The Effect of Different Dietary Crude Protein Content on Growth Performance, Nutrient Digestibility, and Blood Metabolites of Cull Bali Cows Fed on Urea-Treated Rice Straw

Feeding cull cows with a balanced concentrate is a major strategy to improve meat production and quality. The optimal protein level of the concentrate is rarely determined specifically for indigenous cull Bali cows fed urea-treated rice straw. The present experiment was conducted to investigate the effects of feeding concentrate differing in crude protein (CP) content on the feed intake, nutrient digestibility, and growth performance of cull Bali cows fed urea-treated rice straw. We used 24 thin cull Bali cows that were randomly assigned into three groups of 8 animals to receive concentrates containing different CP levels as treatments, i.e. 12.6% (CP12), 14.2% (CP14), and 16.4% (CP16) at dry matter (DM) basis. The concentrate allowance was 2% live weight (LW) and urea-treated rice straw was offered at 1% LW. The experiment was conducted in a completely randomized design. The measured variables included the intake and digestibility of DM and nutrients, rumen ammonia and volatile fatty acids (VFA) concentration, blood plasma of glucose (GLUC), blood urea nitrogen (BUN), average daily gain (ADG), live weight gain (LWG) and feed conversion ratio (FCR). Dry matter intake (DMI) decreased linearly (P 0.05) with increasing CP content of the concentrate, but the digestibility of dry matter as well as other nutrients was not affected. There was a linear increase in rumen ammonia concentration (P 0.05) with increasing CP content in the concentrate. The ruminal total VFA concentration was not affected (P 0.05) by the treatments, but the concentrations of propionate, butyrate, and n-valerate were lowest (P 0.05) in CP16. The GLUC, BUN and blood profiles, including packed cell volume (PCV) and hemoglobin declined by feeding concentrate with increasing CP levels. The levels of ADG, LWG and FCR were significantly higher (P 0.05) in CP12 than in CP14 and CP16. In conclusion, feeding concentrate containing more than 12.6% CP reduces the intake, rumen parameters, blood metabolites and ADG of cull Bali cows when fed at 2% LW.