Graduation date: 2007Two experiments were conducted looking at both acute and sub-acute laminitis. An acute nutritional induction model was used to examine whether blood profiles and gene expression are similar to other studies conducted using an endotoxin induction model. Twelve sheep were randomly assigned to three treatment groups which were control, 4-hour slaughter (4HS) and 48-hour slaughter (48HS). Lactic acid (LA) was infused into the rumen of sheep in 4HS and 48HS and sterile saline solution was infused into the rumen of control sheep using an esophageal tube. 4HS and 48HS were slaughtered 4 and 48 hours after infusion, respectively. Control was slaughtered 48 hours after infusion. Tissue samples were taken and analyzed for cyclooxygenase- 2 (COX-2), Macrophage Inflammatory Protein-1 (MIP-1) and Matrix Metalloproteinases (MMP) -2, -9 and -14 gene expression with RT-PCR. CBC differentials were performed on blood samples to obtain white blood cell (WBC) counts. WBC counts in 4HS and 4HS increased 67% and 99%, respectively, from control groups by 4 hours after induction and returned to pretrial levels by slaughter. Lymphocytes in 4HS and 48HS were reduced by 44% and 39%, respectively, compared to control and remained low for the remainder of the trial. Neutrophils increased in 4HS and 48HS by 151% and 121%, respectively, compared to control and remained elevated for the remainder of the trial. PCR analysis did not yield differential mRNA expression, but trends were observed. MMP-9 expression increased 5-fold by 48 hours. MMP-2 mRNA expression decreased by 50% at 4 hours and returned to pretrial levels by 48 hours. MMP-14 mRNA expression decreased 4 hours after LA infusion and increased 4.5-fold by 48 hours. MIP-1α expression increased 2-fold by 48 hours. COX-2 expression decreased at 4 hours and returned to pretrial levels by 48 hours. Larger sample size is needed for more definitive results. A second experiment was conducted to examine a new induction model of laminitis that focuses on slow induction of laminitis and to test the effects of quercetin, naringin, and white willow bark as a feed additive on nutritionally challenged dairy cows. Eighteen multiparous lactating dairy cows were blocked by days in milk and randomly assigned to three treatment groups which were control, a group that received a high energy ration (HE) and a group that received a high energy ration and an experimental feed additive consisting of quercetin, naringin and white willow bark (HEQ). Cows remained on the diets for 70 days, after which white line measurements and hoof evaluations were taken from each cow and repeated 70 days after the conclusion of the trial. Milk yield, daily feed intake, locomotion scores, rumen pH and milk composition were recorded throughout the trial to measure cow productivity. HE developed pronounced white line separation whereas HEQ did not differ from control. Cow productivity was not negatively impacted by the feed additive and cows had a tendency to eat more with the feed additive. The slow induction model shows promise, but experimental error needs to be reduced for definitive results.