Short-term feed intake is regulated by macronutrient oxidation in lactating Holstein cows

摘要

In addition to plasma metabolites and hormones participating as humoral signals in the control of feed intake, oxidative metabolic processes in peripheral organs also generate signals to terminate feeding. Although the degree of oxidation over longer periods is relatively constant, recent work suggests that the periprandial pattern of fuel oxidation is involved in regulating feeding behavior in the bovine. However, the association between periprandial oxidative metabolism and feed intake of dairy cows has not yet been studied. Therefore, the aim of this study was to elucidate possible associations existing between single feed intake events and whole-body net fat and net carbohydrate oxidation as well as their relation to plasma metabolite concentrations. To this end, 4 late-lactating cows equipped with jugular catheters were kept in respiratory chambers with continuous and simultaneous recording of gas exchange and feed intake. Animals were fed ad libitum (AL) for 24 h and then feed restricted (RE) to 50% of the previous AL intake for a further 24 h. Blood samples were collected hourly to analyze β-hydroxybutyrate (BHBA), glucose, nonesterified fatty acids (NEFA), insulin, and acylated ghrelin concentrations. Cross-correlation analysis revealed an offset ranging between 30 and 42 min between the maximum of a feed intake event and the lowest level of postprandial net fat oxidation (FOX_net) and the maximum level of postprandial net carbohydrate oxidation (COX_net), respectively. During the AL period, FOX_net did not increase above —0.2 g/min, whereas COX_net did not decrease below 6 g/min before the start of the next feed intake event. A strong inverse cross-correlation was obtained between COX_net and plasma glucose concentration. Direct cross-correlations were observed between COXnet and insulin, between heat production and BHBA, between insulin and glucose, and between BHBA and ghrelin. We found no cross-correlation between FOX_net and NEFA. During RE, FOX_net increased with an exponential slope, exceeded the threshold of —0.2 g/min as indicated by increasing plasma NEFA concentrations, and approached a maximum rate of 0.1 g/min, whereas COX_net decayed in an exponential manner, approaching a minimal COX_net rate of about 2.5 g/min in all qows. Our novel findings suggest that, in late-lactating cows, postprandial increases in metabolic oxidative processes seem to signal suppression of feed intake, whereas pre-prandially an accelerated FOX_net rate and a decelerated COX_net rate initiate feed intake.