Chinese Yellow cattle of 200 kg liveweight were allocated at random to receive one of 4 diets namely untreated or ammoniated wheat straw with either 0.5 or 1.0 kg per day of concentrate. The concentrate was offered twice daily and the straw was offered ad libitum. Drinking water was always available.

Liveweight gain was doubled by straw treatment (from 160 to 354 for 0.5 kg/d concentrate and from 269 to 504 g/d for 1 kg/d concentrate). The system of using urea-treated straw was profitable.

Straw is abundantly available in many parts of China. This is partly due to an increased production of cereals and partly due to less use of straw as a domestic fuel. There is an increase in demand for beef both for domestic and export markets. Conversion of straw to beef has however in the past been uneconomical since it had to be supplemented with concentrates in large quantities to achieve sufficient growth rate. Treatment of straw with ammonia appeared to us to offer a possibility to achieve greater intake of straw and thus to decrease the amount of concentrate required for the fattening of cattle.

Sixteen bulls between 15 and 18 months old were bought in the local market. They weighed on average 200 kg live weight. The breed was the Nanyang type of yellow cattle.

The cattle were allocated at random to receive one of 4 diets namely untreated or ammoniated straw with either 0.5 or 1.0 kg per day of concentrate. The concentrate was offered twice daily and the straw was offered ad libitum. Drinking water was always available.

Wheat straw was treated in a pit. 100 kg of straw was mixed with 100 litres of water into which was dissolved 6 kg of urea. The straw was left in the pit covered with plastic for at least 25 days. Before it was fed it was aerated to eliminate the smell of ammonia.

The animals were weighed once weekly. The average of the first 2 days was used as the initial weight.

The straw was analyzed for nitrogen. neutral and acid detergent fibre and ash. In addition the dry matter degradability was measured by the nylon bag method according to Orskov and McDonald (1979).

Table 1: Effect of treatment on chemical composition
	N	NDF	ADF
		% of dry matter ------	---
Urea-treated straw	1.58	77.7	54.4
Untreated straw	0.62	82.5	54.2

The ammoniation was judged to be successful as the treated straw changed to a brown colour. The chemical composition of the untreated and treated straw is given in Table 1.

The nitrogen content of the straw was increased substantially and there was a slight decrease in NDF. The results of the dry matter incubation, using the expression p = a + b(l-e^-ct) are given in Table 2 together with the observed 48 hours degradability. Incubation times were 8, 16, 24, 48, 72 and 96 hours.

The data for in vivo digestibility and live weight gain are given in Table 3.

Straw intake was increased by about 1 kg/d as a result of ammoniation and digestibility by about 8% in agreement with the degradability measurements. Since the animals were group fed it was not possible to carry out an analysis of variance.

Table 2: Washing loss of dry matter, 48 hour disappearance and coefficients of the exponential equation p = a + b(l-e-ct) for the ammoniated straw
	Washing	48hr	a	b	c	RSD
	loss (%)	degrad.(%)
Urea-treated
straw	16.4	55.6	13.1	64.4	0.037	1.7

Table 3: Effect of urea treatment and concentrate consumption on straw intake and diet digestibility
	Concentrate	Straw intake	Digestibility
	(kg/d)	(kg/d)	(%)
Urea-treated straw	0.5	5.92	68.5
"	1.0	5.96	70.2
Untreated straw	0.5	4.96	60.1
"	1.0	4.92	62.2

Table 4: Effect of straw treatment and concentrate intake on changes in liveweight and carcass weight
Concentrate	Initialweight	Final weight	Liveweight	Carcass
(kg/d)	(kg)	(kg)	gain (g/d)	weight
				(kg)
Urea-treated
straw
0.5	200	263	354	134
1.0	199.5	290.2	504	148
Untreated straw
0.5	199	227	160	107
1.0	200	249	269	124
SE of mean	6.4	12.7	35	7.0

The live weight carcass weight and daily gains are given in Table 4. Final live weights, and daily live weight gains were significantly increased (P<0.01) also concentrate intake had significant effects (P<0.05) and also final carcass weight was influenced both by ammonia treatment of the straw (P<0.01) and by level of concentrate feeding (P<0.05).

It can clearly be seen that both ammonia treatment and the level of concentrate had quite dramatic effects on performance. The cattle receiving the ammonia treated straw moreover were fat and ready for slaughter while the cattle receiving untreated straw were not. The feed conversion and total cost in Yuan/kg live weight gain are all given below in Table 5.

Table 5: The effect of ammonia treatment and concentrate supplementation on feed conversion and cost
	Concetrate	Feed consumption/kg gain		Cost
	(kg/day)	(Straw)	(Concentrate)	(Yuan/kg)
Urea-treated straw
	0.5	16.7	1.4	3.5
	1.0	11.8	2.0	3.1
Untreated straw
	0.5	31.1	3.1	5.1
	1.0	18.3	3.7	4.2

Urea-treatment had a very large effect on production cost so much so this type of production is cost effective unlike the feeding of untreated straw and the method has gained popularity in many cropping areas of China.

This work was carried out in a technical corporation project with FAO under the guidance of Dr. E R Orskov and Dr F Sundstoll

(Received 1 July 1994)