We are all aware that to get the best lifelong potential from a heifer, you want it to calve at 24 months. However, the NMR national average figure for age at first calving is 28-29 months.
Studies have shown that a heifer calving at 23-24 months has the best survivability by giving more milk (over her entire lifetime and milk per day of life), easier calving, and having fewer problems later in life. Whereas heifers calving at over 30 months of age are twice as likely to be culled. There are also lower heifer rearing costs and fewer youngstock on the farm, which in turn reduces housing costs and disease susceptibility. AHDB has shown that the cost of rearing a heifer increases by £2.87 per day for every day increase in age at first calving over 24 months.
This means starting to serve heifers at 13 months old if we are to hit the 24 month target. And to hit this target we need calves to GROW. So, is measuring the growth rates of heifer calves really worth the time and effort? YES! By monitoring growth we can check that the early targets are being reached and the earlier we know there is a problem, the more chance we have of rectifying it.
What are the growth rate targets?
Heifers should be 65% of adult bodyweight at bulling and 90% of adult body weight when they calve. Weigh third and fourth lactation cows to find out what your normal adult body weight is.
To achieve this, we should be aiming for a growth rate of between 0.7-0.9kg/day. Good early growth is key so aim higher for the first 3 months and 0.7kg/day following on.
How and when to measure?
Ideally, we would want to monitor growth rates every 2 weeks from birth until 1-2 weeks post-weaning, then again at 6 months of age, and finally at breeding. It is very important that calves are monitored throughout the milk feeding stages as this is when growth is most efficient but can also be when setbacks occur.
The most accurate way to measure weights is by using electronic scales. When this isn’t an option, weigh tapes can be used. They are particularly useful in the early stages of life, even 6 to 9 months, and accuracy can be improved by having one person responsible for taking the measurements. As animals get older, the weigh tape measurements become less and less accurate therefore height can then be used as an alternative. This can be achieved by using a stick or marking target heights on a wall.
Potential growth rate setbacks
There are certain times and stages when growth setbacks can happen, so it is important to manage these stages well and keep stress levels low.
One of the biggest factors to affect a calf’s growth rate in the first two months of life is disease, especially scours and pneumonia. Pneumonia is one of the biggest causes of mortality in calves, but it has a huge impact on a calf’s entire life leading to reduced growth rates and poor performance.
It is therefore vital that calves get the best start to life and that starts by providing a high standard of colostrum management; giving calves the best opportunity to be protected against disease. Vaccination, housing and nutrition also play important roles in disease prevention and the health of calves. When all factors come together, we aren’t just preventing the growth setbacks but we are seeing a consistent progression in the growth rates of calves.
And don’t panic!
The good thing about understanding your targets and monitoring progress is you can always make changes along the way. It is easier to spot when problems are happening, often before any clinical disease is really noticed. And if you find at 9 months old they are significantly over or under weight there’s no need to panic, just readjusting your management, you can get them back on track.
Please contact your vet if you would like more advice on monitoring and achieving growth targets.
Written by Emily Ozols BVSc MRCVS