Nutritive value of conserved maize, amaranth or maize-amaranth mixture as dry season fodder for growing West African Dwarf sheep

O A Olorunnisomo

Department of Animal Production and Health Sciences, University of Ado-Ekiti, Ado-Ekiti, Nigeria
sholanisomo@yahoo.com
Present address: Department of Animal Science, University of Ibadan, Ibadan, Nigeria

Abstract

The nutritive value of conserved maize, amaranth or maize-amaranth fodders as dry season feeds for ruminants were estimated in a digestibility and animal growth study using West African dwarf (WAD) sheep. Whole plant maize (Zea mays), grain amaranth (Amaranthus cruentus) and their mixture, harvested at dough stage were either sun-dried or ensiled and fed to sheep.

Protein concentration of conserved fodders ranged from 9.3 to 22.4 g/100g. Dry matter digestibility of sun-dried maize (SDM), sun-dried maize-amaranth (SDMA), sun-dried amaranth (SDA), ensiled maize (EM), ensiled maize-amaranth (EMA) and ensiled amaranth (EA) was 71.8, 60.7, 57.3, 73.7, 55.3 and 52.6 % respectively. Intake of WAD sheep fed SDM, SDMA, SDA, EM, EMA and EA was 3.64, 3.78, 3.48, 3.45, 2.45 and 2.18% BW while average daily gain was 82.6, 71.3, 65.3, 83.8, 52.2 and 44.1 g/day respectively. Feed conversion ratio ranged from 7.96 to 10.4. Maize fodders had the best feed conversion while amaranth fodders had the poorest. Although amaranth had higher protein concentration than maize, digestibility and performance of sheep fed amaranth or maize-amaranth fodders were lower than those fed maize.

Sun-dried fodders seem to be preferred and better utilized by sheep than ensiled fodders. To derive maximum benefits from amaranth as a ruminant feed, there is need to investigate the presence of anti-nutritional factors in the plant and methods for reducing their effects on nutritive value of the fodder.

Key Words: average daily gain, digestibility, hay, intake, silage, small ruminants, weight gain

Introduction

The dry season presents a problem of feed shortage for ruminants in southwestern Nigeria. Yield and quality of forage from tropical pastures decline rapidly as the dry season approaches, leading to inadequate supply of quality feed for ruminants during this period. Hay and silage made from tropical grasses are often poor in quality and the level of animal production from these products may not justify the effort and cost of conserving tropical grass forage (Gallaher and Pitman 2001). To obtain high animal productivity during the dry season there is need to conserve forage of relatively high quality and high concentration of soluble carbohydrates.

Maize and amaranth fodders contain relatively high concentration of soluble carbohydrates and yield a high quality biomass within a short period, making them attractive as hay and silage crops for tropical areas (Coors and Lauer 2000, Sleugh et al 2001). These fodder crops grown on a small portion of the pasture and conserved for dry season feeding could bridge the gap in feed supply to ruminants at this period. Whole plant maize has been used extensively as a silage crop in both temperate and tropical climates because of its high biomass yield and high concentration of soluble carbohydrates (Phipps 1996, Njoka et al 2005). The main limitation of maize as a livestock feed is its low protein concentration.  Typical maize forage has a crude protein concentration of 8-9% (Carruthers et al 2000, Darby and Lauer 2002). This makes it necessary to supplement ruminants fed this basal diet with large quantities of expensive oilseed cake.

The potential of amaranth as a forage for ruminants was reported by Sleugh et al (2001). The crude protein concentration of amaranth fodder ranges from 15-24% (Kadoshnikov et al 2001, Pisarikova et al 2006). The protein quality of this plant is quite high. It is rich in lysine and sulphur-containing amino acids which are limiting in cereal crops (Sleugh et al 2001, Svirskis 2003). It is also suspected that this plant has a high by-pass protein (Cheeke and Bronson 1980) which is of great value in ruminant nutrition. The protein concentration and quality of amaranth, and its growth habit suggest that it can play a complementary role to maize in traditional crop-livestock systems in southwestern Nigeria. The presence of anti-nutritional factors such as oxalates, saponins, phenols, trypsin inhibitors and nitrates in some species of amaranth however, pose a limitation on its usefulness as livestock feed (Cheeke and Bronson 1980, Gupta and Wagle 1988, Pisarikova et al 2006). Although heat treatment has been suggested as an effective means of reducing the effects of these factors in plants (Andrasofszky et al 1998), this strategy may not be practical for processing large volumes of ruminant feed. A report by Pond and Lehmann (1989) shows that inclusion of up to 50% of amaranth forage in the diet of growing lambs had no ill-effect on productivity of these animals since the vegetative part apparently contained no toxic compounds. Anti-nutritional factors in amaranth fodder seem to be associated with certain species and varieties of the plant and management practice during cultivation. The raw seed also contain significant levels of anti-nutritional factors.  

The objective of this study was to evaluate the effects of mixing amaranth with maize fodder on digestibility of the mix as well as intake and growth of West African dwarf sheep fed a combination of these fodders in the southwest of Nigeria.

Materials and methods 

This study was conducted at the Teaching and Research Farm of the University of Ado-Ekiti, Nigeria (7^o 37΄ N, 5^o 13΄ E) which lies within the rainforest and experiences a tropical climate with distinct wet and dry seasons, high temperature and high humidity. Mean annual rainfall is 1367mm and is spread over 8 months (April to November). The rainy season has two peaks, one in July and the other in September with a dry period in August. Mean annual temperature is 27^oC and varies little throughout the year. The hottest months are February and March with mean temperatures of 28^oC and 29^oC respectively.

Feed preparation

A landrace variety of maize (Zea mays) and grain amaranth (Amaranthus cruentus) cultivated for fodder production were used in these studies. Whole plants of maize (leaf, stem and ear) and amaranth (leaf, stem and seedhead) were harvested 85 days after planting, 15cm above ground. Harvested fodders were chopped to approximately 3-cm length using a locally fabricated chopper. The chopped maize and amaranth were each divided into three parts. The first part was sun-dried while the second part was ensiled. The last part (maize and amaranth) was mixed (weight for weight), divided in half and either sun-dried or ensiled. Fodders were sun-dried on polythene sheets and turned at least twice daily for 5-6 days and stored in sacks for the feeding trial. Silage was made by packing and compressing fodders inside 120 L plastic drums. The compressed mass was sealed with polythene sheet, weighted with a sand bag and covered with a plastic lid.

Animal studies

The nutritive value of conserved maize, amaranth and maize-amaranth fodders for ruminants was estimated in a digestibility and animal growth study using male WAD sheep. Treatments correspond to six experimental diets as follows: sun-dried maize (SDM); sun-dried maize-amaranth (SDMA); sun-dried amaranth (SDA); ensiled maize (EM); ensiled maize-amaranth (EMA); ensiled amaranth (EA).

In the digestibility study, eighteen matured WAD rams approximately 12 months old with mean weight 17.3 ± 2.70 kg were put in metabolic cages with facility for feeding, watering and separate collection of faeces. The animals were divided into three groups according to their weights and randomly assigned to one of the six diets.  Experimental diets were offered ad libitum for 14 days. Feed offered, feed refused and faeces voided were weighed and recorded in the last 7 days.  Feed intake and feacal output were determined.  Ten per cent of feeds and faeces voided were taken daily, dried at 65^oC to constant weight, milled and kept in airtight containers until required for analysis. Dry matter and proximate composition of feed and faeces were determined using AOAC (1995) methods while detergent fibre analysis was done using methods of Van Soest and Robertson (1985). Apparent digestibility of the diets was calculated as the difference between nutrient intake and excretion in the faeces, expressed as a percentage of nutrient intake.

In the growth study 36 male West African dwarf sheep approximately 8 months old with mean weight 10.6 ± 1.80 kg were kept in separate pens with facility for water, forage and concentrate feeding. Animals were divided into six groups according to their weights and randomly assigned to one of the six diets. Before the commencement of the experiment, animals were treated with Ivomectin to suppress internal and external parasites and then vaccinated against peste des petits ruminants (PPR). Experimental diets were offered ad libitum. Fresh water was offered free choice on a daily basis. Feed offered and feed refused were measured daily while live weight of the animals were taken weekly. Average daily intake (ADI) and average daily gain (ADG) were calculated for each animal over a 16-week period. Feed conversion ratio was also calculated for each treatment from the ADI and ADG. The experimental design adopted for both studies was the randomized complete block design. Data obtained were subjected to analysis of variance and significant means (P<0.05) were separated by Duncan’s multiple range tests using SAS (1995) procedures.

Results and discussion 

Chemical composition of diets

Chemical composition of component parts of maize and amaranth used for preparing conserved fodders is presented in Table 1. 

The chemical composition of experimental diets used in the growth and digestibility studies is presented in Table 2.

Dry matter concentration of was similar among sun-dried fodders but varied widely among ensiled fodders. This was due to the wide difference in dry matter concentration of whole plant maize and amaranth fodders. Among the sun-dried fodders, crude protein concentration was highest in amaranth, followed by maize-amaranth mixture and least in maize.

Ensiled fodders, however, followed a different trend with ensiled maize, amaranth and maize-amaranth fodders having similar crude protein concentration. The texture of ensiled maize was firm while ensiled amaranth or maize amaranth mixtures were soft and wet. There was visible separation of liquid from the ensiled mass in silos containing amaranth and maize-amaranth mixture with excess liquid settling at the base of the silo. Although the liquid was not analyzed in this study, high loss of protein in ensiled amaranth or maize-amaranth mixture suggests that nitrogen solubility may be high in amaranth and much of its protein may have been lost to the separated liquid. Further research is required to investigate this and the effect of increased dry matter concentration (wilting) on texture and silage quality of amaranth fodder. Maize fodders had higher fibre concentration than amaranth fodders while the mixed fodders were intermediate between maize and amaranth fodders.

Digestibility of conserved fodders

Apparent digestibility of sun-dried or ensiled maize, amaranth or maize-amaranth mixture is shown in Table 3 and Figure 1.  

There were differences (P< 0.05) between maize and amaranth fodders in dry matter digestibility. In spite of the higher crude protein concentration in amaranth, maize fodders were better digested than amaranth fodders or their mixture. Anti-nutritional factors in amaranth seed-head may have contributed to the lower digestibility observed in amaranth and maize-amaranth fodders.

Crude protein and detergent fibre digestibility of the fodders followed the same general trend as dry matter digestibility showing that conserved maize fodders were better utilized by WAD sheep than amaranth or maize-amaranth fodders. Dry matter digestibility of ensiled maize fodder was slightly higher than that of sun-dried maize, however the reverse was the case for ensiled amaranth and ensiled maize-amaranth fodders with their sun-dried counterparts having slightly higher digestibility values. Protein loss in amaranth fodders during the ensiling process may have contributed to the lower digestibility observed for ensiled amaranth and maize-amaranth fodders compared to their sun-dried counterparts. There were no differences (P> 0.05) in fibre digestibility of sun-dried or ensiled fodders.

Intake and growth rate of sheep

Forage intake, weight gain and feed conversion ratio of West African dwarf sheep were used to evaluate the performance of sheep fed sun-dried or ensiled maize, amaranth or maize-amaranth fodders (Table 4).

Dry matter intake of conserved fodders differed (P< 0.05). Intake of sun-dried fodders (body weight basis) was higher than intake of ensiled fodders, suggesting that dried fodders were preferred by sheep to ensiled fodders. Forage containing maize fodder also seems to be preferred by sheep to amaranth fodders.  Forage intake was highest for sun-dried maize-amaranth and least for ensiled amaranth. The reduced intake observed for ensiled maize-amaranth and ensiled amaranth may be due to the soft texture of amaranth silage compared to the firm texture of maize. Forage intake in this study ranged from 2.18 - 3.78% BW, which is within the range of 1.80 and 4.08% BW obtained in another study where WAD sheep were fed different mixtures of sweet potato forage and root (Olorunnisomo 2008).

Average daily gain of WAD sheep varied (P< 0.05) across the treatments. Weight gain was higher in sheep fed maize than those fed amaranth fodders while animals fed sun-dried fodders generally gained more weight than animals fed ensiled fodders (Figure 2).

This observation is largely a reflection of dry matter intake of these animals which showed that the sheep had preference for maize fodders than amaranth fodders, and sun-dried fodders than ensiled fodders. Digestibility figures also showed that maize fodders were better digested by sheep than amaranth fodders while sun-dried fodders were better digested than ensiled fodders except for ensiled maize which had the highest digestibility value.

Daily weight gain of sheep in this study ranged from 44.1 - 83.8 g/day which is comparable to 56.9 - 86.4 g/day reported for WAD sheep fed mixtures of sweet potato forage and root (Olorunnisomo 2008).

Feed conversion ratio (FCR) differed (P< 0.05) among the treatments. The least FCR was recorded for ensiled maize and the highest for ensiled amaranth, showing that animals utilized ensiled maize better than other diets. Generally, maize fodders were better converted to meat by sheep than amaranth fodders. Except for ensiled maize fodder, sun-dried fodders appear to be better converted by sheep than ensiled fodders.

Conclusions

• In spite of the higher protein concentration in amaranth, maize fodders were better digested than amaranth fodders or their mixture with maize.
  
  
• Dry matter intake was similar among sun-dried fodders but higher in ensiled maize than ensiled amaranth or maize-amaranth fodders.
  
  
• Conserved maize fodders promoted higher growth and better feed conversion in WAD sheep than conserved amaranth or maize-amaranth fodder.
  
  
• In view of its higher protein concentration, amaranth has potential to complement maize as a dry season feed for ruminants if factors limiting its utilization are removed.

Acknowledgements 

Financial support for the execution of this study was provided by the International Foundation for Science (IFS). Technical contributions of staff and facilities made available for this study at the University of Ado-Ekiti, Nigeria are also acknowledged.

References 

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Received 10 December 2009; Accepted 6 July 2010; Published 1 October 2010

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