Introduction:

The national specialized dairy herd has few estimates of genetic trends made in recent years. This lack of information limits the evaluation of both the genetic progress obtained and the estimation of the impact of national genetic evaluations (GE). The aims of this study were to estimate the genetic progress for Jersey and Brown Swiss dairy cattle populations, before and after the implementation of the national GE, and to analyze the main causes of the estimated genetic change.

Method:

The genealogical and productive databases of the respective national associations of registered dairy cattle breeders were used. Breeding values for milk yield (MY), adjusted to 305 and 210 days in lactation, were analyzed for the periods 1994-2015 and 1986-2016, for Jersey and Brown Swiss, respectively. Genetic trends were estimated by weighted regression by the number of animals of breeding values over the years of birth. To analyze the genetic progress, trends were estimated by periods (considering the year of start of the national GE), selection paths, origin of parents, herds, and by weighted averages of the sires’ breeding values.

Results:

In both breeds the general and per period genetic trends for MY were significantly different from zero (p<0.001). For Jersey, the trend for the whole period was -21.3 kg year-1, with a positive trend before the national GE (28.1 kg year-1) and negative (-49.0 kg year-1) after them. For the Brown Swiss breed, the general trend was 2.4 kg year-1; before the national GE the genetic trend was positive but of low magnitude (3.2 kg year-1); after the GE the genetic trend was reduced even further (0.43 kg year-1). In both breeds the genetic improvement before and after the national GE did not affect their structure in terms of the selection paths or origin of parents. The largest differences between weighted and unweighted averages were for those years with high genetic progress, unlike the last 10 years that showed the lowest genetic progress. Also, herds with selection objectives different to the majority of herds were found, and their exclusion (Jersey) or inclusion (Brown Swiss) from the national registered herd contributed significantly to decline the genetic progress for MY in the second period.

Conclusion:

The genetic improvement of MY for the populations studied has been positive but low for Brown Swiss and negative for Jersey. The genetic progress in both breeds decreased after the implementation of the national GE, so they have not had a positive impact on genetic improvement of MY in these populations. The results indicate the need to restructure the national genetic improvement program of the dairy populations studied, with the joint participation of the actors involved in the sector.

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