Salfer I J, Bartell P A, Harvatine K J
Department of Animal Science, The Pennsylvania State University, University Park, PA 16802.
Department of Animal Science, The Pennsylvania State University, University Park, PA 16802.
J Dairy Sci. 2025 Aug;108(8):8920-8933. doi: 10.3168/jds.2024-26215. Epub 2025 May 16.
Dairy cows display daily rhythms of milk synthesis that appear to be driven by a circadian clock located in the mammary gland. These rhythms are altered by the time of feed availability. Fatty acids have been shown to entrain circadian rhythms in liver and adipose tissue in experimental models, but their role in the mammary gland has not been well investigated. Our objective was to determine the effects of the timing of fatty acid absorption on the daily rhythms of milk synthesis. Nine lactating Holstein cows were arranged in a 3 × 3 Latin square design. Treatments were abomasal infusions of 350 g/d of a free fatty acid stock enriched in cis-9 18:1 either continuously throughout the day for 22 h (CON) or for 8 h from 0900 to 1700 h (DAY) or from 2100 to 0500 h (NGT). Treatment periods were 12 d with a 5-d washout. Cows were milked every 6 h during the final 7 d of each period to determine the daily patterns of milk synthesis. A 24-h rhythm was fit to time course data using cosine analysis, and the amplitude and acrophase (time at peak) were determined. Daily milk and milk protein yields were decreased by DAY and NGT compared with CON, whereas milk fat yield was not changed. Milk yield fit a 24-h rhythm in CON and DAY but not in NGT. Furthermore, DAY delayed the peak of the daily rhythm of milk yield by 2 h compared with CON. Fat and protein concentrations exhibited daily rhythms in CON and NGT but not DAY. Fat yield only fit a 24-h rhythm in DAY. Both de novo and mixed-source fatty acid yields were reduced by DAY and NGT, suggesting that the faster infusion rates may have resulted in concentrations of fatty acids that exceeded a threshold sufficient to inhibit de novo fatty acid synthesis. Plasma glucose concentration failed to display a daily rhythm in any treatment, whereas nonesterified fatty acids showed a rhythm in CON and NGT, but this rhythm was abolished by DAY. Insulin fit a rhythm in NGT and tended to fit a rhythm with a lower amplitude in CON, but no rhythm was present in DAY. Blood urea nitrogen exhibited a daily rhythm under all treatments, and both the mean and amplitude were increased by DAY. Daily rhythms of milk synthesis were also modified by DAY, with a slight delay in the daily peak of milk yield and elimination of the rhythms of milk fat and protein concentrations. Infusion at night had little effect. Daytime infusion also modified the daily rhythms of plasma metabolites by reducing the amplitude of nonesterified fatty acid concentration and increased the amplitude of blood urea nitrogen.
奶牛表现出每日的产奶合成节律，这似乎是由位于乳腺中的生物钟驱动的。这些节律会因饲料供应时间而改变。在实验模型中，脂肪酸已被证明能调节肝脏和脂肪组织中的昼夜节律，但其在乳腺中的作用尚未得到充分研究。我们的目的是确定脂肪酸吸收时间对每日产奶合成节律的影响。9头泌乳期的荷斯坦奶牛采用3×3拉丁方设计。处理方式为通过皱胃灌注，每天350克富含顺式-9 18:1的游离脂肪酸储备，CON组为全天持续22小时灌注，DAY组为从09:00至17:00灌注8小时，NGT组为从21:00至05:00灌注8小时。处理期为12天，中间有5天的洗脱期。在每个处理期的最后7天，每6小时对奶牛进行一次挤奶，以确定产奶合成的每日模式。使用余弦分析将24小时节律拟合到时间进程数据中，并确定振幅和峰相位（峰值出现的时间）。与CON组相比，DAY组和NGT组的日产奶量和乳蛋白产量均下降，而乳脂产量没有变化。CON组和DAY组的产奶量符合24小时节律，而NGT组不符合。此外，与CON组相比，DAY组使产奶量每日节律的峰值延迟了2小时。CON组和NGT组的脂肪和蛋白质浓度呈现每日节律，而DAY组没有。脂肪产量仅在DAY组符合24小时节律。DAY组和NGT组的从头合成脂肪酸产量和混合来源脂肪酸产量均降低，这表明较快的灌注速率可能导致脂肪酸浓度超过了足以抑制从头合成脂肪酸的阈值。在任何处理中，血浆葡萄糖浓度均未表现出每日节律，而非酯化脂肪酸在CON组和NGT组表现出节律，但在DAY组该节律消失。胰岛素在NGT组符合节律，在CON组倾向于符合一个振幅较低的节律，但在DAY组没有节律。在所有处理下，血尿素氮均表现出每日节律，DAY组的平均值和振幅均增加。DAY组也改变了产奶合成的每日节律，使产奶量的每日峰值略有延迟，并消除了乳脂和蛋白质浓度的节律。夜间灌注影响较小。白天灌注还通过降低非酯化脂肪酸浓度的振幅和增加血尿素氮的振幅来改变血浆代谢物的每日节律。
