Composition of formaldehyde- and formic acid-treated alfalfa and orchardgrass silages harvested at two maturities and their effects on intake and growth by Holstein heifers.

Alfalfa and orchardgrass herbages were each harvested at two maturities (May 22 to 25 vs June 5 to 7) in primary growth and directly ensiled with 5 kg of a mixture of 30% formic acid and 25% formaldehyde per metric ton of fresh herbage in upright conventional silos. Alfalfa silage contained less NDF (71%) and more N (150%) and hot-water-insoluble N (117%) than orchardgrass silage did. Major differences between silages were that orchardgrass contained 20.4 percentage units more NDF and 1.10 percentage units less N than alfalfa. The NDF increased 104% and total N decreased to 86% with advancing maturity. Twenty-eight yearling Holstein heifers (223 kg BW) were given ad libitum access to the four silages with trace mineral salt, and growth rate was measured in a 119-d period. Daily DE intake was 297 kcal/kg.75 BW for heifers fed alfalfa silage compared with 202 kcal/kg.75 BW for heifers fed orchardgrass silage. Daily gain was 992 g for heifers fed alfalfa compared with 661 g for heifers fed orchardgrass. Gross efficiency, or gain per unit of DE, was similar for heifers fed orchardgrass and alfalfa. Rate of gain was primarily a function of ad libitum intake of DE. Heifers fed alfalfa had greater plasma essential amino acid concentrations (122%) than those fed orchardgrass did. Late alfalfa produced greater ADG than orchardgrass harvested 2 wk earlier.