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Peripheral lactate circadian rhythmicity in dairy cows fed in evening vs. morning
The objective was to establish circadian and postprandial rhythms of peripheral lactate in lactating cows fed once daily in evening vs. morning following 28-d adaptation periods. In midlactation, four multiparous and four primiparous lactating Holstein cows in tie stalls were used in a cross-over design study with two 6-week periods, each with 4-week of adaptation. A total mixed ration (TMR) with 49.8% dry matter-based concentrate was presented at either 0900 h or 2100 h. Jugular blood was sampled every 2-h for two 24-h periods during week-5. The statistical mixed model used for blood lactate analysis included fixed effects of feeding time, parity, hour (of blood sampling), feeding time × parity, hour × parity, and feeding time × hour × parity. The effects of cow within parity, period, and feeding time × period × cow (parity) were considered random. To account for between-hour, within-cow correlations of the repeated measures and thus to minimize Type 1 statistical error risk, the best fitted covariance structure was adopted and modeled. The proportion of daily TMR intake consumed within 3-h post-feeding was 55% in cows fed at 2100 h, but 46% in cows fed at 0900 h (P<0.05). Peripheral lactate exhibited significant circadian rhythms (P<0.01). Postprandial responses in peripheral lactate were altered by feeding time (P<0.01). The evening feeding, and not the morning feeding, increased plasma lactate at 4-h and 16-h post-feeding relative to baseline P<0.01). Feeding time did not affect daily averages of plasma lactate. Results establish that time of feeding orchestrates circadian and postprandial rhythms of feed intake and peripheral blood lactate. Time of eating, therefore, can modulate splanchnic and peripheral lactate assimilation and energy dynamics in lactating dairy cows.
Keywords: Peripheral lactate, Feeding time, Circadian rhythm