Phosphorus availability of oilseed meals determined by the apparent faecal digestibility technique

This study aimed to determine the phosphorus availability of five oilseed meals and the effect of formaldehyde treatment with or without an exogenous phytase supply. Eleven diets were optimised so that 70% of the phosphorus supply was provided by one of the following oilseed meals: untreated (UT) linseed, groundnut, soybean, rapeseed, sunflower meals, formaldehyde-treated (FT) soybean, rapeseed, sunflower meals, the FT oilseed diets being with or without phytase supplementation (FTP). Eleven mature sheep were restrictively fed on five of these diets successively according to a Youden square experimental design so that each diet was fed successively to five different sheep. After 3 weeks adaptation to the diet, the sheep were placed in digestibility crates. Dry matter (DM) intake, and faecal and urinary output were weighed and phosphorus contents determined. Phosphorus intake was 2.85 g per day for each sheep. Apparent phosphorus digestibility was calculated and true phosphorus digestibility was estimated according to three endogenous faecal phosphorus prediction models from the literature. Apparent phosphorus absorption was for soybean meal 0.230 (UT), 0.249 (FT) and 0.235 (FTP), for rapeseed meal 0.126 (UT), 0.193 (FT) and 0.143 (FTP), for sunflower meal 0.041 (UT), 0.182 (FT) and 0.241 (FTP), for groundnut meal 0.127 (UT) and for linseed meal 0.149 (UT). Apparent phosphorus absorption from UT soybean meal was greater than that from other UT meals ( P