Sources of intramammary infections from Staphylococcus aureus in dairy heifers at first parturition.

The study objective was to identify probable sources and modes of transmission of 91 Staphylococcus aureus isolates obtained from the colostrum of 76 heifers at parturition. Sources cultured were milk (including colostrum), heifer body sites (teats, muzzle, rectum, vagina, and lacteal secretions), and environmental sites (bedding, insects, housing, water, feedstuffs, humans, nonbovine animals, air, and equipment). Staphylococcus aureus isolates were characterized by 63 phenotypic traits. A similarity coefficient was calculated by herd to identify the S. aureus that most closely resembled the S. aureus obtained from heifer colostrum. Staphylococcus aureus from a heifer's colostrum was compared with all preexisting S. aureus isolates from that heifer's herd. Isolates that were > or = 90% similar were considered to be identical. Because 30 (of the 91) S. aureus isolates from heifer colostrum were collected prior to environmental sampling, only 61 S. aureus isolates from heifer colostrum were available for comparison among all three sources. Possible sources of S. aureus from heifer colostrum at parturition were milk (70%, 43 of 61 isolates), heifer body sites (39%, 24 of 61), environmental sites (28%, 17 of 61), or no identified source (16%, 10 of 61). Three heifers with intramammary infection (IMI) from S. aureus at parturition had the same S. aureus on their teats prior to parturition. Milk was the only source identified for 41% (25 of 61) of isolates from heifer colostrum. Isolates from heifer body sites were the only source identified for 5% (3 of 61) of heifer colostrum isolates. Staphylococcus aureus from the environment was never the sole possible source for S. aureus from heifer colostrum. Data suggest that the major sources of S. aureus IMI in heifers at parturition are milk and heifer body sites. Contact among heifers may be an important mode of transmission of S. aureus leading to IMI in heifers at parturition.

The visual appearance and somatic cell count of mammary secretions collected from primigravid heifers during gestation and early postpartum.

Mammary secretions, obtained before and after calving, were examined for visual appearance, SCC, and bacteriology as part of a larger study determining the prevalence of IMI in 1588 primigravid heifers. Appearance of secretions was categorized into five groups: thin and watery, honey-like, serumy, milky, or thickened colostrum. Precalving secretions were further characterized as low viscosity (thin and watery, serumy, or milky) or high viscosity (honey-like and thickened colostrum). Postcalving secretions were further characterized as normal (milky, thickened colostrum) or abnormal (thin and watery, serumy, or honey-like). Infected precalving quarters (81%) had low viscosity secretions. Quarters that were uninfected precalving (75%) had high viscosity secretions. Greater than 90% of all postcalving milk samples appeared to be normal, regardless of geographic location, season, or bacterial infection status. Only 77% of the samples from quarters infected with contagious and noncontagious mastitis pathogens had normal appearance. Precalving SCC from bacteriologically negative quarters were lower than SCC from infected quarters. Similarly, postcalving SCC were lower from the bacteriologically negative quarters than from the infected quarters. Infected quarters had higher mean SCC than the uninfected quarters during both pre- and postcalving periods.