Cellulose digestion potential, liquid volume and other rumen parameters of market-transit stressed steers

The objectives of this study were to evaluate the error associated with estimating rumen fluid volume (v2) in field studies using the marker concentration in the rumen fluid sample collected 1 hr after dosing with either lithium sulfate or polyethylene glycol. A comparison of this estimate with the rumen volume (v20) calculated from predicted marker concentration at time of dosing using individual regression coefficients, and that (v20B) calculated from predicted marker concentration at the time of dosing using a common regression coefficient was also made. Rumen parameter (rumen fluid volume, in vitro gas producing potential and pH) changes of 172 weanling feeder-steer calves subjected to the market-transit chain were evaluated and factors affecting these changes were also examined.

Mean V2, V20 and V20B in shipment 7 were 34.6 + 2.01e, 31.6 + 1.88e and 31.9 + 2.01& respectively. In shipment 11, mean V2, V20 and V20B values were higher than those in shipment 7 but the mean difference between V2 and V20 were similar even though different markers were employed. Standard errors of mean V2, V20 and V20B were also similar in the 2 shipments though the coefficients of variation (cv) of the estimates of rumen fluid volume in shipment 7 were larger than the respective Cv values in shipment 11. Mean estimates of V2, V20 and V20B in shipment 12 were slightly higher than those in shipment 7 but lower than the respective estimates in shipment 11. Difference between V2 and V20 in shipment 12 was only 1.0le compared to 3.00e and 2.92e in the shipments 7 and 1l, respectively. Comparison of the analysis of the three estimates V2, V20 and v20B in each of the shipments suggested that the method of calculation had no effect in the statistical interpretation of the results.

In vitro gas production (Gp) of the rumen fluid and rumen fluid volume followed similar trends during the market-transit phase in the three trials. Increases in GP and slight increases in rumen fluid volume were observed on arrival at the auction barn, and GP and rumen fluid volume decreased after a 24 hour starvation period in the auction barn. The rumen parameters return to pre-shipment levels within ll days after arrival at the feedlot.

The factors affecting GP during the market-transit chain include the farm of origin, pre-shipment treatments and the length of time the calves spent in the orderbuyer barn. Rumen fluid volume was significantly affected by the farm of origin differences when measured at the farms 30 days prior to marketing, and at most sampling points at the feedlot. The addition of sodium bicarbonate to the feedlot receiving diet did not have any significant effect on rumen fluid volume. Pre-shipment treatment had a significant effect on rumen fluid volume only at the arrival auction barn and departure orderbuyer barn phase of the market-transit chain in trial 3.