Peripheral lactate rhythmicity in evening- and morning-fed dairy cows: a chronophysiological lactating model

Abstract

The objective of the first experiment was to determine effects of feeding time and dietary forage to concentrate ratio on postprandial rhythms of peripheral blood lactate in lactating cows. Four multiparous and four primiparous Holsteins were used in a 4 × 4 Latin square design study with a 2 × 2 factorial arrangement of feeding time and diet type. A higher concentrate (higher concentrate diet (HC), forage to concentrate ratio = 38.5:61.5) or a lower concentrate (lower concentrate diet (LC), forage to concentrate ratio = 50.6:49.4) total mixed ration (TMR) was fed at either 2100 h or 0900 h. The study had four 21-day periods, each with 14-days of adaptation. Blood was sampled every 2 h for two 24-h periods during sampling weeks. Feeding at 2100 h vs. 0900 h increased feed intake within 3-h post-feeding, from 26% to 37% of total daily intake. Feed presentation at 2100 h vs. 0900 h tended to increase daily averages of plasma lactate. The HC diet produced a higher plasma lactate than the LC diet. The plasma lactate increased by about 50% shortly post-feeding in evening-fed cows, but no noticeable changes occurred in morning-fed cows. The objective of the second experiment was to establish postprandial rhythms of peripheral lactate in evening- and morning-fed lactating cows following the 28-day adaptation period. Four multiparous and four primiparous lactating Holstein cows were used in a cross-over design study with two six-week periods, each with four weeks of adaptation. A TMR with 49.8% concentrate was presented at 0900 or 2100 h. The proportion of daily TMR intake consumed within 3-h post-feeding was 55% in cows fed at 2100 h, but only 46% in cows fed at 0900 h. Peripheral lactate exhibited significant daily rhythms. Postprandial responses in peripheral lactate were altered by feeding time. The evening feeding, and not the morning feeding, increased plasma lactate at 4-h and 16-h post-feeding. Feeding time did not affect daily averages of plasma lactate. Results showed that time of feeding (TF) and, thus, time of major eating activity alters postprandial rhythms of feed intake and peripheral lactate. Time of eating, therefore, can affect splanchnic and peripheral lactate metabolism and energy supply in lactating cows.