Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Animal Science


Four feeding trials were conducted to evaluate the effects of limit feeding on the feedlot performance, carcass composition and economic return of 461 yearling steers (370 kg) of mixed British breeding. In each trial, a high corn grain diet (3.04 Mcal ME/kg DM), supplemented (.23 kg per head per day to all cattle) with an urea-based 40 percent CP, was fed (once a day) on an ad libitum basis or 95, 90 and 85 percent of ad libitum with each of the feed intake level treatments replicated by four pens of cattle. Fecal grab samples obtained from two steers in each pen and feed samples were analyzed for acid insoluble ash content to determine the apparent dry and organic matter digestibilities of the diet as influenced by feed intake level. Cattle were slaughtered as each dietary intake group attained an average final weight of approximately 557 kg. Daily DM intakes for the four intake levels averaged 10.27, 9.76, 9.25 and 8.76 kg. ADG was similar (P >.05) for the ad libitum and 95 percent dietary treatments (1.38 and 1.29 kg./da., P >.05) but significantly higher (P <.0002) than the 90 and 85 percent groups of cattle (1.20 and 1.14 kg./da.). All steers converted feed to gain at similar efficiencies. However, limit-fed steers possessed higher dry and organic matter digestibility values than cattle fed to appetite (97.77 vs. 95.36, P <.0001 for DMD; and 94.40 vs. 89.64, P <.0038 for OMD). All carcass traits were comparable except for higher dressing percentage values associated with steers whose feed intake was controlled (62.12 vs. 61.58%, P <.05). Since all steers were fed to a constant end weight, limit-fed cattle remained 20 days longer on feed (134 vs. 154, P <.0001), thus incurring higher (P <.0001) total feed (127.86 vs. 122.87 /hd) and nonfeed expenses (67.12 vs. 58.10 /hd) than the ad libitum group, respectively. Nevertheless, due to their dressing percentage advantage, limit-fed cattle possessed higher steer sale values (904.47 vs. 867.42 /hd, P < .0001) leading to greater profit returns with controlled feeding (57.28 vs. 35.60 /hd, P <.0030). These results seem to suggest that a slight feed intake restriction may result in higher nutrient digestibility and similar efficiencies of gain without detrimentally affecting the carcass quality of feedlot steers. Further, when marketed on a carcass basis, limit feeding may generate higher financial returns than the conventional ad libitum feeding system.



Digital Repository @ Iowa State University,

Copyright Owner

Abdullahi Hassan Mahdi



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142 pages