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S1013: Genetic (Co)Variance of Parasite Resistance, Temperament, and Production Traits of Traditional and Non-Bos indicus Tropically Adapted Breeds (S-277)

Statement of Issues and Justification

Statement of Issues

Objective 1. Improvement of commercial cow-calf performance in the Southern region of the United States has been due to breed complementary and exploitation of heterosis for calf performance and cow reproductive and maternal traits. Heterosis expressed by crosses of non-Bos indicus tropically adapted breeds with traditional breeds has not been determined in the U.S.such information is needed by producers in the Southern region in order to make the most appropriate choice of breeds to use in crossbreeding programs.

Objective 2. The Southern region of the U.S. produces a large amount of forage that is utilized in cow-calf production. Environmental challenges in this region such as hot, humid weather and a wide variety of parasites have made Brahman crossbred cattle popular. Several breeds have been established in the U.S. based on Brahman-Bos taurus crossbred bases (i.e. Santa Gertrudis, Beefmaster, Brangus, Simbrah, etc.). Other tropically adapted breeds originating in different parts of the world have been evaluated in the U.S. (i.e. Sahiwal, Indu-Brazil, Gir, Nellore, Senepol, Tuli, Boran), and several have just recently been imported (Romosinuano, Bonsmara, Mashona). Knowledge about these tropically adapted breeds is still quite limited compared to more established breeds. Production information is needed on growth, carcass and reproduction characteristics of these tropically adapted breeds, as well as estimates of heterosis, so that cow-calf producers in the Southern region can make informed breeding decisions to profitably produce cattle under their environmental challenges and still produce desirable end-products for consumers.

Objective 3. The Southern region of the U. S. accounts for approximately 42% of the nations beef cows, the majority of which are supported by intensive forage production. Intensive forage utilization in combination with the physical environment (rainfall, humidity, ambient temperature) provides optimum conditions to maintain endoparasite populations that adversely affect cattle performance (Williams and Loyacano, 2001). Research in this region has primarily focused on identifying genetic types that reproduce and grow well under these environmental challenges. However, the genetic types that perform well in this environment tend to be those that provide the most challenge behaviorally (easily excitable, nervous) when restrained for routine management practices. The adverse affects of less desirable temperament on growth rate, meat quality and animal welfare are well documented. Therefore, additional research is needed to determine the genetic variation that exist for internal parasite resistance and for temperament differences.

Objective 4. Economically relevant traits in beef cattle are primarily quantitative in nature. Recent developments in selection tools offer the opportunity to utilize Quantitative trait loci (QTL) data in improvement programs; however, very little is currently known about the importance of QTL x environment interactions. The current selection tools utilize quantitative genetic theories that assume the expression of relevant genes is independent of parent of origin. Recent studies have demonstrated that parent-of-origin effects may have importance for many livestock traits.


Objective 1. Efficient cow-calf production in the Southern region is dependent on heat tolerance and parasite resistance in the cows and calves produced in this region. Brahman and Brahman-derivative cattle have successfully met this need and consequently, most cows and calves in the Southern region have some level of Brahman inheritance. Interest in non-Brahman tropically adapted breeds is emerging in the Southern region because of economic discrimination against Brahman and Brahman-derivative genetic types, particularly feeder and slaughter cattle. However, little is known about the performance of non-Brahman tropically adapted genetic types, particularly as crossbred cows and calves, nor is there sufficient information on the performance of the calves as stockers and feeders in the Southern Great Plains and High Plains regions. Consequently, there is a need to estimate direct breed and maternal additive genetic effects and heterosis for cows and calves resulting from crosses of non-Brahman tropically adapted breeds bred to British, Continental, and American (including Brahman) breeds in specific production environments.

Objective 2. The 13 states in the Southern region (AL, AR, FL, GA, KY, LA, MS, OK, NC, SC, TN, TX, VA) account for 14 million beef cows (42.3% of the nations beef cow inventory) and 406,200 producers (48.9% of the nations cow-calf producers) (USDA, 2002). In addition, the cooperating state of Nebraska accounts for 1.9 million beef cows and 23,000 cow-calf producers. It is important to characterize breeds that have potential to improve productivity in regions that have substantial environmental challenges. It is also necessary to characterize heterosis levels between these breeds so that informed breeding and production decisions can be made to increase profitability for cow-calf producers.

Objective 3. Internal parasites are one of the most economically important constraints in raising livestock (Wells, 1999). Unfortunately, the climatic conditions in the Southern region and the demand for year-round forage makes it difficult, even with rotational grazing, to have sufficient time between grazing bouts to break the life cycle of nematodes that are prevalent in the area. Traditionally, beef cattle management in the Southern region has involved anthelmintic treatment for internal parasite control. Continued dependence on chemical control could lead to resistant parasite populations. Additionally, dependence on chemical control has contributed to consumer aversion to drugs and drug residues in food, and the interest by cattle producers and environmentalists for reduced levels of drug residues in the environment (Donald, 1994; Stear and Murry, 1994; Frisch et al., 2000). The producer concerns about the evolution of resistant parasites, public concerns about residues in food and the environment, and the expense of chemical control could all be minimized if resistance to parasites was achieved.

The 1994 National Non-Fed Beef Quality Audit showed that bruises on cattle cost the beef industry $3.91/animal marketed and $30 million annually (Grandin, 1995). Data show that cattle with excitable temperament ratings produced a higher incidence of borderline dark cutter carcasses than cattle with calm temperament ratings (Voisinet et al., 1997a). Studies on temperament of cattle indicate that lower growth rate and reduced meat quality are associated with greater reactivity of animals during handling as indicated by their chute score (Voisinet et al., 1997a, 1997b). Studies to determine the amount of stress on farm animals during routine handling often have shown variable results and are difficult to interpret as related to animal welfare. It is important to breed animals with a calm disposition to reduce stress and to improve both productivity and welfare. Increasing public concern about animal welfare is a major reason why major restaurant companies and supermarkets are auditing handling and stunning practices in the United States and abroad (Grandin, 1997). Genetics also affects an animals response to stress. However, over-selection for docility may have detrimental effects on economically important traits, such as maternal ability (Grandin, 1997). Therefore, before engaging in a selection program to improve temperament, further research is needed to evaluate the genetic variation for temperament and the potential relationship between reactivity to handling and other traits such as productivity and maternal ability (Grignard et al., 2001).

Objective 4. Using phenotypes and pedigrees animal breeders have developed statistical tools that have contributed to significant changes in the characteristics and performance of the worlds beef cattle populations. These changes have enhanced gross performance and efficiency of beef production resulting in a more stable, relatively inexpensive protein supply.

Previous multi-state beef cattle research projects (S-10, S-243, and S-277) have been successful in leveraging resources from several locations. However, in hindsight technological advances in DNA research have not been utilized because DNA samples from animal populations were not collected and stored. The current proposal would establish protocols for establishment of a DNA bank that could be used in studies for parent-of-origin effects and QTL x environment interactions. Objectives 1, 2, and 3 outline numerous variables that can be measured or evaluated with benefits derived from their analysis. Objective 4 seeks to extend the benefits to take advantage of emerging technologies by preservation of DNA obtained from animals used in the other three objectives.

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