Whole-body glucose metabolism and mammary energetic nutrient metabolism in lactating dairy cows receiving digestive infusions of casein and propionic acid

Abstract

This study analyzed the effect of propionate (C3) and casein (CN) on whole-body and mammary metabolism of energetic nutrients. Three multiparous Holstein cows fitted with both duodenal and ruminal cannulas were used in 2 replicated Youden squares with 14-d periods. Effects of CN (743 g/d in the duodenum) and C3 (1,042 g/d in the rumen) infusions, either separately or in combination as supplements to a grass silage diet, were tested in a factorial arrangement. The control diet provided 97% of energy and protein requirements. Within each period, blood samples were taken (d 11) from the carotid artery and the right mammary vein to determine net uptake of energetic nutrients. Plasma blood flow was calculated using the Fick principle (based on Phe and Tyr). On d 13, [6,6-(2)H(2)]glucose was infused in the jugular vein to determine whole-body glucose rate of appearance (Ra) based on enrichments in arterial plasma. Both C3 and CN treatments increased whole-body Ra (17% and 13%, respectively) but only CN increased milk (18%) and lactose (14%) yields, suggesting no direct link between whole-body Ra and milk yield. When CN was infused alone, the apparent ratio of conversion of CN carbon into glucose carbon was 0.31 but, when allowance was made for the CN required to support the extra milk protein output, the ratio increased to 0.40, closer to the theoretical ratio (0.48). This may relate to the observed increases in arterial glucagon concentrations for CN alone. Conversely, the apparent conversion of infused C3 carbon alone to glucose was low (0.31). With C3, mammary plasma flow increased as did uptakes of lactate, Ala, and Glu whereas the uptake for beta-hydroxybutyrate (BHBA) decreased. Mammary net carbon balance suggested an increase with C3 treatment in glucose, lactate, Ala, and Glu oxidation within the mammary gland. Mammary glucose uptake did not increase with CN treatment, despite an increase in glucose arteriovenous difference and extraction rate, because plasma flow decreased (-17%). Whereas CN, alone or in combination with C3, increased both lactose and protein yields, only mammary AA (and BHBA in CN alone) uptake increased because plasma flow decreased (-17%). These data suggest that the observed variations of milk lactose yield (and other milk components) are linked to metabolic interchanges between several energetic nutrients at both the whole-body and mammary levels and are not explained by increases in whole-body glucose availability.

Response of milk fat concentration and yield to nutrient supply in dairy cows

“…Proteins seem to stimulate the de novo FA synthesis, as suggested by the increase in the percentages of SCFA and MCFA (and the consecutive decrease in LCFA percentages). This increase in SCFA and MCFA could be linked to an increase in arterial concentrations or extraction rates of some mammary FA synthesis precursors (C2 and non-esterified FA: Guinard et al, 1994;b-hydroxybutyrate: Vanhatalo et al, 2003;Lemosquet et al, 2009b). The hypothesis of dietary protein stimulating lipomobilization is not consistent with the observed decrease in LCFA percentages.…”

Different levels of supplied energy for lactating cows affect physicochemical attributes of milk

“…The most noticeable is glucose, the precursor of lactose, which is the primary osmotic regulator of milk volume (Lemosquet et al, 2009b;Wall and McFadden, 2012). In the present study, higher level of supplied energy resulted in higher milk yield and lactose content.…”

Gluconeogenesis in dairy cows: The secret of making sweet milk from sour dough

“…Effects of glucose status on glucose carbon return might involve C3 return from mammary pentose phosphate cycle as this pathway is of importance for NADPH generation for de novo fatty acid synthesis in the mammary gland. Lemosquet et al (50) showed that mammary release of L-lactate was changed to mammary uptake with exogenous supply of glucogenic substrate (propionate and nonessential amino acids). Lactate release by skeletal muscle might as well contribute to the return of glucose carbon to the liver, whereas the PDV release of L-lactate seems primarily related to feed intake (29; Raun and Kristensen, unpublished data).…”