The effects of incorporation of Moringa oliefera leaves and sweet potato vines in the ration of growing grasscutters (Thryonomys swinderianus Temminck)

E K Adu*^,**, H Bagulo* and K Amaning-Kwarteng*

* Animal Science Department, University of Ghana, Legon, Ghana
** CSIR-Animal Research Institute, P. O. Box AH 20, Achimota, Ghana
nhyirapapa@yahoo.com   or   nhyirapapa@gmail.com

Abstract

The effects of incorporation of sweet potato vines and moringa leaves into the freshly cut Panicum maximum diet of growing grasscutters were studied from February to April 2008 using 21 male grasscutters with an average weight of 1.20±0.09 kg at the CSIR Animal Research Institute, Achimota, Ghana.

Mean feed intakes of fresh Panicum maximum alone diet (257±3.06 g/d) and Panicum maximum plus Sweet potato vine diet (262±3.06 g/d) were higher compared to the Panicum maximum plus Moringa leaves diet (173±3.06 g/d) respectively. However nitrogen intake was similar on all diets. Apparent digestibility of both DM and OM were observed to be higher for Panicum maximum plus Sweet potato vines diet than Panicum maximum alone and Panicum maximum plus Moringa leaves diets. There was a tendency for higher growth for grasscutters fed the Panicum maximum plus Sweet potato vine diet compared to animals fed Panicum maximum alone diet (5.88±0.66 g/d v. 4.29±0.66 g/d; p = 0.091) and significantly higher growth when the animals were fed Panicum maximum plus Sweet potato vine compared to Panicum maximum plus Moringa leaves diets (5.88±0.66 g/d v. 3.06±0.66 g/d; p = 0.003). The average daily growth rates were (4.29±0.66 g/d, 5.88±0.66 g/d and 3.06±0.66 g/d) for animals consuming Panicum maximum alone diet, Panicum maximum plus Sweet potato vine diet and Panicum maximum plus Moringa diet respectively.

Key words: apparent digestibility, average daily gain, forage intake, nitrogen intake

Introduction

Grasscutter (Plate A) farming in Ghana is becoming increasingly popular particularly in the urban areas (Tebge 2006), where it is undertaken by many people due to the low capital input and the high capital returns within a short time. Grasscutter meat is very delicious and consumed by a lot of people in the West African sub-region (Adu et al 2005) and is considered a delicacy in South Africa (Van Zyl et al 1999).

Unfortunately, grasscutter production in captivity has been constrained by nutritional factors, which has made it lag behind other livestock with the result that a significant proportion of grasscutter meat consumed in the country  have had to be hunted from the wild. According to Tebge (2006), about 70% of the national grasscutter numbers in captivity are in the hands of smallholder grasscutter farmers, who are usually faced with nutritional problems such as: 1. Low availability of forage during the dry season (Adu et al 1999). 2. Nutritional imbalances caused by feeding mainly Panicum maximum (Plate B) to the stock (Adu and Wallace 2003).

Feeding forages such as leucena, gliricidia, sugarcane, sweet potato vines, stylosanthes, and moringa leaves has been proposed as one way of addressing these nutritional constraints as they are very high in nutrient content and also available all year round, even in the dry season (Schrage and Yewadan 1999). The effects of these forages on growth rates in the grasscutter are however yet to be investigated. The objective of this study was therefore to evaluate the incorporation of Moringa oliefera (Moringa) leaves (Plate C) and sweet potato vines (Plate D) as feed sources for growing grasscutters in captivity. The study was particularly to investigate the dry matter intake and the dry matter digestibilities of moringa leaves and sweet potato vines by growing grasscutters, and to investigate the response in growth by growing grasscutters fed either fresh moringa leaves or sweet potato vines incorporated into the Panicum maximum basal diet.

Materials and methods

Animals, management and experimental design

A total of 21 male grasscutters between 4 and 6 months of age were used in a completely randomized design at the Animal Research Institute CSIR (ARI-CSIR), Achimota in the Greater Accra Region of Ghana, from February to April 2008 to investigate the effects of incorporation of moringa leaves and sweet potato vines in the ration of growing grasscutters under captive breeding. Animals were randomly assigned to one of three dietary treatments based on live weight. Each animal was offered 400 g/day of fresh forage without water following the practice of grasscutter farmers in Ghana (Adu et al 1999) throughout the experimental period. Feed was weighed every morning, and each animal fed 50% of the daily allowance at 8:00 am with the other 50% fed at 4:00 pm. The composition of the test diets is presented in Table 1.

Animals were dewormed using albendazole at a rate of 0.08 ml/kg body weight before the start of the experiment and housed in individual cages measuring 24 cm × 28 cm × 17 cm, length × height × width.  The grasscutters were gradually introduced to the diets for 21 days of adaptation before the experiment started. This period was to make the animals adapt to the feed and also to determine the maximum quantity of feed each animal can consume.

Measurements

Feed samples were taken everyday and bulked per week during the experimental period. Feed refusals were also collected from individual animals every morning before feeding. Both feed samples and feed refusals were weighed and analyzed for dry matter, organic matter, crude protein, mineral, NDF, ADF, hemicellulose, cellulose and lignin. Daily feed intakes of particular nutrients were measured as the difference between feed on offer and feed refusals. Animals were weighed at the start of the experiment and then weekly.

Statistics

Average daily liveweight gains and feed intake were statistically analyzed using the GLM procedure of SPSS for windows (version 10.0) in an analysis of variance. Sex and initial weight were used as covariates in comparing growth of animals on the different diets.
 

Results  

Table 1 shows the chemical composition of the test diets and the feed refusals during the experimental period. Dry matter content of Panicum maximum alone diet (19.5±0.74%) and Panicum maximum plus Moringa leaves diet (20.7±1.10%) were higher compared to that of Panicum maximum plus Sweet potato vine diet (16.3±3.21%). Crude protein content of the Panicum maximum plus Moringa leaves diet was observed to be higher than those of Panicum maximum alone and Panicum maximum plus Sweet potato vine diets (Table 1). ADF and NDF contents were higher in Panicum maximum alone than Panicum maximum plus Sweet potato vine diet (Table 1). Organic matter content of Panicum maximum alone diet (86.6±21.4%) and Panicum maximum plus Sweet potato vine diet were higher (87.1±4.44%) compared to that of Panicum maximum plus Moringa leaves diet (51.1±1.10%) (Table 1). A comparison of the nutrient composition of the feed refusals and feed on offer indicates that the animals consumed the more digestible and more nutritious components of the test diets. 

Table 2 shows the mean ± S.E initial and final weights as well as the average daily gains of the grasscutters on the different treatments.

The mean ± S.E. body weight of the animals at the start of the experiment was 1.20±0.09 kg for all treatments (Table 2). Weekly live weight changes of the grasscutters for all treatments are shown in Figure 1.

Live weight changes on the sweet potato vine supplement was superior to both Panicum maximum and the Moringa leaves ­ supplemented diets (Figure 1). There was a tendency for higher growth for grasscutters fed the Panicum maximum plus Sweet potato vine diet compared to animals fed Panicum maximum alone diet (5.88±0.66 g/d v. 4.29±0.66 g/d; p = 0.091); and a significantly higher growth when the animals were fed Panicum maximum plus Sweet potato vine compared to Panicum maximum plus Moringa leaves diets (5.88±0.66 g/d v. 3.06±0.66 g/d; p = 0.003) (Table 2).

Intakes of fresh forage, dry matter, organic matter and nitrogen and apparent digestibility for growing grasscutters consuming Panicum maximum alone, Panicum maximum plus Sweet potato vines, and Panicum maximum plus Moringa leaves diets are shown in Table 3.

Mean feed intakes of fresh Panicum maximum alone diet (257±3.06 g/d) and Panicum maximum plus Sweet potato vine diet (262±3.06 g/d) were higher compared to the Panicum maximum plus Moringa leaves diet (173±3.06 g/d) (Table 3). A higher dry matter and organic matter intakes were observed for grasscutters fed Panicum maximum alone than grasscutters fed Panicum maximum plus Sweet potato vines and Panicum maximum plus Moringa leaves diets. However nitrogen intake was similar on all diets (Table 3). Apparent digestibility of both DM and OM were observed to be higher for Panicum maximum plus Sweet potato vines diet than Panicum maximum alone and Panicum maximum plus Moringa leaves diets on dry matter and organic matter basis (Table 3).

Discussion 

The grasscutters in this study exhibited selectivity in their feeding habit. This is confirmed by the higher nutrient composition of the diet on offer compared to the refusals (Table 1). This corroborates reports by Schrage and Yewadan (1999) which shows that grasscutters prefer the more succulent portions of forages. Intakes recorded for grasscutters fed Panicum maximum alone, Panicum maximum plus Sweet potato vines and Panicum maximum plus Moringa leaves diets differed from those quoted by Schrage and Yewadan (1999­), who indicated that on mixed diets an adult grasscutters’ intake of forage is 400 g/d with intake of supplemental feed being 200 g/d. This significantly higher fresh forage intake reported by Schrage and Yewadan (1999) could be attributed to the fact that their diet was more acceptable to the animals due to the salt content. Grasscutters have been reported to show a high affinity for salt (Adu 1999). Sprinkling salt on the sweet potato vine or moringa leaves could therefore improve intake of diets incorporated with these forages. This however needs further investigation.

The high dry matter intake of 50.1±0.55 g/d on Panicum maximum alone compared to 35.8±0.55 g/d for grasscutters fed on Panicum maximum plus Moringa leaves diet can partially be explained by grasscutters’ preference for thick-stemmed species (Schrage and Yewadan 1999). Also the characteristic odour of moringa leaves could be a contributory factor to the low intake of the Panicum maximum plus Moringa leaves diet.

Despite the high protein content of the Panicum maximum plus Moringa leaves diet (22.2±7.04%) compared to the Panicum maximum alone diet (15.1±7.04%), grasscutters on the Panicum maximum plus Moringa leaves diet achieved a lower post weaning growth rate of 3.06 g/d compared to grasscutters on Panicum maximum alone diet (4.29 g/d). This lower growth rate could be as a result of the presence of anti-nutritive factors such as tannins, saponins, cynogenic glucoside and glucosinolates which suppress growth by decreasing protein digestibility (Makker and Becker 1995).  

Grasscutters fed the Panicum maximum plus Sweet potato vine diet had a tendency for superior growth compared to the other treatments (Table 2) though nitrogen intake was similar for all treatments (Table 3).  This can be explained by the higher DM and OM digestibilities for animals on the Panicum maximum plus Sweet potato vine diet (Table 3). The similarity in nitrogen intake despite the differences in the nitrogen content of the diets on offer (Table 1) was as a result of increased dry matter intake on the nitrogen-poor diet implying grasscutters have the ability to adjust food intake as dietary protein content fall, suggesting that grasscutters may be able to detect nitrogen deficiencies.

Although intake and digestibility were high for grasscutters fed freshly-cut Panicum maximum, growth rate was still relatively low (4.29 g/d), corroborating reports that nutrient concentrations in Panicum maximum does not support efficient performance of physiological functions such as growth of grasscutters (Adu and Wallace 2003). The growth rate of 4.29 g/d achieved for grasscutters on freshly-cut Panicum maximum was not in consonance with the 12.1g/d reported by Adu and Wallace (2003) on a simillar diet. Age difference could be the main contributory factor for this variation in the growth rates. Adu and Wallace (2003) used younger animals compared to animals in the current study (583 v. 1,200 g). Forage intake was also about four times higher compared to the current study and might also have contributed to the differences in growth rate between the two studies.

The apparent dry matter digestibility of 50.6% for grasscutters on Panicum maximum plus Sweet potato vine diet is about 44% higher than the digestibility of grasscutters consuming Panicum maximum plus Moringa leaves diet. This is explained by the grasscutter’s ability to efficiently utilize high fibrous diets (Van Zyl et al 1999).

Conclusions

• The most important finding of this study is that when given as a supplementary feed to growing grasscutters, sweet potato vine was superior to Moringa leaves in terms of feed intake and average daily gain. However growth rates achieved with sweet potato vines was lower than previously reported (Adu and Wallace 2003) due to low forage intake. It is recommended that sprinkling salt on the forages before feeding such forages might overcome this and improve growth. Also the use of younger animals could provide a better platform for the evaluation of these forages.

  
  

• Although Moringa leaves are highly nutritive, the intake was restricted by the grasscutters due to the characteristic odour. Further processing such a pelletizing to reduce the odour and anti-nutritive content could therefore be an effective solution to increasing intake of Moringa by grasscutters. Intake of Moringa leaves may also be improved by mixing it with other feedstuffs like rice bran and maize or maize bran, to mask the odour of the leaves.

Acknowledgements

This work was made possible by donations of animals by members of the Progressive Grasscutter Farmers Association, Atomic, Kwabenya, Accra. Mr. Louis Azure of the CSIR Animal Research Institute, Achimota, Accra, is acknowledged for care and management of the animals during the period of this study.  

References

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Adu E K and Wallace P A 2003 Growth and reproductive performance of captive grasscutters fed freshly cut Panicum maximum. Journal of the Ghana Science Association 5: 90 – 91.

Adu E K, Alhassan W S and Nelson F S 1999 Smallholder farming of the greater cane rat, Thryonomys swinderianus, Temminck, in southern Ghana: a baseline survey of management practices. Tropical Animal Health and Production 31: 223 – 232.

Makker H P S, Blümmel M and Becker K 1995 Formation of complexes between polyvinyl pyrrolidones and glycols and tannins and their implications in gas production and true digestibility in in vitro techniques. British Journal of Nutrition 73: 897 – 898 http://journals.cambridge.org/action/displayFulltext?type=1&fid=896032&jid=&volumeId=&issueId=06&aid=896024&bodyId=&membershipNumber=&societyETOCSession=

Schrage R and Yewadan L T 1999 Raising Grasscutters. (Deutsche Gesllschaff für Technische Zusamamenarbeit   GTZ) Gmdh.

Tebge E R 2006 Guide for Commercial Grasscutter Farming. University of Ghana, ARC, Kpong.

Van Zyl A, Meyer A J and Van der Merwe M 1999 The influence of fiber in the diet on growth rates and the digestibility of nutrients in the greater cane rat (Thryonomys swinderianus). Comparative Biochemistry and Physiology. Part A: Molecular Integrative Physiology 123, 129 – 135

Received 22 February 2009; Accepted 19 February 2010; Published 10 June 2010

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