SOURCES OF INTRAMAMMARY INFECTIONS FROM STAPHYLOCOCCUS-AUREUS IN DAIRY HEIFERS AT FIRST PARTURITION

The study objective was to identify probable sources and modes of tran smission of 91 Staphylococcus aureus isolates obtained from the colost rum of 76 heifers at parturition. Sources cultured were milk (includin g colostrum), heifer body sites (teats, muzzle, rectum, vagina, and la cteal secretions), and environmental sites (bedding, insects, housing, water, feedstuffs, humans, nonbovine animals, air, and equipment). St aphylococcus aureus isolates were characterized by 63 phenotypic trait s. 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 compare d with all preexisting S. aureus isolates from that heifer's herd. Iso lates that were greater than or equal to 90% similar were considered t o be identical. Because 30 (of the 91) S. aureus isolates from heifer colostrum were collected prior to environmental sampling, only 61 S. a ureus isolates from heifer colostrum were available for comparison amo ng all three sources. Possible sources of S. aureus from heifer colost rum at parturition were milk (70%, 43 of 61 isolates), heifer body sit es (39%, 24 of 61), environmental sites (28%, 17 of 61), or no identif ied source (16%, 10 of 61). Three heifers with intramammary infection (IMI) from S. aureus at parturition had the same S. aureus on their te ats prior to parturition. Milk was the only source identified for 41% (25 of 61) of isolates from heifer colostrum. Isolates from heifer bod y sites were the only source identified for 5% (3 of 61) of heifer col ostrum isolates. Staphylococcus aureus from the environment was never the sole possible source for S. aureus from heifer colostrum. Data sug gest that the major sources of S. aureus IMI in heifers at parturition are milk and heifer body sites. Contact among heifers may be an impor tant mode of transmission of S. aureus leading to IMI in heifers at pa rturition.