|Title||Genetic aspects of somatic cell count in the Italian Holstein Friesian population|
|Source||Wageningen University. Promotor(en): Johan van Arendonk, co-promotor(en): Ab Groen. - [S.I.] : S.n. - ISBN 9789058087966 - 155|
Animal Breeding and Genomics
|Publication type||Dissertation, internally prepared|
|Keyword(s)||zwartbont - rundveerassen - celgetal - genetische factoren - selectiecriteria - fokwaarde - genetische modellen - heritability - melkresultaten - kenmerken - dierveredeling - holstein-friesian - cattle breeds - somatic cell count - genetic factors - selection criteria - breeding value - genetic models - heritability - dairy performance - traits - animal breeding|
|Categories||Cattle / Races, Selection, Genetics|
The objective of this thesis was to evaluate genetic aspects of somatic cell count (SCC) in Italian Holstein Friesian population in order to define how to include this trait in selection criteria. Several values of heritabilities were estimated (.06 to -.21) for three parities using different data sets and model of analysis. A model for breeding value estimations of first parity cows was defined and further improvements of the model were discussed. Genetic correlations with production were highly variable in value and sign depending on parity and model of analysis (-.14 to .24). Variation existed between and within lactation and it was concluded that it is important to account for this variation in selection. When a unique value is necessary, a correlations value around zero, indicating a null genetic relationship between production and SCC, should be used. Using an hazard model, it was estimated that an increase in phenotypic level of SCC in Italian Holstein population resulted in higher rate of culling. The approximate genetic correlation between SCC and functional longevity was .31 associating unfavourable values of SCC to poorer longevity. Favourable genetic correlations resulted between udder conformation traits and SCC. A higher udder, strongly attached to the fore abdominal wall, and with short teats was genetically related to smaller values of SCC. Finally an udder health index, including SCC, udder depth, and fore udder attachment was proposed and the inclusion of SCC in the overall selection index was discussed.