The objective of this study was to determine the incidence of regular or irregular inter-oestrus interval in sows during different months of the year in Northern Italy. In this study, 5,103 sows that returned to oestrus were inseminated and assigned to different groups based on the length of their inter-oestrus interval: - Regular inter-oestrus interval type 1 (Rint-1): sows with inter-oestrus interval of 18-23 days - Regular inter-oestrus interval type 2 (Rint-2): sows with inter-oestrus interval of 36-48 days - Irregular inter-oestrus interval (IRint group): inter-oestrus interval of 24-35. Based on meteorological data of the area in which the farms are located, animals were considered to be under heat stress during the high temperature months of June to August while animals were not considered to be under heat stress during September to May. The proportion of sows with Rint-1 was greater (P<0.05) during the high temperature months compared than during the rest of the year. There was no difference between months for the proportion of sows with Rint-2. The proportion of sows with IRint was greater (P<0.05) during the months of September and October than during the other months of the year. Results from this study indicate that, in Northern Italy, during the high temperature months of June-August, there was an increase in the proportion of sows with regular inter-oestrus interval, suggesting a failure of conception or an increase of early embryos losses, while there was an increase in the proportion of sows with irregular inter-oestrus interval during September- October, suggesting later embryo losses.
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