Vegetable protein supplements in poultry diets
Dr.S.V. Rama Rao
The requirement of feed for the growing poultry industry is about 6.5 million tones per annum. The vegetable protein source constitutes around 30% of the total compounded poultry diet. The commonly used plant protein sources are the seed meals of groundnut, soyabean, sesame, sunflower, mustard etc. The amino acid composition of majority of the oil seed meals is deficient in one or more critical amino acids like methionine, lysine etc. It is because of this that a single oil seed meal cannot be used as a sole source of protein in chicken ration. So combination of two or more oil seed meals are required to complement the deficient amino acid (S) in a single source and to meet the required amino acids balance for a specific type of chicken. Another limiting factor for free use of oil seed meals is the presence of anti-nutritional factors. Nevertheless, several attempts have been made to detoxify the oil seed meals for effective usage of the same in practical rations. Some of the commonly used oil seed meals in poultry are discussed briefly in this article.
Deoiled groundnut meal
Groundnut (Archis hypogaea) meal has been a major source of vegetable protein in poultry diets in our country. However, it contains trypsin inhibitor that limits the use of raw groundnut meal. This trypsin inhibitor can be destroyed by mild heating. So, solvent extracted groundnut meals Is mostly used and it contains 43 to 48% crude protein. It is an excellent source of arginine but deficient in lysine, eystine and methionine. Supplementation of synthetic lysine to groundnut meal can make it an ideal protein source in poultry feeds. However, it has been seen that groundnut meal is susceptible to toxin like mycotoxins, mowarin etc. Groundnut seed coat contains tannins, a polyphensolic substance that lowers the quality of protein compared to soyabean meal.
Soyabean (Glycine max) meal is a good source of protein for poultry. It contains 45 to 52% protein. The amino acid profile of Soyabean meat is well balanced and is an excellent source of lysine but deficient in methionine. Soyabean meal forms an ideal protein to the poultry in combination with sesame meal which contains higher levels of methionine but deficient in lysine, Soyabean seeds have certain anti-nutritional factors like trypsin inhibitors, protein inhibitors, protease inhibitors, phytohemagglutinin, saponins, goitrogen and estrogenic factors that can affect the production performance of chickens. But they are all thermo labile and can be destroyed by roasting, heating or autoclaving. An adequate balance of amino acids by substituting methionine to Soyabean meal based diets can successfully replace even fish meal from poultry feeds.
Mustard /Rapeseed meal
Three varieties of mustard (Brassica Campestris) oil seed were tested in poultry feeds in our country. They were mustard royal, brown or yellow meal and toria. The chemical composition of mustard meal shows an average crude protein (35-37%) with higher lysine and methionine contents than groundnut meal but usage in poultry feed is limited due to presence of deleterious factors like isothiocyanates, 5 - vinyl -1 oxizolidine thione(VOT). Erucie acid, tannins, sinigrin, sinapin, high crude fiber (8-126) etc. VOT is a potential goitrogen which causes enlargement of thyroid gland, consequently reducing the performance of chickens. The process of solvent extraction after initial pressing of the seeds appeared to destroy the goitrogen and isothiocyanates and reduce the toxic effects of the cake. The tannins can be checked to some extent by addition of calcium hydroxide and sodium carbonate in dry form in diets.
Sesame (sesamum indicum) meal contains 40% protein and 8% crude protein fiber. The protein is rich in arginine, leucine and methionine but low in lysine. Since the sesame meal is deficient in lysine its combination with Soyabean meal appears to be useful. Sesame meal has high calcium and phosphorus content but their availability is low because of higher phytate content in the hulls of the seed. The phytic acid reduces the availability of calcium, zinc, magnesium, copper etc. from the diet. Nevertheless, the meal can be included in poultry diets up to 15% in combination with other lysine rich oil cakes.
The sunflower (helianthus sp) meal contains 30 to 40% protein with variable levels or crude fiber depending upon the level of dehulling and the method of oil extraction of the seed. The net protein utilization of sunflower meal is higher than groundnut cake, probably due to higher methionine and cystine content. Sunflower meal is generally not recommended be yond 20% in the diets may be due to high crude fiber content in the meal and also due to the presence of a polyphenolic compound called chlorogenic acid which inhibits the activity hydrolytic enzymes. To overcome this problem, supplementation of additional methionine and choline in the diet is suggested.
Cotton seed meal
In India for every 100 kg of cotton (Gossypium sp.) fiber produce there is an availability of 160 kg of cotton seed. Oil extracted cotton seed meal contains around 25 to 40% crude protein by quality of cotton seed meal is poor due to the presence of gossypol, phenol like compounds that are present in the pigment gland of cotton seed. Gossypol inhibits the activity of digestive enzymes and reduces the palatability of diet. Mechanical pressing of seed followed by solvent extraction reduce the gossypol content to 0.02-0.5% level. Dietary levels of gossypol up to 0.015% levels are believed to be safer in poultry. Detoxification cotton seed meal with solvent mixture containing hexane, acetone and water were found to be useful after initial cooking of the meal. Addition of ferrous Sulphate at the rate of 4 parts to one part of gossypol prevented yolk discoloration of the eggs due to gossypol. Cotton seed has a desirable profile of amino acids except lysine and the digestibility of cotton seed meal is poor due to higher crude fiber.
Neem seed meal
Neem (Azadirachlaindica) seed meal varies in its protein content from 20 to 32% depending on the hull portion left in the meal. Neem seed meal as such is not recommended even at 2.5% leveling the poultry feed due to the presence of the oil bound toxic factors called azadirachtin, salanin which imparts bitter taste to the cake and have growth depressing effects on chicks. Hexane extraction of oil from the meal greatly reduces the toxic factors called azadirachtin, salanin which imparts bitter taste to the cake and have growth depressing effects on chicks,. Hexane extraction of oil from the meal greatly reduces the toxic factors. Complete extraction of oil using a solvent and saponification of the same with potassium hydroxide was found to minimize the toxic principles in the meal. Urea ammoniated or alkali treated neem seed meal can be in poultry diet up to 10 to 15%.
Caster seed meal
The protein content of caster (Ricinus communis) seed meal varies from 21 to 48% depending upon the extent of decertification and oil extraction. It has an ideal amino acid profile with moderately high cystine, methionine and isoleucine. But its antinutritional substances called the ricin, ricinine and an allergen restricts its use in poultry even at low levels of inclusion. Processing of caster meal by heating at 80 c temperature in the presence of GN ammonia or an acid or alkali reduces the toxic content substantially. Detoxified meal needs to be effectively corrected for lysine.
In poultry feed industry other seed meals such as safflower, nigger, coconut, rubber and ambadi have also been tried but with limited success.
A deoiled oil seed meal have great promise in poultry feed industry but is essential that they are relatively free from mycotoxins and intrinsic toxic factors and also should be low in fiber content. Research on improving qualitative attributes of oil seeds may be of immense value to livestock feed industry, particularly when the^ availability of animal protein sources like fish and meat meals have become scarce and economically unviable. Keeping in view the significance oil cakes in poultry feeds it may be desirable to undertake research towards:
• Evolution of suitable bio-technological approaches to counteract the intrinsic toxic principles present in oil seed meals.
• Utilization of suitable breeding technique for minimizing or to eliminate the intrinsic toxic principles like gossypol, tannins cruces acid, saponins, allergens ridns, etc.
• To develop strategies for improving the protein quality of seed meals in terms of critical amino acids like lysine, methionine and cystine.• To develop suitable technology for extraction of fat bound toxins from the seeds without affecting the protein quality of protein composition of oil cakes.