Microbiological quality of goat milk obtained under different production systems

Abstract

Reliability of quality of milk produced by smallholder farmers was assessed by means of a comparative analysis of the microbiological quality and somatic cell counts (SCC) of the raw milk obtained from dairy goats. Information regarding dairy goat farming and goat milk production in and around Pretoria was initially determined by means of a questionnaire. With this information, dairy goat herds were selected for the study, based on the fact that these farms produced milk for both domestic and commercial consumption. The study was conducted on three commercial dairy goat farms each under a different production system, the extensive, semi-intensive and intensive production systems. The method of milking varied with the type of production system; hand milking, bucket system and pipeline milking respectively. Udder health under the respective production systems was assessed by means of bacterial analysis of udder half milk samples. Bacteriology of bulk milk samples was also determined in order to assess the level of hygiene in the milking environment. In addition, water samples from the different farms were analysed for their microbial quality. Results of these parameters were compared between the different production systems using the analysis of variance. Capability of safe raw milk production by smallholder dairy goat farmers was then evaluated from the results obtained. Reliability of the SCC as a reflection of goat udder health was also evaluated. Further assessment was carried out to determine the relationship between udder conformation and presence of intra-mammary infection and SCC of the raw milk. Bacteria potentially capable of producing either food poisoning or enhanced spoilage of raw milk were cultured from the goat milk samples. These included pathogens such as Staphylococcus aureus, Bacillus cereus and Enterococcus faecalis, found associated with use of milking machines as was the case in the intensive and semi-intensive production systems compared to the extensive production system. The prevalence of intramammary infection was 33.3%. Coagulase negative staphylococci were the most common cause of intramammary infection with a prevalence of 86.6% of the infected udder halves. They includedStaphylococcus epidermidis, Staphylococcus simulans and Staphylococcus intermedius. The remaining 13.4% of the infection was due to Staphylococcus aureus. Somatic Cell Counts were not a reflection of udder health status, hence, not reliable in the prediction of goat udder health (p = 0.2 Fisher’s exact test of association). No significant relationship was proved to exist between the udder conformation and presence of intra-mammary infection or SCC of the milk produced. Raw milk obtained by the bucket system milking machine had the lowest total bacterial count (TBC) (16 450 Colony Forming Units per millilitre [CFU/ml]) as compared to that by pipeline milking machine (36 300 CFU/ml) or hand milking (48 000 CFU/ml). In comparison to the other two production systems, it was shown that dairy goat farming under the extensive production system, where hand milking was practised, was adequate for production of safe raw goat milk. Coliforms were found to be the most predominantly isolated organisms from the raw milk obtained under the extensive production system. However, these can be eliminated by pasteurisation of the milk. The extensive production system, therefore, could be a means to promote dairy farming in developing communities through smallholder farmers. This could be facilitated by extension services aimed at monitoring management on the farms. This would, consequently, help alleviate the problem of food security and low income in these communities.