Effects of supplementation of wet brewers’ grains and sugarcane molasses to rice straw on rumen degradation efficiency 

Nguyen Xuan Trach 

Hanoi Agricultural University
 nxtrach@hau1.edu.vn

Abstract 

Effects of supplementation of 10% wet brewers’ grains (WBG) and 10% sugarcane molasses (SCM) to untreated (US) or 3% lime plus 2% urea treated rice straw (TS) on rumen degradation efficiency were determined based on in-sacco degradation characteristics of Pangola hay as an independent fibrous substrate. The degradation efficiency as affected by the supplements was also assessed in terms of rumen liquor pH, ammonia (NH₃) and total volatile fatty acids (VFA).

 

It was found that straw treatment significantly (P<0.05) increased 48 h dry matter degradability (48hDMD) of the hay. Both WBG and SCM were effective in increasing degradation rate "c" and 48hDMD (P<0.001). WBG strongly improved "c" and 48hDMD of hay when the fistulated animals were fed either the US or the TS; whereas, SCM only increased these parameters when supplemented to the US, but did not further improve them when the animals were already fed on the TS. Both treatment and supplementation of straw resulted in significantly lower pH values and higher contents of rumen VFA (P<0.001). Supplementation of the TS with WBG resulted in the lowest rumen pH and highest VFA content. But, there were no significant effects of treatment and supplementation on NH₃ content.

 

The results suggest that supplementation of rice straw with 10% WBG is more effective than with 10% SCM in improving rumen cellulolysis. The supplements are more effective on the US compared with the TS.  

Key words: Molasses, rice straw, rumen degradation, wet brewers’ grains

Introduction 

Rice straw is low in nitrogen, vitamins, minerals and soluble carbohydrates. The shortage of those nutrients essential for rumen microbes hampers microbial biosynthesis and thus cellulolysis in the rumen. Supplementation of rice straw with the deficient nutrients should be a strategy to improve utilization of this abundant by-product as feed for ruminants. Brewers’ grains have a high value of available energy and protein content (Preston et al 1973; West et al 1994). Sugarcane molasses (SCM) is apparently a good source of easily fermentable energy. The objective of the present study was therefore to assess if wet brewers’ grains (WBG) and SCM can be used as good supplements to rice straw based diets.  

Materials and Methods

 

Three rumen-fistulated oxen were fed in a random order on 6 diets arranged according to a 2x3 factorial design using untreated (US) and 3% lime plus 2% urea treated rice straw (TS) without or with 10% WBG or 10% SCM on a dry matter basis. For each diet, the animals underwent a preliminary period of 15 days to stabilize the rumen ecosystem, followed by 10 days for the in-sacco incubation of samples of Pangola hay as a fixed substrate. The nylon bag technique as described by Ørskov et al (1980) was applied.

 

Rumen liquor samples were collected on two consecutive days at the end of each feeding period between three and four hours after the morning feeding. Samples were taken with a 50 ml syringe connected to a 50 cm long plastic tube introduced through the fistula. The pH value of rumen liquor was determined immediately after the sample was taken using a portable pH meter. Each sample of 25 ml was then placed in a 30ml bottle acidified with 5 drops of concentrated sulphuric acid and then stored at -20^oC until analysed for ammonia (NH₃) and total volatile fatty acids (VFA). Ammonia was separated from rumen liquor by steam distillation, collected in boric acid solution and determined by titration with standard acid (Preston 1995). Total VFA was determined by steam distillation according to AOAC (Cunniff 1997).

 

Data were subjected to analysis of variance (ANOVA) based on a fixed 2x3 factorial model, using the General Linear Model (GLM) procedure of the SAS (1996). Animal was also added to the model as random blocking. Comparisons of group means were made using the LSMEANS statement with the PDIFF option.

Results and Discussion

 

Degradation kinetics of hay as a fixed substrate incubated in the rumen of cattle fed on the 6 experimental diets is characterized as in Table 1. Straw treatment significantly (P<0.05) increased 48 h dry matter degradability (48hDMD). Supplementation was effective on increasing both degradation rate "c" and 48hDMD (P<0.001). The interaction between treatment and supplementation was found to be significant for 48hDMD (P<0.01). Both treatment and supplementation did not affect water-insoluble degradability (B) and potential degradability (A+B). The lag time (L) was reduced by supplementation (P<0.05). WBG strongly improved "c" and 48hDMD of hay when the fistulated animals were fed either the US or the TS. Whereas, SCM only increased these parameters when supplemented to the US, but did not further improve them when the animals were already fed on the TS. 

 

It is also possible to see from Table 2 that both treatment and supplementation of straw resulted in significantly lower pH values and higher contents of rumen VFA (P<0.001). Supplementation of the TS with 10% WBG resulted in the lowest rumen pH and highest VFA content. The interaction between treatment and supplementation (P<0.001) reduced their additive effects on VFA.  There were no significant effects of treatment and supplementation on NH₃ content.  

 

The in-sacco study apparently demonstrated very good associative effects on rumen cellulolysis due to WBG. First, as a source of easily fermentable structural carbohydrates (Tamminga et al 1990; Ojowi et al 1997), WBG probably provides readily available energy without detrimental effects to rumen cellulolytic microbes (Silva and Ørskov 1988; Silva et al 1989). Also, as a protein supplement, WBG may serve as a steady supply of amino acids and other growth factors for the optimum growth and cellulolytic activity of rumen microbes (Ojowi et al 1997).

 

Supplementation of the US with 10% SCM  improved rumen cellulolysis in the in-sacco study. A possible explanation is that a small amount of soluble sugars added to an US-based diet, which is short of available energy, would be beneficial for effective capture of ammonia for microbial protein synthesis and thus improved straw utilization (Doyle et al 1986). Like WBG, SCM in this case could help as a readily fermentable energy source to improve the rumen ecosystem adequacy in a positively associative manner (Silva and Ørskov 1985; Ørskov and Ryle 1990; Chenost and Kayouli 1997). However, this level of SCM supplemented to the TS did not further improve rumen cellulolysis and thus apparent digestibility. It is possible that when straw is treated, some fermentable energy becomes readily available, energy supplementation is then no longer synergistic; only additive effects may count. The TS has been reported to contain sufficient amounts of available b-glucans to allow for the synthesis of cellulolytic bacteria (Durand 1989).  

Acknowledgements

 

The present study was carried out with the financial support from the Norwegian Council of Universities' Committee for Development Research and Education (NUFU). The author would like to thank Prof. Cu Xuan Dan, Dr M Mo, Dr F Sundstøl, Dr Le Viet Ly and Dr N P Kjos for their contributions to the present study.

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