Seasonal fluctuations in the steady-state mRNA levels of suppressor of cytokine signaling-3 (SOCS-3) in the mammary gland of lactating and non-lactating ewes

•SOCS-3 mRNA expression in ovine mammary gland is strongly dependent on the season.•SOCS-3 mRNA expression in ovine mammary gland is dependent on the stage of lactation.•The highest expression of SOCS-3 mRNA was noted in non-lactating sheep during SD.•The lowest expression of SOCS-3 was observed in ewes on day 30 of lactation.

Prolactin (PRL) is a hormone that plays a crucial role during pregnancy and lactation. The Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway, which is an important pathway in signal transduction from PRL to target cells, can be modulated by various factors, including suppressor of cytokine signaling-3 (SOCS-3). PRL may increase and decrease SOCS-3 expression, and its actions are mostly dependent on additional factors such as the photoperiod. There is also evidence for a relationship between suckling and SOCS-3 expression in the mammary gland. The aim of this study was to examine the influence of seasonality and physiological status on SOCS-3 expression levels in ovine mammary glands. Mammary gland fragments were obtained from 18 Polish Longwool ewes, and the fine-needle aspiration biopsy technique was used on 4 groups of animals under specific physiological and photoperiodic conditions: non-lactating ewes during long days (LD; n = 6), ewes on day 30 (n = 6) or day 56 of lactation (n = 6) and non-lactating ewes during short days (SD; n = 6). SOCS-3 mRNA levels were measured by real-time PCR. The results of this study confirmed that SOCS-3 mRNA expression in sheep is dependent on the season and stage of lactation. The highest expression of the examined factors was noted in the mammary glands of non-lactating sheep during SD, and the lowest levels were observed in ewes on day 30 of lactation. The transcript levels observed in the tissues collected from non-lactating sheep during SD and LD were higher (74% and 41%, respectively) compared with the expression observed on day 30 of lactation. On day 56 of lactation, the SOCS-3 mRNA level was similar to that observed in the udders of non-lactating sheep during LD. These results indicate that SOCS-3 could play an integrating role between hormones and other factors that are involved in the physiological functions of the mammary gland.