Effects of Static or Oscillating Dietary Crude Protein Levels on Fermentation Dynamics of Beef Cattle Diets Using a Dual-Flow Continuous Culture System

by Paloma de Melo Amaral, Lays Débora Silva Mariz, Pedro Del Bianco Benedeti, Lorrayny Galoro da Silva, Eduardo Marostegan de Paula, Hugo Fernando Monteiro, Teshome Shenkoru, Stefanie Alvarenga Santos, Simon Roger Poulson, Antonio Pinheiro Faciola

The objective of this study was to evaluate the effects of increasing dietary crude protein (CP) levels and also comparing the effects of static versus oscillating dietary CP on ruminal nutrient digestibility, ruminal fermentation, nitrogen (N) metabolism, and microbial efficiency in beef cattle diets using a dual-flow continuous culture system. Eight fermenters (1,223 ± 21 mL) were used in a replicated 4 x 4 Latin square design with periods lasting 12 d each (8 d for adaptation and 4 d for sampling). Dietary treatments were: 1) 10% CP, 2) 12% CP, 3) 14% CP, and 4) 10 and 14% CP diets oscillating at 48-h intervals. Experimental diets consisted of 50% orchard hay and 50% concentrate. Fermenters were fed 72 g/d and solid and liquid dilution rates were adjusted to 5.5 and 11%/h, respectively. Data were analyzed using the MIXED procedure in SAS with α = 0.05. Apparent and true ruminal digestibilities of dry matter and organic matter were not affected (P > 0.05) by increasing dietary CP, nor by oscillating dietary CP. Total volatile fatty acids concentration and molar proportions of acetate, propionate, butyrate, valerate, iso-butyrate and iso-valerate were not affected (P > 0.05) by increasing or oscillating dietary CP. Ruminal NH₃-N concentration increased linearly (P 3-N flows and microbial efficiency did not differ when comparing oscillating versus static CP (P > 0.05). However, there was a quadratic effect (P

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