Abstract:
BACKGROUND: Heifers can calve down with intramammary infections (IMI) and udder damage. This will have a
negative impact on their longevity, future milk yield and financial return. Co-housed pre-weaned calves that are fed
fresh milk have the opportunity to suckle each other’s teats and may infect udders of fellow heifer calves with
pathogens present in milk. The prevalence of IMI in pregnant heifers in South Africa (SA) which were co-housed
and reared on fresh milk as calves, is not known. Quarter secretion samples from both pregnant heifers (n = 2065)
and dry cows (n = 5365) were collected for microbiological analysis from eight SA dairy herds. All heifers tested in
this study were co-housed pre-weaning and were fed fresh milk as calves.
RESULTS: The prevalence of coagulase negative staphylococci, Staphylococcus aureus, Streptococcus agalactiae,
environmental streptococci, coliforms and samples with no bacterial growth in heifers was 26%, 0.9%, 0.08%, 1.4%,
0.4% and 66%, respectively. The overall prevalence ratio between heifers and cows for Staphylococcus aureus IMI
was 0.76 (95% CI: 0.59, 0.98). Four of the individual herds had prevalence ratios of less than one (p < 0.05), one herd
had a prevalence ratio of 3.15 (95% CI: 1.52, 6.32), and the remaining 3 herds had a prevalence ratio not
significantly different from 1.0. Marginally significant differences were found between Staphylococcus aureus IMI in
pregnant heifers compared to cows in their second and later lactations (p = 0.06, p = 0.05, respectively) but no
significant differences between heifers and cows in their first lactation.
CONCLUSIONS: The presence of Streptococcus agalactiae IMI in heifers came as a surprise, especially as herd infection
rates were low. The high prevalence ratio of Staphylococcus aureus between heifers and cows in one herd warrants
further investigation due to the potential danger of udder damage in a young cow at the start of her productive
life. The IMI in heifers with host adapted pathogens can also act as a source of new IMI for lactating dairy cows.
Description:
IMP drafted the manuscript and critically revised it, formatted and edited the
manuscript and was involved in the data analysis. JK was involved in
reviewing the technical aspects of the manuscript as well as assisting in data
analysis, literature review and drafting of the manuscript. JCW and RB were
involved in the sample analysis as well as data input. ML re-evaluated the
data, provided statistical analysis and contributed to the writing of sections
in the text pertaining to statistical analysis. All authors read and approve the
final manuscript.
