GOAT NUTRITION; SIMILARITIES AND DIFFERENCES TO SHEEP NUTRITION

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1 Goat Notes GOAT NUTRITION; SIMILARITIES AND DIFFERENCES TO SHEEP NUTRITION Professor Ronald A Leng AO B.Sc., Ph.D., D.Rur.Sc., FASAP Goats come in all shapes and sizes from the smallest, which is the Black Bengal goat of Bangladesh and the African Dwarf goat that weigh 15 kg at maturity, to the largest Boer goats that push up to 100kg live weight. Irrespective of the size of the goat this animal is a part of the large family of herbivores, the ruminants, which have a fermentative digestion as the initial phase in the overall digestion of feed. They characteristically, chew and swallow their feed and regurgitate and re-chew the same feed: a process that is referred to as rumination. The numbers of goats in the world which is roughly 480 million, is about a third of that of sheep and it is therefore surprising that goat nutrition research has been some what neglected relative to research on sheep. It is however apparent that until recent times the goat has been the poor man s [more often the poor woman s] choice of animals in the developing countries largely because of their ability to thrive on a range of feeds that are not eaten by sheep and cattle or which are deleterious to sheep and cattle. The distinguishing feature of the goat is its well-developed defense against a wide range of potentially toxic compounds in their feed, particularly those that occur in some tree or shrub leaves. Goats have three major attributes that allow them to have should a wide selection of food. They include. The ability to secrete proteins in saliva that bind some toxic compounds found in tree leaves [e g tannins] and prevent adverse effects of these on the microbial digestive system The ability to support in the rumen, microbes that also detoxify a wide range of secondary plant compounds A more developed capacity of the goat liver relative to the liver of sheep to detoxify noxious plant metabolites converting them to soluble compounds that can be excreted through the bile or via the kidneys in urine. Nature, thus, determined that the goat had a broad spectrum of dietary options, from grasses and forbs in natural pastures to an enormous array of plants such as shrub and tree leaves and even prickly cacti such as prickly pair. The apparently better body condition of goats in mixed herds of cattle, sheep and goats grazing on the shrubby savannahs is generally attributable to this great capacity to select a range of feeds not consumed by the other ruminants and therefore they have available more and variable feed sources. In this way they often consume more forage and get a much better balanced feed then the accompanying cattle and sheep in a mixed grazing group. The goat has an enormous capacity to select a balanced diet if given the opportunity. It is an opportunistic feeder and will select the best available nutrient source and if that is a grass then the goat will often prefer to consume the grass as against browse. The goat, in many production systems, is often denied its range of dietary options or is at times limited to single grass pastures, for example perennial rye grass or mixed natural pastures and in developing countries it may have only crop residues such as straw as the major staple. These natural pastures and also straws are at times of low quality in that they are deficient in crude protein and/or minerals. Under these dietary conditions, to enable the goat to efficiently grow, reproduce or lactate or as in the case of the Angora, to produce wool, there is clearly a need to supplement the deficient diets to balance the diet both for the action

2 of the rumen organisms and for the animal s metabolic efficiency. Under conditions where the goat is deficient in crude protein the most appropriate supplement is urea to supply the ammonia required by microbes to grow. However, in the course of presentation of seminars on ruminant nutrition to audiences made up largely of goat breeders I have found a major and widespread misconception about goats and how they digest their feed. Most goat managers have the misconception that urea is toxic to goats and should not be used in any supplement. Even senior nutritionists give the same message. As they have a rumen, goats like all ruminants, effectively convert urea to ammonia in the rumen which is the major source of nitrogen required by the resident microbes to grow and convert forage to nutrients the animal can absorb and digest. The misconception has probably arisen because the goat is able to bite into sources of urea and consume excessive amounts which then are toxic. However when goats are gradually adjusted to sources of urea they will adjust their appetite and there are few dangers from feeding urea so long as the animal have continuous access to the source. To explain further requires some knowledge of the ruminant mode of digestion which is given below. A summary of Ruminant digestion The first priority in ruminant nutrition must always be to establish the efficient fermentative digestion of the feed the animal consumes. Fermentative digestion is a pre-requisite for animals where complex fibrous carbohydrates form the bulk of the diet. This is because no animals have developed intestinal enzymes that can degrade the sugar linkages in cellulose and therefore need microbes to initiate the formation of products that can be used in the animal to produce meat, milk and hair. The rumen of goats on balanced feeds which provides all the essential nutrients for optimum microbial growth will contain a mixed population of: Bacteria Fungi Protozoa Amongst these mixed populations are numerous strains of each group of microbes which work as a consortium to degrade the forage that the animal consumes. Forage is firstly mixed with saliva before being delivered into the fermentative sac [the rumen] of the ruminant. Soluble plant materials are often released into the fluid in the rumen and are directly absorbed and digested by bacteria and protozoa that swim freely in the rumen contents. Anaerobic [growing without oxygen] fungi are a relatively small proportion of the biomass of microbes present, but are the first organisms to produce seeds [zoospores produced from mushrooms or sporangia] that invade forage. Fungi grow a network of roots (termed radii) through the tissue that secrete enzymes along their length and cause the solid fibrous plants to shatter. Bacteria then have the large surface area on the finely broken-up fiber to attach to and begin the process of breaking down the carbohydrates to building blocks for their own synthesis and providing the energy that allows them to grow. The byproducts of this are the acids, [short chain volatile fatty acids] which supply the animal with its energy resources. Most of the bacteria (up to 70%) are on the plant fibers. But as the bacteria achieve their needs for energy the fiber particles decrease in size and some bacteria are released to attach again to new, bigger particles in the rumen or they are washed out of the rumen and provide the animal with protein to digest. The protozoa can also digest fiber or the more soluble plant components but science has shown that because they are unicellular animals, and have a primitive digestive tract, they largely take up particles from the rumen to degrade for their own energy supply. Although it has not been proven while grazing on particles in the rumen, protozoa graze both feed particles and bacteria and do not appear to discriminate between them. Where the feed particles are high in protein or the protozoa take in bacteria (which are high in protein) then both sources of protein are degraded with a loss of protein to the animal. To grow efficiently the rumen organisms need

3 a supply of fermentable substrate that they can convert to acids and with the energy released in this reaction divide and grow. a continuous high availability of ammonia in the rumen to supply the nitrogen for protein components of the cells. a balanced array of essential minerals. Whilst all minerals are needed, the ones that become most deficient in practice are phosphorous and sulphur. When an animal has a rumen microbial ecosystem that is functioning as an efficient fermentative system, the animal optimises its forage intake and maximises the digestion (fermentative) of the feed. The ratio of protein to energy in the nutrients absorbed is also maximised, and on most natural diets this means that the rate of growth of microbes in the rumen is at an optimal level. When this is achieved it leads to large quantities of microbial cells flowing to the lower digestive tract where they are digested by the enzymes secreted by the animal to produce the essential amino acids required by ruminants for growth, milk production and production of wool or hair. Microbial cell are by far the greatest source of these amino acids as most protein in the diet is actually degraded to ammonia. The protein nutrition of goats is optimized when the microbes have a well-balanced culture medium Efficient microbial growth is achieved when the forage fed or the forage fed with added supplements provides (in the rumen) all the minerals and ammonia constantly and at levels that meet the requirements for growth of microbes. The goat has the same requirement for ammonia as sheep and cattle and the ideal method of supplying that ammonia is as urea mixed with carriers and any potential deficient minerals so that they can be consumed in small meals spaced over the full day. Where the protein level of forage is in excess of about 15%crude protein, in general the ammonia levels in the rumen are optimal because of the degradation of the feed protein. Where the crude protein is low, as on many native pastures, where there as an absence of other feeds and crude protein levels are 3-6% then providing a source of urea will overcome the constraint of the low ammonia level in the rumen and the ability of the microbial ecosystem to convert the feed into nutrients the animal needs will not be compromised. Supplying urea to goats on a low protein diet Feeding a source of rumen ammonia is critical for goats on low protein feeds Ammonia in the rumen is the most likely primary deficient nutrient for efficient digestion and growth of microbes in the rumen of goats on low protein feeds On natural diets low in protein, ammonia in the rumen is often the primary limitation to production in the goat but the feed resources are variably deficient in minerals which often quickly become the limiting factor in terms of production as urea is supplemented. Deficiencies of essential microbial growth factors limit the growth of microbes as a goat moves from a green feed well balanced to a dry feed deficient in crude protein and /or minerals the following events occur: Initially as the deficiencies develop, microbial growth slows but, as in yeast fermentation the production of acids increases and we say that microbial growth is inefficient. As the level of protein in the available forage decreases further then the rate of microbial growth slows below the loss rate of microbes being washed out of the rumen and eventually the biomass of microbes falls to such an extent that digestibility of the forage is lowered When digestibility decreases there is a concomitant reduction in voluntary feed intake. The low protein relative to acids together with a reduced feed intake depresses productivity. The deficiency of crude protein has the same effect as a developing mineral deficiency and may at times be the primary constraint to microbial growth in the rumen of goats. However the goat is able to mobilize mineral reserves from sources such as bones [for P and S] and mineral deficiencies in a feed

4 have a long time lag before they create major depressions in rumen function unlike protein deficiency which is almost immediate. Mechanisms for supplying urea and minerals to goats There are numerous routes by which urea can be given to goats safely these include: Spraying a solution of urea onto the forage prior to feeding. About 1% urea in the dry matter is enough for most dry forages to be fortified with urea. Often the water also contains about 10% molasses as a source of minerals. Feeding out a powder mix of salt /urea/ minerals and allowing the goats to access it as and when they need. Powders or loose mixes as they are commonly referred to are a little dangerous but managed well can be effective, this means they are sheltered from rain and fed so that the urea does not gravitate to the bottom of the mix and the supply never runs out. Proprietary mixes are available that contain salt about 10% urea and a balance of other potentially deficient minerals. Liquid feeding is possible by mixing urea at about 10% with molasses which the goats soon learn to recognize as a source of nutrients. This is not a feasible approach because of the intensive labour costs but there are propriety mixes that are highly convenient to use if a little expensive. Possibly the most appropriate way is to use a block lick specifically made to suit goats. The block licks are more costly but their costs are out weighed by their convenience, low labour costs and relative safety of use. One leading manufacturer of block licks recommends the use of multiple licks with grazing animals in which the animals are believed to be able to take sufficient urea from a high urea [10%] block and blend it with the required minerals from a block high in sulphur [9%] or high in phosphorous [12%]. The three blocks are all endowed with a broad spectrum of other potential mineral deficiencies. This system that is called the Indicator system is very convenient as the blocks are put out year round and as deficiencies develop there is good evidence that all grazing ruminants can identify the appropriate block to consume as the seasons change and forage quality declines. The most recent research that indicates the ability of the animals to identify a source of the primary deficient nutrient in a food is that all ruminants will, under deficiency conditions, have a feeling of metabolic discomfort, which is manifest until the deficiency is remedied. Once they take the source usually through trial and error the metabolic discomfort is removed and the animal learns. The best known example of this is where animals become phosphorous deficient and will test [take into their mouth] many materials available on the pasture which might include stones, polythene pipe, wire until they come upon bones which are a source of the missing mineral. Of course this puts the animal at risk from Botulism and it is far better to provide a sterile source of the mineral. Is it worthwhile using supplements with grazing goats? Undoubtedly in a country where either there is a pronounced wet season or where the climate is unpredictable year round or where the soil has inherent low fertility, supplementation is profitable but often difficult to assess. Some years ago a coordinated programme of research with goats was initiated to examine the impact of supplementing goats under a wide range of conditions with a simply made block lick based on molasses containing 10% urea and fortified with sulphur and phosphorous [sponsored by the Joint Division of FAO and IAEA which are divisions of the United Nations Development Programme]. As part of this programme, in Indonesia with native goats grazing native pastures the results were quite outstanding and are shown in the Table below This is just an example of the benefits that can accrue. But it is important to emphasize that an efficient digestive tract is a primary requirement of goats to efficiently produce. Often the most economic benefit from urea/mineral supplements that correct deficiencies of nutrients for microbial growth in the rumen come from the benefits to reproductive efficiency.

5 Table 1. The benefits of supplying urea molasses blocks year round to breeding goats in Indonesia fed native pastures No Supplement offered Molasses urea multi-nutrient block available Kids Birth weight [kg] Live weight gain [g/day Dams Peak milk yield [l/day] Kidding interval [days] Gestation period [days]