Meeting the protein requirement of dairy cows in a long-term feeding experiment.
The aim of this work was to compare three possibilities of meeting the protein requirement of dairy cows. Altogether 72 Estonian Red cows with 200 periods of lactation were used in the experiment. The treatments differed in the composition of concentrate feeds as follows: (a) complete concentrate feed (produced in a feed manufacturing plant), (b) barley meal + oil meal, (c) barley meal + urea. Urea was supplied to barley meal at the rate of 2.5 or 3.5 per cent. The ration of each cow was formulated once a month taking into account 6 g/MJ digestible crude protein (DCP) for maintenance and 60 g DCP per 1 kg ECM. One gram of urea was equivalent to 2 g DCP. The milk yield and feed intake of each cow were determined at every milking and feeding, the milk fat content every 10 days, and the milk protein content once a month.
The results are given per cow and lactation. The milk yield (kg), milk fat and protein content (%), and the milk fat and protein yield (kg) were as follows: (a) 4478, 4.17, 3.555, 186.9 and 159.0, (b) 4556, 4.08, 3.48, 185.7 and 158.6, (c) 4492, 4.11, 3.555, 184.8 and 159.4. The ECM-yield made up: (a) 4594, (b) 4608 and (c) 4569 kg.
On average per cow and lactation the cows consumed the following amounts of metabolizable energy (MJ) and DCP (kg): (a) 39,327 and 354.3, (b) 43,383 and 412.5, (c) 42,424 and 289.4 (without urea) or 381.1 (with urea). The CP content of the rations DM was: (a) 13.8, (b) 15.1, (c) 12.1 (without urea) or 15.6 (with urea) per cent.
It can be concluded that the milk yield was practically on the same level in all the groups. Urea can meet the protein requirement, if it is carefully used. No urea poisoning was noticed.
Key words: Protein requirement of dairy cows, urea supplement, protein nutrition of dairy cows.