Impact of culture positive samples on goat milk composition

Document Type


Publication Date



2019 American Dairy Science Association Annual Meeting: Cincinnati, Ohio


American Dairy Science Association


Journal of Dairy Science










milk, composition, goat


The dairy goat industry is growing worldwide to meet the increased demand for milk and artisanal cheeses. Challenges to produce milk with quality exist due to the impact of microorganism causing intramammary infection (IMI). Milk culture stills a good alternative to monitor mammary gland health status. However, caution should be taken when interpreting the results in goats and its implications on milk characteristics. Thus, the aim of this study was to better understand the impact of an IMI on goat milk quality and composition. A total of 98 milk samples from 49 goats were used. Two simultaneous sterile samples of milk (15 mL) were collected from each half to perform microbiological culture and milk composition. Culture was performed streaking 10 µL of milk onto 5% sheep blood agar, incubated at 37°C for 24/48h and species identification made through MALDI-TOF. Milk composition (protein, fat, lactose, casein, and SCC) for each udder half was performed by a service provider (Eurofins DQCI– MN) using FTIR method. Statistical analysis (considering each half as statistical unit) for milk components were performed by t-test for unequal sample size to compare the means of positive and negative samples. The SCC was transformed to linear score. Milk culture revealed 73 negative samples and 25 positive samples as follow: S. simulans (11), S. aureus (4), S. chromogenes (3), Bacillus spp. (3), S. epidermidis (2), S. caprae (1), and S. warneri (1). For milk composition, culture negative samples contained 0.2% more (P < 0.05) casein, but 0.5% less (P < 0.003) fat and less (P < 0.001) SCC (637 × 103 cells/mL) when compared with culture positive samples. No differences were observed for lactose or protein. Higher levels of fat in subclinical mastitis milk can be explained by a greater permeability of mammary gland tissue to lipids present in blood during inflammatory response or also a concentration effect. Notably, goats with subclinical mastitis can have important decrease in milk quality leading to significant losses in milk yield which has a direct impact on dairy products.