Figure 4. Accessed online at http://digitalcommons.unl.edu/ cgi/viewcontent.cgi?article=1235&context=rangebeefc owsymp on December 3, 2012. 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. . Therefore, it makes sense to cross a straightbred bull on crossbred females to take advantage of maternal heterosis instead of the reverse. Crossing: Crossing refers to the pairing of two different species, variants or races. Furthermore, management of breeding systems where multiple breeding pastures is required poses another obstacle. 2. Choice of breeds becomes an important consideration, as the number of breeds included in a rotation is increased. Backcrosses yield maximum maternal heterosis but only 50 percent of maximum individual heterosis. Cattle breeders already have developed a significant number of composite populations in diverse geographic regions around the U.S. Terminal crossing. What is the difference between the F1 and F2 generation? For example, crossbreeding can increase the milk production of cattle. Individual heterosis is maximized because the maternal line (Angus and Hereford) has no common breed composition with the terminal sire (Charolais). A high percentage of straightbreds are needed to produce straightbred and F1 replacement females, sacrificing the benefits of individual and maternal heterosis. Such a system should be used to take advantage of breed complementarity and heterosis while also fitting the herd size and resources of the operation. Matching Genetics To Environment To optimize reproductive rate in the cow herd, genetic potential for environmental stress, mature size and milk production should be matched with both actual environment and economical, available feed resources. The main difference between crossbreeding and GMOs is the mechanism of each technique used to create a beneficial organism. Terminally sired females are not kept as replacements, but are sold as slaughter animals, A terminal sire crossbreeding system in which replacement females are either purchased or produced from separate purebred populations within the system, A crossbreeding system combining a maternal rotation for producing replacement females with terminal sires for producing market offspring, A hybrid with a least two and typically more breeds in its background. CROSS BREEDING. AHDB Dairy - Commissioned by British dairy farmers, available here . Terminal crossbreeding - Wikipedia This single-sire rotation is expected on average to yield 59 percent of maximum individual heterosis and 47 percent of maximum maternal heterosis for the first twenty years of operation. Crossbreeding and GMOs are two types of techniques used in agriculture to produce plants or animals with desired traits. System which differs from static crossbreeding programs because it is modified to produced replacement females. Informa PLC's registered office is 5 Howick Place, London SW1P 1WG.