This will result in lower production per breeding female than will be seen in crossbred females because 0 percent maternal heterosis results. Small operations can often realize efficiencies relative to labor and pasture utilization by eliminating heifer development from their overall operation. 51:1197. GMO: The desired trait can be genetically engineered at once. Bos indicus breeds have contributed to several composites because of their adaptation to hot climates. Crossbreeding is the mating of two pure breeds, while GMOs are the alteration of the genetic material of an organism. What is the first step in developing a breeding program? A percentage of the breeding females are placed in the two-breed rotation, and another percentage is mated to a terminal sire. Crossbreeding is the mating of two or more breeds to produce crossbred progeny. 1. Approximately 40 to 50 percent of the youngest cows in this system are in the rotational phase and the remaining cows are in the terminal phase. Table 7. Therefore, using specialized sire and dam breeds is not possible. Assuming that, as purebreds, 85 of 100 cows exposed deliver a live calf and 95 percent of calves born survive to weaning; then weaning weight per cow exposed would be 349 pounds for Angus, 351 pounds for Herefords and 396 pounds for Charolais. The three-breed terminal system results in the most hybrid vigor of any crossbreeding scheme. Of course, use of sex-sorted rather than conventional semen for this purpose minimizes the number of steer calves that are produced from maternally-oriented sires. Possibilities for within herd production of crossbred replacement heifers include the use of AI on a fraction of the cows, something not always within the management capabilities of some producers; use of a breed of bull on purchased purebred heifers to produce cows for a terminal cross, which also involves purchase of a fraction of the replacements plus use of at least two breeds of sire; or use of a rotational crossing system either in combination with a terminal sire or as a stand-alone system. All calves from the terminal mating are sold. Static crossing systems work well in species with high reproductive rates (poultry, swine) but less well in species with lower reproductive rates (cattle). No single breed excels in all important beef production traits. Maternal heterosis is maximized because the breeds crossed to produce the maternal line (the black-baldies) have no common composition. Crossbreeding for Beef Production: Experimental Results. J. Anim. 2010. The primary benefit of a three-breed rotation over a two-breed rotation is the increase in hybrid vigor. An example of a two-breed specific cross would be mating Angus bulls to Hereford cows. For example, Breed A averages 610 pounds at weaning, and Breed B averages 590 pounds at weaning. the remaining breed. This phenomenon allows a breeder to blend the superior traits of one animal with the superior traits of another animal into their crossbred offspring. For cow-calf operations that raise and develop their own replacements heifers, beginning the breeding season with artificial insemination can allow the desired breed composition to be maintained in the early-born heifer calves. Use of all heifers calves from the two-breed rotation as replacements can be limiting if death loss is high or if the proportion of calves which are female is low in a particular year. An example of an unfavorable result of heterosis is an increase in fatness of crossbred calves. Composites are a stable intermating population originating from crossbred matings. Both tools offer the benefits of heterosis, breed differences and complementarity to help producers match genetic potential with market preferences, the climatic environment and available feed resources. Specific crossbreeding systems use a specific pattern of consistently mating a particular breed of bull to a particular breed or breed-cross of cow. weaned over 9.4 years) or Herefords (2,405 lbs. Out breeding : Out breeding of unrelated animals as male and female is known as out breeding. Both individual and maternal heterosis are less than maximum because of the common breed composition of sire and dam. Cows express partial maternal heterosis and calves express 100 percent individual heterosis. If a sires daughters are retained as replacements, action needs to be taken to prevent inbreeding. All crossbred BA females are mated to breed C, a terminal sire breed. Three-breed Rotation Modified Rotation this involves using a bull of one breed for a set number of years (recommendation of four years) then rotating to a different breed of bull. Also, assuming 25 breeding-age females per sire, at least 100 breeding-age females are needed for this system to be efficient. In comparing crossbreeding systems for single-sire herds, several conditions will be assumed: Two rotational systems have proven useful in single-sire systems (M. A. Lamb and M. W. Tess, 1989. The downsides are that more labor, management, and breeding pastures are needed than in a two-breed rotation. Management is more complex than for the two-breed rotation. Signifies new breeds or new lines. Figure 1. This advantage may be partially offset by problems associated with choice of a third breed. Breeding Programs Producers in the subtropical regions of the U.S. favor Bos indicus x Bos taurus crosses. 67:28). The resulting offspring are not brought back into the system. A rotation, usually of two maternal breeds, supplies cows for a terminal mating. Backcrosses yield maximum maternal heterosis but only 50 percent of maximum individual heterosis. Because replacement heifers are not being produced, sires can be chosen only on growth and carcass with no attention to maternal traits. A three-breed rotation initiated again with breed A cows would have a breed sequence for sires as shown in Table 3, with the subscripts representing different bulls of breeds A, B, and C. This single-sire rotation is expected to yield 77 percent of maximum individual and 60 percent of maximum maternal heterosis. Sire rotation is a common crossbreeding system. Hybrid vigor, or heterosis, is the increased production of certain traits from the crossing of genetically different individuals. In this system, females sired by Breed A are mated to sires of Breed B, and females sired by Breed B are mated to sires of Breed A. Livestock Breeding Systems - Student Notes Designing a Breeding Program Segment 1. Genetics is the science of heredity and variation. View Livestock Breeding Systems Student Notes-2.docx from SCIENCE 4 at East Bridgewater High. Traits such as growth and reproduction usually respond favorably to crossbreeding. Breeding scheme for a three-breed rotational crossbreeding system. Breeding and genetic management is an essential part of operational decision making, with decisions notably impacting profitability. A crossbreeding system must be a planned process that takes advantage of breed effects and heterosis or it becomes chaos. No one system is optimum for all beef cattle producers. The rotaterminal system is more sensitive to management than are the other systems. In a two-breed rotation, females sired by breed A are always mated to males of breed B. Because preferred feed resources vary by area, breeds chosen for the cowherd should be well adapted to feed resources within a given area. What is the difference between calamari and squid? Identification is easily accomplished with an ear-tagging system with color representing breed of sire. Before implementing a crossbreeding program, a producer needs to have well-defined goals for the operation. Defined as the difference between the average of reciprocal F1 crosses (A x B and B x A) and the average of the two parental breeds (A and B) mated to produce the reciprocal crosses, heterosis was found in one study to increase weaning weight per cow exposed 23%. Crossbreeding and GMO (Genetically Modified Organism) are two types of techniques used in agriculture to develop animals and plants with desired traits. Rotational systems involve a specific cyclical pattern of mating breeds of bulls to progeny resulting from a preceding cross. Genetic engineering is used in crops to improve nutrient composition and quality, disease and pest resistance, crop yield and food security. modified static crossbreeding system definition. The composite breeding system combines desirable traits of how many breeds of cattle? Since cows share approximately ? Similarly, selection of breeds depends on various factors, including feed resources as well as availability of breeding stock. Table 6. system in which replacement females must be purchased from or produced in. Whenever possible, cows sired by breed A bulls should be mated to breed B bulls, cows sired by breed B bulls should be mated to breed C and cows sired by breed C bulls should be mated to breed A. This rotation uses sires of Breeds A, B, and C. Breed A sires are mated to females sired by Breed B, Breed B sires are mated to females sired by Breed C, and Breed C sires are mated to females sired by Breed A. Replacements are retained from within the herd, and three breeding pastures are needed. These systems vary in the direct and maternal hybrid vigor they produce, the number of breeding pastures they require, the number of breeds used, optimal practical herd size, whether or not replacement females are produced or purchased, labor and management requirements, and timing of herd sire purchases. For example, 50 percent of herd females are in the two- breed rotation, and 50 percent are mated to a terminal sire of Breed T. The females in the two-breed rotation produce the replacement heifers, and the females in the terminal cross produce all market calves. Only one breeding pasture is required, and replacement heifers are generated within the herd. A variety of crossbreeding systems are available for breeders to use in their genetic improvement programs. The system does not provide for replacement females internally. The hybrid vigor from this mating can be calculated with the following equation: (Crossbred performance average Straightbred performance average) Straightbred performance average. Another is that the heterosis achieved through the crossing of disparate genetic lines in production of the F 1 generation is lost . Composites usually incorporate a combination of breeds, each of which contributes a characteristic desirable for good performance or environmental adaptation. The two-breed rotation can be used with fewer cows; however, bull expenses per cow will be greater. Commercial cattle producers face input cost management decisions every year. "Genetically Modified Organisms (GMO): Transgenic Plants and Recombinant DNA Technology." A series of alternating backcrosses are used in the two-breed rotation. Crossbreeding is also an important part of commercial production systems because of the improvement in efficiency from heterosis and the potential to exploit differences between breeds or lines. Composite populations developed by mating like animals resulting from two or more breed crosses provide an alternative to more complex crossbreeding systems. mating of related individuals in which the sire and dam share at least one ancestor. In general, EPDs available for bulls from purebreds used in rotational systems tend to be more accurate than EPDs for bulls used in a composite population because they're based on a larger number of records. To effectively design a crossbreeding system, use these standards: Design a cow herd that fits the environment Use breeds for the cow herd that are similar Use a terminal sire breed that fits the market Heterosis1 and breed complementation in crossbreeding systems. Therefore, it makes sense to cross a straightbred bull on crossbred females to take advantage of maternal heterosis instead of the reverse. Why or why not? Farm animals, crops and soil bacteria are genetically modified to produce GMOs. The Mississippi State University Extension Service is working to ensure all web content is accessible to all users. Pen mating is mostly used by which of the following? A crossover design is said to be strongly balanced with respect to first-order carryover effects if each treatment precedes every other treatment, including itself, the same number of times. Angus and ? A dependable supply is needed if they are to be purchased. What method of breeding is used to develop specialized "lines" of animals? Likewise, they must decide on practices that affect productivity and returns. Only one breeding pasture is needed, and sire identification of breeding females is easily recognized. What type of breeding system is designed to take advantage of both hybrid vigor and breeding value? The hybrid vigor, or heterosis, is the tendency of the crossbred animal to display the qualities that are superior to either parent. Considerations when using the two-breed rotation are breed type, resources available to raise replacement heifers, and size of cowherd. It is created by introducing one or more genes of one species into a completely different species. In a Hereford-Angus rotation, progeny resulting from an initial Hereford-Angus cross would be backcrossed to one of the parental breeds, say Angus. What is the proper term for the measure of how inbred an animal is? This is only a slight gain from the three-breed rotation with the added cost of labor, management, and another breed of sire. Disadvantages of the three-breed rotation are that an additional breeding pasture and breed of bull(s) must be maintained. No single system is suited for all herds. GMO: GMO results from the genetic modification of the genetic make-up of an organism. In a three-breed rotation, a third breed is added to the sequence. Using the previous example of 25 females per sire with three breeds of sire, at least 75 breeding age females are needed to be efficient. A three-breed rotaterminal system provides breed complementation in the terminal mating, which involves about the oldest 40 percent of the cow herd. Efficient crossbreeding systems for herds of this size would increase the productivity and profitability of the states beef industry. Figure 1: A Labradoodle, a cross between a poodle and a retriever. Crossing specialized male breeds with crossbred females maximizes the impact of desired characteristics and minimizes the impact of undesired characteristics of each breed. Static-terminal sire crossing systems. This in turn would enable the operation to select natural service bulls of a different breed composition, with selection based purely only on the sires merit for terminal traits. Accessed online at http://digitalcommons.unl.edu/ cgi/viewcontent.cgi?article=1235&context=rangebeefc owsymp on December 3, 2012.