Untreated and formaldehyde-treated urea as nitrogen sources for lactating dairy cows

Abstract

An experiment was performed with 22 Friesian cows, using a double reversal design with two treatments and one similar sequence for the two groups. The lengths of the standardization period, adaptation periods, test period and post-test period were 4, 1, 8 and 4 weeks, respectively. During the standardization and post-test periods the cows received pre-wilted grass silage ad libitum and a small amount of field-dried baled hay. In the test period hay was given ad libitum and the amount of grass silage was restricted. A concentrate mixture (barley, oats, minerals) was given daily to each cow at the rate of 0.3 kg/kg 4 % milk. During the standardization and post-test periods the mixture contained one percent of untreated urea and during the test period 2.5 % of untreated or treated urea. The urea had been treated with 1.5 % formaldehyde on a weight basis. The concentrate mixture was fed individually to each cow, but group feeding was used for the roughage. Among the cows producing more than 15 kg of 4 % milk a day, those receiving formaldehyde-treated urea had a significantly (P< 0.01) higher milk yield, and the fat content of their milk was significantly (P< 0.05) lower than the group receiving untreated urea. Among the cows producing less than 15kg of 4 % milk/day, the group given treated urea had a significantly (P