Recovery of bacteria from goats' milk following freezing and the prevalence of bacterial infection in milk from goats with an elevated somatic cell count

Abstract

Aims. To establish the prevalence of bacterial infection of goats with high somatic cell counts and to determine the effect of freezing milk samples on the probability of culturing the same pathogen again.

Methods. Milk samples were collected from both halves of 99 goats with a somatic cell count > 650,000 cells/ml. The milk samples were split into four aliquots with one of the aliquots being cultured immediately. The other three aliquots were frozen at —20 °C, and successive aliquots of 39 samples from which pathogens were isolated at Day 0 were thawed and cultured 28, 56 and 84 days later.

Results. Coagulase-negative staphylococci were the most common isolates. Freezing and thawing did not significantly reduce either the number of isolates cultured or the number of colony forming units from these successive aliquots. However, three of 39 selected pathogens were not cultured at one or more of the successive thawings. Goats from herds that were housed had a higher probability of having a pathogen isolated from milk than goats from herds kept on pasture.

Conclusions. Freezing of milk samples may be used for subsequent culture of bacteria from goats' milk.

Key words.:

• Goat
• mastitis
• freezing
• bacteriology
• milk