Understanding Beef Quality Development and Different Feeding Regimes Jordan Christie Wicks ABSTRACT Consumption of beef is expected to increase as the world approaches nearly 9 billion inhabitants by the year 2050, adding unprecedented challenges to the future beef industry. Even so, maintaining quality will still be of utmost importance for producers for two reasons. First, the majority of US cattle are sold on the "grid", which offers both premiums and financial penalties based on quality grades. Second, consumers demand quality. Herein, we explored alternative, cost-saving feeding strategies that impact muscle biochemistry and ultimate meat quality in an effort to determine the most feasible management responses during times of sporadic markets. Our results show that reducing feed inputs from intensive feeding (grain-finished) regimes to maintenance diets of forage or grain up to 60 d had minimal effect on metabolic properties of muscle, thus preserving both quality and yield grades. Specifically, muscle metabolism remained largely unchanged, as indicated by lack of significance in oxidative and glycolytic proteins such as succinate dehydrogenase (SDH), citrate synthase (CS), lactate dehydrogenase (LDH), and phosphofructokinase-1 (PFK-1). Additionally, because maintenance rations were fed, we found no difference in non-esterified fatty acid (NEFA) concentration, or O-linked- β-N-acetylglucosamine (O-GlcNAc) protein abundance suggesting a longer or more aggressive feeding approach may be required to evoke such nutrient based muscle and quality differences. Because quality is important and is a factor for optimal pricing at market, intensive feeding practices are often needed to meet such standards. Still, as the cost of feeding increases, producers struggle to balance quality and profitability. To that end, we evaluated carcass quality of cattle subjected to a reduction of time on feed by 30 d, and found quality, yield and color were similar to that of cattle intensively fed for 120 days. Although, little differences were noted between indicators of postmortem metabolism, short-fed (SF) cattle showed a trend for greater adenosine monophosphate deaminase 1 (AMPD1), and significant difference in the expression of myosin heavy chain isoform (MyHC) IIX suggesting muscle of SF cattle is transiting away from that of grass-fed (CON) cattle. Even so, SF cattle proved to have similar color and quality to cattle fed for 120 days, or more traditionally fed. While we failed to detect differences in muscle between days on feed compared to that of CON (grass-fed), we observed differences in quality and yield between long fed and grass-fed cattle. These data suggest variances in quality may be a result of underlying mechanisms yet to be explained. Therefore, we explored the hallmark biomarkers credited for beef quality development. Despite significant differences in quality and yield grades, data resulted in no differences in myoglobin, oxidative or glycolytic proteins, or calpain-1 and calpastatin between varying phases of growth. However, based on our complementary transcriptomics data, we found linear trends in gene expression related to adipogenesis and muscle hypertrophy, implying these differences may simply be a result of growth rather than muscle function. When taken together, our data suggests severe nutrient restrictions may be required to evoke such a shift in muscle that leads to exacerbated differences in quality. A greater understanding of those mechanisms that drive meat quality development from a conventional grain feeding perspective may prove impactful for the future of our industry. / Doctor of Philosophy / As the demand for beef continues to increase, so does the demand for quality. Generally, consumers prefer beef that is bright-cherry red, possess adequate marbling, and offers a tender bite when consumed. These quality attributes are influenced by many factors, however plane of nutrition, or more simply nutrient energy source (grass vs grain) have shown to play a rather impactful role in quality development. Therefore, high-energy intensive feeding systems (feedlot) have been widely adopted by the US beef industry as a means of producing beef. Even so, the cost of gain for cattle is steadily increasing making profitability challenging from a producer standpoint. Therefore, the aim of this dissertation was to investigate low-input feeding strategies and the influence they have on beef quality. First, we tested nutrient availability's effect on muscle plasticity of mature market ready steers. Our results show that reducing feed inputs from intensive feeding (grain-finished) regimes to maintenance diets of forage or grain up to 60 d had minimal effect on metabolic properties of muscle, thus preserving both quality and yield grades. Next, we challenged varying degrees and plane of nutrition on finishing steers to better understand the extent to which intensive feeding has on ultimate beef quality. To that end, we evaluated carcass quality of cattle subjected to a reduction of time on feed by 30 d, and found quality, yield and color were similar to that of cattle intensively fed for 120 days. Although, little differences were noted between hallmark indicators of muscle fiber type, Short-fed (90 d) cattle proved to be transiting away from that of grass-fed (CON) cattle, aligning closer to consumer expectations of quality. Taken together, our data suggest variances in quality may be a result of underlying mechanisms yet to be explained. Therefore, we explored the hallmark biomarkers credited for beef quality development. Despite significant differences in quality and yield grades, data resulted in no differences in myoglobin, oxidative or glycolytic proteins, or calpain-1 and calpastatin between varying phases of growth. However, based on our complementary transcriptomics data, we found linear trends in gene expression related to adipogenesis and muscle hypertrophy, implying these differences may simply be a result of growth rather than muscle function. In conclusion, our data suggests severe nutrient restrictions may be required to evoke such a shift in muscle that leads to exacerbated differences in quality. A greater understanding of those mechanisms that drive meat quality development from a conventional grain feeding perspective may prove impactful for the future of our industry.

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The full text of this thesis/dissertation is not available online. Please <a href="mailto:upetd@up.ac.za">contact us</a> if you need access. Read the abstract in the section 00front of this document. / Dissertation (M Inst Agrar (Animal Production))--University of Pretoria, 2006. / Animal and Wildlife Sciences / unrestricted