373
Timing of feeding orchestrates periprandial rhythms of circulating glucose in dairy cows
The objective was to determine effects of feed presentation time and diet on periprandial rhythms of 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 2100 h or 0900 h in tie stalls. The study had four 21-d periods, each with 14-d of adaptation. Jugular blood was sampled every 2-h for two 24-h periods during sampling weeks. Data were analyzed as repeated measures mixed models. Feeding at 2100 h vs. 0900 h increased eating rate and feed intake within 3-h of feeding from 26% to 37% of total daily intake. BG exhibited significant periprandial rhythms that were altered by feeding time (P<0.01). BG showed a marked decline at 2-h vs. 0-h post-feeding in evening-fed cows (67 vs. 74 mg/dL, P<0.05) but not in morning-fed cows (73 vs. 75 mg/dL, P>0.10). Feeding HC vs. LC diet increased BG (80 vs. 77 mg/dL, P<0.05). Time of feeding did not affect daily averages of BG (78.2 mg/dL). Results demonstrate time of feeding as a major determinant of peripandial and circadian rhythms of BG in once-daily fed lactating dairy cows. The multi-purpose utilization of livestock as suitable models for studying diabetes in humans and periparturient disorders in high-producing ruminants is elucidated. Feeding and eating behavior orchestration of circadian glucose-insulin regulation in dairy cows in different physiological states is delineated. Adopting differential feeding/eating times to manipulate postprandial feed intake patterns, rumen fermentation and acidity rhythms, and peripheral substrate partitioning for more optimal nutrient efficiency and environmental quality is also addressed. Time of feed presentation can consequently affect splanchnic and peripheral energy metabolism and efficiency in lactating cows.
Keywords: Timing of feeding, Glucose, Rhythm