Browsing Journal of Range Management, Volume 40, Number 6 (November 1987) by Subjects
Now showing items 1-2 of 2
Digestive physiology of steers grazing fertilized and non-fertilized blue grama rangelandEight 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.
Evaluation of a single probe capacitance meter for estimating herbage yieldA single probe electronic capacitance meter for estimating herbage yields was field tested on 2 western wheatgrass (Pascopyrum smithii (Rydb.) Löve), a blue grama (Bouteloua gracilis (H.B.K.) Lag. ex Griffiths), crested wheatgrass (Agropyron cristatum (L.) Gaertn.), and Russian wildrye (Psathrostachys juncea (Fisch.) Nevski) stands in the Northern Great Plains. This single probe meter is lightweight, portable, and allows the user to estimate yields of single plants to determine productivity of individual species. Linear regression equations were fitted between probe readings and the green and dry weight of forage clipped from individual plants within a $78.5-cm2 circular plot. An overall coefficient of determination (r2) of 0.50 was obtained with linear relationships being statistically significant between the probe readings and green and dry weight of forage for all regressions (P=0.10). Considering the regression estimates for r2, standard error of the estimate and F values, the best model fit occurred in the western wheatgrass and crested wheatgrass stands. Presence of a litter mat in 1 western wheatgrass stand had little influence on the precision of the instrument, but phenology of the plants strongly influenced meter readings. Therefore, regression lines within a species could not be pooled across all sampling dates. Comparing yields of individual species from the small plots of the single probe meter to yields from a larger, $1,858-cm2 rectangular plot estimated with a multi-probe capacitance meter showed comparisons were not statistically different 50% of the time. A sample size of approximately 150 plots per species was required for each sample period for the single probe meter.