Digestibility of phosphorus in laying hens fed a wheat-soyabean diet and the excreta phosphorus fractions
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Availability of phytate phosphorus (P) was determined in ISA Brown hens 21 and 47 weeks old, fed a wheat-maize-soyabean diet, without a phytase supplement. The diet contained total and phytate P at 4.99 and 1.58 g/kg, respectively. The average body weight and hen-day egg production were 1.56 kg and 0.52, and 1.92 kg and 1.00 for younger and older hens, respectively. Phytate in the feed and faeces was determined by a capillary isotachophoretic method. Availability of phytate P and proportion of dietary Ca retained was non-significantly higher in older hens than in younger ones (47.3 and 56.9% vs 38.7 and 44.4%, respectively). Amount of P retained was similar in both groups (199 and 194 mg/day in younger and older birds, respectively). Amount of Ca retained was significantly higher in older than in younger hens (2.87 and 1.69 g/day, respectively; PO.05). Dry matter of excreta of 47-week-old hens contained significantly (PO.05) more total and phosphate P than excreta of 21-week-old hens (14.8 and 8.9 mg/g vs 12.3 and 5.9 mg/g dry matter, respectively). Phytate P represented 30.9% of excreta P in younger and 23.0% in older hens. Corresponding proportions of phosphate P were 48.0 and 60.1%. Differences between younger and older hens in proportions of P fractions were statistically significant (P < 0.05). Excreta of 21-week-old hens and those of 47-week-old hens contained 78.1 and 63.0 mg of Ca/g dry matter, respectively (PO.05). Thus, the age and different egg production significantly affect retention of Ca and excreta composition in laying hens. The effect of age on phytate availability was less pronounced.
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