No Associative Feeding Effects Between Corn and Haycrop Silages for Dairy Heifers

Four nonlactating Holstein heifers were assigned randomly to a 4 X 4 Latin-square trial.The four diets were urea-treated corn silage and early-ent wilted hayerop silage in dry matter ratios of 100:0, 67:33, 33:67, 0:100, plus 125 g/day of a vitamin-mineral supplement.Feed was offered at .9 times recommended National Research Council (1966) allowances for maintenance and growth.Associative feeding effects were evaluated by comparing predicted and observed animal responses to mixed forage treatments.Ration digestibility and energy and nitrogen balances were determined for each ration.Corn silage was lower in fat, fiber, and minerals but nearly equal in protein to hayerop silage.Digestibility of gross energy, crude protein, dry matter, and ether extract was higher for the 100% corn silage diet than for the 100% haycrop silage diet; the other two diets were intermediate.Percentages of ingested energy lost as feces, urine, methane, and heat were lowest and tissue retention highest for the 100% corn silage diet.There was no difference among treatmerits for percent nitrogen in urine, but tissue nitrogen balance was highest on the all corn silage diet.Positive associative feeding effects were nil.Urea-treated corn silage was more digestible and promoted greater energy and nitrogen retention than did haycrop silage containing a similar amount of crude protein.