Differences in performance, body conformation, and welfare of conventional and slow-growing broiler chickens raised at 2 stocking densities

Abstract

Consumer concern for broiler welfare has increased interest in chicken from slower growing (SG) broiler strains. Broilers from SG strains take longer to reach market weight, which may necessitate differences in management practices, such as stocking density. This study evaluated the effects of 2 stocking densities on production performance, body conformation, and welfare of broilers from 2 strains. Broilers from strains that reach market weight at age 42 D (CONV; N = 284) and at 63 D (SG; N = 284) were exclusively stocked into pens at a density of either 29 kg/m² or 37 kg/m². Birds were provided the same starter, grower, and finisher diets with diet phase changes occurring when SG bird body weight (BW) matched CONV. Live BW, body length, pelvic width, shank length, shank width, keel length, breast width, and breast depth were collected at 4 phases: Phase 1-chick placement, Phase 2-starter, Phase 3-grower, and Phase 4-finisher. At Phase 4, footpad dermatitis (FPD), hock burn (HB), and toe damage (TD) were scored. Feed conversion ratio (FCR) and mortality for each pen were recorded throughout the study. Final BW was similar (2.68 kg) for both strains and stocking densities of birds (P > 0.05). CONV bird FCR was 35% more efficient than SG (P < 0.0001). CONV birds had shorter bodies and shanks compared with SG birds at Phases 3 and 4 (P < 0.05). Slower growing birds stocked at 37 kg/m² had the longest bodies and keel bones at Phase 4 (P < 0.01). Also at Phase 4, SG birds stocked at 29 kg/m² had the lowest prevalence of HB (4%), yet the highest prevalence of TD (28%; P < 0.01). These results indicate differences in the effects of strain and stocking density on male broiler conformation, performance, and welfare and highlight the importance of tailoring management practices to the strain of broiler raised.

Keywords: broiler; performance; stocking density; strain; welfare.

Figure 1

Estimates of the 3 parameter Gompertz curve for the body weight (g) of male broilers from 2 strains (CONV and SG) raised at 2 stocking densities (29 kg/m² and 37 kg/m²). Abbreviations: CONV, conventional; SG, slower growing.

Figure 2

Mortality (%) of 2 strains (CONV and SG) male broilers raised at 2 stocking densities (29 kg/m² and 37 kg/m²). Abbreviations: CONV, conventional; SG, slower growing.

Figure 3

Estimates of the 3 parameter Gompertz curve for the (A) body length, (B) pelvic width, (C) shank length, (D) shank width, (E) keel length, (F) breast width, and (G) breast depth of male broilers from 2 strains (CONV and SG) raised at 2 stocking densities (29 kg/m² and 37 kg/m²). Abbreviations: CONV, conventional; SG, slower growing.

Figure 4

The effects of strain (CONV and SG) and stocking density (29 kg/m² and 37 kg/m²) on the prevalence (%) of hock burn (HB) scores (0, 1) of male market weight broilers at Phase 4. Abbreviations: CONV, conventional; SG, slower growing.

Figure 5

The effects of strain (CONV and SG) and stocking density (29 kg/m² and 37 kg/m²) on the prevalence (%) of toe damage (TD) scores (0, 1) of male market weight broilers at Phase 4. Abbreviations: CONV, conventional; SG, slower growing.