Maintenance Requirements |
For an animal to survive, it needs a certain amount of feed. This feed needs to provide it with the water, energy, protein, vitamins and minerals that are needed to keep the life processes (heart beating, liver functioning, etc.) going. The amount of feed needed to meet these "maintenance" requirements depend, obviously, on the quality of the feed (less high quality feed needs to be eaten to provide the same amount of nutrients as a large amount of poor quality feed). However, the amount of nutrients needed to maintain the animal depends mostly on its size. A large animal clearly needs more feed to keep it alive than does a small animal. However, an animal that weighs twice as much as another does not need twice the nutrients.
Energy Requirements
The relationship between animal liveweight and its energy requirement for maintenance is shown in the figure below. This is the amount of energy needed to maintain the animal when it is fasting, and when it does not need to expend extra energy to overcome challenges from the environment. If it is too hot (or too cold), then the animal will need to use more energy to lose or conserve heat. The very act of eating and digesting feed will also require some additional energy. Fighting off disease will also cost energy (and protein). These are also AVERAGE figures- some species use more or less energy than this (cattle use slightly more, sheep slightly less). There are also likely to be differences between breeds in the amount of energy they actually need for maintenance (and other functions). There are certainly differences between animals of different ages, with younger animals having a higher metabolic rate (and therefore higher maintenance energy requirement for their size) than an adult animal.
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Energy used for
fasting metabolism
for adult animals of
different liveweights
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The amount of energy that an animal will actually need will depend on its productive state (do you want it to grow, produce milk, produce eggs or young, or simply survive?) It also depends on the environment (as mentioned above, it costs energy to keep the animal warm in a cool environment, or cool in a hot environment). Preventing the development of disease also requires energy (see box).
The amount of energy an animal will need, just to maintain itself, will also be greater if it is active. Sheep and goats that are taken out to browse or graze for long periods of the day, and that have to travel a considerable distance to find grazing or browsing, will have much higher energy requirements than animals that are kept tethered and have their feed cut and brought to them. For goats, this can increase their energy requirements by about 40%.
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Energy cost of fighting disease
The wet season is often a time of great challenge for livestock, as the incidence of disease tends to be much greater at this time. This is because all disease-causing organisms thrive in the warm wet conditions of the monsoon. Goats in Nepal (see LPP project R7632) were supplemented with 100 g/d ground maize in the wet season. They were three times less likely to develop any kind of disease than goats that were not supplemented in this way
(see figure below). |
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Protein Requirements
As with energy, the animal needs a certain amount of protein just to maintain itself. Animals are not able to store protein, and so continually need to be supplied with protein because animals are constantly breaking down their body’s proteins and then building them back up again. As this process is never completely efficient, there is always some protein that is being excreted (as ammonia in the urine or as uric acid in the droppings of birds), and this must be replaced if the animal is not to lose weight. Again, combating disease may also require more protein. For example, sheep supplemented with protein develop more resistance to internal parasites (worms) than do sheep that are not fed as much protein.
Meeting an animal’s requirements for maintenance
In the end, feeding animals is as much an art as a science, and requires skilled care by the livestock keeper. If the animals are losing weight and succumbing to disease, then they clearly need more feed. It is likely that it is energy that will be limiting. If the supplementation of the diet with energy (e.g. from cereal grains) overcomes the problem, that is good. If not, some other strategy must be considered, which may be to consider whether it is protein (supplied by leguminous forages or from oilseed residues) or vitamins and minerals that may be limiting. If none of these strategies work, then there may be some underlying disease, which cannot be corrected by better feeding, that is affecting the livestock and that will need to be treated before the livestock will be able to thrive.
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| Requirements for Growth and Production |
When livestock are not just surviving, but growing or producing milk or rearing young, they need extra feed to meet these increased requirements. There is a limit to the amount they can produce, which is determined by their breeding, but it is unusual for any animal to be limited by its breeding and much more usual that its feed supply is limiting its production. Feeding them more will therefore make them produce more, but eventually each increase in feed results in a smaller increase in animal production. Again, in the tropics, it is unusual for livestock to reach this stage and the more usual scenario is that the livestock keeper has to decide when they can afford to concentrate feed resources on particular animals so as to optimize their response in increased production.
Lactation
Lactation is the time of greatest feed requirement for the animal. Increasing the quantity and quality of feed offered to lactating females will improve the health, survivability and growth of the young, as well as reducing the time before the lactating animal conceives again. If the milk is being sold, then the amount of saleable milk that is produced will be increased by improving the animal’s diet. Energy is nearly always the first limiting nutrient preventing further increases in milk yield, but the requirement for protein increases substantially during lactation as well.
Growth
An animal obviously needs more feed when it is growing, and again it is usually energy that is limiting but extra protein is needed as well. If the animal is overfed then it will lay down fat rather than lean meat, but this may be wanted if the market is for fat animals. Giving the animal extra feed for a month or two before it is sold may help to increase the sale price, but the cost of that extra feed has to be compared with the increased sale price to decide whether it is worth the investment.
Egg Production
The composition of the diet does not need to change for laying hens, but when a hen is in full lay she will need to eat more feed to meet her increased requirements for energy and protein. She will also need more calcium because of the high requirement for this mineral in making the eggshell.
Manure
Manure production is an important component of the livestock system when livestock keepers either have land that they farm, or there is a market for the manure. Feeding more fibrous feeds will increase manure production, but the manure will also be more fibrous. Feeding more protein usually increases the water content of the manure, (and certainly increases the nitrogen content). However, unless there is plenty of lush vegetation available, this is an expensive option.
Fibre
Fibre production does not add much to the energy requirements of the animal, but does increase its requirement for particular amino acids in proteins. These are the sulphur amino acids (called methionine and cysteine), and they are found in animal proteins and also soya bean meal and mustard cake. It is important these feeds are cooked before feeding them to livestock as they contain a number of anti-nutritive factors, most of which are destroyed by heating.
Rearing Young
The greatest cost of rearing young for goats, sheep and pigs is the slightly increased feed requirements for pregnancy and the much increased requirements in lactation. The cost to brooding hens is not as great. The composition of their diet does not need to change, and compared with laying hens their feed intake can be reduced.
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| Requirements for Breeding |
Healthy, well-fed livestock are much more likely to breed successfully than those that are weakened by disease and/or poor nutrition. If the animal has to use its feed to fight off disease, it is not able to use that feed to produce healthy young. The housing and the conditions under which the animal is kept therefore need to be as clean as possible. Energy is also used to keep the animal at a comfortable temperature, and so if at all possible, the animal should be protected from very high or low temperatures, and great changes in temperature. This will often not be possible, and so the animal needs to be provided with enough feed to cope with these environmental challenges, as well as sufficient feed to enable it to breed successfully.
Females
Females that give birth to live young (sheep, goats, pigs and rabbits) have a much greater feed requirement for breeding than males. However, there are times when they can be fed a poorer diet without encountering too many problems.
Mating
It is well established that breeding females produce more eggs (and therefore more young) if they are well fed at the time of mating. Ideally, they should also be on a "rising plane of nutrition", which means each day they are fed slightly more than they were fed the day before. This practice, known as "flushing" encourages the development of more eggs. However, if they are too fat, then this reduces their fertility as well, so it is important to try and get them to be fed just the right amount that, at the time of mating, they have a condition score of about 3 (see section on condition scoring).
If a pregnant female becomes sick or if her diet is cut dramatically soon after she conceives she is very likely to lose her young. It is therefore important that she is kept as healthy and well fed as possible for the first third of her pregnancy to reduce the risk of her losing her young.
Mid pregnancy
If the pregnancy is divided into thirds, then in the second third the foetus is much less vulnerable. Provided the mother does not suffer a major disease, or becomes extremely malnourished, it is likely that the foetus will survive. The amount of feed given to pregnant animals in mid pregnancy can therefore be reduced a bit to conserve feed resources for a time of greater need.
Late pregnancy
In the last third of pregnancy, the foetus begins to grow extremely quickly. It also occupies much more space in the mother’s abdomen so that there is less space for her gut. There is therefore insufficient space for her to eat large amounts of bulky, fibrous feed to meet her increased requirements, and the only way that her requirements can be met is to feed more concentrated (higher quality) feed. Disease or malnourishment at this time can also lead to abortion. However, some care must be taken when increasing the amount of concentrated feed offered, particularly to sheep and goats. If too much feed is fed, then the foetus will grow very large and the likelihood of problems at kidding or lambing will increase.
Lactation
Lactation is the time when the animal’s feed requirements are at their highest. Underfeeding her at this time will reduce her milk yield (which will affect the growth and survivability of her young as well), and it will also be more difficult to get her pregnant again. Does, ewes and sows are much less likely to conceive if they are losing weight, and weight loss is very common in early lactation. Now is the time when she should be fed extra, good quality feed if at all possible, and this should continue for the first two months of lactation. If supplementary feed is available, it is much better to feed a small amount each day rather than a larger amount every few days (this applies to all feeding situations, but is particularly true in early lactation). However, particularly with sheep and goats, any new feed should be introduced slowly (a small increase each day) to give her time to adapt to the new feed.
Dry period
In late lactation and once the young have been weaned, the amount of feed offered can be reduced again (depending, of course, on what stage of pregnancy she is in).
Males
The amount of energy and protein needed to produce sperm is extremely small and so extra feed is not required for this. However, adult male animals have much higher metabolic rates than adult females and so need more feed just for maintenance than a dry, non-pregnant adult female does. Keeping adult males for breeding is expensive in terms of the resources needed, and they are usually the most aggressive members of the flock or herd and so require more skilled management. Since breeding males are usually in short supply, they need to work much harder and will require more feed to meet their increased requirements.
When they come on heat, females need to be served quickly to maximize the chances of conception. Walking a long way to a breeding male (and then having to walk all the way back again) will reduce her chances of conception. Although keeping breeding bucks, rams or boars is expensive, it may be worth trying to form a farmers’ group in the village with the aim of keeping breeding males so that does, ewes and sows do not have too far to go when they are on heat. Breeding males need to be changed regularly to reduce the risks of inbreeding.
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| Requirements for Working Animals |
An animal that does not need to go out and forage for its feed uses up much less energy than one that has to walk long distances in search of feed or water. Animals that do need to walk long distances increase their feed requirements by as much as 40%. If they are being used as pack animals, then the need for more feed is increased even more. It may well be that their increased requirements for energy and protein are so great that they cannot get all of their nutrient requirements from forages and fibrous feeds because they cannot eat enough of these feeds (especially if for part of the day they are occupied by work and therefore unable to feed). The appetite limits of the animal may mean that the diet needs to be supplemented with more concentrated sources of energy and protein so that the animal is able to eat sufficient energy and protein (as well as vitamins, minerals and water). Panday and Tiwari (2002) describe the importance of pack animals (including sheep) in mountain regions of Nepal.
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| Requirements for Vitamins and Minerals |
In addition to energy, protein and water, animals also need a range of vitamins and minerals to keep them healthy. Many of the vitamins (particularly copper, zinc and iron) also help them to fight off disease and so supplementation with these minerals may help combat disease. However, all vitamins and minerals are present in only very small amounts in feeds, and it is usually very difficult or impossible to know exactly how much of any particular mineral an animal is consuming. Many of the minerals also interact with each other, so that for example over-feeding an animal with iron or molybdenum can cause the animal to become deficient in copper.
If possible, the best way of ensuring an adequate and balanced intake of vitamins and minerals is to provide the animal with a commercially prepared vitamin/mineral mixture. Such a mixture, though, should be formulated for that species of animal, as requirements between different species vary considerably, as do the tolerances for different minerals. A mineral mixture prepared for a pig, for example, could kill a sheep by copper poisoning.
It is also worth remembering that while feeding sufficient vitamins and minerals is good, feeding them to excess can be extremely harmful. Although with many minerals there is a wide margin between a required dose and a toxic dose, with some minerals (for example copper in sheep and selenium in all species) the margin is quite small. There is therefore the risk of poisoning animals with minerals (and to a lesser extent vitamins) if excessive amounts of vitamins and minerals are fed. Such a practice is also extremely expensive and wasteful. If using commercial mixtures, therefore, make sure that the manufacturer’s recommended intakes are not exceeded by any individual animal (by, for example, inadequate mixing of the mineral mixture in a feed that is then offered to a group of animals).
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| References and Further Reading |
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Panday, S.B. and Tiwari, M.R. (2002). Ruminant Livestock Production and Their Role in Sustainable Development in Mountain Regions of Nepal. In: Wangdi, K., Roder, W. and Gyaltsen, T. (Eds). Sustainable Mountain Development – Agro-Pastoral Systems And Fodder Crops in The Himalayan Region. Proceedings of the Fifth Meeting of the Temperate Asia Pasture and Fodder Network (TAPAFON), held at Renewable Natural Resources Research Centre, Bajo, Wangdue, Bhutan, 29 April to 4 May 2002.
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