Livestock Research for Rural Development 29 (2) 2017 Guide for preparation of papers LRRD Newsletter

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Nitrogen partitioning and growth in grasscutters fed freshly cut Panicum maximum alone or supplemented with Leucaena lecocephala treated with 0, 1 or 2 per cent saline solution

J K Nyameasem, K O Amoah, P A Wallace and E K Adu

Council for Scientific and Industrial Research-Animal Research Institute, P. O. Box AH 20, Achimota, Accra, Ghana   ;


The study was conducted to investigate the effect of supplementing the basal diet of freshly cut Panicum maximum (PM) with 20% fresh Leucaena  leucocephala (LL), treated with 0, 1 or 2 per cent saline solution,  on the growth response of grower-finisher grasscutters (Thryonomys swinderianus). Twenty-four grasscutters, with an initial live weight of 2.0±0.06 kg were allocated in a Completely Randomized Design to four treatments namely: PM alone, PM + LL, PM + LL treated with 1% saline solution and PM + LL treated with 2% saline solution. The trial lasted for a period of 75 days. Forage intake, apparent digestibility, nitrogen balance and daily weight gains were measured during this period.


Supplementing the basal diet with 20% L. leucocephala significantly (P=0.0001) increased CP intake by 31% (5.2 v. 6.8 g/day). Apparent digestibility coefficients were similar (P>0.05) among the treatments for all chemical constituents measured. However, treating the supplemented L. leucocephala with 2% salt solution increased (P=0.0329) biological value of nitrogen and reduced (P=0.005) urinary nitrogen excretion. Average daily gains differed (P=0.001) among treatments, being lowest on PM alone diet and highest on PM+LL treated with 2% saline solution. It can, therefore, be concluded that treating freshly cut L. leucocephala with 2% common salt solution and using it as a supplement of the sole P. maximum diet could increase CP intake and also reduce urinary nitrogen excretion leading to improved daily live weight gain of grower-finisher grasscutters under captive conditions.

Keywords: apparent digestibility, nitrogen retention, salt, Thryonomys swinderianus


The high demand for grasscutter (cane rat) meat coupled with the economic benefit that accrues from its sale has resulted in aggressive hunting for the animal. Fire has been used in hunting to flush them out of their hideouts during the dry season resulting invariably in wild bush fires. The consequence is destruction of forests and farmlands with the gradual decimation of the wild grasscutter population (Ntiamoah-Baidu 1998). Rearing grasscutters in captivity has been suggested as the solution to this obvious environmental problem. The Government of Ghana and some Non-Governmental Organizations (NGOs) have been implementing projects to promote domestic grasscutter production in poor communities.  The main objectives of these projects have been to provide alternative source of income for farmers and to increase farmers’ access and utilization of animal protein for dietary needs (Heul-Rolf 2002; Wontewe 2002).


However, poor feeding of the domesticated grasscutter has resulted in long rearing or fattening periods thus discouraging uptake. In Ghana, many grasscutter farmers feed their stock solely on Panicum maximum (Adu et al 1999). The crude protein contents of this feed source is below the 15-18% required for growth and reproduction (Adu and Wallace 2003) resulting in poor growth performance and low profit margins.


Feeding forages, such as leucaena, gliricidia, sugarcane, sweet potato vines, stylosanthes, and moringa leaves to grasscutters has been proposed (Adu et al 2010) as one way of addressing these nutritional constraints. These forages are rich in nutrients and available even in the dry season (Schrage and Yewadan 1999). Earlier reports indicated that freshly cut Leucaena leucocephala improved feed intake, feed efficiency and animal performance in growing or fattening rabbits when included at a rate of 24-40% (Adejumo 2006; Nieves et al 2002). Adu et al (2010), however, reported low forage intake when fresh Moringa oleifera leaves were included in grasscutter diets at a rate of 20%.  Adu et al (2010) therefore suggested that treatment of these forages with salt water before feeding may enhance feed intake with consequent improvements in live weight gains.


Ru et al (2004) have indicated that saline solution of about 1.5% salt may not affect animal production if the environmental conditions are good. However, over 2% total salts in the drinking water were found to be detrimental to production and survivability of sheep (Wilson 1978). Though there is a dearth of information on the impact of salt on feed intake and growth rate of grasscutters, it is well known that grasscutters have high appetite for salt, hence the use of human urine, which contains about 1% sodium chloride, as a bait in trapping them in the wild (Kwenin et al 2008).The objective of the study was therefore to investigate the effect of treating L. leucocephala with either 1% or 2% salt solution when used to supplement the basal diet of freshly cut Panicum maximum on the growth response of grasscutters.

Materials and Methods

Feeding Trial


Twenty-four growing grasscutters, with a mean live weight of 2.0±0.06 kg, obtained from the stock of animals at the CSIR-Animal Research Institute, Pokuase Station were randomly assigned to one of four dietary treatments balancing for live weight and sex. The animals were housed in individual cages measuring 50 cm × 50 cm × 40 cm with wire mesh floor, each containing a feeder and a drinker. There were six animals per treatment. The experimental diets consisted of either Panicum maximum alone (PM) or P. maximum supplemented with 20% Leucaena  leucocephala treated with 0% (LL), 1% (LLS1) or 2% (LLS2) salt solution (see Table 1).

Table 1: Composition of experimental diets


Diets, g/100 g feed





Panicum maximum





Leucaena leucocephala





Saline water concentration, %





The L. leucocephala leaves were immersed in defined saline water, removed after one minute and allowed to air-dry before feeding to the animals. The animals were fed twice daily at 8.00 am and 4.00 pm. Each animal received a total of 400 g of feed a day with free access to water throughout the experimental period. Feed leftovers were collected after a 24-hour feeding per animal, weighed and used to determine daily feed intakes. The animals were weighed weekly and the average live-weight gains determined. The feeding trial lasted for 75 days.


Digestibility and Nitrogen Balance


Three animals from each group were placed in metabolic cages measuring 24 cm x 17 cm x 28 cm (length x width x height) at the end of the feeding trial to determine apparent digestibility of nutrients.  Faecal samples were collected daily on foil trays placed under the cage. Urine was collected over concentrated sulphuric acid (1 mL) to maintain the pH at about 1.0 (Adu et al 2012). The daily total faecal collection for each grasscutter was weighed and stored in a deep freezer. The collection was done for seven days, at the end of which the faecal collections were bulked and a sample taken per grasscutter for proximate analysis. The urine was also collected each day, the volume measured, bulked and stored in a freezer. At the end of a seven-day collection period the urine sample for each animal was thawed, thoroughly mixed and a sample taken for nitrogen determination. 


Chemical Analyses


Feed and faecal samples collected were dried at 55oC for 4 days, ground and stored. The nutrient composition of the experimental diets was determined according to the methods of A O A C (1990). Feed and faecal materials were analyzed for N content using the micro-Kjeldahl method (A O A C 1990).


Statistical analyses


Data collected were subjected to Analysis of Variance (ANOVA) using the General Linear Model (GLM) as described in CoStat version 6.4 (CoHort 2008). Data on apparent digestibility and nitrogen retention expressed as percentage of nitrogen intake and as percentage nitrogen digested were analyzed using Kruskall Wallis non-parametric test of CoStat version 6.4 (CoHort 2008). Differences between means of significant effects were separated by the Least Significant Difference (LSD).


Chemical Composition of Diets and Nutrient Intake of Grasscutters

Table 2: Chemical Composition of P. maximum and L. leucocephala



Dry matter, g/kg feed



Organic matter, g/kg DM



Crude protein, g/kg DM



Ash, g/kg DM



Ether extract, g/kg DM



Crude fibre, g/kg DM



Gross energy (MJ/kg DM)



The chemical compositions of forages and feed intakes are shown in Table 2 and Table 3, respectively. Total fresh forage, dry matter and organic matter intakes among the experimental animals were not different (P> 0.05). However, L. leucocephala intake increased by 22-23% when treated with 1- 2% saline solutions. Whereas crude fibre intake was similar (P =0.716) for the animals, crude protein intake differed (P= 0.0001), with L. leucocephala supplementation resulting in 31% increase in intake compared to P. maximum alone diet. 1 – 2 % saline water treatment of L. leucocephala increased CP intake by 7 – 9 %. This resulted in a daily crude protein intake of 14.5 – 15% (see figure 1).

Table 3: Forage and nutrient intakes of grasscutters fedPanicum maximum supplemented with fresh Leucaena leucocephala with or without salt treatment








Forage intake, g/day

Panicum maximum







Leucaena leucocephala














Feed fractions intake, g/day

Dry Matter







Organic Matter







Crude Protein







Crude Fibre







Means in a row with the same or no superscripts are not significantly different and vice-versa

Figure 1: Percentage Crude protein (CP) intake (mean±se) by grasscutters fed the experimental diets
Apparent digestibility and nitrogen retention in the grasscutters


Apparent digestibility coefficients for dry matter, organic matter, crude fibre and crude protein were similar across the dietary treatments (see Table 4). N intake differed among experimental animals (P=0.0001) and followed a similar trend as CP intake. Faecal N excretion, N retained and N retained as % of N digested were similar among the experimental animals, however a regression analysis showed a direct linear relationship (R2 = 0.986) between saline solution concentration and N retention (see figure 2). Urinary N excretion was lower (P= 0.005) for LLS1 and LLS2 diets compared to PM and LL diets.  N retained as % of N digested was higher (P=0.033) for LLS1 and LLS2 diets compared to PM diet.

Table 4: Apparent digestibility and nitrogen retention of grasscutters fed P. maximum supplemented withfresh L. leucocephala with or without saline treatment









Apparent digestibility %

Dry Matter







Organic Matter







Crude Protein







Crude Fibre







N balance, mg/day

N intake







N in feces







N in urine







N retained







N retained as % of N digested







Means in a row with the same or no superscripts are not significantly (P>0.05) different and vice-versa.

Figure 2: Relationship between saline solution concentration and N retention in the grasscutters

Growth performance of the growing grasscutters


Initial and final live weights were similar (P>0.05) however live weight gains differed (P=0.0012) among treatment groups. Although final body weights were similar, it followed a trend with final body weight being highest for LLS2 fed animals and lowest for PM fed animals. Average daily gains followed a similar trend but differed (P<0.001) among the dietary treatments with LLS2 fed animals recording the highest gain (see Table 5 and figure 3).

Table 5: Body weight changes and average daily live weight gains of grasscutters fed P. maximum supplemented with fresh L. leucocephala with or without salt treatment









Initial body weight, g







Final body weight, g







Body weight change, g







Average daily gain, g/day







ø Means in a row with the same or no superscripts are not significantly different and vice-versa

Figure 3: Live weight gains of grasscutter fed P. maximum supplemented with fresh L. leucocephala with or without salt treatment.


Nutrient Composition of Diets and Nutrient Intake


Leucaena leucocephala leaf had high CP and relatively low fibre contents indicating its potential as a supplement for grasscutters fed the poor quality P. maximum diet. Supplementing P. maximum with 20% L. leucocephala resulted in diets which met the required crude protein levels of 12 – 18 % suggested for growing grasscutter (Mensah and Okeyo 2005; Kusi  2010).


Though Schrage and Yewadan (1999) have reported high preference of grasscutters for P. maximum over L. leucocephala, treating it with either 1 or 2% salt solution resulted in between 22% and 23% increase in fresh forage intake. This confirms the speculation that salt treatment could increase intake of unpalatable but nutritious plants in grasscutters (Adu et al 2010). The basal diet of P. maximum used in this study is the dominant feed for captive grasscutters in Southern Ghana (Adu 2002), probably due to its prevalence in natural pastures and palatability. Crude protein and organic matter contents of the P. maximum used in this study (Table 2) were comparable to values reported by Adu et al (2010) but lower than those reported by Annor et al (2008). The DM value of 14.5% in this study was lower than the 19.5% reported by Adu et al (2010).  These differences could be due to ecological and seasonal differences between the studies.  Annor et al (2008) obtained P. maximum from a wet semi-equatorial forest zone, whereas in the current study, P. maximum was obtained from coastal Savannah zone with relatively drier conditions. The differences between the current study and that of Adu et al (2010) could be attributed to seasonal differences. Whilst Adu et al (2010) carried out their work during the dry season (February -April) the current study was conducted during the major rainy season (April to June). Climatic factors such as temperature, humidity, precipitation, light intensity and altitude have been cited as factors that could control the nutritive value of forage (Adesogan et al 2002).


Dry matter, organic matter and crude fibre intakes were similar for all treatment groups in this study (Table 3). Fresh forage intake in the current study compares favourably with intakes reported earlier for grasscutters fed P. maximum supplemented with either fresh sweet potato vines or Moringa olefeira leaves (Adu et al 2010) and falls within the 150 – 400 g/day observed for grasscutters fed grass forage (Schrage and Yewadan 1999). In this study crude protein intake differed among treatment groups with animals supplemented with 1% and 2% saline solution-treated L. leucocephala having higher intakes compared to the P. maximum-alone diet. Leucaena leucocephala is known to be high in protein and therefore, has been widely used to increase protein supply in animal diets (Khamseekhiew et al 2001).


Nutrient digestibility and Nitrogen metabolism


Apparent digestibility was found to be similar between treatments in the current study. Neither Leucaena inclusion nor salt treatment altered nutrient digestibility in the grasscutters. Adu et al (2010) reported a similar observation when a Moringa supplemented diet was fed to grasscutters on a basal Panicum maximum diet. Nutrient digestibility is known to be highly influenced by fibre in grasscutter diets (Van Zyl et al 1999; Karikari and Nyameasem 2009). In the current study, however, fibre intake was similar for all dietary treatments (see Table 3). This may explain the similar apparent digestibility coefficients observed for the grasscutters.


Nitrogen intake was significantly low (Table 4) for animals on P. maximum alone diet compared to the L. leucocephala supplemented diets, following a trend similar to crude protein intake (Table 3). Although urinary N excreted differed among treatments, N balance did not differ. This corroborates Adu et al (2012) who reported no significant differences in N balance of grasscutters fed diets varying in crude protein (8.2 to 18.5%) content.  Grasscutters depend on the metabolic faecal N route in meeting their N requirement on poor quality diets (Adu et al 2012). Metabolic faecal N losses were not measured in this study, however, it is indicated that grasscutters on the low N diet (PM diet) may have controlled gut N loses through efficient resorption of digestive enzymes, reduced renewal rate of intestinal epithelial cells or through high retention of cecal and gut microflora to compensate for endogenous urinary nitrogen losses (Adu et al. 2012).


Urinary N excretion was lower for the salt treated diets than the non-salted diets. Mineral load is a major determinant of urine N concentration in cattle (Spek et al 2012). It is also reported that the presence of tannins in diets of ruminants severally causes a shift in nitrogen partitioning. For instance, Hess et al (2006) observed a shift in N excreted from faeces to urine when ruminants were fed diets containing tannins by reducing the amount of volatile urine N and by binding protein. There is paucity of information on effect of salt load and tannins on N partitioning in rodents. However, it is suspected that the presence of tannins and the salt load in LLS1 and LLS2 diets may have played a role in partitioning N excretion in the grasscutters. Reduced urinary N excretion has some beneficial environmental implications as N contamination threatens ground and surface water quality (Monaghan et al 2007) and contributes to losses of ozone in the stratosphere (Ravishankara et al 2009).


Live weight changes


Live weight changes in the current study were positive indicating the adequacy of the diets to support some level of growth in the animals. Supplementation of the basal P. maximum diet with L. leucocephala however resulted in 34% increase in growth. Addition of 1 - 2% saline solution resulted in a 10 – 40% further increase in growth when compared with supplementation without salt treatment (5.3 g/day v. 5.9-7.5 g/day). Adequate Sodium ions ensure efficient absorption of amino acids and monosacharides from the small intestines (Salt Institute 2014). Also, Chloride ion is a necessary part of hydrochloric acid produced by the stomach which is required for digestion. Plant materials do not provide adequate salt in the diet, therefore the need for supplementation (Berger 2006). Although not significant, salt treated diets were relatively more digestible than the LL diet (see table 4).


All the animals in this study maintained some level of growth probably due to the positive nitrogen balance observed across the treatments. The combine effect of L. leucocephala and salt supplementation, with the resultant differences in biological value of N may be responsible for the differed growths observed in the growing grasscutters. The weight gain of 3.3 g/day achieved for grasscutters fed the P. maximum alone diet was similar to reports by Annor et al (2008) but lower than 4.3 g/d reported by Adu et al (2010) despite the relatively higher forage intake (316 v. 257 g/day) and higher dry matter digestibility (63.1 v. 48.1%) reported in the current studies. Adu et al (2010) used younger animals compared to animals used in the current study (1.2 kg v. 2.0 kg) which may have accounted for this difference since younger grasscutters are known to have higher feed conversion efficiency and faster growth rate compared to older ones (Schrage and Yewadan 1999).



We acknowledge Mr. Yram Atipoe and Mr. Noble Defoe for the care and management of the animals during the period of this study. The management of CSIR-Animal Research Institute is thanked for permission to use the facilities of the Grasscutter Unit for this work.


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Received 10 August 2016; Accepted 27 December 2016; Published 1 February 2017

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