Immunoglobulin G1 concentration (IgG1) was measured in presuckle colostrum and calf serum obtained at 36 h and at weaning from inbred and straightbred Angus, Brangus, Hereford, Red Angus and Simmental cattle. Sources of variation considered as dam traits examined for IgG1 in colostrum and 36-h calf serum included line of sire, sire within line, age, and linear regression of IgG1 on inbreeding of dam. Only line of sire and inbreeding of dam were significant in the analysis of 36-h calf serum. Sources of variation considered as calf traits examined for IgG1 in calf serum at 36 h and at weaning included line of sire, sire within line, sex of calf, age of dam, and regressions of calf serum IgG1 on inbreeding of the calf and on dam's colostral IgG1. Only sire within line and the regression on dam's colostral IgG1 were significant for calf serum IgG1 at 36 h. Large differences existed in 36-h calf serum IgG1 between sires both within lines and when lines were ignored. Calves with 36-h serum IgG1 of less than 10 mg/ml were two to four times more likely to die before weaning than calves with higher IgG1 levels. The heritability estimates of IgG1 by paternal half-sib analysis were .41 +/- .30 for colostrum measured as a trait of the dam and .56 +/- .25 for 36-h. calf serum and .05 +/- .17 for calf serum at weaning considered as a trait of the calf. These estimates indicate that IgG1 in colostrum and 36-h calf serum could be increased by selection.(ABSTRACT TRUNCATED AT 250 WORDS)

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The chemical composition and dry matter digestibility of clipped plant species, total herbage, and actual and simulated cattle diets were studied on sandhill grassland in eastern Colorado during the growing season and after dormancy. Clipped plants declined in percent protein and digestibility and increased in other chemical components with advanced maturity. Marked differences in chemical composition were evident among species in early summer, but minimal by winter. Actual cattle diets and those simulated from hand clipped plants were similar in chemical and digestible dry matter composition during each sampling period. In early summer, cattle diets were considerably higher in quality than total herbage but this difference became progressively smaller later in the summer. During dormancy and after weathering chemical composition and dry matter digestibility of herbage and of the cattle diets were essentially the samk. Cattle grazing native grasslands select their diet from plants which are continually changing in chemical composition and digestibility. Because cattle prefer leaf tissue over stem tissue, young growth over old growth, and green material over dry material, their diet is generally higher in quality than total herbage available. In the present study, seasonal changes in chemical and botanical composition and changes in nylon bag dry matter digestibility of total herbage and of actual and simulated diets of cattle grazing sandhill grassland were determined. Chemical and digestibility changes which occurred in major forage species through the year were also studied. This paper is a part of a broad study in grassland nutrition; l A contribution from W-94 Regional Project on Range Livestock Nutrition. Scientific Series Paper No. 1632, Colorado Agricultural Experiment Station, Fort Collins. We thank D. N. Hyder, R. M. Hansen and G. M. Van Dyne for their suggestions in this research and K. L. Knox, C. L. Streeter and R. E. Bement for their constructive reviews of the manuscript.

Yearlong total confinement and partial confinement feeding were compared to conventional range grazing to determine the cultural and digestible energy expended to produce a kilocalorie of dressed-carcass meat from weaner calves and the protein consumed to produce a pound of red-meat protein. The range groups required the least amount of cultural energy to produce a kilocalorie of meat and the total confined groups required the most. The total confined system on a low level of nutrition, where calves were weaned early, converted digestible energy most efficiently but converted digestible protein least efficiently, whereas range groups converted digestible energy least efficiently and digestible protein most efficiently.

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