Evaluation of intramammary infection status in dairy heifers using cisternal and teat end sampling techniques

Intramammary infections occur commonly in dairy heifers; however, there is a lack of understanding regarding the onset and occurrence of IMI in nulliparous heifers during varying stages of development. The objectives of this study were to (1) determine at what age or stage of gestation heifer mammary samples are culture positive, (2) compare the bacterial genera and species found among sample types, (3) assess the potential of using a needle-based mammary gland sampling technique in heifers, and (4) use novel, multimethod diagnostic criteria to more comprehensively define heifer IMI (hIMI) occurrence. An observational cross-sectional study was conducted in which 304 quarters from 152 Holstein dairy heifers between the ages of 6 to 24 mo were sampled. A more rigorous definition of IMI in nulliparous heifers, hIMI, was used to quantify hIMI occurrence. This definition is comprehensive, primarily defined by the culture results of conventionally collected mammary secretions and aspirated mammary secretions or mammary tissue aspirates. Teat canal swabs and mammary skin swabs served as secondary sample types to minimize the influence of skin and teat canal flora on the results of primary sample types. Overall, 304 teat canal swabs, 93 conventionally collected mammary secretions, 304 mammary skin swabs, 43 aspirated mammary secretions, and 257 mammary tissue aspirate samples were collected, of which 24.7% (75), 39.8% (37), 34.5% (105), 48.9% (23), and 10.1% (26) were culture positive, respectively. The most common bacteria identified among all sample types, except mammary skin swabs, were staphylococci, primarily non-aureus staphylococcal and mammaliiococcal species, from both primigravid and nulligravid heifers. The overall hIMI occurrence was 28.5% (43/151) of heifers and 18.1% (54/298) of quarters. The highest proportion of quarter-level infections was seen in the mid-gestation group (42.5%, 17/40), followed by the late gestation group (35.7%, 10/28) and the early gestation group (23.1%, 12/52). The mature (11-16 mo) nulligravid heifers and young (6-10 mo) nulligravid heifers had similar quarter-level hIMI occurrence of 7.8% (7/90) and 9.1% (8/88), respectively. Overall, this study furthers the understanding of when hIMI occur, the bacterial genera and species involved, and provides results based on specific sampling methods that may prove useful for future studies evaluating hIMI status.