Effect of soluble nitrogen level in the ration on protein utilization by high producing dairy cows

Abstract

Twenty Holstein cows, six to 20 weeks in lactation were randomly allotted to four treatments in a complete block design to determine the effect of nitrogen solubility on protein utilization by dairy cows fed rations differing in soluble nitrogen content. Duration of the experiment was eight weeks following one week for adaptation. The four levels of soluble nitrogen were obtained by selecting from natural feedstuffs. Four complete rations of concentrate corn silage were formulated and fed ad libitum. The desired and analyzed nitrogen solubilities were a) N-SOL 15, 18.5%; b) N-SOL 20, 24.68%; c) N-SOL 30, 35.59%; d) N-SOL 40, 46.35%, respectively. All four rations were similar in energy, protein, crude fiber, calcium and phosphorus content. Two five-day nitrogen balance trials were conducted during the eight-week trial using randomly selected cows (two cows per treatment) each period. In vitro dry matter and protein disappearance were determined for the nine weekly composited feed samples.