Evolution of Livestock Breeds How do breeds adapt

Evolution of Livestock Breeds How do breeds adapt and change? What is their history? Why does it matter? 1

I. What is a breed? A. Animals that, through selection and breeding, have come to resemble one another and pass those traits uniformly to their offspring. 1. Unfortunately this definition leaves some unanswered questions. For example, when is a crossbred animal considered a composite breed and when do we stop thinking about them as composites? The Genetics of Populations by Jay L. Lush helps explain why a good definition of "breed" is elusive. a. 2. A breed is a group of domestic animals, termed such by common consent of the breeders, . . . a term which arose among breeders of livestock, created one might say, for their own use, and no one is warranted in assigning to this word a scientific definition and in calling the breeders wrong when they deviate from the formulated definition. It is their word and the breeders common usage is what we must accept as the correct definition. Dr. Lush's definition helps us understand that it is at least in part the perception of the breeders and the livestock industry which decides when a group of individuals constitutes a "breed". 2

I. What is a breed? B. Breeds are primarily distinguished by visual characteristics: color, pattern, polled or horned condition, or extreme differences in form and shape. 1. Composite or synthetic breeds: new breeds being developed that combine the desirable characteristics of several existing breeds. 2. Purebred: purity of ancestry; only animals in that particular breed have been mated to produce the animal in question. 3

II. Breed Development A. The development or evolution of breeds can take different routes. 1. Sometimes, change that can occur as the result of selection for a small number of traits a. Holstein cattle have been selected primarily for milk production and are the highest milk producing cattle in the world. b. The Bedouins of the desert developed Arabian horses with strength, courage and stamina required for survival, and for the speed and responsiveness needed to win the tribal skirmishes. 4

II. Breed Development 2. Other breeds have traits that result from natural selection pressure based upon the environment in which they were developed. a. N’dama cattle from West Africa have, through the centuries, developed a resistance to trypanosomiasis or sleeping sickness spread by the tse-tse fly, which is fatal to most other breeds of cattle. b. The Chincoteague Pony descended from the feral horses on a barrier island off the coast of Maryland Virginia. 80% of their diet is coarse saltmarsh cordgrass and American beachgrass; their diet also includes poison ivy. The high concentration of salt in their diets causes the horses to drink twice as much fresh water as domestic horses and have a "bloated" appearance. 5

II. Breed Development B. Adaptations of an animal determine its niche in the environment. 1. Adaptation: evolution of structural, internal, or behavioral features that help an organism better survive in an environment. a. The large eyes of nocturnal animals. 2. Niche: the role of a particular species in a community regarding food, space, reproduction, etc. 6

II. Breed Development 3. Structure and Behavior Determine Environment a. Structure 1. Sharks have characteristics that enable them to survive in water, a streamlined body design and teeth that re-grow to replace broken ones. 2. The artic fox’s coat changes color for camouflage. b. Behavior 1. Bears survive a long, cold winter by hibernating. 2. Pigs are difficult to herd and move long distances, so they are used mostly in farming communities. 7

II. Breed Development C. Livestock have evolved over time through genetic changes that are both natural and selected by man. 1. Mutation: random error or change in the DNA sequence that may effect whole chromosome or one gene. a. This usually results in a negative result. 2. Natural Selection: a mechanism that explains how populations evolve; organisms with favorable variations survive. a. The Romney breed of sheep respond to it’s geographic and climatic conditions with hooves that are resistant to foot rot and fleeces that remain healthy in harsh weather. 8

II. Breed Development 3. Reproductive Isolation: occurs when organisms that formerly interbred are prevented from producing offspring. a. By developing different mating times. b. By geographic factors c. This is often induced by man. D. All these factors can lead to a new breed or even a new species 9

III. Why is biodiversity important? A. Why are we concerned about preserving information about minor, or relatively unknown, breeds of livestock? 10

III. Why is biodiversity important? 1. Holstein cow example a. Holstein has advantage over other breeds in the production of whole milk, this advantage is based on feeding high levels of cereal grains and pricing that favors low milk-solids content. b. The Dutch Belted breed displayed excellent milking ability in a grass-based dairy situation in trials in the early 1900 s and would be more preferable if cereal grains weren’t available. c. In Australia, composite breeds, such as the Australian Friesian Sahiwal, have been developed which have higher milk production levels than Holsteins in the tropical regions of that country. 11

III. Why is biodiversity important? 2. Natural resistance to diseases or parasites example a. Some breeds of sheep have a natural resistance to internal parasites. Should vaccines become restricted or uneconomical, then a breed such as the critically endangered Gulf Coast Native, with the parasite resistance it has developed through natural selection, could be of critical importance in the sheep industry. 12

III. Why is biodiversity important? B. Genetic diversity should be maintained to help meet the potential challenge resulting from changes in production resources and market requirements. 13

Now, it’s your turn to research! • As is states on your worksheet, you should visit this website: http: //www. ansi. okstate. edu/breeds/ • Click on the species assigned to you by your instructor: cattle, goats, horses, sheep, swine, or other • Click on a breed you have never heard of before and answer the questions on your worksheet as they relate to that breed. – If you pick a breed that does not answer most of the questions, switch to a different breed. • Be prepared to tell the class about the information you find. 14