Adequate nutrition is a major tool in achieving maximum flock health. To a large extent this is related to protein, fat, fibre, vitamins and minerals in diets. The use of some natural herbs also increases the health status of a flock.
By Dr. Salah H. Esmail, Cairo, Egypt
In the poultry industry, there is a tremendous amount of money spent each year for buying medicines and other synthetic preparations to control diseases. It is estimated that about 800 million dollars is spent each year world-wide to only control coccidiosis. This amount should inevitably increase to several billions of dollars, considering the multiplicity of diseases which affect birds at different stages of growth and production.
Despite this, it was found that the use of medicines alone is not an effective means of duly controlling the diseases. Mortality may in many cases exceed 10%, which adds to the losses arising from the cost of medicines, and hence affects the economic returns from the production process.
Recent research studies have, therefore given a prime consideration to the therapeutic nutrition programmes as an alternative or additional means of disease control. They all emphasised the need for utilising the available feed nutrients, and for manipulating them qualitatively and quantitatively to better suit the control of a prevailing disease in a given area of the world, thereby minimising the use of medicines down to the desired economic level.
With most disease outbreaks it may be necessary to increase the level of dietary protein, or at least maintain it within the recommended ranges. Protein is a potent regulator of circulation of hormones such as insulin, glucagon, thyroxine, and growth hormones, all of which affect the immune system and hence improve its disease fighting capability. In other cases, however, the supply of protein should be decreased. This is particularly useful under some disease conditions such as coccidiosis.
If in this case the level of the dietary protein is maintained high, there will be an increased activity of the enzyme trypsin in the small intestine of the bird. This will, in turn, lead to faster release of coccidia from their oocytes, which eventually become so active as to be less responsive to vaccination. The feeding regimen can also affect the severity of coccidiosis. Workers have observed that starving chickens prior to oral vaccination will reduce infection, probably due to lower excystation resulting from the lowered trypsin level induced by starvation.
Adjustment of the protein level up or down, or selection of the protein-feeding regimen at times of vaccination may not always be an adequate means of disease prevention. In fact, some protein sources such as raw soybean, cottonseed meal, and flax cake contain varying amounts of anti-nutritional factors such as trypsin inhibitors, gossypol, and glucosides, respectively. When ingested by the bird, these factors would then exert some damaging effects on the small intestine, thereby impairing the immune apparatus at this particular site which exert not only local but also systemic protective functions. Excessive use of such protein sources in the ration should, therefore, be avoided.
Dietary fat affects immune-competence either by altering the cell membrane structure or by modulating the synthesis of prostaglandins, which play an important regulatory part in many biological processes including the immune response. In one study, the resistance of chickens to disease agents such as E. coli and Mycobacterium tuberculosis were linearly enhanced as the level of lard or safflower oil was increased from 3% to 9%. Mortality associated with such diseases was also reduced with elevated levels of fat in the ration.
Under certain disease conditions, such as coccidiosis, it will be necessary to consider the type of fatty acids to be incorporated into the diet. Coccidiosis most likely impairs micelle formation. Fat with a high content of short- and medium- chain triglycerides may not be taken up into the micelles. The digestion of this fat will be less impaired by the infection than fat with a high content of unsaturated fatty acids, since they are easier incorporated into micelles. Such changes in the manner of fat digestion will, in turn, determine the extent to which weight gain and other fat-related production parameters will be affected by the disease.
The addition of more dietary fats should be considered during hot periods, particularly for broiler chickens, so that the daily energy intake can match the requirements for growth. It is a common practice on tropical farms to exclude fat from the diet during summer and include it during winter, because it is thought that the energy requirement of broilers is less in summer than in winter.
Recent studies, however, have shown that including fat in diets of heat-stressed broilers actually improves feed intake and performance. The heat increment of fat is lower than that of the other energy sources such as carbohydrates and proteins and, therefore, the heat load on the bird during summer will be less with high-fat diets. Also, there will be in this case larger amounts of fat-soluble vitamins ingested by the bird, which help improve resistance to common diseases prevailing in summer.
Experiments have shown that dietary fibre reduces the number of goblet cells present on the villous epithelia. This is a beneficial aspect because the reduced goblet cell number should entail reduction in the amount of goblet mucin. If produced in large amounts, mucin will then act as a luminal barrier preventing some feed nutrients from passing through the intestinal wall. Dilution of diet with fibres was also found to influence micro-organisms in the caeca of the bird. This should provide additional carbohydrate and protein metabolism, and also overcome fermentation problems associated with the small size of the caecum.
In long-term feeding of rations having moderate levels of fibre, there might be an improved utilisation of minerals. This effect, however, might vary with the source of fibre used. For example, it was found that retention of sodium and potassium was increased by oats hulls, but not affected by fibre sources such as alfalfa meal or soybean hulls. On the other hand, retention of copper was found to increase with soybean hulls but not with the other two sources of fibre. The three fibre sources equally increased retention of iron, suggesting that the iron contained in either source has a high relative bioavailability. Selection of the fibre source to be incorporated in the ration could, therefore, be an effective means of satisfying requirements for a specific mineral and correcting deficiency.
Cannibalism and nutrition
It was also found that cannibalism is more troublesome than usual during years when high-fibre feeds such as oats are eliminated from the ration because of scarcity of supplies. Insufficient fibre in the ration appears to be one of a number of causes of cannibalism. Oats are, therefore, so important in poultry rations that it would usually pay producers to buy oats even at what appear to be high prices.
A study was conducted to compare incidence of cannibalism with rations containing 80% yellow corn, and with 8%, 13%, and 18% fibre rations produced by substituting oat mill feed for corn in the aforementioned ration. The percent body parts pecked, the severity of pecking as determined by the scoring system, and the cannibalism mortality are given in Table 1. The relationship of fibre content of the ration and the prevention of cannibalism is not fully understood. Conceivably, it may be related to the increased consumption of feed and the time occupied in eating, or to the increased utilisation of sodium and potassium with high-fibre diets, as indicated earlier.
Minerals and vitamins
Birds should receive more vitamin E if infected with E. coli. In a study with day-old broiler chickens, there was a linear increase in the production of the antibodies specific to the E. coli infection at 2 weeks of age when the level of vitamin E in the diet was increased from 150 IU/kg to 300 IU/kg (IU = International Units). Similar responses were noted with parent stocks fed either 300 IU or 450 IU vitamin E in the diet. At the higher level of the vitamin, there was an increased level of immunity against bacterial infection such as B. abortus in the offspring at 7 days of age.
Also, there is a linear relationship between dietary vitamin A and diseases associated with M. tuberculosis bacteria. Increasing the level of this vitamin from 2200 to 4400 IU/kg resulted in increased serum immunoglobulin specific to this infection and reduced mortality. In a study with vitamin C, it was found that the vitamin has a strong action against S. gallinarum when fed at a high level (1000 ppm) daily for 3 weeks. Similar responses were noted with iron when increased in the diet from 250 to 450 ppm, and mortality was reduced here by 9%.
Uses of herbs
A number of medical herbs and their extracts have been used in the poultry industry in place of chemical medicines which often accumulate in the bird’s tissues and adversely affect the quality of the resulting meat and eggs. Among these is the black cumin (Nigella sativa), which contains 18-24% thymoquinone, based on the total amount of the volatile fraction thereof. The thymoquinone compounds have anti-bacterial, anti-fungal, and anti-parasitic effects, in addition to their effects as anti-cancer agents. It was also found that the black cumin contains about 30% protein with a digestibility value of about 75%. This protein contains most of the essential amino acids, and has a biological value of 1.6 compared to a value of 1.2 for most grains commonly used in poultry feeding.
In one feeding experiment, the incorporation of 2% black cumin into laying diets resulted in improved egg production, high fertility of males, and greater hatchability values. This was attributed to the stimulatory effect of the black cumin on the thyroid gland, and to its inhibitory effect on the bacterial infection which, in turn, improves the general health and production of the bird.
Less bacterial agents
When incorporated into diets of broiler chickens at 2%, the black cumin had inhibitory effects against Newcastle and IBD diseases. It has also promoted growth of the chickens due to its effects on secretion of the bile juices and hence on fat digestion and utilisation. Upon the post-mortem examination of carcasses of birds fed diets with black cumin, fewer bacterial agents such as E. coli, Salmonella, Streptococcus, and Staphylococcushave been detected, suggesting the role of black cumin on production of clean and edible carcasses.
Garlic powder (Allium sativum) is also a natural product that has successfully been used in feeding poultry. It helps overcome the problems of the formation of varying amounts of undesirable cholesterol resulting from the greater amount of saturated fatty acids relative to the unsaturated ones in each molecule of fat formed in the chick’s body. It was found that the incorporation of 3-5% garlic powder into the diet resulted in increased activity of the enzymes that convert cholesterol into bile acids, eventually being catabolised in the body, so a negligible amount is disposed in the carcass.
Other herbal plants that might be used in poultry feeding include the spiny acanthus (Acanthus spinosus), ginger (Zingiber officinale), and the Indian curcuma (Curcuma longa). Studies have shown that such species of plants act as natural antibiotics against coccidiosis and other microbial diseases. They could, therefore, be used in place of the synthetic antibiotics which in many cases reduce body vitamin B and vitamin K due to their effect on the gut micro-flora synthesizing the vitamins, in addition to their high costs relative to the natural plants, as indicated earlier.
Green tea leaves (Camellia sinensis) has also been used in the field of therapeutic nutrition, mainly because of the presence poly-phenol derivatives such as carnitine and catechin, which play an important role in fatty acid oxidation and in the production of ATP. The said derivatives also play an important role in the prophylaxis and/or treatment of neuropathic diseases, striate opacity, pancreatitis, fibroid tumors, etc. These effects, however, have so far been observed with laboratory animals only, and further work is needed to ascertain the potential role of the tea leaves in the therapeutic nutrition of poultry.