Effects of replacing maize bran with sun dried sisal wastes in supplementary diets on growth performance of growing beef cattle

Innocent B Kavishe, Sebastian W Chenyambuga and Ellen S Dierenfeld¹

Department of Animal, Aquaculture and Range Sciences, Sokoine University of Agriculture, PO Box 3004, Morogoro, Tanzania.
chenyasw@yahoo.com
¹ Outreach, Inc., Des Moines, IA, USA

Abstract

This study was conducted to assess the effects of replacing maize bran with sun dried sisal wastes as a source of energy in concentrate diets on feed intake and growth performance of growing beef cattle. A total of 32 weaned Boran calves (16 females and 16 males) with the age of six to eight months were used in the experiment. Four females and four males were randomly allotted to each treatment. Animals on treatment one (T₁) were supplemented with a diet containing sunflower seed cake (49.99%) and maize bran (48.01%) while those on treatment two (T₂) were supplemented with a diet containing sunflower seed cake (55.59%), maize bran (21.22%) and sun dried sisal wastes (21.22%). Animals on treatment three (T₃) were supplemented with a diet comprised of sunflower seed cake (59.97%) and sun dried sisal wastes (38.03%). All diets contained mineral mix (1.5%) and had about 16% CP and 10 MJ/kg DM metabolisable energy. The animals on T₁, T₂ and T₃ were grazed during the day and provided with supplementary diet at 1.5% of their body weight in the evening. Animals on treatment four (T₄, control) were only grazed and not supplemented.

The experimental period lasted for 83 days. Animals on T₁ (87.4 ± 0.834 kg DM) and T₂ (87.9 ± 0.921 kg DM) had higher (P ≤ 0.05) intake of supplementary diets than those on T₃ (70.3 ± 0.619 kg DM). Growth rates of animals on T₁ (0.696 ± 0.0218 kg/day) and T ₂ (0.730 ± 0.0254 kg/day) were higher (P ≤ 0.05) than that of animals on T₃ (0.569 ± 0.0189 kg/day) and T₄ (0.203 ± 0.00772 kg/day). Feed conversion ratios for animals on T₁ (1.83 ± 0.0469), T₂ (1.76 ± 0.0561) and T₃ (1.81 ± 0.0761) did not differ (P ˃ 0.05). The highest gross margins per animal were observed from animals on T₂ (TZS 76,820), followed by those on T ₁ (TZS 69,372) and T₃ (TZS 57,831). It is concluded that replacing 50% of maize bran with sun dried sisal wastes as sources of energy in supplementary diets of grazing animals promotes higher growth rate and results in higher profit than using a diet comprised of maize bran alone as source of energy.

Keywords: Boran, feed intake, feed conversion ratio, gross margin

Introduction

In Tanzania beef cattle production is not only important for its share in the total Gross Domestic Product (GDP), but also for its contribution to national food supply (meat and milk) and food security. Beef cattle contribute about 53% of total meat consumed in Tanzania (MLFD 2010). Moreover, beef cattle production acts as a source of income, employment and an inflation free store of wealth for livestock farmers in rural areas. Cattle breeds used for beef production in Tanzania are the Tanzania shorthorn zebu (TSZ), Ankole and Boran. The TSZ are the majority and contribute about 94% of red meat produced in the country (UNIDO 2012). They are mainly kept under the traditional sector in the agro-pastoral system (80% of the animals) and pastoral system (14% of the animals). The TSZ are also kept in commercial ranches and dairy farms (6%) (MLFD 2010). Boran cattle are considered as improved beef cattle and contribute about 6% of red meat produced in the country. They are kept on commercial ranches, mainly the National Ranching Company (NARCO) and a few private farms.

In the agro-pastoral and pastoral production systems cattle are fed on natural pastures growing on communal lands. Cattle reared in communal lands are faced with challenges of scarce and poor quality feeds (Mtamakaya 2002), especially during the dry season, as the quantity and quality of natural pastures vary with seasons. During the rainy season natural pastures are plentiful and of good quality, but this condition is experienced only for five to six months of the year while the rest of the year (6 - 7 months) is dry season (Mtengeti et al 2008). During the dry season beef cattle suffer from feed unavailability and what they get from communal grazing areas is poor quality roughages. This situation affects productivity as animals lose weight and consequently take a longer time to reach slaughter weight (Mushi 2004).

Several strategies to improve nutrition of ruminant livestock for increased productivity have been suggested. The most common strategy is supplementation of grazing animals with different protein and energy concentrates. The conventional protein supplements include oil cakes such as cotton and sunflower seed cakes. Cereal grains and agro-industrial by-products are the main supplements used to provide energy to cattle under the feedlot system. Maize bran is a product of milling of dried maize grain and comprises the bran coating (with high fibre) with some maize germ and starch particles. It is a good source of energy in ruminant and non ruminant rations (Dotto et al 2004). Previous studies have verified its potential for promoting increased weight gain when mixed with other ingredients (Weisbjerg et al 2007). However, being a popular ingredients in poultry and pig rations, its demand and prices are high, limiting its cost effectiveness for feeding beef cattle.

Sisal pulp can be used as a supplementary feed for cattle in different forms such as dry, ensiled or fresh pulp. The harvested sisal leaf comprises 4% fibre and 96% sisal waste (Magoggo 2011). Studies have shown that up to 27 kg/day of wet sisal pulp can be supplemented to cattle without causing adverse effects (Herrera et al 1980; Kahonga 1994). The study by Herrera et al (1980) further indicated that up to 10 kg DM of dried sisal waste can be used per day for fattening cattle without any problem. In Kenya, grazing steers supplemented with sisal waste gained up to one kg per day (UNIDO 2005). However, ensiled sisal waste have a low concentration of sugar and protein, hence, when fed to livestock, there is a need to supplement rich fermentable carbohydrate and protein sources (Kahonga 1994).

In Tanzania sisal is mainly grown commercially in Tanga, Kilimanjaro, Morogoro, Lindi and Mtwara regions. It is also widely grown in many parts of the country as farm hedges. Tanzania produces about 35,000 tonnes of fibre per year and it is estimated that 300,000 tonnes per year of sisal pulp dry matter are produced (OXFAM 2014). This waste, if not utilized, can result in environmental pollution. The common sisal waste disposal method in Tanzania is to heap solid wastes and leave it to rot and ferment on the ground in an open area. Such heaps normally emit offensive odour and greenhouse gas (GHG) to the environment, and the effluent pollutes streams and rivers (Salum and Hodes 2009).

This study was carried to evaluate the potential of use of sun dried sisal wastes as a ruminant livestock feed in order to mitigate the problem of feed scarcity during the dry season and environmental pollution. The study assessed the effects of replacing maize bran with sun dried sisal waste in supplementary diets on feed intake and growth performance of growing Boran cattle. It was hypothesized that the use of sisal waste in feeding beef cattle will reduce feed cost and hence, increase the profitability of beef cattle enterprises.

Materials and methods

Description of the study area

The study was conducted at Shallom Farm, a privately owned facility that was formerly one of the satellite ranches within the government-owned Mzeri Ranch. The ranch is situated about 35 km north of Handeni district and 45 km south west of Korogwe district, located between latitudes 4⁰ 55` and 6<sup>0</sup> 04`S and longitudes 37⁰ 47` and 38<sup>0</sup> 46`E. The area has temperatures that range from 18 to 32 ^oC and receives average rainfall of 760 to 800 mm/year in a bimodal distribution.

Feed materials and diet formulation

Feed ingredients used to formulate the experimental diets included maize bran, sisal wastes, sunflower seed cake, mineral premix and salts. The proportions of these ingredients in the dietary treatments are shown in Table 1. Fresh sisal wastes (pulp) were collected locally from Mazinde decorticator plant after separation of the fibre from the leaves. The wastes were spread on canvas to dry under the sun for a period three days, with occasional mixing. After drying, fibre was removed from the sisal wastes by manual sorting and sieving. Maize bran and sunflower seed cake were collected from agricultural input supply centres located within the study area.

A total of three diets were formulated and used as supplementary diets in three treatments as shown in Table 1. Treatment one (T₁) comprised of maize bran as the main source of energy and sunflower seed cake as the main source of protein. Treatment two (T₂) was formulated by mixing maize bran and sisal wastes in equal proportions (on dry matter basis) as the energy sources of the diet and sunflower seed cake was added as a source of protein. Treatment three (T₃) was formulated by using sisal wastes as the sole energy source and sunflower seed cake as a source of protein. Locally obtained mineral premix (Maclik super^TM) and common salt (NaCl) were added to all three diets as the mineral sources.

Analysis of chemical composition of feed ingredients and experimental diets

Samples of formulated supplementary diets, pastures from the grazing area, sun dried sisal wastes, maize bran and sunflower seed cake were analysed to determine dry matter (DM), organic matter (OM), crude protein (CP), ether extract (EE), crude fibre (CF), and ash contents (AOAC 1990). Neutral detergent fibre (NDF) and acid detergent fibre (ADF) were determined according to the procedure of Van Soest et al (1991). In vitro dry matter and organic matter digestibilities were determined using the two-stage in vitro technique of Tilley and Terry (1963). Mineral (calcium and phosphorus) contents of the feeds were determined by atomic absorption. Metabolisable energy (ME) contents of the feed samples were computed according to McDonald et al (2010)) using the following formula; ME (MJ/kg DM) = 0.016 DOMD, where DOMD (g) is digestible organic matter per kilogram of dry matter.

Experimental animals and their management

A total of 32 weaned calves belonging to the Boran breed and with the age of six to eight months, were used in the experiment. At the beginning of the experiment all animals were drenched against worms with albendazole (10%) and Injected with Sarmorine^® as a prophylactic measure against tsetse infection. All experimental animals were ear tagged for identification and then randomly assigned to the experimental units. The experimental units were eight pens and each pen had four animals. The experimental animals were weighed before the start of the experiment and randomly assigned to four treatments. All animals in all treatments were grazed during the day, but animals in treatments one, two and three were supplemented with concentrate diets in the evening while those in treatment four (control) were not supplemented. Four weaned calves (two females and two males) were randomly assigned to each treatment and each treatment was replicated twice. Hence, the total number of animals per treatment was eight (four males and four females). The animals were fed in groups of four (two females and two males) per pen. The animals in treatment four (control) were only grazed. All animals were provided with water ad libitum.

Experimental procedure

The experimental period was preceded by a preliminary period of 14 days to allow the animals to adapt to the experimental diets and housing condition. The experiment was conducted for 69 days, making the total experimental period to be 83 days. The experimental animals were grazed during day time and confined in the evening and supplemented with the respective experimental diets. The animals in treatments T₁, T₂, and T₃ were provided with the respective supplementary diets, and the amount given equalled 1.5% of their body weights.

The amount of supplementary diet provided and the refusals for each group were weighed daily and supplementary feed intake was determined by subtracting the weight of the refusals from the weight of the diet provided. The supplementary feed intake per animal was calculated as the total amount of supplementary diet offered minus the amount of the refusals divided by the number of animals per pen. All animals were weighed before the start of the experiment to determine initial body weights, then each animal was weighed every two weeks using a spring balance. Body weight gain for each animal was computed as final body weight minus initial body weight, while growth rate was calculated as final body weight minus initial body weight divided by the number of experimental days. Feed conversion ratio was calculated as the total amount of feed eaten divided by body weight gain.

Gross margin analysis

Cost of supplementary diet for each treatment was determined and the cost of formulated diets was based on the costs of ingredients, including the costs of purchasing the feed ingredients, transportation, and labour. The weights gained due to supplementation were recorded. The benefits of using supplementary diets were obtained by calculating the differences between additional weight gained by supplemented animals and that of unsupplemented animals. The weight gain was multiplied by market live weight price of cattle (TZS 2500.00 per kg live weight) in order to calculate revenue. Gross margin was calculated by subtracting costs of diets, labour and transport (variable cost) from revenue obtained from the sale of extra weight gained.

Statistical analysis

Data on weight gain, growth rate, feed intake and feed conversion ratio were subjected to analysis of variance using the general linear model (GLM) of SAS (2001). The treatment, sex of the animal and interaction between treatment and sex were used as fixed effects in the statistical model. The initial body weights of animals were used as a covariate to remove the influence of differences in initial weight on live weight gain and growth rate. The least significant difference (LSD) was used to test the significance of the differences between two treatment means, at a significance level of P < 0.05.

Results

Generally all 32 animals had normal health throughout the experimental period.

Nutritive values of feed ingredients and formulated diets used in the experiment

Chemical composition of sun dried sisal wastes, maize bran, sunflower seed cake, natural pastures and formulated diets used in the current study are presented in Table 2. Maize bran had the highest dry matter (DM) content while sun dried sisal wastes had the lowest. Sun dried sisal wastes contained higher crude protein (7.68% CP) compared to natural pastures, both before the start of the experiment (4% CP) and at the end of the experiment (2.86% CP). Maize bran had higher CP content than sisal wastes. For crude fibre (CF), natural pastures had higher content (30.04% CF) than the sun dried sisal wastes (17.58% CF). The natural pastures had the highest level of acid detergent fibre (ADF), ranging from 42.50% to 45.18%, while maize bran had the lowest ADF (4.96%). Among the supplementary diets, diet 3 had the highest DM content while diet 1 had the lowest. The results in Table 2 show that diet 3 contained higher amount of CF compared to the other two diets, and diet 1 contained the lowest amount of CF. All formulated diets contained almost similar crude protein contents (16.0 - 16.3%) (Table 2).

Digestibility

Dry matter and organic matter digestibility coefficients for maize bran, sunflower seed cake, sun dried sisal wastes, natural pastures and formulated diets are shown in Table 3. The in vitro dry matter digestibility (IVDMD) and organic matter digestibility (IVOMD) of sun dried sisal wastes was higher than that of natural pastures, but lower than that of maize bran. The IVDMD of formulated diets indicated that diet 2 had higher IVDMD value compared to the other diets. The in vitro organic matter digestibility (IVOMD) of diets 2 and 3 differed slightly. Diet 1 had the lowest organic matter digestibility compared to the other two diets.

Effects of supplementary diets on feed intake and growth performance of weaned Boran calves

Table 4 shows the least squares means for initial body weight, final body weight, weight gain, average daily weight gain, feed intake and feed conversion ratio of weaned Boran calves. The analysis of covariance revealed that the slight variations in initial body weight did not influence (P = 0.5605) the final body weight, weight gain and daily weight gain of the animals subjected to different treatments. Feed intake, final body weight, weight gain and daily weight gain were affected by dietary treatment (P = 0.0001) but not by sex (P ˃ 0.05) or the interaction between sex and treatment (P ˃ 0.05). However, no significant differences were observed on final weight, body weight gain, daily weight gain and feed intake between animals on treatment one (T₁) and those on treatment two (T₂). The final body weight, weight gain, daily weight gain and feed intake of animals on treatment 3 (T₃) were lower than that of animals on T₁ and T₂, but higher than that of animals on treatment 4 (T₄). Feed conversion ratios of animals fed different treatment diets were not different (P ˃ 0.05). However, the feed conversion ratios for animals on T₁ and T ₃ were slightly higher than that of animals on T₂. Animals on T₃ had significantly lower average dry matter intake of supplementary diet than those on T₁ and T₂, but dry matter intakes of supplementary diets for animals on T₁ and T₂ were not statistically different (P > 0.05).

Figure 1 shows the growth performance of weaned beef calves fed different supplementary diets. Body weight of all animals in all treatments increased, although the magnitude of weight gain varied among the treatments. There was only a slight increase in body weight for animals on the control (T₄) (grazing only). The increase in body weight of animals fed all supplementary diets (T₁, T₂ and T ₃) was significantly higher than that of those on T₄. The weight gain of animals on T₁ and T₂ were more or less similar (P ˃ 0.05). The increase in body weight of animals on T ₃ was lower (P = 0.001) than that of animals supplemented with diets T₁ or T₂, but higher (P = 0.001) than that of those on treatment 4, indicating that animals on treatment 4 were growing slowly while those on treatments 1, 2 and 3 showed faster growth.

Figure 1. Growth performance of animals under different dietary treatment

Note: T1 = grazing + supplementation with maize bran based diet, T2 = grazing + supplementation with maize bran plus sisal waste based diet, T3 = grazing + supplementation with sisal waste based diet, T4 = grazing alone

Gross margin analysis

The estimate of gross margin of experimental animals on different treatments was based on the costs of diets, transport, labour and disease treatment while the revenue was based on market price of live body weight gained. The variable costs, revenue obtained and gross margin for different treatments are shown in Table 5. The total variable cost for the animals on T₄ was lower (P ≤ 0.05) than that of animals on treatments T ₁, T₂ and T₃. The highest feed cost was found on T₁, followed by the feed cost of animals on T ₂ and T₃. The other costs (transport, labour and disease treatment costs) were the same for all treatments. Revenues and gross margins obtained from supplemented animals were higher (P ≤ 0.05) than that of unsupplemented animals. The highest revenue and gross margin were obtained from animals on T₂, followed by those on T ₁ and T₃ in that order.

Discussion

Nutritive value of feed ingredients and formulated diets

The objective of the experiment was to formulate a cheap and good quality supplementary diet based on sun dried sisal wastes as a source of energy for feeding growing beef cattle during the dry season. Supplementary diets for beef cattle need to be balanced to meet body nutrient requirements, especially for crude protein and energy to enable better utilization and improved weight gain. The supplementary diets used in this experiment had CP values that are acceptable for supplementation of growing beef cattle. Similarly the ME contents for the three diets are within the recommended ME content of feeds for feeding beef cattle. According to Brown et al (2008) the energy and protein requirements for growing beef cattle range from 10.5 - 11.4 MJ/kg DM ME and 15 - 16% CP, respectively. Therefore, the formulated diets were ideal for feeding growing beef cattle.

The results of the present study show that sun dried sisal wastes have a higher level of crude protein content and digestibility values than natural pastures found in the study area during the dry season. This suggests that sun dried sisal wastes could be used as supplementary feed for ruminant animals, particularly in the dry season when pastures are scarce and of poor quality. This is because the minimum CP content for maintenance requirement ranges from 7 to 8% (McDonald et al 2010) and the CP values which is less than 7% can impair microbial function. According to McDonald et al (2010) dry matter intake declines rapidly as forage CP content falls below 7% and this is attributed to deficiency of nitrogen (protein) in the rumen, which in turn, hampers microbial activity. The crude protein content of sun dried sisal wastes observed in this study is higher than the CP content of 5.4% reported by Dotto et al (2004) and 5.3% CP reported by Kahonga (1994). However, it is lower than the CP content of 8.9% reported by Kategile (1986) and similar to the value of 7.2% CP reported by Gebremariam and Machin (2008). The variations observed could be attributed to differences in growing conditions, varieties, or means of preparation and preservation of sun dried sisal wastes used. This is in line with the observation by Kahonga (1994) who said that the preparation and storage of sisal wastes can affect chemical composition of the sisal pulp.

Sun dried sisal wastes were found to contain higher crude fibre compared to maize bran but lower than sunflower seed cake. The crude fibre content observed in this study is slightly higher than that reported by Kahonga (1994), but lower than that reported by Dotto et al (2004). The variation observed could be caused by differences in varieties, season of harvesting the leaves, stage of growth of the plant at harvest and/or type of soil (McDonald et al 2010). The results of the present study revealed that grasses in the grazing area had higher amounts of ADF and NDF than sun dried sisal wastes. Thus, the dry grasses in the grazing areas had lower digestible energy and animals consuming those grasses had lower dry matter intake than those ate sisal wastes. This is because ADF and NDF values in forages are negatively correlated with digestible energy level and dry matter intake, respectively. The value of NDF content of the sun dried sisal wastes observed in this study is lower than the NDF (63.2%) reported by Kahonga (1994) and slightly lower than the NDF of 49.7% reported by Dotto et al (2004).

The in vitro DMD and OMD of sisal wastes in the present experiment are lower compared to the values reported by Gebremariam and Machin (2008). The difference could be due to differences in the variety, stage of harvesting leaves and processing of the sisal pulps. The observed values of IVOMD of formulated diets in this experiment are also somewhat lower than the IVOMD of 68 to 84% reported by Ayo (2002) for supplementary diets. However, the values of IVOMD for the supplementary diets in the present study are higher than the value of 50% reported by Hango (2005). The difference could be due to differences in ingredients used to formulate the diets. The IVOMD value for sunflower seed cake in this experiment (50%) is lower than the values reported by NRC (2000) of 87% as well as that of 58% reported by Dotto et al (2004). The difference might be caused by variety differences, preparation of the seeds and processing methods (McDonald et al 2010), which affect digestibility. Processing of sunflower seed before removal of oil affects CF and certainly energy content and this, in turn, affects digestibility.

Feed intake and growth performance of weaned Boran calves

In the current study differences in body weight gain and daily weight gain were observed among animals on different dietary treatments. Animals supplemented with diets T₁, T₂ and T₃ gained more weight compared to those which were not supplemented (T ₄). The findings of the current study concur with other research reports by Ndemanisho et al (2007) and Pimentel et al (2011), who observed lower average body weight gain and growth rate on non-supplemented animals compared to the supplemented ones. This could be due to scarcity and poor quality of pastures in grazing land caused by drought condition. The nutritive values of natural pasture observed in this study were far below the recommended nutrient requirements for beef cattle. Hence, animals under treatment T₄ (grazing only) did not meet the requirements for growth. Weisbjerg et al (2007) recommended that an animal grazing on natural pasture need to be supplemented with concentrates to provide nutrients which the animal cannot get from grazing during the dry season.

Body weight gain and growth rate of animals on treatment T₃ was significantly lower than that of animals on treatments T₁ and T ₂. This can be attributed to higher CF and ADF contents and lower digestibility observed in diet T₃ and this, in turn, resulted in lower feed intake and growth rates of animals fed diet T ₃ compared to those fed diets T₁ and T₂. Intake of supplementary diet was not significantly different between the animals fed diets T₁ and T₂, but was significantly different from that of animals fed diet T₃. The animals on diet T₃ consumed lower amounts of dry matter of supplemented diets compared to those on diets T₁ and T_2,, possibly due to high oxalic acid content in the sun dried sisal wastes, which reduces feed intake of animals (Kahonga 1994).

In this study the daily body weight gains of animals which were provided with supplementary diets T₁ and T₂ are close to the growth rate of 0.6 kg/day reported by Mwilawa (2012) and 0.584 kg/day reported by Mawona (2008) for cattle in Tanzania. But the daily weight gain of animals fed diet T₃ is slight lower than the values reported by Mawona (2008). Animals on diet T₂ had higher weight gain than the animals on the other diets. Similarly diets T₂ resulted in a higher digestibility value and better feed conversion ratio than diets T ₁ or T₃. Previous studies have shown that animals supplemented with sun dried sisal wastes have much better growth performance, if they are supplemented with protein and energy concentrates (Kahonga 1994). Thus, inclusion of sunflower seed cake and maize bran in diet T₂ as sources of protein and energy, respectively, improved the utilisation of sisal wastes by the animals.

Profitability for supplementing weaned calves

The results of the present study show that the gross margin was higher for the supplemented weaned calves compared to those which were not supplemented with concentrate. This is due to the fact that un-supplemented weaned calves had lower weight gain compared to those supplemented with concentrates. This is attributed to the fact that animals which were subjected to grazing only did not meet the nutrient requirements for growth as the grasses had lower CP content and digestibility values. Costs of concentrate feed accounted for 70.7% to 76.7% of inputs costs. The proportion of the concentrate cost in this study is within the range of 70 - 80% of the total cost reported by Mwilawa (2012). Mwilawa (2012) reported that the cost of supplementary diets constitutes the highest proportion of production cost when you remove the price of purchasing animals in the feedlot. The cost of feeds can be overcome by higher average daily weight gain (Madsen 2005) and customer willingness to pay higher price for the quality of the product in the market (Mwangosi 2014). In a feedlot operation, higher returns could be obtained by minimizing the costs of inputs for supplemented animals. One of the cheapest materials could be sun dried sisal pulps which are readily available and not commonly used to supplement beef cattle in Tanzania. The use of this by-product can increase profit margins in beef cattle production because they are of minimal cost, the only costs at the moment being labour and transportation costs. According to Madsen (2005), feed cost is cheaper in grazing animals than in supplemented ones, however, weight gain is minimum for grazing animals compared to those supplemented with concentrate, especially during the dry season when there is feed scarcity. In the present study all supplemented animals showed higher profit than those on a grazing only regime.

This study has shown that the sun dried sisal wastes could be used widely as an alternative energy source in places where sisal is grown and where frequent droughts occur. The pulps can be used during the dry periods as the sisal plant survives well in dry condition. The results of chemical composition indicated that sun dried sisal wastes contain higher level of crude protein and have higher digestibility values compared to natural pastures found in grazing area of the study site during the dry season. Animals fed diet T₃, which contained sun dried sisal wastes alone as the source of energy, showed lower growth performance compared to those on diet T₂ which contained equal proportions of dried sisal wastes and maize bran. Moreover, animals on diet T₂ had higher profit margin compared to those on the other diets. Generally animals fed diet T₂ gained more weight, showed higher growth rate and had a lower feed conversion ratio than those fed diets T ₁ or T₃. This shows that diet T₂ was more efficiently converted to body weight compared to the other diets. The results of this study can be used to promote the use of sisal wastes as an energy source in supplementary diets for cattle owned by resource poor small-scale farmers. The use of sisal wastes as a feed for cattle could reduce environmental pollution and improve beef production under smallholder production systems. However, sisal wastes should be used in combination with maize bran (or some other readily available and economical energy sources). The use of sun dried sisal wastes as livestock feeds will benefit the sisal factories as it will provide an opportunity for proper disposal of sisal pulps.

Conclusions

• The use of sisal wastes and maize bran in equal proportion as sources of energy in supplementary diets of growing beef cattle promotes higher growth rate and lower feed conversion ratio than using maize bran or sisal wastes alone.
  
  
• The use of dried sisal wastes as a sole source of energy in supplementary diet lowers feed intake and growth rate.
  
  
• The use of sun dried sisal wastes in supplementary feeds reduces feed cost and increases profit.

Acknowledgement

We would like to express our sincere thanks to Shallom Farm and Outreach International for allowing us to use their animals and facilities. We are also grateful for the financial support from Outreach International which enabled us to carry out this research work. We thank the laboratory technicians Mr. Dominic Allute and Mr. Michael Kusaja of the department of Animal, Aquaculture and Range Sciences, Sokoine University of Agriculture, for their assistance during sample preparation and chemical composition analysis.

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Received 4 December 2016; Accepted 22 April 2017; Published 1 June 2017

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