Effect of imbalance between energy and nitrogen supplies on microbial protein synthesis and nitrogen metabolism in growing double-muscled Belgian Blue bulls.

Six double-muscled Belgian Blue bulls (initial weight: 345 +/- 16 kg) with cannulas in the rumen and proximal duodenum were used in two juxtaposed 3 x 3 Latin squares to study the effect of a lack of synchronization between energy and N in the rumen on microbial protein synthesis and N metabolism by giving the same diet according to three different feeding patterns. The feed ingredients of the diet were separated into two groups supplying the same amount of fermentable OM (FOM), but characterized by different levels of ruminally degradable N (RDN). The first group primarily provided energy for the ruminal microbes (14.6 g of RDN/kg of FOM), and the second provided N (33.3 g of RDN/kg of FOM). These two groups were fed to the bulls simultaneously or alternately with the aim of creating three different time periods of imbalance (0, 12, or 24 h) between energy and N supplies in the rumen. The introduction of imbalance affected neither microbial-N flow at the duodenum (P = 0.65) nor efficiency of growth (P = 0.69), but decreased (P = 0.016) the NDF degradation in the rumen 12.2% for a 12-h period of imbalance. N retention was not affected by imbalance (P = 0.53) and reached 57.8, 58.5, and 54.7 g/d, respectively, for 0-, 12- and 24-h imbalance. It seems that the introduction of an imbalance of 12 or 24 h between energy and N supplies for the ruminal microbes by altering the feeding pattern of the same diet does not negatively influence microbial protein synthesis or N retention by the animal. Nitrogen recycling in the rumen plays a major role in regulating the amount ofruminally available N and allows for continuous synchronization of N- and energy-yielding substrates for the microorganisms in the rumen. Therefore, a lack of synchronization in the diet between the energy and N supplies for the ruminal microbes is not detrimental to their growth or for the animal as long as the nutrient supply is balanced on a 48-h basis. Thus, these dietary feeding patterns may be used under practical feeding conditions with minimal effect on the performance of ruminant animals.