Investigation the effects of quantitative feed restriction on performances, blood parameters, gut microflora and chemical composition of excreta of broiler chickens

Changes in the pattern of animal protein consumption and a greater tendency to consume chicken in the last decade has greatly increased the demand for this product. Considering that 70% of the cost of poultry production is related to nutrition, so, it can be concluded that optimal nutrition is the most important way to reduce production costs in this industry (Abdollahi et al. 2013). Advances in broiler nutrition and breeding have increased growth rate and reduced breeding period over the past few decades. At present, broilers reach slaughter weight at the age of 42 days. Unfortunately, this high growth rate leads to problems such as metabolic disorders (sudden death Syndrome, skeletal disorders and ascites), increased mortality, and abdominal, and carcass fat (Khajali et al. 2007). Slowing down the growth rate by using dietary restrictions will greatly prevent these problems. At the same time, low growth is not economical and it is necessary to compensate for the backward growth of chickens due to food restrictions. Researchers have stated that the main goal of research on dietary restriction in broilers is to improve feed efficiency and reduce carcass and abdominal fat (Zhan et al. 2007). Depriving birds, especially broilers, of rapid growth from full access to the nutrients needed for normal growth is called feed restriction, which is classified into two categories: quantitative and qualitative. The response to feed restriction depends on the duration of the feed restriction (Khetani et al. 2009). In quantitative or physical feed restrictions, the consumption of birds or animals is limited. The practical application of physical feed restriction is not easy due to the problems of regular weighing of poultry and calculating daily feed intake (Zulkifli et al. 2000). Quality restriction is another method of applying feed restriction that aims to use diets with low energy and protein levels (Fanooci and Torki 2010). Urdaneta-Rincon and Lesson (2002) y applying 85, 90 and 95% quantitative feed restriction in male broilers at 5 to 42 days of age, they showed that the application of dietary restriction led to a significant difference in weight at 42 days of age and also a significant reduction in mortality. Bautzen et al (2003) in an experiment on broiler sex mixture and the application of quantitative feed restrictions at the ages of 6 to 16 days and 80% of the previous day's consumption of the control treatment, showed that performance was affected in the early weeks, but the restricted treatments at the age of 42 One day, they achieved the desired compensatory growth and no difference with the control group. Therefore, according to the reports on the use of feed restriction in reducing metabolic diseases and losses, it seems necessary to study feed restriction in broilers. In order to evaluate the effects of quantitative feed restriction, 300 one-day-old Ross broilers were each in a completely randomized design with five treatments, five replications and 12 pieces per replication for 42 days. The birds were fed ad-libitum up to 10 days then they were restricted from 11 to 35 days and they were fed ad-libitum up from 36 to 42 of age. Experimental treatments include: (1) Corn- soybean meal – based diet as a control group (no feed restrictions), (2) feed access to 95% control group, (3) feed access to 90% control group, (4) feed access to 85% control group (5) feed access to 80% control group. Diets were prepared according to the maintenance guidelines of Ross 308 strain. At 42 days of age, one chick from each pen was randomly selected and slaughtered, and the carcass traits such as breast, thigh, gizzard, liver, abdominal fat and carcass yield were determined. On day 35 of the breeding period, one chick from each experimental unit was randomly selected and slaughtered. The cecum of the birds was isolated and examined for the microbial population of Lactobacillus, Coliform and E. coli in the laboratory. Blood samples were also collected and then, centrifuged at 3000 rpm for 10 minutes and transferred to the laboratory to determine blood parameters (Cholesterol, Triglyceride, HDL and LDL). On day 35 of the experiment, some samples were collected and transferred to the laboratory to determine the percentage of dry matter, moisture, ash and volatile solids. To sample the waste, two hours before sampling, it was placed on the bed of each plastic pen and the waste were collected from five points of each pen. Experimental data were statistically analyzed in a completely randomized design using GLM procedure by software (SAS 2004) and the means were compared by Duncan's multiple range test at 5% probability level. The results showed that feed restriction decreased feed intake and body weight gain comparted with the control group (P<0.05). Carcass characteristics, FCR and feces characteristics were not affected by Feed restriction (P>0.05). Also, feed restriction at the levels of 85% and 80% significantly decreased protein excretion in comparison with the control group (P<0.05). Feed restriction at the level of 80%, increased cecal populations of Lactobacillus spp. While decreased cecal populations of E. coli (P<0.05). Feed restriction decreased blood triglyceride and increased blood LDL (P<0.05). Quantitative feed restriction clearly affected body weight gain and feed intake of birds. The degree of change in these parameters depended on the level of feed restriction used. There was a reduction in body weight gain at 42 d for chicks restricted to 95, 90, and 85%, of ad libitum feed intake, relative to the previous day’s intake of the control birds. Such a reduction in body weight is in accordance with results from Khantaprab et al. (1997), Roth et al. (1993), and Santoso et al. (1993a). Results suggest that the growth rate of broiler chickens is related to feed intake, which supports the statement that improvement in body weight of birds is highly correlated to feed consumption (O’Sullivan et al, 1992). Overall the results showed that although feed restriction up to 80%, decreased feed intake and body weight gain of broiler chickens at the total period of experiment, but this restriction improved microbial population of cecum, decreased blood LDL and protein excretion.