Milk composition and health status from mammary gland quarters adjacent to glands affected with naturally occurring clinical mastitis before and after treatment

Abstract

The objective of our first study (article 1) was to compare milk composition [fat, total protein (TP), lactose, solids non-fat (SNF), chloride] and health status [somatic cell count (SCC), differential leukocytes count and lactate dehydrogenase] of milk samples from unaffected mammary glands of an udder with a single clinically inflamed quarter to results of milk samples from healthy mammary glands of healthy cows. The study was designed as a prospective case control study with case and control cows matched by parity and days in milk (DIM). Cases were defined as cows (n = 59) experiencing clinical mastitis in a single mammary gland and controls (n = 59) were defined as cows that had not experienced clinical mastitis. Quarter milk samples were collected from all mammary glands adjacent to clinically affected quarters of cases and from the same mammary glands of controls. A total of 170 quarters were enrolled per group. Milk obtained from adjacent quarters of cases contained lesser concentration of TP, lactose and SNF, but had greater concentration of fat and chloride. The SCC, total leukocyte count and absolute numbers of neutrophils, lymphocytes, and macrophages were all increased in milk obtained from adjacent quarters of case cows as compared to milk obtained from quarters of control cows. The objective of our second study (article 2) was to describe cow and quarter variables and possible associations with milk composition and health status of quarters adjacent to a naturally occurring clinical mastitis gland (n = 170) before mastitis treatment. Cow (parity category, milk yield, DIM, severity of clinical mastitis of case quarter) and quarter (intramammary infection of adjacent quarters; previous cases of clinical mastitis on adjacent quarters) explanatory variables were associated or tended toward an association with several milk composition and udder health status traits. Microbiological analyses of adjacent quarters milk samples had an association with the majority of udder health status outcomes analyzed; however, no associations were found between microbiological analyses and milk composition traits. The objectives of our third study (article 3) was to compare milk composition (fat, TP, lactose, SNF, chloride) and health status (SCC, differential leukocytes) of healthy mammary glands (n = 147) adjacent to a gland previously treated for clinical mastitis with milk samples of healthy mammary glands of healthy cows (n = 147). Cases (n = 50) were defined as cows that previously had a single quarter infected with clinical mastitis treated according to an on-farm protocol and controls (n = 50) were defined as cows that had not suffered clinical mastitis. Cows group were matched by DIM and parity and quarters between cows groups were matched by position. On average 24 days after beginning treatment of the case quarter, milk composition (fat, lactose, SNF, and chloride) and some health status (lymphocyte and macrophage count) of adjacent quarters returned to similar levels as milk from control quarters, while TP, SCC, and neutrophils remained greater.