Polyethylene glycol improves the utilization of a high tannin forage in sheep

Biruk Kebede, Yisekak Kechero and Abegaze Beyene

Department of Animal Sciences, College of Agriculture and Veterinary Medicine, Jimma University,
P. O. Box 307, Jimma, Ethiopia
yisehakkechero@yahoo.com

Abstract

The study was conducted to evaluate the effect of dietary inclusion of tannin-rich (84 g CT/kg DM) Albizia gummifera (AG) leaves in grass-based hay with or without polyethylene glycol 6000 (PEG) on feed use potential in Bonga sheep breed. A 20-day adaptation and 10-day feeding trial were practiced. The dietary treatments consisted of grass based hay (CTL), 30% AG + 70% hay (AG), and hay + AG with 40g PEG/kh AG. (DM basis). The lambs were individually fed and had free access to clean drinking water and mineralized salt licks. Intake and apparent digestibility coefficients were determined for dry matter (DM), organic matter (OM), crude protein (CP), crude fat (EE), neutral detergent fiber (NDF), and acid detergent fiber (ADF).

Feed intake, growth rates and carcass weights were higher, and feed conversion efficiency was improved, in lambs fed a basal diet of hay supplemented with AG and PEG, compared with those fed hay alone or hay supplemented with AG.   Apparent digestibility coeficients of all nutrient sources were higher for AG-PEG and AG diets compared with hay alone.

Keywords: Albizia gummifera, carcass, digestibility, feed intake, growth performance

Introduction

In Sub-Saharan Africa, the dry season is always a critical period when most of herbaceous feed resources dry out (Devendra 1992; Kanani et al 2006; Cheema et al 2011). Foliages of tannin rich trees and shrubs (TRTS) have been recognized as reliable substitute either as sole feed or as protein supplements which can be utilized to prevent a decline in productivity of animals during this period (Makkar 2000; Arigbede et al 2011; Yisehak et al 2013).

Currently smallholder farmers in many Sub-Saharan African countries in general are increasingly relying on various potential TRTS to supplement their livestock especially in dry seasons (Kanani et al 2006; Aremu and Onadeko 2008). Albizia gummifera, among the potential TRTS can provide a green feed throughout the year which may be particularly useful as a feed supplement to the typical low-quality diets (Yisehak and Belay 2011). The presence, however, of high contents of condensed tannins (CT, 85 g/kg DM) in A. gummifera could present major constraints to their use (Yisehak et al 2012). Tannins have high affinity to proteins and other essential nutrients leading to a reduction in animal performance and ruminal gas production (Silanikove et al 2001; Tiemann et al 2008a).

Sheep are the predominant small ruminant species kept in the southwestern Ethiopia where almost all of them are kept under traditional extensive management system and depend almost exclusively on natural grazing. As in many countries in tropics, due to the extended dry season in Ethiopia the nutritive value of natural pastures deteriorates and becomes deficient in many nutrients, especially proteins and soluble carbohydrates. As a result, animals that depend on those pastures progressively lose weight until the wet season comes. Alternatively, animals can be supplemented with TRTS such as A. gummifera to minimize or to prevent weight losses (Yisehak et al 2011). However, to our knowledge, the response in sheeps' nutrient utilization, growth performance and carcass quality to A. gummifera leaf feeding with or without PEG have not been investigated elsewhere.

The present study was undertaken to investigate the effects of dietary inclusion of dried A. gummifera leaves with or without PEG on feed use efficiency in Bonga sheep breed of Ethiopia.

Materials and methods

The study area

The experiment was conducted at Jimma University (JUCAVM) small ruminant research farm, south western Ethiopia located at 7°40′N and 36°50′E / 7.667, 36.833 and at an altitude of 1780 m above sea level. The climate of the area, where A. gummifera (Fig.1) grown and sheep bred, (GOR 2006) is characterized as semi-humid tropical with bimodal rainfall which is ranging from 1200 to 2800 mm per year. The ten years mean annual minimum and maximum temperature of the area was 11.3°C and 26.2°C, respectively. Farmers in the area carry out mixed crop-livestock agriculture. Sheep production is characterized by traditional smallholders that are kept mainly in severely overgrazed private and communal rangelands throughout the year. Foliages of TRTS (Yisehak et al 2010) are becoming potential supplements of ruminants particularly in the dry season.

Figure 1: Albizia gummifera (J F Gmel.) C. A. Sm.)

Animals, feeding management and apparent digestibility of nutrients

Twenty four intact Bonga lambs/yearlings with comparable body weight (24.5±0.02 kg (mean±SE)) and similar body condition score (1 to 5 score scale, Campbell et al 2006) were used for the trial. Before starting the experiment, animals were administered ivermectin, a broad spectrum anthelminthic, and vaccinated against pasteurolosis. Animals were separated in to three equal groups, 8 animals per group. Each animal was separately housed in tie stall pens in a well-ventilated barn with a concrete floor. Each group of sheep was randomly assigned to one of the treatments. The treatment combinations were: hay (control), AG (30% A. gummifera + 70% hay) and AG-PEG (AG + PEG).  PEG, MW6000, HO(C2H4O)nH was purchased from Micron International Trading House Private Limited Company, Addis Ababa. The leaves of A. gummifera were collected from 50 farm grown trees. The leaves were then mixed thoroughly and dried under shade for 7 days to average 90% DM. The hay was from plant mixtures of about 82% Poaceae, 10% Astraceae, 7.5% Fabaceae, 0.5% Cyperaceae and Juncaceae). It  was harvested from Jimma University Kito Furdissa campus natural pasture site. The plant mixture was dried to have average 90 % DM and was considered as control diet. A. gummifera leaves were fed (8:00AM) prior to the provision of basal diet up to 10:00 AM in a separate trough. The sheep had free access to clean drinking water. PEG was mixed in water at a rate of 0.5 g PEG/ml (Getachew et al 2001). The solutions were drenched to every sheep at rate of 40g PEG to 1 kg of AG per day.

The faeces collection bags were harnessed to the animals for daily faeces collection. Total collection of faeces was carried out for 10 consecutive days. All animals from each treatment were used for faecal collection. Representative samples were then taken for the feed offered every morning before feeding, placed in deep freezer to minimize loss of ammonia until a sub-sample was taken for laboratory analysis. Feed refusals were pooled over the experimental period and sub-sampled for analysis. Supplement and basal feed offers and refusals were weighed for each animal daily and their differences were recorded as a daily feed intake per animal. The total faeces voided during the day and nights were weighed, thoroughly mixed for each animal. About 10% of the total weights were sampled every morning, placed in plastic bags and stored at -20oC until analysis. At the end of the experiment sub-samples from frozen samples were taken, mixed /agitated and oven-dried at 60oC for 48 hr. The dried faeces were grounded in a Wiley mil to 1mm screen and stored at an airtight container until analysis (AOAC 2005). Intake and digestibility of the feedstuffs were calculated for each group of animal by following Osuji et al (1993). Feed conversion efficiency (FCE) was measured as proportion of average daily BW gain to daily DM intake (Ball and Pethick 2006). Metabolizable energy intake (MEI) (kJ/kg BW0.75) was estimated according to Luo et al (2004) as: 533 + (43.2×ADG (g/kg BW0.75)).

Slaughtering and carcass evaluation

At the end of experiment, the sheep were fasted overnight, weighed and slaughtered to determine carcass parameters. The slaughter weight, carcass weight, edible and non-edible offal for each animal were weighed and recorded. Dressing percentage values for each treatment was determined based on the empty body weight basis rather than on live weight at slaughter basis, otherwise the influence of digesta (gut fill) would exaggerate dressing percentage (Gibbs and Ivings (1993) and El-khidir et a1 (1998). Hence, dressing percentage was calculated on the bases of empty BW (absence of gut fill) as: dressing percentage = hot carcass weight/empty body weight×100. Total edible offal component was taken as the sum of liver, digestive tracts, small intestine, kidneys, heart and tongue. Total non-edible offal component was computed as the sum of blood, spleen and pancreas, head, skin, testis and penis, gut fill and feet (Clotter 1985).

Chemical analysis and of feed and faeces samples and calculations

A. gummifera leaves and basal diet of hay were ground and analyzed for DM, OM, CP, CA, CF and EE according to AOAC (2005). Neutral detergent fiber (NDF) and ADF were determined by the method of Van Soest et al (1991). Lignin was determined by solubilization of cellulose with H₂SO₄ (Robertson and Van Soest 1981). Hemicellulose (HC) was calculated from the difference between % NDF and % ADF. Determination of total CT was based on the oxidative depolymerization of CTs in butanol-HCl reagent using 2% ferric ammonium sulfate in 2N HCl catalyst (Porter et al 1988) with the modifications of Makkar (2003) and using purified quebracho tannin as standard. Concentration of CT was expressed in g/kg DM, standard equivalent. All chemical analyses were carried out in triplicate. The nitrogen free extract (NFE) was obtained by difference (McDonald et al 2011). The faeces samples was used for estimating DM by oven drying at 105 °C for 24 hours for chemical analysis. Non-oven dried but well-mixed faeces were directly used for nitrogen analyses. Total carbohydrate (CHO) content was estimated according to Ranjhan (1997). On the other hand, protein efficiency ratio (PER) was calculated according to Ranjhan (2001) procedure.

Statistical analysis

Data were subjected to ANOVA using GLM procedure of SAS (2013 version 9.4). Differences between treatment means were compared by Duncan’s multiple range test and significant differences were declared when P<0.05. The statistical model used for data analysis was:

yij = µ + ti + eij;

where yij is the dependent variable; µ is the overall mean; ti is the effect of treatment; eij represents random error that assumed normally and independently distributed. For the analysis of carcass parameters slaughter weight was added as a covariate in the model. Correlation analysis was used to test relationships between protein concentration in the diets and in vivo nutritive value parameters.

Results and discussion

Chemical composition of feedstuffs

Although A. gummifera leaves contained high amount of CT (84 g CT/kg DM), its CP content was higher than for the control diet (hay). The CP content calculated for A. gummifera is much higher than the minimum CP level (70 g CP/kg DM = 45.5 g DCP/kg) required for optimum rumen function (Norton 2003) and for adequate intake of forages.  Voluntary feed intake rapidly falls if CP content of forage is below 62 g/kg DM (Nasrullah et al 2003).

Tree forages with a low NDF content (200–350 g/kg) are usually of high digestibility (Norton 1994). High ADL content can limit the voluntary feed intake, digestibility and nutrient utilization of ruminant animals (Khanal and Subba 2001). Moreover, lignin as a percentage of lingo-celulose is highly correlated with the digestibility of cell wall fraction (Van Soest et al 1991).

The highest CT levels observed in A. gummifera (84 g/kg DM, quebracho tannin equivalent) are consistent with the results pointed out by Yisehak et al (2012). It has been reported that CT values above 50 g/kg DM can become a serious anti-nutritional factor in plant materials fed to ruminants and are even toxic (Leng 1997). Higher tannin levels become highly detrimental as they reduce digestibility of fiber in the rumen by inhibiting the activity of bacteria (Chesson et al 1982) and anaerobic fungi (Akin and Rigsby 1985). High levels also lead to reduced intake (Yisehak et al 2014).

Feed intake, feed conversion efficiency, protein efficiency ratio and growth performance of sheep

Lambs fed AG-PEG (hay + A. gummifera + PEG) showed an increase of 168% of DMI compared to hay.  Lambs fed the hay diet had a low intake for most of the diet components compared to AG and AG-PEG. The highest and lowest ADG of lambs were recorded for AG-PEG (34.9 g/day) and hay (3.00g/day), respectively. In addition, the FCE in lambs fed AG and AG-PEG increased from 362% and 710% over hay, respectively (P<0.001).

A. gummifera supplementation significantly improved DM intake of basal feed by 144 %. The treatment with PEG had a remarkable improvement in DMI over hay by 168%. This figure is relatively greater than DMI recorded for Arsi sheep, in central Ethiopia, fed tanniferous fodder tree leaves of Acacia angustissima (125% improvement over hay based feed) (Asfaw et al 2006) and Santa Ines sheep supplemented with different levels of Leucaena leucocephala (Longo et al 2008). Abou El Nasr et al (1996) reported lower DMI by sheep supplemented with tanniferous fodder (Acacia saligina), which were not supplemented with PEG. The second reason might be due to better digestibility of A. gummifera leaves and also Bonga sheep breed is better adapted to A. gummifera diet. The low DMI in lambs received AG without PEG as compared to AG-PEG might have been principally associated with the inhibitory effects of the higher amount of CT on feed digestion with palatability having a minor influence on DM utilization.

The lower DMI of lambs received grass based hay diet alone (hay) compared other treatment groups could be due to rumen fill that limited feed intake,  preventing maximum intake of the hay. The CP content of the hay is not adequate enough to boost microbial growth in the rumen. The increased total DMI with A. gummifera leaf supplementation could be attributed to a higher intake of CP that led to better efficiency in the utilization of the fiber in the total diet. Moreover, increased availability of nutrients due to the supplementation of A. gummifera with PEG might have promoted the observed higher total DMI intake in the supplemented sheep.

Supplementation of A. gummifera leaves at the levels of 30%  didn’t cause toxicity problems during the feeding trial period.

Better growth performances of sheep fed A. gummifera after drenching with PEG to sheep could be because PEG has the ability to bind tannins and to displace protein from pre-formed tannin-protein complexes. As shown by Makkar (2003), PEG can mitigate the adverse effects of CTs on voluntary feed intake and growth rate.

Apparent digestibility coefficients

Apparent digestibility coefficients of DM, OM, CP, EE and NDF were higher for AG-PEG compared to AG and hay (Table 3). Supplementation of PEG increased apparent digestibility of all the feed nutrients determined for AG-PEG (P<0.01). Inclusion of A. gummifera increased DMDC over hay by 117%; on other hand PEG inclusion in to AG further increased DMDC by 112%. Similar trend was observed for digestibility coefficients of other nutrients.

The low digestibility of the hay compared to other treatments may be explained in part by the high fiber content and low protein in the hay diet. The results of the present study are in accordance with the reports of Yisehak et al (2014b) that in zebu cattle PEG positively reduced the anti-nutritional effects of CTs. In the study of Weigand et al (1995), high levels of CTs depressed the digestibility of NDF. The results of the present study are also in agreement with reports that indicated depression in fiber and N digestibility due to CTs (Reed et al 1990; Salawu et al 1999) when tanniferous tree foliages were used as feed supplement. Low digestibility coefficients observed in AG in this study are also in agreement with the findings of Solomon (2004) in sheep.

Carcass weight and dressing percentage

The highest carcass weight and dressing percentage were found for the AG-PEG diet with lowest values for hay.

Conclusion

• Feed intake, growth rates and carcass weights were higher, and feed conversion efficiency was improved , in lambs fed a basal diet of hay supplemented with AG and PEG, compared with those fed hay alone or hay supplemented with AG.
  
  
• Apparent digestibility coeficients of  DM, CP, EE, NDF and ADF were higher for AG-PEG and AG diets compared with hay alone.

Conflict of interest

None of the authors has a financial or personal relationship with other people or organization that could inappropriately influence or bias the content of the paper

Acknowledgement

The authors would like to thank the VLIR-UOS Institutional University Cooperation project (IUC-JU) for the financial support.

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Received 10 September 2014; Accepted 30 October 2014; Published 1 December 2014

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