Animal Health 3

摘要

Gastrointestinal disease can arise at any time during a dairy cow’s lactationcycle, yet periods of high feed intake and production or greatermetabolic demand can increase susceptibility to opportunistic infection.Clostridium, E. coli, Salmonella, and mycotoxin-producing fungi arecommonly found in the GI tract, however fluctuation in abundance ofthese microorganisms or their virulence genes at different stages oflactation remains unclear. The objective of this study was to quantifycommon microbial marker and virulence genes in rectal swabs fromdairy cows during 3 stages of lactation. Rectal swabs were obtained from370 dairy cows at 26 commercial farms across major US dairy-producingregions, and classified into 3 groups by days post-parturition at timeof sampling: fresh (d1–21, n = 95), early lactation (d22–100, n = 146)and late lactation (>101d, n = 129). Genomic DNA was extracted fromrectal swabs and genus- or species-specific marker or virulence genesfrom E. coli, Salmonella, Clostridium, and Aspergillus were quantifiedusing a panel of qPCR assays. Data were log-transformed and theKruskal-Wallis test, followed by Mann-Whitney pairwise comparisonswere performed to detect differences in gene quantity between lactationstage groups. Cows in fresh and early lactation periods harbored higherquantities (H = 7.51, P = 0.02) of EAST1, a heat-stable enterotoxin genein enteroaggregative E. coli, compared with cows in late lactation (2.06and 2.13 vs. 1.82 log_(10) gene copies respectively). Similarly, quantitiesof Aspergillus 18S rRNA gene (H = 12.93, P < 0.01) and C. difficiletoxin A gene tcdA (H = 7.52, P = 0.02) were elevated in fresh and earlylactation groups. Fresh cows swabs also contained highest (H = 6.91,P = 0.03) quantities of the C. perfringens α toxin gene cpa comparedwith cows in early and late periods (0.76 vs. 0.35 and 0.41 log_(10) copiesrespectively). These results indicate that harborage of several opportunisticmicroorganisms and their virulence genes may be greater duringthe fresh and early lactation periods, providing insight into the increasedvulnerability of cows during these stages.