Samples of sawdust from poplar, alder and Douglas fir, were ground past screens ranging in size from 2.21 mm to 0.25 mm (60 mesh). A reduction in particle size significantly increased the in vitro rumen digestibility of poplar, but had little effect on the digestibility of alder or fir. The above woods, plus sludge (a by-product of the pulping process) were treated with NaOH solutions of 2, 4 and 6%. These solutions were used at three treatment periods of 0.5, 1.0 and 1.5 hours, and all treatments were carried out at 1.05 kg/sq cm and 121° C. NaOH treatment significantly increased the in vitro cellulose digestibility of all woods except fir. The optimum treatment conditions for increasing the in vitro cellulose digestibility of all woods were 4% NaOH at the 1.5 hour treatment period, except in the case of alder which was most digestible when treated with 2% NaOH for 1.5 hours. Gamma irradiation increased the in vitro cellulose digestibility of all woods. Alder and fir were most digestible when treated with 2 x 10⁸ rads, but poplar and sludge reached their peak digestibility when exposed to 1 x 10⁸ rads. Irradiation was found to decrease the cellulose and acid detergent fibre (ADF) content of all the woods studied. Acid detergent lignin (ADL) also decreased in response to irradiation in all woods except sludge. Irradiation had no effect on the ash content of any of the samples. Three methods of cellulose analysis were used on both untreated and irradiated wood, and there was a significant difference shown among the methods. The lowest values were obtained using Van Soests' KMnO₄ method, next were the results from Van Soests' 72% Hg₂SO₄ method, and the highest values were obtained using the Crampton and Maynard procedure for cellulose. Two lignin methods were also compared and it was found that the KMnO₄ lignin values were significantly higher than those obtained using the 72% H₂S0₄ method for lignin. / Land and Food Systems, Faculty of / Graduate

Precision livestock farming is gaining popularity in both the research and production setting. Despite this, current technologies are limited in the ability to explore the rumen environment. The overall goal of this work was to explore sensing technologies that could enable shifts in management to maximize productivity in ruminant production systems. In the first study, we assessed the use of existing sensor technologies to monitor ruminal volatile fatty acid (VFA) concentrations using pH sensing. Four ruminally cannulated Holstein cows at maintenance were included in a Latin Square Design. Treatments consisted of a) chopped grass hay, b) 85% chopped grass hay and 15% cracked corn and soybean meal, c) 70% chopped grass hay and 30% cracked corn and soybean meal, and d) 55% chopped grass hay and 45% cracked corn and soybean meal. Prior to receiving treatment diets, cows were individually housed and underwent a fasting period of up to 24 hours. During each period, cows were allowed access to treatment diets from 0600 to 0800 hours, and rumen fluid samples were collected hourly for twelve hours beginning at feed delivery. A bench pH meter was used to obtain rumen fluid pH levels at sampling times. Concentrations of individual VFA and branch-chain VFA were analyzed statistically using two linear mixed effects models. In one model type, VFA were estimated through fixed effects terms for treatment, time, and the treatment by time interaction. For comparison, the other model estimated VFA concentrations using linear and quadratic effects for the sensed pH data. Both models leveraged random effects for animal and period. Models utilizing diet data and time showed better performance in estimating VFA concentrations compared to models leveraging pH data, indicating minimal predictive capacity was identified for the pH sensing. The second study explored opportunities to track ruminal VFA concentrations based on aqueous sensing of ruminal CO2, temperature, and conductivity across four diets differing in energy and protein supply. Four ruminally cannulated Holstein cows at maintenance were included in a Latin Square Design. Treatments consisted of a) chopped grass hay (9.07 kg), b) chopped grass hay (9.07 kg) plus cracked corn (4.08 kg), c) chopped grass hay (9.07 kg) plus soybean meal (2.13 kg), and d) chopped grass hay (9.07 kg) plus corn (2.38 kg) and soybean meal (0.83 kg). Prior to receiving treatment diets, cows were individually housed and underwent a fasting period of up to 24 hours. During each period, cows were allowed access to treatment diets from 0600 to 0800 hours, and rumen fluid samples were collected hourly for twelve hours beginning at feed delivery. A CO2 electrode and conductivity probe were placed in the rumen of each cow to investigate the relationship between aqueous ruminal CO2, temperature, and conductivity, with sensor measurements recorded every three minutes beginning at 0545h. Concentrations of individual VFA were analyzed statistically using a linear mixed effects model with fixed effect for treatment and sensing data and random effects for animal and period. Single-point-in-time modeling of VFA concentrations from sensor data demonstrated comparable or improved results in terms of error variance and Concordance Correlation Coefficient (CCC) compared to models using diet and time variables. Incorporating time-lagged sensor variables further improved the predictive capacity and reduced residual error variance. Adding diet descriptions to the lagged sensor data did not enhance the ability to explain variability in VFA concentrations. These models indicate VFA concentrations can be well characterized from aqueous, ruminal sensing of CO2, temperature, and conductivity, in a manner apparently independent of and robust across diets. / Master of Science / Cattle feeding practices have shifted over the past several decades to enhance efficiency and better meet increasing energy requirements associated with greater genetic capacity for meat and milk production. In practice, this shift has relied on greater use of high-energy and nutrient-dense concentrate feeds over fiber-rich forages. The synthesis of volatile fatty acid (VFA), a primary product of microbial fermentation which plays a crucial role in supplying up to 70% of the ruminant's energy, is driven primarily by diet characteristics. Dietary nutrient supplies have a reciprocal relationship with the ruminal microbial community, shifting the profile of fermentation, and subsequently influencing the health and efficiency of the host. As such, there has been a long history of investigation of VFA profiles produced from various diets as a strategy to better understand the complexities driving the relationships linking diet, host, microbial community, and fermentation outcomes. Although there are existing rumen monitoring technologies, there are none currently capable of monitoring VFA concentrations in the rumen. The overall goal of this work was to explore the ability of existing sensor technologies to monitor ruminal VFA concentrations. The first study sought to explore the use of pH sensing to estimate ruminal VFA concentrations. Four ruminally cannulated Holstein cows were fed four diets differing in forage to concentrate ratios using grass hay, cracked corn, and soybean meal. Sampling periods for each animal lasted four days, with cows returning to cool season grass pasture between sampling periods. Cows were fasted for up to 24 hours prior to receiving treatment diets, and sampling periods began at 0600 with feed delivery, and rumen fluid samples were collected hourly for 12 hours. Rumen pH was determined at time of sampling using a bench pH meter. Concentrations of individual VFA and branch-chain VFA were analyzed statistically using two linear mixed effects models. In one model type, VFA were estimated through fixed effects terms for treatment, time, and the treatment by time interaction. For comparison, the other model estimated VFA concentrations using linear and quadratic effects for the sensed pH data. Both models leveraged random effects for animal and period. Models leveraging pH data held greater error rates when compared with models including diet and time data, indicating pH alone is an insufficient method of estimating ruminal VFA concentrations. The second study targeted sensing of aqueous ruminal CO2, temperature, and conductivity as indicators of VFA concentrations. Four ruminally cannulated Holstein cows were fed four diets differing in forage to concentrate ratios using grass hay and top dresses of cracked corn and soybean meal. Sampling periods for each animal lasted four days, with cows returning to cool season grass pasture between sampling periods. Cows were fasted for up to 24 hours prior to receiving treatment diets, and sampling periods began at 0600 with feed delivery, and rumen fluid samples were collected hourly for 12 hours. Conductivity and CO2 probes were placed in the rumen prior to feed delivery, and measurements were recorded every three minutes. Concentrations of individual VFA were analyzed statistically using a linear mixed effects model with fixed effect for treatment and sensing data and random effects for animal and period. Models leveraging single-time-point measurements of aqueous ruminal CO2, temperature, and conductivity had similar, and in many cases, improved residual errors when compared with models using diet and time information. Incorporating time-lagged sensor variables further improved the predictive capacity and reduced residual error variance, and adding diet descriptions to the lagged sensor data did not enhance the ability to explain variability in VFA concentrations. The results of the two studies completed indicate that sensing of indicators of ruminal fermentation, like aqueous CO2, temperature, and to a lesser extent conductivity, is a sufficient method of determining ruminal VFA concentrations.

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While the Southeastern U.S. does not produce cereal grains at the same output as Midwestern states, a relatively temperate climate and consistent rainfall allow for abundant forage production. Tall fescue dominated pastures in this region provide a high-quality forage source to support consistent cattle growth and production. Furthermore, the nearly year-round grazing potential serves as a cost-effective feed source. Leveraging forage resources is imperative for the U.S. beef industry to maintain consistent production of a quality human protein source at a consumer-friendly price, but energy content in purely forage diets is lacking to produce comparable growth and carcass performance to concentrate-based diets. Therefore, the objectives of this dissertation are to examine supplementation strategies for growing and finishing cattle in fescue-based systems in the Southeast to optimize value for cattle producers. The first experiment investigated whether steer performance and grazing behavior was affected by supplement feeding time and delivery method in a forage-based backgrounding program. Traditionally, producers choosing to supplement backgrounding cattle with grain or coproduct feeds do so in a single meal event in the early morning. It has been hypothesized that these morning feedings could disrupt the natural diurnal grazing pattern of cattle to negatively affect forage utilization and overall cost of gain. Additionally, while self-feeder systems using supplements containing intake limiters give producers an option to reduce feeding labor compared to daily hand-fed supplementation, alternate methods of supplement delivery also have the potential to influence grazing behavior and cost of gain within backgrounding programs. This experiment used backgrounding steers supplemented daily at 0930 (AM), steers supplemented daily at 1330 (PM), and steers provided supplement through a self-feeder (SELF) to provide cattle performance and economic data directly relevant to regional producers. Combined 2-yr results show that while AM, PM, and SELF cattle all exhibited altered grazing routines, treatments did not result in differences (P ≥ 0.18) in final body weight (BW), average daily gain (ADG), ultrasound 12th rib fat thickness (uFT), or overall forage mass disappearance. Dry matter intake (DMI) in the SELF treatment exceeded the target despite inclusion of intake limiters, resulting in increased (P < 0.01) supplement DMI, a tendency (P = 0.07) towards decreased G:F, and substantially greater (P < 0.01) cost of gain in SELF relative to the hand-fed treatments. Results support that producers have flexibility in scheduling daily supplementation routines without compromising steer performance in pasture-based backgrounding programs. Furthermore, producers should consider the tradeoff between labor efficiency and ration cost when considering utilizing self-feeders containing intake limiters. The second experiment investigated the effects of frame size and supplementation containing a rumen protected fat (RPF) on growth performance and carcass characteristics of pasture finished cattle. Market dynamics continue to favor cattle that produce heavier carcasses, which discounts smaller framed feeder calves at sale barns. At the same time, Virginia is flush with cow-calf production, high quality tall fescue pastures, and access to population dense areas with markets that incentivize pasture-finished beef through price premiums. Together, this provides an alternative marketing channel for smaller framed calves through pasture-finished beef markets, but questions remain on how to optimally produce this specialty beef. Supplemental feeds can increase cattle production on pasture, and RPF offer a feeding strategy to increase energy intake without negatively effecting ruminal fiber digestion. There is limited work investigating the application of RPF within beef cattle systems and carcass traits, and it is unclear if RPF has been utilized specifically within pasture finishing systems. Therefore, this experiment examined growth performance, carcass characteristics, and organoleptic qualities of beef from small-framed (SM) and medium-framed (MED) cattle on novel endophyte-infected fescue pasture finishing systems either offered no supplement (NON) or daily supplementation (SUP) containing RPF. Pasture treatments were compared relative to a grain-fed feedlot control (F) to show these cattle had the genetic merit to meet expectations of the U.S. fed-beef system. Results from this 2-yr experiment indicate that frame size had little impact on growth performance, with SM and MED cattle having similar (P ≥ 0.37) final BW, ADG, and forage DMI in this pasture finishing system. However, MED cattle produced more valuable carcasses compared to SM cattle as evident by greater (P ≤ 0.04) mean HCW, 12th rib fat thickness, and marbling score. Samples of M. longissimus thoracis from MED cattle also had greater (P ≤ 0.02) concentrations of 14:0, 16:0, 18:0, 18:1, and 18:2 fatty acids compared to samples from SM cattle. While NON cattle produced carcasses with a lower (P = 0.01) yield grade than SUP cattle, overall, SUP cattle were more productive by both live and carcass metrics. The SUP treatment produced greater (P ≤ 0.04) final BW, ADG, 12th rib fat thickness, HCW, marbling score, dressing percentage, and concentrations of 14:0, 16:0, 18:0, 18:1, and 18:2 fatty acids. Similarity (P = 0.55) in objective measures of meat tenderness between F and pasture treatments emphasizes the importance of harvesting cattle before 2 years of age to prevent declines in meat tenderness associated with advancement of connective tissue. There tended (P = 0.05) to be a frame by supplement interaction for marbling score driven by lower values in SM-NON in relation to other pasture treatments. Tendencies towards frame by supplement interactions for Warner-Bratzler shear force (P = 0.08) and total energy (P = 0.06) were also driven by increased values in SM-NON relative to other pasture treatments. Taken together, a lack fat deposition in SM-NON cattle appears to have a negative impact on beef tenderness relative to pasture treatments. Overall results of this experiment support low levels of supplementation in pasture-finishing systems to improve carcass value, and that medium framed cattle are more flexible in profit margins compared to smaller framed counterparts. Collectively, these investigations support that tall fescue grazing systems in the Southeast can serve as a nutritional foundation to beef cattle growing and finishing enterprises. Data from these experiments can be directly applied to help producers match cattle type to feed resources when supplementing a pasture-based system to optimize resource management and overall profitability. / Doctor of Philosophy / The U.S. beef cattle industry is unique to any other commercial food animal enterprise. Smaller animals like poultry and swine can be raised within enclosed spaces to control temperature, humidity, and airflow. Beef cattle, however, require a larger land footprint and more feed resources per animal. This exposes cattle to the volatility of outdoor production, which adds another set of variables that cattle managers must account for. Additionally, cattle have the longest lifecycle from conception to harvest relative to all other livestock species, so cattle producers are more vulnerable to long-term financial risk. Despite these challenges the U.S. beef industry succeeds by organizing cattle production into multiple interconnected business sectors. Segmenting the beef cattle industry allows producers to tailor their management practices to what works within their region of the country based on unique resources, climate patterns, and especially feed availability. Collectively the parts of the beef industry work as a dynamic system, but this also creates cattle with a variety of physical characteristics and genetics to complement the array of production styles. Different types of cattle can be valued differently depending on what traits consumers in a specific market desire. Therefore, sustained economic success in the cattle industry often comes down to pairing different cattle management systems with the correct end consumer market. Approximately 20% of the U.S. cattle population resides in Southeastern states where relatively temperate climates and consistent rainfall allows for abundant availability of high-quality forage. Especially in states like Virginia, tall fescue and other cool-season grasses provide nearly year-round forage growth for cattle to graze as a relatively inexpensive and abundant feed supply. However, forages lack the nutrient density of cereal grains, which support higher rates of growth and produce beef with an eating experience that the American palate has grown accustomed to. This creates a gradient of cattle nutritional strategies ranging from primarily forage-based cattle production on one end to primarily grain-based strategies on the other. Therefore, the objective of this dissertation was to evaluate supplementation strategies for growing and finishing beef cattle in fescue-based production systems in the Southeast from the perspectives of both live cattle and meat production. Backgrounding systems are a transitional period following weaning that focuses on lean growth to prepare yearling calves for the feedlot finishing phase. Cattle on these traditionally forage-based systems are frequently supplemented with grain or grain coproduct feeds to increase weight gain, but supplement delivery method and time of feeding varies between producers. This could influence natural cattle grazing cycles to negatively impact pasture utilization, which would increase the cost of gain. Over a 2-yr study post-weaning cattle growth performance and grazing behavior were compared between backgrounded cattle supplemented by hand in the morning, by hand in the afternoon, or through a self-feeder. Although altering the time of day that supplements were provided to cattle changed daily grazing routines, there were no differences in weight gain, body composition, or forage disappearance between all 3 treatments. Self-fed cattle had nearly twice the cost of gain compared to hand-fed cattle, highlighting the importance of accounting for cost of gain when making nutritional program decisions. Market dynamics favor cattle that produce heavier carcass weights, but this has led to smaller framed feeder calves receiving discounts at sale barns. The Southeast is flush with cow-calf production, abundant forage resources, and population dense areas that incentivize pasture-finished beef. This creates opportunity for cattle producers looking to increase the value of smaller framed calves through premiums in specialty beef markets. A 2-yr study examined the effects of frame size and supplementation containing a rumen protected fat on cattle growth performance, forage utilization, and carcass characteristics. Small framed and medium framed cattle on novel endophyte-infected tall fescue pastures were either received daily supplementation or no supplement and were compared against a grain-fed control group. Smaller framed cattle grew at a slower rate relative to medium framed cattle, and produced less valuable carcasses in terms of both the amount of beef produced and meat quality. Low levels of supplementation improved growth performance and carcass value, but overall medium frame, unsupplemented cattle had the greatest profit flexibility relative to other pasture treatments. Collectively, these experiments highlight the profit potential of forage-based beef cattle production in the Southeast. The beef industry will have to continue to adapt to produce more beef to feed a growing global population through tighter constraints, and forage resources will play a key role in providing a cost-effective, high quality feed source. Accounting for differences in resource management, end markets, and cattle type is paramount in maintaining a sustainable and profitable U.S. beef industry.

L'acidose ruminale latente (ou acidose sub-clinique) est une préoccupation majeure pour la nutrition des ruminants à haut potentiel de production. Cet état se caractérise par une instabilité du microbiote et des fermentations ruminales qui s’orientent variablement vers le propionate et/ou le butyrate. L’une des stratégies de prévention de l’acidose latente consiste à distribuer dans l’alimentation des ruminants des probiotiques capables de rééquilibrer le microbiote et les fermentations ruminales (dans un sens favorable pour l’animal). L’analyse de la bibliographie montre toutefois que l’effet des probiotiques, et plus particulièrement des bactéries probiotiques (BP), est variable et parfois contradictoire ce qui serait probablement lié à l’instabilité du microbiote. Afin d’étudier la possibilité de prévenir l’acidose latente par les bactéries propioniques et/ou lactiques, nous avons émis l’hypothèse que leur efficacité dépend des orientations fermentaires dans le rumen. Des acidoses latentes butyrique et propionique caractérisées par des profils fermentaires et microbiens distincts ont été développées chez le mouton non productif et la vache laitière pour étudier l’effet et le mode d’action de la bactérie propionique P63 seule ou associée aux lactobacilles Lb. plantarum ou Lb. rhamnosus (P63, Lp + P63 et Lr + P63) sur le fonctionnement de l’écosystème ruminal et les performances animales. Chez le mouton en situation d’acidose propionique, les BP utilisées ont amélioré le pH ruminal via une réduction de la proportion en lactobacilles. Chez la vache laitière, la stabilisation du pH a été associée à une moindre disponibilité en hydrogène susceptible d’être transformé en protons, suite à une augmentation de la propionogenèse et/ou de la densité bactérienne, deux voies consommatrices d’hydrogène. Au cours de l’acidose latente butyrique, l’amélioration du pH n’a été observée que chez les moutons supplémentés avec Lp + P63. Cet effet semblait être dû à une diminution des acides gras volatils et de la proportion en S. bovis mais aussi à un pH initial faible (pH < 5,5) probablement optimal pour l’action des BP ; ce qui n’était pas le cas chez les vaches pour lesquelles le pH initial était compris entre 5,9 et 6,1. En revanche, l’efficacité digestive a été augmentée par l’association de P63 aux lactobacilles chez la vache laitière. L’association Lp + P63 a augmenté les activités fibrolytiques (cellulase, xylanase) et la digestibilité de la matière organique, tandis que Lr + P63 a amélioré la digestion des fibres et a diminué la production de méthane de 25%. Nous n’avons pas observé d’effet sur les performances zootechniques, ce qui serait probablement dû au dispositif expérimental en carré Latin qui n’est peut-être pas optimal pour mettre en évidence l’effet des BP. Nos résultats sont les premiers à démontrer l’efficacité des bactéries probiotiques pour sécuriser et/ou améliorer la digestion des rations et réduire la production de méthane chez le ruminant en acidose, et l’association de P63 avec les souches de Lactobacillus sont les plus efficaces. Enfin, nous avons validé notre hypothèse selon laquelle l’effet et le mode d’action des bactéries probiotiques pour prévenir l’acidose dépendent des orientations fermentaires dans le rumen. / Subacute ruminal acidosis (SARA) is a major concern for the nutrition of high-producing ruminants. This digestive disorder is characterized by the instability of the microbial ecosystem and fermentations which are oriented towards propionate and/or butyrate at the expense of acetate (propionic or butyric SARA). Among the strategies used to prevent SARA, supplementation with direct-fed microbials (DFMs) is thought to be able to balance the ruminal microbiota and fermentation. The analysis of the literature shows that the effect of DFMs, especially bacterial ones, is variable and sometimes contradictory which is probably related to the instability of the microbiota. To investigate the possibility of preventing SARA by propionibacteria and/or lactobacilli based DFMs, we hypothesized that their effectiveness depends on the ruminal fermentation patterns. Butyric and propionic SARA, characterized by distinct microbial and fermentation profiles, have been developed in non-productive sheep and lactating dairy cows to investigate the effects and mode of action of the Propionibacterium P63 alone or in conjunction with the lactobacilli strains Lb. plantarum or Lb. rhamnosus (P63, P63 and Lp + Lr + P63) on the ruminal ecosystem and animal performances. During the propionic SARA induced in sheep, the DFMs used increased the ruminal pH with a concomitant reduction in the lactobacilli population. In dairy cows, the pH stabilization was associated with a lower availability of hydrogen capable of being transformed into protons, following a stimulation of propionogenesis and/or bacterial growth that consume hydrogen. During butyric SARA, improvement in pH was observed only in sheep supplemented with Lp + P63. This effect appeared to be due to a decrease in VFA production and S. bovis proportion. Moreover, the lower initial pH (pH <5.5) was probably optimal for DFMs action, which was not the case for the dairy cows for which the initial pH was between 5.9 and 6.1. For the dairy cows, diet digestion was improved when P63 and lactobacilli association were fed. Indeed, Lp + P63 increased the fibrolytic activities (cellulase, xylanase) and digestibility of organic matter, while Lr + P63 improved fiber digestion and decreased methane production by 25%. We did not observe any effect on animal performances, which was probably due to the Latin square design that is not the best to evaluate the DFMs effects on animal performances. Our results are the first to demonstrate the effectiveness of bacterial DFMs to secure and/or improve diet digestion and reduce methane production in ruminants. Moreover, it seems that the association of P63 with the lactobacilli strains is more effective. Finally, we validated our hypothesis that the effect and mode of action of bacterial DFMs to prevent SARA is conditioned by ruminal fermentation patterns.