Feeding ammoniated straw to cattle and sheep in Syria

M Hadjipanayiotou*, L Verhaeghe**, A R Kronfoleh, L M Labban, A Shurbaji, M Amin, A R Merawi, A K Harress, M Houssein, G Malki and M Dassouki

Deir El Hajjar Research Station, Ministry of Agriculture and Agrarian Reform, Syria

(Present address: *Agricultural Research Institute, Nicosia, Cyprus; **FAO, Animal Production and Health Division, Via delle Terme di Caracalla, 00100 Rome, Italy)

Five trials, two with heifers and three with sheep, were carried out to evaluate the effect of straw treatment on animal performance. In the first trial with 28 Shami heifers, 14 were offered a control (C) diet composed of 5.9 kg/day of concentrate and hay (1:1 ratio) whereas, in the treatment diet, 20% of the daily feed allowance was replaced by urea-treated straw (US) offered ad libitum. In the second trial 20 Friesian heifers were fed either US or untreated straw (S) and concentrate. In two trials with Awassi sheep, one with 70 ewe lambs and one with 32 dry ewes, US was compared with S as the only sources of feed. In the last trial, 42 lactating Awassi ewes were on a conventional diet (Control) and another 42 ewes were offered 600 g of ammonia-treated straw (AS) daily as replacement for 100 g concentrate, 100 g barley grain, 100 g vetch and barley hay and 100 g whole lentil pods.

Both US and AS had higher crude protein (N x 6.25) content (S 37, US 122, AS 110 g N x 6.25/kg DM) and digestibility (S 40%, US 53%, AS 54%). The Shami heifers on US grew faster (P<0.01) than those on S (US, 660 vs S, 524 g/d). Friesian heifers on the US tended (P<0.08) to grow better than those on the S (US, 680 vs S, 541 g/d). In the two trials with sheep, animals consuming US tended to perform better (p < 0.08) than those with S, although in the study with lambs both groups lost weight. In the trial with dairy Awassi ewes the replacement of concentrate by AS resulted in lower (P<0.05) milk yield (C, 462 vs AS, 432 g milk/d) without any significant (P>0.1) effect on weight changes ( C, 3 vs AS, 26 g/d).

KEY WORDS: Barley straw, ammoniation, urea-treatment, sheep, heifers, growth, milk

Straw is the most abundant of all agricultural residues in Syria, and despite its very low digestibility, a significant amount is fed to ruminants. The use of ammonia to upgrade straws and other low quality roughages has attracted considerable attention in recent years (Sundstol and Coxworth 1984). Urea can be an inexpensive source of ammonia for the treatment of straws (Jackson 1978; Dolberg et al 1981; Hadjipanayiotou 1982; Jayasuriya and Perera 1982; Imbrahim and Pearce 1983; Cloete and Kritzinger 1984).

The experiments reported here studied the possibility of replacing conventional feedstuffs with ammoniated straw in diets of lactating sheep and growing heifers, and also compared the performance of cattle and sheep offered untreated or urea-treated straw.

Five trials were carried out, two with heifers and three with sheep. In all five trials, animals were group-housed and had free access to water. Animals were weighed at the beginning and at the end of the trial.

The Norwegian stack method (Sundstol et al 1978) was used for trea- ting long baled straw, either with ammonia gas (3.5% w/w) or with a 10% urea solution (4% urea w/w).For the latter, the urea solution was applied with a sprayer mounted on a tractor, after each layer of straw of known weight. The stacks of straw measured 2.4 x 2.0 x 12.0 m, and weighed 4-5 tonnes. Straw was treated from July to September 1991, and the stacks opened 5-6 weeks following urea or ammonia treatment. Ammoniated straw was exposed to the air for 24 h prior to feeding to allow excess ammonia to escape.

When chopped straw was used, it was placed in PVC sacks (2.85 x 1.5 m, 0.5 mm thickness). The urea solution was sprayed on the straw, using a garden sprinkler, as the sacks were being filled (about 300 kg straw per sack). The injection of ammonia in the sealed sack was made as in the stack method.

Two trials were carried out, one with 28 Shami heifers at the Deir El-Hajjar Shami cattle station, and another with 20 Friesian heifers at a private farm (Shahada Farm) near Damascus. In both trials animals were divided into two groups based on their live weight and randomly allocated to diets of either S or US. In the study with Shami heifers, the animals on S were offered 5.9 kg/d of concentrate-hay (1:1 ratio); in the US treatment the amount of concentrate-hay was reduced to 4.75 kg/d. The US was offered ad libitum.

In the trial with Friesian heifers, animals were offered equal quantities (fresh matter) of S or US with an allowance of a concentrate mixture. The concentrate given with S had 18.5% of cotton seed cake and the one offered with US contained 6% . Both groups occasionally got a small amount of green forage.

The concentrate mixture offered with S was composed (%) of 49.5 barley grain, 30 wheat bran, 18.5 cottonseed cake, 0.5 salt, 1.0 limestone and 0.5 vitamin-trace mineral mixture.

The Shami heifers on US were offered 10 g/head/d of a vitamin, macro and micro mineral mixture to compensate for those nutrients contained in the concentrate. This mixture contained (%): 3.4 vitamin-trace mineral mixture, 18 NaCl, 25 limestone, 8.6 dicalcium phosphate and 45 Na₂SO₄. The daily mineral/vitamin allowance was mixed with the concentrate. Sodium sulphate was included in the concentrate given to the heifers that received US, in order to provide 1 g of sulphur for every 9 parts of urea.

Three trials were conducted using Awassi sheep. Two were at the Hama research centre with 70 ewe lambs and with 84 lactating ewes; the other was at Kamishly research centre with 32 dry ewes. In each trial the animals were divided in two similar groups and randomly allocated to S or AS treatments. In the trial with lactating ewes, the straw was treated with ammonia gas (AS) and in the other two it was treated with urea (US).

The lactating ewes were offered 600 g of ammoniated straw daily as replacement of 100 g of concentrate, 100 g of barley grain, 100 g vetch and barley hay and 100 g whole lentil pods. Group milk yield was recorded daily, and individual yields measured just prior to the beginning of the experiment and twice more every 30 d. The group milk yield for five consecutive days was pooled and used as a single observation, thus resulting in 12 values per treatment.

In the other two trials with sheep, S and US were offered ad libitum. All animals were given 15 g/head/d of a mineral-vitamin supplement composed of (%): 8 NaCl, 8 Na₂SO₄, 8 wheat bran, 54 dicalcium phosphate, 20 limestone and 2 vitamin-trace mineral mixture.

Data were analyzed by one way analysis of variance. In all five trials the initial live weight was used as covariate for final weight.

Both urea and ammonia gas were effective in upgrading the nutri- tional value of straw. Treated straw had higher N x 6.25 content (S, 37; AS, 110; US, 122 g N x 6.25/kg DM) and in vitro digestibility (S at Kamishly, 39%; S at Hama, 41%; AS, 54%; and US, 53%).

The Shami heifers with US grew faster (P<0.01) than those with S (Table 1). US offered ad libitum successfully replaced 17.8 and 18.9% of concentrate and hay, respectively.

Table 1. Replacement of concentrate and hay (mixture of legumes and cereals) by urea-treated straw (UTS) in diets of Shami heifers.

	Control	UTS	SD	Prob

Initial age (days)	396	398	22	NS

Liveweight (kg)
Initial	203	202	16	NS
Final weight	260	273	16	NS
Daily gain (g/day)	524	660	28	<0.01

Feed intake (kg/day)
Concentrate	2.96	2.44
Hay	2.85	2.31
Urea-treated straw		1.75 (84% DM)

In the trial with Friesian growing heifers, animals on US tended (P<0.08) to grow faster than those on S. The latter group, however, was given more straw on dry matter basis (Table 2).

Table 2. Feeding urea-treated straw (UTS) to Friesian growing heifers*

	Untreated	Urea-treated	SD	Prob

Liveweight (kg)
Initial	220.5	218.9	38.0	NS
Final	269.7	280.8	27.9	NS
Daily gain (g/day)	541	680	297	<0.08
Feed intake (kg/day)
Concentrate	2.67	2.67
Straw (fresh basis)	3.25	3.25
DM (%) in straw	90.7	74.8

* A small amount of green forage was offered occasionally to both groups during the 91-day experiment

In the trial with lactating Awassi ewes there were no differences between control and AS groups for initial and final body weight and for daily weight changes (Table 3). Ewes on the AS diet produced significantly less (P<0.05) milk than those on the control diet (AS, 432 vs 462 g milk/ewe/day).

Although Awassi sheep with US had higher gains and final body weight (Tables 4 and 5) than those with S, differences were not significant. There were no differences either in the voluntary intake of straw.

Table 3: Replacement of conventional feedstuffs with ammonia-treated straw (AS) in the diets of lactating Awassi ewes

	Control	AS	SD	Prob

No. of animals	37	39
Liveweight (kg)
Initial	59.0	59.3	12.0	NS
Final	59.2	61.0	11.3	NS
Daily change (g/day)	3	26	5	NS
Milk yield (g/day)
Milk yield**	468	492	240	NS
Milk yield***	462	432	31	<0.05
Feed intake (g/day)
Concentrate	700	600
Barley grain	250	150
Barley and vetch hay	300	200
Whole pods of lentils	300	200
Cottonseed cake	25	25
Ammonia-treated straw	-	560

Table 4. The effect of feeding urea-treated or untreated straw on the performance of Awassi ewe lambs (Hama research centre)

Untreated	Treated	SD	Prob

No. of animals 35	35
Liveweight (kg)
Initial 40.1	40.1	5.1	NS
Final 34.9	35.7	2.4	<0.12
Daily loss (g) 88	73	43	<0.15
Straw intake (g/day) 744	744

Table 5. The effect of feeding urea-treated or untreated straw on the performance of Awassi sheep (Kamishly research centre)

	Untreated	Treated	SD	Prob

No. of animals	16	16
Liveweight (kg)
Initial	39.8	39.8	4.9	NS
Final	42.1	43.4	5.3	NS
Daily gain (g)	41	65	44	<0.13
Feed intake (g/day)
Barley grain	250	250
Straw	741	792

In line with previously reported data (Dolberg et al 1981; Hadjipa- nayiotou 1982; Sundstol and Coxworth 1984) ammoniation resulted in a significant increase in straw nitrogen content and digestibility. Ammonia gas treatment usually gives better results, though not always significant, than treatment with urea solution in increasing the digestibility of straw as has been reported by Wanapat et al (1985), Cottyn and De Boever (1988) and Alibes and Munoz (1992). Despite the fact that in the present studies the two chemicals were not compared at the same place, the increase in digestibility was greater in the ammonia compared to the urea treatment (15 vs 12 percentage units increase).

Most of the experiments reviewed by Kristensen (1984) showed that with cows in mid-lactation and with a moderate level of milk yield, it is possible to replace part of a high quality roughage with alkali-treated straw without negative effects on performance. Similarly, treated straw could form a substantial part of the diet for growing cattle which do not require energy rich diets. These are only partly in agreement with the findings of this work where US or AS successfully replaced conventional feedstuffs in the diets of growing heifers but reduced slightly the milk yield of lactating ewes.

Urea treatment improved the nutritive value of rice straw and made it at least equivalent to grass hay and when offered alone provided a maintenance diet (Promma et al 1983). This was not the case in the present study where US offered alone reduced weight loss compared to S but animals continued to be on a below maintenance level. Similarly, in the study of Coxworth et al (1977) ammoniated straw fed to beef cows as the only feed did not cover the maintenance requirements.

The positive response to the use of treated straw in the trials with cattle was not confirmed in the trials with sheep where responses were less obvious.

The authors are grateful to the FAO and UNDP offices in Damascus, Drs R Sansoucy (Feed Resources Group, FAO, Rome), S Badawi (AGON, FAO, Rome) and K Qamar (AGON, FAO, Rome) for continuous support and encouragement and to his Excellency the Minister of Agriculture and Agrarian Reform Mr M Gabbash for making available all necessary facilities for the implementation of this work. This work was carried out in conjunction with the Greater and Improved Use of Agricultural Residues for Animal Feeding Project, a joint undertaking between the Government of Syria and the UNDP and FAO.

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