What's the main aim?
The aim is very simple. We have to provide a diet for the animal that will meet all its nutritional needs. From that diet, the animal must extract all the nutrients available from digestion. What is not digested is voided as waste products in dung and urine.
So why does feeding appear complicated?
There are usually three reasons:
- The main feed available in New Zealand ie "Pasture", varies greatly in quantity and quality over the season. Think of the changes that occur in a pasture plant from the juicy spring flush, to the mature plant long past the flowering stage.
- We have a very limited range of supplements to feed stock in NZ because of the high costs in relation to the low world prices we receive. Our supplements are restricted to conserved pasture and some crops. We don't feed large amounts of grain to cattle as happens in Europe and USA.
- The needs of the animal we're feeding are always changing - eg. as pregnancy advances, lactation progresses, or as a young animal grows.
Maintenance & Production
The first concept to understand is that of "Maintenance" and "Production". These two things are what the animal does with the nutrients it eats.
This is the number of nutrients needed to maintain the animal - to allow for healthy functioning of all the body systems - such things as maintaining temperature, movement, the digestive process, blood flow, action of the glands, and excretion. Nutrients are needed to drive all these systems and this is called "maintenance".
The needs for maintenance are worked out using the animal's liveweight. So generally for a dry cow in mid-pregnancy, we calculate that maintenance needs in terms of Dry Matter work out at about 1.2 to 1.3 % of liveweight. A maintenance ration will result in a nil liveweight gain.
So knowing the accurate liveweight of animals is now of increasing importance if we want to feed them correctly. More and more farmers will have scales in the future.
These are nutrients needed over and above maintenance. Examples are milk production, growth, maintaining a foetus in pregnancy, and extra nutrients needed for work such as a long walk to the dairy. In other species, there are the needs for wool growth, antler velvet, eggs, and speed on the racetrack.
So as the cow advances in pregnancy, and we start to have to consider the needs of a calf growing inside her, we increase the percentage of liveweight to 1.5% or 1.6%.
The heifer has the greatest challenge - she is still growing and at the same time is producing so her feeding needs special care.