Characterization of a model of hindgut acidosis in mid-lactation cows: A pilot study

The objective of this pilot study was to generate data to support the development of an experimental model of hindgut acidosis to further understand its systemic consequences independently of rumen acidosis. Four ruminally fistulated multiparous Holstein cows (213 ± 11 d in milk) were subjected to 2 consecutive experimental periods (P1 and P2), separated by a 3-d washout. Experimental periods were 96 h long from the baseline to the final measurements but expanded over 5 calendar days (d 0-4). Abomasal infusions of saline and corn starch (2.8 kg/d) were performed for the first 72 h (d 0-3) of P1 and P2, respectively. Final measurements were performed 24 h after the end of the infusions (d 4). Each cow was used as its own control by comparing P2 to P1. Postruminal-intestinal permeability was assessed by Cr appearance in blood after a pulse dose administration of Cr-EDTA into the abomasum on d 2 (48 h after infusion initiation) of each period. Starch infusion during P2 was associated with a milk protein yield increase (3.3%) and a decrease in milk urea nitrogen (11%). Fecal dry matter increased (8.8%), and starch content tended to increase (∼2 fold) during P2. There was a period-by-day interaction for fecal pH as it decreased during starch infusion (1.3 pH points) but remained constant during P1. Although fecal lactate was not detectable during P1, it consistently increased during starch infusion. Fecal alkaline phosphatase activity also increased (∼17 fold) in association with starch infusion. Two hours after Cr-EDTA administration, blood Cr concentration was higher during starch infusion, resulting in a tendency for a treatment-by-hour interaction. Furthermore, blood d-lactate increased (∼2.5 fold), serum Cu decreased (18%), and blood urea nitrogen, cholesterol, and Ca tended to decrease (9.4%, 1.2%, and 2.4%, respectively), relative to P1. The current results suggest that hindgut acidosis was successfully induced by postruminal starch infusion, leading to gut damage and increased intestinal permeability. However, indications of systemic inflammation were not observed. The herein described preliminary results will require confirmation in a properly powered study.