Ruminal disappearance of nutrients and ruminal phosphorus concentration in cows fed concentrates treated with lactic acid, with or without inorganic phosphorous supplementation

Abstract

Our previous work indicates that lactic acid (LA) treatment of concentrates promotes ruminal fermentation output, and ruminal fungi benefit from LA treatment with inorganic phosphorous (iP) supplementation in dairy cows. In continuation of the previous study, the present work investigated whether treating concentrates with LA and iP supplementation would affect the ruminal release of nutrients of the treated concentrates as well as the fibre degradation in the rumen. Three dietary treatments were tested in a Latin square trial with 6 rumen cannulated dry Holstein cows. Diets were a control diet, without LA treatment, supplemented with iP (CON+iP), and two LA-treated diets: one with (LA+iP) and another without inorganic P supplementation (LA-iP). Monocalcium phosphate and a conventional vitamin-mineral premix were supplemented in CON+iP and LA+iP diets, while LA-iP contained no iP source. All diets were offered as a total mixed ration (forage to concentrate ratio of 53:47 on dry matter (DM) basis) and contained total P levels of 4.1 g/kg DM for LA-iP and 4.7 g/kg DM for both iP supplemented diets. The in situ ruminal disappearance of nutrients in the respective concentrate mixtures and the hay incubated as substrates, as well as the P concentrations of the free ruminal liquid and solid rumen digesta were studied. Data showed that LA-treatment increased the solubility and thus sped up ruminal disappearance as well as increased the effective rumen disappearance of ash, P and crude protein of the concentrates, independent of iP supplementation. The overall in situ disappearance of starch was similar amongst all treatments. The in situ disappearance of nutrients of the hay was minimally affected by LA treatment and the iP supplementation. The ruminal P concentrations were least in LA-iP compared to CON+iP and LA+iP. In conclusion, LA treatment improves ruminal degradation of the treated concentrates, especially P, other minerals and crude protein. With the current total dietary P levels fed, neither LA treatment nor iP supplementation affects the overall ruminal fibre degradation.