is not guaranteed in all instances. Varying amounts of unde- sirable cholesterol, for example, may result from the forma- tion of a greater amount of saturated fatty acids relative to the unsaturated ones in each molecule of fat being formed in the chick’s body. This inevitably leads to possible health hazards for the consumer, unless strict precautions are taken. The cholesterol problem may be alleviated by feed restric- tion. In one study, the cholesterol level was reduced from 132 to 109 mg/ml when chickens were feed-restricted. This was probably due to the fact that feed restriction de- creases the hepatic 3-hydroxy-3-methyl glutaryl Co-A reductase activity in chickens, a rate-limiting enzyme in chlostrogenesis 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 in- creased stress on the birds and can result in metabolic and skeletal disorders that lead to economic losses due to re- duced animal performance, high mortality rates, and carcass condemnation at slaughter houses. In one study, ascites mortality was significantly reduced when a feed restriction regimen was used from either 4-11 or 7-14 days of age, con- sisting of limiting daily intake of the birds to 75% of the ME required for normal growth. Sudden death syndrome (SDS) is also a metabolic problem that occurs in all countries where broilers are grown rapidly under intensive conditions. Mortality may start as early as 3 to 4 days, but most often peaks at around 3 to 4 weeks of age, with the affected birds being found dead on their back. Mortality may range from 1.5 to 2.0% in mixed-sex flocks and as high as 4% 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% has been reported for feed-restricted birds compared to 3.33% under ad libitum feeding. It has been generally assumed that rapid weight gain has been a major cause of skeletal defects occurring in leg bones
Table 2 – Effect of various early feed restriction systems on the amount of abdominal fat formed in the body of broiler chickens.
Treatment Ad libitum
25% of ad libitum ( 3 days) 50% of ad libitum ( 3 days) 75% of ad libitum ( 6 days) Source: U. Santoso (2001).
Fat (% BW) 1.9 1.7 1.6 1.4
and joints. Despite the evidence that there is no genetic cor- relation between skeletal disorders and body weight, nutri- tional 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. In one study, 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 was also observed in broiler chickens exposed to intermittent light or a step-up lighting regimen.
Other benefits of restricted feeding Feed restriction has a beneficial effect on the immune re- sponse of chickens through the expression of some cy- tokines including IL-4 and iNOS. Cytokines are small glyco- proteins produced by a number of cell types, predominantly leukocytes that regulate immunity, inflammation, and he- matopoiesis. They regulate a number of physiological and pathological functions including innate immunity, acquired immunity, and a plethora of inflammatory responses. Feed restriction may also be used as an effective means of combating the cold stress effects on poultry. Under cold temperature, there is an increase in the metabolic rate of the broiler, with a resulting high oxygen requirement and thus an imbalance between the respiration system and the high oxygen requirement, leading to a state of systemic hypoxia. The resulting systemic hypoxia triggers increased generation of reactive oxygen species (ROS) in mitochondria. When the rate of generation of ROS exceeds the protective capacity of antioxidant, the excess ROS oxidizes proteins and DNA with- in the cell, damages the polyunsaturated fatty acids on the bio-membrane, and initiates lipid peroxidation chain reac- tion. Lipid peroxidation severely damages the cell mem- brane and compromises cell function, mainly by damaging the vascular endothelium cells, causing vasoconstriction, thrombosis and vascular remodeling, which then lead to an increase in pulmonary artery resistance and pulmonary hy- pertension. These changes had been attenuated by early time feed restriction. Feed restricted broilers had a lower body weight and consequently reduced metabolic rate and oxygen requirement, which leads to a reduced generation of ROS and lipid peroxidation and hence improves resistance to the invasion of diseases and reduce mortality. From the economic point of view, feed costs per kilogramme live weight and return over feed costs per bird were in many cases affected by restricted feeding as a result of improve- ments in health, viability, and feed conversion rates. Also, when feed is restricted through manipulation of the lighting system, the electricity costs will be reduced and the feed ef- ficiency will be improved, as indicated earlier, both factors will contribute to higher profits.
References available upon request. ▶ POULTRY WORLD | No. 2, 2018 15
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