Krogh U, Storm A C, Theil P K
J Anim Sci. 2016 Dec;94(12):5122-5128. doi: 10.2527/jas.2016-0853.
The objectives of the present study were to design a method to estimate mammary plasma flow (MPF) in lactating sows using downstream dilution of -aminohippuric acid (AH) 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 AH (3.0 mmol/h). Total MPF-AH 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-AH was 6,860 L/d in early lactation and increased to 8,953 L/d at peak lactation ( = 0.003). In early lactation, MPF-AA estimates were greater or tended to be greater (132% to 175%; < 0.10) than MPF-AH estimates for all internal markers, except Met (119%). Moreover, MPF-AH was correlated with MPF-AA only for MET as an internal marker ( = 0.74; = 0.03) in early lactation. In contrast, MPF-AH and MPF-AA estimates did not differ and were well correlated at peak lactation with the strongest correlation observed when Met ( = 0.84; = 0.009) and Phe + Tyr ( = 0.82; = 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; = 0.001) and was correlated with MPF-AH during lactation ( = 0.74; < 0.001), whereas no correlation between litter gain and MPF-AA was observed ( > 0.10). These results suggest that downstream dilution of infused AH and the AA methods are applicable methods to estimate MPF at peak lactation. The reason for the observed discrepancy in early lactation between MPF- AH 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 AH was higher at peak compared to early lactation, which the internal AA marker approach failed to show.
本研究的目的是设计一种利用对氨基马尿酸（AH）下游稀释法来估算泌乳母猪乳腺血浆流量（MPF）的方法，并将这些估算值与基于特定氨基酸（AA）作为内标物的MPF估算值（MPF-AA）进行比较。通过外科手术在8头经产2胎和3胎母猪妊娠76±2标准误（SEM）时，在其股动脉植入一根永久性留置导管，并在右侧乳腺头静脉插入另外两根导管。在泌乳的第3天和第17天，从饲喂前0.5小时至饲喂后6.5小时，每隔1小时采集动脉和静脉血样。通过输注AH（3.0 mmol/h）的下游稀释法测量右侧乳腺头静脉的MPF。根据乳腺血管系统的解剖结构，假设所测流量代表14个哺乳乳腺中5个的流量，计算总MPF-AH。基于乳汁中特定AA标记物的输出量以及该标记物在血浆中作为游离AA的动静脉差异，假设AA从血浆直接转移至乳蛋白，估算总MPF-AA。泌乳早期总MPF-AH为6860 L/d，泌乳高峰期增至8953 L/d（P = 0.003）。在泌乳早期，除蛋氨酸（Met，119%）外，所有内标物的MPF-AA估算值均高于或倾向于高于MPF-AH估算值（132%至175%；P < 0.10）。此外，在泌乳早期，仅当蛋氨酸作为内标物时，MPF-AH与MPF-AA相关（r = 0.74；P = 0.03）。相反，在泌乳高峰期，MPF-AH和MPF-AA估算值无差异且相关性良好，当蛋氨酸（r = 0.84；P = 0.009）和苯丙氨酸+酪氨酸（r = 0.82；P = 0.01）作为内标AA时，相关性最强。窝仔增重从泌乳第3天至第17天增加（2.13对3.46 g/d；P = 0.001），且与泌乳期间的MPF-AH相关（r = 0.74；P < 0.001），而未观察到窝仔增重与MPF-AA之间的相关性（P > 0.10）。这些结果表明，输注AH的下游稀释法和AA法是估算泌乳高峰期MPF的适用方法。泌乳早期MPF-AH和MPF-AA之间观察到差异的原因尚不明显，但可能与泌乳早期观察到的快速代谢变化有关。总之，与泌乳早期相比，通过乳腺输注AH下游稀释法测得的MPF在高峰期更高，而内标AA标记物方法未能显示出这种差异。
