Alfalfa biotypes with putative enhanced cell wall digestibility and effects on performance of growing beef steers.

Three alfalfa biotypes were chosen based on the presumption that they would be sources of alfalfa herbage that differed in lignin concentration and therefore cell wall digestibility. The hypothesis was that a lesser lignin concentration would result in greater alfalfa neutral detergent fiber (NDF) digestibility and greater beef steer growth performance. The three alfalfa biotypes were HarvXtra (Forage Genetics International), Hi-Gest 360 (Alforex Seeds), and a control alfalfa, LegenDairy XHD (Winfield Solutions LLC). High-moisture wrapped bales were prepared from second-harvest, d 30 crops. Digestibility of NDF was determined using in vitro incubations and a steer digestibility trial. Alfalfa baleage and trace mineral salt were fed to Angus steers (300 kg initial body weight, 4 pens/treatment) in an 83-day growing-phase trial. Alfalfa acid detergent lignin concentrations were 75.6, 71.8, and 63.0 g/kg dry matter ( = 0.34) for LegenDairy, Hi-Gest and HarvXtra, respectively. Based on in vitro total-tract NDF digestibility coefficients, HarvXtra tended ( ≥ 0.09) to have the highest NDF digestibility. Alfalfa biotype affected in vivo apparent total tract digestibility of NDF ( 0.001) and there was a trend for an effect on acid detergent fiber digestibility ( 0.051). Hi-Gest and HarvXtra had similar in vivo apparent NDF digestibilities, which were greater than for LegenDairy ( 0.05). There was no alfalfa biotype effect on daily alfalfa dry matter intake (DMI; = 0.51) or average daily gain ( 0.25) by growing steers. The absence of an effect by the novel alfalfa biotypes on DMI by growing steers suggests that the compositional and digestibility differences of the novel alfalfa biotypes compared to LegenDairy were not sufficient to alleviate the limitation of physical fill (if evident) on DMI. If more disparity in cell wall composition and NDF digestibility were to exist between control and reduced-lignin biotypes, then perhaps an advantage in cattle growth performance for a reduced-lignin alfalfa biotype would be detectable.