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

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

doi:10.1371/journal.pone.0169170

Abstract

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 < 0.01) in response to increasing dietary CP. Total N, non-ammonia N, and rumen undegraded protein flows did not differ among treatments or between oscillating dietary CP and static 12% CP. Microbial N and NH3-N flows and microbial efficiency did not differ when comparing oscillating versus static CP (P > 0.05). However, there was a quadratic effect (P < 0.05) for these variables when dietary CP was increased. These results indicate that either ruminal microorganisms do not respond to oscillating CP levels or are capable of coping with 48-h periods of undernourishment.

Highlights

Ruminant animals convert about 20–30% of their dietary nitrogen (N) into animal protein and about 70–80% is excreted in the urine and feces [1] [2] [3]
The results of the present study indicate that increasing dietary crude protein (CP) from 10 up to 14% or oscillating dietary CP between 10–14% at 48-h intervals have no effects on total volatile fatty acids (VFA) concentration and individual VFA molar proportions in beef cattle diets
The results of the present study indicate that increasing dietary CP from 10 up to 14% or oscillating dietary CP between 10–14% at 48-h intervals have no effects on rumen-undegraded protein (RUP) supply in beef cattle diets and this may be related to the source of CP used, which is highly degradable in the rumen

Summary

Introduction

Ruminant animals convert about 20–30% of their dietary nitrogen (N) into animal protein and about 70–80% is excreted in the urine and feces [1] [2] [3]. Microorganism, and plant species experience seasonal periods of undernourishment followed by periods of nutrient abundance. This nutrient oscillation seems to affect the homeostatic and homeorhetic processes in a manner that promotes a period of accelerated growth previously defined as compensatory growth [10] [11] [12]. The mechanisms associated with this enhanced N utilization have been mostly studied from the host animal standpoint

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