Effects of protein content and rumen-undegradable to rumen-degradable protein ratio in finely ground calf starters on growth performance, ruminal and blood parameters, and urinary purine derivatives

There is a need to standardize the NDF procedure. Procedures have varied because of the use of different amylases in attempts to remove starch interference. The original Bacillus subtilis enzyme Type IIIA (XIA) no longer is available and has been replaced by a less effective enzyme. For fiber work, a new enzyme has received AOAC approval and is rapidly displacing other amylases in analytical work. This enzyme is available from Sigma (Number A3306; Sigma Chemical Co., St. Louis, MO). The original publications for NDF and ADF (43, 53) and the Agricultural Handbook 379 (14) are obsolete and of historical interest only. Up to date procedures should be followed. Triethylene glycol has replaced 2-ethoxyethanol because of reported toxicity. Considerable development in regard to fiber methods has occurred over the past 5 yr because of a redefinition of dietary fiber for man and monogastric animals that includes lignin and all polysaccharides resistant to mammalian digestive enzymes. In addition to NDF, new improved methods for total dietary fiber and nonstarch polysaccharides including pectin and beta-glucans now are available. The latter are also of interest in rumen fermentation. Unlike starch, their fermentations are like that of cellulose but faster and yield no lactic acid. Physical and biological properties of carbohydrate fractions are more important than their intrinsic composition.

Catalyzed phenol-hypochlorite and ninhydrin colorimetric procedures were adapted to the Technicon AutoAnalyzer for simultaneous determination of ammonia and total amino acids in ruminal fluid or ruminal in vitro media. The manifold developed was compatible with a sampling rate of 40/h without significant sample-to-sample carryover. With proper storage, reagents for both the phenol-hypochlorite and the air-stable ninhydrin systems were stable for 8 mo or more. Response of individual amino acids in the phenol-hypochlorite system were generally 1% or less than equimolar amounts of ammonia. Certain amino acids inhibited ammonia color yield 10 to 15% when with equimolar amounts of ammonia; however, the inhibitory effect of casein amino acids was only 2 to 3%. Although ninhydrin response, relative to leucine, of individual alpha-amino acids ranged from 62 (valine) to 151% (histidine), recoveries of casein amino acids from ruminal fluid had coefficients of variation of 1% or less. Coefficients of variation for ammonia recoveries from ruminal fluid by the phenol-hypochlorite procedure were about half of those for the Conway microdiffusion technique. Intraclass correlations for the adapted procedures indicated high degrees of accuracy and precision for both ammonia and amino acid analyses.

Ruminal acidosis continues to be a common ruminal digestive disorder in beef cattle and can lead to marked reductions in cattle performance. Ruminal acidosis or increased accumulation of organic acids in the rumen reflects imbalance between microbial production, microbial utilization, and ruminal absorption of organic acids. The severity of acidosis, generally related to the amount, frequency, and duration of grain feeding, varies from acute acidosis due to lactic acid accumulation, to subacute acidosis due to accumulation of volatile fatty acids in the rumen. Ruminal microbial changes associated with acidosis are reflective of increased availability of fermentable substrates and subsequent accumulation of organic acids. Microbial changes in the rumen associated with acute acidosis have been well documented. Microbial changes in subacute acidosis resemble those observed during adaptation to grain feeding and have not been well documented. The decrease in ciliated protozoal population is a common feature of both forms of acidosis and may be a good microbial indicator of an acidotic rumen. Other microbial factors, such as endotoxin and histamine, are thought to contribute to the systemic effects of acidosis. Various models have been developed to assess the effects of variation in feed intake, dietary roughage amount and source, dietary grain amount and processing, step-up regimen, dietary addition of fibrous byproducts, and feed additives. Models have been developed to study effects of management considerations on acidosis in cattle previously adapted to grain-based diets. Although these models have provided useful information related to ruminal acidosis, many are inadequate for detecting responses to treatment due to inadequate replication, low feed intakes by the experimental cattle that can limit the expression of acidosis, and the feeding of cattle individually, which reduces experimental variation but limits the ability of researchers to extrapolate the data to cattle performing at industry standards. Optimal model systems for assessing effects of various management and nutritional strategies on ruminal acidosis will require technologies that allow feed intake patterns, ruminal conditions, and animal health and performance to be measured simultaneously in a large number of cattle managed under conditions similar to commercial feed yards. Such data could provide valuable insight into the true extent to which acidosis affects cattle performance.