Vrzalová D., Zelenka J., Šustala M. (2001): Digestibility of crude protein and nitrogen retention on preruminant calves. In: Book of Abstracts of the 52nd Annual Meeting of the European Association for Animal Production, No. 7 (2001), 26-29 August 2001, p.109. ABSTRACT: In the trial conducted on calves the effect of age on the apparent crude protein (CP) digestibility and nitrogen retention was studied. The experiment was carried out on five Czech spotted male calves from 9 to 91 days of age. Digestibility was determined in 23 three-day balance periods by the chromic oxide indicator method. In all the three-day balance periods it proceeded one 24-hour period in which the urine was quantitatively collected. The calves were fed on milk replacer three times a day ad semi-libitum. The average value of crude protein digestibility was 64.2 ± 1.618% (mean ± standard error of the mean). The crude protein digestibility and nitrogen retention significantly (P<0.01) changed with age of calves. The dependence of coefficients of digestibility or retention (Y) on age in days (X) was expressed by the 2nd degree parabola equation with a maximum on Day 74,81 and 63 for the CP digestibility, nitrogen intake retention and nitrogen digested retention, respectively. The calves utilised on the average 61.5 ± 1.416 % of the nitrogen intake and 89.5 ± 2.146 % of the nitrogen digested.