Our objective was to evaluate changes in the composition and quality of mare’s milk throughout lactation. Milk samples were obtained from fifteen mares immediately after foaling, and then once weekly from the first week of lactation up until the second through eighth week depending on the foaling date of each mare. Samples averaging 3 mL for colostrum samples, 3 mL for weekly sampling thereafter, and 2 oz. for DHI milk composition analysis, were collected after each teat was disinfected with a cotton ball that was moistened with 70% ethanol. Each 3 mL sample was examined for microbial growth via the application of approximately 0.1 mL milk sample on ¼ of a blood agar culture plate which was then incubated for 24 to 48 hours before being analyzed. Each 2 oz. sample was analyzed for fat, protein, lactose, milk urea nitrogen, and somatic cell count. The concentrations of fat, protein, and somatic cell counts decreased as a whole throughout lactation, while lactose and milk urea nitrogen concentrations increased.

The averages for fat, protein, lactose, milk urea nitrogen, and somatic cell count were 1.73%, 2.08%, 6.62%, 25.77mg/dl, and 79,000 cells/ml (39,000 cells/ml without 1 outlier sample), respectively for the collection period. No bacterial infections were found on the culture plates. A California Mastitis Test (CMT) was also conducted, of which no inflammatory results were found. All mares maintained good condition throughout lactation, and foals grew well. Overall, composition was similar to other studies with horses showing excellent mammary health and milk quality.