Effect of slow-release urea source on total tract digestibility of protein, starch and fiber in fattening heifers

U intenzivnoj hranidbi preživača ureja se koristi kao najjeftiniji izvor neproteinskog dušika za mikroorganizme buraga. Cilj ovoga rada je usporediti utjecaj sporootpuštajuće ureje iz dodataka Ubea 70 (70% ureje, 28% bentonita i 2% S; Petrokemija Kutina, RH) i one zaštićene lipidima iz dodatka Optisync™ (88% ureje i 11,2% lipida; Alltech, Nicholasville, SAD) na ukupnu probavljivost sirovih proteina, vlakna, škroba i suhe tvari obroka tovnih junica. Četiri tovne junice pasmine Simmental, u prosjeku teške 380 kg i stare 12,5 mjeseci na početku pokusa, raspoređene su na dva različita dodatka u obroku prema cross-over dizajnu u dva perioda od po 18 dana. Obroci sa oba dodatka sastojali su se od istih krmiva sa 50%:50% omjerom voluminoze i koncentratne krme te 0,7% ureje, a kao indikator probavljivosti korišten je kromov(III)-oksid. Junice hranjene dodatkom Optisync™ u usporedbi s junicama hranjenim dodatkom Ubea 70 bolje su probavljale (P<0,05) sirovi protein (68,6% vs. 59,4%), ukupna vlakna (49,1% vs. 33,2%) i suhu tvar (72,1% vs. 63,1%). S druge strane, dodatak Ubea 70 ima tendenciju za 1,27% više probavljivosti škroba. Izvor sporootpuštajuće ureje nije utjecao na pH fecesa niti razinu ureje u krvi, iako brojčane razlike upućuju da dodatak OptiSync™ u obroku pokazuje ujednačenije otpuštanje ureje u buragu nego dodatak Ubea 70.Urea is a low-cost source of nonprotein nitrogen for rumen microorganism in intensive cattle production. The aim of this study was to compare effect of slow-release urea source Ubea 70 (70% urea, 28% bentonite and 2% S; Petrokemija Kutina, Croatia) and lipid-coated urea from Optisync™ (88% urea and 11,2% lipids; Alltech, Nicholasville, USA) on total tract digestibility of crude protein, fiber, starch and dry matter of ration fed to fattening heifers. Four fattening Simmental heifers, in average 380 kg of body weight and 12.5 months of age at the beginning of the trial, were assigned to two ration additives in a cross-over design with two 18-day periods. Rations with both additives had same feed ingredients in 50%:50% forage:concentrate ratio, and contained 0.7% of urea, while chromium (III) oxide was added as digestibility indicator. Heifers fed Optisync™, compared to heifers fed Ubea 70, had higher digestibility (P