Quanz, Steven Thomas2021-12-032021-12-032022https://hdl.handle.net/2097/41810Gastrointestinal health is exceedingly important in dairy cattle. Gastrointestinal inflammation in the gastrointestinal tract leads to a breakdown of the intestinal barrier, which allows pathogens and other infectious agents to enter the animal’s body. Dairy calves undergo many physiological and environmental stressors during their first few months of life, which can cause the mucosal lining of the intestines to thin, thereby exposing the calf to pathogenic bacteria such as Clostridia species. Previous research has explored diet supplementation, including the use of direct fed microbials, to improve gastrointestinal health in dairy cattle. This dissertation focuses on addressing gastrointestinal health issues in two populations of dairy cattle: mid-lactation cows and calves. In the first study, mid-lactation dairy cows were supplemented with calcium gluconate with the goal of improving milk fat production as well as gastrointestinal health. Unfortunately, during the study, cows were exposed to several unplanned challenges including heat stress, mycotoxins (trichothecenes and zearalenone), and pathogenic bacteria (Clostridium species). Cows experienced sporadic intake and digestive upset, which likely contributed to reduced milk fat content (3.7% ± 0.20 at study enrollment declined to 3.4% ± 0.20 at the nadir). Cows with 3+ parities had greater (P < 0.05) dry matter intake (DMI) compared to 2nd lactation cows. Parity groups did not differ in milk fat content (P > 0.05), but 2nd lactations cows tended (P = 0.098) to have greater milk protein. Calcium gluconate supplementation had minimal effects on production. Supplementation tended (P = 0.056) to increase milk fat concentration (3.75 ± 0.050 vs. 3.66% ± 0.051), but also tended to reduce percent milk protein (P = 0.08) and lactose (P = 0.07) concentrations. Furthermore, there was a shift in milk fat composition. Cows supplemented with calcium gluconate had increased (P < 0.05) production of milk de novo synthesized and mixed-source fatty acids. In addition, plasma NEFA concentrations were elevated in supplemented cows (P < 0.05), but no other differences in blood metabolites were observed (P > 0.05). In the second study, Holstein-Angus crossbred calves were randomly assigned to 1 of 2 treatments at birth and then were sacrificed at 30, 60, or 90 days of life. Treatments consisted of 1) a negative control milk replacer, or 2) a milk replacer supplemented with Lactobacillus and Bacillus species. No differences were found between control calves and probiotic supplemented calves for performance measurements (P ≥ 0.10). There was a treatment × time interaction for starter DMI and total DMI (P < 0.05) with probiotic-supplemented calves having greater intakes for the first 30 d of the trial than control calves. Health scores suggested no differences between treatments (P > 0.05), with the exception of a tendency for ear score (P = 0.08) to be greater (indicative of more negative observations) in probiotic-supplemented calves compared to controls. No treatment effects (P > 0.05) were observed for plasma health biomarkers, intestinal tissue E. coli or other pathogen abundance, fecal E. coli or pathogen counts, or ileal histology. In this study, the combined probiotic delivered with milk replacer had little discernable benefit for calf health and growth, although this cohort of calves was not severely challenged. Across both studies, the interventions evaluated had few impacts on measures of gastrointestinal health, but documented changes in gastrointestinal physiology and barrier function in growing calves and in mature cows undergoing digestive problems provide valuable insights.en-US© the author. This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).http://rightsstatements.org/vocab/InC/1.0/RuminantFeed additiveGut healthDissertation