Location: Livestock Issues Research
Project Number: 3096-32000-009-040-R
Project Type: Reimbursable Cooperative Agreement
Start Date: Jul 1, 2024
End Date: Jun 30, 2029
Objective:
The first objective of this proposal is to validate a minimally invasive model to induce liver abscesses in calves. Based on preliminary data generated by our team, we have developed a liver abscess model with great potential (described later). The repeatability of this model has not been tested and our hypothesis is that the model will consistently lead to the development of liver abscesses in future studies. Our second objective is to develop a model to induce leaky gut symptoms and evaluate subsequent formation of liver abscesses. The role of gut barrier function on liver abscess formation in cattle is not known. Our working hypothesis is that a model of leaky gut such as indomethacin-induced enteropathy model (Cangiano et al., 2022) can be used to change the integrity of the intestinal epithelium and induce leaky gut to allow for the study of liver abscess formation. The third objective is to characterize dietary factors that affect liver abscesses in finishing beef cattle. There is a knowledge gap in evaluating the effects of roughage neutral detergent fiber (NDF) concentration in the diet. Our working hypothesis is optimum dietary factors and concentration of roughage NDF can be identified and will be useful management strategies to decrease liver abscesses and use of antimicrobials in the beef industry.
Approach:
The objective of this study is to develop a model to induce the formation of liver abscesses that is minimally invasive, reliable, and repeatable while attempting to mimic real-world disease etiology. To accomplish Objective 1, the researchers propose to procure 60 weaned Holstein steer calves from a commercial calf ranch or dairy operation in the Texas Panhandle. Calves will be randomly assigned to 1 of 4 treatments: 1) control diet (n = 15); 2) acidotic diet (n = 15); 3) acidotic diet + intraruminal inoculation with Fusobacterium necrophorum spp. necrophorum, Trueperella pyogenes, and Salmonella enterica spp. Lubbock (n = 15); or 4) acidotic diet + intraruminal inoculation of Salmonella enterica (n = 15). The control diet will be comprised of: 46% Sweet Bran, 20% dry-rolled corn, 30% chopped alfalfa hay, 1.5% limestone, and 2.5% vitamin and mineral supplement. The acidotic diet will be comprised of: 58.3% steam-flaked corn (24 lb/bu), 5% ground corn, 15% dry-rolled corn, 5% finely ground alfalfa hay, 12% Sweet Bran, 1.5% limestone, 0.7% urea, 2.5% vitamin and mineral supplement.
At arrival, an intraruminal bolus that monitors pH will be inserted and calves will be placed in individual pens in 2 indoor climate-controlled facilities and allowed to acclimate for 7 days while they are fed the control diet. On d 0, calves in treatments 2, 3, and 4 will undergo a diet change and the acidotic diet will be fed. Calves will be offered 15% more NEg in the form of the acidotic diet than the previous 3-day average NEg consumption on the control diet. This approach was successful in inducing subacute acidosis in our previous challenge model. Calves will be fed the acidotic diet for 3 days, then switch back to the control diet for 2 days. This cycle will be repeated 4-times. Boluses monitoring real-time pH will be evaluated 24 hours/day during the acidotic challenge. If a calf reaches a ruminal pH of less than 4.3 for greater than 4 h, the calf will be given an oral drench of sodium bicarbonate to aid in buffering the rumen. Following the diet change cycles (day 21), the calves in treatments 3 and 4 will be intra-ruminally administered the bacterial inoculation using a frick speculum and rumen tube. Calves in treatments 3 and 4 will be fed the acidotic diet from day 21 to harvest on day 35.
Blood will be collected prior to the diet change (day 0) and collected again every 7 days until harvest (day 35). Blood will be used to quantify complete blood cell counts. At harvest, calves will be evaluated for liver abscesses and/or scarring along with an evaluation of the rumen, lungs, and colon. Rumens from calves with abscesses and abscesses will be cultured for F. necrophorum spp. necrophorum, T. pyogenes, and Salmonella spp. Histopathology samples will be collected from the rumen to evaluate the differences in architectural features between the treatments. This research will evaluate whether our previous model to induce liver abscesses is consistent and repeatable. Additionally, these data should further solidify the connection between acidosis and liver abscess formation.
