The requirements for rumen-degradable protein per unit of fermentable organic matter differ between fibrous feed sources

Abstract

Ruminant feed evaluation systems use constant minimum requirements of rumen-degradable protein (RDP) and often relate this to apparently degradable organic matter (OM). However, studies with tropical forages indicate that RDP: apparently degraded OM might not be constant across high-fiber diets. This was tested with semi-continuous ruminal cultures (Rusitec) using dried contrasting low-protein fiber sources: brachiaria hay (high in fiber, medium lignified), apple pomace (medium in fiber, highly lignified), and sugar beet pulp (medium in fiber and lignification). Each feed was incubated at 14 g dry matter day−1 with 0, 0.85, 1.7, 3.4, 6.8, 13.6, or 27.2 mg g−1 urea. The amount of urea needed to reach a similar basal concentration of ammonia in the incubation fluid was tested for each feed in advance. Apparent fiber and OM degradability were determined after 48 h of incubation. Data was evaluated by regressions and analysis of variance. The response curve of incubation fluid ammonia to urea supplementation was similar in slope in all feeds. Plateaus in apparent OM degradability in relation to ammonia concentration were determined. The ammonia concentration where apparent OM and fiber degradability reached 95% of maximum was approached in the order of pomace < pulp < hay. With regard to fiber degradability, a plateau was reached at ≥ 80 g kg−1 crude protein only with hay and pomace, whilst a linear relationship existed between RDP and OM degradation for pulp. In hay the ratio RDP: OM degraded was equal to 1.6 but was only 1.0 in the other feeds. There was no obvious lack of branched short-chain fatty acids at low RDP. Thus, the hypothesis was confirmed but the demand for RDP seems even higher in tropical forage compared to food industrial byproducts. The efficiency of urea to promote apparent OM and fiber degradation was also variable. Thus, it seems that minimum thresholds of either RDP or ruminal ammonia concentration may not be reflected appropriately by constants.

Variability in microbial population and fermentation traits at various sites within the forestomach and along the digestive tract as assessed in goats fed either grass or browse

“…In addition, the archaeal copy numbers measured after 3 to 4 weeks on the browse diet may not reflect the fully browse-adapted methanogen population because rumen methanogens, in contrast to rumen bacteria, were reported to require an adaptation period of more than 4 weeks (Williams et al, 2009). The NH 3 concentration found in the rumen of grass-fed goats was critically low as it was close to the minimum requirement for optimal microbial protein synthesis (Soliva et al, 2015). However, when considering that its peak would have occurred few hours after feeding (Anantasook et al, 2013), NH 3 concentrations still might have been sufficiently high.…”

“…The higher nitrogen availability might also have favoured the growth of the fibrolytic bacteria (Soliva et al, 2015), which could explain why F. succinogenes and, in tendency, R. flavefaciens were more abundant when browse was fed. Consistent with the corresponding presumed higher H 2 availability, the methanogen abundance tended to be greater in the rumen of browse-fed goats as well.…”

The Type of Forage Substrate Preparation Included as Substrate in a RUSITEC System Affects the Ruminal Microbiota and Fermentation Characteristics

“…The rumen inoculum was collected on the initial day of the experiment from one ruminally fistulated ( Soliva et al, 2011 , 2015 ) Holstein dairy cow (9 years old, 750 kg). The donor animal was housed at The University of Sydney Corstorphine Dairy farm and was cared for in accordance with the guidelines of The University of Sydney Animal Ethics Committee (Project number 2015/835).…”

Supplementation of Pelleted Hazel (Corylus avellana) Leaves Decreases Methane and Urinary Nitrogen Emissions by Sheep at Unchanged Forage Intake

“…This might have resulted in a deficiency of the supply of rumen-degradable protein (RDP). A deficiency of RDP is especially impairing to the activity of the fibre degrading rumen microbes 31 . However, as the decline with increasing hazel leaf proportions was mostly linear for OM and NDF digestion and, therefore, also occurred with the lower level of leaves, a RDP deficiency with the high leaf proportion seems unlikely.…”

“…The amounts of diets offered provided 1.6 times the recommended DM supply for the maintenance requirements of adult female sheep 40 . The pellets were not balanced for CP because the CP content in the complete diets (≥13.2% CP in DM) was always higher than the threshold where the RDP supply is assumed to become critical 31 , although this did not consider possible RDP declines by tannin-protein bonds. Half of the daily portion of the experimental pellets was fed at 08:00 h and the other half at 15:00 h. Around 30 min later, the corresponding proportion of the hay was offered, a time when most to all of the pellets had been consumed.…”