Graduate College of Texas-Msc Thesis-Fecal Nitrogen as an Indicator of Nutritional Stressing Steers

Abstract

The study was conducted in Kenya to determine the relationship of fecal nitrogen, fecal nitrogen fractions and fecal nitrogen ratio to organic matter intake, dietary crude protein, in vivo dry matter digestibility and vitro organic matter digestibility. Two sites were chosen for the study based upon bush cover. One site had higher bush cover than the other, 70% and 30%, respectively. Ten hectares in each -bush type were divided into two five hectare paddocks. One paddock was strategically grazed to create low forage availability level (<400 kg/ha) while the other paddock was left ungrazed (>800 kg/ha). Sixteen steers divided into two groups of 8 steers were used to collect fecal samples from the paddocks. Four fistulated steers were used to sample the forage available to the experimental steers. Samples were collected during the dry season and just after the rains. Fecal and diet samples were analyzed for total nitrogen and bound nitrogen (NDFN). Nitrogen fractions and ratios were calculated. Diet samples were further analyzed for in vitro and in vivo digestibility, and fecal samples were analyzed for condensed tannins and the percentages of monocot and dicot fragments. Simple and multiple regressions were developed to test for predictive relationships between fecal and dietary parameters. Percent fecal insoluble nitrogen was the most important single variable in estimating dietary crude protein and organic matter intake. Dietary crude protein (%) was predicted with the following equation: y = 1.79'+ 8.37 (fecal insoluble nitrogen) R2 = 0.88. Organic matter intake (kg) was predicted with the following equation: y = 1l.07 + 6.24 (soluble/total nitrogen) - 0.12 (tannin) - 0.05 (cell wall) R2 = 0.81. Percent fecal soluble nitrogen was the single most important variable in estimating digestibility. Dietary in vitro organic matter digestibility and organic matter digestibility were estimated by the following equations: y = 53.94 + 13.09 (soluble nitrogen) + 0.06 (monocot fragments) and y = 53.75 + 2.79 (soluble/insoluble nitrogen) + 1.58 (monocot/dicot) with R2 of 0.33 and 0.53, respectively.