Determination of nutrient mass balance in turkeys

Retention and excretion of phosphorus and nitrogen were determined for turkeys fed 2 diets at 3 ages, via mass balance based on the nutrient content of consumed feed, carcasses, and litter. The 2 diets consisted of an industry diet (IND) and a low phosphorus + 600 U of phytase/kg (LP) diet. A subsample of birds was weighed and killed at 12, 15, and 18 wk of age for nutrient retention (via whole carcasses) and excretion (via litter). Diet did not affect BW or feed intake from 12 to 18 wk of age. The mass of phosphorus excreted from 0 to 12, 0 to 15, and 0 to 18 wk of age was 37, 46, and 40% greater for birds fed the IND diets compared with birds fed the LP diets. Phosphorus retained as the percentage of phosphorus consumed was greater at 12, 15, and 18 wk for birds fed the LP diets (67.0, 63.8, and 53.8%) than for birds fed the IND diets (47.3, 44.0, and 32.8%). The difference between the mass of phosphorus excreted, as calculated from litter, compared with feed intake minus carcass retention was less than 5% at 18 wk. The nitrogen retained averaged 90.7, 136.7, and 184.2 g/bird, whereas nitrogen excreted averaged 377.6, 620.7, and 921.8 g/bird at 12, 15, and 18 wk of age, respectively. Additionally, with an 18-wk average litter DM of 78.0%, the unaccounted for nitrogen at 18 wk was 427 and 405 g/bird for birds fed the IND and LP diets, respectively (40 and 37% of excreted nitrogen).