The objective of

this study was to analyze the effect of high inbreeding (F)

levels (≥ 6.25%) on reproductive parameters of Holstein and

Jersey cows born between Jan 1995 and Dec 2010 in specialized

dairy herds in Costa Rica. Data on age at first calving

(AFC), open days (DO) and services per conception (SPC)

from (n=263 804) from the VAMPP national data base, at the

Veterinary School of the Universidad Nacional, was used.

An F value ≥ 6.25% (high/risk) was used as a cut-off point.

The data were processed using descriptive statistics, multiple

linear regression (mixed model), and logistic regression. A

17.9% of animals had some inbreeding, with an F average of

0.42% (0.49% and 0.55% for Holstein and Jersey). 22.6% of

Holstein and 20.3% of Jersey were inbreed; however, in Jersey,

there were cows with higher F. Cows with some inbreeding

have an average F of 2.16% for Holstein and 2.98% for

Jersey. Furthermore, cows with low F had 18 d less of AFC

(p<0.01) compared to those with high F. Regarding the DO,

there were +0.53 d for animals with low F (P= 0.71); while

the cows with low F had +0.08 SPC (P<0.01). There was no

risk of DO or SPC in animals with F ≥ 6.25%; which occurred

for AFC (OR = 1.23; 95% CI: 1.10-1.38). According

to this study, inbreeding did not affect the DO, but slightly

affects the SPC and the AFC in Holstein and Jersey cows.

Keywords: inbreeding, age at first calving, services per conception, open days, dairy cattle.