Changes in mammary blood flow during the lactation period in goats measured by the ultrasound Doppler principle

Thermotolerance capabilities, blood metabolomics, and mammary gland hemodynamics and transcriptomic profiles of slick-haired Holstein cattle during mid lactation in Puerto Rico

Holstein cattle carrying a prolactin receptor gene mutation (SLICK) exhibit short and sleek hair coats (short-haired Holstein [SLK]) enhancing thermotolerance and productivity compared with wild type-haired Holstein (WT) under tropical conditions. The objectives were to unravel the physiological and molecular mechanisms that confer an advantage to this slick genotype in Puerto Rico and determine potential correlations between metabolites and physiological variables. At 160 ± 3 DIM we compared vaginal temperatures (VT) and voluntary solar radiation exposure (VSRE) during 48 h between 9 SLK and 9 WT Holsteins, whereas a subsample of 7 SLK and 7 WT were used to assess udder skin temperature, mammary gland hemodynamics and transcriptomics, and blood plasma untargeted metabolomics at a single time point. The SLK cattle showed lower VT throughout the day and greater VSRE at 1000 h and 1100 h compared with their WT counterparts. Total mammary blood flow (MBF) was greater in SLK Holsteins compared with WT. The metabolite 9-nitrooctadecenoic acid was identified as a potential biomarker for MBF; moreover, SLK cattle had greater amounts of this metabolite in their plasma. Prostaglandin D2 synthase (PTGS) was upregulated in the slick mammary gland, while plasma prostaglandin D2 was positively correlated with milk yield and increased in SLK Holsteins compared with WT. Interestingly, the arachidonic acid metabolism pathway was enriched in the mammary gland transcriptome and perturbed in the blood metabolome in the SLK Holsteins. In conclusion, SLK Holsteins exhibited lower body temperatures, greater VSRE, enhanced blood supply to the mammary gland, and alterations in genes and metabolites involved in arachidonic acid metabolism at the mammary gland and blood plasma. The usage of the SLK Holstein cattle genetics in dairy operations could be a feasible alternative to mitigate the adverse consequences of heat stress.

Modern Imaging Techniques in the Study and Disease Diagnosis of the Mammary Glands of Animals

The study of the structure and function of the animals' mammary glands is of key importance, as it reveals pathological processes at their onset, thus contributing to their immediate treatment. The most frequently studied mammary diseases are mastitis in cows and ewes and mammary tumours in dogs and cats. Various imaging techniques such as computed tomography, positron emission tomography, magnetic resonance imaging, and ultrasonographic techniques (Doppler, contrast-enchanced, three-dimensional and elastography) are available and can be applied in research or clinical practice in order to evaluate possible abnormalities in mammary glands, as well as to assist in the differential diagnosis. In this review, the above imaging technologies are described, and the perspectives of each method are highlighted. It is inferred that ultrasonographic modalities are the most frequently used imaging techniques for the diagnosis of clinical or subclinical mastitis and treatment guidance on a farm. In companion animals, a combination of imaging techniques should be applied for a more accurate diagnosis of mammary tumours. In any case, the confirmation of the diagnosis is provided by laboratory techniques.

The Role of Ewes’ Udder Health on Echotexture and Blood Flow Changes during the Dry and Lactation Periods

Simple Summary

During lactation, the mammary glands of ewes are prone to infections caused by numerous pathogens. Consequently, mastitis and other udder abnormalities frequently occur. Unfortunately, udder inflammation, whether clinical or subclinical, it poses a significant barrier to livestock profitability by reducing milk production, decreasing milk quality, and suppressing ewes’ reproductive performance. The cost of subclinical mastitis often is greater than that of clinical mastitis. Thus, such conditions must be treated during the dry period, which is important for mammary gland repair and recovery. Moreover, an early diagnosis is crucial for effective treatment. Ultrasonography is a useful tool that is employed in the detection of echotextural and hemodynamic changes. During recent decades, there has been an increasing scientific interest in the contributions of B-mode and Doppler to the determination of physiological and pathological conditions occurring in mammary glands, which cannot be detected during a physical examination. Therefore, the aim of the present study was to investigate the alterations in ewes’ udders’ echotexture and blood flow during the end of lactation, the stages of dry period, and the first days of the postpartum period. A further objective was to investigate the hemodynamic and echotextural differentiations between ewes having healthy udders and ewes having subclinical mastitis.

Abstract

The objective of the current study was to investigate the echotextural and hemodynamic changes of ewes entering the dry period with or without subclinical mastitis. B-mode and color Doppler ultrasonography were applied to 12 Chios ewes (6 with healthy udders (group A) and 6 with subclinical mastitis (group B)) before the dry period, during the dry period (the involution phase, steady state, and transition phase), and postpartum. The color Doppler of the mammary arteries was used to evaluate them according to the pulsatility index (PI), resistive index (RI), end-diastolic velocity (EDV), time-averaged maximum velocity (TAMV), blood flow volume (BFV), and artery diameter (D). Udder parenchyma images, analyzed by Echovet v2.0, were used to evaluate the mean value (MV), standard deviation (SD), gradient mean value (GMV), gradient variance (GV), contrast (Con), entropy (Ent), gray value distribution (GVD), run length distribution (RunLD), and long run emphasis (LRunEm). In the involution phase, the PI was higher in group B compared to group A (p ≤ 0.05). The PI and RI were higher postpartum, whereas the EDV, TAVM, and D were higher in the transition phase (p ≤ 0.05). Neither the period nor the ewe group affected the MV, SD, GMV, GV, Con, and GVD values (p ≤ 0.05). In the steady state, the LRunEm was higher in group B, but postpartum, it was higher in group A (p ≤ 0.05). In conclusion, B-mode and Doppler can reveal differences (i) between healthy ewes and ewes with subclinical mastitis and (ii) among the different periods studied. Further research is needed on the blood flow and echotexture indices of the udders of ewes with unilateral subclinical mastitis.

B-mode and Doppler sonography of the mammary glands in dairy goats for mastitis diagnosis

This study aimed to evaluate the sonographic characteristics of the udder and teats and to determine the Doppler indexes of mammary artery in healthy and undergoing subclinical and clinical mastitis goats. Thirty animals among Saanen and Alpine Brown goats were arranged in three groups, healthy goats (HG), goats with subclinical mastitis (SMG) and goats with clinical mastitis (CMG). Using the B-mode, the sonographic characteristics (echotexture and echogenicity) and biometry (diameter and area of the udder cistern, diameter and area of the teat cistern and thickness of the teat wall) were evaluated. Using Doppler ultrasonography, the vascular indexes of the mammary artery were obtained. It was observed hyperechogenicity with solid component in the gland cistern when comparing animals with clinical mastitis and healthy mammary tissue. Regarding the echotexture of the breast tissue, there was heterogeneity in the mammary parenchyma on the three groups, for the milk, it was observed homogeneity for animals on HG and SMG and heterogeneity for animals on CMG. Grey-scale quantitative assessment revealed increase in echogenicity (mean value) for all the structures when comparing the three groups. Biometry did not reveal statistical difference between groups, for none of the evaluated structures. Doppler examination of the mammary artery showed the decrease of end diastolic velocity and raise of pulsatility index between groups. The association of B-mode and Doppler ultrasonography is useful for the evaluation of the udder of dairy goats with mastitis. It is a sensitive and specific method for the study of this disease. Doppler mode was unable to establish reliable criteria for diagnosis of subclinical mastitis. Moreover, the quantification of echogenicity is a useful technique for the evaluation of the milk in animals with mastitis; therefore, it is suggested that it can be used as complementary technique for the diagnosis of mastitis in goats.

Ultrasonographic findings in the ovine udder during involution

The objective of the study was to record, by means of ultrasonographic examination, changes occurring in the udder of ewes during involution and to compare differences between progressive or abrupt udder drying-off. In group A ewes, udder drying-off took place progressively during a period of 22 d; ewes were milked twice daily for the last time on day(D) 0; then, they were hand-milked once daily for a week (D1-D7), which was followed by another week during which ewes were hand-milked once every 2 d (D9, D11, D13), followed by a third week during which ewes were hand-milked once every 3 d (D16, D19, D22). In group B ewes, the procedure took place abruptly; ewes were milked twice daily for the last time on D0 and no milking was carried out after that. B-mode and Doppler ultrasonographic examination of the udder of all ewes was performed throughout the drying-off procedure. Appropriate data management and analysis were performed. Progressive changes of the various parameters evaluated throughout the study period were significant in both groups (P<0.005). Gray-scale results of mammary parenchyma progressively decreased during the study and differed significantly between group A and group B (P=0.049). A temporary increase in cistern volume was evident after cessation of lactation, but differences were not significant between the two groups (P>0.3). Diameter of the external pudendal artery progressively decreased during the study and differed significantly between the two groups (P=0.037). Both resistance index and pulsatility index progressively increased throughout the study period in both groups; for both parameters, differences between the two groups were significant (P<0.0005). B-mode ultrasonographic examination indicated differences in remodelling of the extracellular matrix in relation to the procedure for udder drying-off. Volume of the gland cistern did not appear to be affected by the procedure for udder drying-off. Doppler ultrasonographic examination confirmed that blood flow during initiated involution was lower than during a progressive procedure for drying-off.

B-mode and colour Doppler ultrasonography of the milk vein and musculophrenic vein in eight cows during lactation

Eight cows underwent Doppler sonographic examinations of the milk vein and musculophrenic vein from 9 days prepartum to 300 days postpartum. A 7.5-MHz linear transducer was used to determine the inner diameter of the veins and blood flow velocities and volumes on the left side in standing, non-sedated animals. Cows were weighed and milk yield measured at all examination times. The milk vein appeared as a vessel with an inner diameter of 2.01-2.30 cm immediately beneath the skin. The maximum blood flow velocity ranged from 23.84 to 35.76 cm/s before parturition, increased markedly on the day of calving (day 0), peaked at 61.14 cm/s on day 1 and slowly decreased to 23.84 cm/s by day 300. The profiles of the minimum and mean maximum flow velocities and flow volume were similar. The musculophrenic vein had an inner diameter of 0.76-1.07 cm and its distance from the surface of the skin was 1.15-1.31 cm. The profiles of the blood flow variables were irregular and did not resemble those of the milk vein. The maximum blood flow velocity ranged from 87.35 to 114.41 cm/s, the minimum velocity from 5.47 to 7.60 cm/s, the mean maximum velocity from 48.55 to 78.74 cm/s and the blood flow volume from 1.02 to 2.44 l/min. The milk vein had a larger diameter (2.16 versus 0.90 cm; P<0.01), smaller maximum, minimum and mean maximum blood flow velocities (P<0.01) and a larger blood flow volume than the musculophrenic vein (P<0.01).

Blood flow characteristics of the human lactating breast

BACKGROUND

Despite the increased metabolic activity of the lactating breast, no studies have been carried out to determine mammary blood flow (MBF) parameters or the relationship between MBF and milk production in women. The aim of this study was to measure the MBF in the internal mammary artery (IMA) and lateral thoracic artery (LTA) of lactating women and determine if these were related to milk production.

METHODS

Blood flow in the IMA and LTA was measured with color Doppler ultrasound in 55 lactating women. Twenty-four-hour milk production was determined with the test-weigh method.

RESULTS

IMA contributed the greater proportion of blood flow to the lactating breast (70%). MBF was highly variable between women but consistent between the left (126 L/24 h; interquartile range, 76-169) and right (110 L/24 h) breasts. No relationship between MBF and milk production was demonstrated. For 3 women, MBF was markedly reduced in 1 breast that was synthesizing almost no milk compared to the other that was producing a normal volume of milk.

DISCUSSION

Although no relationship between MBF and milk production was found, the substantial reduction in blood flow in the breasts of lactating women producing almost no milk suggests a threshold below which milk production is compromised.

CONCLUSION

Doppler ultrasound did not demonstrate a relationship between MBF and milk production in lactating women. Further investigation is required to fully understand the role of blood flow in milk synthesis.

Continuous lactation effects on mammary remodeling during late gestation and lactation in dairy goats

The present study aimed to 1) elucidate whether continuous milking during late gestation in dairy goats negatively affects mammary remodeling and hence milk production in the subsequent lactation, and 2) identify the regulatory factors responsible for changes in cell turnover and angiogenesis in the continuously lactating mammary gland. Nine multiparous dairy goats were used. One udder half was dried off approximately 9 wk prepartum (normal lactation; NL), and the other udder half of the same goat was milked continuously (continuous lactation; CL) until parturition or until the half-udder milk yields had dropped to below 50 g/d. Mammary biopsies were obtained from each udder half just before the NL gland was dried off (before dry period), within the first 2 wk after drying-off (early dry period, samples available only for NL glands), in the mid dry period, within the last 2 wk before parturition (late dry period), and at d 1 (the day of parturition), 3, 10, 60, and 180 of lactation. Mammary morphology was characterized in biopsies by quantitative histology, and cell turnover was determined by immunohistochemistry (terminal deoxynucleotidyl transferase dUTP nick end labeling and Ki-67). Transcription of genes encoding factors involved in mammary epithelial cell (MEC) turnover and vascular function was quantified by quantitative reverse transcription PCR. Results demonstrated that omitting the dry period was possible in goats but was not as easy as claimed before. Renewal of MEC was suppressed in CL glands, which resulted in a smaller MEC population in the subsequent lactation. At the time of parturition (and throughout lactation), the mammary glands subjected to CL had smaller alveoli, more fully differentiated MEC, and a substantially larger capillary fraction compared with NL glands. The continuously lactating gland thus resembled a normally lactating gland in an advanced stage of lactation. None of the studied genomic factors could account for these treatment differences. The described characteristics in CL glands compared with NL glands indicated a gland maintained in lactation for a longer period.

Variability of mammary blood flow in lactating Holstein-Friesian cows during the first twelve weeks of lactation

The goals of the present study were to measure mammary blood flow volume (BFV) during the first 12 wk of lactation in dairy cows by using color Doppler sonography and to determine what affects the mammary blood flow. Forty cows were examined via color Doppler sonography on d 1, 7, 14, 28, 56, and 84 after parturition (d 0). The total BFV (BFV(total)) to the 4 mammary glands was calculated by measuring time-averaged maximum velocities (TAMV) and cross-sectional areas (A) of the left and right pudendoepigastric trunks via transrectal color Doppler sonography. Because there were no significant differences in A, TAMV, and BFV between the right and left pudendoepigastric trunks, the means of A and TAMV, and the BFV(total) of both trunks were used for calculations. The intraindividual and interindividual variability of repeated BFV measures quantified by intraclass correlation coefficients were 96 and 98%, respectively. The BFV(total) ranged from 19.9 to 27.9 L/min, with a mean of 22.3+/-4.9 L/min. Interindividual differences in BFV values were attributable to variations in A and TAMV. The interindividual variability of the BFV(total), which was determined using the coefficients of variation of the BFV(total) on individual days, ranged from 16 to 28%. All the cows had similar changes in the BFV(total) during the study. Changes in BFV(total) were not correlated with changes in the mean of A, but there was a good correlation between changes in BFV(total) and in the mean of TAMV (r=0.94). The BFV(total) was highest on d 1 of lactation, decreased 28% by d 7, and remained at this level until d 28. By d 56, the BFV(total) had increased by 15% compared with d 14 and by 10% compared with d 28. The BFV(total) on d 84 was significantly different from all other days except d 56. There were moderate correlations between daily milk yield and BFV on individual days (0.24<r<0.35). In conclusion, Doppler sonography is a reliable method for determining blood flow in the pudendoepigastric trunk of cows. There is great variability in mammary blood flow among cows and in BFV.

The histamine H1 receptor is not involved in local control of mammary blood flow in dairy cows

Low concentrations of the essential amino acid histidine in circulation have been shown to increase mammary blood flow and it has been suggested that this effect is mediated by histamine. The hypotheses tested in this experiment were that interstitial histamine concentrations in the mammary gland are related to arterial His concentrations and that mammary blood flow is reduced by extracellular histamine via H(1) receptors. The hypotheses were tested by infusing saline or chlorpheniramine, a blocker of the H(1) histamine receptor, into the arterial supply of the mammary glands of lactating cows infused with 44 g/h of amino acid mixtures with or without His for 10 h. Infusates were administered in a 2 x 2 factorial arrangement within a 4 x 4 Latin square to 4 multiparous Holstein cows in mid lactation. Exclusion of His from the infusate decreased protein content in milk from the infused udder half from 3.98 to 3.77%, and increased arterial alpha-aminonitrogen concentration from 3.2 to 3.4 mM. Neither the decreased arterial His concentration nor the H(1) blocker affected plasma flow to the infused udder half. We conclude that histamine is not involved in the regulation of mammary blood flow. The H(1) blocker decreased milk production in the infused udder half from 4.6 to 3.5 kg without affecting protein, fat, and lactose percentages, suggesting an inhibition of milk ejection. Cows on chlorpheniramine ate less feed during the infusion than saline-infused cows, which resulted in lower arterial concentrations and mammary uptakes of acetate. The efficiency of plasma triacylglycerol uptake across the mammary glands was decreased by chlorpheniramine but net uptake of long-chain fatty acids was not affected. The mechanism by which an amino acid deficiency influences mammary blood flow does not involve histamine signaling through the H(1) receptor and remains unidentified.

Endocrinology of milk production

The physiology of lactation includes development of the mammary gland from the foetal to the adult stage, further development during pregnancy and onset of lactation, with the accompanying metabolic and behavioural adaptation. At the onset of pregnancy the endocrine system undergoes dramatic changes. The growth of the mammary gland is stimulated by growth hormone and prolactin, adrenocortical steroids, oestrogens and progesterone, and that of the gastrointestinal (GI) tract by gastrin, CCK and secretin. The onset of lactation is accompanied by increases in the blood volume, cardiac output, mammary blood flow and blood flow through the GI-tract and liver, aiming to provide the udder with nutrients and hormones for regulation of milk synthesis. Food intake and distribution of nutrients to the mammary gland are partially regulated by hormones as well as the repartitioning of nutrients away from body stores towards the udder. To improve milk production, administration of growth hormone has been practised, but also much discussed. Besides central mechanisms, local mechanisms within the mammary gland regulate initiation of lactation, maintenance, regulation of blood flow and mammary gland cell apoptosis. Most of the milk in a filled dairy cow udder is stored in the alveolar compartments. The milk ejection reflex must be activated to gain access to the udder milk, i.e. oxytocin contracts the myoepithelial cells. Recent studies show that vasopressin may also elicit milk ejection. More efficient oxytocin release is achieved if the cows are fed during milking. Beyond milk let down, oxytocin influences maternal behaviour and metabolism. Furthermore, it has been indicated that suckling or milking activates a vagal reflex, which may link the milk production to the endocrine system of the GI-tract. The question has been raised whether the mammary gland is a supporting or consuming organ.

Responses to potential vasoactive substances of isolated mammary blood vessels from lactating sows

The purpose of the investigation was to examine the response of the milk vein and the mammary artery to potential vasoactive substances in lactating sows. The response on artery and vein segments from the same sow was measured for the following substances: noradrenaline (NA), serotonin (5-HT), prostaglandin F2alpha (PGF2alpha), prostacyclin (PGI2), histamine (Hi) and potassium (K+). Interestingly, the contractile force in the mammary vein segments expressed per weight unit (mN/mg) was 1.5-2.5 fold larger than in the artery segments when NA, 5-HT and PGF2alpha were used, but similar for K+, Hi and PGI2. In vein segments, the order of sensitivity to the substances expressed by their pD2 values was 5-HT > NA = PGF2alpha > Hi > K+. The present findings suggest that NA, 5-HT, PGF2alpha, PGI2, and Hi are involved in mammary blood flow regulation in the sow, and the mammary venous system may be as important as the mammary arterial system in this regulation.

Regulation of blood flow in the mammary microvasculature

Although milk yield of cows and goats is known to be closely related to the total flow of blood through the udder, a number of studies suggest that milk yield can vary independently. No studies have attempted to measure the proportion of total flow that is nutritive. Within the mammary gland, capillary networks form a basket-like architecture surrounding each alveolus. Notably, flow in individual capillaries is not constant and varies among capillaries. Capillary flow (measured by intravital microscopy) was decreased by oxytocin, which generally increased total flow in the mammary artery, suggesting that the proportion of total flow that is nutritive can vary. In addition to classic metabolic regulators (e.g., carbon dioxide and oxygen) of tissue blood flow, the mammary gland produces a number of vasodilatory compounds, including parathyroid hormone-related protein, insulin-like growth factor-I, prostacyclin, nitric oxide, and endothelin. All of these compounds have been shown to alter mammary blood flow. Mammary tissue also contains kallikrein and angiotensin-converting enzyme, which convert circulating kinins and angiotensin, respectively, into potent vasoactive compounds. A number of these compounds are produced by epithelial cells themselves, providing a mechanism for the functioning epithelium to control its own blood supply and, hence, nutrient flow for milk synthesis. In this review, we examine the nature of the mammary microcirculation, its behavior under different conditions, and some of the regulatory features of the mammary microvasculature.

Changes in mammary uptake of free fatty acids, triglyceride, cholesterol and phospholipid in relation to milk synthesis during lactation in goats

Uptake of free fatty acids (FFA), triglycerides (TG), cholesterol (CHOL) and phospholipids (PL) was measured in both mammary glands of dairy goats during lactation. Arterial concentrations of TG, CHOL and PL as well as arterio-venous difference (AV) and extraction rate (E) for TG were highest in goats with the highest dietary feed intake. AV were linearly related to arterial concentrations for the four lipid classes, and arterial concentrations of CHOL were linearly related to output of lactose, protein and fat in milk. Arterial supply, and not mammary synthetic activity, is the main determinant of mammary FFA, TG and CHOL uptake.

Changes in mammary glucose and protein uptake in relation to milk synthesis during lactation in high- and low-yielding goats

1. Glucose and protein uptake were measured in both mammary glands of two low- and two high-yielding dairy goats during lactation. 2. Low-yielding goats tended to have higher arterial glucose concentrations, but approximately 40% lower arterio-venous differences (AV) and extraction rates (E) for glucose than high-yielding goats. 3. AV and E for glucose (but not protein) were linearly related to yields of both lactose, milk protein and fat. 4. Mammary uptake of glucose is determined primarily by mammary glucose metabolism, not glucose supply; lower intracellular glucose concentration in mammary cells of genetically superior animals thus explains the more efficient mammary uptake.