Effects of urea, molasses, molasses-urea, noug cake and legume hay on the intake and digestibility of teff straw by highland sheep

By

Mopoi Nuwanyakpa and Martyn Butterworth
International Livestock Centre for Africa, P.O. Box 5689, Addis Ababa, Ethiopia

Abstract
Introduction
Materials and methods
Results and discussion
Conclusion
Acknowledgements
References

Abstract

A 37-day digestion trial was conducted to evaluate feed intake and utilization by male castrated Ethiopian highland sheep (initial weight, 17.9 ±0.80 kg). Sheep were randomized across twelve treatments (3/treatment) on the basis of fasted body weights. The treatments were: teff (Eragrostis tef) straw ad libitum (basal), basal + 3 g urea, basal + 88 g molasses or 86 g molasses-urea (2.5% urea). The latter two were also given with 6.5 and 13 g noug (Guizotia abyssinica) cake or 65 and 130 g Trifolium steudneri hay.

Addition of urea to teff straw increased N digestibility significantly, and increased teff straw intake, dry matter (DM) and neutral-detergent fiber (NDF) digestibilities by 3.7, 8.3 and 7.3%, respectively over teff straw alone. Supplementation of teff straw with molasses alone (about 15% of diet DM) depressed teff straw intake, DM, N and NDF digestibilities, and depressed N retention below the levels attained with teff straw + urea, teff straw + molasses-urea (fed also at 15% of diet DM) and with teff straw alone. The depressing effects of molasses were reversed by including urea at 2.5% (2.2 g) of the mixture. Response of sheep to N (urea) supplementation was greater than to energy (molasses) supplementation, indicating the N deficiency in cereal crop residues is a greater cause of poor animal performance than energy deficiency. In addition to showing that molasses-urea was a better supplement than molasses, the data indicated that the effects of urea as a non-protein N supplement on increasing the intake of low quality roughages, nutrient digestibility and N retention were enhanced (often significantly) by giving urea with molasses instead of dissolving it in water and sprinkling onto the straw. Hence, molasses-urea was also a better supplement than urea alone.

The effect of feeding noug cake or Trifolium hay with molasses or molasses-urea on the measured parameters were significantly greater than those of feeding molasses or molasses-urea alone. Additional responses to the higher levels of noug cake and Trifolium hay were not significantly greater than the lower levels. The lower levels of noug cake and Trifolium hay would therefore be more appropriate for peasant farmers using molasses or molasses-urea to supplement cereal crop residues. Although noug cake in Ethiopia is a cheaper source of N than Trifolium hay (0.37 vs 0.95 cents/kg N), the latter is more appropriate and available to small-scale farmers.

Introduction

When N content of the diet is less than 1.2%, rumen function may be impaired, feed intake reduced and animal growth markedly reduced (Conrad and Hibbs 1968). The N content of most cereal crop residues is usually less than 1.0% (Most and Butterworth 1985). Nitrogen deficiency is therefore the most important limiting factor in these feeds (Preston and Leng 1984). In addition to this quantitative protein deficiency, a qualitative deficiency; the limitation of the amino acid precursors of the branched (isobutyric, isovaleric and 2-methylbutyric) and straight chained volatile fatty acids (VFAs) may exist. Since these VFAs are essential nutrients for the growth of the principal cellulolytic and some non-cellulolytic rumen bacteria (Russell and Sniffen 1983), their deficiency may contribute to poor animal performance from unsupplemented or inadequately supplemented cereal crop residues (Butterworth and Nuwanyakpa unpublished data).

The metabolizable energy (ME) requirement for maintenance of a 20 kg sheep kept in a thermoneutral environment is 3.4 meagajoules (MJ)/day (ARC 1980). The ME consumed by sheep fed various cereal crop residues ranged from 2.8 to 4.1 MJ/day (Most and Butterworth 1985), making energy deficiency another important factor limiting animal production from cereal crop residues. The low N and energy contents indicate that unless adequately supplemented, cereal crop residues may provide no more than maintenance rations for sheep and cattle.

Some of the beneficial effects of N supplementation represented by increased digestion, higher intake of low quality roughages and body weight gain in young animals, may be achieved through N fertilization of forages or supplementation with protein or non-protein N (Ammerman et al 1972). Whether the full benefits of urea supplements can be achieved with urea alone or whether preformed carbon skeletons such as molasses are required also, is still debatable (Hunter and Vercoe 1984).

The objectives of this experiment were to compare two methods of administering urea (sprinkled onto straw vs mixed with molasses), to study the effects of energy (molasses) vs N (urea) supplementation and to evaluate the effects of two levels of noug (Guizotia abyssinica) cake and Trifolium (steudneri) hay when fed with molasses or molasses-urea on feed intake and utilization by sheep given a basal diet of teff (Eragrostis tef) straw.

Materials and methods

Thirty-six castrated Ethiopian highland sheep (initial weight: 17.9 ±0.80 kg) were drenched against liver fluke with Ranide (Rafoxanide) and dipped to control ectoparasites two weeks before the trial started. They were allocated to twelve treatments (three/treatment) at random within fasted bodyweight classes.

The treatments were:

1. Teff straw ad libitum + 10% of air-dry straw weight as water (intended to equalize possible effects of water addition in Treatment 2. Water was not sprinkled onto the straw fed in Treatments 3-12).

2. Teff straw + 3g urea (dissolved in 10% weight of straw as water. Elemental sulfur was added to achieve N:S ratio of 10:1 and the resulting mixture sprinkled onto and mixed in the straw).

3. Teff straw + 88 g molasses (Amounts for molasses and the other supplements listed below are on DM basis)*

4. Teff straw + 88 g molasses + 6.5 g noug cake.

5. Teff straw + 88 g molasses + 13 g noug cake.

6. Teff straw + 88 g molasses + 65 g Trifolium hay.

7. Teff straw + 88 g molasses + 130 g Trifolium hay.

8. Teff straw + 86 g molasses-urea (2.5% urea).

9. Teff straw + 86 g molasses-urea + 6.5 g noug cake.

10. Teff straw + 86 g molasses-urea + 13 g noug cake.

11. Teff straw + 86 g molasses-urea + 65 g Trifolium hay.

12. Teff straw + 86 g molasses-urea + 130 g Trifolium hay.

* The ad libitum amount of molasses or molasses-urea offered daily was fixed at 120 g/sheep. Noug cake was offered at 7 and 14 g, and TH at 75 and 130 g/sheep, respectively. The DM contents of molasses, molasses-urea, noug cake and Trifolium hay were 73.3, 71.7, 92.9 and 86.6%, respectively.

Sheep, tethered in metabolism cages, had free access to mineralized salt licks and drinking water. The trial consisted of a 10-day preliminary period followed by three 7-day collection periods, and a 3-day "rest" period between collection periods. During the "rest" periods, faecal and urine collectors were removed. Rumen fluid samples were taken with a stomach tube 1 hour before feeding on the third "rest" day, and acidified with concentrated sulphuric acid.

The mean intake of teff straw by each sheep established during the adaptation period was increased by 15%, and was offered throughout the trial to ensure ad libitum intake. Noug cake and Trifolium hay were given in the morning and were completely eaten before teff straw with molasses or molasses-urea was offered. Molasses and molasses-urea were poured onto and thoroughly mixed with each sheep's daily straw requirement. The ratios of teff straw and molasses or molasses-urea offered each sheep daily were therefore known. The ratios of teff straw and molasses or molasses-urea in the feed offered each sheep was assumed to be the same as those in the feed refused. For example, if 720 g of teff straw + molasses was offered, then the proportion of molasses was 16.7% (120 g/720 g x 100). If the feed (teff straw + molasses) refused was 150 g, then 25 g molasses (150 g x 0.167) was refused. Mixing molasses and molasses-urea with teff straw was necessitated by the refusal of some sheep to eat these supplements when they were fed separately.

During the measurement periods, samples of teff straw, molasses, molasses-urea, noug cake and Trifolium hay offered and teff straw or teff straw with urea, molasses or molasses-urea were taken and composited. Subsamples of the weekly composites were dried at 60°C for 24 hours and ground through a 1-mm screen for analyses. Aliquots were dried overnight at 100°C for DM determinations.

Faeces and urine were collected every 24 hours during each collection period. Urine was acidified with concentrated sulphuric acid and measured volumetrically. Aliquots of each sheep's urine and faecal outputs were refrigerated, bulked at the end of the period and subsampled. Faecal samples were processed as for feeds.

Feed, faecal and urine samples were analyzed for N. rumen fluid for ammonia (AOAC 1980), and feed and faecal samples for neutral-detergent fibre (NDF) (Goering and Van Soest 1970). Apparent digestion coefficients were calculated. All data were subjected to analysis of variance and differences among treatment means were determined (Snedecor and Cochran 1980).

Results and discussion

The N and NDF contents of feeds offered are shown in Table 1, while Table 2 shows the effects of supplementation of teff straw with urea. Adding urea at about 0.7% of the air-dry weight of teff straw offered increased straw intake, apparent DM and NDF digestibilities by 3.7, 8.3 and 7.3%, respectively, but these increases were not significant (P<0.05). Urea supplementation significantly increased N digestibility and rumen ammonia concentration. Since about 80% of rumen bacteria may use ammonia as their sole source of N for microbial synthesis (Bryant and Robinson 1962), the boost in rumen ammonia concentration resulting from the addition of urea could have contributed to increased feed intake and utilization. The rumen ammonia concentration in sheep on the basal diet was lower but that in urea-supplemented sheep was similar to the 5-8 mg % reported by Satter and Slyter (1974). It was lower in all sheep in the study than the 15-20 mg % suggested for optimum utilization of fibrous feeds (Krebbs and Leng 1984). However, rumen ammonia concentration may be an unreliable indicator of the degree of feed utilization if other factors needed for rumen microbial growth are not supplied in adequate amounts (Hunter and Vercoe 1984).

Sheep given urea supplemented teff straw excreted 42% more urine volume, containing significantly (P<0.05) 51% more N than those fed teff straw alone (6.7 vs 10.1 g). Since urea represents about 70% of the total urinary N in ruminants (Living-stone et al 1962), urea-supplemented sheep had a slightly lower N retention than the unsupplemented ones.

Table 1. Nitrogen and Neutral detergent fibre contents (%DM) of feeds offered

Feed ingredients	Nitrogen	Neutral detergent fibre
1. Teff straw	0.6	79.6
2. Molasses	0.7	-
3. Molasses-urea	2.1	-
4. Urea	45.0	-
5. Noug cake	5.4	32.2
6. Trifolium hay	2.1	42.4

Table 2. Effects of supplementing teff straw with urea on feed intake, nutrient digestibility, rumen ammonia concentration and nitrogen retention

Parameters		Amount of urea (g/hd/day)
		0	3	SE
1. Feed intake (g/DM/day)		341	354	23
2. Apparent digestibilities (%)
	a. Dry matter	43.0	46.7	2.9
	b. Neutral-detergent fibre	51.7	55.6	2.0
	c. Nitrogen	16.6b	21.8a	3.0
3. Urinary N excretion (g/day)		6.7b	10.1a	1.2
4. Nitrogen retention (g/day)		-0.6	-0.8	0.2
5. Rumen ammonia concentration (%)		2.4b	6.6a	2.0

a, b Means within rows with different superscript are significantly different (P<0.05).

The effects of molasses or molasses-urea alone, or of molasses or molasses-urea with noug cake and Trifolium hay on feed intake, and DM, N and NDF digestibilities are shown in Table 3. Total feed intake increased significantly (P<0.05) as the level of noug cake nor Trifolium hay with molasses or molasses-urea increased. The 6.5 and 13 g noug cake and 65 and 130 g Trifolium hay supplements represented about 1.5, 3.0, 13.9 and 24.4% of the diet DM intake, respectively. Neither level of noug cake nor Trifolium hay suppressed the intake of teff straw. These results agree with those of Mosi and Butterworth (1985) when a forage legume hay comprised 19 and 22% of the diet DM. Preston and Leng (1984) suggested that supplements may have beneficial effects on the utilization of fibrous feeds if the level of supplementation does not exceed 20% of the diet DM. However, in a trial by Butterworth and Nuwanyakpa (unpublished data), supplementing teff straw up to 42% of the diet DM with a legume hay significantly increased feed utilization.

Table 3. Effects of supplementing teff straw with molasses or molasses-urea and their interactions with levels of noug cake and Trifolium hay on feed intake and nutrient digestibility.

Parameters			Noug cake intake (g DM/hd/day)				Trifolium hay intake (g DM/hd/day)
			0	6.5	13.0	SE	0	65	130	SE
1. Effects of molasses intake (63 g DM/hd/day):
	a. Feed intake (9 DM/Day)
		1) Straw	326	331	347	23	326	320	322	23
		2) Total Feed	393b	400b	423a	12	393c	446b	515a	12
	b. Apparent digestibilities (%)
		1) Dry matter	40.8b	46.9a	48.2a	3.7	40.8b	53.5a	56.9a	3.7
		2) Neutral-detergent fiber	37.3b	43.9a	47.4a	3.9	37.3b	55.8a	56.5a	3.9
		3) Nitrogen	15.1b	30.7a	29.6a	3.0	15.1c	32.4b	39.5a	8.0
2. Effects of molasses-urea intake (68 g DM/hd/day)
	a. Feed intake (g DM/day)
		1) Straw	354	380	364	23	354	355	359	23
		2) Total feed	428b	458a	447a	12	428c	487b	549b	12
	b. Apparent digestibilities (%)
		1) Dry matter	53.1	50.4	53.1	3.7	53.1b	58.1a	59.2a	3.7
		2) Neutral-detergent	53.1	52.3	52.3	3.9	53.1b	57.4a	57.5a	3.9
		3) Nitrogen	37.6c	42.7b	46.7a	3.0	37.6c	44.8c	50.4a	3.0

a, b, c For each of the molasses and molasses-urea effects, means within rows with different superscripts are significantly different (P<0.05)

Adding a small amount (6.5 g) of noug cake with molasses (0.7% N) significantly increased DM, NDF and N digestibilities over molasses alone. However, doubling the amount of noug cake did not significantly increase these parameters beyond the levels obtained with 6.5 g (Table 3). Similar results were obtained when molasses was fed with 65 and 130 g Trifolium hay (except for N digestibility). These data suggest that in a N deficient diet the effects of a N supplement may be greater at the lower levels of supplementation, with additional benefits decreasing as supplementation is increased (Butterworth and Mosi 1985). Therefore, the lower levels of noug cake and Trifolium hay are more appropriate for smallholders.

When noug cake was fed with molasses-urea, DM and NDF digestibilities were affected differently than observed for molasses. Except for N digestibility, neither level of noug cake improved feed utilization beyond the levels attained with molasses-urea alone. This suggests that the amount of N provided by noug cake was not high enough to significantly affect feed utilization more than molasses-urea, which was moderately (2.1%) high in N. As with molasses, the effects of feeding molasses-urea + 24.4% of the diet as Trifolium hay were statistically similar to those of molasses-urea + 13.9% Trifolium hay. The data therefore show that the lower levels of legume and noug cake supplementation were as effective, but more appropriate for small-scale farmers.

Dry matter intake and digestibilities of DM, N and NDF were lower in sheep given teff straw supplemented with molasses alone (Table 3), than in those given either teff straw + urea or teff straw alone (Table 2). Therefore, N deficiency may be a greater cause of poor performance in animals given cereal crop residues, than energy deficiency.

Nitrogen (urea) supplementation did not only result in better feed intake and utilization than energy (molasses) supplementation, but was also more economical. At prevailing market prices in Ethiopia (6 and 80 cents/kg for molasses and urea, respectively), about 0.24 and 0.53 cents were spent/sheep/day for single supplements of urea and molasses respectively. Urea is also easier to transport than molasses. Therefore, even if both urea and molasses were available, and could be handled and fed safely, supplementation with urea alone would be more beneficial for small-scale farmers than with molasses alone.

Nuwanyakpa et al (1986) fed molasses-urea (2.5% urea) ad libitum to Ethiopian highland sheep and observed that teff straw intake and fibre digestibility were negatively correlated with the intake of molasses-urea. The increase in feed utilization associated with molasses-urea (also 2.5% of urea) supplementation in the present study may have been because the amount of molasses-urea on offer was limited. Loosli and McDonald (1969) stated that in order to improve the utilization of forages with molasses-urea as a supplement, intake of the supplement must be restricted by making the mixture "unpalatable" or by limiting the amount offered.

Feed intake and utilization were greater when teff straw was supplemented with molasses-urea than molasses. The inferiority of molasses to molasses-urea could be explained by the fact that when molasses is used, even at restricted levels, as the sole supplement to low quality roughages (Peralta and Hughes-Jones 1981), digestibility, rate of passage and voluntary feed intake may be reduced (Sutton 1979; Van Niekerk and Jacobs 1985). These effects may be caused by the proliferation in the rumen of the fast-growing sugar digesting micro-organisms depriving the slower-growing cellulolytic organisms of what little N is available in the rumen (Gilchrist and Schwartz 1972).

Molasses-urea (Table 3) significantly (P<0.05) improved DM and N digestibilities, and N retention than urea alone (Table 2) or molasses alone (Table 3), although the dietary proportions of molasses (14.8%) and molasses-urea (14.7%) were similar. At each level of noug cake or Trifolium hay, the effects of molasses-urea on teff straw and total feed intake, and nutrient digestibilities were significantly greater than those of molasses, suggesting that the small amount of urea significantly improved the value of molasses as a supplement, perhaps through making more N available for rumen bacterial growth and protein synthesis.

That molasses is a poorer supplement to low quality roughages than urea or molasses-urea is in agreement with the findings of Van Niekerk and Jacobs (1985). These workers reported that the intake of sugarcane tops and liveweight gains in cattle were significantly greater with protein (25% true protein and 75% urea) than energy (molasses) supplementation. The greatest performance in cattle was obtained when both supplements were fed together.

Sheep performance was better on teff straw + molasses-urea than teff straw and urea diets, suggesting that the energy and minerals in the molasses (McKiernan 1982) may not only be beneficial at the whole animal level, but also in enhancing the utilization of urea by rumen microbes. As such, administering urea as part of a molasses-urea mixture rather than dissolving it in water and sprinkling onto straw is recommended.

As shown in Table 4, N retention in sheep given molasses-urea alone was greater than in those given molasses alone. While N retention in sheep supplemented with molasses alone was significantly (P<0.05) lower than in those given molasses + 13 g noug cake, feeding the same amount of noug cake with molasses-urea did not affect N retention. This differential response between molasses and molasses-urea suggests that in the presence of urea, the small amounts of noug cake did not stimulate rumen microbial activity enough to contribute significantly to N retention. Feeding 65 g and 130 g Trifolium hay with molasses or molasses-urea significantly increased N retention over either supplement alone. Greater beneficial effects were obtained with Trifolium hay than with noug cake probably because more N was ingested from Trifolium hay than from noug cake. M.Y. Nuwanyakpa, M. Butterworth and L. J. Lambourne (unpublished data) fed lactating dairy cows a forage legume hay and noug cake at iso-nitrogenous levels, and found that two supplements to be statistically similar in their effects on hay intake, milk production and composition, and molar proportions of straight - and branched - chain rumen VFAs.

Table 4. Effects of supplementing teff straw with molasses or molasses-urea and their interactions with levels of noug cake and Trifolium hay on urinary N excretion, N retention and rumen ammonia concentration.

Parameters		Noug cake intake (g DM/hd/day)				Trifolium hay intake (g DM/hd/day)
		0	6.5	13.0	SE	0	65	130	SE
1. Effects of molasses intake (63 g DM/hd/day)
	a. Urinary N excretion (g/day)	5.9	6.0	7.0	1.2	5.9b	7.8a	8.7a	1.2
	b. Nitrogen retention (g/day)	-0.7b	-0.1a	0.0a	0.2	-0.7c	0.1b	0.7a	0.2
	c. Rumen ammonia concentration (%)	1.9	3.8	3.7	2.0	1.9b	6.2a	5.6a	2.0
2. Effects of molasses-urea intake (68 g DM/hd/day)
	a. Urinary N excretion (g/day)	9.1b	11.3a	10.1 ab	1.2	9.1b	11.6a	12.2a	1.2
	b. Nitrogen retention (g/day)	0.4	0.3	0.5	0.2	0.4c	0.7b	1.4a	0.2
	c. Rumen ammonia concentration (%)	7.9	8.2	10.0	2.0	7.9	7.6	8.1	2.0

a, b, c For each of the molasses and molasses-urea effects, means within the rows with different superscript are significantly different (P<0.05).

Changes in rumen ammonia concentration due to the inclusion of noug cake or Trifolium hay with molasses or molasses-urea were generally non-significant. This may have been due to the fact that the same amount of urea fed was low and that rumen fluid samples were taken 24 hours after noug cake and Trifolium hay had been consumed. With either molasses or molasses-urea, rumen ammonia concentration was higher in sheep fed Trifolium hay than in those given noug cake (more N was offered through Trifolium hay).

Conclusion

The major conclusions drawn from this trial were that:

1. Feed intake and utilization were slightly greater in sheep given teff straw + urea than in those fed teff straw alone, and significantly greater than in sheep on teff straw + molasses indicating that N deficiency in cereal crop residues may be a greater cause of poor animal performance than energy deficiency. At prevailing market prices in Ethiopia, N (urea) supplementation was also more economical than energy (molasses) supplementation.

2. Feed intake was, in general, significantly greater in sheep on teff straw supplemented with molasses-urea than in those supplemented with urea alone. Therefore, urea is more beneficially administered as part of molasses-urea mixture rather than being dissolved in water and sprinkled onto a cereal crop residue.

3. Whether given with molasses or molasses-urea, the lower levels of noug cake and Trifolium hay were as effective as molasses or molasses-urea but more affordable and hence recommended for small-holders.

4. Even when offered at a restricted level, molasses decreased the intake of teff straw and reduced the digestibilities of DM, NDF and N. and the retention of N below the levels observed in sheep given unsupplemented teff straw. Therefore molasses should probably not be used as the sole supplement to cereal crop residues.

5. At each level of noug cake or Trifolium hay, the effects of molasses-urea on teff straw and total feed intake, and nutrient digestibilities were significantly greater than those of molasses, showing that a small amount of urea significantly improved the supplementary value of molasses.

Acknowledgements

The financial assistance of the International Development Research Centre (IDRC) and International Livestock Centre for Africa (ILCA), which made possible the implementation of this and other ARNAB research projects at ILCA, is gratefully acknowledged. We thank Messrs Tewdros Taye, Anbase Kassahun, Samual Wondimu and Mulugeta Habte Michael (Field Assistants); Mesdames Genet Asefa and Alemtsehai Greiling (Laboratory Technicians); Mr Robin Sayers (Statistician) and Mrs Tsedale Layeh (Secretary) for their contributions. The comments and suggestions of our colleagues Drs Jim Lambourne and Douglas Little are also acknowledged.

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