Study of fertility traits in Italian Jersey Cattle

Selection Index of Italian Jersey cattle is composed by breeding values (BVs) of production traits, type traits and somatic cell score. Knowing selection for milk yield has been proved to deteriorate fertility performances, aim of the Italian Holstein, Brown and Jersey Breeders Association (ANAFIBJ) is to develop a fertility index inspired to the model they use for Italian Holstein breed. The model used considers different phenotypes for heifer and cow evaluation, but while for Holstein only the first three parities are considered, for Jersey all parities are considered to overcome the lower size of the population. Starting from two different datasets, containing data on inseminations and lactations we derived several fertility traits. From the inseminations dataset we harvested information on the dates of services, which we grouped in baches of a maximum length of 300 days. The groups of inseminations have then been attached to the calvings happened in an interval of 260–300 days from at least one of the services in the group. Phenotypes estimated for both heifers and cows are Non-Return Rate at 56 days (NRR56) and Interval from First to Last service (IFL); Age at First Insemination (AFI) has been computed only for heifers, while Days from delivery To First Service (DTFS) and Equivalent Milk Yield 305 (EMY305) only for cows. The values of the phenotypes have been filtered to be in line with biological and economic criteria of cattle farming. The final dataset is composed of 35081 records for heifers and 100285 records for cows. Correlations and Co-Variances between the phenotypes have been calculated. For Heifers we observe a slight positive correlation between AFI and NRR56 (ρxy = −0.061) and a negative correlation between NRR56 and IFL (ρxy = −0.349); IFL and AFI are negatively correlated (ρxy = −0.048). For cow fertility traits NRR56 resulted to be positively correlated with DTFS (ρxy = 0.088) and negatively correlated with EMY305 (ρxy = −0.092) and IFL (ρxy = −0.293); DTFS resulted negatively correlated to IFL (ρxy = −0.015) and EMY305 (ρxy = −0.045), while IFL and EMY305 resulted positively correlated (ρxy = 0.083). The next step is to calculate genetic parameters and EBVs for fertility traits for Italian Jersey.