• Digestive physiology of steers grazing fertilized and non-fertilized blue grama rangeland

      Krysl, L. J.; Galyean, M. L.; Judkins, M. B.; Branine, M. E.; Estell, R. E. (Society for Range Management, 1987-11-01)
      Eight field trials [early August 1983 (EAUG83), late August 1983 (LAUG83), early November 1983 (ENOV83), early January 1984 (EJAN84), May 1984 (MAY84), late July 1984 (LJUL84), late August 1984 (LAUG84), late November 1984 (LNOV84)] were conducted on blue grama (Bouteloua gracilis) rangeland in southern rangeland in southern New Mexico to examine relationships among nitrogen (N) fertilization of forage, stage of plant growth, diet botanical and chemical composition, forage intake, digesta kinetics, and ruminal fermentation in beef steers. A fertilized pasture (45 kg N/ha) was evaluated during the year of and year after fertilizer application and compared with an adjacent nonfertilized pasture. Two esophageal- and 4 ruminally cannulated steers/pasture were used in a split-plot design. Dietary organic matter percentage was not affected by fertilization; however, fiber components increased as plants approached dormancy on both fertilized and nonfertilized rangeland. Dietary crude protein levels were numerically higher in the fertilized pasture within all trials. Fertilization had no consistent effect on rate or extent of in vitro organic matter digestibility. Fertilization increased (P<0.05) ruminal ammonia ( NH3) concentrations in all but one trial and levels were adequate for maximal microbial protein synthesis; however in the nonfertilized pasture, ruminal NH3 levels were potentially inadequate during periods of dormancy. Ruminal pH was numerically higher for steers on the fertilized pasture than for those on the unfertilized pasture each sampling trial except LNOV84. Fertilization had little effect (P>0.05) on total volatile fatty acid (VFA) concentration or molar proportion of individual acids. Total ruminal VFA concentration was highest in steers during periods of active plant growth. Voluntary organic matter intake was usually unaffected (P>0.05) by fertilization except in EJAN 84 when intake was higher (P<0.05) in the fertilized pasture and LNOV84 when intake was higher (P<0.05) for steers grazing the nonfertilized pasture. Organic matter intake by steers averaged 21.8 g/kg body weight (BW) and 21.6 g/kg BW across the 8 trials for fertilized and nonfertilized pastures, respectively. Intake in both pastures declined with advancing season. Particulate passage rate (PPR) was not different between treatments (P>0.05) during ENOV83, MAY84 and LNOV84. However, PPR was faster (P<0.05) for steers grazing the fertilized than in the nonfertilized pasture during the remaining 5 sampling periods. Correspondingly, retention time of digesta in the gastrointestinal tract was reduced for steers grazing the fertilized pasture during these 5 trials. Estimated gastrointestinal fill was unaffected (P>0.05) by treatment except during the EAUG83 and LAUG84 trials when steers grazing fertilized pasture had reduced (P<0.05) fill compared with steers grazing nonfertilized pasture. Fluid passage rate (FPR) did not differ (P>0.05) between treatments for any trials except in LAUG84 when steers in the fertilized pasture had a lower (P<0.05) FPR than steers in the nonfertilized pasture.
    • Seasonal diets of herded sheep grazing Douglas-fir plantations

      Leininger, W. C.; Sharrow, S. H. (Society for Range Management, 1987-11-01)
      Use of livestock for biological weed control in timber plantations is gaining popularity in the United States and elsewhere. Efficient use of livestock to control unwanted brush relies upon knowledge of livestock feeding habits. A study was conducted during 1981 and 1982 to determine seasonal diets of herded sheep grazing cutover Douglas-fir (Pseudotsuga menziesii) forests in the Coast Range of Oregon. Study sites included both 4- to 6-year-old non-grass-seeded and 2-year-old grass-seeded plantations. Sheep grazing was monitored in spring, summer, and late summer. Forage on offer ranged from 764 to 2,459 kg/ha. Vegetational composition of sheep diets varied by year, season, and plantation age class. Averaged over the 2 years of grazing, graminoids and forbs were nearly equal, at approximately 40% each, in sheep diets in older plantations. In contrast, diets of sheep in young grass-seeded plantations averaged 70% graminoids and only 16% forbs. Ferns were a minor component (<2%) of sheep diets in both plantation age classes. Browse averaged 15 and 12% of sheep diets in old and young plantations, respectively. Douglas-fir was most palatable to sheep in spring soon after bud break. It was generally avoided, however, and never comprised more than 3% of sheep diets. Our data suggest that sheep can be most effectively used for biological control of unwanted brush species during summer and late summer when differences in relative preference indices for target brush species and Douglas-fir are greatest.