Lactose in plasma during lactogenesis, established lactation and weaning in sows

Sweet taste receptor subunit T1R3 regulates casein secretion and phosphorylation of STAT5 in mammary epithelial cells

During lactation, mammary epithelial cells (MECs) on the apical membrane are in contact with lactose in milk, while MECs on the basolateral membrane are in contact with glucose in blood. Both glucose and lactose are sweeteners that are sensed by a sweet taste receptor. Previously, we have shown that lactose exposure on the basolateral membrane, but not the apical membrane, inhibits casein production and phosphorylation of STAT5 in MECs. However, it remains unclear whether MECs have a sweet taste receptor. In this study, we confirmed that the sweet taste receptor subunit T1R3 existed in both the apical and basolateral membranes of MECs. Subsequently, we investigated the influence of apical and basolateral sucralose as a ligand for the sweet taste receptor using a cell culture model. In this model, upper and lower media were separated by the MEC layer with less-permeable tight junctions. The results showed in the absence of glucose, both apical and basolateral sucralose induced phosphorylation of STAT5, which is a positive transcriptional factor for milk production. In contrast, the T1R3 inhibitor basolateral lactisole reducing phosphorylated STAT5 and secreted caseins in the presence of glucose. Furthermore, exposure of the apical membrane to sucralose in the presence of glucose inhibited the phosphorylation of STAT5. Simultaneously, GLUT1 was partially translocated from the basolateral membrane to the cytoplasm in MECs. These results suggest that T1R3 functions as a sweet receptor and is closely involved in casein production in MECs.

Lactose on the basolateral side of mammary epithelial cells inhibits milk production concomitantly with signal transducer and activator of transcription 5 inactivation

Mammary epithelial cells (MECs) are the only cells capable of synthesizing lactose. During lactation, alveolar MECs secrete lactose through the apical membrane into the alveolar lumen, whereas alveolar tight junctions (TJs) block the leakage of lactose into the basolateral sides of the MECs. However, lactose leaks from the alveolar lumen into the blood plasma in the mastitis and after weaning. This exposes the basolateral membrane of MECs to lactose. The relationship between lactose in blood plasma and milk production has been suggested. The present study determined whether lactose exposure on the basolateral membrane of mouse MECs adversely affects milk production in vitro. Restricted exposure to lactose on the basolateral side of the MECs was performed using a culture model, in which MECs on the cell culture insert exhibit milk production and less-permeable TJs. The results indicated that lactose exposure on the basolateral side inhibited casein and lipid production in the MECs. Interestingly, lactose exposure on the apical side did not show detectable effects on milk production in the MECs. Basolateral lactose exposure also caused the inactivation of STAT5, a primary transcriptional factor for milk production. Furthermore, p38 and JNK were activated by basolateral lactose exposure. The activation of p38 and JNK following anisomycin treatment reduced phosphorylated STAT5, and inhibitors of p38 blocked the reduction of phosphorylated STAT5 by basolateral lactose exposure. These findings suggest that lactose functions as a partial inhibitor for milk production but only when it directly makes contact with the basolateral membrane of MECs.

A dynamic mammary gland model describing colostrum immunoglobulin transfer and milk production in lactating sows

The physiology of the sow mammary gland is qualitatively well described and understood. However, the quantitative effect of various biological mechanisms contributing to the synthesis of colostrum and milk is lacking and more complicated to obtain. The objective of this study was to integrate physiological and empirical knowledge of the production of colostrum and milk in a dynamic model of a single sow mammary gland to understand and quantify parameters controlling mammary gland output. In 1983, Heather Neal and John Thornley published a model of the mammary gland in cattle, which was used as a starting point for the development of this model. The original cattle model was reparameterized, modified, and extended to describe the production of milk by the sow mammary gland during lactation and the prepartum production of colostrum as the combined output of immunoglobulins (Ig) and milk. Initially, the model was reparameterized to simulate milk synthesis potential of a single gland by considering biological characteristics and empirical estimations of sows and piglets. Secondly, the model was modified to simulate more accurately the responses to changes in milk removal rates. This was done by linking the ejectable milk storage capacity to the number of secretory cells rather than being constant throughout lactation. Finally, the model was extended to include the prepartum synthesis of milk and the kinetics of Ig into and out of the mammary gland. A progressive capacity of secretory cells to synthesize milk was used to differentiate the time between the onset of milk synthesis and Ig transfer. Changes in maximum milk removal rate, duration of milk ejection, and nursing interval exerted a great impact on the modeled milk output. Changes by ±60% in one of these parameters were capable of increasing milk output by 28% to 39% during the first 4 wk in lactation compared with the reference parameterization. This suggests that the ability of the piglet to remove milk from the gland exerts a key control on milk synthesis during lactation. Modeling colostrum as the combined output of Ig and milk allowed to represent the rapid decline in Ig concentration observed during the first hours after farrowing. In conclusion, biological and empirical knowledge was integrated into a model of the sow mammary gland and constitutes a simple approach to explore in which conditions and to what extent individual parameters influence Ig kinetics and milk production.

Review: nutritional and endocrine control of colostrogenesis in swine

Colostrum plays an essential role in ensuring the survival, growth and health of piglets by providing energy, nutrients, immunoglobulins, growth factors and many other bioactive components and cells. Both colostrum yield and composition are highly variable among sows, yet mechanisms and factors that regulate colostrogenesis are not fully known. Unlike sow milk yield, sow colostrum yield is not highly determined by litter size and suckling intensity but is largely driven by sow-related factors. Colostrum synthesis is under hormonal control, with prolactin and progesterone concentrations prepartum having, respectively, positive and negative influences on colostrum yield. Less is known about the endocrine control of the end of colostrogenesis in swine, which is characterized by the closure of tight junctions in the mammary epithelium and the cessation of transfer of immunoglobulin G (IgG) into lacteal secretions. Recent studies indicate that exogenous hormones may influence colostrogenesis. Inducing parturition by injecting prostaglandin F2α on day 114 of gestation in combination with an oxytocin-like molecule reduced colostrum yield, and injection of prostaglandin F2α alone either reduced colostrum yield or had no effect. Injecting a supraphysiological dose of oxytocin to sows in the early postpartum period delayed the tightening of mammary tight junctions, thereby prolonging the colostral phase and increasing concentrations of IGF-I and IgG and IgA in early milk. The development of strategies to improve colostrum composition in swine through maternal feeding has been largely explored but very few attempts were made to increase colostrum yield. This is most likely because of the difficulty in measuring colostrum yield in swine. The fatty acid content of colostrum greatly depends on the amount of lipids provided in the sow diet during late gestation, whereas the fatty acid profile is largely influenced by the type of lipid being fed to the pregnant sow. Moreover, various ingredients that presumably have immuno-modulating effects (such as fish oil, prebiotics and probiotics) increased concentrations of IgG, IgA and/or IgM in sow colostrum when they were provided during the last weeks of gestation. Finally, there is some evidence that sow nutrition during late gestation may influence colostrum yield but this clearly warrants more research. This review emphasizes that although progress has been made in understanding the control of colostrogenesis in swine, and that strategies exist to manipulate fat and immunoglobulin contents of colostrum, ways to increase colostrum yield are still lacking.

Review: Mammary gland development in swine: embryo to early lactation

Milk production by the sow is a major factor limiting the growth and survival of her litter. Understanding the process of morphogenesis of the sow's mammary gland and the factors that regulate mammary development are important for designing successful management tools that may enhance milk production. Primordia of the mammary glands are first observable in the porcine embryo at approximately 23 days of gestation. The glands then progress through a series of morphologically distinct developmental stages such that, at birth, each mammary gland is composed of the teat, an organized fat pad and two separate lactiferous ducts each with a few ducts branching into the fat pad. The glands continue to grow slowly until about 90 days of age when the rate of growth increases significantly. The increased rate of mammary gland growth coincides with the appearance of large ovarian follicles and an increase in circulating estrogen. After puberty, the continued growth of the gland and elongation and branching of the duct system into the fat pad takes place in response to the elevated levels of estrogen occurring as part of the estrous cycles. After conception, parenchymal mass of each gland increases slowly during early pregnancy and then grows increasingly rapidly during the final trimester. This growth is in response to estrogen, progesterone, prolactin and relaxin. Lobuloalveolar development occurs primarily during late pregnancy. By parturition, the fat pad of the mammary gland has been replaced by colostrum-secreting epithelial cells that line the lumen of the alveoli, lobules and small ducts. All mammary glands develop during pregnancy, however, the extent of development is dependent on the location of the mammary gland on the sow's underline. The mammary glands undergo significant functional differentiation immediately before and after farrowing with the formation of colostrum and the transition through the stages of lactogenesis. Further growth of the glands during lactation is stimulated by milk removal. Individual glands may grow or transiently regress in response to the intensity of suckling during the initial days postpartum. Attempts to enhance milk production by manipulation of mammary development at stages before lactation generally have met with limited success. A more in depth understanding of the processes regulating porcine mammary gland morphogenesis at all stages of development is needed to make further progress.

Breast Development and Control of Milk Synthesis

We have developed a computerized breast measurement system that can quantitate both long-term (lactation cycle) and short-term (between breastfeedings) changes in breast volume. The increase in breast volume during pregnancy was not related to milk production at one month of lactation, whereas milk production from one to six months of lactation remained constant and was not controlled directly by the suckling-evoked secretion of prolactin. From the measurement of circadian changes in breast volume, it was concluded that infants rarely emptied the breasts at a single breastfeeding and that short-term variation in the rate of synthesis during the day and between the left and right breasts was closely related to the degree of breast fullness. Furthermore, differences between women in the storage capacity of the breasts dictated their flexibility in frequency of breastfeeding. These observations are consistent with the autocrine (local) control of milk synthesis during established lactation in women.

Analytical considerations and general diagnostic and therapeutic ramifications of milk hormones during lactation

In this review, we will discuss the changes that occur in the mammary gland from pregnancy to lactation and the issues surrounding the analysis of circulating and milk hormones during the stages of lactogenesis. There is a cascade of events that must occur to achieve milk synthesis, milk ejection, and successful transfer to the breastfeeding infant. The adequacy and success of this process is no small measure and the assessment of milk production, the hormones involved in this process and the ability to properly diagnose conditions and causes of low milk supply are critical for the health and well-being of the mother-infant breastfeeding dyad. The normative data that have been amassed in past decades suggest that there are certain values or circulating concentrations of milk hormones, that if lacking or low, could explain low milk supply status. Yet, in looking more closely at the tests themselves, the certainly of what constitutes "normal" can vary depending on the preanalytical conditions that the blood or milk sample were obtained, the methods used in obtaining circulating or milk concentrations, and the standardization of how that result is expressed. The standardization of these aspects of breast milk physiology are essential for providing important normative data to health care professionals and researchers and will result in more consistent findings across multi-disciplinary platforms.

Historical and contemporary aspects of maternal immunity in swine

Maternal immunity plays a pivotal role in swine health and production because piglets are born agammaglobulinemic and with limited cell-mediated immunity, i.e. few peripheral lymphoid cells, immature lymphoid tissues, and no effector and memory T-lymphocytes. Swine do not become fully immunologically competent until about 4 weeks of age, which means that their compromised ability to respond to infectious agents during the first month of life must be supplemented by maternal immune components: (1) circulating antibodies derived from colostrum; (2) mucosal antibodies from colostrum and milk; and (3) immune cells provided in mammary secretions. Because maternal immunity is highly effective at protecting piglets against specific pathogens, strengthening sow herd immunity against certain diseases through exposure or vaccination is a useful management tool for ameliorating clinical effects in piglets and delaying infection until the piglets' immune system is better prepared to respond. In this review, we discuss the anatomy and physiology of lactation, the immune functions of components provided to neonatal swine in mammary secretion, the importance of maternal immunity in the prevention and control of significant pathogens.

Amino acids and mammary gland development: nutritional implications for milk production and neonatal growth

Milk is synthesized by mammary epithelial cells of lactating mammals. The synthetic capacity of the mammary gland depends largely on the number and efficiency of functional mammary epithelial cells. Structural development of the mammary gland occurs during fetal growth, prepubertal and post-pubertal periods, pregnancy, and lactation under the control of various hormones (particularly estrogen, growth hormone, insulin-like growth factor-I, progesterone, placental lactogen, and prolactin) in a species- and stage-dependent manner. Milk is essential for the growth, development, and health of neonates. Amino acids (AA), present in both free and peptide-bound forms, are the most abundant organic nutrients in the milk of farm animals. Uptake of AA from the arterial blood of the lactating dam is the ultimate source of proteins (primarily β-casein and α-lactalbumin) and bioactive nitrogenous metabolites in milk. Results of recent studies indicate extensive catabolism of branched-chain AA (leucine, isoleucine and valine) and arginine to synthesize glutamate, glutamine, alanine, aspartate, asparagine, proline, and polyamines. The formation of polypeptides from AA is regulated not only by hormones (e.g., prolactin, insulin and glucocorticoids) and the rate of blood flow across the lactating mammary gland, but also by concentrations of AA, lipids, glucose, vitamins and minerals in the maternal plasma, as well as the activation of the mechanistic (mammalian) target rapamycin signaling by certain AA (e.g., arginine, branched-chain AA, and glutamine). Knowledge of AA utilization (including metabolism) by mammary epithelial cells will enhance our fundamental understanding of lactation biology and has important implications for improving the efficiency of livestock production worldwide.

Urine NMR metabolomics analysis of breastfeeding biomarkers during and after pregnancy in a large prospective cohort study

BACKGROUND

Modern metabolomic profiling has not yet been applied to human breastfeeding research. A common reason for breastfeeding cessation is perceived insufficient milk production. We investigated broad biochemical profiles in maternal urine collected during and after pregnancy to identify biomarkers related to reduced reported breastfeeding.

METHODS

Fasting urine was collected at three consultations (visit V1: gestational week 8-20; V2: week 28 ± 2; V3: 10-16 weeks postpartum) in the STORK Groruddalen program, a prospective, multiethnic cohort study of gestational diabetes involving healthy, pregnant women in Oslo, Norway, and analyzed using NMR spectroscopy. Breastfeeding at V3 was recorded in three categories: Exclusively breastfeeding (n = 326), partially breastfeeding (n = 156) and formula feeding (n = 67).

RESULTS

Five metabolites were relevant to breastfeeding. Lactose was detected at V1 and increased to 0.1 mM/mM creatinine at V2. Postpartum excretion at V3 was significantly higher in exclusively breastfeeding women than partially or non-breastfeeding (median = 0.29, 0.23 and 0.04 mM/mM creatine, respectively; ANOVA p-value = 2e-70). Glycine excretion at V3 (0.12, 0.10 and 0.06, respectively; p = 2e-5) and at V2 were associated with breastfeeding (0.34, 0.33 and 0.26, respectively; p = 4e-5). Creatine and two unidentified substances also correlated with breastfeeding. NMR metabolomics found no other metabolites differing between categories during pregnancy (V1, V2), and did not predict individual breastfeeding postpartum (V3).

CONCLUSION

Decreased glycine excretion at V2 may indicate difficulties meeting the metabolic demands of the growing fetus, but urine profiles contained otherwise little indication of early adaptations during pregnancy towards reduced biological potential to breastfeed.

Effects of antenatal corticosteroids on urinary markers of the initiation of lactation in pregnant women

BACKGROUND

Antenatal corticosteroids are given to most women at risk of preterm delivery, although many do not eventually deliver preterm. Profound disruptions of lactation have been shown in ewes after antenatal corticosteroid treatment, but little is known of the effect on lactation in women. This study aimed to investigate the effects of antenatal corticosteroid treatment on mammary secretion during pregnancy in women.

METHODS

We conducted a prospective cohort study of women receiving betamethasone for anticipated preterm delivery (n = 87). Women collected 24-hour urine samples on days 1, 2, 3, 5, 7, and 14 after treatment if they remained pregnant. We measured urinary excretion of pregnanediol glucuronide (PdG), a major metabolite of progesterone and lactose, which indicates mammary secretion during pregnancy. Withdrawal of progesterone triggers the onset of mammary secretion.

RESULTS

Median (range) gestational age at treatment was 28.8 (23.6-33.6) weeks. A total of 330 24-hour urine samples were collected. Median (range) excretion of PdG was 1.355 (0.139-5.069) mmol/24 hours, and lactose excretion was 0.823 (0.035-6.676) mmol/24 hours. Both PdG and lactose excretion increased with increasing gestational age (P < 0.001). After adjustment for gestational age, there were significant transient increases in lactose excretion (P < 0.001) after betamethasone treatment but no changes in PdG excretion (P = 0.435).

CONCLUSIONS

Antenatal betamethasone treatment was associated with a transient premature secretory activation while women were still pregnant.

Selected parameters in urine as indicators of milk production in lactating sows: A pilot study

Although insufficient milk production in lactating sows may cause tremendous economic losses, reliable methods for estimating milk production in sows under field conditions are not available. This study aimed to investigate whether urine parameters could be used to predict milk production in sows. The milk production of 18 sows was determined during early and mid-lactation. Morning (a.m.) and afternoon (p.m.) urinary levels of potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), lactose and creatinine were analysed. The absolute concentrations, the ratios relative to creatinine, and the fractional excretions of all elements in urine were not significantly associated with milk production. The p.m./a.m. ratios of K, Na and Ca concentrations in urine (K(R), Na(R), and Ca(R)) were significant predictors for milk production, but only during mid-lactation. The total variation in milk production (r(2) value) explained by K(R), Na(R), Ca(R) amounted to 72%, 55%, 42%, respectively. Analysis of minerals and especially K in the a.m. and p.m. urine of sows during mid-lactation provided an acceptable indication of milk production. Further research is necessary to investigate whether the present results can be used to estimate milk production in hypogalactic sows under field conditions.

Immune components in porcine mammary secretions

Immune components present in mammary secretions are reviewed. In swine, the histological structure of the placenta prevents in utero transfer of immunoglobulins and mammary secretions are the sole source of maternal antibody for the neonate. In addition to immunoglobulins, porcine mammary secretions contain significant numbers of maternal cells of various types that may contribute to neonatal immunity, including phagocytes (neutrophils and macrophages), lymphocytes (B and T cells), and epithelial cells. Immunomodulating and/or antimicrobial substances, including lactoferrin, lysozyme, lactoperoxidase, and cytokines, are also present in mammary secretions and may contribute to the protection of the neonate. While the role of immunoglobulins in mammary secretions is well understood, the contribution of cellular components and non-specific immune factors to neonatal immunity remains to be defined.

Serum concentrations of micronutrients, packed cell volume, and blood hemoglobin during the first two gestations and lactations of sows

The objective of the present work was to describe the changes in serum concentrations of some micronutrients during the first 2 gestations and lactations of 33 gilts in order to establish blood reference values for a rapid assessment of nutritional status. In both parities, blood samples were taken from the jugular vein at mating, 5, 10 and 15 wk of gestation and l d and 4 wk after parturition (weaning). Reference values (mean, standard deviation, minimum, maximum) for serum folates, vitamin B12, vitamin B6 metabolites (pyridoxal and pyridoxal-5-phosphate), calcium, phosphorus, sodium, zinc, copper and iron, as well as blood hemoglobin and packed cell volume are reported for each studied time. Differences between parities and between each time are also reported. Results from the present report demonstrate that knowledge of the physiological state of the sows is critical for the assessment of nutritional status of an individual or a breeding herd by interpretation of analyses of blood constituents.

Assessment of mammary gland metabolism in the sow. III. Cellular metabolites in the mammary secretion and plasma following weaning

The concentrations of lactose, glucose, glucose 6-phosphate, glucose 1-phosphate, UDPglucose, UDPgalactose, UDP, UMP, inorganic phosphate, ADP and AMP (metabolites involved in the lactose synthesis pathway), and cAMP, galactose and sodium were measured in the mammary secretion from four or five mammary glands on each of six sows during the first 5 d post weaning. The concentrations of lactose, glucose and galactose were also measured in plasma during this time. Following weaning, the rapid increase in the concentrations of glucose 6-phosphate and UDPgalactose suggested that the rate of lactose synthesis was regulated by the inhibition of hexokinase and/or lactose synthase, while the decrease in glucose and AMP indicated a subsequent decline in glucose and ATP utilization. The rapid increase in glucose 6-phosphate which plays a pivotal role as a substrate for both lactose and de novo fatty acid synthesis, and the rapid decrease in AMP which reflects ATP utilization, were good markers of decreased metabolic activity. These rapid changes in the metabolic activity of the mammary glands were not observed in a second weaning study when two piglets were removed from selected mammary glands for periods up to 5 h during established lactation. Since concentrations of lactogenic hormones remain elevated following partial weaning, but fall following total weaning (Rojkittikhun et al. 1991), these differences in mammary gland metabolism indicate that endocrine rather than autocrine mechanisms are controlling lactose and fat synthesis during the initial stages of total weaning.

Assessment of mammary gland metabolism in the sow. II. Cellular metabolites in the mammary secretion and plasma during lactogenesis II

The concentrations of lactose, glucose, glucose 6-phosphate, glucose 1-phosphate, UDPglucose, UDPgalactose, UDP, UMP, inorganic phosphate, ADP and AMP (metabolites involved in the lactose synthesis pathway), and cAMP, galactose and fructose were measured in the mammary secretion from sucked (n = 9) and unsucked (n = 4) mammary glands of nine sows during the first 5 d post partum. The concentrations of lactose, glucose, galactose and fructose were also measured in plasma during this time. The progressive increase in the concentration of lactose, and changes in the concentrations of cellular metabolites in the mammary secretion from sucked glands were consistent with an increase in the metabolic activity of those glands during lactogenesis II. In contrast, unsucked glands showed a progressive decrease in the concentration of lactose, while the concentrations of cellular metabolites in the milk generally remained unchanged. These results indicated that there was no increase in the metabolic activity of unsucked glands (no increase in lactose synthesis or utilization of glucose and ATP) and that the rate of lactose synthesis prior to milk removal was limited by the availability of glucose and/or UDPgalactose. Therefore, the removal of colostrum from the mammary gland was necessary for an increase in the rate of lactose synthesis (and probably de novo fatty acid synthesis) and implies that autocrine mechanisms are operating to control the rate of milk synthesis during lactogenesis in the sow. The low concentration of glucose in colostrum compared with that in plasma is discussed in view of the paracellular pathway.

Milk whey proteins in plasma of sows: variation with physiological state

The whey proteins alpha-lactalbumin and beta-lactoglobulin have been investigated as potential markers of mammary development in sows by measuring their concentrations in plasma. The whey proteins were isolated from porcine milk by gel filtration, ion-exchange and hydrophobic interaction chromatography, characterized by several criteria and used to raise antibodies. Specific radioimmunoassays were set up for porcine alpha-lactalbumin and beta-lactoglobulin and validated for use in porcine blood and milk. Plasma levels of the whey proteins were measured in sows that were pregnant, suckling litters post partum, weaned abruptly at birth or were pregnant but mastectomized. Both whey proteins showed similar patterns in plasma post partum, falling from a maximum 1 d after parturition to values < 0.02% those in milk by day 4-5 post partum in suckling sows and showing a transient peak associated with early involution before declining to very low concentrations in non-suckling sows. alpha-Lactalbumin was first detected in the last week prepartum, rising markedly in the 3 d before parturition, correlated with rising prolactin (r = 0.986) and falling progesterone (r = -0.998). beta-Lactoglobulin rose much earlier from 5 weeks prepartum, at the time when lobulo-alveolar mammary development is occurring, and correlated (r = 0.929) with oestradiol-17 beta. In mastectomized sows, concentrations of whey proteins in plasma were reduced by 90% or more when compared with intact animals, though following a similar pattern. This study shows that whey protein concentrations in plasma vary with physiological state and reflect aspects of the development of the mammary gland. The very different profiles for alpha-lactalbumin and beta-lactoglobulin prepartum indicate that they are differently controlled.

Hormonal induction of alpha-lactalbumin and beta-lactoglobulin in cultured mammary explants from pregnant pigs

Mammary tissue from pigs on days 60, 80, 90, 100 and 100+ (days 106-111) of pregnancy has been cultured in vitro as explants. The total accumulation in tissue and culture medium of the whey proteins alpha-lactalbumin and beta-lactoglobulin has been measured using specific radioimmunoassays. The control, uncultured tissue showed progressive morphological development from sparse, non-secretory epithelial tissue on day 60 to full lobulo-alveolar development with some accumulated secretion from day 100. In uncultured explants beta-lactoglobulin could be detected consistently from day 90 (13 +/- 12 ng/micrograms DNA, n = 4) and alpha-lactalbumin from day 100 (1.3 +/- 0.5 ng/micrograms DNA, n = 11). At all stages of pregnancy, both whey proteins increased markedly during the period of culture (up to 7 d). Stimulation of alpha-lactalbumin appeared to be primarily under prolactin control. Prolactin increased alpha-lactalbumin accumulation to a similar extent alone, or in the presence of insulin and/or corticosterone. The response to prolactin was dose-dependent over the range 0.4-20 nM (10-500 ng/ml). Porcine prolactin was more potent than ovine prolactin. There was no effect of porcine growth hormone and no synergism detected between prolactin and tri-iodothyronine. By contrast, no specific hormonal requirements were established for accumulation of beta-lactoglobulin, which appeared to increase in vitro if tissue remained viable in various combinations of insulin, corticosterone and prolactin. It was not stimulated by growth hormone. There was some indication of a prolactin-sensitive component in longer term cultures after day 4.

Concentration of citrate in the mammary secretion of sows during lactogenesis II and established lactation

The functional significance of citrate in the mammary secretion of six sows was investigated during the second stage of lactogenesis (lactogenesis II) and established lactation. The changes in the concentrations of progesterone and lactose in the maternal blood, and lactose, Na and K in the mammary secretion, suggested that lactogenesis II began during the final day of pregnancy. The concentration of citrate in the mammary secretion of the sows during lactogenesis II was high and varied from 5.4 (SEM 0.5) mM at day 0.5 post partum to 6.8 (SEM 0.4) mM at day 1.5 post partum. There was a decline of approximately 30% in the concentration of citrate in the milk of sows during the first week of lactation. These findings suggest that, in contrast to all other species studied previously, milk citrate is not a harbinger of lactogenesis II in the sow. However, the changes in the concentration of citrate in the mammary secretions of sows may reflect changes in the rate of de novo synthesis of fatty acids that take place in the mammary glands of sows during lactogenesis II and established lactation.

Alpha-lactalbumin in bovine serum: relationships with udder development and function

Concentrations of alpha-lactalbumin in blood from cattle in various physiological states were measured as an index of udder development and function. Included were primiparous heifers during gestation and the peripartum period, nonlactating, nonpregnant cows hormonally induced into lactation, and cows milked two or three times daily in early, middle, or late lactation. Concentrations of alpha-lactalbumin in serum increased in two phases during gestation. Initial values (7.3 ng/ml, up to 120 d prepartum) rose, then leveled at 29.9 ng/ml on d 120 to 30 prepartum. Concentrations subsequently increased, averaging 133.2 ng/ml over the 30 d prior to parturition. During the peripartum period, alpha-lactalbumin rose from 221.2 ng/ml on d 4 prepartum, peaked at calving (918.8 ng/ml), then declined, stabilizing at approximately 500 ng/ml (1.5 to 3 d postpartum). Concentrations of alpha-lactalbumin in cows induced to lactate were low on d 1 to 9 of hormone treatment (15.7 ng/ml), rose to a maximum on d 17 (803.4 ng/ml), then fell to a plateau (185.8 ng/ml) on d 21 to 25. alpha-Lactalbumin concentrations were higher in early (101.9 ng/ml) than in middle or late lactation (81.4 and 79.2 ng/ml, respectively). Concentrations were also greater in twice versus thrice milked cows (101.9 vs. 73.0 ng/ml). Changes in alpha-lactalbumin concentrations in serum are associated with developmental and functional status of the udder. The measurement provides a noninvasive method to assess mammary gland activity.

Radioimmunoassay for measurement of bovine alpha-lactalbumin in serum, milk and tissue culture media

A sensitive, specific radioimmunoassay for bovine alpha-lactalbumin (alpha-la) suitable for measurement of serum, tissue culture media and milk was developed. alpha-La was not detected in serum from prepubertal male or female cattle, but was detected as early as 60 d of gestation in nulliparous Holstein heifers, the level being greatly increased during the last one third of gestation. Serum from cross bred beef heifers contained less alpha-la and it was not detected until late gestation. Concentrations of alpha-la in serum samples from pregnant multiparous Holstein cows decreased at drying-off and subsequently increased just before parturition. Secretion of alpha-la by mammary tissue explants from steroid-primed prepubertal Holstein heifers was induced by the addition of bovine prolactin, ovine prolactin or human growth hormone to tissue culture media.

Kinetics of intravenously administered lactose in cows

Four adult Norwegian Red cows were employed in an experiment designed to study the kinetics of lactose. The cows were given 50 g or 60 g of lactose by rapid intravenous injection of a 10 % lactose solution. Blood samples were taken at different intervals after injection, and lactose concentrations in the samples determined by an enzymatic/spectrophotometric method.

The mean half-time for lactose elimination was 85.7 min, and for distribution 8.4 min. The mean apparent volume of distribution was calculated to be 0.189 1/kg, and total body clearance 1.55 ml min−1 kg−1.

There was evidence to suggest that lactose mainly is eliminated renally from its distribution volume by glomerular filtration in the cow.