Time of feed provision (21:00 vs. 09:00 h) orchestrates postprandial rhythms of food intake and peripheral glucose in lactating cows

Abstract The objective of the first experiment was to determine the effects of feeding time and dietary forage to concentrate ratio on postprandial rhythms of feed intake and peripheral blood glucose (BG). Four multiparous (83 days in milk) and four primiparous (81 days in milk) Holstein cows in a 4 × 4 Latin square design study were fed either a higher concentrate (HC, forage to concentrate ratio = 38.5:61.5) or a lower concentrate (LC, forage to concentrate ratio = 50.6:49.4) total mixed ration (TMR) at either 21:00 h or 09:00 h. The study had four 21-d periods, each with 14-d adaptation. Jugular blood was sampled every 2-h for two 24-h periods during sampling weeks. Feeding at 21:00 h vs. 09:00 h increased the eating rate, and thus, increased feed intake within 3 h of feeding from 26% to 37% of total daily intake. BG exhibited significant postprandial rhythms that were altered by feeding time. BG showed a marked decline shortly pre- and post-feeding in evening-fed cows but not in morning-fed cows. Feeding HC vs. LC diet increased the BG. The objective of the second experiment was to establish postprandial BG responses to feeding time in lactating cows after 28-d adaptation periods. Four multiparous and four primiparous lactating Holstein cows (82 days in milk) were used in a cross-over design study with two six‐week periods. Each period had four weeks of adaptation. A TMR with 49.8% concentrate was fed at either 09:00 or 21:00 h to permit 5–10% feed refusals. Jugular blood was sampled via catheters every 2 h for two 24-h periods during week-5 of each period. Evening vs. morning feeding increased feed intake within 3-h of feed delivery (55% vs. 46% of daily intake). BG exhibited marked declines at 2 h pre- and post-feeding in cows fed at 21:00 h vs. 09:00 h. Time of feeding did not affect daily averages of BG in any of the experiments. The results establish TF as a determinant of postprandial and diurnal patterns of feed intake and BG in once-daily fed lactating dairy cows. TF can therefore affect splanchnic and peripheral energy metabolism and efficiency in lactating cows. Considering the comparative nature of the splanchnic metabolism for optimal mechanistic understanding of the gut function in any given species, the findings serve as a metabolic model for high-producing ruminants and humans. Keywords: blood glucoseevening feedingenergyfeed intakedairy cow Acknowledgments The Ministry of Science, Research and Technology, and University of Zanjan (Iran) are acknowledged for supporting the author's programs of optimizing global science education.