Intramammary Pressure Research Articles

Controlled trial assessing the effect of gradual cessation of milking prior to dry-off on the risk of new intramammary infection and wellbeing in dairy cows

The importance of the end of lactation and the dry period in the dynamics of intramammary infection (IMI) in dairy cattle has long been recognized. In previous studies, gradual cessation of milking has been shown to decrease daily milk production during the last week of lactation and reduce risk of new IMI during the dry period. Although these results support the use of gradual cessation of milking to end lactation as an aid to improve udder health, only a limited number of recent studies have investigated its suitability in high-producing dairy cows. Consequently, gradual cessation has not been implemented widely in the field and no definite regimen has been recommended to dairy producers. However, due to increased intramammary pressure and subsequent tissue damage, abrupt cessation has been shown to be associated with elevated fecal stress hormones and is therefore subject to increasing concerns regarding animal well-being. The objective of this study, therefore, was to investigate the effect of 2 different drying-off protocols (gradual vs abrupt cessation) on the risk of new IMI, milk production, and somatic cell count (SCC) in the subsequent lactation, as well as concentration of fecal glucocorticoid metabolites in dairy cows. We hypothesized that cows that are enrolled in an intermittent milking schedule (i.e., gradual cessation) for the final week of lactation would have a lower risk of new IMI during the dry period, higher milk production, and lower SCC in the subsequent lactation, as well as lower fecal glucocorticoid concentration compared with their herd mates that are milked 3 times daily and dried-off by abrupt cessation.

Short communication: Teat wall diameter and teat tissue thickness in dairy cows are affected by intramammary pressure and by the mechanical forces of machine milking

The objective of this study was to validate and apply 2 different methods to record changes in teat tissue related to machine milking. Teat wall diameter was measured via B-mode ultrasound cross sectioning with a 7.5-MHz linear probe. Teat tissue thickness was measured using a cutimeter (spring-loaded caliper, spring constant 6.5 N/cm, 0.5 N at closed jaws). Both methods were applied at the teat barrel, 2 cm above the teat tip. In experiment 1, 24 teats from freshly slaughtered cows were used to perform ultrasound imaging (12 teats) or cutimeter measurements (12 teats) while the teat cisterns were filled with water to increase the intracisternal pressure from 0 to 30 kPa in steps of 1 kPa. Teat tissue thickness did not change at an intracisternal pressure from 0 to 10 kPa but increased with intracisternal pressure at levels >10 kPa. In contrast, teat wall diameter decreased with intracisternal pressure between 0 and 7 kPa but did not significantly change at a pressure ≥7 kPa up to 30 kPa. Significant Pearson correlation coefficients between intracisternal pressure and teat wall diameter were observed from 0 to 7 kPa (r = -0.38), and between intracisternal pressure and teat tissue thickness from 10 to 30 kPa (r = 0.45). In experiment 2, ultrasound and cutimeter measurements were performed in 12 lactating Holstein cows. Measurements before and during milking, immediately after cluster removal, with normal milking or with a 5-min overmilking, were performed and continued at 5-min intervals for 60 min and at 10-min intervals until 120 min. Additionally, with the 5-min overmilking treatment, measurements were continued at 60-min intervals up to 10 h after milking. Teat wall diameter decreased in response to milk ejection, followed by a continuous increase during the course of milking, with highest values after 5 min overmilking. Teat tissue thickness did not change during milking but was significantly increased after overmilking. Teat wall diameter and teat tissue thickness recovered to premilking levels within 35 min after normal milking and within 60 min after overmilking. Until 10 h after overmilking, the teat wall diameter decreased steadily, whereas teat tissue thickness was unfluctuating. In the physiologically relevant range of intramammary pressure, ultrasound measurements of the teat wall were affected by both intramammary pressure and mechanical forces, whereas cutimeter measurements were not affected by the intramammary pressure.

Intramammary pressure and udder firmness during a 72-h interruption of milking to simulate dry-off, with and without feed restriction

The goal of the present study was to quantify the increase of intramammary pressure (IMP) in dry-off during an extended milking interval of 72 h. In particular, we tested the hypothesis that feed restriction (no concentrate and roughage with reduced energy) causes earlier cessation of milk secretion and a lower IMP than continued feeding of the lactational diet. In addition to repeated IMP measurements, we tested a noninvasive method that records udder firmness (UF) via external application of pressure on the udder. Two experimental groups consisted of 10 Holstein cows each, with a daily milk yield of 20 to 25 kg. The restricted group (RG) was changed to restricted feeding on the afternoon of the final milking (0 h), whereas late-lactation feeding was continued in the control group (CG). Both IMP and UF were measured before and after the final milking immediately before milking was stopped for 72 h. These measurements represented IMP and UF levels at 10 h and 0 h milking intervals, respectively. Further measurements were performed at 18, 24, 30, 36, 42, 48, and 72 h after final milking. Milk samples (2 mL) were taken through the IMP catheter at each sampling event, for analysis of somatic cell count (SCC) and serum albumin (SA). Both IMP and UF increased with time, and both parameters peaked at 30 h in CG and at 24 h in RG. The mean IMP from 18 to 72 h, compared with the 10-h IMP (normal milking interval) was higher in CG than in RG. The duration of elevated IMP and UF was prolonged in CG compared with RG (>36 h vs. 12 h). The Pearson correlation between IMP and UF was r = 0.67. Thus, the noninvasive measurement of UF is suitable to replace invasive IMP measurements. However, due to individual differences in udder shape, the correlation between UF and IMP was too low to predict exact IMP levels using UF. Both SCC (presented as logSCC) and SA increased after the final milking until the end of the experiment. The mean increase from 18 to 72 h, compared with levels immediately after final milking, was higher in CG than in RG for SCC but did not differ between treatments for SA. In conclusion, feed restriction causes a faster cessation of milk secretion and therefore limits the increase of IMP at dry-off.

Incomplete Milking in Early Lactation Does Not Affect Dairy Cows Resting Behaviors: Results from a Randomized Controlled Trial.

The objective of this study was to investigate the effect of incomplete milking during the first 5 days of lactation on the resting behavior of commercial dairy cows. The hypothesis was that the elevated intramammary pressure resulting from milk retained in the udder in incompletely milked cows could lead to a change in lying behavior. This study was a randomized controlled trial in which cows from two farms were randomly allocated into a treatment (n = 18) or a control group (n = 14). Cows in the treatment group were milked incompletely (10–14 L/days) during the first 5 days of lactation, while cows in the control group were milked as usually done on farm. Resting behaviors were recorded with a data logger. Linear mixed models were used to quantify the effects of treatment group on three dependent variables measured between 2 and 14 days in milk: daily duration of lying time (h/d), lying bout frequency (bouts/day), and mean duration of lying bouts (min/bout). There was no significant effect of treatment on lying time. However, the effect of treatment on frequency of lying bouts and on mean lying bout duration varied by parity level. Incompletely milked cows in second parity had a higher number of lying bouts (11.9 vs. 9.2 bouts/day) and shorter mean lying bout duration (57.8 min/bout vs. 66.7 min) than control cows. In third parity or more, the opposite happened. Therefore, our results suggest that an incomplete milking may be slightly problematic for second parity cows and, possibly, slightly beneficial for older cows. Whether the differences observed resulted from a biologic process (discomfort due to the incomplete milking) or from random error will have to be determined by future research.

Effect of duration of milk accumulation in the udder on milk composition, especially on milk fat globule

Our objective was to study the effect of duration of milk accumulation on milk fat globules (MFG) secretion to better understand relationships between milk yield, milk fat, and MFG secretion. The modification of the milk accumulation duration in the udder is a tool to increase milk fat content. Four milking frequencies were studied on 6 dairy cows averaging 118±22 d in milk: 2 milkings/d separated by 11- and 13-h or by 4- and 20-h intervals and 1 milking/d. The experimental trial was a double Latin square 3×3 with 2-wk periods. Postexperiment, a milking frequency of 36-h was repeated twice. Compared with 2 milkings with 11- and 13-h frequencies, 1 milking/d reduced milk and milk fat yields and increased fat content, without any effect on the size of MFG. Two milkings with 4- and 20-h intervals had no significant effect on milk fat yield and content but tended to increase the size of the MFG. Lipolysis, measured on morning milk, was weaker with 1 milking/d. When data were analyzed according to milk accumulation duration (4, 11, 13, 20, 24, and 36h), the highest fat content and the largest diameters of MFG were obtained on milks from 4 and 36h milkings (62.8g/kg, 4.15 µm and 57.7g/kg, 4.09 µm, respectively). Such observations could have 2 origins: the richness in residual milk of the 4-h milk and the coalescence of MFG related to the long milk accumulation duration in the 36-h milk. For each duration of milk accumulation, a relationship exists between MFG size and fat yield. The positive relation between MFG size and fat content was confirmed at each duration of milk accumulation. Rate of secretion of milk fat (milk accumulation of 4h excluded) was also well correlated with MFG size. For the 36-h milk, this relationship was also observed but with a significantly different slope, assuming phenomena of MFG coalescence in response to the supposed increased intramammary pressure or to slower secretion rate and, hence, fusion events of microlipids droplets in the cytoplasm. Duration of milk accumulation joined with large increases in milk fat content induces changes in MFG size.

Histologic, Molecular, and Clinical Evaluation of Explanted Breast Prostheses, Capsules, and Acellular Dermal Matrices for Bacteria.

Subclinical infections, manifest as biofilms, are considered an important cause of capsular contracture. Acellular dermal matrices (ADMs) are frequently used in revision surgery to prevent recurrent capsular contractures. We sought to identify an association between capsular contracture and biofilm formation on breast prostheses, capsules, and ADMs in a tissue expander/implant (TE/I) exchange clinical paradigm. Biopsies of the prosthesis, capsule, and ADM from patients (N = 26) undergoing TE/I exchange for permanent breast implant were evaluated for subclinical infection. Capsular contracture was quantified with Baker Grade and intramammary pressure. Biofilm formation was evaluated with specialized cultures, rtPCR, bacterial taxonomy, live:dead staining, and scanning electron microscopy (SEM). Collagen distribution, capsular histology, and ADM remodeling were quantified following fluorescent and light microscopy. Prosthetic devices were implanted from 91 to 1115 days. Intramammary pressure increased with Baker Grade. Of 26 patients evaluated, one patient had a positive culture and one patient demonstrated convincing evidence of biofilm morphology on SEM. Following PCR amplification 5 samples randomly selected for 16S rRNA gene sequencing demonstrated an abundance of suborder Micrococcineae, consistent with contamination. Our data suggest that bacterial biofilms likely contribute to a proportion, but not all diagnosed capsular contractures. Biofilm formation does not appear to differ significantly between ADMs or capsules. While capsular contracture remains an incompletely understood but common problem in breast implant surgery, advances in imaging, diagnostic, and molecular techniques can now provide more sophisticated insights into the pathophysiology of capsular contracture. 4 Therapeutic.

Breast milk: friend or FOE?

BackgroundAnaphylaxis is potentially fatal and can occur secondary to breast-feeding.CaseOn day 3 postpartum, a 30-year-old patient complained of chest tightness, shortness of breath and a rash. She was treated for...

Two years of experience with an automatic milking system. 2. Milk yield, milking interval and frequency

The introduction of an automatic milking unit (AMU) changes milking procedures and routines: cows can be milked more than twice a day, and continuously over the day. Three milkings result in increased daily milk yield (MY) (Klei et al., 1997); however, the automatic milking system (AMS) is very different from the three milkings system, because there are not fixed intervals between two consecutive milkings and because the daily milking frequency (DMF) varies among cows and among days. A long milking interval (MI) has a detrimental effect on MY. To maintain the maximum of milk secretion, the udder ought to be empty before the reaching of critical value of intra-mammary pressure. Irregular milking causes a reduction in milk yield (Kelly et al., 1998). In AMS, some cows tend to have DMF less than two because of health problems, low MY or individual attitude.......

Effects of Unilateral Electrolytic Lesion of the Dorsomedial Nucleus of the Hypothalamus on Milk-ejection Reflex in the Rat

The dorsomedial nucleus of the hypothalamus (DMH) has been suggested to be a final relay site for the afferent pathway of milk-ejection reflex (MER). The present experiments were undertaken to examine whether unilateral lesion of the DMH abolished MER induced by unilateral suckling by pups. The unilateral DMHs of urethane-anesthetized lactating rats were electrolytically lesioned. Then 5 pups were applied to nipples ipsilateral or contralateral to the lesioned DMH and the intramammary pressure was monitored to observe the occurrence of MER. The effects of bilateral suckling by 10 pups were also examined. Eighteen of the 29 rats displayed MER during ipsi- or bilateral suckling for about 1 h. Seventeen of these 18 rats did not show MER during contralateral suckling for about 1 h. The remaining rat that showed milk ejection during contralateral suckling had a lesion outside the DMH. In 2 additional rats, extracellular action potentials of single oxytocin (OT) cells located in the supraoptic nucleus ipsilateral to the lesioned DMH were recorded during suckling ipsi- and conralateral to the lesioned DMH. OT cells showed milk-ejection burst during ipsilateral suckling but not during contralateral suckling. The results suggest that the unilateral DMH receives information of suckling stimuli applied to contralateral nipples.

Vacuum level for opening the teat sphincter and the change in the teat end wall thickness in response to the machine milking of indigenous Greek goats

The aim of this paper was to study some of the teat characteristics involved in the milking ability of indigenous Greek goats such as the vacuum level of the milking machine that is required for the opening of the teat canal sphincter and the changes in the teat end wall thickness induced by milking. Thirty-six dams (12 of the first, 12 of the second and 12 of the third and subsequent lactations) were used after weaning (60 ± 5 days). Dams were milked twice a day (8:00 and 18:00 h) for 12 weeks in a milking parlour 1 × 12 side by side of Casse type with 6 milking units and a low milk line and air pipeline. The main functional characteristics of milking machine were: vacuum level 44 kPa, pulsation rate 90 pulsations/min and pulsation ratio 50:50. Every 14 days, during morning and evening milking the vacuum level that was required for the opening of the teat sphincter (VOTS) was measured. The measurement of teat end wall thickness (TEWT) was performed before and after milking. The results of this study showed that during the experimental period the mean VOTS was 23.57 ± 0.36 kPa and decreased significantly as the stage of lactation progressed (<I>P</I>< 0.001). The post-milking TEWT was 3.55% higher in comparison with that before milking (<I>P</I> < 0.01). A continuous and significant decrease in teat thickness was observed during the lactation stage (<I>P</I> < 0.001), which suggests a reaction to intramammary pressure and milk quantity in the udder. The TEWT was affected significantly by the parity (<I>P</I> < 0.01). A positive correlation was found between VOTS and TEWT before and after milking (0.4 and 0.36, respectively). It could be said that a lower vacuum level is required for the opening of the teat sphincter of the udder in goats of the indigenous Greek breed. The thicker teat end wall and more resistant sphincter could be less favourable in the machine milking of goats.

The neurophysiology of neurosecretory cells

With the current trend in neurobiology of increasingly molecular/genetic studies, coupled with the faster payoff and feasibility of in vitro preparations, it is well to reflect on the advances from, and continued need for, the often more difficult systems research in neuroendocrinology. A huge leap in understanding the relationship between the electrical discharge of oxytocin (OT) and vasopressin (VP) neurons and hormone release occurred courtesy of the discovery that the milk ejection known to result from OT release during lactation in mammals could be obtained under anaesthesia (Lincoln et al. 1973). This preparation paved the way for correlating the discharge patterns of antidromically identified neurosecretory neurons with the selective OT release in vivo, and led to an important series of papers by Wakerley, Lincoln and co-workers that set the bar in this field for decades to come. The obvious power of this preparation lay in the ability to precisely record each milk ejection by recording intramammary pressure, whilst simultaneously registering the spike trains of neurosecretory neurons. Two papers from The Journal of Physiology considered here (Lincoln & Wakerley, 1974, 1975) are part of a remarkable series of studies from the same lab during the 1970s. Collectively, these are testaments to the lasting rewards of in vivo electrical recording when combined with appropriate experimental conditions that allow expression of the system's physiological behaviour. They also punctuate the evolution in our understanding of the hypothalamo-neurohypophysial system – from the discovery of the hypothalamic origin and peptidergic nature of VP and OT (Bargmann & Scharrer, 1951), to the acceptance of the parent, large cells (magnocellular) of the supraoptic (SON) and paraventricular nuclei (PVN) as fully neuronal in character.

Oxytocin neurons in the supraoptic nucleus receive excitatory inputs from the bilateral dorsomedial hypothalamic nuclei

To examine whether inputs from the dorsomedial hypothalamic nucleus (DMH) alter the discharge of putative oxytocin (OT) neurons with hypothesis that excitation of DMH neurons would increase the activity of OT neurons, electrical stimulation was applied to the DMH in both sides of the hypothalamus while electrical activity of single OT neurons in the supraoptic nucleus (SON) was recorded in urethane-anesthetized lactating rats. About half of the OT neurons showed orthodromic excitation or inhibition followed by excitation in response to electrical stimulation of the DMH on both sides. Continuous electrical stimulation of the DMH both ipsi- and contralateral to the recording side at 10–50 Hz for 30–60 s increased firing rate in 58% of OT neurons tested. Continuous electrical stimulation of the DMH not only excited spiking activity of single OT neurons but also increased intramammary pressure. The results may suggest that some of the projections from the DMH to the SON are bilateral and possibly contribute to coordinated bilateral activation of OT neurons in the hypothalamus during the milk-ejection reflex.

Incontinentia Lactis: Physiology and Anatomy Conducive to Milk Leakage in Dairy Cows

Incontinentia lactis is a possible predisposing factor for an elevated level of intramammary infection. The goal of the present study was to investigate possible causes of incontinentia lactis in dairy cows. Two farms that differed in breed composition, but that had similar average milk yields were studied: herd A, 28 kg/d, 31 Red Holstein cows; and herd B, 26 kg/d, 16 Brown Swiss cows. Herd A was classified into 2 groups: incontinentia lactis (ILA group) and control, whereas herd B was exclusively a control herd. Milk samples that represented foremilk and the main milk fraction were collected during 4 milking sessions. In addition, milk leakage samples from the ILA group were collected at different time intervals from 0 to 5h before milking. Measurements of the teat, milk flow, fractions of cisternal and alveolar milk, intramammary pressure, and blood oxytocin pattern also were obtained. The ILA cows did not have differences in fat content between milk leakage and cisternal milk fraction. Milk fat content, however, increased during milking in response to continuous milk ejection (1.95, 1.99, and 4.61% for milk leakage, cisternal, and main milk samples, respectively). Teat canals were 9% shorter in the ILA cows, which showed greater milk yield, peak, and average flow rates. Quarter cisternal milk yield of ILA cows tended to be greater (0.50 vs. 0.23 and 0.28kg for ILA and controls from herds A and B, respectively), whereas percentages of cistern milk and alveolar milk did not differ from controls. The greater pressure in the ILA group, both before and after manual udder stimulation (ILA: 4.0 and 6.4 kPa; control: 2.0 and 5.0 kPa, respectively), could be an important cause for the leakage. Nevertheless, the increase in IMP that occurred after udder preparation affirms that milk ejection occurred in response to the tactile teat stimulation, but not before the onset of leakage. Blood oxytocin concentration in ILA cows was low until the start of udder preparation and increased in response to the milking stimulus (reaffirming the hypothesis that milk leakage occurred in the absence of milk ejection). In conclusion, milk losses by leakage are likely due to the large amount of cisternal milk, which creates pressure and causes leakage, in the absence of milk ejection.

Vacuum level for opening the teat sphincter and the change of the teat end wall thickness during the machine milking of mountainous Greek breed (Boutsiko) ewes

The aim of this work was to study some of the teat characteristics involved in the milking ability of dairy ewes, such as the vacuum level of the milking machine that is required for the opening of the teat canal sphincter, and the changes in the teat end wall thickness induced by milking. After weaning, 48 ewes of the mountainous Greek breed, Boutsiko (16 ewes of the first, 16 of the second and 16 of the third and subsequent lactations) were milked for 12 weeks. Every 14 days, during the morning and evening milking, milk fractions and composition were recorded. The vacuum level that is required for the opening of teat sphincter (VOTS) was also measured before milking. The measurement of teat end wall thickness (TEWT) was performed before and after milking and the milk flow was monitored during the morning milking only. The results of this study show that during the experimental period, the ewes had a mean daily milk yield of 862.9 ml, of which the 173.3 ml corresponded to the machine stripped milk (MSM). The mean VOTS was 16.59 ± 0.7 kPa and tended to decrease as the stage of lactation progressed. The TEWT (4.75 ± 0.04 mm) was not modified by milking. A continuous and significant decrease in teat thickness (from 5.03 to 4.3 mm, P < 0.05) was observed, which suggests a reaction to intramammary pressure and milk quantity in the gland. Parity was affected significantly ( P < 0.001) only the TEWT. The type of birth did not influence the VOTS and TEWT. Phenotypic correlations showed that by increasing the VOTS, the machine stripped milk increased as well, and so did the TEWT. These results give rise to the need for a possible reduction of the current vacuum level (44 kPa), which should be applied in the milking of this particular mountainous Greek breed of sheep.

Effects of oxytocin administration on oxytocin release and milk ejection.

In experiment I, the effect of i.m. oxytocin (OT) injection (50 IU) on OT blood pattern was tested. Blood samples from 6 cows were collected for 2 h after OT injection either with or without milking. To test the effect of i.m. OT injection (50 IU) on milk ejection efficiency, intramammary pressure (IMP) was measured in 13 cows (experiment II). Milk ejection was induced by manual teat stimulation. After IMP increased and reached a plateau, OT was injected. In experiment III, the effect of chronic OT treatment on mammary gland sensitivity and endogenous OT release was tested. For 19 d, cows were i.m. injected at each milking with 50 IU OT (n = 13) or 5 mL of NaCl 0.9% (n = 14) 1 min before the start of udder preparation. To test mammary gland sensitivity, IMP recording was performed after a long (11 h, 7 OT cows, and 7 NaCl cows) and a short (3 h, 6 OT cows, and 7 NaCl cows) milking interval at d -1 and d 18. To test the effect of withdrawal of chronic i.m. treatment on OT release, blood sample collection was performed during evening milking at d 0 and d 19. Intramuscular oxytocin injection (experiment I) caused elevated OT blood levels observed at least for 2 h and showed an even more pronounced effect when milking was also performed. Intramuscular OT injection after teat stimulation (experiment II) caused additional milk ejection but only in 6 out of 13 cows. Withdrawal of chronic OT treatment (experiment III) did not reduce OT release during milking. However, ejection time was prolonged during OT infusion after a long milking interval. Ejection pressure tended to be lower after a short milking interval. It seems that the reduction of spontaneous milk removal after chronic OT treatment was due to reduced contractibility of myoepithelial cells in the mammary gland at a physiological range of OT concentrations.

Intramammary pressure in the lactating sow in response to oxytocin and during natural milk ejections throughout lactation.

We developed a simple, non-invasive method to measure the intramammary pressure (IMP) response in sows during natural milk ejection and after i.v. injections of oxytocin. The teats of sows were cannulated and the amplitude and duration of IMP changes were measured via a pressure transducer linked to a computer. During natural milk ejections, the amplitude of the response was 5.5+/-1.8 kPa (mean +/- SD) and the duration of response at half the peak amplitude was 6.8+/-1.6 s. In response to oxytocin a threshold response occurred at 60 mIU oxytocin with no further change up to 200 mIU. The amplitude of the response to an i.v. dose of 60-200 mIU oxytocin (5.5+/-2.2 kPa) and duration (6.4+/-1.7 s) were similar to that during a natural milk ejection. The responses of two galactophorous ducts of a teat measured simultaneously were similar in peak amplitude and duration. When the responses of four glands of a sow were measured simultaneously, there was a lag time in the onset of the IMP peak from the anterior to the posterior glands, and an increase in the peak amplitude from anterior to posterior. Both during natural milk ejections and in response to oxytocin injections, there were significant differences in peak amplitude between sows. We also aimed to determine whether the pressure or duration of milk flow during natural milk ejections was limiting piglet growth rates. IMP of nine sows and the growth rates of their piglets were measured. Both the peak amplitude of IMP response and the growth rate of piglets increased over the course of lactation, but the relationship was not causal. We found that the growth rate of piglets did not depend on IMP amplitude or duration, but we suggest that it may depend on the frequency of suckling and/or the ability of piglets to withdraw milk while it is available.

β-Adrenergic mechanisms modulate central nervous system effects of prolactin on milk ejection

It is known that prolactin (PRL) is produced within the brain and numerous central actions of the hormone have been reported. In anesthetized lactating rats, central administration of PRL, i.e., intracerebroventricular (icv) or intrathecally (it), facilitated milk ejection (ME) by depressing the sympathetically mediated facilitatory tone of the mammary ductal system. However, it is not known whether or not the same effects and similar mechanisms take place in conscious rats after PRL administration. In the present study, the effects of centrally administered PRL, i.e., icv or it, on ME was determined in both conscious and anesthetized rats. In conscious rats, the rate of ME was determined by applying a 15-min period of suckling by the litter, following a 6-h period of isolation. In anesthetized rats, intramammary pressure (IMP) responses of the mammary glands to exogenous oxytocin (OT) were recorded. The results showed that, whereas in anesthetized rats, increased responsiveness of the mammary glands to OT were observed after PRL administration, an intense inhibition of ME occurred in conscious rats. Because, in conscious and anesthetized rats, these effects were prevented by prior administration of the β-adrenergic blocker propranolol (PROP) to the mothers, this suggests that the PRL effects on ME are modulated through sympathomimetic and sympatholytic actions in conscious and anesthetized rats, respectively. Thus, as shown by ductal tone measurements, in conscious, but not in anesthetized rats, the effect of PRL was associated with increased ductal constriction within the mammary glands; an effect that was mimicked by icv administration of the β-adrenergic agonist isoproterenol (ISOP) and that was prevented by PROP. Further, the sympatholytic action of icv-PRL in anesthetized rats prevented the effect on ductal tone of both icv-PRL in conscious rats and of ISOP in anesthetized rats. Taken together, these results clearly suggest that the central effects of PRL on ME are modulated by adrenergic mechanisms.

Effects of mammary engorgement and feed withdrawal on microvascular function in lactating goat mammary glands.

The responses of the mammary microvasculature in lactating goats (n = 8) during feed withdrawal (18-20 h) and mammary engorgement (26-28 h of milk accumulation) were compared using an indicator-dilution technique with FITC-albumin and [(14)C]sucrose as the intravascular and diffusible indicators, respectively. Feed withdrawal and mammary engorgement caused a 50-60% decrease in mammary arterial flow and in the permeability-surface area product (PS) values for sucrose. Only feed withdrawal increased the mean transit time [from 17.3 to 30.0 s, SE of the difference (SED) = 2.16, P < 0.01] of FITC-albumin, whereas only mammary engorgement reduced sucrose extraction (0.63 to 0.51, SED = 0.04, P < 0.05). Mammary engorgement also caused a substantial reduction in the sucrose-accessible extravascular space from 92 to 44 ml (SED = 15.2, P < 0.01). In a separate experiment using five goats, milking after mammary engorgement did not immediately restore arterial flow or sucrose extraction, indicating that the effect of milk accumulation was not mediated simply via increased intramammary pressure. In conclusion, feed withdrawal resulted in slower flow in the capillary bed but apparently no change in capillary recruitment, whereas mammary engorgement caused capillary derecruitment.

Atosiban, an oxytocin receptor blocking agent: pharmacokinetics and inhibition of milk ejection in dairy cows.

Plasma concentrations of the oxytocin receptor blocking agent Atosiban were measured at 2, 4, 10, 15 and 20 min after injection of 5, 10, 20 and 50 micrograms Atosiban/kg body weight in six dairy cows. The half life of Atosiban was 18 min and the total body clearance was 3301 ml/min. Intramammary pressure (IMP) within the teat cistern was measured in six cows before and after i.v. injection of 0 or 20 micrograms Atosiban/kg body weight and repeated injections of 0.2 or 0.5 i.u. oxytocin. IMP was also measured in eleven cows after injection of 0, 10 or 50 micrograms Atosiban/kg body weight: in seven during oxytocin infusions, in four after oxytocin injections in successively increasing dosages (0.05, 0.1, 0.2, 0.5, 1 and 10 i.u.). The occurrence of milk ejection was indicated by a rise in IMP. After injection of 20 micrograms Atosiban/kg body weight, 0.2 i.u. oxytocin did not induce an IMP rise before 48 min, whereas 0.5 i.u. oxytocin induced an IMP rise within 4 min. The time from the start of infusion until the beginning of the IMP rise and the duration of IMP rise during oxytocin infusions both increased, whereas the IMP rise itself was diminished by increasing Atosiban dosages. The amount of injected oxytocin necessary to induce an IMP response increased with increasing Atosiban dosages. Atosiban was shown to have a powerful effect in inhibiting milk ejection in dairy cows.

Compression stimuli increase the efficacy of breast pump function

Objective: The dynamics of milk ejection and also prolactin concentration in the blood during milk expression by means of a breast pump were studied in 82 lactating women. Study design: The design of the breast pump used in this study is new. It is based on the correlation with the amplitude, duration and frequency of vacuum and compression stimuli formed by the baby's mouth apparatus during the suckling process. Results: It was found that during continuous co-action of the vacuum and compression stimuli at a frequency of 1 cycle per second, the rate of milk ejection from the breast changed periodically. The highest rates of milk ejection coincided with the greatest rises in intramammary pressure. When the compression stimulus was turned off, leaving only the vacuum, the period of the first rise in pressure increased 1.5–2 fold, with a 1.5–2 fold reduction in the milk ejection rate as compared with the normal function of the breast pump. The basal prolactin level on day 3 and 5 post delivery in women who used a breast pump was not significantly different from that of puerperal women who only breast-fed their babies. Prolactin concentration in the blood of puerperal women did not change within the 5–6 min of expression and stimulation with the breast pump. The prolactin level began to increase by the 10th minute, whereas by the 25th minute it exceeded the initial concentration 1.3–1.5-fold. Conclusion: It is suggested that by introducing a tactile component to the mechanism of the breast pump, milk secretion is enhanced, as well as stimulating the breast milk flow. This directly improves the dynamics of breast milk expression.