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.

Blood analysis has recently become a popular tool to assess the welfare of the wild cats. However, the estimates of blood parameters may depend on the sampling method. We have tested (1) if the sampling procedure influences blood parameters and (2) what parameters are the most efficient in assessing the physiological status in wild cat species. We assessed the effect of handling time on red blood cells (RBC) and white blood cells (WBC) counts, the ratio of neutrophils to lymphocytes (N/L ratio), and serum cortisol level within 1 hr after the capture of the animal in six far-east wild cats (Prionailurus bengalensis euptilura). Also, we analyzed literature data in 17 cat species to assess the effect of place of study, type of immobilization, and handling time on WBC count and N/L ratio. Serum cortisol level varied significantly with the handling time. RBC and WBC counts were strongly affected by the handling time. N/L ratio was very robust and did not depend on the handling time. However, the analysis of literature data has shown that the prolonged handling time (over 1 hr) and the type of immobilization significantly influence the N/L ratio, whereas the WBC count does not depend on any of considered factors. We conclude that while most blood parameters of cats are affected by routine handling time, the N/L ratio does not vary if the samples are collected within 1 hr after the capture of the animal. All other tested parameters should be treated with caution.

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Social play fulfills an important function in creating and maintaining relations between siblings. However, its relationship with the intralitter social processes is poorly understood. It was noticed that, in Eur asian lynx (Lynx lynx) litters, sex differences in social play are absent in the first 2-3 months of life. It was found that the most intense periods of play behavior (at an age of 9 and 12 weeks) coincide with periods of aggression. Gradual change in play interactions, which require close physical contact by play elements with increased motor activity, are described. This reflects the changes in the relevance of certain skills of lynx cubs as they grow older.

Leukocytes (white blood cells) are an important part of the mammalian immune system preventing the invasion and colonisation by different pathogens. Many factors may affect the number of leukocytes in mammals, including the population density. The population density in the same species of felines may differ 100-300 times and the aim of this study was to estimate an effect of this factor on the leukocytes number and the ratio for two groups of domestic cats (Felis catus) with different population densities. We sampled 47 cats in the surroundings of Daursky State Nature Reserve, counted the number of leukocytes with a microscope immediately upon sampling and the leukocytes formula in the blood smears later in the laboratory. The population density of cats in the village and at herdsman stations differs approximately by 330 times. Domestic cats in the village (with a denser population) had a higher number of leukocytes and neutrophils, but the same number of lymphocytes and neutrophils/lymphocytes ratio. The number of eosinophils was also higher in village cats. Presumably, the higher number of leukocytes and neutrophils in a cat population with higher density is determined by the higher exchange rate of pathogens/symbionts between cats in the village than at the herdsman stations. These results may give some insight into understanding the changes in wild feline populations at different densities.