Genetic evaluation of twinning rate in Italian Holstein

Abstract

Twinning in Holstein cattle is unfavorably linked to calving difficulties, abortions, milk production and reduced calf survival. The twinning rate in the Italian Holstein population is 2.2% and appears relatively stable over time; however, this figure does not account for early abortions and thus it is underestimated. This study aimed to establish a routine genetic evaluation of twinning rate in the aforementioned population. The phenotype of interest was the type of calving (0 = singleton; 1 = twins). The statistical model employed included, as random, herd-year of conception, permanent environmental effect and the cow’s additive genetic effect. Fixed effects comprised year-season of conception, herd, synchronization protocol (classified into three categories: yes, partial or no), days in milk class and parity-age-year of conception. The dataset included 11,329,160 records after filtering, with age at calving restricted to 18-77 months and parity limited to maximum three. Only fixed effects levels comprising at least 100 observations were retained. The minimum number of contemporaries was set to 10. Data editing was loop-based to simultaneously meet all the described restrictions. Genetic parameters were estimated on a sample of 500 randomly selected herds using THRGIBBS1F90 software. Posterior mean of heritability for twinning rate was 1%. To validate the accuracy and stability of the predictions a genomic validation was conducted. Genomic validation yielded a dispersion of 0.94 and validation reliability of 0.18. This study has laid the foundation for the implementation of a routine genetic evaluation of twinning rate in the Italian Holstein breed.