Bennett L L, Hammond A C, Williams M J, Chase C C, Kunkle W E
University of Florida, Gainesville 32611-0910, USA.
J Anim Sci. 1999 Aug;77(8):2252-8. doi: 10.2527/1999.7782252x.
Two methods of determining diet botanical composition, microhistological (MH), and stable carbon isotope ratio (CR) analyses were used to determine botanical composition of ingesta and fecal grab samples in steers grazing rhizoma peanut-mixed tropical grass pastures. Three pastures were used over two grazing seasons, 1992 and 1993, in Brooksville, FL. A weighted-disc double-sampling technique was used to determine forage mass and botanical composition, percentage of rhizoma peanut (Arachis glabrata), grass (Paspalum notatum and Cynodon dactlyon), and forb (primarily Chenopodium ambrosioides) on offer every 28 d throughout the grazing seasons. There was an effect of sampling date (P<.001), sampling date x pasture (P<.001), and sampling date x year (P<.001) on forage mass on offer. There was a pasture x year x sampling date interaction (P<.001) for all botanical components. In 1992 and 1993, using cannulated steers sampled every 56 d, there were interactions with year for rhizoma peanut and forb (P<.05), but not for grass with MH analysis (components: rhizoma peanut, grass, and forb). Ingesta and fecal rhizoma peanut (r = .73 and .92 for 1992 and 1993, respectively) and ingesta and fecal forb (r = .86 and .98 for 1992 and 1993, respectively) were positively correlated (P<.001). Ingesta and fecal grass were positively correlated (r = .52, P<.001), but the correlation was not as high. With the CR analysis (components: Calvin cycle [C3] plants and C4-dicarboxylic acid pathway [C4] plants), ingesta and corrected fecal (corrected for in vitro organic matter digestibility [IVOMD]) C3 plants were positively correlated (r = .62; P<.001). Diet composition of fecal grab samples from noncannulated steers, collected on the same sampling schedule as for hand-clipped pasture samples, differed at times due to the complexity of the sward (both rhizoma peanut and forb constituted a single component, C3, in the CR analysis). Based on these results, if there is a substantial contribution of forb to the diet, fecal microhistological analysis may be more informative than fecal carbon ratio analysis for estimating diet selection by cattle grazing tropical pastures.
采用两种确定日粮植物组成的方法，即微观组织学（MH）分析和稳定碳同位素比率（CR）分析，来测定放牧于花生根茎 - 热带混合草场上的阉牛摄入物和粪便抓取样本的植物组成。在佛罗里达州布鲁克斯维尔，于1992年和1993年的两个放牧季节使用了三块牧场。采用加权圆盘双抽样技术来测定牧草质量和植物组成，即在整个放牧季节每28天测定一次提供的花生根茎（光叶花生）、草（巴哈雀稗和狗牙根）以及阔叶杂草（主要是土荆芥）的百分比。提供的牧草质量受到采样日期（P<0.001）、采样日期×牧场（P<0.001）和采样日期×年份（P<0.001）的影响。所有植物成分存在牧场×年份×采样日期的交互作用（P<0.001）。在1992年和1993年，使用每56天采样一次的瘘管阉牛，花生根茎和阔叶杂草与年份存在交互作用（P<0.05），但对于MH分析中的草而言不存在这种交互作用（成分：花生根茎、草和阔叶杂草）。摄入物与粪便中的花生根茎（1992年和1993年分别为r = 0.73和0.92）以及摄入物与粪便中的阔叶杂草（1992年和1993年分别为r = 0.86和0.98）呈正相关（P<0.001）。摄入物与粪便中的草呈正相关（r = 0.52，P<0.001），但相关性没那么高。对于CR分析（成分：卡尔文循环[C3]植物和C4 - 二羧酸途径[C4]植物），摄入物与校正后的粪便（校正体外有机物消化率[IVOMD]）中的C3植物呈正相关（r = 0.62；P<0.001）。按照与手工剪取的牧场样本相同的采样计划收集的非瘘管阉牛粪便抓取样本的日粮组成，有时会因草皮的复杂性而有所不同（在CR分析中，花生根茎和阔叶杂草均构成单一成分C3）。基于这些结果，如果阔叶杂草在日粮中占很大比例，那么对于估计放牧热带牧场的牛的日粮选择，粪便微观组织学分析可能比粪便碳比率分析提供更多信息。
