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Continuous and Noncontinuous Protein Levels for Growing Calves Fed Corn Silage

University of Kentucky, Lexington 40506^{1 , 2,}

Abstract

Two experiments were conducted to study the influence of feeding different quantities of protein either throughout a growth trial or during approximately the first one-third of a growth trial on performance and plasma nitrogen constituents of calves fed corn silage. In experiment 1, kg of total protein and supplemental protein, respectively, (44% SBM) fed the four treatment groups were: (A) .27, 0; (B) .53, .18; (C) .62, .27 and (D) .71, .36. Steers in group A were offered corn silage ad libitum while those in groups B, C and D were fed quantities of corn silage equal to each other. All groups of steers supplemented with SBM gained faster (P<.01) than steers fed no supplemental protein. Increased (P<.01) dry matter (DM) intakes and lower (P<.01) feed per gain (F/G) ratios were also apparent for the SBM-supplemented steers. Molar percentages of total essential amino acids were lowest when no SBM was fed and highest when .36 kg of supplemental C.P. per head daily was fed. Plasma urea nitrogen (PUN) increased as the level of protein fed increased.

In experiment 2, the effect of feeding different quantities of protein in the early phase of a growth trial was studied. Hereford bull calves were fed corn silage and the following levels of total and supplemental C.P. (44% SBM), respectively, for the first 37 days (period 1) of a 107-day growing trial: (A) .49, .18, (B) .66, .36 or (C) .81, .54 kg per head daily. During period 2 (days 38 to 107) calves in treatment groups A, B and C, respectively, were fed .54, .55 and .55 kg of total C.P. and .18 kg of supplemental C.P. (44% SBM) per head daily plus ad libitum corn silage. Average daily gain (ADG) in period 1 was lower (P<05) and F/G higher for calves fed .18 kg of supplemental C.P. than for those fed diets supplemented with either .36 or .54 kg of C.P. per head daily. Average daily gain and F/G were similar among all treatment groups during period 2. PUN levels in treatments A, B and C were different (P<.01) from each other on day 37 and were generally reflective of the level of protein intake, as was observed also in experiment 1.

¹ Department of Animal Sciences.

² This paper (No. 77-5-90) is published with the approval of the Director of the Kentucky Agricultural Experiment Station.