ABSTRACT
Summary Sheep are frequently used to determine the nutritive value of cattle feeds. However, there is some evidence that digestion coefficients for cattle and sheep may differ and that digestibility may be influenced by feeding level. The purpose of this study was to investigate the effects of feeding level and animal species on the digestibility of pelleted diets containing different ratios of alfalfa hay to barley grain. Five 40-kg yearling crossbred lambs and four 350-kg yearling steers were used to evaluate each diet. The six diets were isonitrogenous, containing the following proportions of barley grain and alfalfa hay (percentage as fed basis): (1) 0% and 98.0%, (2) 18.0% and 80.1%, (3) 36.0% and 62.0%, (4)54.0% and 44.1%, (5) 72.0% and 25.6%, (6) 90.0% and 6.7%. The barley and alfalfa were ground through a 0.64-cm screen, and the complete feed was pelleted (1.59 cm in diameter). Feed intakes were 50, 75, and 100 g/W0.75. Sheep offered 100 g/W0.75 of the high barley diets were at approximately ad-libitum levels of intake. Average digestion coefficients for organic matter (OMD), crude protein (CPD), and acid detergent fiber (ADF) in the six diets were lower (P < 0.05) with sheep than with cattle: 70.4% vs. 71.8%, 71.2% vs. 73.4% and 31.9% vs. 35.3%, respectively. Increasing feed intake from 50 to 100 g/W0.75 reduced (P < 0.05) OMD and CPD but did not affect the digestibility of ADF. OMD and CPD increased by 0.25 and 0.11 percentage units, respectively, for each percentage of increase of barley in the feed for OMD values ranging from 59.9% to 81.2% with sheep and from 61.0% to 83.3% with cattle. The results of this investigation show that while digestion coefficients of the pelleted diets were significantly higher in cattle than in sheep, differences were not large. For routine feed evaluation the digestibility by cattle of pelleted feeds consisting of grain and hay may be estimated from values obtained with sheep, provided that relative feeding levels are similar.
