Effects of carbohydrate and nitrogen supplementation on fermentation of cheatgrass (Bromus tectorum) in a dual-flow continuous culture system1

Abstract

Cheatgrass (CG; ), an introduced winter annual grass, is an aggressive invader of the sagebrush community in the Western United States. Because of its greater flammability, mature CG constitutes a fire hazard leading to repeated wildfires. One fuel-reduction strategy is livestock grazing. The objective of this study was to evaluate the effects of urea, molasses, or a combination of urea and molasses supplementation of a CG-based diet on digestibility, microbial fermentation, bacterial protein synthesis, and nutrient flow using a dual-flow continuous culture system. Eight fermenters were used in a replicate 4 × 4 Latin square design with four 10-d experimental periods. Experimental treatments (DM basis) were 1) forage only (CON), 2) CG plus urea alone (URE; 1.36% urea), 3) CG plus molasses alone (MOL; 15.9% molasses), and 4) CG plus urea and molasses combined (URE+MOL; 1.28% urea plus 19.3% molasses). Each fermenter was fed 72 g/d of DM, and data were analyzed using the GLIMMIX procedure of SAS (SAS Inst. Inc., Cary, NC). The true digestibilities of NDF and ADF were not affected by diets ( > 0.05). Molasses-containing diets had greater true digestibility of OM ( = 0.02). However, true digestibility of CP was increased when molasses was fed alone ( < 0.01). Molasses-containing diets had lower pH ( < 0.01) and greater VFA concentrations ( < 0.01) compared to those of the other diets. The URE+MOL diet resulted in a greater VFA concentration ( < 0.01). Propionate concentration increased ( < 0.01), whereas acetate concentration decreased ( < 0.01) when molasses alone or in combination with urea was added to the diets. Supplying molasses alone resulted in greater ( = 0.03) total branched-chain VFA compared to the other diets. The concentration of NH-N and total N flow increased ( < 0.01) in response to urea supplementation and was greater ( < 0.01) when urea alone was supplemented in the diet. On the other hand, molasses-supplemented diets yielded more non-ammonia N ( < 0.01) and bacterial N ( = 0.04). Supplementation had no effect ( = 0.83) on bacterial efficiency. Results from this study indicate that the addition of urea and molasses in a CG-based diet could improve nutrient supply to animals, notably VFA supply and microbial N supply; however, in the levels tested in this study, it did not improve CG utilization as assessed by NDF digestion.

Unveiling the relationships between diet composition and fermentation parameters response in dual-flow continuous culture system: a meta-analytical approach

“…As NDF concentration in the diet increases, typically dietary NFC decreases, which could explain the response observed in this study. This response of propionate to increased dietary NDF has been widely reported in vivo ( Batajoo and Shaver, 1994 ; Schwab et al, 2006 ) and in DFCCS studies ( Bas et al, 1989 ; Benedeti et al, 2015 ; Silva et al, 2017 ). Therefore, according to the present data, propionate and acetate response to dietary NDF found in DFCCS studies follows a similar pattern as in vivo.…”

“…The DFCCS is a long-term fermentation system with tight variable control, which makes it suitable for evaluating digestion processes. It was developed by Hoover et al (1976) and recently modified to test beef ( Benedeti et al, 2015 ; Amaral et al, 2016 ; Silva et al, 2017 ) and dairy diets ( Paula et al, 2017 ; Brandao, Dai et al 2018; Brandao, Silva et al, 2018).…”

Supplementation of Molasses-Based Liquid Feed for Cattle Fed on Limpograss Hay

“…Forage intake was constant at different levels of liquid supplementation, which indicates, at different levels of supplementation, that there was an additive effect of total intake on the corresponding levels of molasses provided [ 3 ]. The use of low quality forages, with NDF concentration above 60% and CP below 6%, can reduce intake, as a result of the low digestibility of the fibrous fraction [ 17 ]. In the present experiment, the ruminal pH values ( Figure 1 ) were always above 6.5 for all supplementation levels, not representing a limiting factor for forage intake, which may be a justification for the non-difference between intake [ 29 ].…”

“…CP digestibility without the presence of molasses was 34 percentage points lower when compared to the other treatments. According to [ 17 ], this may indicate that molasses energy was used to release protein in the diet content, resulting in greater true CP digestibility.…”

“…The optimal concentration of NH 3 -N for the maximum fermentation rate of forage-based diets is related to the availability of an energy-producing substrate [ 16 ]. Silva et al [ 17 ], evaluating the effects of urea, molasses and their combinations, found that the urea + molasses combination resulted in a greater concentration of VFA. This result indicated that the concentration of short-chain volatile fatty acids (SCVFA) was greater when molasses was fed together with urea, compared to when supplied separately.…”