Investigating hair cortisol dynamics in German Shepherd Dogs throughout pregnancy, lactation, and weaning phases, and its potential impact on the hair cortisol of offspring

Pregnancy, lactation, and weaning are crucial physiological stages in the life of bitches, directly affecting the physiological health of bitches and the growth and development of newborn puppies. This study aims to investigate the physiological stress of bitches during pregnancy, lactation, and weaning, as well as the effects of these changes on newborn puppies, by analyzing the variations in hair cortisol concentrations (HCCs) of bitches and their newborn offspring during different stages. This study selected 24 female German Shepherd dogs aged 2-3 years who were pregnant and giving birth for the first time and their 118 surviving newborn offspring as experimental subjects. Hair samples were collected from the right shoulder and neck of the bitches and their offspring at four key time points: the day of mating (T0), the day of delivery (T1/NT1), the first day of weaning (T2/NT2), and the 60th day after weaning (T3/NT3). The HCCs was detected by enzyme-linked immunosorbent assay (ELISA) to assess their physiological stress. The results showed that the maternal HCCs significantly increased during pregnancy and lactation, reaching a peak during lactation. The HCCs of puppies also significantly increased during the weaning period. Meanwhile, there was a significant but moderate correlation between the cortisol levels in maternal hair and puppies' hair during pregnancy and lactation. In addition, the maternal HCCs during pregnancy and lactation were affected by the litter size, the higher the litter size, the higher the hair cortisol level, while the cortisol levels in the hair of puppies were not affected by the litter size. Bitches may face higher physiological and psychological pressures during reproduction and nurturing offspring, especially when the litter size is large. At the same time, the physiological status of bitches may have a certain impact on puppies. Therefore, care and attention during pregnancy, lactation, and puppy weaning periods should be strengthened to ensure that bitches and puppies receive good feeding management and environmental support, maintain their physiological and psychological health, and further enhance animal welfare.