Diets for broiler chickens

Animal by-products are excluded from most commercially manufactured poultry diets in Australia as a precaution against contamination of feed mills with zoonotic agents that could infect ruminants. Excluding animal by-products from formulations not only reduces the nutritive value of the diets but also creates a constraint in feed formulation. This study was undertaken to compare responses of broiler chickens fed all-vegetable diets with those of chickens fed conventional diets.

Performance of broiler chickens fed diets based on all-vegetable ingredients - Image 1

Three hundred and twenty day-old broiler chicks (initial weight, 46.0 ± 0.88 g) were randomly allocated to five dietary treatments, each of which was replicated eight times using eight birds per replicate. The birds were reared in a temperature-controlled house in brooder cages (600 × 420 × 23 cm) from 1–21 days of age and were then transferred to large metabolism cages where they were held until 35 days of age. The birds had ad libitum access to water and feed throughout the trial period. The diets were cold-pelleted. The birds were held at 33 °C for the first two days, after which the temperature was gradually reduced to 24 °C by 19 d of age and maintained at this temperature until the end of the trial. Sixteen hours of lighting per day were provided throughout the trial period.

Four experimental diets were formulated using maize and wheat as the main energy sources and soybean meal, canola meal or fishmeal as protein sources. The SBM75 and Can75 diets were formulated using plant ingredients to meet or exceed NRC (1994) recommendations. The ratio of total dietary protein derived from soybean meal to that derived from canola meal in the SBM75 diet was 3:1 and the ratio of total dietary protein derived from canola meal to that derived from soybean meal in the Can75 diet was 3:1. The ratio of total dietary protein derived from soybean meal to that derived from canola meal in the SBM50 diet was 2:1 and the ratio of total dietary protein derived from canola meal to that derived from soybean meal in the Can50 diet was 2:1. Fishmeal was included in the SBM50 and Can50 starter diets at levels of 7.74% and 8.39% (DM basis), respectively, and in the SBM50 and Can50 finisher diets at levels of 7.18% and 7.0% (DM basis), respectively. The control diet contained soybean meal, canola meal and mung bean as vegetable protein sources, and tallow. All diets were isoenergetic and isonitrogenous and contained enzymes (Avizyme and Phyzyme, each 0.3 g/kg) and zinc bacitracin (0.5 g/kg). Starter diets (ME, 12.37 MJ/kg; CP, 210 g/kg) were fed for the first 3 weeks of the trial and finisher diets (ME, 12.42 MJ/kg; CP, 191 g/kg) were fed for the last 2 weeks of the trial. Body weight, feed intake and feed conversion ratio were measured weekly until 35 days of age. A subsample of four birds per cage was assessed for visceral organ development and ileal digestibility of nutrients at 21 d of age. At 28 d of age, bone development was assessed through observation of gait and the latency-to-sit test (Berg and Sanotra, 2003). Two birds per replicate were randomly selected at 35 d of age and processed for measurement of meat yield. The right tibia from another bird was used for assessment of mineral content and bone breaking strength. All data were analyzed using one-way ANOVA and Minitab software (Minitab, 2010).

Feed intake up to 14 d and 35 d was highest for the SBM50 diet (P < 0.001) and the Can75 diet (P < 0.05), respectively, and lowest for the control diet (Table 1). Birds fed the Can50 diet were significantly heavier at 21 d (P < 0.001) and 35 d (P < 0.05) than birds in the other groups, of which control group birds weighed the least. Feed conversion ratio differed (P < 0.05) during the first week of the rearing period only and was not affected by dietary treatment during the rest of the trial period, although birds in the Can50 group tended (P = 0.088) to be the most efficient and those in the Can75 group (P = 0.088) tended to be the least efficient. Bone breaking strength was higher (P < 0.05) in SBM50 group than in the other groups. Except for abdominal fat content, meat yield parameters were not significantly affected by dietary treatment. The Can50 group had the highest abdominal fat content (24.9 g per bird) and the SBM75 group had the lowest abdominal fat content (14.7 g per bird). From these results, it may be inferred that broilers fed conventional diets (SBM50 and Can50) containing fishmeal utilized feed more efficiently and grew more rapidly than those fed all-vegetable diets (SBM75 and Can75) or a contemporary commercial diet (control diet). The reasons for these effects may include synergistic effects of animal and vegetable proteins and the amino acid balance of the conventional diet.

References

Berg, C. and Sanotra, G.S. (2003). Can a modified latency-to-lie test be used to validate gait-scoring results in commercial broiler flocks? Animal Welfare 12, 655-659.

Minitab (2010). Minitab Statistical Software User''''s Guide 2: Data Analysis and Quality Tools. Minitab Release 16.Minitab Inc. State College, PA16801-3008,USA.

National Research Council (1994). Nutrient Requirements of Poultry, 9th edition.National Academy Press, Washington, D.C.

This article was originally published in Recent Advances in Animal Nutrition- Australia Volume 18 (99-100). Engormix.com thanks the authors and the organizing committe for this huge contribution.

Diets for broiler chickens

Performance of broiler chickens fed diets based on all-vegetable ingredients