Diurnal Excretion Pattern and Digestibility of Three Complete Feeds

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Abstract
Fifteen grams of Cr2O3 were administered orally at 7:00 A.M. daily to 6 lactating Holstein cows for a period of 14 days. "Grab Samples" of feces were taken every 2 hr. for the last 7 days and composited. The cows were divided into 3 pairs and fed complete feeds I, II, and III ad libitum. The complete feeds contained I - 30% ground (2.54-cm screen) alfalfa-orchard grass hay and 70% concentrates, II - 30% ground (1.59-cm screen) corn cobs and 70% concentrate, and III - 10% cottonseed hulls and 70% concentrate. The composition of these rations was calculated to be similar in protein and TDN [total digestible nutrients] content, based on Morrison''s tables. The actual compositions of these feeds and feces were determined by the proximate analysis. The Cr2O3 excretion pattern was similar (P>0.05) for all 3 feeds. Representative samples of Cr2O3 excretion could be obtained by combining "grab samples" of feces taken at 8:00 A.M. and 7:00 P.M. Digestibility of the feeds was based on the actual feed consumed. The determined TDN values were 67.3% (I), 62.9% (II), and 65.9% (III). The calculated values were 69.1% (I), 69.5% (II), and 67.7%(III). The mean digestion coefficient for protein was 74.0%(I), 73.0%(II), and 77.5%(III); and for fiber, 48.0%(I), 35.0%(II), and 25.0%(III).