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Circadian rhythms of peripheral ß-hydroxybutyrate in morning and evening fed lactating cows
Feeding time-driven rhythms in animal and human physiology requires mechanistic exploration. The objective was to establish effects of feeding time of diets with different forage to concentrate ratios on periprandial rhythms and daily averages of peripheral β-hydroxybutyrate (BHBA). A total of 8 early-mid lactation tie stall-housed Holstein cows including 4 multiparous and 4 primiparous cows were utilized in a 4 × 4 Latin square design study with a 2 × 2 factorial arrangement of feeding time and diet type. 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) was presented at either 2100 h or 0900 h. The study had 4 21-d periods, with 14-d of adaptation. Peripheral blood was sampled every 2-h for two non-consecutive 24-h periods via jugular catheters. The repeated blood measures were equally-spaced and analyzed as Mixed Models with fixed effects of diet, feeding time, parity, hour, and interactions; and random effects of period, sampling day (period), cow (parity), diet × feeding time × parity × cow (parity), and diet × feeding time × parity × day (period). Data were log-transformed for normal residuals distribution and variance homogeneity. Feeding at 2100 h vs. 0900 h increased feed intake within 3-h post-feeding from 26% to 37% of total daily intake, and improved milk energy yield without affecting total daily dry matter intake. Peripheral blood BHBA in all cows exhibited significant periprandial rhythms that were mediated by time of feeding (P<0.01). Peripheral BHBA was higher at 2-h and 4-h post-feeding in cows fed at 2100 h vs. 0900 h. The HC vs. LC decreased daily means of blood BHBA. Data substantiate that evening instead of morning feeding increased eating rate shortly post-feeding and, likely thereby, altered periprandial rhythms of a major peripheral energy and fat metabolism indicator. Feeding time, therefore, can entrain peripheral energy-yielding substrate availability and use in lactating cows.
Keywords: β-hydroxybutyrate, Circadian rhythm, Feeding time