Milk composition and health status of quarters adjacent to an on-farm protocol-treated clinical-mastitis gland
Authors: Paixão Marcel Gomes , Costa Renata Golin Bueno , de Souza Guilherme Nunes , Pinto Sandra Maria , de Abreu Luiz Ronaldo 
Published: February 2024

Context The hypothesis of interdependency among cows’ mammary glands has been shown, and quarters adjacent to glands with clinical mastitis may have their composition and health status impaired. Aims The main focus of this study was to compare foremilk composition (fat, total protein, lactose, solids non-fat (SNF), and chloride) and health status (somatic cell count (SCC), differential leukocytes) of healthy mammary glands adjacent to a gland previously treated (on average, 24 days after treatment, varying from 20 to 39 days) for clinical mastitis with foremilk samples of healthy mammary glands of healthy cows. Our previous study compared these traits (foremilk composition and health status) between healthy mammary glands adjacent to a mastitis-infected quarter and healthy mammary glands from healthy cows (no clinical mastitis) immediately after the identification of mastitis on case quarters. Methods The study was designed as a prospective case–control study and the enrolled cows (cases and controls) were matched by days in milk and parity. Case cows (n = 50) were defined as cows that previously had a single quarter infected with mild or moderate clinical mastitis, and which were treated according to an on-farm protocol 1 day after mastitis identification. Control cows (n = 50) were defined as cows that had not suffered clinical mastitis in the current lactation. Foremilk samples from each quarter of case and control cows were collected so as to assess concentrations of fat, total protein, lactose, SCC, and SNF, conduct microbiological analyses, and determine the concentration of chloride and differential leukocyte counts. Multivariate linear regression and logistic regression analyses were performed to assess possible associations of milk-composition and health-status traits between quarter types (case or control cows). Key results On average, 24 days after the treatment of the case quarter began, milk composition (fat, lactose, SNF, and chloride) and some health status (lymphocyte and macrophage counts) of adjacent quarters returned to similar levels as in control quarters, while total protein, SCC, and neutrophils remained greater for adjacent quarters. No effect of quarter position or microbiological results of enrolled quarters were identified. Conclusions Our results suggested that at least 20 days (average of 24 days) after an episode of clinical mastitis in a neighbouring gland, adjacent quarters were still recovering from this mastitis episode, and we conclude that interdependency of quarters is a physiological systemic two-way immune response route, and each particular milk component has a different behaviour after clinical mastitis. Implications Our results suggest that clinical mastitis is far more costly for producers and industry than has been previously reported. Bovine mastitis is the disease that causes the most economical losses to dairy farmers, including veterinary expenses, milk disposal, loss of production and reduction of animal pregnancies. The milk composition of the mammary quarter affected by mastitis is not the only one compromised, because the milk quality of the entire udder is also affected. A period of 20 days is not enough for animals to fully recover from a case of udder inflammation. Mastitis is more costly to producers and industry than has been previously reported.