Effect of the crude protein level on the utilization of untreated and formaldehyde-treated urea in vitro

Authors

• Jouko Setälä Department of Animal Husbandry, University of Helsinki, 00710 Helsinki 71, Finland
• Liisa Syrjälä-Qvist Department of Animal Husbandry, University of Helsinki, 00710 Helsinki 71, Finland

DOI: https://doi.org/10.23986/afsci.72086

Abstract

Utilization of untreated urea (F0) and urea treated with 1.5 % formaldehyde(F1.5) was tested in vitro on incubation substrates with different levels of crude protein: 9, 10, 11, 12, 13, 14, 15 and 16 % of the substrate dry matter. The content of crude protein was adjusted by addition of urea, the lowest level (9 %) being that of the substrate without urea. The incubation time was five hours. When F0 urea was used microbial protein synthesis, determined by tungstic acid-sulphuric acid precipitation, reached its maximum at the crude protein level of 11 %. When F1.5 urea was added, the synthesis increased up to the level of 15 % crude protein. At the levels of 13-15% crude protein, the synthesis was significantly (P< 0.05) higher with F1.5 urea than with F0 urea. In the bacterial mass obtained by ultracentrifugation the content of methionine was significantly higher (P< 0.01) when treated urea was used. With untreated urea, the proportion of lysine was significantly higher (P< 0.05). Addition of urea did not affect the amino acid composition of the bacterial mass but increased the yield of microbial protein during incubation.