Juvenile broiler nutrition
The broiler industry in India is in a dynamic state, the chicken meat production has increased from 120 thousand metric tons in 1981 (FAO) to 1440 thousand metric tons in 2003 (Watt executive guide, 2004). The rate of growth in the recent past is unimaginable, from 20 th position in world chicken meat production ranking in the year 2000, India has reached the 5 th position in 2003 (Watt executive guide, 2004). The present day broiler is like a machine growing from a 45 to 50 gm body weight on day one to 2 kg body weight in 40 days time, which is nearly 40 times its initial body weight. The magnitude of the growth indicates that every day in the life of a broiler is very important to achieve the target. To plan the nutrition of juvenile broiler lets try to understand the happenings during the first seven days in the life of a broiler.
The yolk and its importance
The chick during incubation is totally on fat and protein diet with fat as the major source of energy. The common impression is that the hatchling is supposed to depend on the yolk for the energy and protein need till it is housed and fed, which may take 24 or 36h. Considering the fact that the yolk contains 50% dry matter with protein and fat in equal quantities the above statement is justified. Although the protein fraction is partly albumen, a large fraction of the egg protein in the hatchling consists of antibodies. Under normal circumstances, maternal antibody is not digested during the incubation process, leaving these immunoglobulins intact and fully functional at the time of hatch, indicating that the protein in the yolk sac is to be used for the passive immunity of the chicks and not as a source of amino acids. Similarly, the residual yolk lipid should be used for growth and not as an energy source for maintenance as some fatty acids in the yolk lipid may influence the partitioning of nutrients and the pace of development of certain organs systems (Dibner et al, 1998).
Development of digestive organs
In the post hatched chicks intense changes occur in the intestines compared to other parts. The proportional weight of the intestine compared to the whole body mass steeply increase from 0.02% on day 1 to 0.08% on day 8 (Sklan, 2001). The pace of development of the intestines is in tune with the concept that supply organs developing in advance of demand organs (Brake, 2001). At hatching the villi of the small intestine are undeveloped and the crypts in the intervillus spaces are not detectable. The crypts begin to form in the first few hours and become defined in 72h time, the process continues and the villi are well defined by 336h after hatch. The total villi surface area in the jejunum increases from about 50 cm 2 at hatch to about 550 cm 2 on the 10 th day (Sklan, 2001). The development of the intestine though is rapid during the first 72h it continues up to the 10 th day indicating that careful planning is needed in the formulation of the diet during the first week of the bird’s life.
Secretion in the Gut and Utilization of Nutrients
The duodenal bile acid secretion increased by more than two fold between 4 th and 7 th day and between 7 th and 10 th day, the pattern of fatty acid (phospholipids) secretion was also similar to the bile salt secretion. Similarly, the nitrogen (enzyme’s) secretion increased by 15 fold between 4 th and 21 st day, with the major increase observed between 4 th and the 10 th day (Noy and Sklan, 1995). The trypsin secretion was the highest at day 4, which was about 8 iu/gm of feed intake, it reduced to about 4 iu/gm of feed intake on day 7. The amylase secretion increased from about 17 IU on day 4 to about 20 IU on day seven and subsequently reduced to about 14 iu/ gm of feed consumed. The lipase secretion increased from about 1.4iu on day 4 to about 2iu on day 7 and subsequently reduced to about 1iu/gm of feed consumed on day 14 (Uni et al, 1995). The sucrase and maltase activity reached a peak on the 4 th day (Dautlick and Stritmatter, 1970). Viewing reports on the enzyme secretion it is understood that the enzymes are secreted in sufficient quantities, but the development of the gut even though faster compared to other organs may be the bottle neck in the utilization of the nutrients.
The rate of passage of the ingesta influences the utilization of the nutrients in the intestines. Slower rate of passage improves nutrient absorption by increased time of contact with absorptive cells and increased the digestibility of fiber by allowing more time for microbial fermentation (Washburn, 1991). The time taken for the passage of the contents in the duodenum and intestines were significantly higher on the 4 th day compared to that on the 7 th day. The time taken for the ingesta to pass through the intestine decreased from 161min on day 4 to 110min on day 14 (Noy and Sklan, 1995), even though the stay time of the gut contents are more in the first week compared to subsequent weeks, due to the incomplete development of the intestines the efficiency of absorption may not be as that of the subsequent weeks, hence enhancing the stay time will be more beneficial. Increase in the content of fiber in the diet has been observed to reduce the rate of passage of the intestinal contents (Horwitz and Bar, 1966).
The persistent question we get from the farmers and feed manufacturers is about the digestibility of fat during the 1 st week of the broilers life as the opinion created is that the secretion of lipase is insufficient and hence supplementation of lipase will be needed if addition of fat is to be done in the feed. But, Noy and Sklan, (1995) observed that the digestibility of starch and fat to be similar during 1 st, 2 nd and 3 rd week of the birds life however the digestibility of the protein during the 1 st week (78%) was significantly lower than during 2 nd and 3 rd week (92%). In a study in this Department (Palanivel, 2004; personal communication) inclusion of palm kernel containing 47% oil in an iso-caloric iso-nitrogenous broiler starter mash at 3,6,9 and 12% levels increased the weight gain, even though the fiber levels increased from 3.86% in the corn soybean meal control to 7.31% in the 12% palm kernel fed group. The better weight gain observed in the palm kernel fed groups may also be due to reduced rate of passage caused by the increased fiber contributed by the addition of de-oiled rice bran added to compensate the higher energy value of the oil in palm kernel.
The hatchling uses the liver glycogen store for its energy purpose immediately after hatch. The embryo utilizes the albumen as a source sugars for glycogen synthesis, the level of blood glucose begin to increase prior to hatching and the liver glycogen store is just sufficient to support the energy need of the hatchling for just one day (Pons et al, 1986), which means that the glycogen store of the early hatchling will be depleted in the hatcher itself and the yolk will be the source of nutrients for meeting the maintenance need of the hatchling, there by wasting important body building units and immunoglobulins. The yolk an important contributor of nutrients for early body building and the immunity of the hatchling, if used for meeting the maintenance need will affect the performance of the bird. Hence it should be planned effectively to meet the nutrient requirements of the chicks at the earliest. Noy and Pinaschov (1993) found that feeding the hatchlings immediately, increased the body weight by 5.7g on the second day, while in the chicks held without feed for 24h a reduction of 7.5g was noticed, the 40 th day body weight was higher in the immediately fed group (1915 vs 1805g). They also observed that feeding of hatchlings with 0.5ml of nutrient solution (starch: glucose: oil at 1:1:1) further increased the 40th day body weight (2032g). The fasting and consequent generation of glucose in the body of the hatchling stimulates the secretion of corticosteroids which are powerful inhibitors of immune cell proliferation not only making the chick vulnerable to infections but also affecting the response to vaccination (Dibner et al, 1998). Vieria and Moran (1999), in addition to the significant increase in the 49 th day body weight in the immediately fed group observed a significant reduction in the mortality (6.3 vs 10.5%) compared to the birds held without feed for the 1 st 24h, confirming the opinion of Dibner et al (1998). Further, feeding the chicks at the earliest possible time was found to influence the absorption of certain nutrients. The glucose absorption increased from less then 50% at hatch to 61% on day 2 in chicks fed immediately, in fasted chicks it was only 56%, on the 4 th day it was 80 and 76% respectively. Similarly, methionine absorption at hatch was also low (43%) and it increased to 62% in fed chicks and 58% in fasted birds. In contrast to glucose and methionine, oleic acid uptake was significantly higher from hatch and throughout in all groups, which was close to 80% (Noy and Sklan, 2001). Early feeding of the chicks enhances the utilization of yolk. The reduction of yolk weight in 2 days time was nearly 4.25g in the fed chicks and 3.75g in the fasted chicks (Sklan, 2001). Early feeding of chicks not only improves the utilization of yolk but also initiates important metabolic changes (Noy and Sklan, 1997).
Feeding of Juvenile Broilers
There are several agencies like NRC, ARC, Breeder companies have come out with various recommendations of the nutrient concentration to be maintained for the starter, grower and finisher feeds. The critical nutrients to be considered are crude protein, ME, lysine, methionine plus cysteine, threonine, tryptophan, calcium, available phosphorus and sodium. A protein level of 22% and a calorie protein ratio of 132, lysine level of 1.3% and methionine + cysteine, threonine and tryptophan , at 72%, 67% and 16% respectively of the level of lysine, calcium at 1%, available phosphorus at 0.5% and sodium at 0.2% levels will be ideal for the 1 st week chick. The crude fiber level not less than 6% and not above 6.5% will be suitable for optimal growth.
The physical characteristics of the feed is also important. Since bigger particle size or fine powder will affect the feed intake and growth. Even though larger particle size is recommended for optimal gizzard development, in the first week the ideal particle size should be between 400 to 600µ for optimal feed intake and growth (Krabbe, 2000).
The feeding of the broiler during the first week needs special care as it forms nearly 16% of its life, further the development of the intestines and other associated organs are also taking place. Hence care should be taken to formulate suitably and manufacture the feed to induce optimal intake and growth.
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|Source : IPSACON-2005|