Effect of concentrate supplementation on live weight change and carcass characteristics of Hararghe Highland sheep fed a basal diet of urea-treated maize stover

Hirut Yirga, Solomon Melaku and Mengistu Urge

Haramaya University, College of Agriculture and Environmental Sciences, School of Animal and Range Sciences,
PO. Box 138, Dire Dawa, Ethiopia
hirutyirga1@gmail.com

Abstract

The effects of feeding different levels of supplement to sheep fed urea treated maize stover on body weight changes and carcass parameters were evaluated at Haramaya University, Ethiopia. The experiment consisted of four treatments; and conducted in a randomized complete block design using twenty male Hararghe Highland sheep. The experimental diets were urea treated maize stover (UTMS) basal diet and graded levels of concentrate mix supplementation (0/control, 150/low, 250/medium and 350 g/high). The mix was prepared from brewers dried grain, peanut cake and wheat bran at a ratio of 1:1:3, respectively.

Urea treatment increased crude protein content of maize stover by 33%. High level of concentrate supplementation resulted in lower basal feed intake and higher total DM intake per kg W^0.75 of sheep than the non-supplemented. Higher weights of total edible offal component, empty body weight and dressing percentage were observed as a result of high level of supplementation than the control treatment. Supplementation resulted in higher average daily gain and rib eye area. The mean slaughter weight and hot carcass weight were higher for sheep in medium and high level of supplementation than the control groups. The control treatment resulted in a negative return (-47.3 ETB/sheep) while high level of supplementation resulted in the best return (45.7 ETB/sheep). Based on the result of the present experiment, it is concluded that supplementation of Hararghe Highland sheep fed UTMS basal diet with 350 g concentrate mix resulted in better biologic and economic performance.

Key words: edible offal, non-edible offal, profitability

Introduction

The productivity of indigenous sheep breed is low as compared to temperate breeds due to limited genetic capacity, and mainly environmental factors. Among the environmental factors, the main bottleneck is the inadequate supply and low level of feeding due to serious shortage of feedstuffs. The major feed resources for small ruminants in Ethiopia are forage from natural pastures, crop residues and agro-industrial by-products (Ben Salem et al 2004). Among these feed resources, the expansion of cropping area as a result of growing human population pressure makes crop residues to be very important, especially during the dry season (Alemayehu 2004). The scenario holds true where limited areas of permanent grazing are available and livestock depend upon thinnings from annual crops during the growing season and crop residues and stubble grazing during the dry season (Anderson 1987). Quality of these crop residues is limited by deficiencies of crude protein (CP), metabolizable energy (ME), minerals and vitamins.

Kassahun (2000) indicated that in Ethiopia, most sheep are slaughtered at about 12 months of age with 18-20 kg body weights (BW). This implies that through better feeding, reproductive and health care management, the efficiency of growth could be increased to the desired market weight so that the economic benefit of sheep production could be enhanced. One of a feeding management practice is improving the nutritive value of low quality feed resources. Supplementation with agro-industrial by-products to be used as protein and energy sources and ammonia treatment of low quality roughages (Ben Salem et al 2004) are the most popular in improving the nutritive values of low quality feeds. Urea can be used as a source of ammonia and urea treatment is a practical method of increasing the nitrogen content of low quality roughages. But, urea is not well utilized because the carbohydrate in low quality roughages appears to be slowly available to the rumen bacteria (Ensminger 2002). The same source indicated that these could be provided by including energy and protein supplements during the preparation of rations.

It is important to know whether urea treatment alone can make sheep to maintain body weight or not. With this regards, there is limited information in the study area. Moreover, the level of supplementation using the available agro-industrial by-products to enhance sheep production in urea treated roughage based diet should be identified. Therefore, the objective of this experiment was to evaluate the combined effects of urea treatment and supplementation on body weight change, carcass characteristics and profitability of Hararghe Highland sheep.

Materials and Methods

Study area

The experiment was conducted at Haramaya University which is located 515 km east of the capital city Addis Ababa. The site is located at an altitude of 1950 m above sea level at 9.0° North and 42.0° East. The mean annual rainfall and temperature of the study area is 790 mm and 16°C, respectively (Mishra et al 2004).

Animals and feed management

Twenty yearling male Hararghe Highland sheep with a mean initial BW of 17.2 kg were purchased from local markets. All sheep were quarantined for 21 days, and treated against internal and external parasites. In addition, they were adapted to the experimental diets and site for another fifteen days before the actual data collection.

The basal diet used for the experiment was UTMS. Concentrate mixtures (CM) were prepared from peanut cake (PNC), brewers dried grain (BDG) and wheat bran (WB) at a ratio of 1:1:3, respectively. Higher proportion of WB was used to provide higher energy source for rumen microbes in order to efficiently utilize UTMS. All animals had free access to water and mineral licks.  The basal diet was offered ad libitum but CM in two equal portions at 0800 and 1600 hours according to the treatment. Basal feed offered were adjusted once every week.

Photo 1. Sheep in individual pens

Urea treatment of maize stover

Hundred kilogram dry matter (DM) of the chopped stover was treated with a solution of 4 kg of urea in 100 liters of water (Dolberg 1992). The treated stover was placed in a pit with a dimension of 2m x 2m x 2m, and its floor and sides lined by a polyethylene sheet. The treated stover was trampled with foot to ensure proper packing.

Photo 2. Urea treatment of maize stover

After filling, the pit was covered with plastic sheet and compacted with soil and stone and was left to incubate for 21 days. The pit was uncovered on the 22^nd day and aerated for a day in order to remove excess ammonia (Zhang and Qiaojuan 2002), after which the required amount was removed every day and offered to the animals.

Experimental design and treatments

The experiment was conducted in a randomized complete block design with four treatments and five replications. The sheep were blocked based on their initial BW into five blocks and each animal within each block were randomly assigned to one of the four dietary treatments. The treatments were:

Treatment 1= UTMS alone, (control) = UTMS

Treatment 2= UTMS supplemented with 150g of CM, (low level) = UTMSLow

Treatment 3= UTMS supplemented with 250g of CM (medium level) = UTMSMed

Treatment 4= UTMS supplemented with 350g of CM, (high level) = UTMSHigh

Feeding trial

The feeding trial lasted for 90 days. For each sheep, the amounts of feed offered and refused were recorded daily and their difference is considered as daily feed intake. Samples of feeds were taken on batches of feed offered. While from basal feed refused, samples were taken daily, pooled per treatment, thoroughly mixed and sub sampled at the end of the experiment for chemical analysis.

Weight change and carcass parameters

Body weights were taken every ten days after overnight fasting and average daily gain (ADG) was determined by regressing BW of each animal on days of feeding. Feed conversion efficiency (FCE) was calculated as a proportion of ADG to daily feed DM intake.

All sheep were fasted overnight, weighed and slaughtered. Blood, tongue, liver with gall bladder, heart, kidneys, tail, testis, fat (omental, intestinal and kidney) and empty gut were weighed and considered as total edible offal components (TEOC). While the weights of skin, head, lung with trachea, penis, spleen, feet and gut content were recorded and considered as total non-edible offal components (TNEOC). The empty body weight (EBW) was calculated as the difference between slaughter weight (SW) and gut content. Total usable product (TUP) was taken as the sum total weight of hot carcass weight (HCW), TEOC and skin. Dressing percentage (DP) was calculated as proportion of HCW to SW and EBW.

Both the right and left halves were cut between the 11^th and 12^th ribs perpendicular to the backbone to measure the cross-section of the rib-eye area (REA). The REA was measured by using mechanical polar planimeter.

Chemical analysis

Feed samples were analyzed for DM, ash and nitrogen according to the procedures of AOAC (1990). The CP content was estimated as nitrogen*6.25. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) were analyzed by the method of Van Soest and Robertson (1985).

Partial budget analysis

Partial budget analysis was performed to evaluate the profitability of feeding UTMS supplemented with graded levels of concentrate mix by considering the main cost components. Three experienced animal dealers estimated the selling price of each experimental sheep. The difference in sale and purchase price was considered as total return (TR) in the analysis. The calculation was done by using the formulae;

Net return = Total return – Total variable cost;

Marginal rate of revenue = ∆ Net return /∆ Total variable cost (Upton 1979).

Statistical analysis

The data was subjected to analysis of variance in a randomized complete block design using the general linear model procedure of SAS (1998). Treatment means were separated using Tukey honestly significant difference test. The model for data analysis was: Y_ij= µ + t_i + b_j + e_ij  

Where; Y_ij= the response variable; µ= overall mean; t_i = treatment effect (feed);

b_j = block effect (initial body weight) and e_{ij =} error component of interaction

Results and Discussion

Feed intake

The concentrate mix used in the experiment was found to contain more than 3 folds of protein than the basal feed (Table 1). Urea-treatment increased CP content of maize stover by 33%. An increase in CP content of the stover as a result of urea treatment was supported by Getahun (2006). The CP content of UTMS was comparable with the results reported by Zhang and Qiaojuan (2002) and Wambui et al (2006), which were 8.7 and 8.3% CP, respectively.

As a result of urea treatment, the amount of ADF was increased whereas, NDF decreased. This result was in line with previous reports (Misra et al 2006; Weldegebriel 2007). Reduction in NDF content could be due to the dissolving effect of urea on the hemicellulose fraction and subsequent removal from cell wall constituents (Givens et al 1988).

The daily basal feed DM intake of sheep in UTMS group and UTMSMed were higher than that of sheep in UTMSHigh (Table 2). As the level of supplementation increased (from UTMSLow to UTMSHigh), basal diet DM intake decreased by 6.4, 1.8 and 15.4%, respectively as compared to the non-supplemented sheep. But sheep in UTMS consumed lower amounts of total DM than sheep in UTMSMed and UTMSHigh. CP consumption was significantly different among treatments, and increased with increasing level of supplementation.

The lower basal diet DM intake in high level of supplementation could be attributed to the high intake of the supplement DM as a proportion of total DM intake, thus preventing maximum intake of the basal feed. Indeed, Topps (1997) indicated that if the level of supplementation is less than 30-40% of the DM intake of the animal, there is an increase in the intake of the basal diet. But if it is more than this, it will have a reduction effect. Lower total DM intake (g/kg W^0.75) in UTMS than in UTMSMed and UTMSHigh indicated that supplementation has a positive effect on daily total DM intake. Moreover, the lowest CP intake in UTMS may contribute for lower total DM intake (g/kg W^0.75). This is supported by the idea that supplementation with protein sources improved total DM intake of sheep (Bonsi et al 1996). The reason could be attributed to the ability of these levels of supplementation to provide CP and energy for the cellulolytic microbes up on degradation in the rumen than the other treatments.

Body weight change

The current study revealed that final BW, ADG and FCE were positively affected by supplementation (Table 3). The final BW of sheep in the UTMS group was lower than in UTMSMed and UTMSHigh. Even though the difference was not significant, UTMSHigh was superior in ADG by about 96.6% and 16.4% as compared to UTMSLow and UTMSMed, respectively. The control group was the least in FCE from all the treatments.

Since DM intake affects BW change, the control group, which obtained the lowest DM, lost 14.4 g BW per day, while the supplemented groups gained BW. Similar to the current study, Hadjipanayiotou et al (1993) and Weldegebriel (2007) reported BW loss of 73 and 55.5 g per day in sheep fed only urea treated barley straw and urea treated maize stover, respectively. Weight loss in the control group might indicate that urea treatment alone did not support the maintenance requirement of the sheep. Hadjipanayiotou et al (1993) noted that although animals fed with urea treated crop residues perform better than animals with un treated crop residues, they continued to be on a below maintenance level of nutrient intake. Dolberg (1992) suggested that treatment of crop residue alone is not sufficient to meet the animals’ maintenance and production requirement. However, Getahun (2006) indicated that sheep offered sole urea treated wheat straw gained 10.7 g BW per day.

The positive effect of supplementation on BW change was in line with other study that showed improvement in ADG and FCE as a result of increased concentrate feeding of finisher lambs (Karim et al 2007). Massae and Mtenga (1992) also reported that high plane of nutrition (400 g CM) resulted in higher growth rate of lambs than low plane of nutrition (100 g CM). The positive effect of supplementation might be explained by an increased nutrient content through higher feed intake (Economides 1983) and increased rate and efficiency of microbial biomass production than the control. Moreover, a more balanced uptake of nutrients and efficient utilization of available energy might have enhanced the growth rate of the animal (Economides 1983). Similar to the current study, Awet (2007) recorded a negative FCE in the control group that were fed urea treated teff straw than supplemented with WB.

Carcass parameters

The SW and HCW of sheep in UTMSMed and UTMSHigh were higher than in UTMS (Table 4). Lower SW and HCW in UTMS group than UTMSMed and UTMSHigh were due to lower nutrients consumption. The supplemented group showed numerically lower gut content than non-supplemented. Since EBW was calculated as a difference between SW and gut content, the higher EBW in the supplemented sheep might be due to the lower gut content. The higher EBW could also be due to BW increase (Jadish 2004). The mean EBW of Hararghe Highland sheep was within a range of 9.6-17.1 kg, which was lower than 19.9 kg and 20.4 kg reported by Ewnetu et al (2006) for Horo and Menz sheep, respectively.

Since DP is yield and value determining factor (Massae and Mtenga 1992), the lower DP in the control group might be due to the lower HCW and SW. The cross section area of rib eye muscle, which is frequently used as a measure of carcass lean, showed higher values in the supplemented sheep. This indicated that supplemented sheep were able to develop a better muscle than the non- supplemented.

The weight of TUP was higher for all the supplemented than the non- supplemented group. Moreover, sheep in UTMSHigh has higher weight of TEOC and TUP than UTMS and UTMSLow. In addition, UTMSMed resulted in heavier weights of empty gut, tail, testis, blood, head without tongue, skin and lung with trachea than UTMS group. But there was no difference between UTMS and UTMSLow groups in penis, head without tongue, skin, lung with trachea, spleen and skin weights.

Higher weight of TEOC in the supplemented group indicated that supplementation positively influenced the growth of edible organs and tissues in addition to the main carcass. The higher total fat and tail in UTMSHigh showed that sheep fed well stored fat in viscera and tail. This was similar with the result reported by Awet (2007). Generally, nutritional status of the animals and BW affects the production efficiency of the offal (Kirton et al 1995). Higher TUP in the supplemented group revealed that supplementation increases the quantity and proportion of usable carcass components. The decreasing trend of gut content with increasing levels of supplementation could be attributed to the expected higher rate of digestion and faster passage rate of the diet through the tract due to consumption of more digestible feed.

UTMS fed group has higher gut content as a percentage of SW and lower ratio between TEOC and TNEOC than UTMSMed and UTMSHigh. The proportion of gut content decreased numerically as the level of supplementation increased (Table 5). Moreover, UTMS fed group has higher TNEOC as percentage of SW than the supplemented group. But, TEOC as a percentage of SW was lower in UTMS group than in UTMSHigh group.

Higher TEOC: TNEOC in UTMSMed and UTMSHigh than UTMS can be explained by the fact that as the level of supplementation increased, the weight of TEOC is higher than the weight of TNEOC.

Partial budget analysis

The cost of feeds and materials used in the experiment was indicated in Table 6, and the result of partial budget analysis was shown in Table 7.

The result of partial budget analysis revealed that high level of supplementation resulted in higher profit margin than low, medium and no supplementation. Sheep fed UTMS alone had the lowest net return and UTMSHigh group recorded the highest net return.  The marginal rate of return indicated that each additional unit of 1 ETB per sheep cost increment resulted in 1 ETB and 1.1, 1.0 and 3.8 ETB benefit for UTMSLow, UTMSMed, and UTMSHigh, respectively.

The difference in net return was in a similar trend with their weight gain, i.e., sheep in UTMS lost weight and resulted in the lowest net return, while UTMSHigh resulted in higher ADG and recorded the highest net return. In addition, UTMSLow resulted in a negative and lower net return than UTMSMed and UTMSHigh. This could be due to the numerically lower ADG as a result of numerically lower nutrient intake. Generally, sheep that has a better nutrient intake had superior ADG, as a result of which they fetched higher sale price, and earn higher net return.

Conclusion

• High and moderate levels of supplementation resulted in higher total DM intake than non-supplemented. Among the treatments, non supplemented and moderately supplemented groups had higher basal DM intake.
  
  
• The control treatment resulted in lowest ADG, REA, weight of TEOC and weight of TUP as compared to the supplemented treatments.
  
  
• Medium and high level of supplementation resulted in higher SW, HCW, empty gut weight, testis weight, tail weight and blood weight than the control.
  
  
• High level of supplementation resulted in a higher EBW, DP on SW basis, weights of heart, kidney, tongue, fat, lung with trachea and penis than the control.
  
  
• The partial budget analysis showed that high level of supplementation returned the highest profit margin than other treatments.
  
  
• Supplementation of UTMS with 350 g of concentrate mixture used in the present experiment resulted in higher ADG, carcass parameters and profit margin of Hararghe Highland sheep.

Acknowledgments

The senior author is grateful to SIDA/SAREC project Haramaya University Female Students Scholarship Program for sponsoring the study. 

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Received 25 October 2011; Accepted 24 November 2011; Published 1 December 2011

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