Negative correlation of suckling behaviour and foal weight gain during the first week after birth

•Suckling has been reportedly not a useful predictor of milk intake in foals.•The method used to observe and categorise the behaviour was improved for the analysis.•Negative correlations of suckling and foal weight gain were founded.•Mare parity affected the relationship. After their birth, foals are usually housed with and nursed by their mares. Because a foal’s growth and survival depend greatly on the mare’s milk for a certain time after birth, it is said that observations of suckling behaviour can indicate a foal’s growth. Nevertheless, the results of earlier studies suggest that foal suckling behaviour is not a useful predictor of milk intake. This study investigated the relationship between suckling behaviour and foal weight gain, referring to several definitions of suckling bouts and sufficient sampling methods, and including several confounding factors in the analyses. Observations were made of 17 mare–foal pairs from days 1–7 and days 14, 21, and 28 after birth from 18:00 to 06:00 h. The suckling behaviour was recorded using a continuous recording method and suckling bouts, successful suckling bouts, and unsuccessful suckling bouts were calculated from the recordings of suckling behaviour. The terminator of the behaviours was also recorded. Behavioural data of the ‘first week’ (data from days 1–6 were averaged) and the ‘next three weeks’ (data of days 7, 14, 21, and 28 were averaged), foal weights, mare parity, and foal sex were used for statistical analysis using generalised linear mixed models with Gaussian error distribution. For the ‘first week’, negative relationships were found between suckling, suckling bouts, successful suckling bouts, several foal terminating behaviours, and foal weight gain, but no relation was found between all behaviours and foal weight gain for the ‘next three weeks’. The number of mare parity was found to have a positive relationship with the foal weight gain of the ‘first week’ and negative relationships were found between suckling, suckling bouts, successful suckling bouts, and the number of mare parity in the ‘first week’. The results of this study suggest that suckling behaviours in the first week after birth are negatively correlated with foal weight gain and that mare parity affected the results. It is also suggested that in horse reproduction systems, suckling behaviour terminated by the foal can be a negative indicator of foal growth, especially in the first week after birth.