GENETIC IMPROVEMENT OF BEEF CATTLE

GENETIC IMPROVEMENT OF BEEF CATTLE ADAPTATION IN AMERICA
W. Hohenbokena
, T. Jenkinsb
, J. Pollakc
, D. Bullockd
and S. Radakoviche

Introduction
Management systems and environmentsf differ widely for beef cattle populations across
the United States. A typical animal occupies several environments during its lifetime,
each presenting a unique set of challenges. No animal or breed maximizes the
conversion of input to salable product across all environments, nor is the genetic makeup
of any animal or breed optimally suited to the challenges encountered in any one
environment. To a certain degree, therefore, all beef cattle in America are less than
optimally adapted. The opportunity exists to improve profitability of beef cattle
production and to maintain integrity of cattle production environments through programs
designed to achieve balanced genetic potential for adaptation, production and product
quality within specific environments.
With financial support from the USDA Agricultural Research Service and the Beef
Improvement Federation and under the auspices of the National Beef Cattle Evaluation
Consortium, concerned geneticists and cattle producers met in March, 2004g
to define
adaptation in beef cattle, characterize important stressors in major production
environments, and identify opportunities to improve adaptation through genetic means.
Results were presented to the beef cattle industry in a symposium in October, 2004.
Participants and registrants agreed that the problem was critically important to profitable
and sustainable beef cattle production and that new programs should be designed to foster
the genetic improvement of adaptation of beef cattle in America. The goal of this
document is to present those conclusions to a wider audience of stakeholders.
Why are American beef cattle less than optimally adapted?
Response mechanisms to environmental challenges have been evolving in cattle
populations for millions of years. Adaptation has been successful, and populations
capable of sustained production now exist throughout most inhabited regions of the
world. Why, then, are American beef cattle less than optimally adapted? There are
several reasons.

a
Professor Emeritus of Animal Science, Virginia Polytechnic Institute and State University.
b
Research Animal Scientist, U. S. Meat Animal Research Center, Clay Center, NB. c
Professor of Animal Breeding, Cornell University and Executive Director, National Beef Cattle
Evaluation Consortium.
d
Associate Professor of Animal Science and Extension Beef Cattle Specialist, University of Kentucky. e
Radakovich Cattle Company, Earlham, IA.
f
Italicized words within regular text are defined in the Glossary.
g
Facilities provided by the Noble Foundation, Ardmore, OK.
2
Prior to domestication, cattle had a demanding but uncomplicated job description; they
had first to survive and then to reproduce. To accomplish these goals, they evolved
anatomical, physiological, immunological and behavioral mechanisms appropriate to
conditions in Eurasia, their center of origin. Thousands of bovine generations hence,
domestic descendents in contemporary America face vastly different parasites, diseases,
stresses and nutritional challenges. It is not surprising that a gene pool conferring
adaptation to past and distant environments confers less than optimum adaptation
to current and, indeed, to future conditions.
Cattle were domesticated in western Asia some 10,000 years ago. Cattle and cattle
production technologies subsequently migrated outward from centers of domestication,
eventually to colonize much of Europe, Africa and Asia. With an estimated initial
migration rate of six miles per decadea1
, natural selection could easily accommodate
adaptation of cattle to their newly encountered environments. During recent times,
however, the speed of migration has accelerated (air freight can transport animals,
gametes and embryos throughout the world in a matter of hours). Beef cattle
management systems are changing more rapidly as well, typically in the direction of
greater intensification. Compared to only a few decades ago, for example, cows now
produce their first calf at two rather than three years of age, animals are maintained at a
higher density per unit of land area, and cattle are fed to market on higher energy diets.
In many instances, management systems and environments are changing more
rapidly than animal populations can adapt to such changes through natural
selection2
.
Domestication created opportunities for the formation of and differentiation among many
locally adapted cattle populations. Our ancestors lived in a society of small tribes at that
time, with limited material and cultural exchange among groups3
. The role of cattle was
determined by the needs of each tribe- milk and meat production, power generation, the
accumulation of wealth and religious or cultural iconography, for example. Tribal
definition of value thus imposed a new ‘environmental’ challenge on cattle populations,
that of fulfilling an economic role. Phenotypic selection was applied4
, as animals more
successful in meeting the community standard of value were allowed to reproduce while
less successful individuals were not. Planned matings and natural selection exerted by
local environmental challenges also promoted the creation of populations well adapted to
local requirements. As social organization gradually evolved from tribes to communities,
communities to villages, villages to cities, cities to states and states to nations,
interactions among human populations increased5
, and the isolation of local cattle
populations diminished. When allele frequencies and gene combinations favorable to
production in a local environment were disrupted through exchange of breeding animals,
adaptation to specific environments declined. National and international trade in
breeding animals, gametes and embryos now allows an animal to produce offspring in
environments very different from the one to which that individual is adapted. While
providing many benefits to efficient livestock production, movement of genes into new
environments also can reduce adaptation of a resident herd to its unique conditions
and challenges.

a
Numerical footnotes correspond to literature citations listed at the end of the document.
3
An idea whose time has come back
Beef cattle geneticists in the American South and West concluded in the 1970s that
“genetic adaptation to local environments is important in commercial beef cattle
production”6
. Furthermore, “indiscriminate distribution of breeding stock (or their
semen) to different environments” should be avoided until something is known of the
adaptive merit of that stock. They advised that animals be performance testeda
under
environmental conditions similar to those that their progeny were likely to encounter.
Evidence supporting these recommendations was provided by their classical experiment
to investigate genotype by environment interaction. They started with two genotypes, a
line of Hereford cattle selected in and adapted to Montana and another Hereford line
selected in and adapted to Florida. These states also constituted the production
environments; half of each herd was transferred to the other location, where production
of the cows and their descendants was monitored over an 11-year span. Genotype by
environment interaction would occur if the production difference between cows of
Montana versus Florida origin differed depending upon the location in which they were
compared. Such was the case. At Miles City, Montana, the Montana cows and their
descendents exceeded Florida cows and their descendants by an average of 14 pounds in
calf production per year. In Brooksville, Florida, average annual calf production of
Florida cows and their descendants was 84 pounds greater than that of Montana cows
and their descendants! As might have been expected, cows from each origin were most
productive in the environment to which they were adapted.
Gradual response to mild selection to increase production traits, as occurred during most
of the history of the co-dependence between cattle and man, generally does not detract
from an animal’s ability to survive and reproduce. In fact, selection to increase sustained
annual production selects automatically for traits important to adaptation. In recent
decades, however, the application of refined knowledge of inheritance, improved
information technology and advanced reproductive techniques has allowed dramatic
increases in selection intensity and selection response. Rapid response to intense
selection for increased product (as opposed to increased sustained production) can
sequester resources formerly utilized to support reproduction and survival. Rapidly
increased genetic potential for production may be achieved, therefore, at the
expense of decreased genetic merit for adaptation.
Hidden costs of selection
Among domestic food animals, broiler chickens are the poster species for rapid rate of
response to selection. They are highly prolific and turn generations rapidly, allowing for
a high intensity of selection. Furthermore, commercial poultry breeding companies have
clear, consistent objectives, most prominently to increase growth rate, feed conversion
efficiency and breast meat yield. Selection responses in these traits have not been
without cost. Undesirable correlated selection responses include reduced fertility of
broiler breeders and increased severity and incidence of ascites, sudden death syndrome,
distortion of long bones and tibial dyschrondroplasia throughout the life cycle7
. In a

a
Words in regular print within italicized text are defined in the Glossary.
4
similar manner, progeny testing and artificial insemination have fostered rapid response
to selection for increased milk yield in dairy cattle, for which undesirable correlated
responses are poor rebreeding performance and increased incidence of metabolic
imbalan

Results (English) 3:

在美国
W hohenbokena
肉牛适应性遗传改良，T. jenkinsb
，J. pollakc
，D. bullockd
和美国radakoviche

介绍
管理系统和environmentsf大相径庭肉牛群体在
美国。一个典型的动物在它的一生中占有几个环境，每一个呈现出独特的挑战。没有动物或品种最大限度地提高输入转化为可销售的产品在所有的环境中，也不是遗传
任何动物或品种最适合在任何一个
环境中遇到的挑战。因此，在一定程度上，美国的所有肉牛都不到最佳的适应。提高肉牛养殖收益的机会生产和维护牛生产环境的完整性，通过程序设计，以实现平衡的遗传潜力，适应，生产和产品质量在特定的环境中，有关遗传学家和养牛者遇见三月，2004g
定义
肉牛改编，描述主要生产
环境重要的压力源，并识别改进机会通过遗传的方式适应。
结果在十月的一个座谈会，对肉牛产业的2004。
参与者和注册人同意的问题是非常重要的和可持续的盈利
肉牛生产和新项目的设计应以培养
在美国肉牛适应的遗传改良。本文件的目标是提出这些结论的利益相关者的更广泛的观众。为什么美国牛肉牛不到最佳的适应？在牛的人口中，有数以百万计的年的环境挑战的响应机制一直在不断发展。适应已经成功，和人口的能力，能够持续生产现在存在的世界大多数居住地区的世界。为什么，那么，美国的牛肉牛不到最佳的适应？有
几个原因。

一
动物学荣誉教授，弗吉尼亚理工学院的研究动物科学家，美国肉类动物研究中心，粘土中心，NB。动物育种学教授，康奈尔大学和执行主任，国家肉牛饲养管理专家，肯塔基大学动物科学与推广肉牛专家。E
radakovich牛公司，除了，IA。
F
斜体在常规文本词汇在词汇表中定义的。
G
设施由高贵的基础，该提供的，好的。在驯养之前，牛有一个要求，但简单的工作描述；他们是先生存，然后再繁殖2。为了完成这些目标，他们进化了解剖学、生理学、免疫学和行为学机制，适合于欧亚大陆的情况，它们的起源中心。成千上万的牛代以后，
国内后裔在当代美国面临不同的寄生虫，疾病，营养
压力和挑战。这是不令人惊讶的是，一个基因池赋予的，以适应过去和遥远的环境赋予小于最佳适应的电流，事实上，未来的条件。牛在10000年前在亚洲被驯养了。牛和牛
生产技术，随后从中心向外迁移
归化，最终在欧洲大部分地区，非洲和亚洲。与估计的初始
迁移率每decadea1
六英里，自然选择可以轻松容纳
牛他们遇到的新环境的适应。在最近的几次，
然而，迁移速度加快（航空货运运输的动物，
配子和胚胎的整个世界在一个小时）。牛的管理系统也在不断变化，通常在更大的方向发展。与几十年前相比，例如，奶牛现在在两个而不是三岁制作第一小牛，动物都维持在一个
高密度每单位面积土地的，和牛喂的是市场对更高能量的饮食。
在许多情况下，管理系统和环境的变化更迅速
比动物种群适应自然
selection2
这样
变化。驯化创造了许多本地适应牛种群的形成和分化的机会。我们的祖先生活在一个小的部落社会，
时间，在3
有限的物质和文化交流。牛的作用是由每个部落的需求决定的，每一个部落的需要，牛奶和肉类的产量，发电量，财富和宗教或文化意象的积累，例如。部落的价值观，从而强加了一个新的“环境”的挑战，对牛的人口，实现经济的作用。表型选择是applied4
，动物更
成功会议的社区价值标准被允许复制而不成功的人不
。计划交配和自然选择产生的
当地环境的挑战也促进了适应当地需求的人群
创作。作为社会组织逐渐从部落社区，
社区村庄，村庄，城市，州和国家的城市国家，
人群提高
之间的相互作用，和隔离的地方牛
人口减少。当等位基因频率和基因组合有利于生产在当地环境被破坏，通过交换繁殖的动物，适应特定的环境下降。国内和国际贸易
饲养动物，配子和胚胎现在允许动物在
产生后代不同的环境，这是个人的适应。而
高效畜牧业生产提供许多好处，运动基因为新
环境还可以减少居民群体以其独特的条件
和挑战的适应。

一
数值对应文献引用脚注列在结尾的文件。3一种思想的时代已经回来
肉牛遗传学家在美国南部和西部的结论在上世纪70年代，
遗传适应当地环境，是重要的商业
肉牛生产“6
。此外，“不加选择地分布在不同的环境中的育种股票（或它们的精液）”应避免，直到有一点是已知的股票的自适应优点。他们建议动物性能testeda
下
环境条件类似，他们的后代可能会遇到。
支持这些建议的证据被他们的经典实验
提供探讨基因型与环境的相互作用。他们开始有2个基因型，一个适应蒙大纳和另一个赫里福德线
选定在赫里福德牛选线和佛州。这些州也构成了生产的环境中，一半的每一个牛群被转移到其他地点，在那里生产的奶牛和他们的后代被监测超过11年的跨度。基因型如果奶牛的生产差异，蒙大纳与佛罗里达州的原产地不同的位置，他们在哪一组相比，环境的相互作用会发生。这样的情况。在蒙大纳，万里城，蒙大纳奶牛及其后代超过
佛罗里达州奶牛和在
小牛生产每年平均14英镑他们的后代。在奥卡拉，佛罗里达州，佛州牛及其后代的平均年产量为84磅，比蒙大纳牛和后代大！正如预期的那样，奶牛从每一个起源是最有生产力的环境中，他们的适应。在牛和人之间的共同依赖的历史，一般不影响从动物的生存能力和繁殖能力。事实上，选择增加持续的年度生产选择自动的特征重要的适应。在最近的几十年里，然而，对继承的精炼知识的应用，提高了信息技术和先进的生殖技术已经允许戏剧性的增加，在选择强度和选择响应。为提高产品的激烈
选择快速响应（而不是增加持续生产）可以
封存以前用来支持繁殖和生存的资源。快速增加的遗传潜力，可以实现生产，因此，在以降低遗传优点为代价的情况下，在国内食品动物中，选择了一种快速增长率的招贴。他们是高度多产的，并迅速转一代，使高强度的选择。此外，商业家禽育种公司有明确的，一致的目标，最突出的增长速度，饲料转化效率和乳房肉产量。在这些特性中的选择反应没有成本，没有成本。不良的相关选择反应包括生育能力降低的
肉种鸡和严重程度和发病率增加腹水，猝死综合症，
整个生命cycle7
长骨头和胫骨dyschrondroplasia失真。在

一词在
定期打印斜体文本在词汇表中定义的。
4
相似，子代测定和人工授精培育快速反应
选择对奶牛产奶量增加，而不良反应相关
繁殖性能差、老化代谢
发病率增加