Stressed by Maternity: Changes of Cortisol Level in Lactating Domestic Cats

SIMPLE SUMMARY: Milk feeding is the most important part of maternal care in the first weeks of the offspring’s life as it contributes to growth and development of the young, but at considerable energetic expense to the mother. One of the indicators that can be used to assess the physiological state of the female is the cortisol level relating to the stress of animals. Presumably, the more offspring there are in the litter, the higher the level of stress on the mother and, accordingly, the higher the cortisol concentrations. This study presents our data obtained in domestic cats whose litter size varied from 1 to 7 kittens. We found that the highest cortisol concentrations were observed at the peak of lactation, i.e., in 4 weeks of kittens’ life, when the offspring’s milk needs were at maximum. Moreover, during the period of offspring’s growth, the hormone level was higher in females with 1–3 kittens. In addition, cortisol concentrations in less productive cats were very high, even before mating. ABSTRACT: Lactation is the most energetically expensive component of maternal care in mammals. Increased reproductive investment can lead to physiological stress for the mothers, based on the exhaustion of energy resources and increase in glucocorticoids level. This study aimed to estimate the changes in cortisol concentrations during lactation in domestic cats and compared the differences among litter sizes. Eleven females gave birth to 27 litters, which were divided in two groups—small (1–3 kittens) and large (4–7 kittens) litters. Blood samples were collected from each female before mating, after parturition, at 4 and 8 weeks of lactation. We showed that the cortisol level in females changed significantly during lactation—the highest concentrations were observed at the peak of lactation at 4 weeks. Cortisol levels varied significantly among females but did not depend on their maternal experience. We also revealed that there were no differences in cortisol levels between females with small and large litters, but at 4 weeks of lactation, the hormone concentrations were higher in females with small litters. It is likely that these females initially invested less in reproduction, giving birth to fewer offspring.