Short communication: Short-day photoperiod during the dry period decreases expression of suppressors of cytokine signaling in mammary gland of dairy cows.

Suppressors of cytokine signaling (SOCS) are induced by prolactin and act through negative feedback to inhibit cytokine signaling. We hypothesized that lower prolactin concentrations in cows exposed to short-day photoperiod (SD; 8 h light:16 h dark) lead to decreased expression of SOCS, which mediate the effects of SD on mammary proliferation during the dry period. Multiparous Holstein cows were dried off 60 d before expected calving and were assigned to long-day photoperiod (LD; 16 h light:8 h dark) or SD during the dry period. Mammary biopsies were obtained at -40, -20, -10, and +10 d relative to expected calving, and expression of SOCS-1, SOCS-2, SOCS-3, and cytokine-inducible SH2-containing protein (CIS) mRNA was assessed by real-time, quantitative, reverse transcription-PCR. Expression of all SOCS increased over time and expression of SOCS-3, SOCS-2, and CIS mRNA was lower in mammary gland of SD cows. These data suggest that lower SOCS expression in cows exposed to SD during the dry period may enhance prolactin signaling to the mammary gland, thereby augmenting mammary development during pregnancy and milk production in the subsequent lactation. Changes in SOCS expression during pregnancy and lactation imply that SOCS may regulate mammary gland development and function in dairy cows.