The objective of this experiment was to study the interaction between feeding frequency and supplementation of a protein-deficient diet with an undegradable protein and energy source on milk production and composition. Eight Holstein cows were used in a 2 × 2 factorial arrangement, using a replicated 4 × 4 Latin square design with 14-d experimental periods. The main factors were feeding frequency of the basal diet (two vs. seven times daily) and the addition of a protein-energy supplement fed in seven meals daily. Intake of the basal diet was individually restricted to 95% of previous ad libitum intake. The supplement consisted of 1.71 kg of Pro-Lak® (70% rumen-undegradable protein) and 0.94 kg of dried molasses. The basal diet provided 69, 89, 54, and 95% of the daily requirements of crude protein, rumen-degradable and rumen-undegradable proteins and NEL, respectively. Milk protein yield increased (P = 0.06) by 4% with increased feeding frequency. Milk and milk protein yield both increased (P < 0.01) by 12% with the supplement, but no interaction between feeding frequency and the supplement was observed. Urinary excretion of purine derivatives, an index of rumen microbial protein synthesis, was not affected by treatments. Thus, the results indicate that microbial growth was not affected by meal frequency or the protein-energy supplement, maybe due to the high supply of rumen-degradable protein from the basal diet. The effect of increasing meal frequency on milk protein yield might be related to an increased post-ruminal digestibility of organic matter. Key words: Dairy cows, feeding frequency, milk production, protein, purines
Incremental amounts of rumen-protected histidine increase plasma and muscle histidine concentrations and milk protein yield in dairy cows fed a metabolizable protein-deficient diet
