Mammary nutrient uptake in sows fed supplementary dietary fiber and fat during lactation

Dietary fiber (DF) and fat, as precursors of ketogenic energy substrates, are hypothesized to enhance de novo milk fat synthesis and thereby increase milk yield in lactating sows. This study aimed to evaluate the effects of high DF and fat supplementation during lactation on mammary nutrient uptake, milk production, and growth performance of the piglets. Ten cross-bred gestating sows (Danish Landrace × Danish Yorkshire; initial average body weight: 276.00 ± 17.53 kg, mean ± SD; parity: 3 to 5, with a distribution of 4, 4, and 2 sows at parities 3, 4, and 5, respectively) were selected and assigned to either a control diet (Con; n = 5) or a high fiber and fat supplemented diet (FF; n = 5) from day 5 of lactation until weaning on day 28 of lactation. Sows were surgically fitted with two indwelling catheters in the mammary vein and one in the femoral artery on day 75 ± 2 of gestation. A blood flow marker was infused into one of the mammary veins at a rate of 3.0 mmol/h, and eight blood samples were collected at hourly intervals on day 7 and day 17 of lactation, respectively. One sow from the Con and two sows from the FF group had low feed intake (<1.5 kg/d) during the experimental period; thus, these sows were excluded from the experiment. Sows fed the FF diet exhibited lower apparent total tract digestibility of gross energy, dry matter, and organic matter than the Con group (P < 0.05). On day 17 of lactation, the contents of milk dry matter, fat, and energy were 27.6%, 59.8%, and 40.7% higher, respectively, in FF sows compared to Con sows (P < 0.05). The proportion of ketogenic energy substrates as a percentage of total carbon uptake by the mammary gland did not change with lactation stage in sows fed the Con diet but increased by 18.6% in those fed the FF diet from day 7 to day 17 of lactation. On day 7 of lactation, the mammary carbon balance was positive in both the Con and FF groups. However, by day 17 of lactation, the balance had turned negative, with values of -24 mol C/d in the Con group and -44 mol C/d in the FF group. In conclusion, supplementing lactating sows with high levels of DF and fat significantly reduced nutrient digestibility and increased milk fat content at peak lactation. This increase may be partially attributed to enhanced mobilization of mammary adipose tissue to compensate for the nutrient deficit required to support milk production.