Effects of urea treatment on chemical composition and in vitro digestibility of meadow hays of Northern Portugal

Abstract

Samples of 250 g of two meadow hays (H 1 and H 2) were sprayed with urea solution to increase the moisture content up to 400 g kg −1. The level of urea applied was 60 g kg −1 dry matter (DM). The samples were stored in sealed plastic bags at 25°C for 3, 6, 9, 45 and 60 days. Unhydrolysed urea, changes in chemical composition, in vitro cell wall digestibility (IVNDFD) and in vitro organic matter digestibility (IVOMD) were measured. The hydrolysis of urea was extensive and significantly ( P < 0.001) increased by treatment time. The pH of treated samples was clearly alkaline at all treatment times, and after 45 and 60 days of storage averaged 10.98 and 11.07, respectively. Urea treatment promoted major chemical changes in the composition of cell walls; neutral detergent fibre, hemicellulose and lignin contents being significantly ( P < 0.001) reduced and cellulose content significantly ( P < 0.001) increased. These effects were increased by treatment time. Concomitantly, the amount of soluble phenolics dissociated from the cell wall matrix in urea-treated samples was significantly ( P < 0.001) increased and the number of saponifiable groups significantly ( P < 0.001) reduced. Consequently, IVNDFD and IVOMD were significantly ( P < 0.001) increased. After 60 days of storage, urea-treated samples showed an increase in total nitrogen content from 16.4 and 12.1 to 28.9 and 29.8 g kg −1 DM for H 1 and H 2, respectively. Of the increment, most of the nitrogen was analysed as water-soluble nitrogen, the amount of nitrogen bound to fibre (ADF-N) being negligible. The results indicate that urea can be successfully used to improve the nutritive value of poor quality meadow hays in northern Portugal, but more information is needed concerning the effectiveness of the treatment under the conditions of high temperature which occur during the warm season in this region.