Coccidiosis in modern broiler chickens : targeted nutritional modulations for consequences on bone quality

Abstract

This thesis aimed to assess the consequences of coccidiosis on broiler long bone quality and to explore ameliorative nutritional strategies. The impact of coccidiosis on long bone mineralisation, as well as resistance and tolerance to coccidian infection, was similar in two broiler lines differing in their genetic growth rate (GR) potential. Penalties of infection on bone quality persisted after the impaired GR of infected birds attained a similar level as that of their non-infected counterparts [Chapter 2]. Offering 25-hydroxycholecalciferol (OHD) instead of cholecalciferol (D3) as the source of dietary vitamin D (VitD), and higher VitD levels (4000 vs 1000 IU/kg) improved bone mineralisation and performance of both infected and control birds [Chapter 3]. Although, the performance of infected birds was penalised to a higher degree when offering low VitD, offering OHD or high VitD increased parasite burden, suggesting that dietary VitD supply is crucial for broilers during coccidiosis. Offering marginally deficient Ca/P diets reduced mineralisation of both control and infected birds [Chapter 4]. Offering OHD instead of D3 at high levels (4000 IU/kg) did not ameliorate effects of either coccidiosis or reduced Ca/P supply, but promoted higher mineralisation in birds offered adequate Ca/P diets. Parasite burden and performance was similar for 4000IU/kg OHD- and D3-fed broilers, suggesting that the benefits of OHD over D3 were limited at 4000 IU/kg. Chapter 5 investigated the benefit of diet dilution-induced reduction in early GR on coccidiosis-impaired long bone mineralisation. Bone quality, especially femur strength, was improved by reducing GR whilst coccidiosis-impaired bone mineralisation was independent of GR. Overall, the effects of coccidiosis on bone development were provided; they persisted at later stages of infection and differed amongst femur and tibia bones. Genetic and dietary-induced differences in GR and dietary level of VitD and Ca/P improved responses of both control and infected birds whilst infected birds additionally benefited from a higher VitD supply.