Milk Cortisol Research Articles

Cortisol in mother's milk across lactation reflects maternal life history and predicts infant temperament.

The maternal environment exerts important influences on offspring mass/growth, metabolism, reproduction, neurobiology, immune function, and behavior among birds, insects, reptiles, fish, and mammals. For mammals, mother's milk is an important physiological pathway for nutrient transfer and glucocorticoid signaling that potentially influences offspring growth and behavioral phenotype. Glucocorticoids in mother's milk have been associated with offspring behavioral phenotype in several mammals, but studies have been handicapped by not simultaneously evaluating milk energy density and yield. This is problematic as milk glucocorticoids and nutrients likely have simultaneous effects on offspring phenotype. We investigated mother's milk and infant temperament and growth in a cohort of rhesus macaque (Macaca mulatta) mother-infant dyads at the California National Primate Research Center (N = 108). Glucocorticoids in mother's milk, independent of available milk energy, predicted a more Nervous, less Confident temperament in both sons and daughters. We additionally found sex differences in the windows of sensitivity and the magnitude of sensitivity to maternal-origin glucocorticoids. Lower parity mothers produced milk with higher cortisol concentrations. Lastly, higher cortisol concentrations in milk were associated with greater infant weight gain across time. Taken together, these results suggest that mothers with fewer somatic resources, even in captivity, may be "programming" through cortisol signaling, behaviorally cautious offspring that prioritize growth. Glucocorticoids ingested through milk may importantly contribute to the assimilation of available milk energy, development of temperament, and orchestrate, in part, the allocation of maternal milk energy between growth and behavioral phenotype.

Human milk cortisol is associated with infant temperament

The implications of the biologically active elements in milk for the mammalian infant are largely unknown. Animal models demonstrate that transmission of glucocorticoids through milk influences behavior and modifies brain development in offspring. The aim of this study was to determine the relation between human milk cortisol levels and temperament of the breastfed infant. Fifty-two mother and infant pairs participated when the infants were three-months old. Milk cortisol levels were assessed and each mother completed the Infant Behavior Questionnaire (IBQ), a widely used parent-report measure of infant temperament. Analyses revealed a positive association between milk cortisol and the negative affectivity dimension of the IBQ (partial r=.37, p<.01). No correlation was found between elevated cortisol levels and the surgency/extraversion or the orienting/regulation dimensions. Further, the positive association between increased maternal milk cortisol and negative affectivity was present among girls (β=.59, p<.01), but not among boys. (Although, the sex by milk cortisol interaction term was not statistically significant, suggesting that these results require replication.) Environmental factors such as maternal demographics and negative maternal affect (depression and perceived stress) at the time of assessment did not account for the positive association. The findings support the proposal that exposure to elevated levels of cortisol in human milk influences infant temperament. The findings further suggest that mothers have the ability to shape offspring phenotype through the transmission of biologically active components in milk.

Variation in milk cortisol during lactation in Murciano-Granadina goats

Fifty-seven goats were included in an experiment designed to study the effect of lactation stage, parity number, and mammary gland health status on milk cortisol concentration as a method to assess the welfare of Murciano-Granadina goats. The relationships of milk cortisol concentration with different production parameters (milk yield, milk composition, and mechanical milking ability: milk fractioning during milking and milking time) were also studied. The experiment lasted 8mo and monthly samplings were carried out to determine total milk yield (MY), fractioning during milking (machine milk, MM; machine stripping milk, MSM), and milking time (MT), and a sample was taken from the total milk yield to determine milk cortisol concentration, somatic cell count, and milk composition (fat, protein, and lactose). To determine the infection status of the gland, an aseptic sample was taken for bacteriological analysis before each monthly sampling. Third-parity goats presented higher concentrations of milk cortisol than those of 1, 2, or ≥4 parities. Intramammary infection had no effect on milk cortisol concentration, and somatic cell count did not correlate with cortisol concentration. Cortisol presented a significant correlation with MY and MM, but showed no significant correlation with MSM, MT, or milk composition parameters. Variations in milk cortisol concentration in goats may be associated with different physiological factors in the animal (e.g., milk production level, lactation stage, and parity number) and therefore need not always indicate stress for the animal.

Are there benefits in introducing dairy heifers to the main dairy herd in the evening rather than the morning?

Twenty-eight Holstein Friesian dairy heifers were assigned to 1 of 2 treatments after calving. These experimental heifers were introduced to an established group of resident cows either between 0600 and 0800h (i.e., after morning milking, a.m.) or between 1600 and 1800h (i.e., after evening milking, p.m.). The size of the resident group remained constant at 18 animals (12 multiparous cows and 6 primiparous cows). There were 5 replicate or resident groups in total, and 2 to 3 nonexperimental primiparous cows in each group were replaced by a.m. and by p.m. heifers as they calved. Fresh total mixed ration was provided daily between 1000 and 1030h, and concentrate feed was offered in the milking parlor. The behavior of the experimental heifers was assessed over a 2-h period immediately after mixing into the resident group, and also after feed provision during the first month in the group. In addition, time spent lying was assessed each week for 1 mo using data loggers attached over 24-h periods. The lying behavior and location of the entire group was also assessed by direct observations during the 2-h period before evening milking on 2 consecutive days each week for 1 mo. The time spent feeding by experimental heifers was recorded automatically using computerized feeding gates. Milk production, milk cortisol concentrations, and changes in body condition and body weight were also assessed over the first month after calving. Heifers in the a.m. treatment spent longer in receipt of aggressive behaviors such as threats, butts, and chases immediately after mixing compared with those in the p.m. treatment. During the feeding periods, heifers in the a.m. treatment were observed feeding for longer, showed less pen exploration, and also received more butts. No significant treatment effects were shown on overall feed intake levels, milk yield, milk cortisol concentrations, body weight, or body condition score loss. However, feed intakes were higher in the a.m. treatment during the second week after mixing, and automated recordings showed that a.m. animals spent longer average periods of time feeding. No significant treatment differences were shown in overall time spent lying, with heifers in both treatments lying for less than 4h during the first 24h in the group. Observations of the entire group showed that p.m. heifers spent less time lying than resident animals or a.m. heifers. In conclusion, the reduction in received aggression and the lack of adverse effects on performance (milk production and weight and condition loss) suggest that heifers should be introduced to the main dairy herd after evening rather than morning milking. Further research to determine the relative importance of time of day and time since feeding on behavior immediately after mixing would be beneficial.

Adrenocortical Response in Cows after Intramuscular Injection of Long‐Acting Adrenocorticotropic Hormone (Tetracosactide Acetate Zinc Suspension)

The objectives of this study were first to show adrenocortical response to a long-acting adrenocorticotropic hormone preparation (tetracosactide acetate zinc suspension) (ACTH-Z) and its effect on adrenocortical function in beef cows (Experiment 1) and second to apply the ACTH-Z challenge in dairy cows based on cortisol concentrations in milk collected at routine milking (Experiment 2). In Experiment 1, four beef cows in luteal phase were challenged with ACTH-Z, and plasma cortisol concentrations were determined for 48 h after the injection at 30-min to 2-h intervals. A rapid ACTH test was conducted 3 days before and 2 h after the completion of ACTH-Z injection for 48 h to investigate the effect on adrenocortical function. Plasma cortisol concentrations increased significantly 30 min after ACTH-Z injection (p < 0.001), and the high cortisol levels were maintained for approximately 10 h after the injection. In Experiment 2, eight dairy cows were subjected to ACTH-Z challenge 1-2 weeks and 4-5 weeks post-partum. Blood and milk samples were taken at morning and afternoon milking. All the cows showed a significant increase in cortisol concentrations in plasma as well as in skim milk 8 h after ACTH-Z injection 1-2 weeks and 4-5 weeks post-partum (p < 0.001). There was a significant correlation between plasma and skim milk cortisol concentrations 8 h after ACTH-Z challenge (r = 0.74, p < 0.001). The results obtained in this study suggest that elevated levels of plasma cortisol are maintained for approximately 10 h after ACTH-Z treatment without adverse effect on adrenocortical function and a long-acting ACTH-Z challenge based on cortisol concentrations in milk, which were collected at the morning and the afternoon milking, can be a useful tool to monitor adrenocortical function in cows.

Relationship between milk cortisol concentration and the behavioral characteristics of postpartum cows introduced to a new group

The objective of this study was to examine the relationship between milk cortisol concentration (MC) and behavioral responses to stress. As a stress response, the behaviors of 37 postpartum cows were observed when they were introduced into a new group. Milk samples for MC measurement and milk trait data were collected on the test day every 2 months after calving. The best linear unbiased prediction (BLUP) was estimated from each behavioral and milk trait data. Behavioral BLUP data were subjected to principal component (PC) analysis and three PCs were extracted. The first PC, with large loadings for eating and allogrooming, was positively correlated with milk yield. Therefore, individual differences in behaviors closely related with PC1 would have been unconsciously paid a lot of attention in terms of productivity. However, the second PC, with large loadings for drinking and self-grooming, uncorrelated with any milk traits, had a negative correlation with MC. The third PC, with large loadings for exploring, fighting and the frequency of agonistic behavior, was uncorrelated with all traits. Both PC2 and PC3 were independent of productivity, and individual differences in behaviors related with these PCs may be scarcely considered.

Medium-term effects of repeated exposure to stray voltage on activity, stress physiology, and milk production and composition in dairy cows

The medium-term effects of permanent or random exposure to stray voltage applied to the water trough were evaluated on milk production and stress physiology in lactating dairy cows. Seventy-four Holstein cows were assigned during two 8-wk experimental periods to 1 of 3 treatments. The treatments were permanent exposure to voltage (PERM, 1.8V, n=23) applied to the water trough, random exposure to voltage (RAND, 1.8V, 36 h/wk, n=25), and no exposure to voltage (control, n=26). On the first day of voltage exposure, PERM cows had higher activity levels than control cows (9.8±2.70 vs. −2.3±2.74 14-s periods of movement/h). During the eighth week of exposure, RAND cows had higher activity levels than control cows (4.2±3.64 vs. −7.7±3.54 14-s periods of movement/h) and higher milk cortisol concentration than PERM cows (0.21±0.024 vs. 0.14±0.020 ng/mL). No differences were observed between treatments for cortisol response after an ACTH challenge during the seventh week of exposure. No effects of voltage exposure were observed on production traits and daily water intake. There was a transient decrease in milk yield on the second day of exposure in PERM cows (−1.4±0.74kg) and on the third day of exposure in RAND cows (−3.5±1.03kg) compared with control cows. In dairy cows, permanent or random exposure to stray voltage (1.8V; 3.6mA) could induce a transient stress response. Moreover, unpredictable voltage exposure could be considered a mild stressor, with slight modifications in stress physiology and activity but no impairment in production in the medium term.

Stress-induced changes in immune response of dairy ewes

Two groups of 16 Comisana ewes were selected from a group of 30, and divided, according to their cortisol secretion after isolation in a novel environment, into HC ewes, having a cortisol secretion <90 ng/mL, and LC ewes having a cortisol secretion <80 ng/mL. Blood samples were collected immediately before and immediately after isolation, and 60, 120, 300min and then 24h and 48h after isolation, to evaluate the percentage of lymphocyte T-helper (CD4+) and lymphocyte T-cytotoxic (CD8+) by flow cytometry analysis, and IL-1β and IL-6 concentrations by ELISA. The day before the isolation test, the ewes were milked in the afternoon at 1500h (-19h from isolation), and then milked for the three days starting from the day of the isolation test (at 0, 5, 24, 29, 48 and 53h from isolation) to evaluate milk cortisol secretion, and IL-1β and IL-6 concentrations. Results suggest that the levels of cortisol secretions can influence the immune competence of dairy ewes and cytokines concentrations. Milk cytokine concentrations, and not milk cortisol concentrations, can be considered indicators of the magnitude of the hypothalamic-pituitary-adrenal axis activation.

Chronic stress, hormone profiles and estrus intensity in dairy cattle

The objectives of the present study were to determine if lameness, a model for a natural chronic stressor, affects hormone concentrations in milk prior to estrus and/or the subsequent expression of estrus in the postpartum period. Dairy cows > 20 days postpartum were scored for lameness and observed for estrus intensity using a weighted scoring system (> 100 points = estrus = Day 0). Increasing lameness score was not associated with daily profiles of milk progesterone (throughout Days − 18 to 0), estradiol (Days − 6 to 2) or cortisol (Days − 18 to 2) around estrus, maximum estradiol values or estradiol concentrations on Day 0. However, post hoc pair wise comparisons revealed that prior to estrus, severely lame cows had lower maximum progesterone concentrations compared to nonlame cows (1.3 ± 0.1, 1.2 ± 0.2, 0.7 ± 0.1 ng/ml milk; P = 0.042). Furthermore, severely lame cows expressed behavioral estrus with lower intensity (284 ± 128 points, n = 9) compared to moderately lame (662 ± 310 points, n = 9) or nonlame animals (583 ± 275 points, n = 18; P = 0.05 and P = 0.02, respectively). Resting concentrations of cortisol (Days 20–80 postpartum) did not vary between days postpartum or lameness score. The incidence of behavioral estrus was not affected by increasing lameness score, as 54.2%, 56.2% and 50.0% periods with low progesterone were associated with spontaneous estrus expression, respectively. Concluding, in this biological model of chronic stress, lameness did not affect the incidence of behavioral estrus but did reduce estrus intensity once ovarian cyclicity had resumed after calving. This reduced intensity of estrus was associated with lower maximum progesterone values prior to estrus but not abnormal daily cortisol or estradiol values in milk.

Effect of lactation stage, season and parity on milk cortisol concentration in Holstein cows

This experiment was designed (1) to study the effects of lactation stage, season, and parity on milk cortisol concentrations in Holstein cows, and (2) to elucidate the relationships between milk yield, quality, and milk cortisol concentration. Subjects of this study were 24 dairy cows kept in a free stall barn. Milk samples were taken on test day in May, August, November, and February. Data of milk yield, quality, and cortisol concentration were collected. Random effects of animals and fixed effects of lactation stage, test day, and parity on milk yield, quality, and cortisol concentration were analyzed using mixed models. We estimated the best linear unbiased prediction of each trait (BLUP) which was an animal-specific value. Correlation among milk yield, quality, and cortisol concentration was calculated using raw data and BLUP. The effect of the lactation stage on milk cortisol concentration was significant: the value observed in early lactation was higher than in other stages. However, the correlation between milk yield and cortisol concentration was low. The beginning of lactation might be a strong stressor for every cow. Calculated with raw data, milk cortisol concentration had respectively significant negative correlation with milk protein contents and solid not-fat contents. Calculated with BLUP, milk cortisol concentration showed a significant and negative correlation with milk protein contents. The lactation stage and milk protein contents should be considered for measurement of milk cortisol concentrations.

Postnatal maternal cortisol levels predict temperament in healthy breastfed infants

Background The implications of the biologically active elements in breast milk for the breastfed infant are largely unknown. Animal models suggest that ingestion of glucocorticoids during the neonatal period influences fear behavior and modifies brain development. Aims To determine the association between postnatal maternal cortisol levels and temperament in breastfed infants. Study design The relation between maternal cortisol and infant temperament was examined in breastfed and formula-fed infants. Plasma cortisol was used as a surrogate measure for breast milk cortisol levels (plasma and milk levels are correlated in the 0.6 to 0.7 range; [Patacchioli FR, Cigliana G, Cilumbriello A, Perrone G, Capri O, Alemà GS, et al. Maternal plasma and milk free cortisol during the first 3 days of breast-feeding following spontaneous delivery or elective cesarean section. Gynecologic and Obstetric Investigations 1992;34:159-163.]. If exposure to elevated cortisol levels during infancy influences temperament, then a relation between the two should be found among the breastfed infants, but not among the formula-fed infants. Subjects Two hundred fifty-three two-month-old infants and their mothers. Outcome measures Fearful temperament assessed with the Infant Behavior Questionnaire [Garstein MR, Rothbart MK. Studying infant temperament via the revised infant behavior questionnaire. Infant Behavior and Development 2003;26:64-86]. Results Among the breastfed infants, higher maternal cortisol levels were associated with reports of increased infant fear behavior (partial r = 0.2; p < 0.01). This relation did not exist among the formula-fed infants. Negative maternal affect at the time of assessment did not account for the positive association in the breastfed group. Conclusions The findings are consistent with our proposal that exposure to cortisol in breast milk influences infant temperament. Biologically active components in breast milk may represent one avenue through which the mother shapes the development of the human infant during the postnatal period.

Milk Cortisol Concentration in Automatic Milking Systems Compared with Auto-Tandem Milking Parlors

Milk cortisol concentration was determined under routine management conditions on 4 farms with an auto-tandem milking parlor and 8 farms with 1 of 2 automatic milking systems (AMS). One of the AMS was a partially forced (AMSp) system, and the other was a free cow traffic (AMSf) system. Milk samples were collected for all the cows on a given farm (20 to 54 cows) for at least 1 d. Behavioral observations were made during the milking process for a subset of 16 to 20 cows per farm. Milk cortisol concentration was evaluated by milking system, time of day, behavior during milking, daily milk yield, and somatic cell count using linear mixed-effects models. Milk cortisol did not differ between systems (AMSp: 1.15±0.07; AMSf: 1.02±0.12; auto-tandem parlor: 1.01±0.16nmol/L). Cortisol concentrations were lower in evening than in morning milkings (1.01±0.12 vs. 1.24±0.13nmol/L). The daily periodicity of cortisol concentration was characterized by an early morning peak and a late afternoon elevation in AMSp. A bimodal pattern was not evident in AMSf. Finally, milk cortisol decreased by a factor of 0.915 in milking parlors, by 0.998 in AMSp, and increased by a factor of 1.161 in AMSf for each unit of ln(somatic cell count/1,000). We conclude that milking cows in milking parlors or AMS does not result in relevant stress differences as measured by milk cortisol concentrations. The biological relevance of the difference regarding the daily periodicity of milk cortisol concentrations observed between the AMSp and AMSf needs further investigation.

Milking of Brown Swiss and Austrian Simmental cows in a herringbone parlour or an automatic milking unit

Automatic milking systems (AMS) are becoming increasingly common on dairy farms and should be evaluated for their effect on cow welfare. Dairy cows’ stress responses during normal successful milking in a 2×6 herringbone milking parlour (HMP) were compared with their responses during normal successful voluntary milking in an automatic unit (AMU). We observed 42 cows: 12 Simmental and 11 Brown Swiss in the AMU, and 10 Simmental and 9 Brown Swiss in the HMP. Both prior to and during the observations each cow was milked in one system only. Behaviour during milking and durations of different phases of the milking procedure were observed directly two to six times per cow. Heart rate was recorded telemetrically. Samples of composite milk were analysed for cortisol using an enzyme-immunoassay. Milking lasted longer in the HMP than in the AMU (general mixed model: F 1,39=12.06, P=0.0013), after significant effects of milk yield, day of lactation and time of day had been taken into account. Location of the teats by the robot took longer in Simmental than in Brown Swiss cows (Mann–Whitney- U-test: U 11,12=32, P=0.037). Kicking and stepping with the hind legs was less frequent in the AMU than in the HMP ( U 23,19=76.5 for kicks; U 23,19=85 for steps; P<0.001 in both cases). Brown Swiss cows stepped less than Simmental cows in the AMU ( U 11,12=32, P=0.036). In the HMP, kicks occurred more frequently during the time period from the beginning of udder cleaning until cluster attachment was completed, than at other times (Friedman test: F 19,4=32.41, P<0.001; Bonferroni-corrected post-hoc-comparisons: P<0.01). There was no difference between groups in heart rate during milking. The AMS group had higher milk cortisol values than the HMP group ( U 23,19=130.5, P=0.026). This was probably not related to milking itself, but to other aspects of the system, and absolute values were not very high. In conclusion, Simmental cows may be more vulnerable during milking than Brown Swiss. Limiting the study to successful voluntary milking events without AMU attachment failure, there were no indications of more stress in the AMU than in the HMP.

Studies on step–kick behavior and stress of cows during milking in an automatic milking system

The objective of the present study was to examine the behavior and stress response of cows during milking in an automatic milking system compared to those milked in a milking parlor. Three parameters—step–kick behavior, milk cortisol concentration and heart-rate—were measured simultaneously. Investigations were carried out on 39 cows milked automatically (experimental group) and 15 cows milked twice daily in a double-sided parlor (control group). All cows were chosen randomly out of their herds. Data collecting was done either in the morning or afternoon due to the circadian rhythm of cortisol. Statistical analysis was performed with parametric tests. Step behavior occurred significantly more often in the milking stall of the automatic milking system than in the milking parlor. The heart-rate of cows milked automatically rose significantly between minute 5 and minute 1 prior to entrance into the milking stall. The mean milk cortisol concentration of cows milked in the automatic milking system was considerably higher than that of the control cows milked in the parlor. The results show a difference in behavioral and physiological condition between cows milked in an automatic milking system and in a milking parlor. Reasons for this have not yet been identified. Further studies could pay particular attention to differences in the two milking systems.

Relationships between human-animal interactions and productivity of commercial dairy cows.

This study examined the relationships between a number of stockperson and cow variables at 66 commercial dairy farms. Variables such as the attitudes and behavior of stockpeople toward their cows and the behavioral response to humans and productivity of cows were studied over one lactation. There were consistent and significant correlations between some of these stockperson and cow variables. For example, a positive attitude by stockpeople toward the behavior of dairy cows was negatively correlated with the number of forceful, negative, tactile interactions used by stockpeople in handling cows (r = -0.27, df = 127, P < 0.01). Furthermore, based on farm averages, the number of forceful, negative, tactile interactions used by stockpeople was negatively correlated with the percentage of cows approaching within 1 m of an experimenter in a standard test (r = -0.27, df= 64, P< 0.05). Although not confirming a fear-productivity relationship, a moderate but nonsignificant correlation was found between flight distance of cows to an experimenter in a standard test and milk yield (r = -0.27, df = 33, P > 0.05). Support for the existence of a negative fear-productivity relationship was the finding that the use of negative interactions by stockpeople was significantly and negatively correlated with milk yield, protein, and fat at the farm (r = -0.36, -0.35 and -0.33, respectively, df = 64, P < 0.01) and was significantly and positively correlated with milk cortisol concentrations at the farm (r = 0.34, df= 64, P < 0.01). Furthermore, the percentage of cows approaching within 3 m of an experimenter in a standard test was positively correlated with conception rate to the first insemination (r = 0.38, df = 46, P < 0.01). The significant correlations found in the present study between stockperson attitudes and behavior and cow behavior and productivity, although not evidence of causal relationships, indicate the possibility of targeting these human characteristics to reduce fear responses of dairy cows to humans and improve the cows' productivity.

Characterization of Milk Cortisol Concentrations as a Measure of Short-Term Stress Responses in Lactating Dairy Cows

AbstractThis study compares cortisol concentrations in plasma and milk over a time-span of 1-4h following injection of an adrenocorticotropic hormone (ACTH) or a physiological stressor. Its aim was to characterize the usefulness of milk cortisol concentrations as short-term measures of acute stress.Experiment 1: three groups of lactating cows (Groups B - D; n = 5, each) were injected with ACTH1-24 at 4, 2 and 1h before milking, respectively, so that each experienced a similar period of elevated adrenocortical activity, but presented at milking with varying plasma cortisol concentrations. Another group (Group A; n = 5) was a saline-treated control. Mean plasma cortisol concentrations at milking were 7, 8, 24 and 56ng ml−1 for Groups A, B, C and D, respectively. Mean cortisol concentrations in milk were similar for Groups A and B (1.2 and 0.5 ng ml−1, respectively), higher in Group C (2.4ng ml−1), and greatest in Group D (11.7 ng ml−1; p &lt;0.001).Experiment 2: lactating dairy cows (n = 15) were injected with ACTH, transported by truck, or blood-sampled only (control) during the 2h before milking. Mean plasma cortisol concentrations at milking were 6, 20 and 72 ng ml−1 following control, ACTH and transport treatments, respectively; mean concentrations of cortisol in milk displayed a similar pattern (1.1, 2.4 and 12.0 ng ml−1, respectively; p &lt;0.001).Milk cortisol concentrations were highly correlated with plasma levels at milking, but did not reflect those situations where, following a period of elevation within the previous 4h, plasma cortisol concentrations had returned to basal levels. Concentrations of cortisol in foremilk and composite milk were highly correlated, but the mechanisms of cortisol flux may differ between these two compartments. Milk cortisol concentration can be a useful indicator of responses of lactating cows to acute stressors which act up to 2h before collection of samples.

Characterizations and psychoneuroimmunologic implications of secretory immunoglobulin A and cortisol in preterm and term breast milk

This article combines data from two separate investigations. One study examined relationships between psychosocial factors and preterm milk immune variables. The other examined relationships between psychosocial and breastfeeding satisfaction factors and perceived milk sufficiency in term mothers. Milk samples were collected on the fifth postpartum day and frozen. Both studies collected data on anxiety, but other psychosocial variables differed. Mood states and social support were studied in preterm mothers, while breastfeeding satisfaction, milk maturation, and infant suckling characteristics were studied in term mothers. Milk samples were assayed for secretory immunoglobulin A (sIgA) and cortisol. sIgA and cortisol levels were higher in the milk from preterm mothers and were inversely related to each other in both preterm and term milk. In preterm mothers, anger and vigor were positively correlated with higher milk sIgA. The findings suggest that cortisol is present in milk and may potentially influence the secretion of milk sIgA. The relationships that were found when comparing psychosocial, dyadic, and stress factors with milk sIgA and cortisol are provocative and suggest new paradigms for studying lactation.

The effects of handling by humans at calving and during milking on the behaviour and milk cortisol concentrations of primiparous dairy cows

This study examined the effects of human presence at the time of calving of primiparous cows, and the behaviour of the stockperson during milking on the behaviour of the cows during milking and in response to an experimenter in a standard 5-min test (human test). Cows which were not handled around the time of their first calving ( n=7) displayed a higher ( P<0.05) number of flinch, step and kick (FSK) responses during the first 20 weeks of lactation than cows which were handled ( n=7); most of these FSK responses occurred in the close presence of the stockperson. It is of interest that although the two treatments did not differ in the amount of extra assistance given by the stockperson, the number of FSK responses of cows was strongly ( P<0.01) and positively correlated with the amount of extra assistance given by the stockperson in the form of attaching a kick-bar, replacing dislodged cups or steadying the cow by holding the tail or leg. Cows in the no handling treatment were also slower ( P<0.05) to enter areas within 1 and 2 m of the experimenter in the human test conducted in the sixth week of lactation and had higher ( P<0.05) mean cortisol concentrations in their milk than cows in the handling treatment. It is proposed that the lower FSK response of cows that received human contact at the time of their calving was a result of these cows being less fearful of humans. Although the two stockpersons differed significantly ( P<0.01) in the proportion of physical interactions which were negative (aversive) in nature that they directed towards cows, the stockpersons had no significant influence on the behaviour of the cows during milking. However, the number of physical interactions that the cow received that were of a positive nature was significantly ( P<0.05) correlated with the total number of FSK responses displayed in the first 2 weeks of lactation. It appears that stockpersons recognize those cows with a high FSK response and attempt to quieten them with the use of interactions that are positive in nature.

Comparison of Total and Free Cortisol in Bovine Serum and Milk or Colostrum

Total (free plus protein-bound) and free cortisol concentrations in paired samples of serum and skim milk or colostrum were determined by specific radioimmunoassay after extraction or ultrafiltration. For 11 cows in established lactation mean total cortisol concentrations±SE in serum and milk were 4.5±.7ng/ml and .35±.06ng/ml, respectively. Concentrations of free cortisol in serum and milk were about .3 ng/ ml, which is at the lower limit of the present assay. Following 200 IU Synacthen injection to 5 cows, total cortisol in serum and milk rose to 67±6.0ng/ml and 11.4±1.5ng/ml by 8h postinjection, while free concentrations increased to 4.3±.7ng/ml and 6.5±.8ng/ml in serum and milk, respectively. Eight additional cows were sampled at 1 to 2 d after parturition, and total cortisol in serum and colostrum was 16.6±1.6ng/ml and 4.4±1.3ng/ml, and free cortisol was 2.4±.4ng/ml and 1.8±.5ng/ml, respectively. Free cortisol concentrations in colostrum or in milk from cows in established lactation, before or after adrenal stimulation, are directly related to free cortisol concentrations in the blood, while the bound cortisol in milk is more related to these two stages of lactation rather than the bound hormone in the blood. Measurement of free cortisol in milk should allow the monitoring of changes in plasma free cortisol in studies of stress in dairy cows.

Changes in the concentration of cortisol in milk during different stages of human lactation.

A study was undertaken to determine by radioimmunoassay the changes in concentrations of cortisol in the mammary secretion of individual women during late pregnancy, lactogenesis, established lactation and after cessation of breast-feeding. The concentration of cortisol in colostrum averaged 7.5% of that found in serum during late pregnancy. The concentration of cortisol (mean +/- S.E.M.) was relatively high in the mammary secretions during late pregnancy (25.5 +/- 1.8 ng/ml) and decreased within 2 days after delivery (10.2 +/- 2.0 ng/ml) to reach low values by 10 days post partum (1.8 +/- 0.7 ng/ml). During advanced lactation the cortisol values varied between 0.2 to 32 ng/ml but the mean concentration was significantly (p less than 0.05) less (7.2 +/- 0.8 ng/ml, n = 75) than during late pregnancy. With the abrupt termination of breast-feeding, the concentration of cortisol generally increased above the values determined during established lactation, but, even during involution, the progressive changes in concentration varied markedly (range 0.5-40.0 ng/ml). The function of milk cortisol for the newborn is now known. However, it is possible that cortisol in breast milk may help to control the transport of fluids and salts from the gastrointestinal tract of infants.