Measurement of blood flow through the mammary gland in lactating sows: methodological aspects1

Abstract

Two replicates of three multiparous crossbred Large White x Landrace lactating sows were used to develop a technique for the continuous direct measurement of the blood flow through the mammary gland using transit time ultrasound. Four to six days after farrowing, an ultrasonic transit time flow probe was implanted around the right external pudic artery in order to measure the short-term variations of mammary blood flow through this vessel in response to postural change (standing vs lying), meal distribution, hand-milking, and weaning. After surgery, all sows were fed 3.8 kg/d of a lactation diet and housed either at 20 or 28 degrees C. The implantation of the ultrasonic blood flow probe was successful in all six operated sows. Postmortem examination did not indicate the presence of infection, any collateral bypassing the flow probe, or a reduction of artery diameter. The right pudic artery mammary blood flow (PMBF) was measured for 8.5 h over two periods of three days (d 11 to d 13 and d 18 to d 20 of lactation). The PMBF averaged 910 +/- 238 mL/min but was variable within 1 d. Compared with the lying position, PMBF was decreased (- 6%, P < 0.05) when sows were standing. Between 0 to 15 and 16 to 30 min after oxytocin injection (t = 0) and hand-milking, PMBF remained constant (P = 0.05; 801 vs 767 mL/ min) and increased (P = 0.02), respectively, in comparison with the mean calculated over the preceding 30-min period (982 vs 784 mL/min). The PMBF increased (P < 0.05) after meal distribution and reached a peak 65 min later (i.e., 980 mL/min). The PMBF decreased regularly after separation of piglets at weaning; at 8 and 16 h after weaning, PMBF was 60 and 40% of the value recorded before weaning, respectively. Assuming that PMBF drains one-quarter of the whole mammary gland, it can be calculated that blood flow through the entire mammary gland averages 3.6 L/min and that about 470 L of blood are required to produce 1 kg of milk. The proposed methodology constitutes a new technique to measure direct mammary blood flow and its short-term factors of variation.

Review: Current knowledge on mammary blood flow, mammary uptake of energetic precursors and their effects on sow milk yield

“…injection of 20 IU of oxytocin and returned to pre-injection values 12 min after the start of milking. Thereafter, blood flow increased and reached a maximum value 22 min after the onset of milking (Renaudeau et al 2002). These authors suggested that the post-suckling increase in mammary blood flow could be related to the nursing event and/or the increase in milk synthesis in response to the decreased milk volume in the udder.…”

“…The Fick approach offers the advantage of not requiring arterial mammary blood per se; hence, catheter placement for arterial infusion or blood sampling may be done in any arterial sites. However, in contrast to the direct flow probe approach (Renaudeau et al 2002), the Fick approach may only be used to determine long-term changes in blood flow (i.e., daily) as opposed to changes occurring in the short term (i.e., minutes). In contrast to Linzell et al's study (1969a), other studies (Trottier et al 1997;Nielsen et al 2002a,b;Guan et al 2002Guan et al , 2004a,b) applied Fick's law of diffusion to measurement of mammary blood flow using internal markers.…”

“…Mammary blood flow and milk yield determined in a total of seven perfused mammary glands from four sows (Linzell et al 1969a indicating low oxidative catabolism of these amino acids in the sow mammary gland. Recently, Renaudeau et al (2002) obtained direct measurements of blood flow through the mammary glands of lactating sows by implanting an ultrasonic blood flow probe around the right external pudic artery (Fig. 2).…”

“…2). In contrast to classical electromagnetic and Doppler methods, the method used by Renaudeau et al (2002) has the advantage of not being dependent upon the diameter of the blood vessel. Average pudic mammary blood flow (supplying approximately one-quarter of the whole mammary gland) was 9109283 mL min…”

“…Renaudeau et al (2002) reported that mammary blood flow decreased by 6% when sows were standing compared with lying, and increased by 7.7% following meal distribution, reaching a post-prandial peak at 65 min. The importance of suckling demand on mammary blood flow is illustrated by the reported decreases of 40 and 60%, respectively, 8 and 16 h after weaning (Renaudeau et al 2002) and a positive relationship between litter size and mammary plasma flow (Nielsen et al 2002b). Indeed, as litter size increased from 3 to 13, mammary plasma flow increased linearly from approximately 2000 L d (1 to over 5000 L d…”