Biases in relative estimates of dietary mineral status from esophageal extrusa

Abstract

An experiment was conducted to determine whether or not the effects of forage type and time into feeding period precluded use of esophageal extrusa to estimate relative dietary mineral status of cattle. Four esophageally fistulated Angus-Hereford X Jersey crossbred steers (340 to 545 kg.) were alternately fed Coastal bermudagrass hay (Cynodon dactylon) (BGH) and fresh green-chopped. TAM 105, wheat (Triticum aestivum) (GCW). Extrusa was sampled at 5 and 20 minutes into the feeding period. Significant additions of Na, P, and K occurred in the extrusa of both forages. Ash, Mg, and Ca concentrations were higher in the extrusa of BGH. Calcium, Zn, and N concentrations were similar in extrusa of both forages. Changes in Na, P, ash, Ca, and Mg concentrations were as expected; however, the changes in K, Cu, and Zn disagree with published results. Previous research suggested K, N, Ca, Cu, and Mg content of the diet could be estimated from esophageal extrusa. The current experiment indicated dietary Cu, Mg, and K content of diets could not be extrapolated from extrusa concentrations of these minerals. Forage type had significant effects on the extent and form of change in the associated extrusa. The magnitude of these effects precludes use of esophageal extrusa for relative comparisons among plant communities within and among seasons, if selected forages are markedly different in maturity, moisture content, and physical form. Time into feeding period had no detectable effect on amount or percent of change in extrusa from the forage.