Effects of dietary amino acid levels on performance and carcass composition of broilers 42 to 49 days of age

Dietary balanced protein in broiler chickens. 1. A flexible and practical tool to predict dose–response curves

An empirical model of exponential form was developed, different versions of which can be used to predict growth rate, feed conversion and carcase and breast meat yield of broiler chickens as a function of dietary balanced protein (DBP) content. The model was developed to support decision-making by nutritionists. The model helps in determining DBP contents that maximise profit. The model avoids the practical disadvantages of existing methods. In contrast with mechanistic models, only data that are generally known by broiler nutritionists are required as input. Compared with predictions derived from one or a few feeding trials, the model predictions are more accurate (because the model was derived from many data-sets) and more flexible (because a description of the type of broiler was included as input for the model). Broiler response studies from the literature and the Nutreco Poultry and Rabbit Research Centre (27 data-sets in total) were used in the model development to select significant variables, to quantify the parameters and to evaluate the accuracy of the predictions. Input variables were DBP content, maximum performance level, age, year (indicating genetic potential) and sex. The model, including the assumption that the shape of the dose-response curves to DBP content is independent of broiler and feed characteristics, gave an accurate simulation of growth rate, feed conversion and breast meat for nearly all data-sets. Effects of DBP content on carcase yield were relatively small, except for carcases without skin and skin fat.

Effects of dietary sulphur-containing amino acids on performance and breast meat deposition of broiler chicks during the growing and finishing phases

1. Two growth trials were performed to measure the effects of dietary methionine and cystine (SAA) on growth rate, food conversion efficiency and breast meat deposition in male broilers. 2. In experiment 1, broilers were grown on 6 experimental diets covering a range from 6.9 to 9.6 g SAA/kg. The diets were fed from 15 to 33 d of age. Similarly, in experiment 2, 6 diets containing 6.0 to 8.5 g SAA/kg were fed to finishing broilers 33 to 43 d of age. In each experiment 60 birds per treatment were processed, and carcase yield and breast meat percentage were determined. 3. Significant responses in weight gain, efficiency of food conversion and breast meat percentage were detected, which could be described well by exponential regression curves. Dietary SAA requirements to obtain maximum efficiency of food utilisation and maximum breast meat deposition were estimated to be about 9.0 g/kg from 15 to 33 d of age, and about 8.0 g/kg from 33 to 43 d of age. 4. Economic aspects were considered to calculate optimum SAA specifications from the results. In both trials, the dietary optimum of SAA was found to be higher for birds to be further processed than for birds to be marketed as whole carcases.

Effects of dietary sulfur amino acids and crude protein on the performance of finishing broilers

The effects of different combinations of dietary methionine + cystine (Met + Cys) and dietary crude protein (CP) in finishing broilers were investigated in two growth studies. In Exp. 1, male broilers 29 to 42 days of age were fed 18 diets containing 16.9%, 18.7%, or 20.4% CP with six levels of Met + Cys within each protein level. Similarly, in Exp. 2 another 12 diets containing either 18.0 or 21.5% CP were fed to male broilers 29 to 48 days of age. In general, the Met + Cys requirement for optimum feed conversion was higher than for maximum growth. In both experiments, between 0.80% and 0.85% methionine + cystine optimized feed conversion. These dietary levels were valid for a 13.05 MJ ME/kg diet fed to broilers growing from 1.2 kg to 2.2 kg (Exp. 1), or for a 13.60 MJ ME/kg diet fed to broilers growing from 1.3 kg to 3.0 kg (Exp. 2). The Met + Cys requirement was not consistently affected by the dietary CP content in Exp. 1. In Exp. 2, increasing dietary CP from 18.0% to 21.5% tended to increase the Met + Cys requirement for optimum feed conversion. A dietary CP level of 18.0% to 18.7% supported performance and carcass fat deposition equal to diets containing 20.4% or 21.5% CP, respectively, when the sulfur amino acid content was adequate.

Effects of protein and amino acid level fed zero to forty-two days on response of broilers to protein and amino acid levels fed forty-two to forty-nine days of age

Three studies were conducted to evaluate the effect of protein and amino acid (AA) levels fed 0 to 42 days posthatch on response of broiler chickens to levels of protein and AA fed during the finisher period. Birds were grown to 42 days on diets formulated to contain a minimum of 105 or 120% of recommended AA levels, and then randomly assigned to diets formulated to contain a minimum of 70, 80, 90, 100, 110, or 120% of recommended AA levels for 42 to 49 days. No minimum protein level was imposed on the diets. Body weight, feed intake, feed utilization, dressing percentage, abdominal fat content, and parts yield were determined. The protein and AA level fed 0 to 42 days had significant effects on 42- and 49-day body weight and 42- to 49-day feed intake of male but not female broilers. However, there was no interaction of protein and AA levels fed 0 to 42 days on response to protein and AA levels fed 42 to 49 days for these criteria. Weight gain, feed intake, and feed utilization of both males and females 42 to 49 days were significantly influenced by protein and AA levels fed during this time; protein and AA requirements of females during this time appeared to be equal to, or greater than, those of the male broiler. Although there were significant interactions of protein and AA levels 0 to 42 and 42 to 49 days on various carcass parameters for both male and female broilers, these followed no consistent pattern. Protein and amino acid levels fed 0 to 42 days had a significant influence on both quantity and percentage of abdominal fat in both male and female broilers processed at 49 days but not on any other carcass parameters. The protein and AA levels fed 42 to 49 days had a significant effect on both quantity and percentage of abdominal fat in male but not female broilers. The protein and AA levels fed 42 to 49 days significantly influenced quantity but not percentage of breast meat in male but not female broilers. The results of the current study indicate that there was minimal carryover effect of protein and AA levels fed 0 to 42 days on response to AA levels fed 42 to 49 days.

Effects of dietary amino acid level and duration of finisher period on performance and carcass content of broilers forty-nine days of age

Two studies were conducted to evaluate feeding reduced levels of amino acids (AA) to broilers during the finisher period. Birds grown to 42 days on nutritionally complete diets were fed diets formulated to contain a minimum of 70, 80, 90, 100, or 110% of recommended AA levels for periods of 3, 5, or 7 days prior to slaughter at 49 days of age. Body weight, feed intake, feed utilization, dressing percentage, and abdominal fat content were determined. For finisher periods of 3 to 5 days, a reduction in recommended dietary AA levels may be utilized without impairment of body weight gains of broilers. Extending the finisher period to 7 days resulted in significant (P less than .05) reduction of body weight gains on diets with AA levels less than 90% of recommended levels. Feed utilization was more sensitive to reduction in AA levels and may be affected adversely even by a 5-day withdrawal period. Dressing percentage was reduced in some instances, and abdominal fat generally increased when reduced AA levels were fed. The economics of feeding reduced AA levels must be considered in evaluating the results of the present studies.