Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Animal Science

First Advisor

Allen Trenkle


A 2-period grazing experiment was designed to determine the effects of cottonseed meal (CSM) supplementation on forage intake (FDMI), forage digestibility (FDMD) and weight gain (ADG) of steers on a natural pasture in Sub-Saharan Africa during 120 d in the dry season and the residual effects when pasture regenerates during 120 d in the rainy season. Thirty steers (229 kg and 2.6 years) were randomly assigned to a complete block design of 3 treatments (0,.5 and 1.0 kg of CSM per steer per day). After hand-feeding CSM to individual steers in the mornings, all were allowed to free grazing a pasture dominated by Andropogon spp. Every month, 2 steers per treatment were brought into digestion crates and ad lib. fed hand-clipped forage of similar botanical composition as that grazed by the remaining steers. Feeding CSM increased crude protein absorbed (CPA), rumen turn over rate (k[subscript]2) and ADG. Forage intake was increased only with.5 kg CSM. Forage and cell wall digestibility tended to be decreased with 1.0 kg of CSM compared with.5 kg or none. Dry season supplementation increased FDMI and k[subscript]2, but had no effect on cell wall digestibility, FDMD, CPA and ADG during the rainy season. Data from this study suggest that.5 kg of CSM can increase FDMI, k2, and ADG of cattle during the dry season and that improvement can be maintained during the rainy season;These data and information from the literature were developed into a simulation model to estimate the energy and protein requirements for maintenance and to predict when feeding supplements to steers was economically beneficial. The simulation indicated that energy from FDMI seemed adequate for maintenance or moderate weight gain, while protein was deficient to meet maintenance requirement of grazing steers during the dry season. Consequently, protein or nitrogen supplementation was required to prevent weight loss. The model also indicated that cattle could respond to modest amounts of urea (50 to 60 g of urea daily) whenever forage CP was below 10%. The use of the lowest estimates of ADG by the metabolizable protein or the net energy system predicted when weight loss or gain of steers occurred.



Digital Repository @ Iowa State University,

Copyright Owner

Aboubakar Njoya



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117 pages