Four fertility traits were evaluated:
- współczynnik zapłodnienia jałówek (CRj)
- współczynnik zapłodnienia krów (CRk)
- długość przestoju poporodowgo (PP) – odstęp czasu od pierwszego ocielenia do pierwszego zabiegu unasieniania.
- długość okresu międzyciążowego (OMC) – odstęp czasu od pierwszego ocielenia do ponownego zacielenia.
The CRj and CRk indices were determined as CR = 100/number of inseminations from first to successful. If the series consisted of more than 15 inseminations or no insemination was marked as successful, then CR = 100/16.
| Trait | CRj | CRk | PP | OMC |
| CRj | 0.027 | 0.483 | 0.581 | -0.012 |
| CRk | 0.056 | 0.025 | 0.024 | 0.022 |
| PP | -0.003 | 0.043 | 0.053 | 0.713 |
| OMC | -0.005 | -0.215 | 0.609 | 0.080 |
Model #
Breeding values for fertility traits were estimated using the BLUP method – a multi-trait animal model, taking into account the following effects in the linear model:
- For CRj and CRk: fixed effect of insemination month, fixed regression on age at first insemination, random effect of herd-year of first insemination, and additive effect of the animal.
- For PP and OMC: fixed effects of herd-year and month of calving, as well as regression on cow’s age at calving.
Breeding values for all traits were expressed as deviations from the base average and then transformed into a variable with a mean of 100 and a standard deviation of 10. For CRj and CRk, a higher breeding value means that on average, fewer insemination procedures are needed for successful breeding. A higher breeding value for OMC or PP indicates shorter intervals between calvings or postpartum periods.
Genetic database #
The genetic base was set as the average breeding value of bulls born between 2009-2011, evaluated based on at least 50 daughters from at least 30 herds.
Subindex of fertility traits #
Fertility subindex PI_PŁOD:
PI_PŁOD = 0.70 × CRj + 0.10 × CRk + 0.10 × PP + 0.10 × OMC
The fertility subindex has been standardized to a mean of 100 and a standard deviation of 10.