Technical note: Measurement of mammary plasma flow in sows by downstream dilution of mammary vein infused para-aminohippuric acid

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The objectives of the present study were to design a method to estimate mammary plasma flow (MPF) in lactating sows using downstream dilution of para-aminohippuric acid (pAH) and to compare these estimates with MPF estimates based on specific AA as internal markers (MPF-AA). A permanent indwelling catheter was surgically implanted in the femoral artery, and another 2 were inserted in the right cranial mammary vein of 8 second- and third-parity sows on d 76 ± 2 SEM of gestation. On the 3rd and 17th days in milk, arterial and venous blood samples were drawn in hourly intervals from 0.5 h before until 6.5 h after feeding. The MPF in the right cranial mammary vein was measured by downstream dilution of infused pAH (3.0 mmol/h). Total MPF-pAH was calculated assuming that the measured flow constituted the flow from 5 out of 14 suckled glands on the basis of the anatomical structure of the mammary vascular system. Total MPF-AA was estimated on the basis of the output of the specific AA marker in milk and the arteriovenous differences of the marker as free AA in plasma, assuming a direct transfer of AA from plasma to milk protein. Total MPF-pAH was 6,860 L/d in early lactation and increased to 8,953 L/d at peak lactation (P = 0.003). In early lactation, MPF-AA estimates were greater or tended to be greater (132% to 175%; P < 0.10) than MPF-pAH estimates for all internal markers, except Met (119%). Moreover, MPF-pAH was correlated with MPF-AA only for MET as an internal marker (r = 0.74; P = 0.03) in early lactation. In contrast, MPF-pAH and MPF-AA estimates did not differ and were well correlated at peak lactation with the strongest correlation observed when Met (r = 0.84; P = 0.009) and Phe + Tyr (r = 0.82; P = 0.01) were used as the internal AA markers. Litter gain increased from d 3 to 17 of lactation (2.13 vs. 3.46 g/d; P = 0.001) and was correlated with MPF-pAH during lactation (r = 0.74; P < 0.001), whereas no correlation between litter gain and MPF-AA was observed (P > 0.10). These results suggest that downstream dilution of infused pAH and the AA methods are applicable methods to estimate MPF at peak lactation. The reason for the observed discrepancy in early lactation between MPF- pAH and MPF-AA is not obvious but might be related to the rapid metabolic changes observed in early lactation. In conclusion, MPF measured by downstream dilution of mammary infused pAH was higher at peak compared to early lactation, which the internal AA marker approach failed to show.
TidsskriftJournal of Animal Science
Sider (fra-til)5122-5128
Antal sider7
StatusUdgivet - 28 nov. 2016

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