Genetic and phenotypic changes in litter size traits for dam breeds of pigs

The data from pig performance control of the animals born since 1990 were used to analyze genetic and phenotypic trends in litter size traits for dam breeds. 250000 litters of Large White sows and more than 68000 litters of White Meaty, Landrace, and Black-Spotted sows were used in the analysis. The 7-trait animal model implemented in routine genetic evaluation in Slovakia since January 2000 was used to estimate the breeding values of animals. Two litter size traits - number of piglets born alive in the first litter, and number born alive in the second and later litters as repeatability trait were used in the analysis. Genetic trend was estimated as average breeding values over the years of birth. The estimated genetic trend in both traits studied was not linear. The average breeding values of litter size traits decreased in the first two years, while in the next years we found positive improvement. However, the genetic changes were very small and cumulative improvement did not overcome 0.2 piglet per litter during 9 years. A little bit higher gain was found for animals born since 1995, estimated genetic gain were 0.14 for number of piglets born alive in the 1st litter and 0.10 in number born in the 2nd and later litters for Large White breed. The corresponding values for other breeds were 0.12 and 0.10. The phenotypic means for number born alive in the 1st litter fell down during the first two years (from 9.63 to 9.45 in Large White and from 9.83 to 9.60 in other breeds). In the next years, the phenotypic means for number born alive in the 1st litter gradually improved (from 9.45 to 9.77 for Large White pigs and from 9.60 to 9.87 for the other breeds), but animals born in 1998 only slightly overcame the animals born in 1990. The phenotypic values for number of piglets born alive in the 2nd and later litters in Large White grew up from 10.23 to 10.51 piglets per litter during the whole period studied, while for the other breeds the values varied between 10.36 and 10.51. We did not find significant differences among breeds in genotype or phenotypic changes. As can be concluded from the results, the improvement of litter size traits was very low during 9 years. A better testing organization and selection using the advanced method of breeding value estimation MBLUP animal model should help to improve the situation