet, I come across disappointing results and bad outcomes from heifer mating multiple times each year.

So, what’s the secret to achieving the sort of results you hear about at the pub? The stories about a 95% calving rate with no assisted calvings… which, despite ‘pub chat’, do happen. What are the successful farmers doing that you are not?

Unfortunately, there is no single magic bullet to ensure a successful heifer mating. As with most things in farming, it is about doing the small things well.

Feeding is number one (as always), closely followed by bull selection and ratio, mineral supplementation and a robust animal health plan (in particular regard to BVD and parasites). Reaching target liveweights is key and to achieve these requires some attention to detail.

A number of studs are selecting for calving ease so pay particular attention to the calving ease EBVs when choosing a bull.

All these things start at or before birth, in order to ensure the heifer, as a calf, gets off to a good start. This begins with ensuring the cows are in good condition, well fed and producing enough milk to provide for the needs of the calf until weaning.

The heifer calves need to be weaned on to good quality pasture in order to maintain growth rates and reach liveweight targets for mating. Consideration also needs to be made for parasite control and minerals (Se and Cu), particularly during the autumn months leading into winter and again in spring prior to mating.

Combination drenches provide the best protection against the broadest range of parasites and oral or injectable drenches are preferred. In addition, BVD needs to be managed to ensure this does not impact on reproduction.

Exposure to BVD should at least be monitored and this can be as simple as testing 15 animals at 10 months of age. For herds with high exposure, all replacement heifers should be tested prior to mating and vaccination considered for herds at risk of infection during mating.

Bull selection also needs some attention, this should be done well in advance of mating to ensure the right bulls can be sourced. Calving ease should be the main consideration and at the very least a breed chosen that is the same as the heifers or one known for ease of calving.

A number of studs are selecting for calving ease so pay particular attention to the calving ease EBVs when choosing a bull. Age of the bull is another factor to bear in mind and often yearling bulls are used due to their size. However, if yearlings are used, extra bulls may be needed due to the relative inexperience of both parties.

As a general rule for heifers, a bull ratio of 1:30, potentially as high as 1:20 for yearling bulls, should be used to maximise reproductive outcomes.

An alternative and one gaining some traction for heifer mating, is artificial insemination. By mating heifers artificially we can reduce the number of bulls needed and select a sire that has the required attributes for calving ease without breaking the bank. There are obvious management considerations and costs associated with artificial breeding, but this is an option for those that are set up to handle it.

The next consideration might be mating date and length. Assuming heifers are well grown it is good practice to mate the heifers at the same time or about 7-10 days before the cows. This will allow enough time after calving for the heifers to recover in time for their second mating as a two-year-old (R3). It is also worthwhile restricting the mating length to no more than two and a bit cycles (about 45 days). A tight, condensed mating will help to reduce the likelihood of a poor scanning result as an R3.

Target liveweights at mating will depend somewhat on breed but, as a rule, heifers should be 60% of their mature weight at 15 months. If the mature weight of cows is 550kg, then you should be targeting heifers at 330kg to the bull. That’s not to say lighter heifers won’t get in-calf, but these smaller heifers are more likely to give you problems in spring and less likely to get back in calf as a two-year-old. If you do not know the mature weight of your cows, you should start by weighing a selection of cows that are in “good” condition (not too fat or skinny).

Feeding continues to be the number one priority during and after mating, getting heifers to target mating weights is only step one.

There is a misconception by some in the industry that heifers need to be held back to ensure the calf does not get too big. More often this creates problems through impact on heifer size – in particular, the size of her frame and pelvis.

The growing foetus is essentially a parasite, in times of nutritional stress it will continue to grow, while growth of the heifer itself stalls. This can result in proportionally large calves in comparison with the size of the heifer’s pelvis. Poorly grown heifers is one of the most common reasons for difficult calvings, followed by poor sire selection. I’m sure I speak for most vets when I say clients with the best-grown heifers seldom have calving difficulties.

In the lead up to calving, feeding remains important and too often I see heifers held back behind a wire with nothing to eat until they’ve calved. This has an impact on energy reserves needed for the heifer during labour and on milk/colostrum production which ultimately impacts the newborn calf. However, feeding in late pregnancy is a balancing act and too much feed can also have a negative impact.

Heifers should be fed at a level that avoids excessive growth or fat deposition during late pregnancy but ensures the requirements of the heifer are met. Subsequently, a targeted daily weight gain of 0.5kg/day is often talked about in the last 42 days of pregnancy. Once calved, heifers should be fed ad lib to maximise milk production and the subsequent mating performance as an R3.

Heifer mating can be a great way to boost farm income and the lifetime productivity of your breeding cows. However, done poorly it can result in negative outcomes and additional stress, along with reduced reproductive performance of R3s. Feeding and sire selection remain the top considerations for a successful outcome and artificial insemination is an option for those that can manage it. Do these things right and it could be you telling the success story next time you’re at the pub.

  • Andrew Cochrane is a vet with Northern Southland Vets, Riversdale.