Photoperiod manipulation, specifically a long-day photoperiod (LDPP), increases milk production in lactating @entity291 . We have previously reported that the galactopoietic effect of LDPP is associated with an increase in circulating @entity4208 , which seems to occur independently of changes in concentrations of GH, @entity21904 , and @entity37644 . This study tested the hypothesis that LDPP increases the expression of @entity7036 ( @entity7036 ) 1A messenger RNA (mRNA) in the liver. Two groups of Holstein steer @entity291 (98 +/- 4 d old) were maintained indoors and exposed to LDPP (16-h light: 8-h dark; n = 6) or short-day photoperiod (SDPP; 8-h light: 16-h dark; n = 6) for 60 d. @entity291 were individually fed a grain- and alfalfa-based diet. Jugular blood samples were collected weekly and via cannula at 15-min intervals for a 4-h period on d 1, 26, and 55 of the study to monitor pulsatile hormone secretion. Serum was harvested and assayed for @entity4208 , @entity5947 (PRL), and GH using RIA. Liver biopsies were obtained at 3-wk intervals to quantify changes in hepatic @entity4208 and @entity7036 1A mRNA using real-time PCR. Steer BW increased during the study but did not differ between treatments. No differences in ADG or total DMI were observed. Relative to SDPP, @entity291 on LDPP had higher (P < 0.05) serum @entity4208 concentrations. Concentrations of PRL increased (P < 0.01) in @entity291 exposed to LDPP compared with @entity291 exposed to SDPP. Differences (P < 0.05) in pulsatile GH secretion were also detected. Hepatic @entity4208 and @entity7036 1A mRNA were positively correlated with circulating @entity4208 concentrations, and although both increased with time, they were not affected by photoperiod treatment. These results confirm that LDPP increases circulating concentrations of @entity4208 , but this occurs independently of changes in @entity4208 synthesis and @entity7036 1A mRNA expression in the liver. Therefore, our hypothesis that LDPP increases the expression of @entity7036 1A mRNA in the @entity291 liver is rejected.

Effect of photoperiod on hepatic growth hormone receptor 1A expression in steer XXXX .

@entity7036 :: ('280805(Tax:9913)', 'Gene') :: ['GHR', 'GH receptor'] @entity4208 :: ('104978413', 'Gene') :: ['IGF-I'] @entity5947 :: ('280901(Tax:9913)', 'Gene') :: ['prolactin'] @entity21904 :: ('282260(Tax:9913)', 'Gene') :: ['IGFBP-2'] @entity37644 :: ('282261(Tax:9913)', 'Gene') :: ['IGFBP-3'] @entity291 :: ('9913', 'Species') :: ['Calves', 'cattle', 'bovine', 'calves']
@entity291 :: (9913,Species) :: ['calves']
