Effects of nitrogen level on the utilization of maize offal and sorghum brewer's grain in sheep diets

O A Olorunnisomo, M K Adewumi* and O J Babayemi*

Department of Animal Production and Health Sciences,
University of Ado-Ekiti, PMB 5363, Ado-Ekiti, Nigeria
sholanisomo@yahoo.com
*Department of Animal Science, University of Ibadan, Nigeria

Abstract

Inadequate supply of quality feeds is still a major problem in livestock production in the tropics, especially Nigeria. Use of agro-industrial by products such as maize offal (MO) and sorghum brewer's grain (SBG) in ruminant diets may provide a sustainable means of ameliorating this problem.

In two trials, maize offal and sorghum brewer's grain or a mixture of both were fed in a supplementary diet to growing West African dwarf (WAD) sheep given a basal diet of guinea grass (Panicum maximum) hay. In Trial 1, the diets were offered without urea while in Trial 2 urea was added to make the diets isonitrogenous. Feed intake and growth rate of animals improved significantly (P<0.05) with increasing levels of SBG in the diets, however when the diets were isonitrogenous, feed intake, digestibility and growth of animals were not significantly different (P> 0.05). With equal levels of nitrogen in the diets, MO and SBG showed similar effects on performance of WAD sheep.

Since sorghum brewer's grain is cheaper, it may be a better option than maize offal for inclusion in sheep diets.

Keywords: maize offal, nitrogen, sheep, sorghum brewer's grain

Introduction

In most tropical areas, forage yield from natural grasslands is low and of poor quality (Adebowale et al 1993). To increase productivity of ruminant animals from natural grasslands, some form of concentrate supplementation is required (Adewumi et al 2004; Adeneye and Sunmonu 1994; Devendra and McLeroy 1982).

The conventional sources of carbohydrates and protein for livestock feeds are the cereal grains, root crops, oil seed cakes, and fishmeal. However, there is a steady increase in the price of these feed ingredients due to competition with humans and rising demands for poultry feeds. Inclusion of these ingredients in ruminant diets therefore, may lead to a substantial increase in the cost of ruminant production.

Maize offal (MO) and sorghum brewer's grains (SBG) which are by products of maize processing and local brewing are alternative sources of carbohydrates and can wholly or partially replace the conventional grains in ruminant feeding (Olorunnisomo and Ososanya 2002; Dairo 1999). These by-products are cheap and readily available, hence can reduce the cost of feeding ruminants and minimize the effect of seasonal shortages of feeds for these animals.

Chemical analyses have shown that the protein content of MO and SBG is higher than that of their respective grains but the utilizable energy content is lower (Adeneye and Sunmonu 1994). The gross energy content of MO and SBG is similar but the protein content of SBG is much higher than that of MO. This may be attributed to the microbial action on the sorghum grain during the brewing process.

The objective of these trials was to evaluate the performance of WAD sheep fed varying proportions of MO and SBG, with or without urea addition in a supplementary diet.

Materials and Methods

In Trial 1, fifteen male WAD sheep (7.28 ± 0.22 kg live weight) approximately 6 months old, were randomly assigned to three experimental diets containing varying proportions of MO and SBG in a completely randomized design. The treatments were replicated five times with one animal in each treatment / replicate.

In Trial 2, the diets above were made isonitrogenous by addition of urea. Twelve male WAD sheep (10.8 ± 0.43 kg) were assigned to the diets with four animals per treatment in a completely randomized design. Each of the trials lasted for 94 days. The animals were allowed 10 days to adapt to the diets and experimental measurements were taken in 84 days. The various components of the experimental diets are shown in Table 1.

Animals were housed individually and fed the experimental diets together with guinea grass hay. The diets and hay were offered at the same time (9am) in separate feed troughs. Hay was offered ad-libitum at 110% of previous day's intake while the supplements  were offered at 2% of animal body weight. Fresh water was offered daily. Feed offered and feed refused were weighed each morning and daily feed intake recorded for each animal. Animal weights were recorded weekly and average daily gain calculated for each treatment. At the end of the growth evaluation in both trials, animals from each treatment were transferred to metabolic pens with floors adapted for faecal collection. Experimental diets were offered ad-libitum (110% of previous day's intake) for 14 days. Fresh water was also offered each morning. Total faeces and feed refused were collected and weighed in the last 7 days. Ten per cent of faeces collected were kept for chemical analysis. Data obtained were subjected to analysis of variance and Duncan's multiple range tests using the SAS (1995) procedures. The proximate composition of MO, SBG experimental diets (Table 2) and faecal samples were determined by the AOAC (1995) methods. Detergent fibre of feed and faeces was determined by methods of Van Soest and Robertson (1985) and gross energy values calculated from organic matter components using the relationship of Nehring and Haenlein (1973).

Results and Discussion

The dry matter intakes of sheep fed hay and the supplementary diets are presented in Table 3. In Trial 1 there were significant differences (P<0.05) among the treatments for hay and total DM intake. Increasing levels of SBG in the diets stimulated higher intakes of hay and consequently increased the total DM intake of the animals. This may be attributed to the higher protein content of SBG compared to MO.

In Trial 2 when the diets were made isonitrogenous, there was no significant difference among the treatments for hay and total DM intake, showing that sheep had equal preference for MO and SBG when nitrogen level is adequate in the diets. The nitrogen content in the basal hay diet was low, leading to low DM intake. Increasing levels of nitrogen in the supplementary diets stimulated rumen function and consequently stimulated higher DM intake by the sheep.

The dry matter and nutrient digestibility of the diets fed to WAD sheep are presented in Table 4.

There were no significant differences (P>0.05) among treatments for DM, energy and CP digestibility in Trial 1, however the digestibility of NDF, ADF and lignin differed significantly (P<0.05). Energy digestibility did not follow the expected trend since more energy is expected to be available with improved digestibility of cell wall constituents. This is probably due to the method used for energy determination in feed and faeces, which was based solely on calculations from proximate analysis without consideration for the digestibility of cell wall constituents. The digestibility of the fibre and lignin fractions improved with higher inclusion of SBG in the diets, suggesting that the higher content of N in SBG aided the digestion of fibre in the diets. In Trial 2, when urea was added to the diets, the apparent digestibility of DM and other nutrients did not differ significantly (P>0.05) among the treatments.

The growth rate and feed efficiency of sheep fed the different diets are given in Table 5.

The growth rate of WAD sheep improved significantly (P<0.05) with increased level of SBG in the diets when urea was not added, the feed efficiency however was not affected. When the diets were isonitrogenous, growth rate and feed efficiency did not significantly differ (P<0.05) among the treatments. Since the gross energy content of MO and SBG are similar, it may be concluded that the difference noted among the treatments in Trial 1 was due mainly to the higher protein content of SBG compared to MO. When nitrogen levels in the diets were the same, SBG had no apparent advantage over MO for growing WAD sheep.

Conclusions

• Sorghum brewer's grains stimulated a better performance in the sheep than maize offal when the protein content of the diet was low, however when protein content was adequate, SBG and MO had similar effects on performance of WAD sheep.

• Since sorghum brewer's grain is cheaper and has a higher protein content than maize offal, it may be a better option for inclusion in sheep diets in Nigeria.

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