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Orchestration of circadian peripheral non-esterified fatty acids rhythms in dairy cows: feeding timing and diet effects
The objective was to establish effects of feeding time (0900 vs. 2100 h) of higher (HC, forage to concentrate ratio = 38.5 : 61.5) and lower (LC, forage to concentrate ratio = 50.6 : 49.4) concentrate diets on periprandial and circadian rhythms and daily averages of peripheral non-esterified fatty acids (NEFA) as a marker of dairy cow energy metabolism. A total of 8 tie stall-housed early-mid lactation 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. The study had 4 21-d periods, each with 14-d of adaptation. Peripheral blood was sampled every 2-h for two non-consecutive 24-h periods via jugular catheters. The repeated measures were 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). Feeding at 2100 h vs. 0900 h increased DMI within 3-h post-feeding in all cows from 26% to 37% of total daily DMI, and improved milk energy yield without affecting daily DMI. Peripheral blood NEFA in primiparous cows exhibited significant periprandial rhythms (P<0.01) with preprandial rises and postprandial declines. In multiparous cows, however, blood NEFA exhibited rather constant circadian levels with no apparent periprandial changes. Primiparous cows had higher average daily blood NEFA than multiparous cows (0.14 vs. 0.10 mmol/L; P<0.01). Diet and its interaction with feeding time and parity did not affect circadian rhythms and daily averages of blood NEFA (P>0.05). Evening instead of morning feeding increased eating rate and DMI shortly post-feeding in all cows and, likely thereby, altered periprandial rhythms of a major peripheral energy and fat metabolism marker. Feeding time is suggested as a main regulator of peripheral energy-yielding substrate availability in lactating cows, depending on parity.
Keywords: Diet, Feeding time, Non-esterified fatty acid