The majority of cow-calf beef cattle enterprises in the Great Basin produce beef cattle on rangelands. In general, ranching operations have minimal cow contact through widespread use of natural service by breeding bulls that are rotated yearly or every few years. Calving can take place on open ranges and is not assisted by veterinarians. Under these conditions, paternity of calves cannot be assessed. Tracking paternity in calves on a herd basis can improve breeding decisions. For example, bulls not producing calves or with a poor performance based on calf weaning weights could be culled.

DNA-technologies allow for paternity testing. DNA-markers of choice in paternity testing are usually microsatellites (Fries et al., 1990) that are co-dominant DNA markers although single nucleotide polymorphism (SNP) have also been proposed (Heaton et al., 2002). Essentially, the typing of several microsatellites is carried out in the offspring and in the alleged parent. A sire is eliminated as a parent when the genotype of the offspring is not compatible with the parental genotype for at least one microsatellite. Probabilities of exclusion are generally estimated in order to evaluate DNA markers for paternity testing in a given population. The probability of exclusion is the probability of rejecting an alleged parent that is a random individual within the population, the probability of exclusion depends on the marker type, the number of alleles, and the allele frequencies in the population to be used for paternity testing.

DNA paternity identification open new possibilities for the genetic improvement of open free range beef cattle operations. Progeny testing of bulls based on weaning weights of their calves might be used for culling decisions but also to produce replacement bulls for the herd. The rancher must sell or trade the calves with highest breeding values to other ranchers if natural service is used for breeding.

We have estimated probabilities of exclusion in eight Nevada beef cattle ranches for a panel of 15 microsatellites and arrive to the conclusion that they can be used for DNA paternity identification across Nevada beef cattle operations (Gomez-Raya et al., 2007). However, implementation of a DNA paternity program requires a systematic sampling of biological tissues in bulls and calves, systematic data storage and analysis of paternities. The latter includes software able to discriminate alleged parents. An economically sound paternity program (high benefit-cost ratio) might require fewer microsatellites than required for full paternity identification.

The goals of this current project proposal are aimed at developing strategies that will increase the efficiency of DNA paternity testing programs by decreasing the time required to obtain results, analyzing test accuracy and decreasing the costs associated with DNA testing.

The results of this research will greatly aid in the development of a DNA paternity testing program at UNR which would be available for use by Nevada cattle producers for the lowest possible price. In order to accomplish the goals of this research we plan to complete the following research aims:

1. To evaluate the economic value of an optimized DNA paternity testing program using six Nevada beef cattle ranches which operate in a free range setting.
2. To investigate the benefit-cost ratios of using sire-dam-calf trios versus sire-calf duos in DNA paternity testing.
3. To investigate the ability to reduce genotyping costs using a sequential paternity rejection strategy.
4. To investigate the increased benefits of using DNA parentage information in heifer selection.
5. To develop methods to incorporate animal disease surveillance with a paternity testing program to allow for increased traceability of livestock carriers and reducing the incidence of disease outbreaks.