Determination of dietary crude protein level required for optimum growth of the grasscutter in captivity

C Kusi, A K Tuah, S Y Annor and K T Djang-Fordjour

Department of Animal Science Education, College of Agriculture Education,
University of Education, Winneba.
PO Box 40, Asante Mampong, Ghana
nanakusi75@yahoo.com

Abstract

The study aimed to determine the dietary crude protein level required for growing grasscutters (from weaning to sexual maturity) in captivity. Thirty six (36) young grasscutters, between the ages of 2 and 3 months, of both sexes (18 males: 18 females) were fed diets which contained 10%, 12%, 14%, 16%, 18% and 20% crude protein. Parameters measured included daily feed intake, daily water intake, daily weight gain (growth rate), final body weight and feed conversion ratio (FCR). The Completely Randomized Design was used for the study. The data were analyzed using Analysis of Variance (ANOVA) in Mathematics Statistics (MSTAT) package.  The differences between means were separated using Least Significant Difference (LSD).  

Daily feed intake (g) differed significantly (P<0.05) between animals fed diets containing 10% (96.9) and 12% (100.6), and those fed 14% (95.1), 16% (90.4), 18% (87.7) and 20% (88.2) crude protein. Dietary protein significantly (P<0.05) influenced daily weight gain, as well as final live weights of the animals. The mean daily weight gain (g/day) of the animals fed the diet 20% (11.1±1.0) was not significantly different from those fed diet 18%  (10.1±1.06) but was significantly higher than animals fed 16% (9.92±1.06), 14% (8.72±1.06), 12% (7.45±1.06) and 10% (7.05±1.06) crude protein. The mean feed conversion ratios of the animals fed the diets with 20% (8.05±1.87), 18% (8.87±1.87) and 16% (9.15±1.87) CP were significantly better than those of animals fed diets with 14 (11.2±1.87), 12 (13.8±1.87) and 10 (14.3±1.87) %CP.  A 1% increase in percentage protein in the diet led to 0.43g increase in daily weight gain and 0.69 decrease in FCR. It was concluded that the dietary crude protein level required for optimum growth of grasscutters from weaning to reproductive stage is 18%. It was also concluded that the grasscutter could be raised solely on concentrate diet.

Key words: Body weight gain, feed and water intake, feed efficiency, reproductive stage, Thryonomys swinderianus

Introduction

Protein consumption among Ghanaian populace is low. An average Ghanaian consumes 59.8 g of protein per day of which 16.7 g (27.9%) is from animal origin (FAO, 2007). This falls short of the recommended daily protein requirement of 70-80 g of which 50% should be of animal origin (FAO 1990). The low meat consumption is not deliberate but is as a result of low meat production in the country leading to high price hikes.  

Attempts have been made to increase the production of existing breeds of ruminants but no substantial progress has been made. One major factor contributing to this is the nature/types of breeds of animals raised in Sub - Saharan Africa. Tropical animals are characterized by small birth weights, slow growth rates and relatively small mature weights. Another factor hindering the production of livestock and poultry in sub - Saharan Africa is nutrition. Non - ruminants, probably due to similar digestive system, compete with man for food. The scarcity of feed, coupled with escalating cost of cereal grains, makes meat production from poultry and pigs a problem as cereal grains form 50 – 60% of commercial poultry feeds (Olubamiwa et al 2002). One other factor is that, nutritional value of tropical grasses fluctuates with changing climatic conditions. For instance, the crude protein content of elephant grass (Pennisetum purpureum) declines from 9.25% in the major rainy season in southern Ghana to 5.10% in the dry season (Annor 2011). This poses a challenge to ruminant production in the sub – Saharan Africa. High prevalence of diseases such as PPR (Peste des petits ruminats), helminthosis and trypanosomiasis also tend to hinder ruminant production in sub - Saharan Africa.  

It is therefore important to find alternative animal protein sources for human consumption other than the traditional domestic animals. The grasscutter (Thryonomys swinderianus) is being developed as mini livestock species for meat production in most West African countries including Ghana (Adu 2005). The grasscutter has been identified to be hardy (disease resistant), highly prolific and eats a wide range of feedstuffs including kitchen waste (Fritzinger 1997; Mills 1997). Grasscutter meat is expected to serve as an alternative meat supply to supplement the conventional meat sources such as cattle, sheep, goats, pigs and poultry. However, it  is recently that the domestication of this wild animal has gained popularity, and therefore very little is known about nutritional requirements of this favorite animal. This gives a compelling reason to study the digestive physiology and nutrient requirements of the species if growth is to be enhanced and be efficient for maximum economic exploitation.  

The main objective of this experiment was to determine the crude protein requirement for optimum growth of grasscutters in captivity.  The study also determined whether the grasscutter can successfully be raised solely on a non- forage (concentrate) diet. 

Materials and methods

Experimental location: The experiment was carried out at the Non - Traditional Animal Section of the College of Agriculture Education, University of Education, Winneba, located in Asante Mampong. The duration of the experiment was 24 weeks (6 months) starting from June 6, 2008 through to November 21, 2008.  

Sources and preparation of feedstuffs

Dried Cassava Chips

The cassava used in this study was a variety called ‘Tek bankye’. The tubers were soaked in water for 4 hours before they were washed to reduce hydrogen cyanide concentration, especially the peels (Johnson and Raymond 1965).  The unpeeled cassava tubers were chopped into pieces of about 2 – 3 cm in length and 2.5 – 3.5 cm thick. The cassava chips were dried in a mechanical drier to a moisture content of about 12%. The dried chips were then milled through a 10mm sieve in a Hammer mill. 

Cocoa pod husks (C P H)

The cocoa (hybrid) pod husks (C P H) were obtained from the cocoa plantation of the  College of Agriculture Education of the University of Education, Winneba – Asante Mampong. The cocoa pod husks were gathered fresh and chopped into pieces of about 1.5 – 2cm size. They were dried in a mechanical dryer for about two and half hours to moisture content of about 12%. The husks were then milled through a 10mm sieve in a Hammer mill. 

Other feed ingredients

The other feed ingredients including soya bean meal, wheat bran, dicalcium phosphate, vitamin mineral premix and common salt (NaCl) were purchased from a commercial poultry feed seller in Kumasi, the Ashanti Regional capital in Ghana.         

Experimental animals 

A total of thirty six (36) animals consisting of 18 male and 18 female grasscutters were used for the study. The animals were weaners with ages between 2 and 3 months. The initial body weights of the experimental animals on the various treatment diets were similar (P>0.05). The average weight of the animals was 0.66 kg.   

Animal management 

The experimental animals were housed singly in three - tier battery cages. Each tier had three sub-cages, with each sub-cage measuring 60cm x 50cm x 40cm. The cages were partitioned with crimped wire mesh. The floor of the cages was also covered with wire mesh through which faeces and feed leftovers could pass. Each cage had a removable drawer placed at the base to collect the faeces and leftover feeds. The animals were individually caged to ensure easy identification and accurate data collection. 

Feed and water were provided each day. The animals were fed twice each day: morning (07 hours GMT) and evenings (17 hours GMT). One hundred and fifty grams (150 g) of feed was measured and fed to each animal each day during the first two months of the study. Of this, 100 g was given in the morning and 50 g in the evening. From the third to the sixth month 250 g of feed was fed to each animal each day. Of this, 150 g was fed in the mornings and 100 g in the evenings. Feed leftovers were collected and weighed prior to subsequent feeding. Water was offered ad libitum throughout the experimental period.  

Experimental Treatment and Design 

The thirty six (36) grasscutters were randomly allocated to the dietary treatments but balanced for sex and weight in a Completely Randomized Design. There were six (6) treatments diets, each of which was replicated six (6) times.  The treatment diets, containing varying levels of crude protein (10, 12, 14, 16, 18 and 20% were formulated, compounded and offered to the animals. The proportions of the individual feed ingredients used as contained in each of the six (6) dietary treatments are presented in Table 1.  

Chemical Analysis of Feedstuffs and Diets 

The experimental diets were also analysed for moisture, protein, ether extract, crude fibre and ash according to procedure outlined in A.O.A.C (1996).   

Data Analysis 

The data were analyzed using Analysis of Variance (ANOVA) in Mathematics Statistics (MSTAT) package (MSTAT 2012).  The differences between means were separated using Least Significant Difference (LSD) (MSTAT 2012).

Results and discussion

Chemical composition of experimental diets 

Table 2 shows the results of the proximate analysis of the six diets used for the experiment.

The minimum crude protein content of 9.93% was used as control diet because most grasscutter farmers in Ghana and elsewhere in Africa feed their animals with Panicum maximum (Adu 2005; Schrage and Yewadan 1999) and according to Annor et al (2008), Panicum maximum during the onset of rains, may have crude protein content of 9.25% which is similar to crude protein content of 9.93% used as a control diet of this research. The maximum dietary crude protein level of 19.9% used in this study agrees with the suggestion made by Adu and Rhule (2005) that for optimum growth, grasscutters should be fed with 17% dietary crude protein.

The protein – calorie ratios for the six diets were near unity (1:1). Adu (2005) emphasized that the protein to energy ratio must be close to unity to ensure better utilization of feeds by grasscutters. The protein – energy ratios obtained in the current study (0.88, 1.05, 1.17, 1.33, 1.44 and 1.69) were similar to those (0.83, 1.04, 1.26) reported by Adu and Rhule (2005).

Animal Performance 

The average performances of animals on the experimental diets are shown in Table 3.  

Mean feed intake 

A significant difference in feed intake (P<0.05) was observed between animals fed CP 10% and 12% on one side and those fed CP 14, 16, 18 and 20% on another side. Feed intake of animals fed CP 16, 18 and 20% were not significantly different (P>0.05) from each other.  

The lower feed intake recorded for those fed CP 16, 18 and 20%  could be attributed to the high energy levels (Table 2) contained in these diets. The reason is that, generally, animals eat to satisfy energy requirements; therefore animals that are fed with relatively high energy diets will tend to eat less than their counterparts that are fed with low energy diets (McDonald et al 1992).    

Mean feed wastage 

There were no significant (P>0.05) differences between the amounts of feed wasted by animals under various dietary treatments (Table 3). However, the rate of wastage observed in this study was lower than the 70% reported by Mensah et al (2001). The differences here could be attributed to the nature of the feeders used in each of the studies. The feed troughs used in this study were relatively deeper (about 11cm deep) than those (5cm deep) which were used by Mensah et al (2001). The depth of the troughs made it very difficult for the animals to use their limbs to scratch and spill the feed; giving an indication that the depth of a feeding trough affects the rate of feed wastage. This report agrees with the findings made by Schrage and Yewadan (1999) that the design of the feeder contributes to the extent of feed wastage by grasscutters.  

Mean water intake 

On the average, 102 ml of water was drunk by an animal per day. Water intake of animals on the six dietary treatments did not differ significantly (P>0.05) and could be attributed to similar moisture contents of the diets (Table 2). However, the mean water intake of 102 ml/animal/day recorded in this present study is relatively higher than 90 ml/animal/day reported by Schrage and Yewadan (1999). This was expected because according to Ward (2007), water content of the animal’s diet influences its drinking habits. The mean moisture content of 8.5% of diets used in the present study was relatively lower than 22.1% moisture content of the diet fed by Schrage and Yewadan (1999).  Further more, the diet fed by Schrage and Yewadan (1999) was a supplement to grass which contained about 70% moisture (Annor et al 2008). Currently, some grasscutter farmers are of the view that grasscutters do not drink water; which is false. The fact is, grasscutters when fed with grass (about 70% moisture) (Annor et al 2008), obtain their water from the grass so they either refuse water or drink a very small amount of water in a day (Aitken and Wilson 1962).  

Growth rate of grasscutters on dietary treatments 

There was no significant (P>0.05) difference between the initial body weights of the animals on the various treatment diets (Table 3). No significant differences were observed (P>0.05) between mean final body weights as well as daily weight gain of grasscutters fed CP 20 and CP 18%. However, there was a significant difference (P<0.05) between mean final body weights and daily weight gain of grasscutters fed CP 20 and 18% on one hand and grasscutters fed CP 16, 14, 12 and 10% on another hand. This difference could be attributed to increased levels of protein available for growth in CP 20 and 18% compared to CP 10, 12, 14 and 16% if growth is considered as an increase in size of body cells, tissues and organs which occur as a result of consumption, digestion and assimilation of dietary proteins.

Figure 1 shows the regression of daily weight gain on dietary crude protein level. A 1% increase in crude protein level in the diet led to 0.43g increase in daily weight (Figure 1). The percentage of protein in the diet explained 94.4% of the variation in daily weight gain.

High protein levels might have increased the breakdown and digestibility of fibre contained in diets containing CP 20 and 18% because microbes in the caecum, which are responsible for breakdown of fibre, are basically proteins (Radzicka and Wolfenden 1995) and would need dietary protein to build body proteins for effective breakdown of fibre. High protein levels might have also increased the digestibility of nutrients contained in the diets fed since the enzymes responsible for digestion are proteins. Thirdly, since protein forms the greatest portions of muscles, nails, hairs and hooves of farm animals, (Schaible 1970), increased levels of protein in diets could directly be associated with an increase in weight gain.    

This study therefore suggests that the minimum crude protein level required for growing grasscutters in captivity for optimum growth should be 18% because the total weight gained by animals fed diet with 18% CP was significantly higher than that of animals fed diets with 16, 14, 12 and 10% CP but not different from that of 20% CP. Grasscutter farmers can therefore feed their animals with diets containing 18% CP to achieve optimum growth.  

Feed conversion ratio (FCR) 

As protein in the diets increased, the efficiency of the animals to convert feed into body weight also increased.  Figure 2 shows the regression of FCR on dietary crude protein level. A 1% increase in crude protein level in the diet led to 0.69 decrease in FCR (Figure 2). The percentage of protein in the diet explained 93.4% of the variation in FCR.

Since the fibre levels of the six diets were similar, the differences that existed between the FCR values could directly be attributed to the different levels of dietary protein. This means that when animals are put on rations of relatively high protein content, the efficiency of the animals to convert feed into body weight increases and vice versa. This agrees with the assertion made by Wellock and Toplis (2009) and BPEX (2011) that the efficiency of utilization of dietary nitrogen for protein deposition decreases when low quality diet is fed because such diets lack the essential amino acids needed for the synthesis of body proteins or are inadequate for the synthesis of body proteins.   

Mortality 

Schrage and Yewadan (1999) reported that mortality rate of grasscutters in captivity could be as high as 66%. However, none of the 36 animals fed the six (6) diets died throughout the entire six (6) month period of the study (Table 3). This was ensured through good management practices, namely; (1) Feeding: type of feed and nutrient composition, (2) good sanitary practices, (3) adhering strictly to times of feeding and (4) stress management: the farm was not situated in a noisy area and human traffic was strictly monitored. One other factor which has been identified to be responsible for high mortality of captive grasscutters is worms (Schrage and Yewadan 1999). To control this however, the animals were drenched with Albendazole 2.5% (Mobedco-Vet, Jordan) during the third month of the experiment to control worms.  

Conclusions

• Generally, the grasscutters fed each of the six diets performed well, based on the growth parameters measured. However, it was concluded that the dietary crude protein level required for optimum growth of grasscutters from weaning to reproductive stage is 18%.

  
  

• This work has also proven that grasscutters can be raised solely on non-forage diets.  People in urban centres can therefore raise grasscutters at their backyards where there is scarcity of forage (grass).

  
  

• Since grass contains about 7-11% crude protein and does not meet the protein requirement of growing grasscutters, resource poor farmers can supplement grass with agro-industrial by-products and/or feed leftovers to boost the protein levels of diets of their animals.

Acknowledgement

The authors are grateful to the Teaching and Learning Innovative Fund (TALIF) for providing grasscutter facilities for this research.

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Received 14 February 2012; Accepted 15 August 2012; Published 1 October 2012

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