Comparisons of total fecal collection, lignin ratio, and in vitro techniques in determining dry matter digestibility of tall fescue and fescue-legume fed to cattle

Three different digestibility techniques were compared in the study. These techniques are the total fecal collection (TFC), the acid detergent lignin ratio (ADL), and the in vitro techniques. The objectives of this study were to determine the similarities and differences among the values obtained from these techniques.

Six TFC experiments were conducted using clipped fescue and legume fed to steers in confinement. Each trial consisted of a 7-day preliminary period and a 5-day collection period. In the ADL technique, pasture and fecal samples from grazing animals were analyzed for the ADL content. The pasture samples were clipped from the grazing pasture. In the in vitro experiment, strip samples from the grazing pastures were analyzed. These stripe samples represented the portion of the forage available to the grazing cattle. In addition, fescue and legume samples from the TFC experiment were also analyzed employing the in vitro technique.

From the TFC experiments, it was evident that an increase in percent legume did not increase total fecal collection DM digestibility (TFCDM) (P<.01). On the other hand, both the ADL ratio and the in vitro techniques detected.an increase in ADL DM digestibility and the in vitro DM digestibility (IVDMD), respectively over the warmer time of the year with the exception of ADL DM of high quality pasture of 1977. However, the fescue in vitro DM digestibility (FESIVDMD) and legume in vitro DM digestibility (LEGIVDMD) were different in time trend. LEGIVDMD was observed to decrease at an increasing rate while FESIVDMD was decreasing at a decreasing rate.