19.0 FEED UTILIZATION
The ruminant needs a daily supply of nutrients required for maintenance and production. Their diets must provide all components required in vital activities linked with growth, pregnancy, plus milk and meat production.
This is the energy required just to keep the animal alive for movement, production of body warmth, respiration and for the maintenance of body tissue without increasing or decreasing body weight. If the feed supply is insufficient for maintenance, the animal will begin to metabolise its stored body fat and in cases of severe feed shortage, its muscular tissue as well. This results liveweight loss. The amount of energy (feed ) required for maintenance depends on:
- Size: the larger the animal, the higher its maintenance requirement. This is an important consideration when thinking of using large crossbred cable, instead of local stock..
- Age: Young animals need proportionally more feed for maintenance and of better quality than older animals. This applies to animals of the same size.
- Climate: The energy required for body heating is higher in cool weather and daring the rainy season.
- Husbandry system: Penned or tethered animals are restricted in their movement and so use less energy. However they can only eat and depend on the feed brought to them, whereas free ranging animals can search for feed.
- Type of food: Feed with a high fibre content e.g. old mature grass, require more
energy to be broken down into its basic components in the rumen than better quality
feed such as fresh pasture or concentrates.
Growth can be defined as the increase in body size in a young animal; to achieve this energy is
required for the production of new body tissue, bone and muscle. The rate of growth is
important as it determines
(i) The age when the animal reaches suitable weight for sale for slaughter and
(ii) Body weight is important in determining the moment when an animal can commence
breeding. Younger animals should be given high quality feed, especially at weaning, to ensure a good rate of growth.
19.3 Milk Production
Calves suckling badly fed cows are usually unable to receive enough milk from their dams for normal growth. Milk production stops if feed supply becomes extremely poor. If calves are very young when this happens, they may die. If severe feed shortage occurs when the calves are older it is preferable to wean the calves and give them priority access to supplementary feed of good quality and feed the poor rations to the dry cows. when cows suckling calves are poorly fed they will often stop heat cycle activity, and will only return to breeding after the calf is weaned.
The quantity and quality of the feed ingested will influence the weight of the growing heifer. This determines when she will come on heat for the first time and prepare to commence breeding. inadequate feed when she is growing can delay successful breeding by up to one year. Nutrition also controls the presence of heat cycles after calving. Poor nutrition rules out mating for up to six months after she has calved and it can influence whether the mating is or is not fertile. Well fed cows should be able to mate with the bull about two months after they have calved and this mating has a good chance of being fertile. when feed is in short supply, reproduction is the first activity which is affected. Cows which are permanently undemourished will fail to reproduce.
Cows will usually lose some weight following calving as the nutrient demand to meet milk production increases, this mobilisation of resources is particularly important in high-producing cows, such as Friesian cows. Hence the cow must store body weight reserves before calving; Furthermore in the last weeks of pregnancy calf development shows rapid growth. Therefore during this period the feed requirements of the cow are greatly increased. She should have adequate high quality feed especially during the last two months of pregnancy to meet demands from the growing calf and to increase her own body weight.
19.6 Weight gain
Only when enough feed is available for maintenance and all other needs of an animal, can surplus energy be turned into weight gain. Weight gain is the increase in size of individual muscle fibres ( unlike growth which is increased in number of fibres ) caused by storage of surplus energy within them. Fat is also created as an energy store. Both tissues are used for energy by the animals when feed becomes in short supply. when this happens the animal loses weight. In other words it uses nutrients stored in its own tissues to substitute short supplies of feed.