Effects of nutrition and management during the stocker phase on quality grade
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Certified Angus Beef
Clint R. Krehbiel*, Phillip A. Lancaster*, Evin D. Sharman*, Gerald W. Horn*, D. L. Step**, and Deb L. VanOverbeke*
*Department of Animal Sciences, Division of Agricultural Sciences and Natural Resources; and **Department of VeterinaryClinical Sciences, Center for Veterinary Health Sciences, Oklahoma State University, Stillwater, 74078
INTRODUCTION
The 2011National Beef Quality Audit Survey reported that “Eating Satisfaction” (defined by packers as tenderness, flavor-marbling) is the second most important attribute in beef consumption behind food safety (Igo et al., 2012). Retained ownership, alliances, and vertically coordinated supply chains are becoming an increasingly larger percentage of cattle on feed, resulting in an estimated 50% or greater of the cattle in the U.S. trading outside of the cash market (Ritchie, 2002). As segments of the beef industry become more coordinated, it becomes increasingly important to understand the effects that management and nutrition in each segment has on all subsequent phases of production, final carcass value, and “Eating Satisfaction” of the final products. Improving nutritional and management strategies for growing beef cattle to enhance final carcass quality will not only benefit the beef industry as a whole, but will provide producers with more incentive to produce high-quality beef to meet consumer demand. Because consumer dollars ultimately drive the beef cattle industry, meeting consumer demand/desires will continue to determine profitability in the future.
Studies of nutrition and management practices that influence marbling (intramuscular fat) deposition have primarily focused on the feedlot phase of production (Owens and Gardner, 2000). However, pre-feedyard management strategies (health status, stocker/backgrounding, nutrient supplementation, etc.) can influence marbling development (Anderson and Gleghorn, 2007). Therefore, changes in management practices during early phases of the production cycle that increase intramuscular fat deposition and decrease fat deposition in other depots could enhance the efficiency of beef production and enhance carcass quality. Due to the current price of grains and harvested forages, cattle are entering the feedlot at heavier weights indicating that post-weaning management programs are being used to decrease the number of days cattle spend in the feedyard. Understanding how these post-weaning nutrition and management programs impact carcass growth and development is becoming increasingly important.
Depending on biological type of cattle, calves are oftengrazed or placed on a growing diet after weaning to achieve adequate frame size and carcass weight before entering the feedlot for finishing. Across the Southern Great Plains and the Southeastern U.S., grazing systems are commonly used for growing programs during the winter. Cool season forages, including wheat pasture, are utilized to grow cattle to desirable weights for feedlot entry (Byers, 1982). In addition, each year in the Southern Great Plains fall-weaned calves are wintered on dormant native range. Cattle that are wintered on dormant native range are typically fed a protein supplement to gain 0.25 to 0.50 kg/day through the winter months until spring forage growth occurs. These calves then graze summer pasture in either intensive-early stocking or season-long grazing programs prior to entering the finishing phase. In the Northern Great Plains, cattle are usually either grown on crop residues, dormant grass pastures, or placed in confinement and program fed for a moderate rate of gain on harvested and ensiled crops such as corn silage. Albeit stocker programs are increasing due to costs of gain in the feedyard, some larger-framed calves may go directly on to a high-concentrate diet immediately following weaning. High-concentrate diets may be fed at restricted levels in the growing phase to provide a desired rate of gain while allowing for lean tissue growth (Sip and Pritchard, 1991). Because of the variability in growing programs among different regions of the country and in diets that may consist of grazed or harvested forage and/or grain-based diets, performance and weight gain of cattle before and after feedlot entry may be vastly different (McCurdy et al., 2010). In addition, development of fat depots in relation to BW and maturity of the animal could be impacted toalter carcass quality. Because economic value of carcasses is dependent primarily on carcass weight and carcass quality, cattle producers have a strong interest in factors associated with maximizing these two variables. This review will focus on stocker cattle nutrition and management strategies that have the potential to impact marbling score and carcass quality.
MARBLING DEPOSITION DURING THE STOCKER PHASE
Adipose (fat) tissue development is of major importance to beef production because it influences production efficiency, product quality and consumer acceptance, and, therefore, product value(Smith et al., 1987). Growth of the intramuscular fat depot (i.e., marbling) is especially desirable due to consumer preference for well-marbled beef, whereas growth of other fat depots results in excess fat and production inefficiencies (Hausman et al., 2009). In addition, the amount of fat deposited in the intramuscular depot is the basis for carcass price premiums (marbling; USDA Quality Grade) and fat deposited in other depots can result in carcass discounts (subcutaneous fat; USDA Yield Grade). Anderson and Gleghorn (2007) suggested that marbling deposition is a lifetime event and that pre-feedlot nutrition has a significant impact on marbling deposition. Peel (2003) estimated that 76% of the yearly calf crop enters a backgrounding or stocker program prior to finishing; therefore, there is tremendous opportunity to improve carcass quality attributes by influencing adipose tissue development during the stocker/backgrounding phase of production. During the stocker/backgrounding phase of production, significant muscle growth occurs and the primary structures of marbling deposits are developed. Although increasing intramuscular fat deposition relative to other fat depots would be beneficial, little is known about the association between muscle growth,metabolism and marbling development.
Fat Cell Differentiation and Development
Understanding the molecular mechanisms responsible for fat celldevelopmentmay provide insight into how fat deposition can be influenced during the stocker phase of production, whether from nutrition,management, or genetics. Growth of intramuscular fat appears to occur due to adipocyte (fat cell) acquisition by differentiation of preadipocytes(adipogenesis; Minoshima et al., 2001). Adipocytes represent between 1/3 and 2/3 of the cells inadipose tissue. The remaining 1/3 to 2/3 consists of blood cells, endothelial cells, pericytes, preadipocytes, and fibroblasts (Ailhaud et a1., 1992). Late in embryonic lifethe first preadipocytes appear. However, expansion of white adipocytes does not occuruntil shortly after birth (Slavin, 1979; Cook and Kozak, 1982). The expansion of whiteadipocytes that occurs shortly after birth includes both an increase in the size (hypertrophy) and number (hyperplasia) of adipose cells. Interestingly, even in adult animals, the potential to increase the numberof adipose cells exists (Gregoire et al., 1998). Lineage of adipose is derived frommultipotent stem cells of mesodermal origin. These multipotent stem cells candifferentiate into muscle, cartilage, as well as fat (Cornelius et al., 1994). Adipogenic cells, as well as osteogenic and chondrogeniccells, may arise from sclerotomal cells (Gregoire et al., 1998). Adipoblasts formed from multipotent stem cells undergocommitment to form preadipocytes. Preadipocytes are characterized as possessingearly geneticmarkers of adipocytes, but they have not at this point accumulated triacylglycerol(lipid) stores (Ailhaud et al., 1992). The process of adipose differentiation corresponds to phenotypicchanges beginning with the adipoblast, progressing to the preadipocyte,becoming an immature fat cell, and finally, terminally differentiating into the maturefat cell (Ailhaud et al., 1992).
In order to induce the differentiation of preadipocytes to mature adipocytes,external inducers are required. Inducers considered to be required for adipocyte differentiation to occur include insulin-like growth factor-1 (IGF-1), glucocorticoid, cyclic adenosine monophosphate (cAMP), and long chain fatty acids. Considerable numbers of IGF-1 receptors are found on preadipocytes. In addition,insulin and growth hormone, driven by nutrition and management (e.g., anabolic implants),are able to induce adipocyte differentiation via the IGF-lreceptor. Glucocorticoid is an adipogenic agent required for preadipocytes to undergoclonal expansion and terminal differentiation (MacDougald and Lane, 1995). In addition, increasedlevels ofcAMP are required for preadipocyte cells to undergo differentiationinto mature adipocytes (Vassaux et al., 1992). It has also been shown that long chain fattyacids can induce differentiation of preadipocytes. For example, palmitic acid (C16:0) can inducegrowth arrested cells to undergo post-confluence mitosis (clonal expansion), to accumulate triacylglycerol,andto express several adipocyte markers (Amri et al., 1995).
Intramuscular fat cells develop within the perimysium of muscle bundles in close association with the skeletal muscle satellite cells responsible for postnatal muscle growth. Therefore, skeletal muscle growth and metabolism might influence marbling development. Intramuscular fat content is positively correlated (r = 0.46 to 0.49) with fiber area of oxidative muscle fiber types (Melton et al., 1974; May et al., 1977) and number of capillaries per muscle fiber (r = 0.63; Melton et al., 1975). In addition, Kim et al. (2009) reported that gene expression of NADH dehydrogenase and cytochrome c oxidase, both involved in oxidative phosphorylation within mitochondria, were greater in muscle from the loin, which had greater intramuscular fat content, compared with muscle from the top round. Gene expression of NADH dehydrogenase and cytochrome c oxidase explained 84 and 97% of the variation in intramuscular fat content of loin muscle, respectively, in Korean cattle (Kim et al., 2009). These data suggest that muscle metabolism influences marbling development.
Possible mechanisms by which muscle influences marbling development could include increased angiogenesis (growth of blood vessels) within muscle providing greater blood flow to sustain new adipocytes and changes in intercellular signaling mechanisms such as growth factors that stimulate adipocyte differentiation. Angiogenesis is an important aspect of adipose tissue development, and adipocyte differentiation may be regulated by factors that stimulate angiogenesis (Hausman and Richardson, 2004). Under the microscope, it can be seen that intramuscular adipocytes develop in close proximity to a capillary network (Harper and Pethick, 2004), and an important player in angiogenesis, the plasminogen activator-plasmin system, is involved in the migration of endothelial cells and preadipocytes (Hausman and Richardson, 2004). Thus, enhancing vascular development of muscle tissue could stimulate recruitment of preadipocytes to new locations within the muscle forming new intramuscular fat deposits.
As compared to other adipose tissues, intramuscular adipose tissue is more likely to be influenced by the environment within the muscle tissue. Intramuscular adipose tissue has smaller mature adipocytes (Smith and Crouse, 1984; Cianzio et al., 1985; May et al., 1994) and preadipocytes from intramuscular adipose tissue have reduced capacity to differentiate (Grant et al., 2008; Ortiz-Colon et al., 2009) compared to other adipose tissue depots. This may be due to effects of the intramuscular environment or differences in the genetically determined growth potential. Postnatal growth of bovine adipose tissue occurs by hypertrophy(cell size) through fat synthesis, and hyperplasia (cell number) due to differentiation of preadipocytes (Gerrard and Grant, 2003). As mentioned, several studies (Smith and Crouse, 1984; Cianzio et al., 1985; Schoonmaker et al., 2004) have reported that intramuscular adipose tissue has a greater number of smaller adipocytes compared to subcutaneous and perirenal adipose tissue. In addition, perirenal adipose tissue has greater mean adipocyte diameter than subcutaneous adipose tissue (Prior, 1983; Cianzio et al., 1985). These differences in hypertrophy may be related to rate and substrate utilized for triacylglycerol synthesis. Smith and Crouse (1984) reported that intramuscular adipose tissue had greater rates of fatty acid synthesis from glucose compared to subcutaneous adipose tissue, whereas, subcutaneous adipose tissue had greater rates when acetate or lactate were provided in vitro. However, rates of glycerol synthesis were greater for subcutaneous adipose tissue irrespective of carbon source suggesting that subcutaneous adipose tissue has greater rates of triacylglycerol synthesis and lipid storage than intramuscular adipose tissue. Results of Rhoades et al. (2007) also indicated that rates of glycerol synthesis were greater in subcutaneous than intramuscular adipose tissue. In addition, glucose incorporation into lipids in intramuscular adipose tissue responded to insulin, whereas insulin had no effect in subcutaneous adipose tissue (Rhoades et al., 2007). The response of intramuscular adipose tissue was also modulated by diet, such that a corn-based high-glucose diet resulted in an insulin response, whereas, a hay-based low-glucose diet did not. Differences in insulin response related to diet may also exist between subcutaneous and internal fat depots.
Developmental differences between intramuscular and other fat depots have lead to an interest in nutrition and management strategies to enhance marbling deposition while decreasing fat deposition in other depots. Because intramuscular fat deposition is a lifetime event and potentially associated with muscle growth and development, stocker programs that vary in nutrient quantity and quality and cattle growth rates likely have a significant impact on marbling deposition.
FACTORS THAT IMPACT MARBLING IN STOCKER CATTLE
Several factors have been shown to alter carcass quality in stocker cattle including animal health, nutrition, management and genetics.
Animal Health
Bovine Respiratory Disease. Verification of health or preconditioning programs for feeder calves before they begin the finishing phase of production is becoming more common in the beef cattle industry. With the demand for higher quality products, the increase in value-based marketing, and the increase in vertical coordination systems, both cow-calf producers and feedlot operators have become more in-tune to health management practices that have the potential to increase overall profitability. The health status of calves upon arrival to the feedyard has been shown to impact the efficiency of cattle in the feedyard, and also to affect the quality attributes of the cattle at slaughter. McNeill (1994, 1995, 1996, 1997, 1998) and Montgomery et al. (1984) documented that morbid cattle during the finishing phase of production had carcasses with a lower degree of marbling and subsequently lower USDA Quality Grades. Therefore, although the medical costs attributable to the treatment of bovine respiratory disease (BRD) are substantial (Martin et al., 1982; Perino, 1992), the economic impact of BRD on animal performance, carcass merit, and meat quality are likely even more devastating.
Morbidity rates account for approximately eight percent of all production costs without consideration of losses due to decreased performance (Griffen et al., 1995). McNeill et al. (1996) reported that “healthy” steers had greater daily gains and 12% more USDA Choice carcasses than cattle identified as “sick” at some point during the finishing period. Gardner et al. (1999) showed that steers with lung lesions plus active lymph nodes had $73.78 less net return, of which 21% was due to medicine costs and 79% due to lower carcass weight (8.4% less) and lower quality grade (24.7% more USDA Standards). This negative impact on carcass traits 200 d after receiving the cattle illustrates the importance of preventing BRD. Roeber et al. (2001) documented that although cattle treated more than once in the feedyard had lower marbling score and hot carcass weight (HCW) than those not treated, within a quality grade class, no differences for tenderness or palatability traits existed in cattle stratified by number of hospital visits or preconditioning treatment program.
Garcia et al. (2010) evaluated the effects of BRD on carcass composition and meat quality traits in two separate herds at the U.S. Meat Animal Research Center, Clay Center, NE. Cattle showing signs of BRD experienced a 11lb decrease in HCW, and a 10 to 15% decrease in 12th-rib fat thickness resulting in a 5 to 7% decrease in USDA Yield Grade. These authors also evaluated the effects of overall pathogenic disease on carcass traits. If an animal experienced any disease event, 12th-rib fat thickness was decreased 12 to 14%, and USDA Yield Grade was decreased by 0.2 units. Similarly, Schneider et al. (2009) reported a 2.5% decrease in HCW, a slight decrease in LM area, a 7.0% decrease in 12th-rib fat thickness, and a 2.5% decrease in marbling score in treated vs. non-treated cattle. Gardner et al. (1999) examined the effects of the number of times treated on carcass characteristics. Hot carcass weight was decreased 4.1%, 12th-rib fat thickness was decreased 26.5%, and KPH and USDA Yield Grade were also decreased in treated vs. non-treated calves. Similarly, HCW was decreased by 4.7%, 12th-rib fat thickness by 43.4%, and KPH and USDA Yield Grade by 21.1 and 18.2%, respectively, when cattle were treated more than once compared with cattle only treated once (Gardner et al., 1999). When morbidity was defined by the presence of lung lesions at slaughter, Gardner et al. (1999) observed morbid steers had HCW that were 94% of HCW of steers with no evidence of prior disease. Additionally, when active bronchial lymph nodes were present, indicating an ongoing disease process, HCW were less than HCW of animals with no lesions. In general, evidence of prior morbidity was associated with decreased dressing percentage, internal fat, external fat, smaller LM area, and lower marbling scores. Similar results were noticed when carcass characteristics were examined based on BRD treatment records. Cattle that received more than one treatment for BRD had an additional 5% decrease in HCW compared with those that were treated only one time (Gardner et al., 1999).
Roeber et al. (2001) reported a 3% decline in HCW in steers treated more than one time for BRD compared to those treated one time. However, in their report, no differences in HCW were observed between cattle never treated and those treated one time, and no differences in HCW across number of BRD treatments were reported by Waggoner et al. (2007). Although fewer differences in carcass weights and no differences in LM area were reported by Roeber et al. (2001), measures of carcass fatness were affected by BRD incidence. While internal fat was not different among treatment groups, 12th-rib fat thickness, calculated yield grade, and marbling score were all greatest for cattle never treated, intermediate for those treated once, and lowest after multiple treatments. As a result of differences in marbling, the distribution of USDA Quality Grades has been shown to be affected by BRD. Gardner et al. (1999) observed that treated steers, or steers with lung lesions, had a greater percentage of USDA Standard carcasses at the expense of Choice and Select compared with healthy animals. Similarly, McNeill et al. (1996), in an evaluation of over 7,000 cattle, reported 39% of cattle never treated for BRD graded USDA Choice or better, but only 27% that were treated graded USDA Choice or better. Holland et al. (2010) noted a trend for a linear decrease in marbling score with increasing number of treatments for BRD when cattle were fed to a targeted 12th-rib fat thickness of1.27 cm. There were no differences in proportions of USDA Yield Grades or Quality Grades; however, meat color score and overall appearance of strip loin steaks decreased as the number of times treated for BRD increased. There was no effect of number of BRD treatments on Warner Bratzler Shear Force (WBSF), but there was a trend for an increased amount of connective tissue determined by trained sensory panelists as the number of treatments increased.