Effects of Photoperiod During the Dry Period on Prolactin, Prolactin Receptor, and Milk Production of Dairy Cows

Abstract

Cows exposed to short day photoperiod during the dry period produce significantly more milk in their subsequent lactation than cows exposed to long days. The mechanism(s) underlying this effect are unknown. Because concentrations of prolactin (PRL) in circulation are consistently affected by changes in photoperiod, we hypothesized that alterations in the prolactin axis and sensitivity of the mammary gland to prolactin signaling may mediate photoperiodic effects in dry cows. The objective of this study was to determine the effects of exposure to different lengths of daylight during the dry period on circulating PRL and PRL receptor (PRL-R) mRNA expression in lymphocytes and mammary tissue during the transition to lactation. Multiparous Holstein cows were dried off 62 d before calving and assigned to long day (16 h light: 8 h dark) or short day photoperiod (8 h light: 16 h dark). During the dry period, PRL and PRL-R mRNA were analyzed biweekly in plasma and lymphocytes, respectively. Expression of PRL-R mRNA was assessed in mammary biopsies during the dry and periparturient periods. Dry matter intake (DMI) was recorded through 21 d of lactation, and milk yield was recorded until 120 d in milk. Short day photoperiod was associated with reduced PRL, whereas milk yield and expression of PRL-R mRNA in lymphocytes and mammary tissue were increased. Cows on short days had higher DMI during the dry period but did not differ in DMI after parturition. These data support the concept that greater responsiveness and sensitivity to PRL during transition to lactation may be associated with an increase in subsequent milk yield.

Cow management modulates gene expression in the mammary gland, a possible epigenetics role

“…Miller et al (2000) observed that the milk yield of animals exposed to shortdays in the dry period was 3.2 kg/day higher than those exposed to long-days. Prolactin plasma level was similar in short-and long-days-exposed cows during the dry period, but during lactation, cows exposed to short-days showed lower prolactin plasma level, and consequently, a higher number of prolactin receptors through the next lactation (Auchtung et al, 2005;Wall et al, 2006). Similar results were also obtained in goats (Mabjeesh et al, 2007).…”

Effect of pregnancy and feeding level on cell turnover and expression of related genes in the mammary tissue of lactating dairy cows

“…However, regulation of PrlR expression and its affinity for Prl may counteract variations in plasma Prl concentrations, and the quantitative expression of PrlR may be a major determinant in Prl bioactivity. In dry dairy cows, a short-day photoperiod results in reduced plasma Prl, but increased PrlR gene expression and PrlR affinity for Prl (Auchtung et al, 2005). Low feeding level results in lower plasma Prl (Lacasse et al, 1994), and a greater gene expression of Prl receptors in cows on low feeding level may counterbalance a low Prl plasma concentration.…”

Novel SNPs of the Bovine PRLR Gene Associated with Milk Production Traits

“…In mammals, the hormone prolactin (PRL) is best known for its role in the regulation of lactation (Bole-Feysot et al 1998;Auchtung et al 2005;Lee et al 2007). Recent evidence indicates that PRL affects multiple reproductive and metabolic functions via the JAK2/STAT (Janus kinase 2/signal transducer and activator of transcription) signaling pathway (Clevenger and Kline 2001;Bachelot and Binart 2007).…”