In a recent experiment with young beef cattle, three types of straw were used: a 5% urea treated wheat straw (AS), an untreated wheat straw (US), and a microbial fermented wheat straw (MS). Thirty Simmental-Chinese Yellow cross beef cattle, approximately 12 months old and weighing 200 kg, were randomly allocated to 3 treatments and received one of the three straws as basal diet. A daily supplement of 2.5 kg concentrate, consisting of 40% cottonseed cake, 40% maize and 20% wheat bran was givento all animals. The feeding trial lasted 60 days to assess intake, live- weight gains and feed conversion. Faeces were collected during the last 7 days to determine in vivo apparent digestibility. In sacco rumen degradability of the straws was determined with rumen- fistulated animals.

The mean values for daily live weight gain (calculated from the regression of live weight on time on experiment) were: 672, 1201 and 1164g/d for the untreated, 5% urea and microbial treatment, respectively. Mean values for apparent digestibility of diet dry matter (30% concentrate; 70% straw) were: 0.48, 0.54 and 0.55, for the three treatments

It appeared that the microbial treated straw has potentially the same feeding value as straw treated with urea. Further studies are needed to examine the changes in chemical composition caused by microbial fermentation, its effect on the rumen environment and the interaction with effects of supplementation.

In most developing countries the feed resources for ruminant production are predominantly based on crop residues especially cereal straws. Thus the upgrading of straw quality is still a central issue as a strategy for improving ruminant livestock production (Preston and Leng 1987). During the last two decades both scientists and extension workers have shown great interest in chemical and physical treatment of straw (Sundstol and Owen 1974). The ammoniation method using urea has received major attention as an appropriate system for developing countries (Owen and Jayasuriya 1989a). However, the success of ammonia treatment as well as other chemical methods in application on the farm level has generally been disappointing. There are several reasons for this, but the economic constraints may be the main one (Devendra 1991; Owen and Tayasuriya 1989b). Zhang Weixian (1994) developed an economic model for the ammonia treated straw feeding system and concluded that if the price ratio between urea-ammonia and concentrates rose above 2.5:1, this system would not be profitable. In the meantime, in many developing countries the urea:concentrate price ratio has already been close to this figure. In China a breakthrough occurred in the application of urea treatment by small farmers during 1987-1992 (Orskov and Sundstol 1990; Dolberg and Finlayson 1993). The reason was that the farmer could get the urea at a subsidized price under the country's planned economic system. From 1993 onwards, however, China has promoted the so-called market economy. The farmer is no longer getting the subsidized urea and as a result they are facing the same problem as other developing country farmers. For instance, before 1993 the urea price was less than 1000 yuan per tonne versus concentrates at 1000 yuan per tonne, but from 1994 the urea price has risen up to 2000 yuan per tonne while the price of concentrate is still at 1000 yuan per tonne.

It is therefore necessary to develop alternative treatment technologies for ruminant livestock production. Many attempts have been made by scientists to find other efficient approaches to this problem. The use cereal-based concentrates is not along term solution because with a large and increasing human population and limited grain production, the animal production industry in China must direct its attention toward the use of crop residues whoch totals some 570 million tonnes per annum. It is estimated that at the moment the utilization rate for livestock feed is less 30%. Some 15% is consumed by the paper industry, the remainder being either used as a fuel to cook food in the remote areas or burnt in the field after harvesting (Liu Jiang 1991; Zhang Weixian 1995b).

A promising alternative to urea treatment is a microbial fermentation method which has been developed recently in China (ref 19??). This method is simple in application and is of low cost, and the farmer can use the same urea-ammonia treatment facilities to carry out the process.

However, although the possibility of a biological method of straw treatment has a great appeal as an alternative to the use of expensive (in terms of money and energy) chemicals and environmental pollution (Jackson 1978), so far, despite encouraging laboratory experiments, none of the microbial processes has has an impact with farmers (Sundstol 1988). Many failures of biological straw treatment have been described in the literature, although some improvement in nutritive value seemed possible, this was usually at the expense of a significant part of the organic matter being fermented in the process (Tamminga 1993). Thus, before any new biological fermentation method is applied extensively, many aspects need further investigation.

The objective of this study was to evaluate the new microbial method as a technologically feasible alternative to the chemical treatment system under conditions simulating those of the commercial farmer.

The urea treatment method used in this experiment was to add 5 kg urea and 60 kg water per 100 kg air dry straw. After the urea was dissolved in the water, the solution was uniformly sprayed on the wheat straw. Then the straw was put into a cement pit and covered with plastic film, and the edges were sealed with mud. The ensiling period was 25 days with air temperatures of 20-30°C. Before the feed was used, the ammoniated straw was allowed to aerate for one day to allow for the escape of volatile ammonia.

An inoculum of 3 g freeze-dried and vacuum packed microbial preparation and 600 kg of 1% saline water was added to 1 tonnr chopped wheat straw. As an initial step, the microbial inoculum and 2 g sugar were put into 0.5 kg water for 2 hours to revive the microbes. After that the microbial solution was put into the prepared saline water and the solution sprayed on the straw. The next step was the same as used in making urea-treated straw, namely putting the wet straw into the cement pit and covering with plastic film, and sealing the edges with mud. A layer of soil (20-30 cm thickness) was put on the top to put pressure on the straw to ensure a anaerobic fermentation conditions. The ensiling period was 30 days and the air temperature was 20-30°C.

When the feed was used, the plastic film was removed and the feed withdrawn starting with the upper layer and working downwards to the lower layers. An amount was taken out just sufficient for one day's feeding. The fermented straw was fed immediately to the animals after being taken from the pit and the plastic film was put back to keep the pit sealed.

The DM degradability of the different treated straws was measured by incubating 3 g air dry samples, which had passed through a laboratory hammer mill with a 3-mm screen, in nylon bags in the rumens of three cannulated sheep and withdrawing them at either 8, 16, 24, 48, 72, or 96 hours of incubation (Orskov et al 1980). The size of the bags was 140 x 90 mm and they were made from nylon filter cloth with a pore size of 45 Tm, obtained from Rowett Research Institute, Scotland (Zhang et al 1992).

Thirty young bulls of Simmental-Chinese Yellow cross cattle were used. They were approximately 12 months old and had an average initial weight of 200 kg. The initial live weights were based on three consecutive daily weighings after a period of 20 days pre- adaptation. The animals were randomly allocated to 3 treatments to receive either untreated wheat straw (US), urea- treated wheat straw (AS) or microbial-fermented wheat straw (MS),. They all received an equal daily allowance of 2.5 kg concentrate which consisted of 40% cottonseed cake, 40% maize and 20% wheat bran. For the untreated straw and urea-treated straw groups a salt and vitamin mineral mixture was supplied; for the microbial-fermented straw group the salt was left out of the mixture because the straw already contained salt from the inoculation process.

The cattle were penned individually indoors on dry earth bedding and the concentrate was supplied twice daily (9:00 am, 5:00 pm). The straw was given ad libitum and food residues were removed once daily for measuring intake. The experiment continued for 60 days and the animals were weighed three consecutive days at the beginning and the end, and once every 15 days during the experimental period. Apparent digestibility of the diets was measured by collecting total faeces during the first 7 days and the last 7 days of the experiment. The trial was carried out at the Feed Resources and Animal Nutrition Centre of Zhoukou, Henan Province of China.

The results were statistically analysed by use of the variance analysis method and the dfferences in treatments were analysed by using the Tukey-HSD procedure. Live weight gains were computed by calculating the linear regression of live weight on time.

Table 1: DM degradation characteristics of the feeds determined by the nylon bag method
	a	b	c	100-(a+b)	RSD	48 hr DMD
US	4.8	44.9	0.0225	50.3	0.99	44.7
AS	8.2	50.9	0.0476	40.9	1.82	53.4
MS	8.6	51.5	0.0387	39.9	1.08	53.8
CSC	27.8	57.3	0.0373	14.9	1.80	77.3
Maize	18.6	81.4	0.0347	0	0.22	88.2
Bran	47.1	34.3	0.0242	18.6	1.00	84.1

The degradation characteristics determined by the nylon bag method and represented by the equation P = a + b x [1 - exp(-ct)] (Orskov and McDonald 1979) are given in Table 1 together with the determined 48 hour degradability. As expected, the a, b and c values were increased as a result of urea-ammonia treatment and microbial fermentation. The 48 hour degradability increased 8.7 and 8.5 percent units, respectively due to urea-ammonia treatment and microbial fermentation. The parameters were similar for both the urea-ammonia treatment and microbial fermentation systems.

Table 2: Mean values for live weight gain, digestibility, DM intake and feed conversion by cattle receiving diets containing untreated straw (US), urea-treated straw (AS) and microbial-fermented straw (MS)
Treatment	US	AS	MS	SE/Prob
Live weight, kg
Initial	206	204	205
Final	246	276	275
Daily gain	0.67	1.20	1.16	±0.013/0.001
Straw intake, % LW	2.77	2.90	2.97
Feed DM digestibility
coefficient	0.62	0.67	0.69
Intake, kg/d
Total DM	8.75	8.96	9.09
DDM	5.47	6.01	6.29
Feed efficiency
Gain/DDMI	12.0	18.8	17.5
Gain/100 kg feed DM	7.5	12.6	12.1

The mean values for the in vivo digestibility, intake, liveweight gains and food conversion efficiency by the cattle receiving the different straw-based diets are given in Table 2. The differences in apparent digestibility and the straw voluntary intakes between diets containing urea-treated wheat straw and microbial fermented wheat straw were not significant, but both of them were significantly (P<0.05) higher than the diet containing the untreated wheat straw. The differences in daily gain for both urea-ammonia straw and microbial treatment compared with the untreated straw group were highly significant (P=0.001), but there was no significant difference between urea-ammonia treated straw group and microbial fermented straw group. The information on feed conversion efficiency indicated the superiority of both methods of straw treatment compared with untreated straw.

It can be seen that the in vivo digestibility of the diets and straw DM degradation characteristics were related to the intakes and to the growth rates. Due to urea treatment and microbial treatment the size of the indigestible fraction 100 - (a+b) is obviously reduced. This not only increases potential and actual digestibility, it also reduces the amount of indigestible "bulk" which has to pass the digestive tract. As a result feed intake is increased. The tendency for daily weight gain to be higher for animals fed urea-ammonia treated straw compared with microbial treatment may be due to the higher NH₃-N of the former diet.

There are some deficiencies in this paper which normally would have led to the authors being asked to provide additional data. For instance we are not told of the nature of the inoculum. Is it a fungal or bacterial preparation? Is it a proprietary compound and if so what is the cost?`Who supplies it? Moreover, the relatively high rate of supplementation (2.5 kg/d) is feasible in very few situtations and is not likely to be so even in China in the future? Will the microbial treatment be equally effective if supplementation is at a much lower level?

Table 3: In vitro gas production from rice and wheat straw incubated with the microbial inoculum used in this paper (Source rskov E R , unpublished data)
	Untreated	Saline water)	(+microbes)
Gas production (ml)
Rice straw	19.8	19.1	18.6
Wheat straw	13.8	13.3	12.0

The "treated" samples of straw were incubated at for 30 days before being evaluated using the in vitro gas production technique (Menke K H, Raab L, Salewski A, Steingass H, Fritz D and Scheider W 1979 The estimation of the digestibility and metabolizable energy content of ruminant feedingstuffs from the gas production when they are incubated with rumen liquor in vitro Journal of Agriculture Science (Cambridge) 93: 217-222).

Dr E R rskov at the Rowett Research Institute has made an in vitro measurement of gas production of both rice and wheat straw following incubation with the microbial inoculum. The results are given in Table 3.

It would seem that if the microbial inoculum is improving te nutritive vlaue of the straw the mechanism is not through improvements in digestibility by rumen micro-organisms. Obviously more research is needed.

Despite these reservations we believe the work should be published so as to encourage debate and further research in this important area. Interested colleagues are encouraged to get in touch with Mr Zhang Weixian who will be happy to provide further information.

(Received 1 November 1995)