Livestock Research for Rural Development (15) 3 2003

Citation of this paper

Responses of growing cattle to wet brewers’ grains or sugarcane molasses supplemented to diets based on untreated or treated rice straw

Nguyen Xuan Trach

Hanoi Agricultural University


Two 3-month feeding trials were carried out to determine responses of growing cattle to 10% wet brewers’ grains (WBG) or 10% sugarcane molasses (SCM) supplemented to diets based on either untreated (US) or 3% lime plus 2% urea treated rice straw (TS).

Supplementation with SCM and, especially, WBG improved intake and digestibility of rice straw as well as the average daily gain (ADG) of young beef cattle. In Trial 1, ADG of the groups fed simply on US and TS were -107 and 154 g head-1 day-1, respectively. When the US and TS diets were supplemented with WBG or SCM, ADG were increased to 302 or 180 and 476 or 347 g head-1 day-1, respectively. In Trial 2, the respective figures were 146 and 339 head-1 day-1 for US and TS based diets, which included 10% green grass and 10% whole cotton seed in addition to rice straw, and increased to 419 or 284 and 557 or 432 g head-1day-1, respectively, when WBG or SCM was added.

The present study suggests that supplementation of rice straw with 10% WBG is more effective than 10% SCM and that those supplements can result in better effects when supplemented to the US in comparison with the TS.

Key words: Growing cattle, molasses, rice straw, wet brewers’ grains


Low degradability of rice straw due to its high lignification and shortages of essential nutrients for rumen microbes has lead to the search for appropriate treatments and supplements to improve its nutritional value. There has been substantial attention to treatment, but less to supplementation strategies. The first limitation of straw is the imbalance of nutrients both for rumen microbes and for the host animal (Preston and Leng 1987). Therefore, supplements which are nutritionally synergistic with rice straw are of great interest to maximize the rate and extent of fermentation of its cell walls, improve voluntary intake and thus increase absorbed nutrients. In search for such supplements, the present studies used wet brewers’ grains (WBG) and sugarcane molasses (SCM) in an effort to correct the nutrient imbalance of rice straw. Brewers’ grains were anticipated to be good in this respect, based on their high values of available energy and protein content (Preston et al 1973; West et al 1994) as well as easily fermentable fibres (Tamminga et al 1990. Ojowi et al 1997). SCM was considered to be an easily fermentable supplement that provided readily energy to cellulolytic microbes, thus improving rumen fermentation of straw (Doyle et al 1986; Preston 1995; Chenost and Kayouli 1997).

Materials and methods

Two feeding trials were carried out for 90 days each following 15 day adaptation periods. In each trial, 24 young bulls of a small tropical breed (Bos indicus) at 12 to16 months of age and 133.4±3.4 or 130.4±2.1kg live-weight (LW) were divided into 6 groups that were fed diets in a 2 x 3 factorial design. Three groups were fed on untreated straw (US) and the other three on TS, which had been made by mixing rice straw with 2% urea plus 3% quick lime at 50% moisture and stored hermetically for 3 weeks. Within each type of straw, one group of bulls received no supplement (Control), one received 10% WBG and the other 10% SCM on a DM basis in proportion to rice straw. US was sprayed with 16 g urea dissolved in 0.8 l water per kg prior to feeding to equalized N and moisture levels with the TS. All groups were supplemented with 10g of bone meal and 10g of a commercial mixture of minerals and vitamins (A, D, E) per kg straw DM. The diets used in Trial 2 were similar to those used in Trial 1, except that in all groups 10% elephant grass (EG) and 10% whole cottonseeds (WCS) on a DM basis of rice straw were included. Diets were offered ad libitum to animals housed in individual pens with new feed being given at 8 a.m. and 4 p.m. every day. At the beginning and the end of the trials the animals were weighed for two consecutive days at 7 a.m. before the morning feeding to measure average daily gain (ADG).

There were three feed and faeces collection periods of 7 days each in the middle of each month of the trials for measurement of intake and digestibility according to conventional procedures. Feeds and faeces samples were analysed for DM and total ash to compute apparent organic matter intake (OMI) and digestibility (OMD).

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). Comparisons of group means were made using the LSMEANS statement with the PDIFF option.

Results and discussion

Responses of growing cattle in the two feeding trials in terms of OMI, OMD and ADG are presented in Tables 1 and 2. Supplementation of straw with 10% WBG or SCM gave different intake responses between types of straw and between trials. In Trial 1 both WBG and SCM significantly increased OMI of US (P<0.05) but not that of TS, which had already improved by treatment. No significant differences in straw OMI were found between the two supplements. The OMI of both US and TS was apparently higher in Trial 1 than in Trial 2 in which 10% EG and 10% WCS were also included in the basal diet for all groups.

The effect of supplementation on apparent digestibility was different between the two trials, two types of straw as well as two supplements. In Trial 1, both WBG and SCM highly improved OMD of US and US-based diets. Interactions between treatment and supplementation were also found to be significant (P<0.05). For TS, which had a higher OMD than US, WBG supplementation continued to improve straw OMD to a significant extent, but SCM supplementation did not improve it any more. Combination of treatment and 10% WBG supplementation resulted in the highest straw OMD (60.7%) as well as total diet OMD (62.5%) in this trial. In Trial 2, WBG also showed significant positive effects on OMD of both US and TS, whereas SCM had almost no effect on OMD of both types of straw. Unlike in Trial 1, no significant interactions between treatment and supplementation on straw and diet OMD were found in Trial 2.

In both trials, ADG was dramatically increased by straw treatment (P<0.001) and supplementation (P<0.001). There was a significant interaction between treatment and supplementation in Trial 1 (P<0.01), but not in Trial 2 (P>0.05). In both trials, it was consistently clear that WBG was much more effective than SCM in improving ADG. On an average, the ADG of animals given WBG were 126 g and 130 g head-1 day-1 higher than that of those given SCM in Trial 1 and Trial 2, respectively. It was also apparent that the effects of straw treatment and supplementation were greater in Trial 1 than in Trial 2.

Table 1. Organic matter intake (OMI), organic matter digestibility (OMD) and average daily gain (ADG) in growing beef bulls fed on untreated or 3% lime plus 2% urea treated straw without or with 10% wet brewers’ grains (WBG) or sugarcane molasses (SCM) in feeding trial 1


Untreated straw

Treated straw

No supplement



No supplement



Initial weight, kg head-1














Diet OMD, %







Straw OMD, %







ADG, g head-1day-1







NB: Means by diet in the same row having a similar superscript (a, b, c, d) are not significantly different; LW: live weight


Table 2: Organic matter intake (OMI), organic matter digestibility (OMD) and average daily gain (ADG) in growing beef bulls fed on untreated or 3% lime plus 2% urea treated straw without or with 10% wet brewers’ grains (WBG) or sugarcane molasses (SCM) in feeding trial 2


Untreated straw (US)

Treated straw (TS)


No supplement



No supplement



Initial weight (kg head-1)







OMI (% LW)







Diet OMD  (%)







Straw OMD (%)







ADG (g head-1day-1)







NB: In Trial 2, 10% whole cottonseed and 10% green grass were added to the basal diets; Means by diet in the same row having a similar superscript (a, b, c, d, e) are not significantly different; LW: live weight


It is of interest from the present feeding trials that high growth rates (for a small tropical breed) were obtained when rice straw based diets were supplemented with 10% WBG. As a source of easily fermentable structural carbohydrates (Tamminga et al 1990; Ojowi et al 1997), WBG probably provides readily available energy to rumen cellulolytic microbes without detrimental effects (Silva and Ørskov 1988; Silva et al 1989). Also, as a protein supplement, WBG may possess two potential advantages: (1) a steady supply of amino acids and other growth factors for the optimum growth and cellulolytic activity of rumen microbes (Ojowi et al 1997), and (2) a source of relatively undegradable protein to escape rumen degradation to a large extent (Tamminga et al 1990; Ojowi et al 1997; Pereira et al 1998) to directly provide intact protein for the host animal. The positive associative effects at the rumen level may be diminished when other feeds with the nutritionally correcting factors are provided in the basal diets (Trial 2), but the effects of intact protein should always remain at the post-rumen level.


Supplementation of US with 10% SCM increased OMD of straw and ADG of cattle in Trial 1. A possible explanation is that a small amount of soluble sugars added to a US-based diet, which is short of available energy, would be beneficial for effective captures 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 in a positively associative manner (Silva and Ørskov 1985; Chenost and Kayouli 1997). However, this level of SCM supplemented to TS did not further improve OMD. 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. TS has been reported to contain sufficient amounts of available b-glucans to allow for the synthesis of cellulolytic bacteria (Durand 1989).


If part of the treatment effect is synergistic stimulation of rumen fermentation due to easily fermentable energy made available, the relative advantage of TS over US would be less marked due to supplementation because the US based diet can receive the limiting nutrients from the supplements (Schiere et al 1985). This would also be the case of Trial 2 where the effects of WBG or SCM supplemented to US were not as dramatic as in Trial 1 because of the presence of EG and WCS in the basal diets. It may also be a reason for the less apparent differences between US and TS in terms of responses to both WBG and SCM supplementation Trial in 2. On the other hand, comparing between WBG and SCM in this situation, both supplements would have been neutral as far as energy is concerned, but microbial protein production from sugar fermenting bacteria was supposed to be low and there was likely to be some amount of digestible undegraded protein from WBG; so protein supply to the small intestine as a result of WBG supplementation must have been of greater importance in explaining the better responses to WBG (Ørskov E R, personal communication).


From the present study it can be concluded that


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 also like to thank Prof. Cu Xuan Dan, Prof.. Le Viet Ly, Dr. Mo, Prof. Sundstøl, and Dr. Kjos for their contributions to the study.


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Received 6 March 2003; Accepted 17March 2003

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