Energy and Protein Utilization in Forages Fed to Dry Cows1,2

Abstract

Four mature, nonlactating Holstein cows were fed wilted haycrop silage, urea-treated corn silage, field-cured hay, or dairy concentrate as the sole ration in a 4×4 Latin square design. Haycrops were harvested from the same fields; hay was cut June 15, 12 days after haycrop silage. Rations were offered just above maintenance; data were adjusted to equal metabolizable energy intake across rations. Corn silage and haycrop silage were 26 and 35% dry matter as fed. Only the forages are discussed in detail. Percentage of ingested gross energy and nitrogen lost in feces was higher for hay than for the silages. Gross energy excreted in urine was highest for haycrop silage and lowest for corn silage. Percentage of ingested nitrogen lost in urine was higher for haycrop silage than for hay or corn silage. Body retention of gross energy and nitrogen was higher with corn silage than with either haycrop. No differences were between rations in proportion of gross energy lost in methane or heat production. Digestibility of dry matter, nitrogen, and nitrogen-free extract, as well as total digestible nutrients, was higher for silages than for hay. Crude fiber digestibility was similar for all forages, but digestibility of ether extract was higher for silages than for hay. Apparent maintenance metabolizable energy requirements for corn silage, haycrop silage, and hay were 122, 121, and 132 kcalAg W.75. Efficiency of conversion of metabolizable energy to tissue (fat) was low for haycrop silage.