Abstract
This study evaluated the naturally occurring microorganisms within the gastrointestinal tract (GIT) and yolk sacs of day-old commercial broiler chicks. Across 6 independent trials, day-old chicks ( n = 10 per trial) were obtained from various commercial hatcheries, humanely euthanized, and necropsied. The entire intestine (duodenum to colon) and the yolk sac were isolated, homogenized, serially diluted, and plated onto selective media to enumerate total aerobes, Clostridium spp., Clostridium perfringens , Staphylococcus aureus , Gram-negative bacteria, Escherichia coli , total coliforms, and yeast and molds. Intestinal microbial loads were consistently high, with counts for both total aerobes and Clostridium spp. (8.14 and 8.11 log 10 cfu/mL, respectively). High counts for intestinal S. aureus , Gram-negative bacteria, E. coli , and total coliforms were also observed (6.57, 7.44, 6.57, and 7.60 log 10 cfu/mL, respectively). Intestinal yeast and mold counts averaged 5.49 log 10 cfu/mL. Intestinal C. perfringens counts were uniformly low, averaging 2.06 log 10 cfu/mL across all trials. In comparison, yolk sac microbial counts were lower, averaging 3.70, 3.67, and 1.52 log 10 cfu/mL for total aerobes, Clostridium spp., and C. perfringens , respectively. These results demonstrate that commercial broiler chicks harbor dense aerobic and anaerobic intestinal populations immediately upon hatch, whereas the yolk sac maintains substantially lower microbial loads. The discrepancy suggests that colonization occurs via trans-shell migration of eggshell microorganisms during incubation. Conversely, the high intestinal microbial loads appear to be primarily driven by the ingestion of environmental microorganisms circulating within the commercial hatchery environment at the time of hatch.