Effect of supplementary protein source on the performance of indigenous meat goats fed Guinea grass hay

H W Kato, F Kabi* and D Mutetikka*

Department of Animal Production and Range Management, Faculty of Agriculture and Environment
Gulu University P. O. Bo x 166 Gulu, Uganda
kwalusimbih@gmail.com
* Department of Animal Science Faculty of Agriculture, Makerere University Kampala.

Abstract

The effect of different supplementary protein sources on average body weight gain, feed intake, digestibility, nitrogen balance and feed conversion  was studied using twenty-four yearling Mubende goats. The animals, which averaged 15.4±2.1 kg, were assigned to four treatment diets in a randomized complete block design.  The basal diet consisted of guinea grass hay fed together with 200g of maize bran/mineral mixture. The four protein supplements included lablab hay (LBLB), sweet potato vines (SPV), cassava leaf meal (CLM) and sunflower meal (SFM). The protein supplements supplied 10g N daily for a feeding period of 100 days.  Thereafter, all male goats were transferred to metabolic cages for a nitrogen balance trial. 

Cassava leaf meal supported better growth and feed conversion and higher N retention compared with Lablab hay, sweet potato vines and sunflower seed meal.

Key words: average daily gain, cassava leaf meal, dry matter intake, feed conversion ratio, lablab hay, mubende goats, nitrogen balance, sunflower meal, sweet potato vines

Introduction

About 94% of the World’s goat population is found in developing countries with 33.8% of this population in Africa (FAO 2007). East African Community (Uganda, Kenya Rwanda, Burundi and Tanzania) has 10.8% of Africa’s goat population, which is 4.5% of the global goat population of 832 million heads (FAO 2007).  Uganda’s goat population has been rising steadily since 1985 at 2.5 million heads, through 1994 at 3.9 million heads (Nsubuga 1996) to 12.3 million in 2008 (UBOS 2010).  In Uganda, goats make an important contribution to the subsistence sub- sector of the economy.  Goats are prolific breeders giving the resource poor farmers an opportunity to earn quick income.

Despite the role they play in the peasant communities, goat productivity in Uganda is still low.  This is mainly attributed to poor supply of energy and protein to the goats (Tolera et al 2000).  One of the strategies to improve goat productivity is using locally available basal feed resources in form of high biomass forages like elephant grass, gaint guinea grass, giant Setaria, and Brachiaria mulota, with proper supplementation using cheap sources of protein and energy like crop residues, legumes, cereal grains, and agro-industrial by-products. With increasing production of cassava and sweet potato among small holder farmers in Uganda, the use of cassava leaf and sweet potato vines in animal feeding has become popular among goat farmers.  However, there are no data on the performance of indigenous meat goats supplemented with sweet potato vines and cassava leaf available to guide farmers in Uganda on how best to utilize these feed resources. 

This study was aimed at investigating the effect of cassava leaf meal and sweet potato vines as protein supplements on the performance of indigenous meat goats fed a basal diet of guinea grass hay.

Materials and methods

Experimental Design

Twenty four Mubende goats 7-9 months old (twelve females and twelve entire males) weighing 15.4kg ±2.1 kg, were treated against internal parasites using Albendazole drench, blocked according to initial body weight and confined in individual pens at National Livestock Resources Research Institute Namulonge.  Goats in each block were randomly allocated to four treatments constituted by protein supplements (Table 1) in a completely randomized block design. 

The protein supplements supplied 10g N/day. The experiment lasted for 110 days including an adaptation period of ten days. At the end of the growth trial, all male goats were transferred to digestion cages and feeding for both female and male goats continued as in the growth trial.  The digestion trial lasted for twenty four days including an adaptation period of ten days.
 

Data collection

All feeds offered and rejects in the two experiments were weighed using an electronic digital weighing scale.  Rejected feed was removed from the troughs at the time of offering fresh feed after every 24 hours.  Representative samples of feeds offered and rejects were collected for chemical analysis to establish the dry matter, crude protein, gross energy, Neutral detergent, and acid detergent fibre contents. During the digestion trial, urine was collected in a 5 litre plastic bucket containing 100 ml of 0.1M sulphuric acid to avoid loss of ammonia.  The total daily urine output from the goats was measured after 24 hr every day.  A 50 ml sample of urine was collected and packed in labeled plastic bags (Ziploc), sealed and frozen.  All goats in the growth experiment were weighed every seven days throughout the experiment.  

Chemical analysis of feed, urine and feces 

All feed, refusals and fecal samples were dried at 60⁰C for 48hours, ground and passed through a 1 mm sieve.  Dry matter, N and CP calculated as N x 6.25, and gross energy in feeds, refusals and in fecal samples were determined according to AOAC (1995).  ADF and NDF in feeds, refusals and feces were analyzed by methods outlined by Georing and van Soest (1970).   Urine samples were analyzed for N using the micro-Kjedhal procedure.

 Statistical analysis

The data were analyzed using the general linear model (GLM) procedure of SAS (2003).  Means were separated using the LSD procedure.   The following statistical model was used in the analysis:
 

            Y_ij = μ + B_i + T_j + e_ij

Where Y_ij is the dependent variable; μ is the overall mean; B_i is the Block (initial body weight) effect, T_j is the treatment (protein supplement) effect; e_ij is experimental error.

Results and discussion

The high cell wall content (36.4% ADF and 78.6% NDF) coupled with low CP content (5.1%) (Table 2 is in agreement with values reported in the literature (Suckhchain 2001), and makes guinea grass hay a low quality forage as earlier observed by Wiedmeier et al (2001).  As the NDF content of forage increases, the dry matter intake of that forage by a ruminant decreases (Linn and Martin 1999). Elsewhere, forage intake has been reported to decline sharply when sheep were fed forages of low CP levels below 7% of dry matter (Melaku et al 2004). Therefore, low CP and high cell wall content of guinea grass hay is a critical nutritional limitation to its potential intake and utilisation by meat goats which can be ameliorated by complementary supplementation. 

The protein supplement source affected DM intake (Table 3).  Guinea grass hay intake was highest with sunflower meal supplementation.  Generally total DM intake of goats in this study (4.04 - 4.44 % LW) was higher than the level (3%) reported by Devendra and McLeroy (1982).  The higher total dry matter intake observed (Table 3) among goats on sweet potato vines and those on cassava leaf meal could be attributed to the low NDF content (Table 2) of sweet potato vines and cassava leaf meal. 

The apparent digestible of DM was lower on cassava leaf meal supplementation than on lablab hay supplementation.  This is in agreement with results reported in the literature (Sokerya and Preston 2003; Nguyen et al 2003).  Ngo Van Man and Wiktorsson (2002) attributed this to presence of tannins in cassava leaf meal. Several researchers have reported a reduction in dry matter digestibility in ruminants fed diets containing high levels of condensed tannins (McSweeney et al 2000; Reed 1995).  In addition to complexing with dietary proteins, tannins combine with, and hinder digestibility of cellulose, hemicellulose and pectin either by preventing microbial digestion or by directly inhibiting cellulolytic micro organisms (McSweeney et al 2000). 

The highest N retention was recorded for goats fed cassava leaf meal (Table 4).  The high value for N retained as percent of N digested indicates a high biological value of the cassava leaf meal protein. The data for LW gain and DM feed conversion confirmed the superior value of this protein source as a supplement to low quality forages as reported by several researchers (Ayo et al 2001; Ho Quang Do et al ; Sokerya and Preston 2003; Hossain et al 2003; Keo Sath et al 2008). The presence of  condensed tannins in the cassava leaf meal (Barry and Manley 1984; Reed 1995)  increase the dietary by-pass protein reaching the lower gut, thus increasing the protein; energy ratio in absorbed nutrients (Preston and Leng 1987). Perez-Maldonado and Norton (1996) reported that all tannin-protein complexes formed in the rumen between the dietary protein and the condensed tannins dissociate in the lower digestive tract making dietary protein available for digestion in the small intestines.  Wanapat (2002) attributed this to the dissociation of the tannin-protein complexes at low pH (below 3.0) in the abomasum and at high pH in the small intestines (above 8.0).

Conclusion

• Cassava leaf meal supported better growth and feed conversion and higher N retention compared with Lablab hay, sweet potato vines and sunflower seed meal as a protein supplement for indigenous meat goats fed a low quality Guinea grass hay.

Acknowledgements

The authors extend their gratitude to ENRECA project, Belgium Technical Cooperation (Uganda Office), for the financial support during the study, Professor Felix Bareeba for the technical guidance during manuscript preparation.

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Received 12 February 2012; Accepted 5 January 2013; Published 5 February 2013

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