Comparison of carcass condemnation causes in two broiler hybrids differing in growth rates

Abstract

Experimental studies concluded that genetic factors enabling fast growth rate might negatively affect broiler health and welfare. Recently, the proportion of slower-growing broilers has been increasing. However, studies of health in broilers with different growth rates in commercial systems are still scarce. This repeated cross-sectional study aimed to describe causes of carcass condemnations in two broiler hybrids with different growth rates, Ross 308, and Hubbard JA787, and to estimate the effect of hybrid. The study sample consisted of 63 209 415 broilers slaughtered in 4295 batches from 139 farms. All broilers were slaughtered from January 1st, 2015, to June 22nd, 2021, by the same company (Norsk Kylling). All causes of condemnation, except fractures, were more prevalent in Ross 308. The five most common causes (ascites, discolouration, hepatitis, small and skin lesions) were investigated in greater detail, and the effect of hybrid was assessed using mixed effects negative binomial models with the condemnation codes as outcome variables. For the five selected causes, variation in prevalence between slaughter batches was considerable for Ross and minor for Hubbard. The notable differences between hybrids in prevalence and causes of condemnation have important implications for animal health, welfare, economy, and sustainability in broiler production.

An analysis of the welfare of fast-growing and slower-growing strains of broiler chicken

“…This is the case even when the 'fairest' comparisons are made at equivalent bodyweights (when SG birds are older) and when conducted under matchedenvironmental conditions, experimentally or on farm. From the most recent studies SG strains showed better walking ability (Dixon, 2020;Abeyesinghe et al, 2021;van der Eijk et al, 2023); leg health (Guz et al, 2021), skin conditions (Dixon, 2020;Abeyesinghe et al, 2021;Forseth et al, 2023;van der Eijk et al, 2023;Weimer et al, 2020) and spent more time standing or walking (de Jong et al, 2021;Guz et al, 2021;van der Eijk et al, 2023). The quantitative analyses confirmed this impression with SG strains having an estimated mean gait score 0.65 points lower than FG strains, the latter primarily scoring midway between 2 (definite and identifiable gait abnormality that does not affect ability to move) and 3 (obvious gait defect that affects its ability to move); 15% fewer birds/flock with FPD and 25% fewer birds/flock with HB.…”

“…Most welfare problems (musculoskeletal, locomotor, cardiovascular) increase with age and bodyweight (e.g. Forseth et al, 2023). Because conventional FG strains have been selected for high feed efficiency they reach slaughter weight at an early age.…”

“…Sample sizes varied from small experimental studies with welfare measures taken on 5 or 6 individuals per strain to studies conducted at commercial abattoirs where measures were taken on 30 million or more individuals (e.g. Forseth et al, 2023). Confounding factors further complicate any simple aggregation of studies.…”

“…A longitudinal study conducted between, 2015 and, 2021 provides a particularly valuable insight into strain effects under commercial conditions because it followed flocks from the same farms during a period when farmers were switching from using FG Ross 308 birds to SG-mid Hubbard 787 birds (Forseth et al, 2023). The conditions on the farms were not substantially altered and so the impact of many of the usual confounding factors was greatly reduced, although statistical models still examined the potential influence of season and slight variations in stocking density.…”