Effects of medicated urea-molasses block supplementation on productivity and gastrointestinal nematode infestation of sheep in central Kenya

R M Waruiru, W K Munyua, S K Mavuti¹, R O Otieno, M N Mutune and V M Maina

Department of Veterinary Pathology, Microbiology and Parasitology, Faculty of Veterinary Medicine, University of Nairobi, P O Box 29053-00625, Kangemi Nairobi, Kenya
rmwaruiru@yahoo.co.uk
¹ Directorate of Veterinary Services, Ministry of Agriculture, Livestock and Fisheries, Kenya

Abstract

A 14 months study was undertaken to determine the effects of feeding medicated urea-molasses blocks on production parameters and gastrointestinal (GI) nematode parasitism of sheep under field conditions in central Kenya. Forty five Corriedale crossbred female lambs with an average age of 6 months were initially treated subcutaneously with ivermectin (0.2 mg/kg body weight) and randomly assigned into 3 groups: group I were fed fenbendazole incorporated urea-molasses blocks (MUMB), group II urea-molasses blocks (UMB) and group III (control) received no block supplementation (NBS). Parameters measured included fecal egg counts (FEC), worm burdens (WB), live-weight (LW) and greasy wool production.

Significant differences (p < 0.05) were found in LW changes of the MUMB group compared with the NBS (from September) and the UMB (from October) groups, respectively. The mean LW responses of the UMB group were significantly (p < 0.05) greater than those of the NBS group. On study termination, the MUMB group had gained an average of (+ s.d.) 21.9 + 2.4 kg, the UMB group 17.3 + 2.7 while, NBS group gained 10.9 + 2.6 kg. Greasy wool production was significantly higher (p < 0.05) in the supplemented groups and the rank order of production/animal was 3.6 kg (MUMB), 3.3 kg (UMB) and 2.1 kg (NBS). The estimated monetary gain/animal based on meat and wool production were equivalent to US$ 47.51, US$ 37.26 and US$ 27.59 for the MUMB, UMB and NBS groups, respectively. The FEC for the MUMB group differed significantly (p < 0.05) compared to those of the UMB and NBS groups. However, no significant differences (p > 0.05) in FEC were found between the UMB and NBS groups. On necropsy, the mean (+ s.d.) group WB for MUMB was 425 + 76, for UMB 1279 + 240 while that of NBS was 1619 + 402. Haemonchus contortus was the predominant nematode recovered from slaughtered sheep on study termination. These results indicate that the MUMB was effective in reducing and maintaining a low level of GI nematode infestation with subsequent improved performance of grazing young sheep.

Keywords: FEC, fenbendazole, grazing, Haemonchus, pasture, UMB

Introduction

Gastrointestinal (GI) helminth parasites are a major constraint to the production of small ruminants in the tropical and subtropical regions of the world and causes substantial economic losses to small-scale farmers (Perry et al 2002). In Kenya, Haemonchus contortus infestation of sheep is one of the most important causes of economic loss to producers of wool and mutton, both in high and low rainfall agro-climatic zones (Gatongi1996; Perry et al 2002). Control of the parasite is becoming increasingly difficult, due to the presence of widespread resistance to the available anthelmintic groups (Gakuya et al 2007; Geurden et al 2014; Martínez-Valladares et al 2015) and increasing concern about chemical residues in livestock products and the general environment (Mckeller 1997; Cooper et al 2012; Beyene 2016). These limitations have resulted in the search for alternative control strategies (Torres-Acosta and Hoste 2008;Vatta et al 2009; Bowie 2014).

Supplementation with high quality protein has been shown to enhance the ability of sheep to resist infestation with GI nematode parasites (Van Houtert and Sykes 1996). Economic restrictions imposed by the high cost of protein feeds for livestock limit the application of this knowledge in smallholder sheep rearing systems. Research has indicated that provision of non-protein nitrogen (NPN) to stimulate feed intake and increase rumen outflow of microbial protein, can also enhance the ability of infested hosts to overcome the detrimental effects of nematode parasitism (Leng et al 1991). In situations where low quality forages are the predominant ruminant feed resource, urea-molasses blocks (UMB) can provide a ready means of delivering NPN, energy and minerals to promote efficient rumen function (Knox 1996; Abid et al 2016). Positive effects of multinutrient blocks on the performance of grazing ruminants have been reported in sub-Saharan Africa (Waruiru et al 2004; Boukila et al 2006; Geleta et al 2013).

Benzimidazole (BZ) anthelmintics were selected as they are readily available in Kenya and because it has been shown that adminstration of BZ anthelmintics over a number of days is a more effective method of removing nematode parasites than a single dose, as regards both potency and spectrum of activity (Prichard et al1978). Similarly, administration to sheep and goats of low and sustained levels of fenbendazole (FBZ) incorporated into UMB is also effective therapeutically and prophylactically (Knox 1996; Abid et al 2016). The purpose of this study was to evaluate a FBZ molasses supplement block treatment on GI nematodes and productivity of naturally infested grazing sheep in Kenya.

Materials and Methods

Study area

The study was conducted at a farm in Kinangop sub-county in Nyandarua County, Kenya. The area lies at an altitude of 2100 m above sea level and receives a mean annual rainfall of between 1400 and 2500 mm. The rainfall is bimodal in distribution with the long rains falling between March and May, and the short rains from October to December. Temperatures range between 12.3 °C during the cold months (June and July) and 25°C during the hot months of January and February (Anonymous 2005). Daily records of rainfall for the study period were obtained from Kiracha Forest Station in Lari sub-county, Kiambu County and about 2 km from the study farm (Fig. 1).

Most of the residents are small holder mixed farmers and the livestock enterprise is mainly for milk production and sheep rearing. The farms have permanent, non-irrigated pastures comprising mainly Kikuyu grass (Pennisetum clandestinum) that were grazed each year by cattle, donkeys and sheep. Problems related to gastrointestinal parasites have been reported and anthlmintics are used regularly (Munyua et al 1997).

Study design

The study was undertaken from July 2006 to August 2007. Forty five Corriedale crossbred female weaner lambs were randomly selected for the study. They were ear-tagged and treated subcutaneously to remove residual nematode infestation with ivermectin (IVM) (Ivomec®, MSD Agvet, 0.2 mg/kg body weight and one week after this, the animals were shorn and weighed. At the start of the study, the average age and fleece-free live weight (LW) were 6 months and 18.0 kg, respectively. The sheep were divided according to LW into 3 groups of 15 animals each. Group I (MUMB group) were fed urea-molasses supplement blocks having FBZ at a rate of 0.5 g/kg in conjuction with unmedicated urea molasses blocks (1 week MUMB, 4 week UMB) daily (Manueli 1997) while, group II (UMB group) were fed UMB only. Both the UMB and MUMB were provided at approximately 30 g/head/day as recommended by FAO (2002). The animals had unrestricted access to the blocks while they were housed each night. Group III (control group) lambs received no block supplementation (NBS). All the lambs grazed together during the day but were housed separately at night for supplemental feeding.The feed blocks were provided by the Helminthology Section, National Veterinary Research Centre, Muguga and were prepared as outlined by Sansoucy (1986) and Waruiru (2004). Individual LWs in kgs were taken using a measuring table band and recorded for each animal before the study commenced and then at monthly intervals until study termination. Greasy fleece weights were obtained at shearing at the end of the experiment.

Parasitological methods

Rectal fecal samples were collected at the start of the study and at monthly intervals thereafter. A modified McMaster technique was used to determine the number of nematode worm eggs per gram (epg) of feces (Sloss et al 1994). Group bulked feces were cultured and infective nematode larvae (L3) recovered and identified to genus level (MAFF1986). Three sheep from each group were randomly selected at the end of the study and slaughtered for total and differential worm counts. The worms were recovered using standard techniques (MAFF 1986).

Economic analysis

The cost in US$ of the medicated and non-medicated UMB, anthelmintics and labor was determined. The value of the LW gain and wool production for each group was calculated by multiplying the mean LW gain and wool production for the group by the return/kg LW of mutton and greasy wool, respectively. Subtraction of the cost from the return gave the benefit (Waruiru et al 2002).

Data analysis

The serial data on LW, wool production, strongyle fecal egg count (transformed as log10 (x +10) were analyzed by repeated measures analysis of variance, using the general linear model procedure on the SAS package (SAS Institute Inc. 1996). Group differences in total WBs were analyzed by one-way analysis of variance but after a log10 (x + 1) transformation. P values less than 0.05 (p < 0.05) were considered significant.

Results

Fecal worm egg counts and worm burdens

Most of the fecal samples from the naturally infested sheep before treatment with IVM had low to moderate numbers (mean, 480 epg) of strongylid-type eggs. Small numbers of other worm eggs were seen during the study in the following order of magnitude: Nematodirus spp.> Trichuris spp.>Strongyloides spp. The monthly geometric mean fecal egg counts (FEC) for the 3 groups are given in Fig.1. The initial administration of IVM was effective in reducing the existing nematode infestations, as evidenced by the reduction in FEC to zero in August 2006. The mean FEC for the NBS group rose from 0 in August to reach a level of 271 epg in January 2007, with a 2^nd peak of 364 epg in June 2007. The 1^st peak occurred after the short rains while the 2^nd peak coincided with the unusually low rainfall in March to May. The UMB group showed the same trend although, after October, the mean FEC of this group was consistently lower than that of the NBS group. Over the study period, the mean FEC of the MUMB group were significantly lower (p < 0.05) than those of the other groups between which there were no significant differences (p < 0.05) (Fig. 1).

Figure 1. Geometric mean faecal worm egg counts for MUMB, UMB and NBS groups of sheep during July 2006 to August 2007 and total rainfall

The strongylid-type larvae from faecal cultures were predominantly those of Haemonchus spp. (mean 66%) and Trichostrongylus spp. (mean 21%), with small proportions of larvae of Bunostomum spp. and Oesophagostomum spp. (mean 3 % and 10, respectively). There was no significant difference in the geometric composition of the larvae from the three groups.

Worm burdens (WB) of the MUMB group were significantly (p < 0.05) lower than those of UMB and NBS groups. The mean WB for the MUMB group was 425 + 76 (range 75-1286), the UMB group 1279+ 240 (range 268-2877) while that of NBS was 1619 +402 (range 441-3527). Haemonchus contortus was the most prevalent GI nematode. Other nematodes recovered in a decreasing order were Trichostrongylus colubriformis, Oesophagostomum columbianum, Nematodirus filicollis, Bunostomum trigonocephalum and Trichuris ovis.

Animal productivity

Monthly liveweights of the three groups of sheep from July 2006 to August 2007 are as shown in Figure 2. The three groups had similar growth rates up to September 2006, thereafter MUMB and UMB groups gained significantly (p< 0.05) more weight than the NBS group. Live-weight differences between the MUMB and UMB group were statistically different (p < 0.05) from October 2006 to August 2007. On study termination, the MUMB group gained an average (+ s.d) of 21.9+ 2.8 kg; UMB, 17.3 + 1.9) while the NBS group gained an average of 10.9 + 1.3 (Table 1).

Figure 2. Mean live-weights of MUMB, UMB and NBS groups of sheep during July 2006 to August 2007

The rate of wool production was measured for the study sheep at the end of the experiment. The total amount of wool produced by the MUMB and UMB groups was significantly (p < 0.05) higher than that produced by the NBS group (Table 1).

A summary of the cost-benefit analysis of urea-molasses supplementation is presented in Table 2. The rank order of net benefit over the NBS group was US$ 19.92 and 9.67 for the MUMB and UMB groups, respectively.

Discussion

Strongylid faecal egg counts (FEC) showed a clear seasonal pattern and the overall trend was related to the weather conditions. This was reflected by the UMB and NBS groups where FEC reached their peaks immediately after the short and long rains (January and June 2007), respectively. The FEC for the NBS group were low to moderate (i.e., subclinical nematodosis) throughout the study period, and H.contortus was the predominant nematode species recovered on necropsy. These results are similar to observations reported in earlier studies on sheep in the central highlands of Kenya (Munyua et al 1997; Nginyi et al 2001).

The FECs and WBs for the MUMB group were significantly lower than those of the UMB and NBS groups. Although the FECs for the UMB group were consistently lower, they were not significantly different from that of the NBS group. This was in agreement with the general consensus from various studies (Van Houtert et al 1995, Waruiru et al 2002) that supplementation of the basal diet with additional protein does not appear to influence initial establishment of nematode infections, although the pathophysiological consequences are generally more severe in animals not supplemented (Coop and Kyriazakis, 1999). Also, there was no significant difference in the species composition of strongylid worms between the groups, indicating that supplementing the sheep with UMB at maintenance levels had no effect on the distribution of these parasites in the study animals. These observations concur with earlier findings in sheep (Van Houtert et al 1995, Waruiru et al 2002) and cattle (Magaya et al 2000).

The overall greater efficacy of the medicated blocks in reducing the numbers of adult worms is in agreement with the findings of other workers using BZ anthemintics (Tan 1996; Manueli 1997). Not all of the sheep with access to the MUMB ingested a sufficient quantity of the anthelmintic and the “shy” sheep could act as a source of contamination for pastures. A low level of contamination may have little effect on production and may in fact delay the development of anthelmintic resistance by providing a population of non-resistant strongylids (Tan 1996).

This study showed that urea-molasses supplementation improved productivity of subclinically infested sheep on pasture as these animals had significantly higher LW and produced significantly more wool than the NBS group at the end of the study. Molasses urea blocks were recommended as a supplement for fattening grazing sheep in Ethiopia by Geleta et al (2013).The MUMB group out-performed the UMB group with regard to LW gain as additional benefits were gained by reducing nematode numbers to very low levels through the inclusion of FBZ in the feed block. Abid et al (2016) reported that feeding of MUMB had significant effects in controlling of sub-clinical nematodosis in goats and also provided nutrients required (i.e., energy and protein) in order to perform normal metabolism process of the body. In the present study, the cost-benefit analysis showed that the highest net financial benefit was realized by the supplemented groups, with the MUMB group out-performing the UMB group.

Conclusions

• This study has shown that higher net financial benefits were realized by the supplemented groups
  
  
• MUMB group out-performed the UMB group

Recommendations

• Further research is required to determine if further reductions in MUMB use can occur without compromising productivity
  
  
• Alternatively, studies should be conducted to determine if animals could be supplemented using UMB with a possible selective application of anthelmintic treatments to targeted sub-populations within a flock as advocated by Hoste et al (2002)

Acknowledgements

The present investigation was made possible by financial support from the Livestock Helminth Research Project within the Danish International Development Agency (DANIDA) ENRECA program.

Competing interests

The authors have no competing interests

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Received 9 July 2017; Accepted 17 July 2017; Published 1 August 2017

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