Analysis of reproductive seasonality in Entrepelado and Retinto Iberian pig varieties under intensive management

•Farrowing distribution can be properly analyzed by von Mises circular mixed models.•Iberian sows under intensive management practices have low reproductive seasonality.•The parity number delays (adult sows) or advances (gils and old sows) farrowing peak.•Farrowing distribution in Iberian sows have small or null genetic background. Seasonal patterns in the farrowing distribution of two Iberian pig varieties (Retinto and Entrepelado) and its environmental and genetic sources of variation were analyzed within the context of a von Mises circular mixed model solved through Bayesian inference. Estimates about the dispersion parameter supported a low seasonal pattern for both Entrepelado and Retinto varieties with the farrowing peak located between March and April. Nevertheless, seasonality was corroborated by the deviance information criterion when comparing against a uniform circular model by the deviance information criterion (DIC); the uniform model increased more than 100 DIC units in both Iberian pig varieties. Regarding systematic effects, only the parity number of the sow had a relevant impact on farrowing distribution, advancing the farrowing peak in gilts and old sows. Genetic variability was only suggested in the Retinto population although with a small estimate, which would indicate little chance to modify farrowing distribution by genetic selection in the Iberian pig.