Importance of Feed Restriction in Broiler Production
Growth performance of broiler chicken improved by genetic progress, improvement in nutrition and controlled environment. Unfortunately, when birds are fed ad libitum, the fast growth rate is accompanied by body fat deposition, mortality and incidence of metabolic disorders such as ascites, sudden death syndrome and high occurrence of skeletal problems. Fat is an undesirable product that not only increases the occurrence of metabolic diseases and skeletal deformities, but also causes problems in feed efficiency, difficulties in meat processing, and rejection of meat by consumers for health reasons . It is a proven fact that broilers with heavy deposits of abdominal fat indicate poor finishing . Over the last two decades there has been increase in consumer preferences for leaner meat because of correlation between cardiovascular diseases and consumption of certain fats by human. This thing in turn led the researchers to concentrate on reducing abdominal fat deposition in broiler chicken and produce leaner carcasses . One of the managemental interventions to reduce fat deposition is feed restriction. As feed cost encompasses more than 70% of the total production cost in broiler chicken, restricted feeding prevents the feed wastage and thereby minimizes the cost of production. There are different methods of feed restriction employed in broiler production to improve efficiency of feed utilization and weight gain, and these include intermittent feeding, skip-a-day feeding , appetite suppression with glycolic acid , time of restriction , diet dilution and quantitative feed restriction . The researchers documented that feed restriction reduced feed intake, weight gain and body weight in all feed restricted birds. However, other investigators observed no significant effects of feed restriction on body weights, average daily gain and average daily feed intake at week 6.
Very fast growth rate is usually increased body fat deposition, high incidence of metabolic disorders, high mortality and high incidence of skeletal diseases and those are results of continuous genetic and improvement in nutrition . Early feed restriction programs used to reduce abdominal and carcass fat in broiler chickens rely on the phenomenon called compensatory growth to produce market body weight similar to control groups . A period of low food availability is a challenge that young birds are likely to experience . During development, chickens need to allocate their available energy between maintenance, growth and maturation, and food availability consequently plays an important role during this period . Temporary feed restriction reduces growth at a critical time in a broiler chick’s life cycle when it is the feeding highly concentrated energy diets without restriction of feed intake, and it increases the incidence of metabolic disease. These diseases not only lead to economic losses for the producer, but they greatly affect the comfort of the broilers . Quantitative restriction is to limiting the amount of feed daily given to the animals whereas a qualitative restriction is related to nutrient dilution in the diet . Compensatory growth is defined as a recovery from a growth deficiency resulting from a limited nutrient intake . The mechanism for compensatory growth has not been completely known but two theories have been proposed to explain how compensatory growth is regulated. First, compensatory growth mechanisms may involve a setpoint or reference for body size appropriate for age and that the control resides in the central nervous system and second theory is peripheral control which suggests that tissues, per se, control body size through cell number or by the total content of DNA . Feed restriction increases enzyme secretion such as amylase, sucrase and lipase and also can alters functional development of the enzymes of protein digestion such as dipeptidase and amino peptidase and may therefore influence growth rate of broilers. One of involving factors in accelerated growth may be hormonal change during the feed restriction period. It has been reported that thyroid hormones concentration decreases after feed restriction period but increases and reaches to control by refeeding . Auckland and Morris had been reported that birds subjected to feed restriction for short periods during the early growth phase show improvement of feed efficiency and reach a weight equal to that of birds fed ad libitum at the time of slaughte. The improvement in feed efficiency perceived in feed restricted chickens has been attributed to reduced overall maintenance requirements caused by a transient decrease in basal metabolic rate . However there are several reports shown that chickens subjected to feed restriction have lower weight gain than those fed ad libitum at the end of experiment . Tumova et al concluded that feed restriction resulted in accelerated growth. Feed restriction mainly reduces growth rate and consequently, metabolic demands, during the critical periods of the life span of a bird and it is associated with improvement in arterial oxygenation . Feed restriction can exert negative effects on the body weight at marketing age and on the relative weight of breast muscle . Plavnik and Hurwitz used a severe feed restriction program at 6 to 7 days of age for a one-week period in birds and indicated the birds were much reduced in weight by two weeks of age, as compared to the control birds, but they body weights in market age were equal, feed efficiency was improved. Wilson and Osbourn showed compensatory growth in poultry, following a period of growth retardation by early feed restriction.
Although early feed restriction in broiler reduces growth performance, compensatory growth in the refeeding period will be attained to accelerate growth so as to reach the target weight of birds at the time of marketing. Feed restriction has been adopted in broiler production to avoid rapid growth rate, which is associated with ascites, lameness, mortality and poor reproductive health. In addition, feed restriction in the early stage is beneficial for improving the feed efficiency and decreasing the rearing cost. This article will provide some insight into feed restriction methods, duration and advantages, along with the strategies to be considered for maximum benefits of that system.
Feed Restriction Methods:
The following are the procedures that can be applied to manipulate the feeding strategies of poultry in order to decrease growth and metabolic rate to some extent and also alleviate the incidence of some metabolic diseases as well as improving feed conservation in broiler chicken.
- Physical Feed Restriction:
Physical feed restriction supplies a calculated amount of feed per bird, which is often just enough to meet maintenance requirements. Practical application of feed restriction however is not simple due to the problems of regularly weighing birds, and calculating feed consumption on a daily basis. Moreover, it is necessary to provide sufficient feeder space in order to prevent competition among restricted birds and to prevent the unequal growth. The feeding of high fiber diets has been used as an alternative to the physical feed restriction method. In some cases, however, birds were able to adapt to high fiber diet containing up to 55 per cent rice hulls. Such adaptation enables them to digest and get more energy (and possibly other nutrients) than is required to achieve the desired growth retardation during the under nutrition period. The situation will obviously interfere with the total energy and other nutrient intake of the birds during under nutrition, thereby changing their growth pattern.
- Skip-A-Day Feeding:
Removing feed for 8-24 hour periods during the starter period has been reported to decrease early growth and reduce the incidence of ascites without affecting the body. It has been reported that a skip-a-day feeding for 3 weeks starting at day-old would improve carcass quality and reduce sudden death syndrome which is often associated with birds that are on ad libitum feed intake.
- Lighting Programmes:
Lower cumulative feed intake and significantly improved feed conversion and compensatory growth were observed in chicken under an intermittent lighting programme (1 light : 3 dark from 8 to 49 days) compared with those under a continuous lighting schedule (23 light : 1 dark). The use of intermittent lighting programme also the advantage of reducing electricity cost, the incidence of leg abnormalities and sudden death syndrome with no reduction of weight of market age. Genotype, sex, feeder space, diet composition and stocking density are the main aspects that can interact with the lighting programme and affect broiler’s final performance.
- Low Protein Diets:
Early growth can be retarded by the restriction of intake of specific nutrients, such as protein. Broilers require 220, 200 and 180 g/kg dietary crude protein during the starting, growing and finishing periods, respectively for optimum growth. They tend to increase their feed intake to make up for deficiencies when fed with diets that are marginally deficient in crude protein. However, feed intake is depressed by feeding diets that are severely deficient in crude protein. Studies however have shown that ad libitum feeding of diet containing only 94 g/kg crude protein from 8 to 14 days decreased the feed intake of broilers by some 57 per cent. This decrease in feed intake resulted in 41 per cent growth retardation, which was not recovered after 6 weeks of re-alimentation.
- Low Energy Diets:
Low energy diets can also be used to reduce the body weight of broilers by 4 weeks of age. Two levels of diet ME (13.0 and 14.2 MJ/kg) were used during an under – nutrition period of 6 to 12 days of age and were fed to birds at 167 KJ ME / bird / day. All growth retarded birds observed complete growth compensation by 56 days of age. Female birds however required less energy to recover from the lost body weight occurring during the preliminary feeding of low energy diets than males. The consumption of mash feed at different phases of the broilers growth may be employed as a method of limiting feed intake. Birds offered mash type feed spend more time for consuming their feed compared to birds fed pellets.
- Chemical Methods: The use of 50 g/kg of calcium propionate is an appetite suppressor resulted in gains of birds close to those obtained under a recommended programme of Quantative feed restriction between 2 to 6 weeks of age. Glycolic acid has also been used as chemical means of restricting feed intake of broilers. The feed intake of birds given diets supplemented with 1.5 per cent and 3 per cent glycolic acid was depressed by 17 per cent and 45 per cent, respectively. These reductions in feed intake due to glycolic acid supplementation resulted in growth retardation during the under nutrition period to 71 per cent and 41 per cent, respectively, relative to the growth of control birds. Male broilers exhibited complete body weight recovery at 49 days of age, with no difference between the birds restricted by the dietary glycolic acid addition or those subjected to physical feed restriction. Due to its natural occurrence, glycolic acid may serve as a safe and useful anorectic compound for restricting feed intake in poultry.
- Timing Of Restricted Feeding: The longer the period of underfeeding, more difficult for broilers to compensate for the reduction in weight gain. Most of the Veterinarians recommended feed restriction of not more than 5 and 7 days for female and male broilers, respectively, to allow for full body weight gain. The restriction of the feed intake of birds to 90 per cent of that of control of birds from 7 to 49 days of age had resulted in a significantly lower final body weight at 56 days of age, probably due to the insufficient time allowed for the birds to exhibit complete growth competition. Initiation of 6 days feed restriction at any age between 3 and 11 days of age seems to permit complete body weight recovery by 8 weeks of age in broilers. On the other hand, when initiating a feed restriction programme at 3 weeks of age, very little evidence of compensatory growth has been noticed, probably because of the little time allowed for recovery.
Feed Restriction and Growth Performance:
Feed intake, body weight gain, feed conversion ratio, and final weight at market age were not significantly affected by feed restriction. The lack of significant effects of feed restriction systems may be due to gradual physiological adaptation of the birds to the different feeding regimes which probably improved the efficiency of conversion of the feed available.
Feed Restriction and Carcass Quality:
The largest and most obvious fat deposit is the abdominal fat pad which may comprise up to 4 per cent of body weight. The abdominal fat is usually discarded during processing of meat, the cost of which is directly or indirectly charged to the consumer, which causes an additional economic burden. With feed restriction, fat accumulation is reduced. This feed restriction is explained by two basic mechanisms, Feed restriction results in lower hepatic acetyl-CoA carboxylase activity, a rate limiting enzyme for fatty acid synthesis. This may limit hepatic triglyceride synthesis causing lower serum triglyceride concentration and hence reduces fat accumulation in the body.
Feed restriction influences the recovery of the fat cell number during re-feeding and hence decreases total body fat and abdominal fat contents. Varying amounts of undesirable cholesterol may result from the formation of a greater amount of saturated fatty acids than unsaturated fatty acids. This leads to all possible health hazards for the consumer, unless strict precautions are taken. The cholesterol problem may be alleviated by feed restriction. The cholesterol level was reduced from 132 to 109 mg/ml when chicken were feed restricted. The fact behinds this decreasing cholesterol level is that the feed restriction in chicken decreases the hepatic 3-hydroxy-3-methyl glut aryl Co-A reductase activity in chicken, a rate limiting enzyme in cholesterogenesis and that the activity of this enzyme is not recovered by re-feeding.
Control of Metabolic Disorders and Skeletal Defects:
Early fast growth in modern broilers is associated with increased stress on the birds and can result in metabolic and skeletal disorders that lead to economic losses due to reduced bird performance, high mortality rates and carcass contamination of slaughter houses. As cites mortality was significantly reduced when a feed restriction regimen was used from either 4-11 or 7-14 days of age, consisting of limiting daily intake of the birds to 75 per cent of the ME required for normal growth. Sudden Death Syndrome (SDS) is also a metabolic problem that mostly occurs in all countries where broilers are grown rapidly under intensive conditions. Mortality may range from 1.5 to 2.0 per cent in mixed flocks and as high as 4 per cent in male flocks. Lowering energy intake by changing feed texture or density (mash), or management methods such as feed restriction or long dark periods will reduce mortality from SDS. A mortality level of 0 per cent has been reported for feed restricted birds compared to 3.33 percent under ad libitum feeding.
Rapid Weight Gain and Skeletal Defects:
It has been generally assumed that rapid weight gain has been a major cause of skeletal defects occurring in leg bones and joints. Despite the evidence that there is no genetic correlation between skeletal disorders and body weight, nutritional evidence suggests that dietary strategies that depress growth rate by altering dietary energy and protein levels and offering various feed forms decrease the incidence of skeletal disorders. The incidence of skeletal disease was three fold lower in feed restricted birds compared to the full-fed birds. A similar reduction in the incidence of skeletal disease was also observed in broiler chicken exposed to intermittent light or set up lighting regimen.
Other Benefits of Restricted Feeding:
Feed restriction has a beneficial effect on the immune response of chicken through the expression of some cytokines including IL-4 and IL-3. Cytokines are small glycoprotein produced by a number of cell types, predominantly leukocytes that regulate immunity, inflammation and hematopoiesis. They regulate a number of physiological and pathological functions including innate immunity, acquired immunity and inflammatory responses.
Compiled & Shared by- Team, LITD (Livestock Institute of Training & Development)
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ROLE OF POULTRY NUTRITION & MANAGEMENT ON THE CARCASS QUALITY (MEAT)
