Variation in milk somatic cells of heifers at first calving.
To evaluate variation in milk somatic cells, 24 primiparous cows (paired by calving date) were sampled during the first 75 d of lactation. Milk somatic cell counts were lowest at 9 to 10 wk. For differential cell counts in milk, only percentage of macrophages changed significantly during first 75 d (33% at 1 wk, 25% at 6 wk, and 34% at 11 wk). Epithelial cells were identified and ranged from 11 to 20% of total. For milk somatic cell count, variation between cows within pairs sampled contemporaneously was small (3 to 24%). However, variation between cows was much greater for the differential cell counts (46% of total for lymphocytes and 34% for epithelial cells). Of 1021 quarter foremilk samples, 26 were positive for major pathogens, but 326 were positive for various species. Prevalence of bacteria was significantly higher during first 10 d after calving. Rear quarters had significantly higher bacterial presence: 47% for left rear versus 21% for left front and 37% for right rear versus 24% for right front. Total milk somatic cell count after first calving appears to depend primarily on differences in temporary factors and is not a stable characteristic of individual cows. Proportions of the different somatic cell types in milk may vary consistently by cow in early first lactation.
Miller
R H
RH
Milk Secretion and Mastitis Laboratory, Livestock and Poultry Sciences Institute, Beltsville, MD 20705.
Paape
M J
MJ
Fulton
L A
LA
D000704:Analysis of Variance; D000818:Animals; D001419:Bacteria / Q000254:growth & development; D002417:Cattle; D002452:Cell Count / Q000662:veterinary; D004847:Epithelial Cells; D005260:Female; D007774:Lactation / Q000502:physiology; D008264:Macrophages / Q000648:ultrastructure; D008321:Mammary Glands, Animal / Q000166:cytology; D008414:Mastitis, Bovine / Q000235:genetics / Q000276:immunology*; D008854:Microscopy, Electron; D008892:Milk / Q000166:cytology* / Q000382:microbiology; D013211:Staphylococcus aureus / Q000302:isolation & purification; D013291:Streptococcus / Q000302:isolation & purification