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家畜繁殖学文献翻译作业12动科3班付越2012513038指导老师：张居农 正文： INTERACTIONS OF MANAGEMENT AND DIET ON FINAL MEAT CHARACTERISTICS OF BEEF ANIMALSDr. Francis L. FluhartyDepartment of Animal Sciences, The Ohio State University1680 Madison Ave., Wooster, OH 44691ph: (330) 263-3904, fluharty.1osu.eduWhy are some calves actually worth more than others to feedlots and packers even though the cattle are similar in breed, type, frame size, and muscle thickness? Today, the answer is likely to be differences in average daily gain, feed efficiency, yield grade, marbling score, or percent retail yield. As a seedstock or cow-calf producer, how do you select breeding animals and manage their offspring so that the calves actually achieve their optimum genetic potential? These are questions that you may need to be able to answer as the beef industry continues to move from a commodity market to a value-based, grid marketing industry where individual animals are identified and priced according to their consumer desirability. To answer these questions, you probably need to understand some basics of ruminant nutrient use as well as some windows of opportunity that exist where management can improve carcass characteristics so that your cattle achieve their genetic potential.First, you need to understand that all nutrients (energy, protein, vitamins, minerals, and water) are used in a hierarchy that goes from maintenance development growth lactation reproduction fattening. This means that an animal must have sufficient nutrients to maintain its body before bone or muscle growth can occur, and these must occur before fattening can occur. In breeding cattle, lactational anestrous occurs when an animal that is nutrient deficient, but milking heavily, cant rebreed. The second thing that you need to understand about ruminant nutrition is that feed is digested in the rumen by ruminal bacteria that attach to the surface of a feed particle to digest it. In ruminants, maintaining the digestive organs (rumen, reticulum, omasum, abomasum, small intestine, and large intestine) plus the liver and kidneys can take as much as 40-50% of the energy and 30-40% of the protein consumed in a day. Forage diets that are very bulky and only 40-60% digestible increase the weight of the digestive tract, because more undigested feed remains in each segment of the digestive tract. In contrast, grain-based diets result in decreased organ weights compared with forages, because grains are 80-100% digestible, and have a much smaller particle size, which allows them to have a faster rate of digestion and passage through the digestive tract. The result is that grain is more digestible than forage, plus it decreases an animals maintenance requirement by resulting in less digestive organ mass, leaving more nutrients for muscle growth and fattening. Feedlots take advantage of the energy content and digestive characteristics of grains to finish cattle. However, if you have a grass-based system for your cows (like most of the world), you arent going to switch to grain. One way to increase an animals performance with forages is grinding the forage to increase its digestibility by making more surface area available to ruminal bacteria and increasing the rate of passage of the forage through the digestive tract, decrease the bulk fill inherent with the forage, and decrease the animals maintenance requirement by decreasing the digestive tract weight. However, increasing the surface area of a forage diet is not the only answer, because not all gain is the same, and what you feed an animal affects the carcass characteristics.Producing consistently tender meat, and reducing excess external fat production while maintaining intramuscular fat deposition are still three of the major challenges in the beef industry, even though they were recognized in the 1992 National Beef Quality Audit sponsored by the National Cattlemens Association. Nutrition and genetics are the two major factors contributing to these concerns. Excessive external back fat and internal seam and KPH fat production causes inefficiencies in both feedlots, due to the higher energy cost of depositing fat compared with protein, and the packing industry, due to the high cost of trimming and the low price received for the fat. Developing management strategies to produce well-marbled, tender meat products are critical to the advancement of a high-quality beef industry.Typically, cattle are finished on high concentrate diets for a period of time ranging from 80-280 days prior to slaughter. This finishing period allows for more rapid, efficient growth, and increased intramuscular fat (marbling) deposition so that the cattle carcasses grade choice compared with cattle grown on forage-based feeding systems. In general, tissues are deposited in the order of: 1. brain, 2. bone, 3. muscle, and 4. fat, however, some animals seem to totally skip the brain portion. Nevertheless, A young, rapidly growing animal that is in a linear phase of growth will naturally put on more bone and muscle. As an animal ages, and its genetic potential for muscle growth begins to plateau, it will put on fat. Guenther et al. (1965) reported on the effects of feeding steers on a high or moderate level of nutrition. Steers fed the high level of nutrition deposited both lean and fat at a faster rate than steers fed at a moderate level of nutrition on both age- and weight-constant bases. Bone growth was not different among the two treatments and was more closely related to age than to nutrition. However, in both groups, the rate of fat deposition accelerated as the animals aged, whereas the rate of lean deposition decreased. The rate of fat accumulation was most rapid in the latter part of the feeding period, after lean deposition had begun to subside, which caused a decrease in the lean:fat ratio as the animals matured. As a result of much of this early work, the general idea has been developed that marbling is the last fat that is put on, and occurs only after an animal has already put on most of its muscle. However, under conditions that are designed to maximize marbling, the age at which an animal is allowed to start expressing marbling is much younger than many people think.The major volatile fatty acids (VFA) produced by rumen microorganisms are acetate, propionate, and butyrate. These VFA are the main products of the digestion of feed by bacteria in the rumen, and serve as the main precursors for both glucose and fat in ruminants. On a forage based diet, the proportion of VFA would be approximately 65-70% acetate, 15-25% propionate, and 5-10% butyrate. Feeding diets high in readily fermentable carbohydrate (starch) increases the proportion of propionate produced through ruminal fermentation, and results in VFA proportions of approximately 50-60% acetate, 35-45% propionate, and 5-10% butyrate. This shift toward more propionate is extremely important to carcass characteristics. Recent research by Johnson et al. (1982) and Bines and Hart (1984) found that increased peak insulin concentrations with increased propionate production will also lead to increased insulin secretion. Insulin increases fat and protein syntheses while inhibiting the breakdown of fat and protein at the tissue level. The increase in fat and protein synthesis due to insulin secretion is due to enhanced rates of nutrient uptake by tissues.In order to understand how different management strategies can affect the ability of an animal to produce a choice carcass, and the yield grade of that carcass, some basic understanding of fat cell (adipocyte) growth is necessary. First, keep in mind that the marbling score is determined by the amount of intramuscular fat, and the preliminary yield grade is determined largely by the subcutaneous fat (backfat) measured at the 12 th rib. These two sites of adipocyte (fat cell) development may vary in synthesis rate with changes in age and nutrition. Adipose tissue mass increases by hyperplasia (cell proliferation), hypertrophy (cell enlargement), or a combination of both. Adipose tissue synthesis requires a source of fatty acid and glycerol 3-phosphate, almost all of which comes from glucose. In adult ruminant animals that are grazing forages, acetate is the major fatty acid precursor for adipocyte synthesis. When animals are fed a high concentrate diet, the amount of propionate produced increases relative to acetate. The importance of this is that propionate is the major glycogenic fatty acid. The reason that ionophores work on forage based diets is that more propionate is produced, and more glucose is produced in the liver, resulting in more net energy available to the animal.The age at which cattle are thought to develop sufficient intramuscular fat to achieve the choice grade is debatable, because of the ability of ruminants to use different feedstuffs for growth and the fact that we have management systems for nearly every possible feedstuff. Smith (1995) stated that the age of an animal dictated the timing of the onset of lipogenesis (the formation of fat), but the diet modulated the amplitude of the rate of lipogenesis. In combining data from different studies, Smith (1995) concluded that cattle needed to be on feed 167 to 236 days and weigh between 835 to 945 pounds before ATP citrate lyase activity was in sufficient quantity to allow for lipogenesis. The steers used in this analysis were 265 days of age when they were started on the experiment (Smith et al., 1984), which made them 432 to 501 days of age when were predicted to be able to start lipogenesis. However, Smith et al. (1984) reported that backfat thickness and the activities of several enzymes involved in lipogenesis were greater in steers fed a high concentrate, corn based diet versus steers fed a forage based, alfalfa pellet diet, even though the metabolizable energy intake was higher with the pelleted forage diet. Therefore, the end products of ruminal fermentation as well as net energy intake are interrelated in terms of adipocyte formation. This is substantiated by Smith and Crouse (1984) in a study where they fed either a corn silage (low energy) or ground corn (high energy) diet to Angus steers from weaning, at 8 months of age, to a terminal age of 16 or 18 months of age. They reported that acetate provided 70 to 80% of the acetyl units for lipogenesis in subcutaneous adipose tissue, but only 10 to 25% of the acetyl units for lipogenesis in intramuscular adipose tissue. Conversely, glucose (from propionate) provided 1 to 10% of the acetyl units for lipogenesis in subcutaneous adipose tissue, but 50 to 75% of the acetyl units for lipogenesis in intramuscular adipose tissue. The authors concluded that different regulatory processes control fatty acid synthesis in intramuscular and subcutaneous adipose tissue. Therefore, the enzymes responsible for fatty acid synthesis, and therefore lipogenesis and adipocyte hypertrophy, are regulated by the end products of ruminal fermentation, which are determined by diet.The age at which actual initiation of adipocyte growth begins is probably very early in life as reported by Vernon (1980) that hypertrophy of adipocytes begins after 100 to 200 days of age. Additionally, the age at which lipogenesis and adipocyte growth occurs is highly related to the age at which cattle are started on a high concentrate diet, due to days on a high concentrate diet, and a propionate fermentation being the major determining factor. This represents one window of opportunity for cow-calf producers. Fluharty et al. (2000) reported that 85% of steer calves weaned at 103 days of age, immediately started on a high concentrate diet, and harvested at 385 days of age (282 days on feed) graded choice, with 60% of the calves being in the upper 2/3 of the choice grade. Similarly, Myers et al. (1999) weaned steers at 117 days of age and either started them directly on a high concentrate or put them on pasture until 208 days of age at which time they were moved to the feedlot and fed the high concentrate diet. The calves started directly on a high concentrate diet were 394 days at slaughter (268 days on high concentrate diet), and the pasture calves were 431 days of age at slaughter (222 days on high concentrate diet). At harvest, 89% of the concentrate fed calves graded low choice or higher, with 56% average choice or higher, and 89% of the pasture fed calves also graded low choice or higher, with 38% average choice or higher. These kinds of results would not have been possible if the steers had been brought into the feedlot at a year of age. It would not have been genetics, but management that prevented the cattle from grading choice at a year of age.In summary, much of the bias toward older cattle in the feedlot industry has nothing to do with there being a magical age at which cattle will grade choice, but rather is directly related to the length of time cattle have been fed a high concentrate diet that results in a propionate fermentation which results in more glucose production. In fact, Midwestern feedlots that predominantly feed calves often achieve 70-80% choice cattle. However, many southwestern feedlots that feed yearlings often achieve only 50% choice cattle. Although there are definitely differences due to sorting loads of cattle, the ability of young cattle to grade choice cannot be argued from a scientific or practical standpoint. Additionally, if cattle were all harvested between 12 to 16 months of age, there would be much less variation in carcass weight, because cattle would not be as close to approaching their mature weight, and the genetic variation that exists in the beef industry would have less of an effect on consistency of carcass weight.Literature CitedBines, J. A., and I. C. Hart. 1984. The response of plasma insulin and other hormones to intraruminal infusion of VFA mixtures in cattle. Can. J. Anim. Sci. 64(Suppl.):304.Fluharty, F. L., S. C. Loerch, T. B. Turner, S. J. Moeller, and G. D. Lowe. 2000. Effects of weaning age and diet on growth and carcass characteristics in steers. J. Anim. Sci. 78:1759-1767.Guenther, J. J., D. H. Bushman, L. S. Pope and R. D. Morrison. 1965. Growth and development of the major carcass tissues in beef calves from weaning to slaughter weight, with reference to the effect of plane of nutrition. J. Anim. Sci. 24:1184.Johnson, D. D., G. E. Mitchell, Jr., R. E. Tucker, and R. W. Hemken. 1982. Plasma glucose and insulin responses to propionate in preruminating calves. J. Anim. Sci. 55:1224.Myers, S. E., D. B. Faulkner, T. G. Nash, L. L. Berger, D. F. Parrett, and F. K. McKeith. 1999. Performance and carcass traits of early-weaned steers receiving either a pasture growing period or a finishing diet at weaning. J. Anim. Sci. 77:311-322.Smith, Stephen B., 1995. Substrate utilization in ruminant adipose tissues. In: S. B. Smith and D. R. Smith (Ed.) Biology of Fat in Meat Animals. pp.166-188. American Society of Animal Science. Champaign, Ill.Smith, Stephen B. and John D. Crouse. 1984. Relative contributions of acetate, lactate and glucose to lipogenesis in bovine intramuscular and subcutaneous adipose tissue. J. Nutr. 114:792-800.Smith, Stephen B., Ronald L. Prior, Calvin L. Ferrell, and Harry J. Mersmann. 1984. Interrelationships among diet, age fat deposition and lipid metabolism in growing steers. J. Nutr. 114:153-162.Vernon, R. G. 1980. Lipid metabolism in the adipose tissue of ruminant animals. Prog. Lipid Res. 19:23-106. 翻译：管理及饮食对牛肉动物的末期肉质性状相互作用 为什么有些小牛实际价值超过别人饲养场和包装商虽然牛品种很相似,类型,帧大小,和肌肉厚度吗? 今天，答案很可能是在平均日增重，饲料利用率，产量等级，大理石纹评分，或百分比的零售收益率的差异。作为种猪或牛小腿生产者，你如何选择养殖动物和管理他们的后代，让小牛真正实现其最佳遗传潜力？这些是你可能需要能够回答的牛肉行业将继续从商品市场转向以价值为基础，电网营销行业里的动物个体根据自己的消费愿望鉴定和定价问题。为了回答这些问题，你可能需要了解一些反刍动物营养应用基础以及一些机会，存在管理可以提高胴体特性使你的牲畜达到其遗传潜力。 首先，你要明白，所有的营养物质（能量，蛋白质，维生素，矿物质和水）在层次结构中，它从维护发展成长哺乳期复制育肥用。这意味着，动物必须有足够的营养来维持它的身体之前，可发生骨骼或肌肉的生长，并且育肥前可能会出现这些必须发生。在种牛，泌乳休情发生时，动物是营养缺乏，但大量挤奶，不能繁育。您需要了解反刍动物营养中的第二件事情是，饲料是由附加到饲料颗粒来消化它的表面瘤胃细菌消化在瘤胃。在反刍动物,保持消化器官(瓣胃,瘤胃、网胃、小肠、大肠)以及肝脏和肾脏可以高达40 - 50%的能量和蛋白质消耗的30 - 40%。 饲料的饮食非常差,只有40 - 60%消化消化道的重量增加,因为更多的未消化的饲料仍在消化道的每个部分。 相比之下,谷物饮食导致减少器官重量与牧草相比,因为粮食是消化80 - 100%,和更小的粒度,使他们更快的消化和通过消化道。 结果是,粮食比饲料消化,加上它减少动物的维护需求减少导致消化器官质量,留下更多的营养对肌肉的增长和增肥。饲养场利用谷物的能量和消化特点完成牛。 然而,如果你有一个草基系统为你的奶牛(世界上最喜欢的),你不会切换到粮食。 提高动物的性能的一种方法与牧草研磨的饲料,以增加其消化率,使更多可用的表面积以细菌和增加的速度通过饲料通过消化道,大部分填补内在的饲料,减少和降低动物的维护需求减少消化道的重量。 然而,增加饲料的饮食的表面积并不是唯一的答案,因为并不是所有的获得都是相同的,你喂动物影响机体特征。 持续生产肉质细嫩，减少多余脂肪的外部生产，同时保持肌内脂肪沉积仍然是三个在肉牛业面临的主要挑战，尽管他们在1992年全国牛肉质量审核由全国养牛协会主办的确认。营养和遗传学是导致这些关注的两个主要因素。过度的外部回脂肪和内部焊缝和千米/小时脂肪生产原因在这两个饲养场，由于沉积脂肪与蛋白质和包装行业中，由于切边和收到为脂肪的低价格的高成本相比更高的能源成本效率的低下。发展中国家的管理战略，以生产出良好大理石，肉质鲜嫩的产品对提高地位的高品质牛肉行业至关重要。 通常情况下，牛完成对高精料日粮一段时间，从屠宰前80-280天。这肥育期，可以更快速，高效的经济增长，并增加肌内脂肪（大理石花纹）的沉积，使档次的选择与种植的牧草为基础的进料系统比较牛的牛的尸体。在一般情况下，组织被存入的顺序： 1。脑， 2骨，3肌肉，和4脂肪，然而，一些动物似乎完全跳过脑的部分。然而，一位年轻的，快速成长的动物是在增长的线性相位，自然把更多的骨骼和肌肉。作为动物的年龄，和它的遗传潜力肌肉生长开始高原，它会生长脂肪。冈瑟等。 （1965）报告了喂养肉牛的营养高或中等程度的影响。阉牛饲喂营养水平高以更快的速度比阉牛在营养上都与年龄和体重恒定基地中等水平饲喂两种沉积瘦肉和脂肪。骨骼的生长是不是不同的两个处理间，并更密切相关的年龄，而不是营养。然而，在这两个群体，脂肪沉积率作为加速岁的动物，而瘦肉沉积率降低。脂肪堆积的速度最为迅速的在哺乳期的后期，后瘦肉沉积已开始消退，这就造成了跌幅，肌肉：脂肪的比例为动物成熟。由于很多早期工作的结果，一般的想法已经开发出大理石花纹是放在最后的脂肪，而且只发生后的动物已经把大部分的肌肉。然而，旨在最大限度地提高大理石花纹的条件下，年龄在动物被允许开始表达大理石花纹是年轻得多是许多人的想法。 通过瘤胃的微生物产生的主要挥发性脂肪酸（ VFA）的乙酸酯，丙酸酯，丁酸酯和。这些挥发性脂肪酸饲料是由细菌在瘤胃中降解的主要产品，并作为葡萄糖和脂肪在反刍动物的主要前体。在基础饲料饮食，挥发性脂肪酸的比例将醋酸约65-70 ,15-25 丙酸，和5-10 丁酸。喂食饮食中容易发酵的碳水化合物（淀粉）增加丙酸通过瘤胃发酵产生的比例，结果在醋酸约50-60 ,35-45 丙酸酯和5-10的丁酸VFA的比例。这种转向更多的丙酸是胴体品质极为重要。最近的研究由约翰逊等人。 （ 1982）和Bines和哈特（ 1984）发现，高峰期增加胰岛素浓度与增加丙酸的生产也将导致胰岛素分泌增加。胰岛素增加脂肪和蛋白质的合成而抑制脂肪和蛋白质的分解在组织水平。脂肪和蛋白质的合成，由于胰岛素分泌的增加是由组织中的养分吸收增强率。 为了了解不同的管理策略如何影响动物的生产能力和选择胴体，胴体产量，等级，脂肪细胞（脂肪细胞）生长的一些基本的了解是必要的。首先，请记住，大理石纹评分是通过肌内脂肪的含量测定，并初步产量等级是由皮下脂肪（脂肪）决定在12届肋测量。这两个部位的脂肪细胞（脂肪细胞）的发展可能会有所不同的合成。由增生（细胞增殖）的脂肪组织质量增加，肥大（细胞扩大） ，或者两者的组合。脂肪组织合成需要的脂肪酸和甘油-3 - 磷酸源，其中几乎全部来自于葡萄糖。在成年的反刍动物被放牧牧草，乙酸是主要的脂肪酸的前体为脂肪细胞的合成。当动物被饲喂高浓缩物日粮，丙酸的生成量相对于醋酸增大。这一点的重要性在于，丙酸是主要的生糖脂肪酸。该离子载体基于草料日粮工作的原因是，更丙酸的生产，并且更葡萄糖在肝脏中产生，从而导致更多的净能量提供给动物。 牛的年龄被认为发展足够的肌内脂肪达到选择年级是有争议的,因为反刍动物能够使用不同的饲料的增长和我们对几乎每一个可能的饲料管理系统。 史密斯(1995)指出,动物的年龄决定的时机出现脂肪生成(脂肪)的形成,但饮食调制振幅脂肪生成的速率。 在结合数据从不同的研究中,史密斯(1995)得出的结论是,牛需要养活167至236天,体重在835至835磅之前ATP柠檬酸裂解酶活性在足够的数量,以便脂肪生成。 这个分析中使用的引导是265天的年龄时开始实验(史密斯et al .,1984),这使得他们432岁501天的预计什么时候能够开始脂肪生成。 然而，史密斯等人 (1984) 报告那背膘厚和几种相关酶活性的脂质被更大的阉牛喂高精料、 玉米基于饮食与操纵美联储的基础，牧草苜蓿草颗粒饲料，即使代谢能量摄入量较高的颗粒的饲料喂养。因此，最终产品的瘤胃发酵，以及净能量摄入量是相互关联的脂肪细胞形成。这属实由史密斯和克劳斯 （1984 年） 在一项研究，他们对安格斯喂青贮玉米 （低能量） 或地面玉米 (高能量) 饮食指导从断奶，在 8 个月的年龄，到终端的 16 或 18 个月的年龄年龄。他们报道，醋酸在皮下脂肪组织提供70 至80的乙酰单位为脂肪生成，但只有1025的乙酰单位为脂肪生成中肌内脂肪组织。相反，葡萄糖（来自丙酸酯）提供1到的乙酰单位10脂肪生成在皮下脂肪组织，但50至75 的乙酰单位为脂肪生成中肌内脂肪组织。作者的结论是不同的监管过程控制脂肪酸合成肌内和皮下脂肪组织。因此，这些酶负责脂肪酸合成，因此脂肪生成和脂肪细胞肥大，由瘤胃发酵的终产物，这是由饮食确定调节。 在其中脂肪细胞增长的实际起始开始的年龄可能是在生命早期所报告的弗农（ 1980）是脂肪细胞的肥大后的100天到200天开始。此外，在该脂肪生成和脂肪细胞生长时的年龄是年龄在哪个牛都开始在高精料日粮，由于在高精料日粮天，和丙酸发酵为主要决定因素高度相关。这代表一个窗口的牛-犊牛生产者的机会。福勒啼等人(2000) 报道 85%的 steer 犊牛在 103 日龄断奶，立即开始节食高浓缩，及收获在 385 天龄 (282 天饲料) 分级的选择，有 60%的小牛在上部 2/3 的选择品位。同样，迈尔斯等人(1999 年) 断奶阉牛在 117 天的年龄，要么开始他们直接上高集中或把它们放在草地上，直到 208 天的时代，当时他们被移到饲养场，喂高集中的饮食。小牛开始直接在高精料日粮为屠宰394天（高精料日粮268天）和牧场小牛是431天年龄屠宰（高精料日粮222天） 。在收获时，精矿犊牛补料，89等级低的选择或更高，有56 的平均水平选择或更高，和牧场喂养牛犊也分级低的选择或更高的89，与38 的平均水平的选择或更高。这些种结果不会是可能的，如果公牛曾在一岁时被带入饲养场。它不会是遗传的，但管理是防止黄牛从在岁分级选择。 总之,偏向于老牛饲养场行业无关,有一个神奇的牛的年龄等级选择,而是直接相关的时间长度的牛被喂食高集中的饮食导致丙酸发酵生产导致了更多的葡萄糖。事实上，中西部饲养场的饲料主要是犊牛通常达到70-80 。然而，许多西南饲养场的饲料一岁龄往往只能实现50 的牛。虽然有肯定，由于分拣牛负荷的差异，年轻的牛级选择的能力，无法从科学或实用的观点来看争论。此外，如果牛人12至16个月的年龄之间的所有收获，就不会有胴体重的变化少得多，因为牛也不会接近接近其成熟的重量，存在于牛肉行业的遗传变异将有少对胴体重一致性的效果。 第 8 页