The influence of the previous plane of nutrition on water and nitrogen metabolism of grain versus forage fed beef cattle
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Authors
Moreira da Silva, Aghata Elins
Issue Date
2022
Type
Dissertation
Language
Keywords
Efficiency , Gene expression , Nitrogen , Water
Alternative Title
Abstract
The beef cattle production system is mainly segmented into three main sectors corresponding to life stages: cow-calf, backgrounding, and finishing. In each one of those phases, nutritional status of animals can vary greatly according to the feedstuff available within growth phases. In the background phase, for example, the supply of high-quality forage can be very limited at times, which will be followed by periods of reduced performance. In the U.S., once these animals are transitioned into the finishing phase, often upon backgrounding in forage-based systems, they will transition into one of two feeding managements, a grain-fed (conventional beef production) or grass/forage-fed. Growing concerns regarding the environmental impacts of grain-fed systems, often creates a pursuit for grass/forage-fed finishing systems as perceived as a more sustainable alternative for the beef industry goal of being a steward of our natural resources. In order to reach a desirable carcass finishing point within a feasible time frame, cattle will require a high-quality feed, which is usually associated with high levels of energy for grain-based on protein for forage based systems. Increased protein levels in the diet is usually associated with an increase in water requirements �" a very limited resource and of high environmental concern for the beef industry. Research on the environmental impact of grass/forage-fed beef vs grain-fed beef is still very limited, and to the best of our knowledge, there is no scientific literature investigating the influence of the previous plane of nutrition on nitrogen and water metabolism at the animal level altogether. This dissertation explores the physiological and molecular mechanisms regulating the water and nitrogen metabolism at the animal level of different background and finishing systems and their respective interactions in order to address the key role of sustainable use of natural resources. The first chapter provides a literature review about the beef cattle industry in the U.S., as well as the mechanisms that regulate water intake, nitrogen metabolism, and nitrogen recycling in cattle. Then, the second chapter explores how the backgrounding diet can affect the next phase on regards to water intake, animal performance and efficiency of steers under grain or forage-based finishing diets. This study revealed that grain-fed animals are usually more efficient in regard to fresh water use, but that adequate plane of nutrition on earlier stages of life are required to mitigate water requirements/use and ensure the final carcass quality is achieved. From this study, it was observed that the concentration of crude protein was one of the main components controlling water intake, thus fresh water use. Therefore, in the third chapter, it was evaluated how different backgrounding and finishing systems altogether might affect nitrogen metabolism, and consequently water requirements of cattle. The results from this study indicated that animals fed a low plane of nutrition during the background phase were able to reduce their excretion of nitrogen without affecting their water and nitrogen requirements due to a more efficient nitrogen recycling; and once they were transitioned to a grain-fed finishing system, they were still able to carry over those characteristics. Therefore, in the last chapter, it was investigated how the molecular mechanisms controlling water and urea metabolism at the finishing phase can be affected by the previous plane of nutrition. Overall, the results suggest that the previous plane of nutrition can impact gene expression associated with water and urea metabolism during the finishing phase, namely AQP3, AQP7, ATP1B1, and SGK1 in the kidney, and AQP7 and UT-B in the rumen. Our results highlight the often overlooked “elephant in the room” regarding the carryover effects that previous planes of nutrition may carry in beef cattle production systems. Further, we empirically demonstrate that opposite to common belief, grain-fed and not grass/forage-fed beef is more sustainable in regard to fresh water utilization.