Performance of cattle given crop residues supplemented with high-quality forages and agro-industrial by-products
George W Ocen
Department of Animal Science, Makerere University, PO Box 7062, Kampala, Uganda
Two feeding experiments were conducted at Makerere University Research Institute, Kabanyolo (MUARIK) to determine intake and liveweight change in growing Friesian steers given maize stover as basal diet supplemented with urea/molasses, immature fresh green elephant grass and cotton seed cake (CSC). In experiment 1, sixteen steers aged 9 months and averaging 173 kg liveweight were used in a randomized block design. The diets used were: chopped maize stover (C) as control; chopped maize stover + urea/molasses (CU); chopped maize stover + 2 kg/animal/day of immature fresh green elephant grass (CG); and chopped maize stover + urea/ molasses + 2 kg/animal/day of immature fresh green elephant grass (CUG). Each animal got a constant input of 1 kg/day of cotton seed cake.
Mean maize stover dry matter intakes (DMI) for the four treatments were C 1.6, CU 2.1, CG 1.7 and CUG 2.2kg/animal/day. Total DMI was C 2.5, CU 3.2, CG 2.9 and CUG 3.6 kg/animal/day. The average daily liveweight gain (ADG) was C 357, CU 611, CG 525 and CUG 718 g/day. The differences in maize stover DMI, total DMI and ADG were significant (P<0.05).
In experiment 2, the treatment CUG was used as the basal diet in order to measure the response of growing Friesian steers aged 15 months and averaging 327 kg liveweight to graded levels (0, 500, 1000, 1500, 2000 g/animal/day) of cotton seed cake. The regressions of total DMI, ADG and kg CSC/kg gain ratio on cotton seed cake were significant (P<0.05).
Under the conditions of these experiments, urea/molasses (experiment 1) and the 500 g level of cotton seed cake (experiment 2) may be recommended as the best supplements on the basis of labour and cost.
KEY WORDS: Cattle, feed, supplements, urea, molasses, cottonseed cake, agricultural byproducts, elephant grass.
One of the major limiting factors to animal production in Uganda is nutrition. Yet in this country exist vast feed resources that are untapped and could make a major impact on ruminant livestock production. Crop production gives rise to considerable amounts of agricultural wastes and by-products that ruminants can convert into highly nutritious animal products for man. A number of reasons, including human population pressure on the land, scarcity and high cost of concentrate feeds, long dry seasons in most parts of the country, and the economic need to match ruminant livestock production systems with available resources, justify increased use of these non-conventional feed resources for ruminant animal feeding. However, nutrient analyses of crop residues indicate that they fall within the definition of Balch (1977) of a low-quality roughage. They are low in protein (20 - 65g N x 6.25/kg DM) and phosphorus, marginal in calcium and high in fibre and lignin. This unbalanced nature of nutrients causes a big limitation to ruminant livestock productivity on crop residues.
Leng (1986) proposes two major strategies for improving ruminant production in animals fed crop residues or mature tropical pastures: (1) to supplement nutrients to ensure efficient rumen function, and (2) to provide bypass supplements to balance those available from fermentative digestion. These strategies aim to ensure maximum intake and efficiency of utilisation of the absorbed nutrients by the animal.
Non-protein nitrogen (NPN) sources such as urea, and readily available energy sources such as molasses optimise rumen function. The beneficial effects of NPN and urea/molasses mixtures on DM intake (DMI) and digestibility are well documented (eg: Campling et al 1962; Winter and Pigden 1971). Although NPN and readily available energy optimise rumen function, Preston (1989) and others have shown that growing and lactating animals have a very high requirement for amino acids, glucose and long- chain fatty acids (LCFA), and that high growth rate and milk production cannot be supported on the products of fermentative digestion alone. Several workers, including Saadullah et al (1982) and Preston and Leng (1987) have pointed out the importance of protein-nitrogen in promoting growth rate in growing animals and milk production in lactating animals.
Bypass protein supplements are now considered essential to take advantage of the volatile fatty acids (VFA) energy generated from roughage fermentative digestion. Also, Leng and Preston (1976) have emphasized the need to supplement diets in order to ensure adequate amounts of glucose and/or glycogenic compounds to obtain high ruminant productivity from low-protein tropical feed resources. Many products, including oilseed cakes and meals, animal and fish by-products, and cereal grains have been reported to improve animal performance owing to their high glucogenic potential and good rumen escape characteristics (see Saadullah et al 1982).
Supplementation of low-quality or high fibre diets with high- quality forages (fresh green grass, leguminous plant leaves) is an area in ruminant nutrition that has not been extensively investigated. However, available literature suggests that a potential exists in the use of high-quality forages to upgrade the nutritive value of the low-quality roughages especially in the low input/low output production systems of the tropics. Guttierez et al (1983), Leng (1982), Preston and Para (1981), Singh (1980) and Moran et al (1983) have noted the stimulatory effect of small amounts of fresh green forage on increasing DMI and digestibility of low-quality roughages.
The principal objective of this study was to apply the strategies mentioned above to evaluate the potential of urea/molasses, fresh green elephant grass (Pennisetum purpureum) and cotton seed cake as supplements to maize stover. Two experiments using growing Friesian steers were conducted. Experiment 1 compared the effects of urea/molasses, fresh green elephant grass and their combination while experiment 2 studied the effects of varying the level of cotton seed cake in the diet. In both experiments dry matter intake (DMI) of maize stover and average daily gain (ADG) were measured. Total DMI was calculated.
Materials and methods
Two feeding experiments were conducted at Makerere University Agricultural Research Institute, Kabanyolo (MUARIK) to determine intake and liveweight change in growing Friesian steers given maize stover as basal diet supplemented with urea/molasses, fresh green elephant grass and cotton seed cake (CSC).
Experiment 1 was laid out in a randomized block design with four animals per treatment. Altogether sixteen growing Friesian steers aged 9 months and averaging 173 kg liveweight were used. The animals were blocked according to their initial liveweight. The experiment examined effects of two factors, urea/molasses and fresh green elephant grass as supplements to maize stover with each animal getting a constant input of 1 kg/day of CSC. The treatments were as follows:
C: Chopped maize stover (control)
CU: Chopped maize stover + urea/molasses
CG: Chopped maize stover + 2 kg/animal/day of immature fresh green elephant grass.
CUG: Chopped maize stover + urea/molasses + 2 kg/animal/day of immature fresh green elephant grass.
Intake was measured in individual metabolism cages. Supplements were offered once daily (at 09.00 h). Cotton seed cake was given first followed by elephant grass for those animals on treatments CG and CUG. When the supplements were eaten up then maize stover was offered. Chopped maize stover (10 mm particle size) was offered ad libitum in all the treatments. The urea used was of fertilizer grade (46% N) and was mixed in the proportions of 5% urea, 45% molasses and 50% water. The animals on treatments CU and CUG each received 1 litre/day of this mixture sprinkled on to the maize stover given in three feedings (09.00, 14.00 and 18.00h). To achieve ad libitum intake, maize stover was offered with the aim of having at least 10% refusals daily. A commercial mineral supplement (5% phosphorus) in the form of blocks was available as licks. Animals had free access to water from automatic water troughs. The experiment lasted for 70 days.
|Table 1: Composition of the diet ingredients|
|Dry Matter||Nutrient content (g/kg DM)|
Initial liveweight was taken at the start of the experiment and thereafter measurements were taken bi-weekly. Daily maize stover intake for each animal was obtained by difference between feed offered and refusals. There were no refusals for the supplements. Dry matter (DM) was determined for both feeds and maize stover refusals for purposes of calculating dry matter intake (DMI). Elephant grass was analyzed for DM weekly while cotton seed cake, maize stover and molasses were analyzed for DM at the beginning and end of the experiment. The nutrient composition of the diet ingredients was determined by proximate analysis. Data were analyzed using analysis of variance; the differences between individual pairs of treatment means were compared using Least Significant Difference (LSD) procedures (Snedecor and Cochran 1967).
Experiment 2 used the best diet in terms of ADG from experiment 1 (CUG) to measure the response of growing Friesian steers aged 15 months and averaging 327 kg liveweight to graded levels (0, 500, 1000, 1500, 2000 g/animal/day) of cotton seed cake. Two animals per treatment were used and the response in terms of DMI and ADG was measured and analyzed by regression using linear models of SAS computer programme. The experimental procedure (eg: animal management) was similar to that in experiment 1. The composition of the feed ingredients was also similar to that used in experiment 1. The experiment lasted for 90 days.
|Table 2: The effects of treatments on DMI of maize stover, total DMI and ADG|
|Dry matter intake|
SEM: Standard error of the mean
abc: Similar superscripts denote no significant difference
between the treatment means.
The differences in maize stover DMI between treatments were significant (P<0.05). However, separation of individual pairs of treatment means using LSD did not show significant differences between some pairs. The highest significant difference (P<0.01) was between treatments C and CUG. Total DMI did not show significant differences between treatments C and CG, CU and CG, and CU and CUG. The differences in total DMI were significant between C and CU (P<0.05), very highly significant (P<0.001) between C and CUG, and highly significant (P <0.01) between CG and CUG.
The differences in ADG were significant between treatments C and CU (P<0.01), C and CG (P<0.05), C and CUG (P,0.05). There were no differences in ADG between CU and CG and between CU and CUG.
The original data on which regression analysis was carried out in experiment 2 is shown in Table 4.
The regression coefficient (1.80-04) of maize stover DMI on cotton seed cake is not significant at the 5% level, and the lower r5 value (0.14) indicates that only 14% of the variation in DMI of maize stover is explained by the level of cotton seed cake. On the basis of these tests, the estimated model Y = 3.32+1.80 -04X is not statistically accurate.
|Table 3: Response of growing Friesian steers fed on maize stover to graded levels of cotton seed cake.|
|Level of cotton seek cake (g/d)|
|Dry matter intake (kg/d)|
|Table 4: Regression of various parameters on cotton seed cake intake|
|maize stover||1.80 -04||0.37 3.32+1.80 -04X||0.41 2.59-04||0.69|
|Total DMI||1.17 -03||0.93||3.13+1.17 -03X||0.41 2.59 -04||4.47*|
|CSC/gain||1.36 -03||0.94 0.32+1.36 -03X||0.45 2.84 -04|
|feed/gain||-4.8 -03||-.79||15.96-4.8 -03X||3.28 2.08 -03|
b=regression coefficient; r=correlation coefficient;
Sy.x=standard error of estimate; X = level of cotton seed cake;
Sb=standard error of regression coefficient;
* Significant at P<0.05
The regression coefficient for total DMI (1.17 -03) is significant (P<0.05); and the high r5 value (0.87) for this parameter indicates that 87% of its variation is explained by the level of cotton seed cake in the diet. On the basis of these tests, the model Y = 3.13+1.17 -03X is statistically accurate.
The regression coefficient (0.26) for ADG is significant (P<0.05); and its high r5 value (0.88) indicates that 88% of the variation in this parameter is accounted for by the level of cotton seed cake in the diet. On the basis of these tests, the estimated model Y = 244.20+0.26X for ADG is statistically accurate.
The regression of kg CSC/kg gain ratio on cotton seed cake (1.36 -03) is statistically significant and 94% of the variation in this ratio is explained by the level of cotton seed cake. The estimated model Y = 0.32+1.36 -03X is statistically accurate on the basis of these tests. The regression of kg total feed/kg gain ratio on cotton seed cake was not significant, though a large variation (62%) in this ratio was accounted for by the level of cotton seed cake.
Experiment 1 compared the effects of urea/molasses with those of immature fresh green elephant grass on maize stover DMI and ADG. Urea/molasses had beneficial effects on both maize stover DMI and ADG. These results agree with those of Campling et al (1962) and Winter and Pigden (1971) who reported that NPN and readily available sources of energy optimise rumen function resulting in increased DMI and improved performance in animals fed diets based on low-quality roughages. There was also a tendency for the fresh grass to increase total DMI (see CG vs C; and CUG vs CU) although the differences were not statistically significant at the 5% level. This is in agreement with Preston and Para 1981, Leng 1982, Guttierez et al 1983.
The highest DMI of maize stover and ADG were obtained from CUG. This is not surprising considering the optimal balance of nutrients was expected on this diet. However, there was only slight differences between CUG and CU in their effects on both total DMI and ADG. It appears that in this study, the effect of fresh green elephant grass was marginal in optimising rumen function; possibly the quantity was less than optimum.
Although animals on CU appeared to eat more maize stover and grow faster than those on the CG diet, these differences were not significant. It is probable that the small number of animals per treatment made it difficult to detect statistical differences, especially in maize stover DMI where absolute differences were small. Except for the difference between C and CUG which was significant at the 1% level, all other differences could only just be detected at the 5% level.
Experiment 2 studied the effects of varying the level of cotton seed cake in the diet on various parameters. Response of maize stover DMI to increasing levels of cotton seed cake was erratic as indicated by the low correlation coefficient (0.37); and it can be said that in this study, the effect of increasing the level of cotton seed cake on maize stover DMI was negligible. In other studies (eg: Alvarez and Preston 1976) response of DMI of a low-quality roughage to bypass protein supplement has been found to be curvilinear, probably owing to the effects of substitution as the high quality supplement is increased. The highest DMI of maize stover (3.9 kg) was achieved at the 500g level. This level also gave the lowest CSC/gain ratio.
Considering the amount of supplement/kg liveweight gain and the rate of increase in the intake of maize stover, the supplementary value of cotton seed cake at the 500 g level is preferred in this study than other levels since the economic benefits realized from supplementation of crop residues are mostly assessed based on the balance between the biological outputs (liveweight gain) and the cost of purchased inputs and labour.
Total DMI and ADG responded linearly to increased cotton seed cake. The linear response of ADG to increasing levels of cotton seed cake is in agreement with the results reported by López et al (1976) using rice polishings to supplement chopped sugarcane. However, Saadullah (1984) and Perdok and Leng (1987) have reported curvilinear relationships between ADG and bypass protein supplement. In their work, response was found to be greater with the first level of supplement and then reached a plateau with succeeding levels. This suggests that once optimum level is reached, further additions of supplement are uneconomic.
The linear relationship between ADG and cotton seed cake reported here appears to reflect substitution of maize stover by cotton seed cake at the higher levels, though the pattern of substitution was not explicit. Total feed/gain ratio was reducing though not significantly with increasing levels of cotton seed cake. López et al (1976) have also reported similar trends. However, this parameter has little economic significance in this study since the largest part of total feed was constituted by maize stover which was not purchased.
The results reported here agree with most published data on animals fed crop residues supplemented with urea/molasses and fresh green forage. However, there is a need to further verify the role of elephant grass as a supplement to low-quality roughages. There is also a need to study the rumen ecology and function (especially degradability, ammonia and VFA production) in animals fed these diets so that firm conclusions can be drawn from the observed relationships. This will also enable nutrient availability to the animal fed these diets to be calculated with a greater degree of certainty.
Under the conditions of these experiments, urea/molasses (experiment 1) and the 500 g level of cotton seed cake (experiment 2) may be recommended as good supplements to maize stover on the basis of labour and cost.
I wish to thank the International Foundation for Science (IFS) for funding the research (AB/4581) which has resulted into this publication. My thanks also go to the IFS scientific advisors who through their suggestions and recommendations during the conception period of the project made it possible for this research project to be accepted for funding. I am also grateful to my Assistant Mr. John Okanya without whose dedication this work would not have been possible.
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(Received 30 May 1992)