Response of Lactating Cows Fed Urea-Treated Corn Silage Harvested at Varying Stages of Maturity1,2

Abstract

Corn harvested for silage at 30, 36, and 44% dry matter was treated with 0 or 0.5% urea at ensiling time. Yields of dry matter for the respective maturities were 10.4, 12.2, and 10.2 ton/ha. Losses of dry matter in the silo were highest for the high-dry matter silage (15.1%) compared to the medium (6.4%) and low-dry matter silages (7.0%). Urea-treated silage lost more dry matter than control silages (12.8 vs. 6.1%). Silages were fed to nine groups of lactating cows (six per group) as the only forage during an 80-day treatment period. Six groups were fed untreated silages; three received a 13.8% crude protein concentrate and three an 18.7% crude protein mix. The groups fed urea-treated silages received a 13.8% concentrate. Silages were fed ad libitum and concentrates at 1 kg/2.5kg of milk for all milk over 11.4 kg/day. Milk yields were not affected by urea-treatment of silage, but were decreased (P<.05) with increasing maturity of silage. A significant interaction (P<.05) between urea-treatment of silages and maturity was shown with milk persistencies higher for urea-treated than control silages at the early and medium maturities, but markedly lower for the late-maturity silage. Silage dry matter intake was significantly higher (P<.01) for urea-treated than for control silages. There was a trend towards lower intakes on the 45% silage compared to 37 and 30%, but differences were not significant.