Influence of Weaning on Fecal Shedding of Pathogenic Bacteria in Dairy Calves

Influence of Technological Housing Conditions on the Concentration of Airborne Dust in Dairy Farms in the Summer: A Case Study

This research shows the size composition of airborne dust fractions in selected dairy barns down to the smallest particles, including factors that influence this composition. Measurements with a Dust-Track 8530 laser photometer took place in the summer at external temperatures of 29.5 to 36 °C. In barns with straw bedding, the average total dust concentration TDC was 66.98 ± 28.38 μg·m^-3 (PM₁₀ 60.11 ± 19.93 μg·m^-3, PM₄ 49.48 ± 13.76 μg·m^-3, PM_2.5 44.78 ± 10.18 μg·m^-3, and PM₁ 38.43 ± 9.29 μg·m^-3). In barns without straw bedding, the average TDC was 55.91 ± 36.6 μg·m^-3, PM₁₀ 33.71 ± 13.86 μg·m^-3, PM₄ 30.69 ± 15.29 μg·m^-3, PM_2.5 27.02 ± 13.38 μg·m^-3, and PM₁ 22.93 ± 10.48 μg·m^-3. The largest TDC of 108.09 ± 32.93 μg·m^-3 (PM₁₀ 69.80 ± 18.70 μg·m^-3, PM₄ 68.20 ± 18.41 μg·m^-3, PM_2.5 53.27 ± 14.73 μg·m^-3, and PM₁ 38.46 ± 5.55 μg·m^-3) was measured in an old cowshed with stanchion housing for 113 cows, straw bedding, and ventilation through windows. In a modern cowshed for loose housing of 440 lactating cows without straw bedding, with natural ventilation and 24 axial fans, TDC was 53.62 ± 49.52 μg·m^-3, PM₁₀ 20.91 ± 5.24 μg·m^-3, PM₄ 17.11 ± 3.23 μg·m^-3, PM_2.5 13.71 ± 0.92 μg·m^-3, and PM₁ 12.69 ± 2.82 μg·m^-3. In all investigated barns, a large proportion of airborne dust particles (54.38 ± 20.82% of TDC) consists of the smallest PM₁ dust particles (from 12.69 ± 2.82 μg·m^-3 to 48.48 ± 1.18 μg·m^-3).

Invited Review: Antimicrobial Use and Antimicrobial Resistance in Pathogens Associated with Diarrhea and Pneumonia in Dairy Calves

Antimicrobial use (AMU) is the major driver of antimicrobial resistance (AMR) among bacteria in dairy herds. There have been numerous studies on AMU and AMR in dairy cows; however, studies on AMU and AMR in dairy calves are limited. A comprehensive overview of the current state of knowledge of AMU and AMR among pathogens in dairy calves is important for the development of scientifically supported and applicable measures to curb antimicrobial use and the increasing risk of AMR. Therefore, we performed a systematic review of research on AMU and AMR in dairy calves. A total of 75 publications were included, of which 19 studies reported AMU data for dairy calves and 68 described AMR profiles of the four most prevalent bacteria that are associated with calf diarrhea and calf pneumonia. Large variation in AMU was found among herds across different regions. There seems to be a positive association between exposure to antimicrobials and occurrence of resistance. Most AMU was accounted for by treatment of diseases, while a small proportion of AMU was prophylactic. AMU was more common in treating calf diarrhea than in treating pneumonia, and the resistance rates in bacteria associated with diarrhea were higher than those in pathogens related to pneumonia. Organic farms used significantly fewer antimicrobials to treat calf disease; however, the antimicrobial resistance rates of bacteria associated with calf diarrhea and pneumonia on both types of farms were comparable. Feeding waste or pasteurized milk was associated with a higher risk of AMR in pathogens. Altogether, this review summarizes AMU and AMR data for dairy calves and suggests areas for future research, providing evidence for the design of antimicrobial use stewardship programs in dairy calf farming.

Antimicrobial Resistance in Fecal Escherichia coli and Salmonella enterica from Dairy Calves: A Systematic Review

The discovery of antibiotics brought with it many advances in the health and well-being of humans and animals; however, in recent years development of antimicrobial resistance (AMR) has increasingly become a concern. Much of the antibiotic use on dairy farms is for disease management in mature cattle, and AMR in fecal organisms is relatively rare in this group. However, young dairy calves often carry high levels of AMR in their fecal Escherichia coli and Salmonella enterica, which could provide a potential reservoir of AMR genes on dairy farms. To develop practical and effective antibiotic stewardship policies for dairy calf rearing, it is vital to have a solid understanding of the current state of knowledge regarding AMR in these animals. A systematic review process was used to summarize the current scientific literature regarding AMR in fecal S. enterica and E. coli and associations between management practices and AMR prevalence in dairy calves in the United States and Canada. Seven online databases were searched for literature published from 1997 to 2018. Multiple studies indicated an association between preweaned calves and increased risk of fecal shedding of resistant bacteria, compared to other animal groups on dairy farms. There also was evidence, although less consistent, of an impact of antibiotic treatment, antibiotic-containing milk replacer feeding, and feeding nonsalable or waste milk (WM) on the presence of AMR bacteria. Overall, the research summarized in this systematic review highlights the need for continued research on the impact of management practices, including antibiotic use, WM feeding, and disease prevention practices in reducing AMR in E. coli and S. enterica in dairy calves. In addition, few data were available on physiological and microbiological factors that may contribute to the high relative populations of resistant bacteria in young calves, suggesting another valuable area of future research.

Effects of antimicrobial use in agricultural animals on drug-resistant foodborne salmonellosis in humans: A systematic literature review

Controversy continues concerning antimicrobial use in food animals and its relationship to drug-resistant infections in humans. We systematically reviewed published literature for evidence of a relationship between antimicrobial use in agricultural animals and drug-resistant meat or dairy-borne non-typhoidal salmonellosis in humans. Based on publications from the United States (U.S.), Canada, and Denmark from January 2010 to July 2014, 858 articles received title and abstract review, 104 met study criteria for full article review with 68 retained for which data are presented. Antibiotic exposure in both cattle and humans found an increased likelihood of Salmonella colonization, whereas in chickens, animals not exposed to antibiotics (organic) were more likely to be Salmonella positive and those that had antibiotic exposure were more likely to harbor antimicrobial resistant Salmonella organisms. In swine literature, only tylosin exposure was examined and no correlation was found among exposure, Salmonella colonization, or antimicrobial resistance. No studies that identified farm antimicrobial use also traced antimicrobial-resistant Salmonella from farm to fork.

Evidence supporting vertical transmission of Salmonella in dairy cattle

We set out to investigate whether Salmonella enterica could be recovered from various tissues of viable neonatal calves immediately following parturition. Eleven samples were aseptically collected from each of 20 calves and consisted of both left and right subiliac and prescapular lymph nodes (LN), mesenteric LN, spleen and liver, as well as intestinal tissue (including luminal contents) from the small intestine, caecum, spiral colon and rectum. In addition, a faecal sample was collected from 19 of the dams. Salmonella was recovered from at least one sample from 10 of the 20 neonates. Across all calves, Salmonella was recovered from 12·7% of all samples and from LN in particular, Salmonella was recovered from 10·0%, 5·0%, and 5·0% of subiliac, prescapular, and mesenteric LN, respectively. Within calves, Salmonella was recovered from 0% to 73% of samples and across tissues, estimates of Salmonella prevalence were greatest in the caecum (30%) but was never recovered from the right pre-scapular LN. These data provide evidence of vertical transmission from a dam to her fetus such that viable calves are born already infected and thereby not requiring faecal-oral exposure for transmission. This new knowledge ought to challenge - or at least add to - existing paradigms of Salmonella transmission dynamics within cattle herds.

Evaluation of feeding distiller's grains, containing virginiamycin, on antimicrobial susceptibilities in fecal isolates of Enterococcus and Escherichia coli and prevalence of resistance genes in cattle

Dried distiller's grains (DG) produced from ethanol fermentations dosed with 0 (control), 2, or 20 mg/kg virginiamycin-based product or spiked with virginiamycin (VM) postfermentation were fed to cattle and effects on antimicrobial susceptibility, and prevalence of antimicrobial resistance genes in commensal bacteria was examined. Biological activity assays of DG (from each fermentation) indicated a concentration of 0, 0.7, and 8.9 mg/kg VM, respectively. Twenty-four crossbred beef steers were fed 1 of 4 diets (containing 8% of each of the different batches of DG) and a fourth using 8% of the control DG (0 mg/kg VM) + 0.025 g/kg V-Max50 (positive control) for 7 wk. Fecal samples were collected weekly throughout the experimental period and cultured for Escherichia coli and Enterococcus, and isolates were examined for antimicrobial susceptibility, antimicrobial resistance genes (vatE, ermB, and msrC in Enterococcus), and integrons (E. coli). No treatment differences (P > 0.05) were observed in antimicrobial susceptibility of the E. coli isolates. Enterococcus isolates were resistant to more antimicrobials; however, this was influenced by the species of Enterococcus and not treatment (P > 0.10). The prevalence of ermB was greater (P < 0.05) in the control isolates after 4 and 6 wk while at wk 7, prevalence was greater (P < 0.01) in the 0.7 and 8.9 mg/kg VM treatments. Taken together, the minor treatment differences observed for the presence of ermB coupled with the lack of effect on antimicrobial susceptibility patterns suggest that feeding DG containing VM residues should have minimal if any impact on prevalence of antimicrobial resistance.

Evaluation of the effects of weaning diets on Escherichia coli O157 shedding, body weight, and fecal bacterial communities in beef calves

Cattle are considered to be one of the primary reservoirs of Escherichia coli O157. In this study, the effects of weaning diets on E. coli O157 shedding, body weight, and fecal bacterial communities in beef calves were evaluated. A total of 60 calves (28 heifers and 32 steers) were weaned and randomly assigned into two groups. A peanut/soy hull-based diet (Dry Feed, DF) and a corn silage-based diet (High Moisture, HM) were fed to the two groups, respectively, during the weaning and preconditioning period. Calf body weight was measured before weaning (BW) and 14 days after weaning (AW14), and a fecal sample was collected from each calf at BW, AW14, as well as 56 days after weaning (AW56). The prevalence of O157 in feces was determined by CHROMagar(™) O157 and polymerase chain reaction (PCR). Denaturing gradient gel electrophoresis (DGGE) was employed to analyze fecal bacterial communities. A significant decrease in body weight was observed during weaning, regardless of the calf diet (p<0.05). Calves fed the HM diet lost more weight than the DF-fed calves determined at 14 days after weaning (p<0.05). Both the CHROMagar(™) and PCR results showed that the overall prevalence of O157 increased significantly during weaning. Based on the CHROMagar(™) method, O157 increased from 16.6% at BW to 38.3% at AW14 (p<0.05) and stayed at the higher level during the preconditioning period (AW56). The increase in O157 prevalence was observed in HM-fed calves during weaning but not in DF-fed ones. Weaning also changed the profile of fecal bacterial communities (p<0.05). These results showed that weaning is a critical step in beef cattle production, not only because of its effects on body weight but also due to its impact on O157 shedding and gastrointestinal tract bacterial community establishment.