Performance and bone characteristics of broilers fed diets supplemented with vitamin A at different concentrations.

This work evaluated the influence of vitamin A on performance, organ weight, and bone and skin characteristics in broilers (Cobb 500) at 21 and 42 days of age. A total of 1920 chickens were distributed in a randomised design, considering six vitamin A supplementation levels (0, 6000, 16,000, 26,000, 36,000, and 46,000 IU kg-1 ), with 16 replicates and 20 chickens per experimental unit, established due to rising the range of vitamin levels observed in the literature to evaluate the effect of vitamin A on broilers. At 22 days, half of the replicates from each treatment continued receiving the initial diet, and the other eight repetitions received diets without vitamin A (0 IU kg-1 ) until 42 days. The level of vitamin A influenced feed intake (FI) and body weight gain (BWG) until 21 days for all treatments. Broilers at 21 days of age had a more significant BWG at a vitamin A supplementation level of 28,209 IU kg-1 . At 42 days, vitamin A influenced the BWG and FI of broilers at treatments that were not supplemented after 21 days. Treatments supplemented up to 42 days showed quadratic responses to vitamin A for BWG, FI, and feed conversion. The vitamin A levels influenced the relative weights of the small intestine, pancreas, gizzard, abdominal fat, Seedor index, and breaking strength at 42 days, where the adequate supplementation of vitamin A improved these characteristics in broilers. Vitamin A supplementation from 22 to 42 days old did not affect broiler performance. An increased BWG was obtained when vitamin A supplementation occurred until 42 days, with supplementation of 29,375 IU kg-1 and a lower response of feed conversion with the addition of 27,775 IU kg-1 .

Combination of phytase and citric acid, but not phytase alone, ensures regular rates of growth and bone mineralization in quails under severe phosphorus restriction.

An experiment was conducted to evaluate the effects of phytase (PHY), alone or in combination with citric acid (CA), on growing Japanese quails under moderate and severe phosphorus (P) restriction. For this, 504 one-day-old female quails were distributed in a completely randomised design with seven treatments and six replications. Treatments consisted of the following diets: (a) positive control (PC): formulated according to quails nutritional requirements; (b) negative control 40% (NC40 ): PC with 40% less aP; (c) NC40 +PHY; (d) NC40 +PHY+CA; (e) negative control 65% (NC65 ): PC with 65% less aP; (f) NC65 +PHY; (g) NC65 +PHY+CA. Phytase and CA were included at 300 FTU/kg and 40 g/kg, respectively. Performance, bone mineralization and plasma mineral concentration were evaluated at day 35; calcium (Ca) and P metabolism, between days 36 and 39. No significant differences in performance, plasma Ca and P were detected between quails fed PC or NC40 ; however, NC40 decreased tibia ash (p < 0.01). Treatment NC65 impaired daily weight gain (p = 0.01), tibia ash (p < 0.01), and tibia optical densitometry (p = 0.03), as well as modified plasma Ca (p < 0.01) and P (p = 0.03) concentrations when compared to PC. Both NC40 and NC65 reduced P excretion (p < 0.01). Phytase alone restored tibia ash of NC40 quails to regular rates. Nevertheless, only PHY and CA combined returned plasma P, tibia ash, tibia optical densitometry, and daily weight gain of quails fed NC65 to similar values as those observed in PC. In conclusion, PHY alone suppresses the negative effects of moderate P restriction in growing Japanese quails, but fails in this task under severe P restriction. In such a situation, only the combination of PHY and CA ensures regular rates of growth and bone mineralization. This concept should be better explored by producers in order to take full advantage of the reduction in P excretion achieved by lowering dietary P concentrations.