Contributions of Portuguese cattle breeds to genetic diversity using marker-estimated kinships.

The quantitative assessment of genetic diversity within and between populations is important for decision-making in genetic conservation plans. In our study, we applied the livestock core set method to define the contribution of 15 cattle breeds, 11 of which are Portuguese indigenous cattle breeds, to genetic diversity. In livestock core set theory genetic diversity is defined as the maximum genetic variance that can be obtained in a random-mating population that is bred from the populations present in that core set. Two methods to estimate marker-estimated kinships to obtain the contributions to the core set were used in this study: the weighted log-linear model (WLM) and the weighted log-linear mixed model (WLMM). The breeds that contributed most to diversity in the core set were Holstein-Friesian followed by the Portuguese Mertolenga and Cachena for both WLM and WLMM methods. The ranking of relative contributions of cattle breeds was maintained when we considered only the Portuguese cattle breeds. Furthermore, we were able to identify the marginal contributions and respective losses of diversity for each of the 11 Portuguese cattle breeds when we considered a subset of populations that are not threatened of being lost (the Safe set composed of the four exotic breeds present in this study). When WLM was used losses in genetic diversity ranged from 2.68 to 0.65% while the loss in founder genome equivalents ranged from 37.37 to 8.43% for Mertolenga and Brava de Lide breeds respectively. When WLMM was used losses in genetic diversity and founder genome equivalents were less extreme than for the WLM method, ranging from 1.27 to 0.69 and 26.8 to 12.99 respectively.

Sister chromatid exchange (SCE) in cattle: a comparison between normal and rob (1;29)-carrying karyotypes.

Fifty-one phenotypically normal Maronesa cattle (28 males and 23 females) from North-Portugal were studied to ascertain the frequency of SCEs in normal karyotypes and in karyotypes carrying rob (1;29). In the 1852 examined cells, the mean value of SCEs was 7.1 +/- 3.6. In the 841 cells from 23 normal karyotype animals the mean value of SCEs was 6.6 +/- 3.6; in the 611 cells from 17 heterozygous carriers of rob (1;29) the mean value of SCEs was 7.1 +/- 3.3; in 400 cells from 11 homozygous carriers the mean value of SCEs was 8.1 +/- 3.8. All these differences were highly significant (P < 0.001). No statistical differences were found between the mean values of SCEs in male (7.0 +/- 3.7) and female (7.1 +/- 3.5) cells in the total sampling. However, in 280 cells from two pairs of heterosexual twins, we found that the mean value of SCEs in female cells (7.9 +/- 3.0) was significantly higher than that in male cells (5.7 +/- 3.1).