18.0 FEED QUALITY
Feeds are complex materials; different foodstuffs have quite specific physical and chemical characteristics that affect the results of the animal nutrition process. Knowledge of the type of feed eaten by the animal is very important when calculating their rations and in determining how to best meet the amount of nutrients required for animal maintenance and production.
18.1 The physical characteristics of forage
The walls of plant cells are rich in fibre and they are broken down by the action of enzymes; these come from micro-organisms living in the rumen. After the wall is broken down substances inside the plant cells ( cell contents ) are released, they become accessible and are readily digested by the animals. As grasses and crop plants grow and mature, changes take place in the structure and content of their cells that affect their digestibility by animals. As the plant matures, weight proportions among leaf sheath stem show changes; these are slow at first but become more rapidly as the plant begins to set seed.
The maturation process brings about a general decline in the digestibility of each of these plant component parts. This is due to an increase in the cell wall of complex carbohydrates (fibre) that causes thickening and hardening of plant material. This is partly due to a non digestible component called lignin. As maturation takes place, the proportion of cell contents that are readily digestible parts of the plant, decline. In addition, as the plant matures the weight proportion of stem increases and that of leaf declines. For example: in Samoa this phenomenon Is very intense and clearly visible during dry season ( May June and July ) when fodder production levels from annual and perennial graminae in both natural pastures and improved grasses as Batiki Bluegrass (Ischaemum aristatum) tend to fall markedly as plants prepare to seed. At this stage low feed digestibility and intake levels are widely observed.
Legumes have higher digestibility than grasses and at a comparable age their plant structure shows different growth characteristics. They continue to produce vegetative, leafy growth without much change even during flowering. This difference between legumes and grasses Is very important in animal nutrition. A relatively small proportion of high quality legumes in a grass-legume mix pasture, can greatly increase the feed value, compared with grass alone. Likewise the provision of feed supplements to unbalanced rations containing low quality forages would boost rumen microbial activities and digestion; this would cause intake levels to be improved substantially. There is a wide range of foodstuffs options in Island Countries which are found in residues from cropping systems and in by-products from food processing results from food crops; these have a high potentially value as feed supplements. Common are:
copra meal, spent grain, cassava leaves and roots, rejected banana and banana pseudostems, rejected squash, molasses, fish waste, breadfruit, mill by-products.
When animals eat feed of relatively low energy value ( low digestible energy ), its passage through the digestive system of the animal is slow compared with feed that is easily digestible. The effect of this slow passage is to reduce the appetite of animal. The combined effects of reduced appetite, reduced feed intake and slow release of digestible energy, that results from feeding of poor quality feed, reduces weight gain, milk production and/or work output of the animal. Ruminants can eat a large amount of poor quality feed but it is of very limited value to them because they have to make a great effort and spend much energy in digesting such material. When good quality feed is in short supply, a good strategy is to give the better feed to animals categories which will gain the most benefit - i.e.: weaned calves, pregnant cows and lactating cows.
18.2. Chemical composition of foodstuffs
Foodstuffs are complex both in composition and structure. It is convenient to classify the various foodstuffs in groups having similar physical or chemical characteristics, The two main components of foodstuffs are: water and dry mailer.
Clean fresh water is required by all animals in addition to that obtained from the feed they eat. The water content of feeds varies greatly e.g. from 80 to 90% of the total weight of the fresh green grass, root leaves, banana pseudostems, bananas skin; 75 to 50% of the weight of <(semi-dry " breadfruit, root crops; rejected bananas; down to as low as 8% to 12% of " dry>) feed such as copra meal and dried root crops.
The drier the feed that is fed to livestock, the greater the amount of additional water required by the animal to maintain water content in its body. Shortage of water can severely reduce growth, milk production and work output. Because of the very variable content of water in different feeds one can normally refer to the feed intake by animals in terms of kilograms (kg) of dry matter (DM ). For example the water requirement of dairy cows varies from 5 to 8 litres per each kilogram of dry mailer eaten.
18.2.2: Dry Matter
This is made tip of (i) organic mailer and (ii) inorganic mailer. Inorganic mailer contains macro-elements namely minerals such as calcium, phosphorus, sodium and other trace elements. Organic mailer is made up of materials that are produced during the development process of the plant. The organic content is by far the most important element to meet the needs of livestock nutrition and in large grazing animals it represents almost its entire feed intake. Organic mailer is composed mainly by the following elements:
a. Carbohydrates and fats (lipids)
Dry mailer content in plants is made of tip to 70 - 80 % of carbohydrates. These substances
derive from the end product of photosynthesis, a plant process which combines energy from
sunlight, water and carbon dioxide (C02 ) to produce a simple sugar. Lipids [fats] are present
in plants but in much smaller quantities , about 5% to 10% of dry mailer. After digestion and
absorption both carbohydrates and fats are used by the body to provide the energy that is
necessary for all muscular activity (including digestion), to generate warmth and to fuel all vital body activities. Any surplus energy may be stored as surplus fat in fairly tissues or
elsewhere in the body. Ruminant feeds are often classified according to the quality of their
(i) Concentrate foodstuffs have a high content of rich-carbohydrate components u'~ the form of various sugars and starch which make up the greater part of cereal grains and root crops. They are readily and almost entirely digested in the rumen. However when large amounts of concentrates are included in a ration (up to 50% on dry mailer basis ) the rapidly fermentable qualities of rich carbohydrates will cause a significant drop in acidity levels of the rumen; this can depress growth of rumen microbes, and if this activity is reduced it results in decrease forage digestion and intake will drop. A practical consequence of this observation is that these feed supplements should not be fed in large quantities in just one daily feeding; it is best to feed it in fractionated rations each day or even better, by continuous mixing feed concentrates with the basic ration.
(ii) The chemical composition of cell walls of plants corresponds to complex carbohydrate substances mainly in the form of cellulose, hemicellulose and lignin The fibre of dry plant material is composed by these substances, they represent the main constituent of forage. Fibre contents in forage is highly dependant on the maturity stage of the specific plant. Fibre contents are digested much more slowly in the rumen than the carbohydrate types found in concentrates and they are therefore the most important factor that control the speed of the digestion process and that therefore determine intake levels of forage by the animal.
Protein content in foodstuffs is normally measured as a crude protein ". This protein level estimate is calculated by measuring the amount of nitrogen content and applying a factor of 6.25. The average nitrogen content of proteins is 16% therefore Total Crude Protein ( % CP.) = % N X 6.25. while not all protein types in plants are of equal value to different categories of animals, this estimate is in practice a useful indicator. During digestion protein is broken down into its component parts known as anuno- acids. These are then absorbed and used by the animal for building body tissue, milk production, and other vital body activities.
In most grasses and other green feeds only a part of the nitrogen provision comes from protein; the balance consists of inorganic nitrogen, salts, amino nitrogen, amides and other forms. This difference in origin does not affect, however, the digestive process of protein in ruminants because these animals can utilise inorganic nitrogen as well as protein nitrogen through the microbial activity in the rumen. Bacteria in the rumen thrive on the non-protein nitrogen and incorporate it in the production process of their own proteins. The protein content in the bodies of microbes is then digested in the intestinal tract of the ruminant and absorbed there; the same thing happens to the fraction of feed protein that has escaped microbial degradation in the rumen and has reached the intestine. Hence as ruminants can be assisted by hosted microbes to digest cheap sources of nitrogen and from it build protein, expensive true protein supplements are not essential to them and can be saved to feed non-ruminant categories of livestock. This ruminant feed strategy is particularly true at a low level of ruminant productivity.
In ruminant nutrition, fertiliser grade urea is the most frequently used supplement source of inorganic nitrogen. Urea contains 46% nitrogen, therefore each kilogram of urea is equivalent to 2875 g of crude protein ( 6.25 X 460 g Nitrogen = 2875 g Crude Protein ). This content should be compared to composition levels of other foodstuffs, which are indicated in Table 13; for instance each kg of dry mailer of: (i) young batiki bluegrass, at 8 weeks, contains 75 g CP.; copra meal contains 205 g CP. and Spent grain contains 260 g CP.
The crude protein content of foodstuffs varies according to the type of fodder and in growing plants, with the stage of maturity. Young growing grasses have CP. percentage content ranging from 8 - 16 %, while grass legume mixtures can reach up to 25 %. But mature grasses only have CP. levels of 3.5 - 8 %. As an example, during early dry season in Samoa (May, June and July) crude protein content in batiki bluegrass is dramatically decreased and ranges only between 3~9 and 5.3%. Molasses show low levels of CP., usually less than 2%; root crops (cassava, yams, potato, taro) and bananas by-products are less than 5% CP., Breadfruit and Cocoa Pods have 5 - 7% CP. Copra meal has 20.5% CP., Spent grain has 26.5% CP., while Cassava leaves have 23.5% CP. and poultry litter has 26.5% CP. Feed additives such as fish meal have 45 - 68% CP.
Growing and lactating animals require higher levels of protein in their diets Thus adding rich-protein supplements to the diet of animals grazing native and improved grasses under coconut plantation can improve substantially the nutritive value of these feeds.