ABSTRACT

Mastitis in cows was investigated by surveying a number of herds located within and around Maiduguri, Nigeria. Five thousand cows (in lactation and dry) were examined. The prevalence of mastitis was assessed by the results of physical examinations of the mammary gland by palpation, and by evaluation of milk secretion. Bacteriological examination also was carried out on all milk samples collected from affected cows, as well as some selected control cows. One hundred and four (2.1%) of the 5,000 cows examined showed evidence of clinical mastitis. There was no significant difference in the number of quarters affected in relation to their anatomical positions (fore- and hindquarters). The survey revealed that the majority of cases occurred in cows between 4 and 7 years of age and that the incidence declined as the animals became older. One hundred and fifty-four apparently normal cow udders (53%) contained bacterial pathogens. On a cultural examination of 104 milk samples from affected cows, the recovery rate was 77%. Staphylococcus aureus (34.6%) occurred most frequently in the mastitic milk, followed by coagulase negative staphylococci (15.4%). Other bacteria isolated from mastitic cows milk were Streptococcus sp. (9.6%); Escherichia coli (6.7%); Actinomyces pyogenes (5.8%); Bacillus spp. (2.9%) and Salmonella sp. (1.9%). The prevalence of bovine mastitis in this area was sufficiently high as to cause substantial economic loss to farmers. It is therefore imperative that measures aimed at prevention and control of the disease (mastitis) be instituted in all the herds.

Key words: bovine mastitis, disease prevalence, etiology, Nigeria

Introduction

Nigeria has abundant livestock resources, the majority of animals being concentrated in the northern parts of the country (AJAYI et al., 1987), although there are numbers of cattle elsewhere in Nigeria (NAWATHE, 1992). Borno State, located in the extreme north of the Sahel region, accounts for about one quarter of the total ruminant population (NGERE et al., 1984).

Milk comprises 16% of the total value of all food products produced from livestock in sub-Saharan Africa (ANON., 1986). Milk and milk products constitute a complete food, as they contain proteins, fats, lactose, minerals and vitamins, together with natural enzymes derived from milk micro-organisms. (LEWIS, 1986).

Despite the important role of milk in the national economy, local production is unable to sustain the increasing demand for milk and milk products, initially at cheaper rates (AJAYI et al., 1987). This situation has worsened over recent years due to foreign exchange constraints and the fall in the value of the local currency, the naira. Currently, high prices are being demanded for milk and milk products, with the result that such items are denied to average Nigerians.

Mastitis is the most widespread infectious disease in cattle and, from an economic aspect, the most damaging (DODD, 1985). Certain udder characteristics, breeds, teat injuries, poor hygiene, poor management, faulty milking machines, accumulation of milk and the presence of bacteria in or around the udder, are all factors which predispose cows to mastitis (SCHALM et al., 1971; ADDO et al., 1980; AMEH et al., 1993; EGWU et al., 1994).

Mastitis is an inflammatory disease affecting the mammary gland, characterised by an increased somatic cell count (SCC) in milk and/or by pathological changes in mammary tissue (ANON, 1971). Mastitis is usually caused by pathogenic bacteria and other microbes entering the gland through the teat duct (SCHALM et al., 1971).

The prevalence of this disease in Nigeria has not been studied in any depth, although there is extensive literature on mastitis from countries with farming practices similar to those followed in Nigeria (KALRA and DHANDA, 1964; HAMIR et al., 1978; FALADE et al., 1989). There is therefore a pressing need to assess its clinical prevalence and causal agents (bacteria) involved in bovine mastitis in Nigeria.

Materials and methods

The present study was carried out on selected herds located in a 25-km radius of Maiduguri during the period 1994-1997. This area has numerous smallholdings (farms) and a small number of larger herds. The standard of milking hygiene is very poor and preventive measures, such as the use of udder disinfectants, post-milking teat dipping and dry cow therapy, are infrequent in these herds.

During this period, 5,000 cows were examined clinically for the presence of mastitis. Mastitis was diagnosed when there were visible or palpable signs of udder inflammation, change in milk secretions, or through bacteriological examination of milk. During the study, 104 cases of clinical mastitis were encountered and studied in detail, the following being recorded for each cow: age, clinical state (acute, subacute, chronic and gangrenous) (Table 1), and which were classified as follows:

Acute mastitis: Severe inflammation of the mammary gland without any marked systemic reaction.

Subacute mastitis: Inflammation of the mammary gland with abnormalities in milk.

Chronic mastitis: Inflammation of the mammary gland, with little change in milk, often characterised by induration of glandular tissue. The gland may either be enlarged or reduced in size.

Gangrenous mastitis: Characterised by swollen mammary gland, cold to the touch and bluish-black in colour. The affected skin area peels off, with oozing of serous fluid. Milk is usually bloody and watery.

Milk collection and analysis

Milk samples were collected from 104 cows from the 202 quarters clinically affected, and 154 samples from apparently normal udders. Samples were obtained using sterilised sample bottles, with the usual aseptic precautions being taken. They were placed immediately on ice (Coleman Flask) and brought to the Veterinary Microbiology Laboratory, University of Maiduguri.

Prior to quarter sampling, initial streams of milk were discarded. A hundred and four milk samples were collected and examined bacteriologically from mastitic quarters, and 154 milk samples from apparently normal cows and quarters were similarly examined (control).

Random number sampling was used in selecting the 154 apparently normal cows on the farms visited.

A wire loop was used for milk inoculation onto 5% sheep blood and MacConkey agars. Plates were incubated aerobically at 37 ^oC for 24-72 h. Plates were examined for bacterial growth on a daily basis. Organisms were examined for morphological, staining and cultural characteristics, and for biochemical reactions according to standard keys (COWAN and STEEL, 1974; KING, 1983). Staphylococci were studied in particular for haemolysis and coagulase production (tube method using oxalated rabbit plasma in a 1:10 dilution in a nutrient broth incubated at 37 °C and inspected at 30 min intervals for 5-6 h for clot formation). A positive coagulase test was judged as any degree of clotting from a loose clot suspended in plasma to a solid clot (LENNETTE et al., 1974).

Statistical analysis

The chi-squared (c2) test was used to compare certain values in the test. P<0.05 was considered statistically significant.

Results

Prevalence of clinical mastitis

One hundred and four cows from a total of 5,000 (2.1%) displayed evidence of clinical mastitis, involving 202 quarters. Data were examined relevant to the position of affected quarters. There was no significant difference in the number of quarters affected in relation to their anatomical positions. The number of quarters affected were: left fore, 49; right fore, 45; left hind, 51; right hind, 57.

The age of affected cows ranged from 4 to 13 years. Results are shown in Table 1. These figures show that the majority of clinical cases occurred in cows between 4 and 7 years of age. With regard to the clinical state of the mammary gland, the greatest number were acute cases (25%), followed by sub-acute cases (21%), chronic (19%), and gangrenous mastitis (3%) (Table 1). There was no statistical difference in age distribution with respect to the form of clinical mastitis (P>0.05).

Table 1. Cows from Maiduguri, Nigeria, with mastitis, grouped according to the clinical state of the mammary gland in various age groups

Bacteriological examination of milk

On cultural examination of 104 milk samples collected from clinically affected cows, recovery rate was 77% (80/104) (Table 2). In the examination of 154 samples from apparently normal cow udders, bacteria were detected in 81 (53%) samples; 73 (47%) samples had no bacterial growth. Staphylococcus aureus (34.6%) occurred more frequently in mastitic milk, (P<0.001) than in non-mastitic milk. This was followed by coagulase negative staphylococci (15.4%). Other bacteria isolated from mastitic milk were Streptococcus spp. (9.6%); Escherichia coli (6.7%); Actinomyces pyogenes (5.8%); Bacillus spp. (2.9%) and Salmonella spp. (1.9%). Of the bacteria isolated from apparently normal milk, Staphylococcus aureus predominated (16%), followed by coagulase negative Staphylococci (13%), E. coli (6%). Bacillus spp. (2%) occurred less frequently (Table 2).

Table 2. Frequency of various types of bacteria isolated from mastitic and apparently normal milk of Nigerian cows

*P<0.001

Discussion

In this survey, the prevalence of bovine mastitis was evaluated by clinical and bacteriological methods in order to define the nature of this economically important disease. The prevalence of clinical bovine mastitis was found to be 2.1% in the Maiduguri area. This figure is within the range reported elsewhere (BRAMLEY, 1984; WILESMITH et al., 1986) who reported a prevalence of 4.35% and 3.4% respectively. Similarly, (HAMIR et al., 1978) observed 2.5%, 3.0% and 3.0% prevalence in three consecutive studies (1971, 1972 and 1973) in Kenya.

There was greater single quarter involvement, with hindquarters being more commonly affected. The number of cases found in fore- and hindquarters showed no statistical difference. Various authors in India (SHARMA and RAI, 1977) and in Kenya (HAMIR et al., 1978) observed no significant difference in the number of fore- and hindquarter cases. However, KALRA and DHANDA (1964) found in their survey that hindquarters were more frequently affected with mastitis, and that this difference was statistically significant.

The higher prevalence of clinical mastitis with increasing age has been reported (KALRA, 1967; SHARMA and RAI, 1977; HAMIR et al., 1978). It was observed (KING, 1981) that the increase in clinical mastitis with advancing age is entirely due to there being more infections among older cows. In our present survey, clinical mastitis increased up to the age of seven years of age, but decreased after that point. There was no statistical difference in age distribution with regard to the form of clinical mastitis.

Results of the survey revealed 19% chronic cases. The reason for this may be due to the fact that veterinarians are seldom requested to diagnose and treat the acute state of the disease (CHINEME and ADDO, 1984). The same authors further observed that, typically, veterinarians are called upon to diagnose and recommend treatment for the condition when it has progressed to the chronic state.

A predominance of Staphylococcus aureus mastitis in cows has been reported (KALRA and DHANDA, 1964; WATTS, 1988; FALADE et al., 1989; CARLOS, 1990). In this study, it was found that S. aureus and coagulase negative Staphylococci were the most frequently isolated bacteria from mastitic cows. It has been reported by (LAFI et al., 1994) that coagulase negative staphylococci and S. aureus occurred predominantly in both clinical and sub-clinical bovine mastitis.

Escherichia coli is an environmental pathogen, and E. coli mastitis is a major disease in cows. Previous studies in Nigeria have shown that E. coli is an important aetiological agent of clinical mastitis (AMEH et al., 1993; EGWU et al., 1994). In this study, E. coli was found in 6.7% of cases.

The isolation of mastitis pathogens from apparently normal quarter milk in the present study was in agreement with previous observations, that is to say, mastitis-causing bacterial pathogens can be isolated from clinically normal ruminant mammary glands (WALTER, 1967; ADDO et al., 1980; AMEH et al., 1993; EGWU et al., 1994).

The higher prevalence of intra-mammary staphylococcal (S. aureus) infection indicates the potential of a food hazard problem. CARLOS (1990) drew attention to the great public health significance of this organism in milk.

In conclusion, this study showed that bovine mastitis definitely poses a serious problem in the Maiduguri area of Nigeria, and that the disease is caused by a variety of bacterial organisms. We therefore recommend that measures for the use of udder disinfectants, post-milking teat disinfection, and prompt treatment of clinical cases designed to prevent and control the disease (mastitis) be instituted in all the herds.

Acknowledgements
This investigation was supported by Senate Research Grant (R/ACA. 93/C/9/Vol. xvi), provided by the University of Maiduguri. Gratitude is also expressed for the advice and encouragement we received from colleagues during this investigation. Special thanks are extended to Mr. Samson Onyikokwu for his technical assistance, and to Mrs. C. Ebenezer for her Secretarial services.

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Received: 26 October 1998
Accepted: 30 March 1999

AMEH, J. A., T. EDGBE-NWIYI, L. T. ZARIA: Ucestalost govedeg mastitisa u pokrajini Maiduguri Borno u Nigeriji. Vet. arhiv 69, 87-95, 1999.