VALIDATING LABORATORY TECHNIQUES THAT INFLUENCE ESTIMATES OF INTAKE AND PERFORMANCE IN BEEF CATTLE

Two experiments were conducted to evaluate effects of inoculum source on in vitro and in situ digestion procedures performed on grass hay and corn residue samples. Steers were fed 70% brome or 70% corn residue. Inoculum from each steer was used to perform in vitro procedures to determine IVDMD, organic matter digestibility (OMD), and neutral detergent fiber (NDF) digestibility and for in situ procedures to determine NDF digestibility. There were no interactions for inoculum source and IVDMD, OMD, or NDF digestibility. Three cattle digestion studies were used to evaluate the relationship between TDN and digested OM (DIGOM). Total tract collection and OM analysis of feed and feces were used to determine digested OM. Gross energy of feed and feces was determined using bomb calorimetry and used to calculate TDN. The difference between TDN and DIGOM was least (3.58 percentage units) for traditional corn diets. However, the difference between TDN and DIGOM was greater (9.96 percentage units) for diets containing wet distillers grains. n-Alkanes and long-chain alcohols were used as markers to delineate the parts of the corn plant and, separately, 8 western rangeland grasses and legumes. The corn plant parts were easily delineated with over 98% of the variation between variables described within a 2-dimensional plane with visible separation. The PCA for the 8 species of the western rangeland had less distinctive separation with only 90.5 or 93.2% of the differences described 2-dimensionally, depending on the growth stage. Plant waxes were utilized to predict dietary intake of 26 heifers that were individually fed a ration of 70% corn silage and 30% alfalfa with a daily dose of an internal marker. Predicted values of intake overestimated actual intakes, but improved if the diet was assumed to be a total mixed ration. A sensitivity test was conducted to examine the effects of incomplete dose consumption. Predictions were improved when accounting for losses in the amount of internal marker eaten, which likely occurred in practice. Advisor: James C. MacDonal

VALIDATING LABORATORY TECHNIQUES THAT INFLUENCE ESTIMATES OF INTAKE AND PERFORMANCE IN BEEF CATTLE

Two experiments were conducted to evaluate effects of inoculum source on in vitro and in situ digestion procedures performed on grass hay and corn residue samples. Steers were fed 70% brome or 70% corn residue. Inoculum from each steer was used to perform in vitro procedures to determine IVDMD, organic matter digestibility (OMD), and neutral detergent fiber (NDF) digestibility and for in situ procedures to determine NDF digestibility. There were no interactions for inoculum source and IVDMD, OMD, or NDF digestibility. Three cattle digestion studies were used to evaluate the relationship between TDN and digested OM (DIGOM). Total tract collection and OM analysis of feed and feces were used to determine digested OM. Gross energy of feed and feces was determined using bomb calorimetry and used to calculate TDN. The difference between TDN and DIGOM was least (3.58 percentage units) for traditional corn diets. However, the difference between TDN and DIGOM was greater (9.96 percentage units) for diets containing wet distillers grains. n-Alkanes and long-chain alcohols were used as markers to delineate the parts of the corn plant and, separately, 8 western rangeland grasses and legumes. The corn plant parts were easily delineated with over 98% of the variation between variables described within a 2-dimensional plane with visible separation. The PCA for the 8 species of the western rangeland had less distinctive separation with only 90.5 or 93.2% of the differences described 2-dimensionally, depending on the growth stage. Plant waxes were utilized to predict dietary intake of 26 heifers that were individually fed a ration of 70% corn silage and 30% alfalfa with a daily dose of an internal marker. Predicted values of intake overestimated actual intakes, but improved if the diet was assumed to be a total mixed ration. A sensitivity test was conducted to examine the effects of incomplete dose consumption. Predictions were improved when accounting for losses in the amount of internal marker eaten, which likely occurred in practice. Advisor: James C. MacDonal

Delineating Complex Forage Mixtures Using Plant-Wax Markers

Plant waxes provide a marker profile of individual plants that, when sufficiently distinct, can be used to estimate the diet composition of grazing cattle. They also may provide a tool for reliably predicting feed intake. The traditional method (nonnegative least squares) to use these markers to predict diet composition has limitations. A newer statistical approach (Bayesian linear unmixing) deemed more efficient was tested with simulation. Samples from 8 forage species in Nebraska were analyzed for their plant- wax marker contents. Those concentrations were used to simulate 1000 diets for 4 mixtures containing 2, 3, 5 or 8 plants. The efficiency of the two methods to predict diet composition was compared. The newer approach outperformed the traditional one in all of the mixtures considered. However, predictions were considerably worse when the number of plants in the mixture was 5 or 8. When forage mixtures are complex, additional steps will be needed to predict diet composition, and thereby feed intake, in grazing cattle

Effects of Isolated Nutrients in Distillers Grains on Total Tract Digestibility and Digestible Energy in Forage Diets

A digestion study was conducted to evaluate the contribution of individual nutrient components of distillers grains on nutrient digestibility and digestible energy. All diets contained 56% brome hay with a control diet containing either 40% corn; or 40% modified distillers grains. Four additional diets compared the contribution of fat, protein, fiber, and solubles components of distillers grains. No differences were observed for digestibility of DM, OM, and NDF among treatments. Feeding the isolated protein resulted in similar digestible energy to modified distillers grains, suggesting the bypass protein component contributes heavily to energy in distillers

Evaluation of Plant- waxes to Estimate Forage Intake in Grazing Cattle

Although key to the efficiency of a cattle operation, feed intake is challenging to evaluate in a grazing setting. However, even within forage- based systems, plant- wax markers may be used to predict dietary choices and feed intake. Plant- waxes are a complex mixture of lipids found on the surface of plants. When sufficiently unique among plants, the composition of diets can be determined from the pattern of these compounds in the forages ingested. These markers were used to delineate the parts of the corn plant and, separately, 8 western rangeland grasses and legumes. Using plant waxes, the components of the corn plant were clearly distinguished. Th is technique therefore could be useful in a monoculture, such as a corn residue field, to determine the plant parts predominating in the diet. Delineating plants in a complex sward was more difficult, particularly among like species. Th e use of more markers may help to more explicitly distinguish plants within diverse pastures, such as western rangelands

Effects of Brown Midrib Corn Silage Hybrids with or without Kernel Processing at Harvest on Nutrient Metabolism in Beef Steers

A 2 × 3 factorial digestion study evaluated three corn silage hybrids and kernel processing for finishing steers. The three hybrids included a control corn silage, a brown midrib, and a brown midrib with a softer endosperm. Both brown midrib hybrids had greater fiber digestibility than the traditional control corn silage hybrid. No differences were observed between brown midrib hybrids for all other nutrients. Cattle fed brown midrib hybrids had a lower average ruminal pH compared to the control suggesting more fermentation, but no differences in volatile fatty acid concentration or proportions. Kernel processing had no effect on apparent total tract nutrient digestibility for any nutrients measured in this study. Kernel processing did not impact any ruminal characteristics or metabolism by beef steers. In finishing diets including elevated levels of corn silage, brown midrib corn silage hybrids allow for improved fiber digestibility and more energy available to the animal for improved growth performance over cattle fed control corn silages. Kernel processing did not appear to affect any ruminal fermentation and digestibility parameters, despite an observed improvement in feed efficiency in a similar finishing trial

Evaluation of the Energy Value and Nutrient Digestibility of Distillers Grains That Have Undergone a Fiber Separation Process in Finishing Diets

A digestion study was conducted to determine the effects of feeding a new, high protein distillers grains and corn bran plus solubles on nutrient digestibility. Treatments included a corn-based control, high protein distillers at both 20% and 40%, corn bran plus solubles, traditional wet distillers grains and traditional dry distillers grains all at 40% of diet DM. Feeding high protein distillers grains or corn bran plus solubles resulted in decreased digestibility compared to corn or traditional wet and dry distillers grains, but increased energy intake. Traditional wet and dry distillers grains also resulted in decreased digestibilities while energy intake was increased. Volatile fatty acid profiles and pH parameters were not different across treatments. Overall, nutrient digestibility for high protein distillers grains and corn bran plus solubles is similar to traditional wet or dry distillers grains

Impact of Corn Silage Inclusion on Nutrient Digestion and Rumen Fermentation in Finishing Cattle

A digestion study was conducted comparing different inclusions of corn silage used as a roughage source on digestibility, feeding behavior and rumen environment. Treatments consisted of 3 inclusions of corn silage at 0, 7.5 and 15% of the diet DM, and a control treatment with 7.5% alfalfa. As expected, increasing available energy and decreasing roughage (either silage or alfalfa) showed an increase in diet digestibility and ruminal propionate concentrations. However, average ruminal pH was least, with more time spent in subacute acidosis (pH \u3c 5.3) when cattle were fed no roughage. These data suggest that feeding cattle increasing silage inclusions as a roughage source prevented ruminal conditions from entering and remaining in subacute acidosis. Feeding corn silage at 15% gave similar digestibility responses compared to 7.5% alfalfa. Including silage as a roughage source at 15% could help prevent acidosis and digestive upset in feedlot cattle

Relationship between Dietary Total Digestible Nutrients and Digestible Organic Matter in Beef Cattle Finishing and Growing Diets With or Without Distillers Grains

The relationship between organic matter digestibility and total digestible nutrients is unestablished for diets containing distillers grains. Three cattle digestion studies were used to evaluate the relationship between total digestible nutrients and digestible organic matter. Results suggest digestible organic matter is consistent relative to total digestible nutrients content for traditional, corn based diets. In finishing and growing diets containing distillers grains additional digestible energy supplied by distillers grains is not accounted for when evaluating only digestible organic matter. Measuring digestible energy content of diets used in digestion trials is essential

Effect of binary collisions on electron acceleration in magnetic reconnection

Context. The presence of energetic X-ray sources in the solar corona indicates there are additional transport effects in the acceleration region. A prime method of investigation is to add collisions into models of particle behaviour at the reconnection region.<p></p> Aims. We investigate electron test particle acceleration in a simple model of an X-type reconnection region. In particular, we explore the possibility that collisions will cause electrons to re-enter the acceleration more frequently, in turn causing particles to be accelerated to high energies.<p></p> Methods. The deterministic (Lorentz) description of particle gyration and acceleration has been coupled to a model for the effects of collisions. The resulting equations are solved numerically using Honeycutt’s extension of the RK4 method to stochastic differential equations. This approach ensures a correct description of collisional energy loss and pitch-angle scattering combined with a sufficiently precise description of gyro-motion and acceleration.<p></p> Results. Even with initially mono-energetic electrons, the competition between collisions and acceleration results in a distribution of electron energies. When realistic model parameters are used, electrons achieve X-ray energies. A possible model for coronal hard X-ray sources is indicated. Conclusions. Even in competition with energy losses, pitch-angle scattering results in a small proportion of electrons reaching higher energies than they would in a collisionless situation.<p></p&gt