Abstract: Background and Objective: Poor nutrition in the dry season is a critical constraint to ruminant production in the tropics, however, supplementation with protein feed is one method of ameliorating this problem. The aim of the study was to determine the effect of ensiled water hyacinth combined with dried cassava peels supplementation on digestibility and nitrogen balance in sheep fed NaOH-treated Rice Straw (TRS). Materials and Methods: Experimental diets were TRS, TRS and Water Hyacinth Leaves (WHL), TRS and Water Hyacinth Whole Plant (WHLS), TRS and Water Hyacinth Leaves Combined with dried Cassava Peels (WHL-CP) and TRS and water hyacinth whole plant combined with Dry Cassava Peels (WHLS-CP). Five matured rams (±26 kg) were used in a 5×5 Latin square design. Animals were put in metabolic crates and fitted with faecal bags and urine tubes. Data were collected for seven days after 14 days and analyzed using a one-way analysis of variance applicable to a 5×5 Latin square experiment. Means were separated using Least Significant Difference (LSD) at 5% probability level. Results: Dry matter digestibility was 52.2, 65.7, 68.3, 75.6 and 77.2%, for TRS, WHL, WHLS, WHL-CP and WHLS-CP, respectively (p<0.05). The WHL and WHLS had the highest crude protein digestibility. Nitrogen retention values were-4.6, 1.3, 2.2, 2.6 and 3.3% for TRS, WHL, WHLS, WHL-CP and WHLS-CP, respectively (p<0.05).The high crude protein digestibility and low nitrogen retained for WHL might be due to anti-nutritional factors in the leaf, which make protein unavailable to the animal. The high nitrogen retained by WHL-CP and WHLS-CP resulted in improved nutrient digestibility. Conclusion: Water hyacinth supplementation improved digestibility and nitrogen retention. Inclusion of cassava peels, further improved nutrient digestibility and nitrogen retention compared with sole water hyacinth supplementation.
INTRODUCTION
Rice straw is a major agricultural by product in many countries which can be used as livestock feed1,2 but they are usually underutilized because of their low digestibility which limits feed intaket2. Feeding rice straw as a sole diet usually leads to weight loss and poor reproductive performance by the animal3 thus there is need to improve its quality and utilization. Straw digestibility can be improved by supplementation with protein and energy with feeds like water hyacinth and cassava peels. Other interventions such as chemical treatment with urea and NaOH to break down lignin content in the straw, making available the potential fermentable dry matter for the animal have been reported4,5.
For effective rumen function there is the need for supply of readily fermentable carbohydrates to the rumen microbes. One such product that supplies readily available carbohydrate is cassava peel. Cassava peels, like most root crops, supplies 1-6% crude protein and provides 3,200 kcal kg–1 gross energy6,7. Although the protein in cassava peels by-passes rumen degradation, they are not enough to support growth in ruminants8. There, is therefore a need to provide additional protein source if animal production is to be enhanced. Water hyacinth, an invasive aquatic weed, is known to have high biomass9 and rich in crude protein (20-35%)10,11 and has been reported to improve digestibility when used as a supplement11.
Considering the high protein content of water hyacinth and the readily available energy of cassava peels, one could speculate that the combination of these will improve the digestibility and nitrogen needs of sheep. The objective of this study was therefore to investigate the effect of water hyacinth, plus cassava peels supplementation on the digestibility and nitrogen retention of sheep fed a basal diet of NaOH-treated rice straw.
MATERIALS AND METHODS
Ethics: All protocols used were cleared by the Animal Ethics Committee of the University of Ghana.
Study location: The study was conducted at the Livestock and Poultry Research Centre Legon in the Greater Accra region of Coastal Savannah ecosystem, from September 2014-January 2015.
Collection and treatment of feed ingredients
Water hyacinth: Water hyacinth was collected from the Volta River in Ghana. Water hyacinth was divided into 2 group: 1st group comprised only the leaves whiles the 2nd group comprised the whole plant without the root. These portions were wilted separately under shade for 48 h and then chopped using an electric forage chopper (CeCoCO forage SFC1400, Central Commercial Company, Osaka Japan) to about 3 cm in length before ensiling for 3 weeks in a concrete culvert lined with polythene.
Cassava peels: Cassava peels (150 kg, one collection only) was obtained from a processing facility, chopped into about 3 cm units and sun-dried to a moisture content of 15%. Dried peels were stored in jute sacks until ready for use.
Rice straw: Rice straw (1,000 kg, one collection only) was chopped to approximately 3 cm length using a forage chopper. For straw treatment, 200 g of NaOH was mixed with 1 L of water and mixed with 4 kg of straw. The treated straw was stored in concrete culvert lined with polythene sheets for a minimum of 21 days.
Experimental diets: All animals received a basal diet of NaOH-treated rice straw at a feed allowance of 5% of animal body weight. Diets were:
| • | Naoh-Treated Rice Straw alone (TRS) |
| • | Ensiled Water Hyacinth Leaf (WHL)+TRS |
| • | Ensiled Water Hyacinth whole plant (WHLS)+TRS |
| • | Ensiled Water Hyacinth Leaf+dried Cassava Peels (WHL+CP)+TRS |
| • | Ensiled Water Hyacinth whole plant+dried Cassava Peels (WHLS+CP)+TRS |
Water hyacinth was given at 7 g crude protein per 10 kg body weight of the animal and cassava peels offered at 10% of feed intake.
Data collection: Five intact Djallonke sheep with an average weight of 26 kg were randomly assigned to 5 treatments in a 5×5 Latin square design in wooden metabolic cages. Drinking water was provided ad libitum to the animals. Daily feed offer and refusal were weighed. Experiment lasted for 21 days comprising 14 days adjustment and 7 days of data collection.
Faeces were collected in the morning before feeding. Fresh weight of the faecal samples was taken; 10% of each collected feacal sample was oven dried at 55°C, then milled and stored in polythene bags until chemical analysis. The faecal sample remaining after the 10% was collected for each day per treatment was oven dried at 105°C for 24 h to determine gross faecal dry matter.
Urine was collected using funnels attached to the genital region of the animals and connected to rubber tubes which led to a plastic bottle containing 20 mL of 10% H2SO4. Ten percent of total urine sample was bulked per treatment per animal and frozen until analysis.
Chemical analysis: Proximate analysis was done on feed ingredients, faecal material and urine12. Acid Detergent Fiber (ADF) and Neutral Detergent Fiber (NDF) were also determined13.
Calculations:
Nutrient digestibility (%) = [(nutrient in feed-nutrient in faeces) ÷ nutrient in feed]×100
Nitrogen balance (%) = nitrogen intake- (fecal + urine nitrogen)
Statistical analysis: Data for digestibility and nitrogen retention were subjected to a one-way analysis of variance14 applicable to a 5×5 Latin square experiment and mean separation was done using Least Significant Difference (LSD) at 5% probability level.
RESULTS AND DISCUSSION
In vivo dry matter and nutrient digestibility: Table 1. Shows the chemical composition of the feed ingredients whilst. Table 2 shows mean in vivo digestibility of all 5 diets. The non-supplemented diet (TRS) had the lowest digestibility for all nutrients. For diets with supplement, WHLS-CP had the highest Dry Matter Digestibility (DMD), Organic Matter Digestibility (OMD) and Neutral Detergent Fiber Digestibility (NDFD), whiles WHL had the lowest (p<0.05). However with respect to crude protein, WHL had the highest digestibility whiles WHL-CP was the lowest (p<0.05).The high DMD and OMD digestibility in WHL-CP and WHLS-CP diets might also be attributed to the supply of degradable nitrogen in the rumen synchronizing with the supply of fermentable carbohydrate. This is contrary to other reports15 that protein source had no effect on DMD and OMD. Similar observations have been reported16, when a source of readily available carbohydrate (cassava chips) was added to cotton seed meal compared with cassava chips and rice straw and also when urea-molasses was compared to ammoniated rice straw5.
Although the TRS diet had the lowest DMD and OMD (Table 2), the OMD of 551.0 g kg–1 DM observed was comparatively higher than 483 g kg–1 DM observed for untreated rice straw5. The observed DMD of 551 g kg–1 DM for TRS in this study is within the general range of (500-590 g kg–1) DM reported17. Sodium hydroxide treatment results in disruption of lignin complexes and cell wall carbohydrates which leads to increased intake and digestibility18.
Since, crude protein level of feed has an effect on feed intake and digestibility, it was expected that WHL supplementation which had higher crude protein than WHLS (Table 1) would result in a higher DMD and OMD than WHLS. The reverse happened in this study (Table 2) and this observation might be due to the plant part. Water hyacinth leaves have higher level of tannins (2%) compared to the whole plant (1%)19. Although this is not significant for it to be lethal to the animals it might be the cause of the lower DMD and OMD observed for WHL diet compared with WHLS diet. A similar observations of lower digestibility of water hyacinth leaf supplement compared to water hyacinth whole plant supplement to rice straw has been reported20.
| Table 1: | Chemical composition of feed ingredients |
| Table 2: | Effect of water hyacinth and cassava peel supplementation on digestibility of NaOH-treated rice straw |
Data were presented as average ±SD, Means in the same rows with different superscripts are different (p<0.05),TRS: NaOH treated rice straw, WHL: Water Hyacinth Leaf, WHLS: Water Hyacinth whole plant, WHL-CP: Water Hyacinth Leaf plus Cassava Peels, WHLS-CP: Water Hyacinth whole plant plus Cassava Peels |
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| Table 3: | Effect of water hyacinth and dried cassava peels supplementation on nitrogen retention in sheep fed NaOH-treated rice straw |
Data were presented as average ±SD, Means in the same rows with different superscripts are different (p<0.05), TRS: NaOH treated rice straw, WHL: Water Hyacinth Leaf, WHLS: Water Hyacinth whole plant, WHL-CP: Water Hyacinth Leaf plus Cassava Peels, WHLS-CP: Water Hyacinth whole plant plus Cassava Peels | |
In this study, there was a higher Crude Protein Digestibility (CPD) for animals on diets without cassava peels (WHL, WHLS) compared to diets with Cassava Peels (WHL-CP, WHLS-CP). Higher CPD might be due to better rumen environment created by WHL and WHLS diets for microbial degradation. The lower CPD for WHL-CP and WHLS-CP diets might be due to an increase in ruminal microbial growth and greater quantity of nitrogen of microbial and endogenous origin ending up in faeces (Table 3). This led to an over estimation of crude protein in faeces resulting in lowered apparent digestibility. Similar observations have been reported when cassava chips was added to cotton seed meal and when cassava chips was added to rice straw16 and also when urea-molasses was compared with ammoniated rice straw5. The CPD value of 638 g kg–1 DM for WHL-CP diet was comparable to a range of 645-709 g kg–1 DM observed when sheep were fed grass supplemented with cassava peels21,22. Crude protein digestibility of 925 and 786 g kg–1 DM for WHL and WHLS, respectively were higher than 550 g kg–1 DM observed when TRS was supplemented with mucuna leaves17suggesting that water hyacinth leaf is of better quality in terms of CPD compared with mucuna leaves. This might be due to the favorable rumen environment such as higher rumen ammonia levels.
Supplementation with water hyacinth led to improved NDF Digestibility (NDFD) (p<0.05) with the highest being observed with diets that included Cassava Peels (WHL-CP and WHLS-CP). High NDFD has been associated with high passage rate and as a result high feed intake23. This could also explain the higher DMD and OMD observed in diets which included cassava peels. The higher NDF digestibility observed with the inclusion of cassava peels (WHLS-CP and WHL-CP) might also be attributed to a better rumen environment created by the cassava peels.
Nitrogen retention: From Table 3, significant differences (p<0.05) were observed in the mean nitrogen intake (N-I) with the highest observed in WHL whilst TRS was least. The highest (p<0.05) mean feacal nitrogen (N-F) value was observed in WHL-CP diet and the lowest in WHLS diet. Significant differences (p<0.05) were observed in the mean urine nitrogen (N-U) values; with WHLS having the highest N-U and the lowest observed in TRS. There were significant differences (p<0.05) among the various treatment in terms of nitrogen retained (N-R) with TRS recording a negative nitrogen retention an indication that sheep cannot be maintained on diet of NaOH treated rice straw without supplementation.
The addition of cassava peels to water hyacinth resulted in an increased N-F nitrogen for both WHL-CP and WHLS-CP diet (Table 3). Soluble nitrogen in faeces is mostly from microbial degradation and endogenous sources more than dietary. This means, these diets provided a better rumen environment from microbial growth and therefore, more microbes escaping from the rumen to the intestines for usage by the host. This might also be the result of the lower CPD in WHL-CP diet.
From Table 3, as the N-F increased, the N-U reduced, with the least N-U showing in WHL-CP diet. Low N-U observed might be attributed to the presence of condensed tannins which bind protein and other macro-molecules in the rumen and reduce the availability of nutrients to microbial degradation24,25. They mainly reduce excessive ammonia production in the rumen and thus decrease N-U losses23,26 leading to increased N-R in ruminants fed tannin-rich plants27. The high N-R observed when cassava peels were added to the water hyacinth (WHL-CP and WHLS-CP) means more nitrogen was retained by animals on those diets and may contribute to the better growth rate. Higher N-R was observed when Tithonia forage was fed together with cassava chips as a fermentable carbohydrate28 and when urea-molasses was compared with urea-ammoniated straw5.
The lower faecal and higher urine nitrogen observed in diets without cassava peels (WHL, WHLS) might be due to an increased dietary protein intake without an associated increase in energy intake (WHL-CP, WHLS-CP). This also means the full benefit for the metabolism of protein was not achieved as there was high protein metabolism into ammonia in the rumen23, resulting in the reduction of the quantity of protein digested in the small intestine and an increase in N-U (Table 3).
In the study, feeding NaOH treated straw solely resulted in a negative nitrogen balance implying that there is need for supplementation, since it cannot sustain animal growth. The study further shows that, the combined use of cassava peels with ensiled water hyacinth resulted in improved nitrogen retention and therefore better growth performance will be expected.
CONCLUSIONS AND RECOMMENDATION
The study shows that both water hyacinth leaf and whole plant are rich in crude protein and could be used as supplements. All supplemented diets led to an improvement in the nutrient digestibility and nitrogen retained compared with the basal diet alone. However in ranking the supplements, water hyacinth combined with cassava peel resulted in better nutrient digestibility and nitrogen retention than water hyacinth only diets.
It is therefore, recommended that water hyacinth be fed together with cassava peels for enhanced animal performance.
SIGNIFICANCE STATEMENTS
This study discovers the improved nitrogen retention in sheep due to the synergistic effect of combined water hyacinth and cassava peels supplementation. It will help the researcher to discover the critical area of dry season feeding (energy and protein combination) that many researchers have not explored.
Thus a new theory on the combination of water hyacinth and cassava peel supplement that can reduce the effects of oxalates, which occurs when water hyacinth is fed alone, may be explored.
ACKNOWLEDGMENTS
The authors gratefully acknowledge the massive support of the Livestock and Poultry Research Centre, School of Agriculture, University of Ghana, who provided all the materials and technical staff for the study.