Abstract: Eight multiparous Holstein‐Friesian dairy cows in late lactation were used to investigate the potential of using perennial ryegrass with a high concentration of watersoluble carbohydrate (WSC) to increase the efficiency of milk production. After a pretreatment period on a common pasture, the cows were each given ad libitum access to one of two varieties of zero-grazed grass continuously for 3 weeks. Treatments were: high sugar (HS), an experimental perennial ryegrass variety bred to contain high concentrations of WSC; or control, a standard variety of perennial ryegrass (cv. AberElan) containing typical concentrations of WSC. The two grass varieties were matched in terms of heading date. All animals also received 4 kg day ‐1 standard dairy concentrate. Grass dry matter (DM) intake was not significantly different between treatments (11AE6 vs. 10AE7 kg DM day ‐1 ; s.e.d. 0AE95 for HS and control diets respectively), although DM digestibility was higher on the HS diet (0AE71 vs. 0AE64 g g ‐1 DM; s.e.d. 0AE23; P <0 AE01) leading to higher digestible DM intakes for that diet. Milk yield from animals offered the HS diet was higher (15AE3 vs. 12AE6 kg day ‐1 ; s.e.d. 0AE87; P <0 AE05) and, although milk constituent concentrations were unaffected by treatment, milk protein yields were significantly increased on the HS diet. The partitioning of feed N was significantly affected by diet, with more N from the HS diet being used for milk production (0AE30 vs. 0AE23 g milk N g ‐1 feed N; s.e.d. 0AE012; P <0 AE01) and less being excreted in urine (0AE25 vs. 0AE35; s.e.d. 0AE020; P <0 AE01). In a separate experiment, using the same grasses harvested earlier in the season, the fractional rate of DM degradation, measured by in situ and gas production techniques, was higher for the HS grass than for the control. It is concluded that increased digestible DM intakes of the HS grass led to increased milk yields, whereas increased efficiency of utilization of the HS grass in the rumen resulted in the more efficient use of feed N for milk production and reduced N excretion.

Abstract: In several studies lactation has been shown to be associated with a hypothalamic-pituitary-adrenal axis hyporesponsiveness to physical and psychological stressors. As it is not known whether the marked blunting of endocrine stress reactivity in women can be ascribed to suckling as a short-term effect or to lactation in general, the acute effects of suckling on the hypothalamic-pituitary-adrenal axis and the sympathetic-adrenal-medullary system responses to mental stress were investigated in lactating women. Forty-three lactating women were randomly assigned either to breast-feed or to hold their infants for a 15-min period with the onset 30 min before they were exposed to a brief psychosocial stressor (Trier Social Stress Test). Both breast-feeding and holding the infant yielded significant decreases in ACTH, total plasma cortisol, and salivary free cortisol (all P < 0.01). There were no significant differences in baseline hormone levels between the groups 1 min before the stress test. In response to stress exposure, ACTH, total plasma cortisol, salivary free cortisol, norepinephrine, and epinephrine were significantly increased in all lactating women (all P < 0.001). However, total cortisol and free cortisol responses to stress were attenuated in breast-feeding women (P = 0.001 and P = 0.067, respectively), who also showed significantly decreasing PRL levels during the stress test (P = 0.005). In addition, there was no change in plasma oxytocin or vasopressin in response to the stressor. Breast-feeding as well as holding led to decreased anxiety (P < 0.05), whereas, in contrast, stress exposure worsened mood, calmness, and anxiety in the total group (all P < 0.001). From these data we conclude that lactation in women, in contrast to that in rats, does not result in a general restraint of the hypothalamic-pituitary-adrenal axis response to a psychosocial stressor. Rather, suckling is suggested to exert a short-term suppression of the cortisol response to mental stress.

Abstract: Studies in animals indicate that various types of stressful stimuli can depress lactation, but there is much less information in humans. Experimental studies in breastfeeding women have shown that acute physical and mental stress can impair the milk ejection reflex by reducing the release of oxytocin during a feed. If this occurs repeatedly, it could reduce milk production by preventing full emptying of the breast at each feed. Prospective observational studies indicate that both maternal and fetal stress during labor and delivery (e.g., urgent Cesarean sections or long duration of labor in vaginal deliveries) are associated with delayed onset of lactation. The effects of chronic emotional stress on lactation are not known. Mothers who experience high levels of stress during and after childbirth should receive additional lactation guidance during the first week or two postpartum.

Abstract: Pregnancy and lactation both place significant demands on the mother to provide sufficient calcium (among other minerals and nutrients) to the fetus and neonate. Despite facing similar demands for calcium during pregnancy and lactation, the maternal adaptations differ significantly between these two reproductive periods. Women lose 300 to 400 mg of calcium daily through breast milk, and this calcium demand is met by a 5–10% loss of skeletal mineral content during 6 months of exclusive lactation. Most importantly, the lost mineral is fully restored within a few months of weaning, such that women who have breastfed do not have a long-term deficit in skeletal mineral content. This article will review our present understanding of the adaptations in mineral metabolism that occur during pregnancy and lactation, and will focus on recent evidence that the breast itself plays a central role in regulating the adaptations during lactation.

Abstract: In most mammalian species lactation suppresses fertility. There is no doubt that it is the suckling stimulus that provides the controlling signal, and, in human reproduction, this is the only truly physiological signal that suppresses fertility in normally nourished, healthy women. In breastfeeding women, the return of normal fertility follows a relatively well-defined path progressing through: an almost complete inhibition of gonadotrophin-releasing hormone/luteinizing hormone (GnRH/LH) pulsatile secretion in the early stages of lactation; return of erratic pulsatile secretion with some ovarian follicle development associated with increases in inhibin B and oestradiol; a resumption of apparently normal follicle growth associated with a normal increase in oestradiol, but often an absence of ovulation, or formation of an inadequate corpus luteum; and a return to normal ovulatory menstrual cycles. A key element in controlling the rate of this progression is the impact of the suckling stimulus on the GnRH pulse generator, a common feature of lactation in those species for which there is information. The variability in the duration of lactational amenorrhoea between women is related to the variation in the strength of the suckling stimulus, a unique situation between each mother and baby. Full breastfeeding can provide a reliable contraceptive effect in the first 6 to 9 months, but the precise mechanisms whereby the suckling stimulus affects GnRH pulsatile secretion remain unknown. Many studies on the hypothalamic pathways that might be involved in the translation of the neural suckling stimulus to suppression of hypothalamic GnRH secretion have been undertaken, principally in rats. In women, suckling increases the sensitivity of the hypothalamus to the negative feedback effect of oestradiol on suppressing the GnRH/LH pulse generator, a mechanism that appears to be common across species. In contrast, the role of prolactin in the control of GnRH appears to be species-dependent, with the importance varying from none to an important role in late or throughout lactation. In women, there is little evidence for a role of leptin, opioids or dopamine, although this may merely reflect the ethical dilemma of being able to give sufficient drug to test the system in the mother since these drugs will pass through the breast milk to the baby. Regardless of mechanism, practical guidelines for using breastfeeding as a natural contraceptive have been developed, which allows mothers to utilize the only natural suppressor of fertility in women as an effective means of spacing births.

Abstract: Lactogenesis stage II, the onset of copious milk secretion, takes place during the first 4 d postpartum in women and involves a carefully programmed set of changes in milk composition and volume. The evidence is summarized that progesterone withdrawal at parturition provides the trigger for lactogenesis in the presence of high plasma concentrations of prolactin and adequate plasma concentrations of cortisol. Although the process is generally robust, delayed lactogenesis does occur with stressful deliveries and in poorly controlled diabetes. Failure of early removal of colostrum from the breast is associated with high milk sodium and poor prognosis for successful lactation in many women. We speculate that this problem may result from accumulation of a substance in the mammary alveolus that inhibits lactogenesis, even in the face of appropriate hormonal changes after parturition.

Abstract: Conjugated linoleic acid (CLA) supplements containing a variety of isomers reduce milk fat yield. We have recently identified trans-10, cis-12 CLA as the isomer responsible for inhibiting milk fat synthesis in dairy cows. Our objectives were to determine milk fat yield and fatty acid composition responses to different doses of trans-10, cis-12 CLA. Multiparous Holstein cows (n = 4) were used in a 4 x 4 Latin square design. Treatments consisted of a 5-d abomasal infusion of four doses of trans-10, cis-12 CLA, i.e., 0.0, 3.5, 7.0 and 14.0 g/d. Milk fat yield was decreased 25, 33, and 50%, and milk fat concentration was reduced 24, 37 and 46% when cows received 3.5, 7.0 and 14.0 g/d of trans-10, cis-12 CLA, respectively. Feed intake, milk yield, and milk protein content and yield were unaffected by treatment. Milk fatty acid composition revealed that de novo synthesized fatty acids (short and medium chain) were extensively reduced when cows received the two highest doses, but at the low dose (3.5 g/d), decreases in de novo synthesized fatty acids and preformed fatty acids were similar. Changes in milk fatty acid composition also demonstrated that (9)-desaturase activity was inhibited at the two high doses of trans-10, cis-12 CLA, but was unaffected by the low dose. Results indicate minimal quantities of trans-10, cis-12 CLA (0.016% of dietary dry matter) markedly inhibited milk fat synthesis (25% reduction) and that a curvilinear reduction in milk fat yield occurred with increasing quantities of trans-10, cis-12 CLA.

Abstract: To investigate the role of β-catenin in mammary gland development and neoplasia, we expressed a stabilized, transcriptionally active form of β-catenin lacking the NH2-terminal 89 amino acids (ΔN89β-catenin) under the control of the mouse mammary tumor virus long terminal repeat Our results show that ΔN89β-catenin induces precocious lobuloalveolar development and differentiation in the mammary glands of both male and female mice Virgin ΔN89β-catenin mammary glands resemble those found in wild-type (wt) pregnant mice and inappropriately express cyclin D1 mRNA In contrast to wt mammary glands, which resume a virgin appearance after cessation of lactation, transgenic mammary glands involute to a midpregnant status All transgenic females develop multiple aggressive adenocarcinomas early in life Surprisingly, the ΔN89β-catenin phenotype differs from those elicited by overexpression of Wnt genes in this gland In particular, ΔN89β-catenin has no effect on ductal side branching This suggests that Wnt induction of ductal branching involves additional downstream effectors or modulators

Abstract: We have previously observed that female MF1 mice appeared to reach a limit in their food intake and milk production during late lactation, reaching a plateau between days 13 and 16 of lactation and between litter sizes of 9 and 15. These mice did not increase their food intake when forced to raise more offspring or when manipulated to be concurrently pregnant during late lactation, yet they did eat significantly more food at the peak of their second sequential lactation or when challenged with food of reduced energy content. These data suggest that apparent limits on sustained energy intake in this strain may not reflect central limitations but rather peripheral constraints at the mammary glands. In this study, we aimed to determine whether these were indeed limits by increasing the demands on the females during late lactation by cold-exposure (8 degrees C). Females responded to this manipulation by significantly increasing their food intake (F1,73=77.53, P<0.001) above that of lactating females kept in warmer conditions (21 degrees C). In addition, there was a significant reduction in the number of pups raised in the cold (t=2.36, d.f.=18, P=0.03), with the majority of the mortality occurring within the first 2 days of cold-exposure. The mean mass of the pups raised in the cold was significantly lower (F1,74=13.8, P<0.001) than that of those raised in the warm. Despite the cold-exposure and the increased food intake, there was no difference in the resting metabolic rates of the two groups of mothers or in the lengths of their small intestine. The greater food intake of lactating mice during cold-exposure supported our previous observations that they were capable of eating more food than the previously suggested limit of 23.1 g x day(-1). However, the milk energy output of females in the cold was also significantly higher than in the warm (F1,15=11.99, P=0.003), indicating that the asymptotic food intake of females in the warm was not mediated by limitations in their milk production. Sustained energy intake in these mice does not appear to be centrally or peripherally limited. Rather, the mice may restrain their use of energy during their first lactation because of life-history consequences for future reproductive attempts.

Abstract: To determine whether mice were limited in their capacity to absorb energy during late lactation, we attempted to increase the energy burden experienced by a group of female mice during late lactation by mating them at the postpartum oestrus, hence combining the energy demands of pregnancy and lactation. These experimental mice were therefore concurrently pregnant and lactating in their first lactation, and were followed through a normal second lactation. In a control group, females also underwent two lactations but sequentially, with the second mating after the first litter had been weaned. Maternal mass and food intake were measured throughout the first lactation, second pregnancy and second lactation. Maternal resting metabolic rate (RMR) was measured prior to the first mating and then at the peak of both the first and second lactations. Litter size and litter mass were also measured throughout both lactations. In the first lactation, experimental mice had a lower mass-independent RMR (F1,88=5.15, P=0.026) and raised significantly heavier pups (t=2.77, d.f.=32, P=0.0093) than the control mice. Experimental mice delayed implantation at the start of the second pregnancy. The extent of the delay was positively related to litter size during the first lactation (F1,19=4.58, P=0.046) and negatively related to mean pup mass (F1,19=5.78, P=0.027) in the first lactation. In the second lactation, the experimental mice gave birth to more (t=2.75, d.f.=38, P=0.0092) and lighter (t=-5.01, d.f.=38, P<0.0001) pups than did the controls in their second lactation. Maternal asymptotic daily food intake of control mice in the second lactation was significantly higher (t=-4.39, d.f.=37, P=0.0001) than that of the experimental mice and higher than that of controls during their first lactation. Despite the added burden on the experimental females during their first lactation, there was no increase in their food intake, which suggested that they might be limited by their capacity to absorb energy. However, control females appeared to be capable of increasing their asymptotic food intake beyond the supposed limits estimated previously, suggesting that the previously established limit was not a fixed central limitation on food intake. As RMR increased in parallel with the increase in food intake during the second lactation of control mice, the sustained energy intake remained at around 7.0xRMR.

Abstract: Organochlorine pesticides, due to their persistence, accumulate in food chains and cause elevated contamination in human beings. These residues bioconcentrate in lipid-rich tissues according to the equilibrium pattern of internal transport and lipid tissue content. The analyses of maternal adipose tissue, maternal blood serum, umbilical blood serum, colostrum, and mature milk indicate circulation of these compounds through all compartments of the maternal body, including their crossover of the placental barrier. The greatest residue levels found correspond to DDTs, with highest levels determined in colostrum (5.71 mg/kg of DDT total), followed by adipose tissue with 5.66 mg/kg and in mature milk with 4.70 mg/kg. Among DDTs, pp'DDE is the most predominant compound. The paired analyses of organochlorine pesticide residue levels between mother blood serum and umbilical blood serum demonstrate significant correlation and their transfer from mother to fetus through the placenta. The paired analyses of adipose tissue and colostrum and mature milk contamination levels indicate a high degree of coherence, principally of DDT, in the body and lactation as a decontamination means.

Abstract: Background: In mammals the composition of milk changes during early lactation showing a rapid decline in fat-soluble vitamins and a continuous increase in total lipids. Changes in t

Abstract: The proapoptotic proteinase inhibitor TIMP-3 is the only molecule of this family thought to influence cell death. We examined epithelial apoptosis in TIMP-3-deficient mice during mammary gland involution. Lactation was not affected by the absence of TIMP-3, but glandular function, as measured by gland-to-body weight ratio and production of beta-casein, was suppressed earlier during post-lactational involution than in controls. Histological examination revealed accelerated lumen collapse, alveolar-epithelial loss, and adipose reconstitution in Timp-3(-/-) females. Epithelial apoptosis peaked on the first day of involution in Timp-3-null glands but at day 3 in wild-type littermates. Unscheduled activation of gelatinase-A was evident by zymography and correlated with earlier fragmentation of fibronectin in Timp-3(-/-) mammary. To obtain independent evidence of the proapoptotic effects of TIMP-3 deficiency, we introduced recombinant TIMP-3-releasing pellets into regressing Timp-3(-/-) mammary tissue and showed that this treatment rescued lumen collapse and epithelial apoptosis. Ex vivo, involuting Timp-3(-/-) mammary tissue demonstrated accelerated epithelial apoptosis that could be reduced by metalloproteinase inhibition. The physiological relevance of TIMP-3 became apparent as Timp-3(-/-) dams failed to reestablish lactation after brief cessation of suckling. Thus, TIMP-3 is a critical epithelial survival factor during mammary gland involution.

Abstract: SUMMARY Laboratory mice (strain MF1) were used to determine whether sustainable rates of energy intake are limited during lactation. Mice raising natural-sized litters ( N =71) reached an asymptote in their daily food intake between days 13 and 16 of lactation at 23.1gday −1 and also between litter sizes of 9 and 15 pups (22.8gday −1 ). A second group of 37 females had their litter sizes manipulated at birth to raise more or fewer offspring than they gave birth to. When the litter size was increased, females did not increase their food intake to match their new litter size. However, when litter size was decreased, females decreased their asymptotic daily food intake during late lactation in relation to the extent of reduction in litter size. Therefore, it appeared that females were limited during late lactation and with large litter sizes. The milk energy exported amounted to 44% of the gross energy intake, and the estimated daily energy expenditure was therefore considerably lower than the sustained energy intake [8.0×RMR(gross), 6.6×RMR(assimilated)], and averaged 3.1×RMR, where RMR is resting metabolic rate. It was not possible to determine whether the apparent limit on sustained energy intake was acting centrally or peripherally because of the asymptotes in both food intake and milk energy output with increasing litter size.

Abstract: In the present chapter the behavioral and neuroendocrine alterations accompanying pregnancy and lactation will be discussed. It will be shown that many are dependent on the innate level of emotionality of the rats. In late pregnancy the level of anxiety, as measured on the elevated plus-maze is increased in rats with both high and low level of innate anxiety-related behavior, whereas lactating rats display less anxiety in such tests and higher degrees of aggressive behavior in tests for agonistic behavior. There is a dramatic reduction in the responsiveness of the hypothalamo-pituitary-adrenal (HPA) axis to various physical or emotional stimuli in both pregnant and lactating rats. This appears to be due to changes throughout the HPA axis. Oxytocin has been implicated in the control of the axis at this time, but the inhibitory action of central oxytocin on ACTH or corticosterone secretion seen in virgin female rats is not evident during pregnancy and lactation. However, central oxytocin is involved in the regulation of emotionality at this time. In addition to its anxiolytic effect, prolactin, acting at brain prolactin receptors, seems to exert an inhibitory effect on HPA axis responsiveness. At the time of parturition, the HPA axis is not stimulated by parturition-related stimuli and is under strong inhibition by endogenous opioids as revealed by the application of the opioid receptor antagonist naloxone.

Abstract: The vital role played by prolactin during pregnancy and lactation is emphasized by the physiological adaptations that occur in the mother to maintain a prolonged state of hyperprolactinemia. In many species the placenta provides a source of lactogenic hormones in the circulation, ensuring the continued presence of a hormone capable of activating the prolactin receptor throughout pregnancy. In addition, the tuberoinfundibular dopamine neurons, which normally maintain a tonic inhibitory influence over prolactin secretion, show a reduced ability to respond to prolactin during late pregnancy and lactation, allowing high levels of prolactin to be maintained unopposed by a regulatory feedback mechanisms. There is clear evidence that systemic prolactin gains access to the cerebrospinal fluid, from where it can diffuse to numerous brain regions. Prolactin receptors are expressed in several hypothalamic nuclei, including the medial preoptic and arcuate nuclei, and we have observed marked increases in expression of prolactin receptors in these nuclei during lactation. Moreover, a number of hypothalamic nuclei, including the paraventricular, supraoptic and ventromedial nuclei, in which prolactin receptors were not detected in diestrous rats, were found to express significant amounts of prolactin receptor during lactation. These observations have important implications for the variety of documented actions of prolactin on the brain. Prolactin has been reported to influence numerous brain functions, including maternal behavior, feeding and appetite, oxytocin secretion, and ACTH secretion in response to stress. In light of the high circulating levels of prolactin during pregnancy and lactation and the increased expression of prolactin receptors in the hypothalamus, many of these effects of prolactin may be enhanced or exaggerated during lactation. Hence, prolactin may be a key player in the coordination of neuroendocrine and behavioral adaptations of the maternal brain.

Abstract: The effects of high ambient tempera- ture and level of dietary heat increment on sow milk production and piglet performance over a 28-d lactation were determined in 59 multiparous crossbred Large White × Landrace pigs kept at a thermoneutral (20°C) or in a hot (29°C) constant ambient temperature. Exper- imental diets fed during lactation were a control diet (NP; 17.6% CP) and two low-protein diets obtained by reduction of CP level (LP; 14.2% CP) or both reduction of CP and addition of fat (LPF; 15.2% CP); the NE:ME ratio was 74.3, 75.6, and 75.8% for NP, LP, and LPF diets, respectively. All diets provided 0.82 g of digestible lysine/MJ of NE, and ratios between essential AA and lysine were above recommendations. Creep feed was provided after d 21 of lactation. Reduction of CP level did not influence (P > 0.10) milk production, milk com- position, or piglet performance. Despite higher nursing frequency (39 vs 34 sucklings per day), milk production decreased (P < 0.01) from 10.43 to 7.35 kg/d when tem- perature increased from 20 to 29°C. At d 14, DM (18.6 vs 18.1%) and energy (4.96 vs 4.75 MJ/kg) contents in milk tended (P = 0.09) to be higher in sows kept at 29°C. Over the 28-d lactation, piglet BW gain and BW at weaning decreased (P < 0.01) from 272 to 203 g/d and 9.51 to 7.52 kg, respectively, when temperature increased from 20 to 29°C. Daily creep feed intake over the 4th wk of lactation was higher (P < 0.01) at 29°C than at 20°C (388 vs 232 g/litter, respectively), which was reflected in a greater increase in BW gain between wk 1 to 3 and wk 4 at the higher temperature (147 vs 130%); BW gain between weaning and d 14 postweaning was higher (P < 0.05) for piglets originating from sows kept at 29°C (280 vs 218 g/d). In connection with their lower growth rate, DM (31.2 vs 33.0%), protein (15.5 vs 16.0%), lipid (12.3 vs 13.9%), and energy (8.39 vs 9.09 kJ/g) contents in weaned, slaughtered piglets were lower (P < 0.01) at 29 than at 20°C. In conclusion, modi- fication in the CP:NE ratio in order to decrease dietary heat increment did not affect milk production and piglet performance in thermoneutral or hot climatic condi- tions. Our results confirm the negative effect of high ambient temperatures on milk yield and emphasize the importance of creep feed supply to improve pre- and postweaning growth of piglets in these conditions, espe- cially when weaning occurs after 3 wk of age.

Abstract: Summary 1. Female mammals increase energy expenditure during lactation to support the high cost of milk production. The extent to which lactation in a small phocid species, the Harbour Seal Phoca vitulina L., was fuelled by food vs body stores, how this allocation varied with maternal body mass and the consequences of maternal expenditure on offspring growth were studied. 2. The proportional body composition of 30 females was independent of initial postpartum body mass, but larger females had absolutely more stored energy than smaller ones. 3. Females lost 32% of postpartum body mass and 62% of body energy by late lactation; 97% of energy loss was derived from body fat. Percentage loss of body energy was independent of initial body mass, indicating that females limit their allocation of body stores to offspring by expending a constant proportion of stores rather than a constant amount. 4. Females spent more time diving and individual dives were deeper and longer as lactation progressed. By late lactation, these characteristics of diving were inversely proportional with initial postpartum mass. 5. During early lactation, female expenditures were covered mainly by a reduction in body energy stores. By late lactation, food intake increased six-fold but the extent of this increase varied inversely with postpartum mass. 6. Pup growth rate and weaning mass were positively related to postpartum mass and total daily energy expenditure of females, but were independent of the source of energy used by females during lactation. Pups of heavy females had higher survival than pups of light females. 7. Our results support the hypothesis that maternal body mass is an important determinant of lactation strategies in pinnipeds.

Abstract: The non-stimulated and phorbol 12-myristate 13-acetate (PMA)-stimulated luminol-augmented cellular chemiluminescence (CL) response and viability of milk and blood polymorphonuclear leukocytes (PMN) were determined in lactating dairy cows during different stages of lactation. In the first study, ten healthy cows each in early, mid and late lactation were compared. In a second study, the same measurements as in the first study were evaluated longitudinally in 12 cows during 1 month following parturition. The CL activity and myeloperoxidase (MPO) content of milk PMN and macrophages (M) were also compared. Milk M did not possess MPO activity and were devoid of any luminol-enhanced CL. The CL activity of milk and blood PMN was significantly lower in early lactation than in mid and late lactation (P < 0.001). Whereas little changes were observed in viability of blood PMN, the viability of milk PMN was lower in early lactation than in mid and late lactation (P < 0.001). The percentage of PMN in isolated milk cells was also lower during early lactation than during mid and late lactation (P < 0.001). The CL activity in response to PMA during early, mid and late lactation increased 13, 59 and 42-fold in blood PMN and 1.7, 2.6 and 2.4-fold in milk PMN, respectively, in comparison with non-stimulated PMN. The CL activity, both in milk and blood PMN. the milk PMN viability and the percentage of milk PMN were lowest between 3 d and 11 d post partum. These observed changes immediately after calving could contribute to a higher susceptibility to mastitis in that period.

Abstract: To study the involvement of the IGFs in mammary development and lactation of the cow, the temporal expressions of IGF-I and -II, its receptor type 1 (IGFR-1), IGF-binding proteins (IGFBPs)-1 to -6 and GH receptor (GHR) mRNA were examined. This was carried out for different stages of mammogenesis, lactogenesis, galactopoiesis and involution in the bovine mammary gland of 26 animals. Furthermore, IGF-I was localised by immunohistochemistry. The highest mRNA concentrations for IGF-I were detected in the mammary tissue of late pregnant heifers (days 255-272) and significantly lower expression was detected during lactogenesis and galactopoiesis. Immunohistochemistry of IGF-I revealed only a weak staining in the epithelium of the ducts during mammogenesis. The epithelium of the alveoli were negative during mammogenesis, lactogenesis and galactopoiesis but displayed distinct IGF-I activity during involution. In the stroma a distinct staining of the cytoplasm of adipocytes and of vascular smooth muscle cells was observed. A certain percentage of fibroblasts (usually 20-30%) were also immunopositive. In contrast, highest expression for IGFR-1 was detected during galactopoiesis and involution. The lowest mRNA concentration for IGFR-1 was found during pregnancy (days 194-213). In general, the expression of IGF-II was not regulated during mammogenesis and lactation, but decreased during involution. The mRNA for the six binding proteins was detected in the bovine mammary gland. The dominant binding proteins were IGFBP-3 and -5. The highest expression of IGFBP-3 was observed during mid-pregnancy and the lowest during late lactation, involution and in non-pregnant heifers. The mRNA for IGFBP-5 increased during late mammogenesis and lactogenesis followed by a decrease thereafter. In general, the mRNA concentrations for IGFBP-2, -4 and -6 were barely detectable during all stages. In contrast, the expression for IGFBP-1 was upregulated in the mammary gland of virgin heifers and increased around the onset of lactation. mRNA for GHR was found during all stages examined without outstanding fluctuations. In conclusion, locally produced IGF-I and -II may mediate mammogenesis. The high mammary IGFR-1 mRNA during lactation suggests a role for peripheral IGF-I in maintenance of lactation. The role of IGFBPs in the mammary gland needs further evaluation.

Abstract: UNLABELLED: While breast milk appears to be superior to formula for the development of very low birthweight (VLBW) infants, it is supplemented to meet the metabolic demands of the rapidly growing premature infant. To estimate the nutritional variability of breast milk from mothers of VLBW infants, protein (bicinchoninic acid method) and fat content (creamatocrit) were measured in breast-milk spot samples from mothers of 20 VLBW infants, collected 4 times a day during the first 4 wk of lactation. Protein content (median 1.9 g dl(-1), range 1.1-3.5 g dl(-1)) and fat content (3.8/1.0-14.6 g dl(-1)) were highly variable and lacked a normal distribution over all samples and in individual women's milk. There was only a weak correlation between fat and protein (rs=0.416, p < 0.001). Fat but not protein was lower in morning samples than in samples collected later in the day (p < 0.001). Protein but not fat content decreased during the weeks of lactation (rs =-0.446, p < 0.001). No impact of the baby's gestational age was observed. CONCLUSION: The fat and protein content of breast milk from mothers of VLBW infants is highly variable, calling into question the clinical feasibility of individualized supplementation of breast milk for VLBW infants based on spot sample measurements.