Effect of teat stimulation on sympathetic tone in bovine mammary gland

Adrenergic Tone as an Intermediary in the Temperament Syndrome Associated With Flight Speed in Beef Cattle

The temperament of farm animals can influence their resilience to everyday variations within the managed production environment and has been under strong direct and indirect selection during the course of domestication. A prominent objective measure used for assessing temperament in beef cattle is the behavioral flight response to release from confinement in a crush or chute. This behavioral measure, termed flight speed (also known as escape velocity) is associated with physiological processes including body temperature, feeding behavior, growth rate, carcass composition, immune function, and health outcomes. This review examines the functional links between this suite of traits and adrenergic activity of the sympathetic nervous system and the adrenomedullary hormonal system. It is suggested that flight speed is the behavioral aspect of an underlying “flightiness” temperament syndrome, and that elevated adrenergic tone in animals with a high level of flightiness (i.e., flighty animals) tunes physiological activities toward a sustained “fight or flight” defense profile that reduces productivity and the capacity to flourish within the production environment. Nonetheless, despite a common influence of adrenergic tone on this suite of traits, variation in each trait is also influenced by other regulatory pathways and by the capacity of tissues to respond to a range of modulators in addition to adrenergic stimuli. It is suggested that tuning by adrenergic tone is an example of homeorhetic regulation that can help account for the persistent expression of behavioral and somatic traits associated with the flight speed temperament syndrome across the life of the animal. At a population level, temperament may modulate ecological fit within and across generations in the face of environmental variability and change. Associations of flight speed with the psychological affective state of the animal, and implications for welfare are also considered. The review will help advance understanding of the developmental biology and physiological regulation of temperament syndromes.

Blood perfusion of teat tissue in dairy cows: Changes associated with pre-milking stimulation and machine milking

Mechanical forces during machine milking of dairy cows evoke circulatory impairment of the teat tissue that may affect the teats' defense mechanisms against mastitis pathogens. Ample research describes dimensional changes of different teat traits after machine milking, whereas reports that describe changes in blood circulation of dairy cows' teats are limited. Therefore, the objectives of this study were to (1) describe changes in teat blood circulation that occur after pre-milking teat stimulation and machine milking and (2) study the effect of 2 different milking liners on machine milking-induced changes in teat blood flow. In a randomized trial, Holstein dairy cows were stratified by parity, stage of lactation, and average daily milk yield during the previous week, and allocated to 1 of 2 treatment groups. Treatment consisted of 1 milking observation with either a round or multisided concave milking liner. Teat scans were taken of the left front and the right hind teats using power Doppler ultrasonography. Imaging occurred before pre-milking udder preparation (T1), after completion of pre-milking udder preparation but before milking-unit attachment (T2), and immediately after unit detachment (T3). Perfusion intensity measurements from teat scans were performed with a commercially available software program. Data from 109 cows were analyzed. A general linear mixed model showed differences in perfusion intensity between time points. Least squares means (95% confidence intervals) for T1, T2, and T3, respectively, were 0.035% (0.026-0.047), 0.124% (0.093-0.164), and 0.095% (0.073-0.124). Conversely, no statistically significant differences between treatment groups were observed. We conclude that teat blood circulation is subjected to several influences, including inherent circulatory regulation mechanisms, as well as extrinsic factors such as machine milking. Future research is warranted to decipher the magnitude of their influence and to further our understanding of how these changes relate to the susceptibility to intramammary infection and milking performance.

Infrared thermography and ultrasonography to indirectly monitor the influence of liner type and overmilking on teat tissue recovery

Eight Danish Holstein cows were milked with a 1-mm thick specially designed soft liner on their right rear teat and a standard liner mounted under extra high tension on their left rear teat. Four of the animals were overmilked for 5 min. Rear teats were subjected to ultrasound examination on the first day and to infrared thermography on the second day. Teats were submersed in ethanol 20 min post-milking on the second day. Ultrasonography measurements showed that teat canal length increased by 30–41% during milking. Twenty minutes after milking, teats milked with modified standard liners still had elongated teat canals while teats milked with the soft liner were normalized. Overmilking tended to increase teat wall thickness. Approximately 80% of variability in teat canal length, from before teat preparation to after milking, could be explained by changes during teat preparation. Thermography indicated a general drop in teat temperature during teat preparation. Teat temperature increased during milking and continued to increase until the ethanol challenge induced a significant drop. Temperatures approached pre-challenge rather than pre-milking temperatures within 10 minutes after challenge. Teat temperatures were dependent on type of liner. Mid-teat temperatures post-challenge relative to pre-teat preparation were dependent on overmilking. Thermography and ultrasound were considered useful methods to indirectly and non invasively evaluate teat tissue integrity.

Teat Anatomy and its Relationship with Quarter and Udder Milk Flow Characteristics in Dairy Cows

Anatomical and functional characteristics of the teat are supposed to have considerable influence on milk flow performance. In the present study, various teat and milking characteristics in 148 quarters of 38 cows were analyzed via 3 different approaches. Teat canal length, teat wall thickness, and teat diameter were measured by ultrasound. In addition, the vacuum needed to open the teat canal (VO) was determined and milk flow profiles were measured in each quarter separately. Rear teats were shorter and thicker than front teats, whereas teat canal length and teat wall thickness did not differ according to quarter position. Milk yield and peak flow rate (PFR) were higher in rear than in front quarters. Teat canal length and VO were negatively correlated with PFR and average flow rate (AFR) but no correlations were observed between milkability traits and externally measurable teat characteristics like teat length or teat diameter. Individual milkability at an udder level is a complex characteristic that is determined by the milkability at a quarter level and the distribution of quarter milk yields. The anatomical and functional characteristics of single teats can partly explain the milk flow characteristics of individual quarters.

Sympathoadrenal and immune system activation during the periparturient period and their association with bovine coliform mastitis. A review

Increased incidence of clinical mastitis in high-yielding cows during early lactation has been attributed to a depressed functional capacity of the immune system. Sympathoadrenal factors are known to play an important role in modulating the host susceptibility and resistance to infectious diseases. Of primary importance in combating acute intramammary infections are polymorphonuclear leukocytes (PMN), as they represent one of the early lines of immunological defense. The release of stress hormones at parturition and during the first weeks of lactation has been proposed to partly contribute to the impaired function of PMN. Here, we summarize the current understanding of the stress-induced peripheral effectors, i.e. the limbs of the sympathetic system and the hypothalamic-pituitary-adrenal axis, on PMN function around parturition and during coliform mastitis. The questions as to whether and how stress induced secretion of glucocorticoids and catecholamines might affect the lactating dairy cow's udder health will be addressed.

The effect of manual forestripping on milking performance of Holstein dairy cows

The objective of this study was to evaluate the effects of forestripping as a premilking stimulation technique on milk yield, milking unit attachment time, and milk flow rates in Holstein dairy cattle. Multiparous Holstein cows (n = 24) were divided into two groups (HPE, high producing, early lactation; LPL, low producing, late lactation) based on prestudy milk yield and stage of lactation. Within the production group, cows were randomly assigned into treatment (n = 6) and control groups (n = 6) in a switchback design. Cows were milked twice daily and treatments were switched after 20 milkings. Premilking udder preparation for the treatment group was as follows: forestripping, predipping with 0.5% iodine, and drying with paper towels followed by unit attachment. Udder preparation for the control group was identical except forestripping was not performed. Data were analyzed by using the PROC Means and PROC Mixed models described by SAS. During the study, cows in the HPE group produced significantly more milk and had longer milking unit attachment times compared with cows in the LPL group. The milk flow rate was 0.36 kg/min faster for the HPE cows compared with the LPL cows. There was no significant effect of order of treatment administration on any outcome variable. There were no significant differences in milk yield, milk unit attachment time, or milk flow for animals that were forestripped compared with animals that were not forestripped. In this study, the addition of forestripping to an otherwise acceptable premilking udder preparation routine did not increase milking performance of multiparous Holstein dairy cows.

Oxytocin release and milk removal in ruminants

Before milking, less than 20% of the milk yielded by dairy cows is stored within the cistern, where it is immediately available for removal. Most of the milk is available for the milking machine only after milk ejection, which occurs in response to tactile teat stimulation and oxytocin release. For complete milk removal, milk ejection is necessary throughout the entire milking process. The continuation of stimulatory effect of the milking machine until the end of milking is, therefore, essential. Premilking teat stimulation causes induction of alveolar milk ejection before the start of milking. Thus, bimodal milk flow curves (i.e., interruption of milk flow after removal of the cisternal milk) are avoided. Continual ejection of milk is dependent on the presence of elevated oxytocin concentrations during the entire milking. Any interruption of the milk ejection process can disturb milk removal. Disruption of milk removal can be caused by peripheral inhibition of oxytocin effects on the mammary gland or by inhibition of oxytocin release by the central nervous system. Peripheral inhibition is induced by elevated concentrations of catecholamines through stimulation of alpha-adrenergic receptors in the mammary gland, likely via changes in ductal resistance. Inhibition of oxytocin release by the central nervous system has been observed in primiparous cows immediately after parturition, during peak estrus, and during milking in unfamiliar surroundings; concentrations of beta-endorphin and cortisol are elevated in this situation. However, the role of endogenous opioid peptides in the inhibition of oxytocin release in cows remains unclear. In conclusion, during machine-milking, the physiological requirements of the cows need to be considered, and, most importantly, stressors must be minimized.

B-mode ultrasonography of mammary glands of cows, goats and sheep during alpha- and beta-adrenergic agonist and oxytocin administration

Teat and gland cistern of the mammary glands of five dairy cows, five goats and five sheep were scanned in a water bath during alpha- and beta-adrenergic agonist and oxytocin administration. A 5 MHz linear array scanner was used to create vertical cut pictures with the scan plane longitudinally through the teat channel. The i.v. injection of the alpha-adrenergic agonist phenylephrine (30 micrograms/kg) induced diminution of the section area through teat and gland cistern by 38 +/- 17% on average within 1 min in all three species. In contrast, the i.v. injection of the beta-adrenergic agonist isoproterenol (1 microgram/kg) did not change the cisternal areas. The i.v. injection of oxytocin (2.0 x 10(-3) i.u./kg) elicited an enlargement of teat and gland cistern area by 48 +/- 12% on average. Ultrasonography proved to be a valuable system for visualizing changes of the cisternal volume. Smooth muscle contractions in response to phenylephrine administration are thought to cause area reduction, whereas an expected smooth muscle relaxation after injection of isoproterenol could not be observed by ultrasonography. Milk ejection as induced by oxytocin administration caused dramatic enlargement of the cistern area in all three species.

Catecholamines, oxytocin and milk removal in dairy cows

Experiments were designed to study the effects of catecholamines on oxytocin responses and milk removal in dairy cows. Adrenalin, noradrenalin, dopamine, isoproterenol (a beta-adrenoceptor agonist), phentolamine (an alpha-adrenergic blocker) and propranolol (a beta-adrenergic blocker) were infused intravenously. In addition, adrenalin was infused together with phentolamine and/or propranolol. Infusions started 8 min before milking and lasted until the end of milking. In some cases electroshocks (for 5 s) were applied immediately before milking in the absence and presence of phentolamine and propranolol. Adrenalin, noradrenalin and dopamine reduced milk removal, but only if administered in supraphysiological amounts. The effect of adrenalin and electroshocks on milk removal could be inhibited only partly by phentolamine. Inhibition of milk removal was not mediated by reduced oxytocin responses. Enhanced local release of catecholamines from sympathetic nerves was presumably responsible for lowered milk removal in response to electroshocks. Milk removal was facilitated during alpha-adrenergic blockade and during beta-adrenoceptor stimulation.

Relationship between milkability and adrenoceptor concentrations in teat tissue in primiparous cows

Milking characteristics were measured on 19 primiparous cows of the Red Pied breed at morning milkings. Measurements included maximum and average rate of flow, yield of milk through the 1st, 2nd, and 3rd min, amount of milk through the first 2 and first 3 min of milking, and milking time. Subsequently cows were slaughtered and teats immediately removed. Adrenoceptors on membranes isolated from teat tissue were identified by radiolabeled antagonists: [3H]dihydroalprenolol for beta 2-adrenoceptors, [3H]rauwolscine for alpha 2-adrenoceptors, and [3H]prazosin for alpha 1-adrenoceptors. Measurements of milking characteristics were highly repeatable within cow. Cows showed five distinct and significantly different milk flow patterns, which were characteristic for fast (type I, II), relatively fast (type III), and slow (type IV, V) milking cows. Covariance analysis for the five different types revealed an average regression between alpha 2-adrenoceptor density and milking rate 1st min as well as between beta 2:alpha 2-adrenoceptor ratios and milking rate 2nd min and milking time. A hypothesis is presented to explain these observations. During milking, tone of efferent sympathetic nerves in the teat is low. This phenomenon is more pronounced in fast milking cows. The typical presynaptic adrenoceptor pattern in the teat of fast milkers (low beta 2:alpha 2-adrenoceptor ratio) results in a decline of norepinephrine release by feedback mechanisms.

Effects of intermittent electrical shock on responses related to milk ejection

Electrical shock is perceived to be a problem on many dairy farms. Thirteen cows were subjected to intermittent electrical shock (5 s on, 25 s off) at a.m. and p.m. milkings for 7 days. Seven cows were subjected to 3.6 mA shocks starting with preparation (1 min udder wash and dry) and six cows to 6.0 mA. One additional cow initially in the 6.0 mA group had to be removed from the study because of severe behavioral responses to shock. Compared to 5-day preshock and postshock periods, milk yield, milking time, and Wisconsin Mastitis Test scores were not affected by shock. Maximum rate of milk flow increased slightly. The number of behavioral events such as lifting legs during milking increased with a greater increase in the 6.0 mA group. Heart rate was elevated (+3 beats/min) only in response to shock during preparation (initial shock). For selected days, time to peak oxytocin response was delayed in the 3.6 mA group, and peak prolactin and area under prolactin response curves increased similarly for both groups during shock. There were significant a.m.-p.m. differences in milk yield, milking time, maximum rate of milk flow, heart rate, and responses of oxytocin and prolactin. We think that milk yield can be maintained, at least in the short term, in cows subjected to electrical shock due to power-line problems if dairy producers take exceptional care to accommodate behavioral responses.

Is oxytocin really necessary for efficient milk removal in dairy cows?

This review examines the potential importance of mechanisms other than the release of oxytocin for efficient milk removal. First, evidence is presented that oxytocin release is not always essential for efficient milk removal. Second, potential roles for the release of oxytocin during suckling or milking not directly related to milk removal are discussed. Third, alternative mechanisms that potentiate or induce milk ejection are introduced. Finally, the role of the autonomic nervous system in the milk removal process is examined.

Endocrine responses of cows subjected to controlled voltages during milking

For the relative influence of central and of peripheral inhibitive mechanisms on the milk-ejection reflex, dairy cows were subjected to control voltages during milking. Integrated 1-min jugular vein samples were taken at -20, -12, -9, -2, -1, 2, 4, 6, 10, and 20 min relative to the start of milking for measurement of norepinephrine, epinephrine, dopamine, oxytocin, and prolactin. Cows were subjected to voltages that resulted in body currents of 5 mA. For the response of cows to continuously applied voltage, the voltage remained on for 20 min starting 10 min prior to milking. For the response to intermittently applied voltage, the voltage was on for 5 of every 30 s. Milk yield and milking time were decreased in cows subjected to stimulation by intermittent voltage. This decrease could not be explained by changes in peripheral concentrations of either oxytocin or catecholamines. Plasma prolactin did decrease; however, it seems unlikely the prolactin would affect the milk-ejection reflex. We hypothesize that this decrease in milk yield resulted from neural mediated changes within the mammary gland.