Occurrence and factors associated with udder infections in small holder lactating dairy goats in Arumeru district, Tanzania

E S Swai, E Mbise and P F Mtui 

Veterinary Investigation Centre, PO Box 1068, Arusha, Tanzania
ESSwai@gmail.com     /     pfmtui@yahoo.com

Abstract 

A study was conducted to determine the prevalence of sub clinical mastitis, identify and quantify udder and teat lesion/deformities in smallholder dairy goat farms in Arumeru district, Tanzania during the period of October-December 2007. A total of 99 smallholder farms comprising 149 pure and crossbred lactating does were included. 

Of the 298 udder halves and 297 teats investigated, proportion found to have physical lesion or defects were 14.8% for teats and 13.4% for udder halves, respectively. The common observed teat lesions were black spot, vesicles and presence of multiple or extra teats whereas presence of hard or firm udder halves, unsymmetrical attachment was more evident for the individual halves screened. The prevalence of sub-clinical mastitis based on California Mastitis Test (CMT) at flock, doe and udder half level was 51.5 %( 95%Confidence interval [CI], 41.2-61.6), 38.92% (95%CI, 31.05-47.2), and 28.9 %( 95%CI, 23.8-34.47), respectively. None had signs suggestive of clinical mastitis at a time of visit although 12% and 7% of the screened does and surveyed farms had evidence of clinical mastitis 2 to 3 years prior to the current study.  

The results of multivariate logistic regression analysis identified administrative location of goats and housing system as the major risk factors. Prevalence of mastitis varied significantly between the administrative study divisions. It was higher in Poli (74.6%) and Kingori (22%) and lower in Moshono (3.4%) division. The results also indicated that there was a statistically significant decrease in prevalence to sub clinical mastitis in lactating goats kept on raised slatted than earth floor houses (OR = 0.68 , P = 0.05 for raised slatted floor houses).  

The results of this study showed that sub clinical mastitis is an endemic and widely distributed production condition and may contributed to sub-optimal milk production and culling of goats in Arumeru district. 

Key words: CMT, lactating does, risk factors, sub-clinical mastitis, Tanzania, udder and teat lesion

Introduction

In Tanzania, small ruminants (sheep and goats) production is popular and they play vital role in rural economies through provision of meat, milk, insurance, household income, hides, skin and manure(Mtenga et al 1986). Goats can also be used for research purposes. Other advantages include their low cost, low risk of total loss and high reproductive rates (Ngategize 1989; Peacock 2005). Current estimates of small scale dairy goats in Tanzania suggests that there are about 29,000 households holding 126,000 dairy goats of different breeds and stages of maturity (Kilongozi et al 2006). This figure is low (less than 1.1%) compared with the local goat population of over eleven million given by Ministry of livestock Development (MoLD) (MAFS 2002). Distribution of these goats is concentrated in the medium to high potential (highlands) areas of the country. 

Milk production from these improved/graded stocks, is characterised by low input low output system and does not satisfy the individual household and even the country’s milk requirement due to a multitude of factors(Mtenga et al 1986; Das and Sendalo 1991; Mtenga and Kifaro 1993; Kiango 1996; Kilongozi et al 2006). Physical deformities(natural or acquired) of the udder/or teats and the disease of the mammary gland known as mastitis are among the various factors contributing to premature culling and reduced milk production(Maina et al 1993; Blackburn 2003) 

Studies on udder health so far conducted in Tanzania (Moshi 1998; Mbilu 2007) have largely focused on Institutional/Research farms that comprise only a small proportion of the country dairy goat population. Systematically studies targeting disease prevalence and the associated economic loss are inadequate. Information on the udder health and mastitis is sparse and little is known about the disease in the rural small holder setting. Henceforth, information relating to the magnitude of the problem and the associated influencing factors in small holder settings that is increasingly being dependent on for rural household livelihood is scanty. Such information is important to envisage and design appropriate strategies that would help reduce the prevalence and effects of the disease in the small scale sector. This study was thus designed to elucidate the prevalence and factors associated with udder health in pure and graded goats of small holder farms in Arumeru district, northern Tanzania. 
 

Materials and methods 

Study area 

This study was carried out from October 2007 to December 2007 in Arumeru district. Arumeru district is one of the 6 districts which form Arusha Region in northern Tanzania. The district is located between Latitude 3.5⁰ to 3.7⁰ S and Longitude 26.5⁰ to 37.5⁰E. The district experiences both sub-humid and semi-arid climate with elevation ranging from 1200-1900 metres above sea level and average annual rainfall ranging from 700 to 2000 millimetres. Rainfall is distributed into two distinct seasons, the wet season, which extended from March to June and the dry season that runs through the remaining part of the year. The mean annual minimum and maximum temperatures are 15^oC and 30^oC, respectively. Agriculture, dominated by crop-livestock production system, is the main stay of the population in the district. Administratively, the district is divided into 6 divisions, composed of three major ethnic groups which are the more sedentary Wameru and Waarusha and the pastoralist Maasai. 

Study animals and husbandry system 

Study animal included149 lactating pure and cross-bred goats belonging to Saanen, Toggenburg and local breed managed under traditional husbandry practices. Animals are allowed to graze on local natural pasture close to homestead and occasionally, grasses cut from crop fields, tree shrubs are provided. Crop residues also serve as additional sources of feed during post harvest and long dry season.  Goats were kept on raised stall with slatted and on earth floor houses. Farmer acquisition of dairy goat was through cash purchase from neighbours or through subsidized price or loan from Non-governmental Organisation (NGO’s~mainly Heifer Project International, Farm Africa etc) 

Pre weaning kids management system 

During pre weaning stage, kids were allowed to stay with their dams during the day and separated at night. During this period, farmers milked their goats once a day in the morning, to allow more milk for the kids. Kids were weaned at 18 weeks of age and at post weaning periods, milking was twice a day (morning and evening). 

Study design/selection of villages and households 

A two stage sampling technique was adopted in selecting the goats for the study. Simple random sampling at each stage was employed with primary sampling units being villages and secondary units being households (flocks) within villages. The list of total villages in each district was obtained from District Livestock Office. All household owning milking goats (improved/graded, pure) within each village was considered as sampling frame and each household (farm) as primary sampling units.  

As the prevalence of sub clinical mastitis was not known a priori, a 50% prevalence was assumed when calculating the total number of farms required for the study with a 5% allowable error. The formula (n = π (1-π) /e²) which was used to estimate the sample size was obtained from Kirkland (1988). At the end, a total of 100 farms were selected. (Where π = desired/assumed prevalence, and e = allowable error). 

Data collection 

Semi-structured questionnaire (SSQ) comprising farm, goat bio-data, udder and teat lesions/defects were developed during the period of October 2007. Administration of the SSQ on each selected farm and on farm inspection were used to collect flock management and mammary gland data of each goat.  Data collected were flock size, age classified as kids (<6 months); weaners: (>6 to 18 months) and adult: (>18 months). Lactating does were further categorized as  young adults(>18 to 36 month), adults(>3 to 6 yrs) and old(>6 yrs), stage of lactation categorised as early(1-4 months),mid(>4 to 8 months) and late(>8 months), parity categorised as few(<3), moderate(4-6) and many(>6). Body condition of goats was assessed visually through procedures developed by McNulty et al (1997) and rated as poor, moderate and good. Other information collected includes breed codes, housing and history of udder infection. The housing condition was categorized as small pen with raised slatted floor (RSF) and non slatted earth floor (SEF). Frequency of manure removal was rated as once per day (High), once every three days (Moderate) and once every week (Low). 

Clinical examination of the udder 

Clinical examination of the lactating doe consisted of detailed visual inspection and systemic palpation of udder and teats. Teat ends were observed for alterations such as wounds, scars, markers, vesicles, warts, patent orifice and ease of milking. Inspection of the udder included visual examination posteriorly to ascertain size and disproportional symmetry. Right and left halves were expressed relative to the examiner position. All individual udder halves were observed for abnormal consistency like firmness, presence of super-numerary or multiple teats, fibrosis, oedema, warmth and other physical defects. 

Detection and evaluation udder infection 

All selected goats (n = 149) were clinically examined for evidence of clinical mastitis as manifested by visible changes in milk and the udder. The examination was complemented by testing milk from lactating halves (n= 298) for sub clinical mastitis using California Mastitis Test (Bovi vet CMT test, Denmark) as a side pen (or quick field) test. Briefly, milk samples were collected from each udder half after discarding the initial fore milk streams, following teat disinfections. Examination was carried out by mixing equal amount of milk and CMT reagent (Kruuse Denmark) into the two cups of the CMT paddle. The paddle was gently rotated to mix the contents. Results were read immediately as per manufacturer’s recommendation and were scored as 0 (negative or trace), 1+ (weak positive), 2+ (distinct positive), 3+ (strong positive) depending on the amount and thickness of gel formed as described by Schalm et al (1971) and Ikram (1997) (Table 1). 

Udder infection was concluded based on clinical examination, nature and appearance of milk with secretion and CMT (Radostits et al 2000). Accordingly, milk with pus, flakes, clots, blood tinged, watery secretion yet no visible and palpable changes in udder halves and acute mastitis with signs of systematic involvement was diagnosed as clinical mastitis.  

Data relating to previous history of udder exposure to infection were obtained from clinical records of the farms and interviews with the owners of the goats. Sub-clinical mastitis was diagnosed based on CMT results (Radostits et al 2000; Harmon 1994). An udder half was defined as CMT positive, if it had a score of >1+ and a doe was defined as CMT positive when it had at least one of the udder half with a CMT score of >1+.

Statistical analysis 

The unit of analysis for CMT response (sub clinical mastitis) was flock, doe and individual goat udder half. Analysis of risk factor was based on a dichotomous outcome (flock, doe, udder half was positive or negative) based on CMT results. Data were analysed using both Epi-Info (Version 6.04b, CDC, Atlanta, USA 1996) and Egret for windows version 2.0 (Cytel Inc, Seattle, USA 1999).  Relationships between explanatory variables and outcome variables were investigated by logistic regression (Egret for windows 1999) with ‘flock’ as a random effect because animals on one flock may not be statistically independent of one another (Kristula et al 1992). Statistical significance between variables was examined using P-value at critical probability of P<0.05. 
 

Results

Flock characteristics 

All selected farms except one were visited; farmer interviewed and lactating does screened. One farmer declined to participate. A voluntary participating rate of 99% was thus achieved. A total of 149 lactating goats of varying age, parity, lactation stage kept on 99 farms were therefore examined. The mean (mean ± SD) number of lactating goats per farm was 1.49 ± 0.87 and ranged from 1 to 5. The overall average flock size per household was 4.32 ± 2.78 and ranges from 1 to 17. Details of the flock structure by age category are given in Table 2.

There were relatively more kids and adults in Kingori than the Poli and Moshono division. Irrespective of the division, females constituted about 65% to 75% of the flock and the average sexually mature and therefore potential breeding male to breeding female was 0.5: 1, 0.23: 1 and 0.27: 1 for Poli, Kingori and Moshono division, respectively.

Previous evidence of clinical mastitis 

Over all, 12% of the examined goats and 7% of the flocks/farms visited were reported to have had at least one case of clinical mastitis within a period of 2 to 3 years prior to the current study. 

Prevalence of udder and teat physical deformities /lesion 

The common identified individual teat and udder (half) lesions or defects are graphically shown in Figures 1 and 2.

Of the overall (298) udder halves and (297) teats examined, 40(13.4%) and 44(14.8%) respectively, were affected by lesion. 258(86.6%) halves and 253(85.2%) teats respectively, were normal. Black spot, extra/multiple or super-numerary teats and vesicles were the common teat lesions/defects identified, with left teats (LT) recording a higher frequency than right based teats (RT). Evidence of blind and multiple orifices teat was recorded in one doe. All the cases in doe were unilateral. Of all the udder halves investigated, oedema, evidence of being firm or hard upon touch and with unsymmetrical rear attachment was singled out as the commonest sign observed. However, there was no difference in distribution between udder halves (P > 0.05).

Prevalence of sub clinical mastitis 

Of the 149 lactating goats examined, 38.92 %( 58) had sub clinical mastitis and none had clinical mastitis at a time of visit. Prevalence rate was significantly higher in the right (32.2%) than left halves (25.5%) (p< 0.05). The overall flock, doe and udder half level prevalence were 51.5 %(95%Confidence interval [CI], 41.2 - 61.6), 38.92 %( 95%CI, 31.05 - 47.2), and 28.9 %(95%CI, 23.8 - 34.47), respectively. The prevalence rate was found to vary from 0% to 100% between flocks/farms and from 3.4 to 74.6% between the administrative divisions. The prevalence rates were higher in Poli (74.6%), Kingori (22%) and lowest in Moshono (3.4%) (P< 0.05).

Factors influencing sub clinical mastitis 

The prevalence and proportions of lactating goats in each category of each variable investigated during the study are shown in Table 3.  

Multivariate analysis of risk factors showed that the administrative location of goat and housing was the major risk factor for the occurrence of sub clinical mastitis in lactating goats (p< 0.05). Goat kept in Kingori division and on raised slatted floor houses had significantly lower odds for sub clinical mastitis compared to the ones kept on earth floor houses and residing in Moshono and Poli division, respectively. 
 

Discussion 

This study showed the overall prevalence of mastitis in pure and cross bred does in Arumeru to be 38.9%, which is in agreement with reports on caprine mastitis recorded in developed countries (Schaeren and Maurer 2006; Moroni et al 2005; Manser 1986). On the other hand the reported prevalence of 34% in Morocco (el Idrissi et al 1994) was lower than the present findings, and the reports of sub-clinical mastitis in institutional and smallholder farms in Morogoro, Tanzania and other developing countries were higher than the present findings (Moshi 1998; Mbilu 2007; Kalogridou-Vassiliadou et al 1992). The variability in the prevalence of caprine mastitis between reports could be attributed to difference in management of the farms, milking management practices, breed considered or technical know of the investigators. 

The relative high prevalence of mastitis in right halves (32.2%) than left halves (25.5%) in this study agrees with the findings of other studies carried out in lactating does (Kyozaire et al 2005; Min et al 2007). This may be due to either greater production capacity of right halves or ease of first grasping by milkers hand during milking. On the contrary, there was bilateral enlargement of the mammary gland amongst investigated does. Sometimes both halves were unequally enlarged. This agrees with the finding of other workers (Anyam and Adekeye 1995). 

Kid-rearing system (bucket feeding or residual kid suckling) which is considered to be a potential risk factor for udder infection was not adequately addressed in this study (Mavrogianni et al 2007). Partly this was because of the nature of the study, the cross-sectional study, which was aiming to look at an event at one point in time. However, some studies have shown and reported restricted suckling to have a positive mastitis and other non-mastitis bacterial infection reduction (Meador and Deyoe 1991). This practice is good in that poor and irregular milking by the milker can be corrected by the kids. On the contrary, kids may be as well an efficient transmitter of udder infections between does. 

The recorded lower odds for sub clinical mastitis in lactating goats maintained in raised slatted floor houses where there is little contact with manure and wet bedding substantiated the importance of sanitation and epidemiology of mastitis. Heavy faecal contamination and gradual deposition of wet, dirt coupled with low faecal evacuation frequency may enhance the build up of mastitis pathogen infection and transmission. In agreement with our observation, bedding materials were reported to have crucial role in the microbial contamination of the environment and transmission to infection from animals to animals (Radostits et al 2000). Contrary to previous studies (Dulin et al 1983; Fast et al 1987; el Idrissi et al 1994; Leitner et al 2004), parity, stage of lactation, breed and large flock sizes were not significantly associated with mastitis prevalence in this study. 

Interpretation of CMT result should be taken with caution. CMT as a quick, field diagnostic test is based on the reaction between the CMT reagent and DNA in the somatic cells (Ikram 1997). Mammary gland irritation (irrespective of causes) will inevitably lead to the higher level of neutrophils and hence higher somatic cells (Smith and Roguinsky 1977). Some studies have shown that elevated somatic cells may be due to increased days in milking and reduced milk production (Wilson et al 1995; Fast et al 1987). Therefore CMT may be referred to as an indicator test rather than definitive test for mastitis. Positive CMT samples should be subjected for thorough microbiological screening in order to establish the associated aetiological agents. 

Although udder and teat lesions do occur in all flocks and may arise from a variety of causes, they are important in dairy goats because they are painful and make milking difficult and predispose the animal to mastitis. Super-numerary teats or multiple teats, black spot and vesicles were the most prevalent teat lesions. These lesions are quite common in goats and in case of super-numerary; incidences may be as high as 30 %( Oppong and Gumedze 1982). Detected teat vesicles, which may due to teat injuries/deformities in this study suggests prevailing inadvertence to udder management and health. These may ultimately cause udder damage and exposure to serious secondary bacterial infection (Radostitis et al 2000). Detected super-numerary teats in this study were always cranial to the main teats and distribution between udder halves was not significant. Presence of super-numerary teats is hereditary often attributed to inbreeding (Blackburn 2003). They cause little harm but often interfere with milking and contributed to the culling of does (Blackburn 2003). Under ideal situation, a good udder should be proportionately medium to large in size with no tendency to be pendulous (Blackburn 2003). Texture should be free of lumps and scar tissue, fairly firm and smooth. Rear attachment should be symmetrical, high, with halves evenly balanced. Front attachment should be well forward without pocket, blending smoothly to the body. Teats should be two of uniform size and length, symmetrically placed on the udder and free of deformities. 
 

Conclusion and recommendations

• The udder infection rates as determined by CMT in dairy goats were very high an indicative of a health and production problem condition in the smallholder dairy goat farming.

  
  

• Consistent with other factors recorded to be associated with mastitis, udder and teat lesions were identified and quantified. Whether these have more significant effect on the udder health and culling rates of the does remains to be investigated.

  
  

• Sub clinical mastitis, as detected by CMT in this study need careful interpretation due to the higher rate of epithelial cell sloughing and the presence of cytoplasmic mass in goat milk. However, there is a need to prevent mastitis through regular screening for early detection, the establishment of good husbandry practices, sanitation, sound milking procedures including post-milking-teat dipping and treatment during non-lactating period, prompt treatment of teat/udder injuries and culling older with repeated attacks does.

Acknowledgements 

The authors are very grateful to the farmers, field staff who gave their time to this research. In addition, thanks are due to the staff of VIC for their cooperation in the study. We also thank the Director, Directorate of Veterinary Services, for permission to publish this work.
 

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Received 21 February 2008; Accepted 17 June 2008; Published 5 December 2008

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