Straight-run vs. sex separate rearing for 2 broiler genetic lines Part 1: Live production parameters, carcass yield, and feeding behavior.

The objective of this experiment was to evaluate the effects of raising broilers under sex separate and straight-run conditions for 2 broiler strains. Day-old Ross 308 and Ross 708 chicks (n = 1,344) were separated by sex and placed in 48 pens according to the rearing type: sex separate (28 males or 28 females) or straight-run (14 males + 14 females). There were 3 dietary phases: starter (zero to 17 d), grower (17 to 32 d), and finisher (32 to 48 d). Birds' individual BW and feed intakes were measured at 12, 17, 25, 32, 42, and 48 d to evaluate performance. At 33, 43, and 49 d, 4 birds per pen were sampled for carcass yield evaluation. Additionally, from 06:00 to 06:30, 13:00 to 13:30, and 22:00 to 22:30, video records were taken to assess behavior at 45 days. Data were analyzed as CRD with a 2 × 3 factorial arrangement of treatments over time. Throughout the experiment Ross 308 were heavier than the 708, and after 17 d, male pens had the heavier birds, followed by straight-run and then females. Straight-run pens had higher BW CV in comparison with sex separate pens. Sex separate male BW was negatively impacted from 17 to 32 days. On the other hand, females raised sex separate were heavier than females raised straight-run with lower CV from 25 to 41 days. Post 25 d, FCR was the lowest in male pens whereas feed intake was the highest for these pens after 17 days. Overall, males had total carcass cut-up weights higher than straight-run and females at the 3 processing times. The Ross 708 had higher white meat yields, whereas 308 had higher yields for dark meat. Feeding behavior results were not consistent over time. However, from 13:00 to 13:30, birds in female pens spent more time eating, followed by straight-run and then males. In conclusion, raising females in a straight-run system negatively impacted performance and CV, whereas males benefited from straight-run rearing, with the differences being possibly related to feeder space competition.