Preference of broiler chickens for animal and vegetable protein diets

Background: Vegetable protein (VP) diets are cheaper and safer than animal protein (AP) diets. Performance on VP diets may be similar to that on AP diets, however, the former tend to contain anti-nutritive factors and may not be as acceptable to poultry. Objective: To determine the preference of broiler chicks for VP and AP diets when fed simultaneously. Design: In experiment 1, 14d-old Ross-308 male and female chicks were randomly allocated to VP or AP grower (15-21d) and finisher (22-28d) diets. In experiment 2, 7d-old Cobb-500 male chicks were offered two VP diets, with soybean meal (SB) or canola meal (CM) as the major protein source, until 21 days of age. All diets were supplemented with microbial enzymes (Avizyme 1502 and Phyzyme XP; Danisco Animal Nutrition, UK) and each was fed to six replicate groups. Both experiments were conducted as part of larger projects to assess poultry productivity on the diets being tested. In experiment 2, the effect of SB and CM diets when offered in the first week prior to feeding of a diet containing fishmeal was tested. The selection of the diets offered was recorded for each period. Data collected were analysed by one-way ANOVA and mean values were considered significant at P≤0.05. Outcomes: In experiment 1, birds generally preferred the AP diet when given a choice. On the grower diet, birds ate 62 % of AP and 38% of VP, while on the finisher diets, the selection was 82 and 18%, respectively. Preference was significant in the grower (P<0.01) and finisher (P<0.001) periods. On the main study, birds on the VP diets attained final (42d) weights that were similar to those on the AP diets. In experiment 2, birds preferred the CM diet, consuming it at 62.2% in preference to the SB diet between 8 and 14 days (P<0.01). Between 15 and 21 days, the birds selected CM in preference to SB, at the rate of 58:42% (P<0.001). Birds started on the SB diet in the main study were heavier (P>0.05) than those on the SB diet at 21d of age. Conclusion: The results suggest a preference by chicks for AP diets even if the diets are nutritionally similar to VP diets. The chicks also preferred a diet containing CM, even if it did not support better growth. The causes of these preferences, particularly the strong aversion to VP diets, warrant investigation.