Effects of undegradable protein supplements on the performance of weaner steers fed veld hay sprayed with urea

S Sibanda ^1,2, L R Ndlovu ² and T Smith ¹

¹ Grasslands Research Station
P Bag 3701, Marondera, Zimbabwe

² Department of Animal Science
University of Zimbabwe
PO Box MP 167, Mount Pleasant, Harare, Zimbabwe

ABSTRACT

The effects of different sources of undegradable protein supplements (cottonseed, soybean, meat and bone and blood meals) on the performance of Hereford x Africander weaner steers (205 kg liveweight) offered veld hay sprayed with 1% urea were investigated. Supplementation with undegradable protein increased dry-matter intake of veld hay offered ad libitum by 18% (P<0.05) and reduced loss of live- and carcass weight in steers offered sub-maintenance quantities of veld hay, but had little effect on rumen pH and ammonia concentration, or degradation of veld hay in the rumen. The results confirm the beneficial effects of supplementing low quality roughages with a supply of undegradable protein, but suggest that the undegradable protein from the four supplements studied was of equal value.

RESUME

Effet des sources de protéines non dégradables sur les performances de veaux sevrés recevant du foin traité par pulvérisation avec de l'urée

L'effet de diverses sources de protéines non dégradables (graines de coton, de soja, farine de viande et d'os et farine de sang) sur les performances de veaux sevrés de race croisée Hereford x Africander pesant en moyenne 205 kg de poids vif et recevant du foin de veld traité par pulvérisation avec de l'urée à 1% a été étudié. La complémentation entraînait une augmentation de 18% (P<0,05) de l'ingestion de matière sèche de veld offerte ad libitum Elle freinait en outre la baisse du poids vif et du poids de la carcasse même lorsque les quantités de veld offertes étaient inférieures aux niveaux nécessaires à l'entretien. Cependant, la complémentation n'avait qu'un effet limité sur le pH et la concentration en ammoniac du rumen ainsi que sur la dégradation du foin de veld dans le rumen. Ces résultats confirment les avantages de la complémentation de fourrages de qualité médiocre avec des sources de protéines non dégradables. Ils permettent de conclure par ailleurs que les quatre sources de protéines évaluées ici sont de valeur comparable.

INTRODUCTION

The poor performance of ruminants fed low quality roughages is mainly due to a deficiency of nitrogen which results in low intake and digestibility of dry matter (Topps, 1972). Protein and non-protein nitrogen supplements may be used to correct this deficiency (Topps, 1972; Siebert and Hunter, 1982).

One of the problems of supplementing low quality roughages with a single daily meal of urea is that the urea is rapidly degraded into ammonia in the rumen (Falvey, 1982). This results in non-synchronised release of ammonia and energy, leading to poor utilisation of urea for microbial protein synthesis and substrate fermentation (Satter and Slyter, 1974). This problem may be overcome by using slow-release forms of non-protein nitrogen (Ferero et al, 1980) but these alternatives are generally more expensive than urea.

Spraying urea onto poor quality roughages just before feeding has been suggested as a way of ensuring uniform release of ammonia to rumen microbes (Hennessy, 1984). Urea supplementation at the rate of 1% seems adequate for roughages containing 3-4% crude protein (Verma and Jackson, 1984). However, the optimum level of urea is likely to vary with the type of roughage.

Further improvements in animal performance may be expected when roughages fed with urea are supplemented with a source of dietary undegradable protein (UDP) (Kempton et al, 1979; Smith et al, 1980; Mullins et al, 1984). The magnitude of the response at equal levels of UDP may depend on the quality of the protein (Petersen and Clanton, 1981).

A study was carried out to determine the effects of different UDP supplements on the performance of weaner steers fed veld hay sprayed with 1% urea. A combined supplement containing iso-nitrogenous levels of cottonseed, soybean and meat and bone meals was also tested in order to determine if these proteins were complementary.

MATERIALS AND METHODS

Animals and housing

Twelve rumen-cannulated Hereford x Africander steers (average weight 535 kg) were used to measure the degradation patterns of veld hay. The cannulae (Pigot Maskew (Pvt) Ltd. Bulawayo, Zimbabwe) were made of rubber with an internal diameter of 8 cm. In addition, 84 Hereford x Africander weaner steers (average weight 205 kg) were used to measure intake of veld hay and growth response to protein supplementation.

The steers were housed in individual pens with concrete floors, asbestos roofing and sides made of wooden rails. Each pen had a permanent food trough at one end and a water trough at the other. No bedding was provided.

Experimental design, protein supplements and basal diet

The 84 weaner steers were stratified by weight and randomly allocated to two groups of six animals and six groups of 12 animals. One group of six animals was used to determine the initial carcass weight, to provide the baseline for the growth performance assessment. The animals were fasted for 24 hours and weighed. They were then slaughtered and their carcasses were weighed. Initial carcass weight was estimated from the regression equation

ICW = 10.36 + 0.452ISLW (RSD = 3.266; R² = 0.906)

where:

ICW = initial carcass weight (kg)
ISLW = initial starved liveweight (kg)

The other group of six animals, and five of the groups of 12 animals, were used in the feeding trial. The treatments were:

1. Basal diet of milled veld hay sprayed and mixed with 1% urea just before feeding (control, six animals)

2. Basal diet plus cottonseed meal supplement (12 animals)

3. Basal diet plus soybean meal supplement (12 animals)

4. Basal diet plus meat and bone meal supplement (12 animals)

5. Basal diet plus bood meal supplement (12 animals)

6. Basal diet plus a combined supplement of cottonseed, soybean and meat and bone meals (12 animals)

The remaining group of 12 animals was used to measure intake of veld hay for the six treatments.

The basal diet was prepared by dissolving urea in warm water and spraying it onto milled (25-mm screen) veld hay just before feeding. Five litres of a 20% urea solution were sprayed onto 100 kg of hay to give a 1% level of application. A mechanical mixer fitted with a horizontal auger was used to prepare the feed, to ensure that the hay and urea were well mixed. Half of the urea solution was sprayed onto the hay in the mixer, using a watering can fitted with a rose on the spout, and the mixer was run for 10 minutes. The remainder of the solution was then added and the mixing repeated.

The composition of the protein supplements (Table 1) was based on effective degradabilities determined in an earlier experiment (Sibanda, 1989).

Table 1. Composition of protein supplements offered to weaner steers fed 1 %-urea-treated veld hay

Ingredient meal	Composition of treatment diets supplemented with
	Cottonseed meal	Soybean bone meal	Meat and meal	Blood supplements a	Combined
As-fed composition of supplements (g/kg)
White maize grain	780	783	815	815	815
Cottonseed meal	143	-	-	-	29
Soybean meal	-	207	-	-	120
Meat and bone meal	-	-	104	-	14
Blood meal	-	-	-	30
Urea	14.7	-	16	26	7.6
Gypsum (calcium sulphate)	12	-	12	12	11.7
Salt (sodium chloride)	25.1	5	26.5	58.5	1.4
Monocalcium phosphate	25.2	5	26.5	58.5	1.3
Calculated chemical composition
Dry matter (g/kg)	900	905	900	900	935
Rumen degradable protein (g/kg DM)	131	125	126	131	124
Undegradable protein (g/kg DM)	49	53	56	51	50
Total crude protein (g/kg DM)	180	178	182	182	174
Metabolisable energy (g/kg DM)	12.8	12.8	12.8	12.8	12.8

^a Cottonseed, soybean and meat and bone meals

Determination of degradation patterns of veld hay

The 12 rumen-cannulated steers were used in an incomplete (6 x 2) Latin Square design with two periods of 24 days each and two animals per treatment; the treatments were the six diets used in the feeding trial. The steers were offered veld hay sprayed with 1% urea once daily at the rate of 36 g DM/kg^0.75. Animals on treatments 2 to 6 were also fed 300 g/day of the protein supplement split into two equal parts and fed at 0800 and 1400 hours. Water was freely available. After 21 days on each feeding regime the degradation patterns of veld hay were measured using the nylon-bag technique (Mehrez and Ørskov, 1977; Ørskov and McDonald, 1979). Six bags containing veld hay samples (2.5-mm screen) were incubated in the rumen and one bag at a time was withdrawn after 12, 24, 36, 48, 60 and 72 hours. The constants of the degradation curve (p = a + b(1 -e^-ct)) were determined according to Mehrez and Ørskov (1977).

Rumen liquor samples were taken after all the bags had been withdrawn, two hours after offering the morning supplement. The contents of the rumen were mixed by hand before a 200 ml sample was taken with a beaker. The rumen liquor was strained through four layers of cheesecloth.

Measurement of intake of veld hay

The 12 steers allocated to the intake measurement group were paired in such a way that animals with weights as similar as possible were placed in one cell. Intake of veld hay was measured for each of the treatments in an incomplete (6 x 3) Latin Square design with three four-week periods.

The animals were fed individually for a preliminary period of three weeks, followed by a period of seven days when intake was measured. Veld hay sprayed with 1% urea was offered ad libitum (15% more hay than the previous day's intake) on a daily basis, with the previous day's refusals being weighed, recorded and removed before fresh hay was offered. The protein supplements were offered in two equal meals of 150 g at 0800 and 1400 hours. Water was freely available.

Performance of weaner steers fed veld hay and protein supplements

The feeding trial lasted 90 days. The animals were housed in individual pens and fed the basal diet (veld hay (sprayed with 1% urea) at the rate of 36 g DM/kg^0.75) once a day in the morning. The protein supplements were offered in two equal meals at 0800 and 1400 hours at the rate of 300 g/head per day. The animals were weighed weekly and the allowance of veld hay adjusted if necessary. Water was freely available. After 90 days the animals were fasted for 24 hours and weighed. They were then slaughtered and their carcasses were weighed.

Laboratory analyses

The dry-matter content of veld hay and protein supplements was determined by drying in a forced draught oven at 100°C for 24 hours. Nitrogen was determined by a macro-Kjeldahl technique.

The pH of the rumen liquor was measured within 10 minutes of sampling. For rumen ammonia determination, a mixture of 50 ml rumen liquor, 200 ml water and 100 ml 50% NaOH was distilled and the distillate collected over 2% boric acid. Released ammonium ion was titrated against 0.1 M HCl using screened methyl red indicator.

Statistical analysis

Analyses of variance for the degradation curve constants of veld hay and the protein meals and intake of veld hay were done with the MINITAB statistical package. Analyses of variance of live- and carcass weights, with initial starved liveweight as a covariate, were carried out using the GENSTAT programme. In all cases differences between treatments were determined by Student's l-test.

RESULTS

Degradation of veld hay

The crude-protein content of the veld hay before and after spraying with 1% urea was 49 and 73 g/kg DM, respectively. Veld hay degradation constants, rumen pH and ammonia concentrations did not differ (P>0.05) between any of the treatment groups (Table 2).

Hay dry-matter intake

Intake of veld hay dry matter by steers fed the basal diet ad libitum is shown in Table 3. Steers fed the protein supplements ate 18% (P<0.05) more hay than the steers fed no supplement. However, differences among the supplemented groups were not significant (P>0.05).

Table 2. Degradation constants for veld hay dry matter and rumen pH and ammonia concentration in steers fed 1%-urea-treated veld hay (36 g DM/kg^0.75 per day) with or without protein supplements

Treatment	Degradation constants for veld hay a			Rumen pH b	Rumen ammonia (mg/litre) b
	a	b	c
1. Basal diet (C): milled veld hay treated with 1% urea	10.3	75.4	0.016	7.2	309
2.(C) + cottonseed meal	11.1	71.8	0.011	7.1	339
3. (C) + soybean meal	7.0	72.7	0.025	7.4	301
4. (C) + meat and bone meal	10.3	76.4	0.010	7.1	336
5. (C) + bood meal	7.0	63.7	0.015	7.1	293
6. (C) + combined supplement c	8.4	60.2	0.012	7.2	306
SE	2.65	15.80	0.0083	0.16	62.0

^a From the equation p = a + b (1 - e^-ct)

where

p = dry-matter loss (%)
a = readily degradable fraction (%)
b = potentially degradable fraction (%)
c = rate of degradation of the b fraction
t = time (hours)

^b Rumen liquor samples were taken 2 hours after offering the morning supplement

^c Cottonseed, soybean and meat and bone meals

Table 3. Intake of veld hay dry matter by weaner steers fed 1%-urea-treated veld hay ad libitum with or without protein supplements

Treatment	Intake of veld hay dry matter (g/kg0.75 per day)
1. Basal diet (C): milled veld hay treated with 1% urea	52.1
2. (C) + cottonseed meal	62.5
3. (C) + soybean meal	61.1
4. (C) + meat and bone meal	65.4
5. (C) + bood meal	61.5
6. (C) + combined supplement a	66.1
SE	2.87

^a Cottonseed, soybean and meat and bone meals

Live- and carcass weight changes of steers on restricted hay intake

The live- and carcass weight changes of steers fed restricted amounts of veld hay sprayed with urea (36 g DM/kg^0.75) and offered different protein supplements are shown in Table 4.

All steers lost live- and carcass weight. Steers fed the combined supplement lost 8.8 kg more (P<0.05) liveweight than the steers offered other supplements, but this was not significantly different to the performance of the control steers. The steers in the other supplemented groups lost similar amounts of liveweight but only the steers fed cottonseed meal performed better (P<0.05) than the control steers.

Table 4. Live- and carcass weight changes of weaner steers fed 1%-urea-treated veld hay (36 g DM/kg^0.75 per day) with or without protein supplements

Treatment	Starved liveweight (kg)			Carcass weight (kg)
	Initial	Final	Change	Initial	Final	Change
1. Basal diet (C): milled veld hay treated with 1% urea	190.8	151.5	-39.3	98.9	72.5	26.4
2. (C) + cottonseed meal	196.2	162.7	-33.5	98.9	79.9	-19.0
3. (C) + soybean meal	195.8	161.7	-34.1	98.9	80.6	-18.3
4.(C) + meat and bone meal	195.4	160.0	-35.4	98.9	80.8	-18.1
5. (C) + bood meal	195.4	160.4	-35.0	98.9	78.9	-20.0
6. (C) + combined supplement a	199.2	155.9	-43.3	98.9	77.4	-21.4
SE	6.60	2.53	2.53	0.01	1.41	1.40

^a Cottonseed, soybean and meat and bone meals

The steers the control group lost 7 kg more (P<0.05) carcass weight than the steers fed supplements. Among the supplemented steers the only significant (P<0.05) difference was between the steers fed the combined supplement and those fed soybean and meat and bone meal supplements.

DISCUSSION

Protein source had no significant effect (P>0.05) on the extent and rate of degradation of veld hay in the rumen of steers on the different treatments. This indicates that the rumen environments in the steers on the different treatments were similar. The rumen pH and ammonia concentrations confirm this view. Preston and Leng (1987) have recommended rumen ammonia concentrations of at least 150 mg/litre for roughages of similar quality to the hay used in this experiment. The concentrations recorded in this experiment were more than double this recommended figure. However, only one sample was taken, and sampling could have coincided with peak concentrations.

The absence of a significant effect of protein supplementation on the degradation of veld hay suggests that the basal diet supplied adequate nutrients for the rumen microbes and that the supply of pre-formed amino acids, peptides and carbon chains from protein nitrogen sources provided no added advantage.

Other studies (Kellaway and Leibholz, 1983; Sriskandarajah and Kellaway, 1984; Ndlovu, 1985) have found that when rumen ammonia concentrations are adequate the response to rumen degradable protein from protein nitrogen sources is negligible. Thus, while acknowledging diurnal variation and the fact that spot samples were used, it may be inferred that the ammonia concentrations found in this experiment were adequate for both maximum microbial protein production and optimum degradation of veld hay.

Although there was no increase in the rate or extent of degradation of veld hay with protein supplements, there was a significant (P<0.05) increase in intake of veld hay dry matter. Kempton et al (1979) obtained similar results. Since the degradation of veld hay was similar in all treatments, it may be inferred that the increase in veld hay intake was not due to an improvement in the rumen environment of the supplemented animals compared to the control ones.

Supplementation with protein, in addition to urea sprayed on the veld hay, resulted in a significant (P<0.05) reduction in live- and carcass weight losses in weaner steers offered sub-maintenance amounts of veld hay. This suggests that the effects of protein supplementation were achieved not only through an increase in roughage intake, but also through an improvement in nutrient supply. This agrees with the findings of Smith et al (1978) and Ortigues (1987) who offered fish meal to growing dairy heifers and steers fed restricted amounts of fibre-rich diets, although their animals were fed in excess of maintenance requirements.

However, the reduction in live- and carcass weight losses with protein supplemented treatments compared to the control may be partly explained by an increase in energy intake. Assuming a metabolisable energy (ME) content of 6.72 MJ/kg DM for veld hay (Topps and Oliver, 1978), an intake of 36 g of veld hay DM/kg^0.75 would be equivalent to about 0.242 MJ ME/kg^0.75. Taking a steer of about 178 kg liveweight (mean of the initial and final weights), the 300 g/day of supplement translates to 6.2 g/kg^0.75, equivalent to 0.079 MJ ME/kg^0.75. This level of supplementation is equivalent to an increase of about 33% in ME intake. The average improvement in carcass weight change with supplementation was about 27%.

While the contribution of ME intake in reducing live- and carcass weight losses of the supplemented steers is acknowledged, it is possible that part of the response was due to UDP (undegradable protein) supply. Several studies (Smith, 1978; Lindsay and Loxton, 1981; Fattet et al, 1984; Ortigues, 1987) have shown the beneficial effects of UDP supplementation compared to energy at equal ME intakes. Smith (1978) used multiple regression analysis to show that for diets with high roughage and low protein content (85 g CP/kg DM), as used in this experiment, ME and UDP intake accounted for about 10 and 25%, respectively, of the total variation in liveweight gains of growing dairy heifers and steers.

The metabolisability (ME/GE) of the diet used in the current experiment was estimated to be about 0.42. This would give a k_m value of 65% (ARC, 1980). Therefore the contribution of increased energy intake to the reduction in carcass weight loss in this experiment would be about 79% of the total response to supplementation. The remainder would be due to UDP supply.

The reason for including the combined protein supplement was to determine if the individual protein sources would complement each other and result in improved performance. There was no evidence of this for either veld hay intake or live- or carcass weight changes of steers. In fact, there was a slight negative response to the combined supplement compared to the individual protein sources.

The lack of difference in the degradation and intake of veld hay and, possibly, in the performance of weaner steers fed restricted quantities of veld hay and offered different protein supplements, supports the observations by Oldham (1981) and Ørskov (1982) that there is little likelihood of improving animal performance by manipulating the quality of protein supply to the animal. This is because the amino acid composition of digesta passing into the duodenum was found to vary little under different feeding conditions (Oldham, 1981).

CONCLUSIONS

This study confirms the positive effects of UDP supplementation, in addition to adequate rumen degradable protein, on the performance of growing steers offered restricted quantities of low-protein roughages. The feeding of protein supplements led to an increase in intake of low-protein veld hay irrespective of protein source. However, the source of UDP had no effect on either intake or the performance of steers, suggesting that the UDP from the four proteins was of equal value.

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