Relationships between pasture forage components and fecal chemical composition

Abstract

A major problem in evaluating nutritional quality of the grazing animal’s diet is collecting forage representative of that being grazed. We compared the chemical composition of simulated diet (SD) and mower clipped (MC) forage samples to each other and to fecal chemical composition data. Forage from crested wheatgrass [Agropyron desertorum (Fischer ex. Link) Schuhes], western wheatgrass [Puscopyrum smititii(Rydb.) A. Love], smooth bromegrass (Bromus inermis Leyssor), Russian wildrye [Psuthyrostachys juncea (Fisher) Nevskil, and native range pastures was collected every 2 weeks beginning 14 June and continuing through 20 September 1983. Fresh fecal samples from grazing steers were obtained 2 days following forage collections. Variability among individuals hand clipping forage to simulate a grazing animal’s diet was less than the variability between mower strips for in vitro digestible organic matter (IVDOM), calcium (Ca), and magnesium (Mg). Correlation coeffkients between SD and MC residuals were low. Coefficients between SD and fecal residuals were higher for acid detergent fiber (ADF), IVDOM, Ca, and phosphorus (P) than coefficients for the same variables obtained with MC and fecal data. The highest coefficients using residual data were achieved with fecal Ca and SD ADF, cellulose, Ca, and Mg r = -0.84, -0.81, 0.84, and 0.81, respectively. Interactions Involving pastures and sample dates were significant for the same effects for P, ADF, cellulose, and IVDOM for SD and fecal data. Data suggest that some fecal components, primarily Ca, may be useful in predicting the diet quality of grazing cattle, but these relationships need further examination.