A.F. Mustafa, T.A. Mohammed and A.E. El-Tayeb

Institute of Animal Production, University of Khartoum, P.O. Box 32,
Khartoum North, Sudan.

SUMMARY

Twenty four mature Western Sudan Baggara bulls (364.5± 4.7 SE) were divided into four similar groups of six animals each and employed in a feeding trial that lasted for eight weeks. The groups were allotted at random to one of four diets contained 0, 25, 35 or 45% milled sorghum stover (MSS) incorporated in a conventional concentrate diet (CCD) based on sorghum grain and cottonseed cake. All diets contained 1% NaCl. The average daily dry matter intakes, liveweight gains (kg) and feed conversion ratios for the four groups were 10.4, 1.4, 7.4; 11.0, 1.5, 8.0; 10.7, 1.4, 7.6 and 11.8, 1.4, 7.9, respectively. All performance parameters were not affected ( p>0.05) by dietary treatments.

Digestion coefficient of dry matter (DM), organic matter (OM) and crude protein (CP) as determined by sheep were significantly lower (P<0.05) for diets contained MSS than for the zero MSS diet. Digestion coefficient of acid detergent fibre (ADF) was not affected (P>0.05) by treatments. The estimated DM, OM, CP digestion coefficient and total digestible nutrients percentage kTDN%) of MSS alone were 47.2, 43.6, 28.3 and 49.1%, respectively.

INTRODUCTION

Finishing beef cattle in the Sudan is heavily depending on feeding concentrate diets. The diet of choice to feedlot operators consists of equal parts of sorghum grain and cotton seed cake. The simplicity of formulation and availability of ingredients are among the reasons behind the popularity of this feeding regime. However, recent increased demands of sorghum grain and cotton-seed cake elevated prices to levels that limited the expansion of feed lot operations in this country. Therefore the attention of ruminant nutritionists has been devoted to crop r.,sidues and agro-industrial by-products as means of decreasing the cost of finishing beef cattle. In the Sudan the estimated annual yield of crop residues of which sorghum stover is the major one is about 5.5 million tons of dry matter (El Hag and Kurdi, 1986).

Beef cattle performance on sorghum stover could be improved by chemical treatments and supplementation (El Hag and Kurdi, 1986 and Herrera and Balderas, 1987). Mohammed Salih (1986) and El Hag and Goerge (1981) have shown the feasibility of incorporating MSS in a concentrate beef finishing diet up to 30%. Hence the objective of this study was to investigate the effects of partial replacement of the CCD with high proportions of MSS on performance of Western Sudan Baggara Cattle and to assess the nutritive value of MSS.

MATERIALS AND METHODS

Feeding trial

Twenty four mature feeder bulls of Western Baggara type were stratified according to liveweight into four groups of six animals each.-

Then these groups were randomly allotted to one of the dietary treatments described in Table 1. Bulls in each group were subdivided into two subgroups of three animals each and fed their respective diets (3 animals/pen) with water being freely available through out the experimental period. The diets were introduced through a 7 day adaption period followed by a 56 day experimental period during which the diets were offered ad lib. Daily feed intakes (kg) were recorded and the experimental animals were weekly weighed following ar, over night fast.

Digestibility trial

A digestibility trial was conducted to evaluate nutrients digestion of the experimental diets. Sixteen mature Sudan desert rams were involved in this trial. They were allowed a 5-day adaptation period during which the experimental diets were gradually introduced, followed by another 5-day adjustment period during which the ad libitum intakes were determined. Thereafter faeces were collected daily for a total collection period of 5 days. Chemical composition of diets and faecal samples were determined by standard method (A.O.A.C., 1980), acid detergent fibre (ADF) was determined by the procedure of Goering and Van Soest (1970). Gross Energy (GE) for both diets and faeces was determined using plain oxygen calorimeter (Parr Instrument Co. Moline, IL. 61265, U.S.A.) Digestion coefficients and TDN were calculated as described by McDonald a al. (1982). The nutritive value of MSS alone was estimated using regression equations relating digestion coefficients of different nutrients to the level of MSS in the CCD.

Data from the feeding and digestibility trials were subjected to analysis of variance (ANOVA) and differences among treatment means were detected using Duncan’s multiple range test (Steel and Torrie, 1980).

RESULTS

Feeding trial

The effects of dietary level of MSS on feed-lot performance of Western Sudan cattle are shown in Table 2. Inclusion of MSS with the CCD up to 45% (W/W) had no effect (P>0.05) on intake parameters, final body weight, liveweight gain and feed conversion ratio.

Table: 2 Effect of dietary level of milled sorghum stover on feedlot performance of western Sudan cattle.

Digestibility trial

The results of the digestibility trial are shown in Table 3. Inclusion of MSS significantly (P<0.05) decreased DM, OM, CP and energy digestion coefficient without effect on ADF digestion coefficient. Significant (P<0.05) reduction in TDN% was observed when the level of MSS was increased from 0 to 25% of the diet.

Estimated nutrients digestion coefficients, and TDN% of MSS alone are given in Table 4. Digestion coefficients of DM, OM, CP and TDN% were estimated to he 47.2, 43,6, 28.3 and 49.1% respectively.

The partition of TDN consumed by the experimental groups is shown in Table 5. The amount of TDN required for maintenance was calculated using the initial body weight according to NRC (1976). The ratio of conversion of TDN above maintenance (cofficiency of TDN utilization) into weight gain was calculated by dividing the amount of TDN consumed above maintenance requirements by the average weight gains. The efficiency of TDN utilization for gain was 3.2, 2.6, 2.1 and 2.7 for 0, 25, 35 and 45% MSS groups, respectively.

DISCUSSION

In this study sorghum stover was incorported with the CCD up to 45% (W/W) without negative effects on performance parameters. This is in agreement with the reports of Swan and Lamming (1970) and Lamming a oL (1966) who used milled barley starw as a substitute for maize. In contrast to our results, significant reduction in daily liveweight gain of beef cattle was reported by Gebrewolde t aL (1978) as the level of corn stover in the finishing diet was increased from 30 to 50%.

The effects of inclusion of MSS with the CCD were more pronounced with nutrients digestion than with feedlot performance. The results obtained in the digestibility trail are in accord with the results reported by Lamming ft oL (1966), Levy a oL (1972) and Smith

(1980). The reduced CP consumption observed with diets containing increased levels of MSS contributed to the observed depressed CP digestion coefficient because of the higher proportional effect of metabolic faecal nitrogen. This portion of nitrogen is a constant tax regardless of the level of dietary protein intake.

The estimated nutrients digestion coefficients of MSS indicated its low nutritive value. The estimated TDN% was 49.1%. This value was higher than the value reported by Nour (1986) for rice straw and was lower than the value reported by Osman (1985) for sorghum stover. The value of OM digestion coefficient was similar to that of barley straw as reported by Andrews a oL (1972).

The animals fed on diets contained MSS consumed less TDN` (Kg/day) while those on the CCD consumed more TDN than what is

recommended by NRC (1976) to produce similar weight gains. These results showed clearly that in local type animals a considerable amount of energy (about 1 kg TDN for each kg gain) could be wasted by feeding the CCD to finishing Sudan Baggara cattle. In this respect Mohammed Salih (1986) indicated that Sudan Baggara cattle are highly efficient in converting energy in the agro-industrial by-products into beef.

It was concluded that traditional system of free choice concentrate feeding is wasteful. MSS could be employed satisfactorily as cheap energy with the GCD up to 45% (w/w) without negative effects on performance parameters. Under the prevailing conditions of the Sudan, milling of sorghum stover is in-convenient to some feedlot operators and definitely increases the cost of production. Nevertheless, it is thought that the feasibility of using high levels of MSS as a substitute for the CCD would be more tempting to more feedlot operators to adopt t.

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