Abstract
Long-chain fatty acids mobilized during early lactation of dairy cows are increasingly used as energy substrate at the expense of acetate. As the synthesis of acetate in the rumen is closely linked to methane (CH4) production, we hypothesized that decreased acetate utilization would result in lower ruminal acetate levels and thus CH4 production. Twenty heifers were sampled for blood, rumen fluid and milk, and CH4 production was measured in respiration chambers in week −4, +5, +13 and +42 relative to first parturition. Based on plasma non-esterified fatty acid (NEFA) concentration determined in week +5, animals were grouped to the ten highest (HM; NEFA > 580 μmol) and ten lowest (LM; NEFA < 580 μmol) mobilizing cows. Dry matter intake (DMI), milk yield and ruminal short-chain fatty acids did not differ between groups, but CH4/DMI was lower in HM cows in week +5. There was a negative regression between plasma NEFA and plasma acetate, between plasma NEFA and CH4/DMI and between plasma cholecystokinin and CH4/DMI in week +5. Our data show for the first time that fat mobilization of the host in early lactation is inversely related with ruminal CH4 production and that this effect is not attributed to different DMI.
Highlights
Animals were grouped according to their plasma non-esterified fatty acids (NEFA) concentrations at the time of the respiration chamber measurements in week 5 ± 0.2 of early lactation in which plasma NEFA concentrations amounted to 811.2 ± 61.9 μmol/L for the ten highest (HM; NEFA > 580 μmol) and 379.1 ± 61.9 μmol/L for the ten lowest (LM; NEFA < 580 μmol) mobilizing cows (P < 0.001; Supplemental Fig. 1a)
In an earlier study we have shown that highest mobilizing (HM) cows have greater preprandial ghrelin concentrations than lowest mobilizing (LM) cows, and that this difference was prominent during early lactation and less in late pregnancy[14]
We investigated the individual CH4 production of first lactating dairy cows to characterize the impact of body fat mobilization during the exceptional metabolic state in early lactation on ruminal fermentation characteristics
Summary
During this time of lactation provision of energy by dietary derived acetate is lowest and as an adaptive response cows mobilize their body fat reserves leading to increased concentrations of circulating long-chain, non-esterified fatty acids (NEFA). These mobilized NEFA are mainly composed of C16 and C18 and are intensively oxidized to allocate energy and used by the mammary gland for milk fat synthesis[9]. The increase in plasma NEFA concentrations reduces the level of acetate utilization, at least in the mammary gland, but whether plasma NEFA concentrations are negatively related to CH4 yield remains to be investigated. We hypothesized that increased body fat mobilization resulting in higher plasma NEFA concentrations would negatively affect metabolic acetate utilization, and as a kind of negative feed-back regulation, acetate production in the rumen and CH4 production
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