An evaluation of intramammary infection status in dairy heifers
Contrary to expectation, intramammary infections (IMI) caused by bacterial organisms are prevalent in prepartum dairy heifers. Though awareness of the problem has increased, there are still many questions surrounding the etiology and epidemiology of heifer IMI. It is not known when heifers become susceptible to IMI or when the greatest risk of IMI occurs during the heifer life cycle, which, are critical questions for the development of prevention and treatment protocols. Answers to these questions require the development of reliable, targeted, mammary gland sampling methods. The most common approach previously used to evaluate IMI status in dairy heifers is through collection of mammary secretion samples through the teat end. However, secretion samples from nonlactating heifers can be difficult to collect, and contamination by microbes inhabiting the teat end or teat canal are a concern. Therefore, the aims of this thesis were to evaluate culture results of heifer mammary samples collected at different ages and stages of gestation and to compare bacterial species found in mammary samples collected through the teat end to those collected using methods that bypassed the teat end.
Mammary gland sampling techniques were evaluated on primigravid and nulligravid dairy heifers at the University of Missouri Foremost Dairy Research Center, aged 6 months to 24 months. From each quarter sampled, a teat canal swab sample, secretion sample collected through the teat end, secretion sample collected by cisternal puncture, and a fine needle aspirate (FNA) of the mammary tissue were collected. Additionally, a skin swab of the mammary gland puncture site was collected. Heifers were grouped by age or stage of gestation for analysis.
Consistent with previous studies, the IMI occurrence was significantly greater among primigravid heifers compared with nulligravid heifers. Generally, the odds of a quarter being IMI positive increased as gestation progressed, with the highest odds seen amongst mid-gestation heifers. Interestingly, while there was no difference in IMI occurrence between younger (6 – 10 months of age) and more mature (11 – 16 months of age) nulligravid heifers, heifers as young as 6 months were found to be IMI positive based on FNA mammary tissue sampling methods.
Overall, our findings identified that there was an increase in the occurrence of IMI due to streptococci beginning mid-late gestation, while staphylococci were the most common genus of bacteria identified among IMI positive quarters among all groups. Furthermore, comparison of culture results from teat canal swabs and secretion samples collected through the teat end, within each sampled quarter, indicated that teat canal or teat end microbes are a potential source of contamination for mammary secretions collected through the teat orifice. Conversely, no similarity was observed between skin swab and cisternal puncture or mammary tissue FNA results.
In the heifers where secretion was not able to be collected, the FNA method was relied on to make diagnoses in this study. While the FNA sampling method has not been validated, known IMI-causing organisms, such as Staphylococcus aureus, non-aureus staphylococci and mammaliicocci, and streptococci, were isolated using this method, indicating it may be a useful technique for future research in heifers. Overall, this study advances understanding of IMI timing in heifers and supports the use of alternative mammary sampling methods that bypass the teat canal to improve accuracy and detection of IMI in future research on heifer udder health.
Alyssa Novo studied Dairy Science at Virginia Tech Polytechnic Institute and State University in Blacksburg, Virginia. She then began graduate studies at the University of Missouri-Columbia, where she recently obtained her Master’s in Biomedical Sciences. Alyssa is currently working towards earning her PhD from the same university.
