Intermingling heavy and light strain chickens may cause social stress

The present study examines the effects of intermingling day-old broiler chicks with 2-wk-old light strain chicks, on body weight, general activity, feeding behavior, feather condition, and heart size of the broilers. Fifteen groups of chicks (five for each treatment) were raised until 6 wk of age in 1 x 2 m experimental pens. Each group consisted of 10 broiler chicks in Treatment 1 (control pens), 8 broiler, and 2 light strain chicks in Treatment 2 (8:2), and 5 broiler with 5 light strain chicks in Treatment 3 (5:5). The feeding program consisted of a commercial starter ration (21% protein, 3,000 kcal ME/kg) for the first 4 wk followed by a finishing ration (18% protein, 3,150 kcal ME/kg). Feed and water were provided for ad libitum consumption. Body weight did not differ between Treatment 1 (controls) and the "intermingled" broilers. Feather condition was significantly poorer among the 5: 5 groups than in the controls. Heart weight (a possible indicator of chronic stress) in broilers of the 5:5 groups was significantly heavier than in the controls. No differences in the general activity parameters were found between broilers of the various treatments. Pecking at feed among broilers was significantly greater (P < 0.05) in the 8:2 groups than in both control and 5:5 groups. During the first 6 wk after hatching, intermingling broiler chicks with equal numbers of light strain chicks that are 2 wk older may lead to long-term chronic stress for the broilers.