title: Effect of somatic cell count and mastitis pathogens on milk composition in Gyr cows.
abstract: BACKGROUND
  Gyr cows are well adapted to tropical conditions, resistant to some tropical diseases and have satisfactory milk production. However, Gyr dairy herds have a high prevalence of subclinical mastitis, which negatively affects their milk yield and composition. The objectives of this study were (i) to evaluate the effects of seasonality, mammary quarter location (rear x front), mastitis-causing pathogen species, and somatic cell count (SCC) on milk composition in Gyr cows with mammary quarters as the experimental units and (ii) to evaluate the effects of seasonality and somatic cell count (SCC) on milk composition in Gyr cows with cows as the experimental units. A total of 221 lactating Gyr cows from three commercial dairy farms were selected for this study. Individual foremilk quarter samples and composite milk samples were collected once a month over one year from all lactating cows for analysis of SCC, milk composition, and bacteriological culture.
  
  
  RESULTS
  Subclinical mastitis reduced lactose, nonfat solids and total solids content, but no difference was found in the protein and fat content between infected and uninfected quarters. Seasonality influenced milk composition both in mammary quarters and composite milk samples. Nevertheless, there was no effect of mammary quarter position on milk composition. Mastitis-causing pathogens affected protein, lactose, nonfat solids, and total solids content, but not milk fat content. Somatic cell count levels affected milk composition in both mammary quarters and composite samples of milk.
  
  
  CONCLUSIONS
  Intramammary infections in Gyr cows alter milk composition; however, the degree of change depends on the mastitis-causing pathogen. Somatic cell count is negatively associated with reduced lactose and nonfat solids content in milk. Seasonality significantly affects milk composition, in which the concentration of lactose, fat, protein, nonfat solids and total solids differs between dry and wet seasons in Gyr cows.
authors.affiliation: Department of Nutrition and Animal Production, School of Veterinary Medicine and Animal Sciences, University of São Paulo, Pirassununga, Brazil.
authors.forename: Carolina Barbosa
authors.initials: CB
authors.lastname: Malek dos Reis
authors.forename: Juliana Regina
authors.initials: JR
authors.lastname: Barreiro
authors.forename: Lucinéia
authors.initials: L
authors.lastname: Mestieri
authors.forename: Marco Aurélio de Felício
authors.initials: MA
authors.lastname: Porcionato
authors.forename: Marcos Veiga
authors.initials: MV
authors.lastname: dos Santos
mesh_terms: D000818:Animals; D058345:Asymptomatic Infections; D001938:Brazil; D002417:Cattle; D002452:Cell Count / Q000662:veterinary; D003352:Corynebacterium; D003354:Corynebacterium Infections / Q000662:veterinary; D005223:Fats / Q000032:analysis; D005260:Female; D007774:Lactation / Q000378:metabolism; D007785:Lactose / Q000032:analysis; D008321:Mammary Glands, Animal / Q000378:metabolism / Q000382:microbiology; D008414:Mastitis, Bovine / Q000378:metabolism / Q000382:microbiology*; D008892:Milk / Q000737:chemistry / Q000166:cytology*; D008894:Milk Proteins / Q000032:analysis; D012621:Seasons; D013203:Staphylococcal Infections / Q000662:veterinary; D013290:Streptococcal Infections / Q000662:veterinary
chemical_list: D005223:Fats; D008894:Milk Proteins; D007785:Lactose