Effects of fungal phytase addition, formaldehyde treatment and dietary concentrate content on ruminal phosphorus availability

Abstract

Two trials were carried out to determine the effects of (i) formaldehyde treatment, (ii) concentrate supplementation, and (iii) fungal phytase addition on degraded dry matter (D-DM) and rumen phosphorus solubility (S-RP) as measured by the nylon bag technique. In trial 1, rumen phosphorus solubility of untreated (UT) and formaldehyde-treated (FT) rape seed meals (RSM), UT and FT soybean meals (SBM) was measured in lactating goats by the nylon bag method. The goats were fed three different diets consisting of 70% forage or 70% concentrate or 70% concentrate with addition of fungal phytase (2000 IU). In trial 2, rumen phosphorus solubility of UT- and FT-RSM, SBM and wheat (W) was measured in dry cows by the nylon bag method. The cows were fed two different diets consisting of 70% forage or 70% forage with addition of fungal phytase (2000 IU). Both trials demonstrated a decrease in S-RP after formaldehyde treatment ( P<0.01, W: 76.1 versus 91.9%, SBM: 58.6 versus 74.9%, RSM: 37.7 versus 62.1%, for cows fed the 70% forage diet). Concentrate supplementation reduced ( P<0.01) the D-DM from UT-RSM (61.6 versus 82.0%) and increased ( P<0.01) the S-RP from both types of RSM (UT: 81.3 versus 69.6% and FT: 69.1 versus 53.5%). Phytase supplementation to the concentrate diet reduced ( P<0.1) D-DM from both types of SBM (UT: 63.6 versus 70.4% and FT: 50.6 versus 58.8%), but not with either type of RSM. It increased S-RP from UT-SBM and UT-RSM ( P<0.1) and from FT-RSM (77.7 versus 69.1%, P<0.01). Phytase supplementation in the forage diet (trial 2) modified S-RP only from FT-W (79.8 versus 76.1%, P<0.01). Rumen fermentation parameters changed as expected with a concentrate-supplemented diet. Fungal phytase did not affect rumen fermentation parameters with the forage diet (trial 2) whereas it increased the molar proportion of propionate (28.4 versus 23.4%, P<0.01) and decreased the molar proportion of butyrate (12.4 versus 16.3%, P<0.01) with the concentrate diet (trial 1). The reasons for a possible limitation of rumen phytase activity were discussed. As phytate phosphorus bonds with starch, phytase supplementation may have improved starch degradation explaining the observed fermentation parameters. Fungal phytase activity being highly dependent on pH, the lower rumen pH induced by concentrate diets probably led to increased phytase activity, which would explain the rise in S-RP from the FT meals. Inversely, the rumen pH induced by forage diet was probably less optimal for phytase activity.