Effects of riboflavin supplementation level on health, performance, and fertility of organic broiler parent stock and their chicks.

Data from breeder hens and chicks are particularly critical for the development of vitamin B2 recommendations for organic poultry. To test safe thresholds of supplementation, 100 breeder hens (Hubbard JA 57 K) and ten cockerels were allocated to ten housing groups, with each receiving supplementation of either 4.0 (treatment CON) or 2.5 mg (treatment RED) riboflavin per kg feed. After 15 weeks of experimental feeding, 256 eggs were incubated. From the hatched chicks (Hubbard S757), 192 were allocated to four treatments based on their parents' treatment (CON- or RED-) and on their own supplementation of either 4.0 (-CON) or 2.5 mg (-RED) riboflavin per kg feed. Two groups of each combination (CON-CON, CON-RED, RED-CON, RED-RED), each with 24 chicks of both sexes, were fattened for nine weeks and slaughtered. Analysis of total riboflavin (sum of native concentrations and supplements) in the parent's feeds revealed an average, over the 15 weeks, of 7.8 and 5.8 mg per kg feed for CON and RED, respectively. Body weight, plumage integrity, gait appearance, footpad, claw and keel bone integrity, lesion scores, laying performance, and egg mass were found to be of similarly high levels for all hens without any treatment effects. Performance traits of the hens in both treatments reached the specifications of the producer for this genotype. Yolk and albumen riboflavin concentrations were not affected although yolk colour in the RED treatment group became darker. Fertility was not affected, and hatchability was 100 per cent. Total riboflavin concentrations in the broiler diets were on average, over 9 weeks, 8.2 and 6.1 mg/kg for CON and RED, respectively. In chicks, RED treatment of their parents led to significant depressions of feed intake and growth. The RED treatment of the chicks themselves also impaired growth. Growth rates of the CON-CON treatment were in line with the specifications of the producer for this genotype. Plumage scores, footpad integrity and walking appearance of the broilers, and dressing percentage of the carcasses were not affected by treatment. The RED treatment of chicks caused lower spleen and heart weights, while pancreas and liver weights, and liver riboflavin concentrations were not affected. In conclusion, supplementation of 4.0 mg/kg to organic diets did not evoke any health or performance problems for breeder hens or broiler chicks, while a supplementation level of 2.5 mg per kg feed led to reduced weight gains, although without any other riboflavin deficiency symptoms.