Limestone particle size, calcium and phosphorus levels, and phytase effects on live performance and nutrients digestibility of broilers.

Limestone particle size (PS) affects its solubility and thus can influence broiler performance by altering the rate of calcium (Ca) release into the gastrointestinal tract. The objective of this research was to determine, using 2 × 2 × 2 factorial arrangement, the influence of PS (fine and coarse) and supplemented phytase (0 and 1,000 FYT/kg) in diets formulated with 2 Ca and Pi levels (positive control [PC]; negative control [NC]) on live performance, bone ash, and apparent ileal nutrients digestibility (AID). Starter PC: 0.9 Ca and 0.45 Pi; NC: 0.72 Ca and 0.03 Pi. Grower PC: 0.76 Ca and 0.38 Pi; NC: 0.58 Ca and 0.23 Pi. The 8 diets were assigned randomly to a total of 1,512 birds, with 21 birds per pen and 9 pens per treatment. The main effects of PS and Ca and Pi levels had no influence on feed intake (FI), body weight gain (BWG), or feed conversion ratio. Adding phytase improved BWG by 8 g and 50 g and FI by 25 g and 56 g at 0-14 D (P ≤ 0.05) and 0-35 D (P ≤ 0.05), respectively. Interaction between Ca and Pi levels and phytase improved BWG and FI for 0-14 D (P ≤ 0.05) and BWG during 15-28 D (P ≤ 0.05) for PC without phytase and for PC and NC with phytase when compared with NC without phytase. Birds fed PC without phytase, or either PC or NC with phytase were about 96 g heavier than NC without phytase. Birds fed either PC or NC diet with coarse limestone or PC with fine limestone gained approximately 14 g more (P ≤ 0.05) than birds fed NC with fine limestone for BWG at 0-14 D (P ≤ 0.05). Phytase increased tibia bone ash (14 D) by 1% (P ≤ 0.05). AID of Ca and Pi at 14 D was improved (P ≤ 0.05) by 66% when phytase was added to coarse limestone. Results indicate that phytase improved broiler performance without being affected by PS. Furthermore, phytase had greater influence on coarse limestone than on fine limestone for bone ash and AID. Ca and Pi levels were the most influential factors in determining bone ash although phytase inclusion could lead to an improvement during early days.

Effect of elevated dietary inorganic zinc on live performance, carcass yield, and quality of male and female broilers.

This study evaluated the effects of elevated dietary inorganic zinc (Zn) on live performance, carcass and parts yield, and carcass and meat quality of broilers. A total of 288 d-old Ross 344 × 708 broilers were distributed among 3 dietary treatments with 12 replicate cages per treatment and raised sex-separate with 8 birds per cage. Birds were fed practical diets supplemented with either 0, 120, or 240 mg Zn/kg diet. Feed intake and body weight (BW) were measured and feed conversion ratio (FCR) was calculated. At 42 d, 3 birds per cage were processed to assess carcass and meat quality. Male BW at 42 d was increased (P ≤ 0.05) by 120 mg Zn/kg. The FCR to 42 d was also improved (P ≤ 0.05) for males supplemented with 120 mg Zn/kg as compared to 240 mg Zn/kg with the 0 mg Zn/kg diet intermediate. Dietary Zn had no effect on BW or FCR of females. Dietary Zn had no effect on carcass weight and parts yield but absolute weights of male, but not female, total breast and tenders were increased by 240 mg Zn/kg relative to 0 mg Zn/kg with 120 mg Zn/kg intermediate. Breast fillets cook yield and tenderness as well as color were not influenced by Zn in either sex. Supplementing 120 mg Zn/kg resulted in increased Zn in male breast muscle (P ≤ 0.01) whereas 240 mg Zn/kg reduced Zn in breast muscle of females. The 240 mg Zn/kg diet increased Zn in femurs (P ≤ 0.05) of males relative to the other diets. For females, Zn concentration in femurs was increased (P ≤ 0.05) by 240 mg Zn/kg relative to 120 mg Zn/kg with the non-supplemented birds intermediate.