In vivo and in vitro comparisons of selected grass silages

A three-year study with growing-finishing beef heifers was conducted to determine: (1) if grass or small grain silage can be effectively harvested and fed during the summer to slaughter heifers; (2) if there are differences in feeding value between stages.of maturity and/or the species of grass used; (3) if the results using laboratory techniques for estimating the feeding value of silages are similar to those obtained in the feedlot; (4) whether the digestibility of grass would be different if harvested either earlier or later than the usual recommended harvesting times? Each year 48 or 56 heifers weighing 400-500 pounds and grading medium or good were allotted into eight lots of six or seven each. Two lots were randomly assigned to treatment. The total finishing period was divided into a silage phase and a concentrate phase. When the heifers reached weights of 700-900 pounds and an average condition grade of Good, they were slaughtered. Statistical analysis proved there was no significant difference (P > .05) in average daily gain (ADC) or feed efficiency between the small grain silages (oat and wheat) and permanent grass silages (alfalfa-orchardgrass and ladino-orchardgrass). There was also no significant difference (P > .05) in ADG or feed efficiency between the two ensiled stages of maturity. The digestible dry matter (DDM) difference between samples air dried or freeze dried was nonsignificant (P > .05). Samples fermented in simulated and conventional silos did not have significantly different (P > .05) DDM. Silage harvested before the recommended harvesting time had significantly higher (P < .05) DDM. This early-cut silage also had a higher proximate analysis. The proximate analysis decreased for harvesting at later maturity stages except for the last two stages which increased slightly.