Lufadeju E A, Olayiwole M B
National Animal Production Research Institute, Ahmadu Bello University, Private Mail Bag 1096, Zariaand
Umunna N N
Department of Animal Science, Ahmadu Bello University Zaria
Abstract
Introduction
Materials and methods
Results
Discussion
Conclusions
Acknowledgement
References
Intake and digestibility of urea-treated gamba (Andropogon gayanus) hay with or without urea supplementation was studied. Organic matter intake was improved from 57.5 to 72.8 g/kg 0.75/d while organic matter digestibility was improved from 564 to 699g/kg. Results indicate no significant differences in the utilization of all hays containing urea either as feed additive or for treatment. All treatments involving the addition of nitrogen gave positive nitrogen retention. It is concluded that urea supplementation at the rate of 1 percent of total dry matter intake sprayed on hay at feeding time would elicit similar improvement in utilization as would urea treatment.
Nigeria has about 140 million hectares of natural range which serves as the major source of forage for livestock, supplemented in a few places by sown pasture, grazing reserves and crop residues. Nomadic communal grazing involving migration of herds and families is gradually being replaced by limited transhumance, in which extensive grazing both in the range and in government approved grazing reserves is practiced. Under this system, animals rely almost totally on natural forages. Crop residues become available after harvest, at the onset of the dry season.
The Fulani pastoralists and agro-pastoralists together control about 90 percent of the national herd. Recently, because of the realisation that land development and expansion of crop farming activities will continue to reduce the available grazing land, efforts are being made to encourage the settlement of pastoralists and to integrate them with the non-pastoralists. The implication of this is that economic feeding systems must be developed, especially for dry season feeding. This would eliminate the need for migration in search of feed and water and limit the cyclical weight gain/loss of livestock.
Most of the 90 genera and 300 species of grasses found in Nigeria are members of the Paniceae and Andropogoneae tribes. One natural feed resource on which feeding systems can be based in Nigeria is the Gamba grass, Andropogon gayanus. Gamba grass is available in abundance in almost all ecological zones in Nigeria. The problem with gamba like other tropical grasses is the rapid decline in crude protein and soluble carbohydrate with age. This is coupled with a progressive increase in crude fibre and lignin (Agishi 1985; de Leeuw 1979). Consequently, tropical grasses are low in voluntary intake and digestibility after maturity (Obioha and Ndukwe 1976 Adu and Adamu 1982). It is therefore well established that significant alteration of plant composition occurs and decreases their nutritive value and adversely affects animal performance (Zemmelink 1973).
Mature fodder plants could be improved by alkali treatment. Urea treatment of crop residue is not new (Sundstol et al. 1977). Improved utilization of low quality tropical hays by treatment with urea, ammonia, sodium and ammonium hydroxide has been reported (Sherma et al. 1972: Sundstol 1981: Buettner et al. 1982; Green halgh 1984; Nwakatundu and Owen 1974; Utley et al 1978; Umunna 1982).
Preliminary trials at Napri, Shika in Nigeria, have shown significant improvement in the rumen degradation of urea-treated gamba hay when 40g urea was dissolved in 600g of water and sprayed on 1 kg of hay sealed in polythene bags for 20 days (Lufadeju, et al. 1986).
The objective of the study reported here was to compare the utilization of untreated and urea-treated gamba hay, with or without feed grade urea supplementation as the sole diet for Friesian/Bunaji dairy heifers.
Animals
Three Friesian/Bunaji heifers approximately 18 months old and weighing 194 ±10 kg liveweight were used. They were fitted with permanent rumen cannulae with an internal diameter of 50 mm. The animals were kept in individual pens to facilitate separate collection of faeces and urine.
Experimental diets and treatment arrangement
The heifers were allocated at random to receive ad libitum diets of (A) Untreated gamba alone; (B) Untreated gamba plus urea; (C) Urea treated gamba alone; (D) Urea-treated gamba plus urea in four experimental periods, so that each animal received each diet once in random order. By this arrangement four different rumen environments were created, which contained varying amounts of nitrogen.
Feed preparation
The hay used in this experiment was cut in February, during the dry season. Two tons of untreated mature gamba hay containing 5.5 gN/kg DM, and two tons of urea-treated gamba were used as the sole diet. The hay was treated with 40g of urea, dissolved in 600g of water per kg hay. The stack was covered with a polythene sheet in a pit and left to stand for 20 days. After the polythene was removed, the stack was allowed to aerate for 2 days to eliminate volatile ammonia before animal feeding commenced.
Feeding and management
For diets containing supplementary urea, 12.5g urea/kg DM intake (maximum 50g Urea/head/day) were dissolved in water (50:50 W/V) and sprayed on the hay at feeding time. The heifers were fed twice daily at 8.00 and 16.00 hours. The animals were fed to appetite with each receiving 5 kg DM hay per day, for 28 days for each treatment. Bone meal, trace minerals, sodium sulphate, salt licks and vitamin premix were mixed with the urea solution or water before being sprayed on the hay. Sodium sulphate was added to give a calculated 10:1 N to S ratio. Fresh water was available at all times. Voluntary intakes were recorded daily and the animals were weighed weekly.
During the last 7 days of each period, total faeces and urine were collected, faeces from the gutter behind the animals, and urine was collected in plastic buckets through transparent polythene tubes 15 cm diameter glued around the vulva, in a manner similar to that described by Cowan et al (1981). Urine was kept acid by adding 50 ml of 4 M-H2 SO4 (ph 2-3) to the 15 litre bucket for preservation.
Daily collections of faeces and urine were weighed, mixed thoroughly and a 10 percent subsample of each was taken. Samples of urine were stored at -16°C, and faecal samples dried immediately at 70°C for 48 hours and stored. At the end of the collections, samples were bulked, mixed thoroughly and sub-samples of urine analysed for nitrogen and of faeces for dry matter, nitrogen, neutral and acid detergent fibre and ash.
Feed and faeces were analysed for dry matter by oven drying at 105° for 24 hours; for nitrogen by micro-kjeldahl technique, using Markham micro-distillation apparatus; and for neutral and acid detergent fibre by the methods of Van Soest and Wine (1967).
Treatment of gamba hay with urea significantly (P<0.01) improved the nitrogen content from 0.55 to 1.78g/100g (Table 1); there were no significant differences in the proportions of other components. Prolonged exposure after the treated stack was opened did not affect chemical composition or rumen degradation (Table 2).
The intakes and digestibilities of all treatments containing urea, whether supplemented or from treatment were not significantly different from each other, and all significantly exceeded the figures from untreated hay (P<0.05, Table 3).
Table 1. Chemical composition of untreated versus urea-treated gamba hay.
|
Item |
Untreated |
Treated |
|
Percent |
||
|
Dry matter |
90.3 |
89.8 |
|
Cellulose |
44.0 |
47.2 |
|
NDF |
76.4 |
75.9 |
|
ADF |
56.2 |
60.5 |
|
Nitrogen |
0.55 |
1.78 |
|
Ash |
5.4 |
5.6 |
|
48-hr. Rumen degradation |
45.8 |
54.1 |
Table 2. The effect of prolonged exposure of treated Gamba hay on the chemical composition and rumen degradation.
|
Item |
Days after stack opening |
|
|
22-28 |
108-114 |
|
|
Dry matter |
88.70 |
90.98 |
|
Cellulose |
47.07 |
47.51 |
|
NDF |
76.82 |
75.03 |
|
ADF |
60.69 |
60.39 |
|
Nitrogen |
1.79 |
1.77 |
|
Ash |
5.53 |
5.80 |
|
48-hr. Rumen degradation |
52.9 |
55.4 |
Significantly higher (P<0.05) urinary nitrogen excretion was observed in animals fed treated compared with untreated hay (Table 4). The amount of nitrogen apparently absorbed differed among all treatments (Table 4), increasing with increased dietary concentration of nitrogen; it was negative for the untreated unsupplemented hay.
Apparent nitrogen retention did not differ significantly between treatments using the treated hay, and exceeded those figures recorded from the untreated hay. There were no significant differences between treated hay alone and untreated urea supplemented hay. The control hay gave a negative nitrogen balance (Table 4). Similar proportions of absorbed nitrogen were retained in the treated diets despite differences in dietary nitrogen concentration.
Table 3. Voluntary intake and digestibility of cattle given untreated and urea-treated Gamba hay with or without supplementary urea.
|
Item |
Treated |
Treated |
Untreated |
Untreated |
SED |
|
+ Urea |
alone |
+ Urea |
alone |
||
|
Intake of DM g/kg W0.75/d |
80.2a |
75.2a |
77.8a |
61.1b |
5.42 |
|
Dry matter digestibility g/kg |
680a |
640a |
663a |
536b |
26.02 |
|
Intake of organic matter g/kg W0.75/d |
74.5a |
70.1a |
73.8a |
57.5b |
5.00 |
|
Organic matter digestibility g/kg |
697a |
639a |
673a |
564b |
26.14 |
|
Neutral detergent Fiber digestibility g/kg |
770a |
736a |
750a |
636b |
24.10 |
|
Acid detergent Fiber digestibility g/kg |
714a |
675a |
675a |
568b |
22.98 |
Means with identical superscript within each row are not significant at 5% level.
Table 4. Apparent nitrogen absorption and retention by cattle given untreated and urea-treated Gamba hay with or without supplementary urea.
|
Item |
Treated |
Treated |
Untreated |
Untreated |
SED |
|
+ Urea |
alone |
+ Urea |
alone |
||
|
N intake g/d |
94.0a |
67.0b |
44.3c |
16.6d |
2.09 |
|
Faecal N g/d |
35.5 |
25.5 |
21.5 |
21.5NS |
7.48 |
|
Urinary N g/d |
21.2a |
15.2a |
4.1b |
4.4b |
4.13 |
|
N apparently absorbed g/d |
58.5a |
41.5b |
22.8c |
-4.9d |
6.03 |
|
N apparently retained g/d |
37.3a |
26.3ab |
18.7b |
-9.3c |
7.63 |
|
Apparently retained N (% apparently absorbed) |
63.7 |
63.3 |
82.0 |
- |
- |
Means with identical superscript within each row are not significant at 5% level.
The urea treatment of gamba hay in this study enhanced its nitrogen content threefold. This extent of increase in nitrogen has been reported previously (Orskov et al. 1983). Urease enzyme present in plant material, converts urea to ammonia at high temperature and moisture. Ammonia then penetrates plant material. Exposure of hay for 2 days after plastic cover removal allowed excess ammonia to escape and the pungent odour of ammonia to disappear. However, the amount of nitrogen which penetrated plant material did not change significantly with prolonged exposure. This is similar to the finding of Gordon and Chesson (1983).
The in vivo dry matter digestibility reported here for treated hay varied from 64 to 68 percent, similar to values of Greenhalgh (1984) and Fahmy and Orskov (1984). Urea supplementation of treated hay slightly but non-significantly improved dry matter intake and digestibility. However, significant improvements of 28 and 25 percent in intake and digestibility respectively were obtained when untreated hay was supplemented with urea. This level of improvement falls within the range reported by Sharma et al. (1972). There were no significant differences between treated and untreated hay supplemented with urea in either intake or digestibility. This observation raises fundamental economic questions about the efficiency of urea treatment in view of the requirement for labour and water, a question even more relevant to arid areas where water for human consumption is scarce. The degree of improvement in animal performance from urea treated forage resulting from the combined effects of higher digestibility and additional nitrogen has been reported to be similar to those of urea supplemented untreated hay (Verma and Jackson 1984). Under dry tropical conditions, nitrogen not energy has been identified as the first nutrient limiting animal performance (Verma and Jackson 1984). The lack of significant differences in nitrogen retention from treated or urea supplemented treated hay indicated that the nitrogen in treated hay was adequate for the amount of energy available from its fermentation, and further urea supplementation of treated material was of no benefit in the absence of additional energy. Animals fed untreated unsupplemented hay in this study had negative nitrogen retention, as did the sheep of Adu and Adamu (1982) which were fed three low crude protein tropical grass hays; the poor utilization of these grasses was attributed to low energy availability and inadequate nitrogen supply.
A consideration of the economic rearing of cattle requires the use of cheap fodder, either grass, legume, browse or crop residues. With regard to mature tropical grass of poor quality, one way their utilization can be enhanced is through urea supplementation either as feed additive or for treatment. The choice of method of supplementation depends on availability of labour and water. Addition of urea supplements to urea-treated roughages appears wasteful unless supplementary energy can be provided. Urea supplementation at the rate of 1 percent of total dry matter intake sprayed on hay at the time of feeding would elicit similar improvements in intake and digestibility as would urea-treated hay.
It is tentatively suggested that urea supplementation of hay would enhance its utilization, reduce the need for concentrate supplementation, and limit animal weight loss during the dry season.
The authors are grateful to Professor V. Buvanendran, and Dr. W.S. Alhassan for their valuable suggestions, and also to Dr. A G Jagun for assisting in the surgical preparation of the animals.
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