By Roelof Bezuidenhout
Understanding how animals grow can help you feed your livestock more efficiently.
The growth curve – often illustrated by a flat S-curve – shows how an animal’s body changes over time. By growth we mean the increase in body size as the animal gets older, but it’s not just about size. As animals grow, the balance between muscle, fat and bone in their bodies also changes. And organs such as the brain and digestive tract each have their own growth curves. Knowing this helps you make better feeding decisions at every stage of development.
An animal’s growth can be divided into three basic phases: from conception to birth; from birth to weaning; and from weaning to old age and death. Different breeds grow at different rates, so they have slightly different growth curves. For example, indigenous breeds tend to grow more slowly and reach maturity later than European breeds.
All animals, however, go through a period of accelerated growth, followed by a phase of slower growth as they age and their bodies eventually start to break down faster than new tissue can form. In other words, they reach maturity and then begin to age.
Many livestock farmers wait too long to sell their young animals or to cull their older ones. Some keep lambs or calves longer because they believe the animals will gain more weight and sell for a better price. Others hold on to older ewes or cows because they don’t have enough young breeding animals, hoping the older ones will produce a few more offspring. These decisions can reduce the efficiency and profitability of the herd or flock.
Know when to sell
The key to efficient farming is to sell young animals just before they start gaining too much fat – this is when they turn feed into weight most effectively, giving you the best return. Older animals should be sold before their bodies start to break down or their teeth become too worn to graze properly. This is especially important in dry areas where grazing is poor.
Females that struggle to feed themselves will also struggle to produce enough milk, especially in the first month after giving birth, when milk is vital for the young. Once sheep and goats are past their prime, they not only produce less wool or hair, but they also become harder and more expensive to fatten for market. That’s why it’s best to sell them while they still have value.
Young animals grow slowly in the first few weeks, but if they get enough milk and feed, their weight increases quickly. Eventually, they reach a stage where they begin to store fat as well as build muscle. This is an important point for meat production because animals need much more feed to put on 1 kilogram of fat than they do to add 1 kilogram of lean muscle.
Keeping a young animal for too long is inefficient. It will eat feed that could be used more effectively by other animals in the flock or herd, and its carcass may sell for less per kilogram at the abattoir because the meat industry does not like over-fat carcasses.
Feeding at every stage
Understanding the growth curve will also help you plan feeding more accurately at every stage of your animals’ lives, from before they are born.
The rate at which an animal grows depends largely on its nutrition. A foetus usually grows fastest during the last part of pregnancy. This is the time to give ewes a little extra feed if grazing conditions are poor – especially young pregnant ewes, because they are still growing themselves. However, overfeeding can cause problems during birth.
It is also very important for a growing lamb to get enough milk and access to good grazing. If it does not receive proper nutrition during this critical time – when its growth rate is high – it may take a very long time to grow properly, or it might never reach its full potential.
Scientists use detailed growth curves to design feedlot rations, but there is still much we do not fully understand about how different feed ingredients affect growth. Still, any livestock farmer can benefit from understanding the basic principles of the S-shaped growth curve to manage their animals better.
Fortunately, there is something called compensatory growth. This means that if a young animal experiences poor growth due to a lack of food, it may catch up when good nutrition is restored. But this does not always happen – many animals never fully recover from early growth setbacks.
Also read:
• Smarter parasite control, healthier livestock
• Genetics and breeding technologies in livestock farming
•‘Deteriorating livestock disease monitoring puts farmers at risk’
 | Roelof Bezuidenhout is a fourth-generation wool, mohair, mutton and game farmer and freelance journalist. Attended Free State University, majoring in animal husbandry and pasture science. Other interests include agricultural extension and rural development. |
