Does the circadian system regulate lactation?

Abstract

Environmental variables such as photoperiod, heat, stress, nutrition and other external factors have profound effects on quality and quantity of a dairy cow's milk. The way in which the environment interacts with genotype to impact milk production is unknown; however, evidence from our laboratory suggests that circadian clocks play a role. Daily and seasonal endocrine rhythms are coordinated in mammals by the master circadian clock in the hypothalamus. Peripheral clocks are distributed in every organ and coordinated by signals from the master clock. We and others have shown that there is a circadian clock in the mammary gland. Approximately 7% of the genes expressed during lactation had circadian patterns including core clock and metabolic genes. Amplitude changes occurred in the core mammary clock genes during the transition from pregnancy to lactation and were coordinated with changes in molecular clocks among multiple tissues. In vitro studies using a bovine mammary cell line showed that external stimulation synchronized mammary clocks, and expression of the core clock gene, BMAL1, was induced by lactogens. Female clock/ clock mutant mice, which have disrupted circadian rhythms, have impaired mammary development and their offspring failed to thrive suggesting that the dam's milk production was not adequate enough to nourish their young. We envision that, in mammals, during the transition from pregnancy to lactation the master clock is modified by environmental and physiological cues that it receives, including photoperiod length. In turn, the master clock coordinates changes in endocrine milieu that signals peripheral tissues. In dairy cows, it is clear that changes in photoperiod during the dry period and/or during lactation influences milk production. We believe that the photoperiod effect on milk production is mediated, in part by the 'setting' of the master clock with light, which modifies peripheral circadian clocks including the mammary core clock and subsequently impacts milk yield and may impact milk composition.Keywords: mammary, lactation, circadian rhythm, photoperiod, metabolism ImplicationsThe circadian system coordinates internal physiological processes in mammals and synchronizes these processes to the animal's environment. We review the literature and discuss recent findings from our laboratory and others that suggest the circadian system regulates lactation, including coordinating changes in the dam's physiology needed to initiate and maintain lactation and mediating the photoperiod effect on milk production. Identification of environmental and physiological inputs that affect genes that control circadian rhythms will enable development of approaches to alter gene expression to maximize production efficiency in farm animals. IntroductionNearly all physiological and behavioral functions of animals are rhythmic including secretion patterns of hormones, sleep-wake cycle, metabolism and core body temperature.A circadian rhythm is a roughly 24-h cycle in the biochemical, physiological or behaviora...

Exposure to chronic light–dark phase shifts during the prepartum nonlactating period attenuates circadian rhythms, decreases blood glucose, and increases milk yield in the subsequent lactation

“…Almost all physiological and behavioral functions of animals are rhythmic, including hormone secretion patterns, sleep-wake cycles, metabolism, and core body temperature. These circadian rhythms (i.e., 24-h cycles of biochemical, physiological, or behavioral processes) evolved as a common strategy among animals to coordinate internal systems and synchronize these systems to the environment (Casey and Plaut, 2012;Plaut and Casey, 2012). In mammals, circadian clocks are regulated hierarchically, with the master circadian clock located centrally in the suprachiasmatic nuclei of the hypothalamus.…”

Continuously Changing Light-Dark Phase Decreases Milk Yield, Fat, Protein and Lactose in Dairy Cows

“…plasma hormone levels and core body temperature) or behavior (e.g. sleep-wake cycle) that appear to have evolved as a common strategy among animals to coordinate internal systems and synchronize these systems to the environment [18,19]. In mammals, the circadian system is comprised of the master circadian clock in the suprachiasmatic nuclei (SCN) of the hypothalamus and peripheral clocks that are distributed in every organ of the body.…”

The bovine anterior hypothalamus: Characterization of the vasopressin–oxytocin containing nucleus and changes in relation to sexual differentiation

“…Although no OXT neurons can be found in the SCN, the timekeeping and synchronicity role of VIP has been demonstrated (Maywood et al, ). The peculiarity of the situation in cattle may be related to advanced breeding selection for milk production, which is indeed influenced by the circadian rhythm (Plaut & Casey, ).…”