• Contrasts of esophageal-fistula versus bite-count techniques to determine cattle diets

      Ortega, I. M.; Bryant, F. C.; Drawe, D. L. (Society for Range Management, 1995-11-01)
      To understand how different techniques might affect diet estimates for cattle, the esophageal-fistula and bite-count techniques were compared using trained cattle. For the Texas Coastal Bend, bite-count was not as reliable a technique as the esophageal fistula. These techniques differed in estimation of forage classes and plant species in cattle diets. The esophageal-fistula technique was more accurate however, the bite-count technique may be acceptable if analyses are limited to only those plant species making up >2% of the diet.
    • Ecosystem changes associated with grazing intensity on the Punta Ninfas rangelands of Patagonia, Argentina

      Beeskow, A. M.; Ellisalde, N. O.; Rostagno, C. M. (Society for Range Management, 1995-11-01)
      Changes in the vegetation and soil surface were assessed along a grazing intensity gradient on rangelands of the Punta Ninfas area in southern Argentina. Thirty-two transects were sampled in areas with different grazing intensity. Bray-Curtis polar ordination and simple correlation were used to display changes in community composition and measure association between different community attributes. The first axis expressed the changes in species composition along a gradient of grazing intensity. The extremes of the gradient were represented by shrub and grass steppes. Shrub steppes dominated in heavily grazed areas close to permanent water points, while grass steppes dominated in lightly grazed areas in the extremes of the paddocks. A significant negative relation (r = -0.81, P<0.05) between grass and shrub cover suggested that grasses decreased as shrub increased. Flechilla (Stipa tenuis Phil.) and fiechilla negra [Piptochaefirrm napostaense Speg.) Hackel ap Stuckert.] were the main decreaser grasses while quilembai (Chuquiruga avellanedue Cav.) was the main shrub invading the grass steppes. Uneroded soil surface conditions decreased, and the size and frequency of crusted and desert pavement areas and mounds increased with shrub cover. Three states or stages of range degradation were identified along the gradient of grazing intensity. Grass steppe represented the most desirable state in term of livestock production and soil stability, while shrub steppe represented the most degraded and least productive state.
    • Genetic aspects of diet selection in the Chihuahuan desert

      Winder, J. A.; Walker, D. A.; Bailey, C. C. (Society for Range Management, 1995-11-01)
      Fecal microhistology and chemistry were used to evaluate botanical composition and quality of diets selected by Brangus cattle grazing Chihuahuan desert range in 3 seasons; fall: October, 1991; winter: January, 1992; and summer: July, 1992. Fecal samples were collected from 100 head in fall (58 2-8 year cows and 42 calves), 53 head (2-8 year-old cows) in winter, and 44 head (2-8 year-old cows) in summer. Paternal half sib analyses were used to estimate genetic and phenotypic variances and heritability estimates. Heritability is the proportion of total (phenotypic) variation which is due to additive genetic effects. The effect of sire within age was observed for percentage of Aristida spp. (P= 0.01), Sporobolus spp. (P= 0.09), total grasses (P = 0.02), Croton pottsii (Klotzsch) Muell.-Arg. (P= 0.03), and total forbs (P =0.02) in fall diets. The number of grass species in diets was also affected by sire (P=0.03). Heritability estimates were 0.87, 0.51, 0.78, 0.76, and 0.79 for percentages of Aristida spp., Sporobolus spp., total grasses, Croton pottsii, and total forbs, respectively. Heritability estimates for number of grass and forb species in fall diets were 0.68 and 0.26, respectively. Heritability estimates for winter samples were 0.40, 0.00, 0.37, and 0.27 for percentages of Sporobolus spp., total grasses, Yucca elata Engelm., and total shrubs, respectively. Heritability estimates for the number of grass and total species observed in winter diets were 1.11 and 0.47, respectively. Heritability estimates for percentages of Bouteloua spp., total grasses, Croton pottsii, Dalea spp., and total forbs in summer samples were 0.20, 0.55, 0.58, and 0.46, respectively. Heritability estimates for the number of grass and total species in summer diets were 0.49 and 0.79, respectively. These data suggest that genetic composition of beef cattle may affect diet selection under Chihuahuan desert conditions.
    • Plant response to soils, site preparation, and initial pine planting density

      Pearson, H. A.; Wolters, G. L.; Thill, R. E.; Martin, A.; Baldwin, V. C. (Society for Range Management, 1995-11-01)
      This study described the effects of soils, site preparation, and initial pine regeneration spacings on tree growth and the associated understory woody and herbaceous plant succession. Although Sawyer soils appeared more productive than Ruston soils before the harvest and regeneration treatments, woody and herbaceous plant differences were not apparent between the soils after regeneration. During the first 3 years after treatment, the mechanical site preparation method (shear-windrow-burn) reduced woody plant heights more than the underplant-release method; however, these height differences disappeared by the 6th year of post-treatment. Woody plant densities decreased initially, increased by the 6th year after treatment, and decreased to pretreatment levels by the 10th year. Herbage yields increased significantly after site preparation and pine regeneration through the 3rd year, decreased by the 6th year, and declined to levels below pretreatment by the 10th year. initial pine planting densities did not significantly influence the understory herbage yields during the first 10 years as a result of the confounding effects of the other woody plant growth.
    • Relative abundance and diet composition of Chacoan cavies in relation to range condition

      Rosati, V. R.; Bucher, E. H. (Society for Range Management, 1995-11-01)
      The relative abundance and dietary botanical composition of the Chacoan cavy (Pediolagus salinicola) was studied on sites of very good, good, and poor range condition in the Western Chaco, Argentina. Pellet count data showed that Chacoan cavy densities varied (P<0.001) among these areas. In both seasons, the highest number of pellets was found in the area of poor condition. This area was characterized by an absence of grasses, dense cover of a creeping fern (Selaginella sellowii), thorny shrubs and a scarcity of dicot herbs. In contrast, a decrease (P<0.05) in Chacoan cavy densities was found in the good and very good range condition areas, coincident with the increase of grass and forb cover. Fecal analysis showed that Chacoan cavy diets were greatly influenced by the amount of forage available, which varied according to the condition of the rangeland. Forbs were the main forage class consumed in all range conditions, but the species composition differed among condition classes. For example, several species of dicot forbs were consumed in areas of very good and good range condition, but Selaginella sellowii was the main dietary forb when the range condition was poor. We concluded that range condition affected the relative abundance and diet of Chacoan cavies of Western Chaco, Argentina. High Chacoan cavy density should be considered as an indicator of vegetation depletion caused by other factors rather than a primary cause of savanna degradation.