Craig R. Baumrucker

Membranes of mammary gland. X. Adenosine triphosphate dependent calcium accumulation by Golgi apparatus rich fractions from bovine mammary gland.

Abstract Golgi apparatus rich fractions from lactating bovine mammary gland had an Mg 2+ -dependent, Ca 2+ -stimulated adenosine triphosphatase. These Golgi apparatus fractions also accumulated Ca 2+ in vitro. Accumulation of Ca 2+ required ATP and could be abolished by treatment either with low concentrations of deoxycholate followed by ultrasound, or by heating at 100 °C for 10 min. The adenosine triphosphatase activity of Golgi apparatus was strongly stimulated by low concentrations of Ca 2+ and moderately stimulated by high concentrations of K + . This activity was unaffected by Na + and was not inhibited by ouabain. The pH optimum for the Mg 2+ -dependent hydrolysis of ATP was 7.5, the K m was 5 × 10 −5 M and the activation energy was 6 000 calories/mole. This Mg 2+ -dependent adenosine triphosphatase activity was also found in rough endoplasmic reticulum, smooth microsomes and milk fat globule membrane, the latter membrane being derived directly from the apical plasma membrane. All of these membrane fractions had the ability to specifically accumulate Ca 2+ . Specific accumulation was highest with smooth microsomes and lowest with milk fat globule membrane with Golgi apparatus and rough endoplasmic reticulum being intermediate. These observations provide one plausible explanation for intracellular Ca 2+ accumulation and secretion into milk. Further, these results help explain the ultrastructural observations of casein micelle formation in secretory vesicles elaborated by Golgi apparatus.

Colostral and milk insulin-like growth factors and related substances: mammary gland and neonatal (intestinal and systemic) targets.

The identification of hormones and regulatory factors in colostrum and milk has led to intensive investigations on their roles in the development and maintenance of the mammary and neonatal tissues. Insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) in transgenic mice influence mammary biology gland towards the end of lactation. In the bovine, IGFBP-3 is the major IGFBP in mammary secretions. In addition to binding IGFs, IGFBP-3 also binds to lactoferrin (Lf). Secreted IGFBP-3 re-enters mammary epithelial cells and with the presence of a nuclear localization sequence, IGFBP-3 and Lf enter the nucleus. Nuclear IGFBP-3 affects apoptotic signaling through the retinoic-x-receptors, while Lf affects apoptotic events through unknown mechanisms. Such interactions likely influence mammary development and involution. Furthermore, ingested colostral bioactive factors can exert regulatory functions in neonates. Intestinal receptors for IGFs and insulin are modified by age and/or diet. Feeding IGF-I had no effect, but colostrum extracts had small intestinal effects (stimulation of proliferation and villus size), suggesting that several factors, rather than one single bioactive factor were responsible. Systemic changes of metabolic and endocrine profiles in neonates depend on composition, amounts, time and duration of feeding colostrum. Early postnatal colostrum intake is not only important for the provision and absorption of immunoglobulins. Thus, in neonatal calves the lack of colostrum intake during the first 24h after birth results in a low immunoglobulin G, beta-carotene and Vitamin A status that persists for weeks and plasma patterns of fatty acids, essential amino acids and the glutamine/glutamate ratios are affected. In calves oral administration of IGF-I had no and feeding of colostrum whey extracts had only minor effects on metabolic and endocrine traits. Thus, mammary secretions influence regulatory functions of mammary and neonatal tissues.

Insulin-Like Growth Factor (IGF) System in the Bovine Mammary Gland and Milk

Primary bovine mammary cells express the two IGF receptors (IGF-IR, IGF-IIR),4 insulinreceptor, and four IGFBPs (IGFBP-2, -3, -4, and -5). Examination of the IGF-IR during themammary gland lactation cycle shows that IGF-IR number declines at parturition, a changethat coincides with decreases in the blood level of its ligand, IGF-I. IGF-II and IGF-IIR arelargely unchanged. IGFBP-3 is the predominant mammary IGFBP and its concentration alsodeclines in blood and milk during lactation compared to prepartum and involution periods.Time of lactation and pregnancy were the main determinants of milk but not bloodIGFBP-3 levels. IGFBP-3 binds to membrane proteins of bovine mammary tissue; an IGFBP-3 bindingprotein has been identified as bovine lactoferrin. Lactoferrin has the capacity to compete withIGF binding to IGFBP-3. Appearance of both IGFBP-3 and lactoferrin in conditioned mediaof primary cultures of bovine mammary cells was stimulated by all trans retinoic acid (atRA).Furthermore, atRA was necessary for the entry of exogenously added lactoferrin into themammary cell nucleus, while IGFBP-3 entry into the nuclei of atRA treated cells requiredthe presence of lactoferrin. These findings reveal a novel role for lactoferrin, suggesting thatlactoferrin is critically involved in the regulation of the IGF system during the involution period.

Insulin-Like Growth Factors (IGFs), IGF Binding Proteins, and Other Endocrine Factors in Milk: Role in the Newborn

The role of colostrum and milk in the neonate has been chiefly recognized as a comprehensive nutrient foodstuff. In addition, the provision of colostrum-the first milk-for early immune capacity has been well documented for several species. Colostrum is additionally a rich and concentrated source of various factors that demonstrate biological activity in vitro. Three hypotheses have been proposed for the phenotypic function of these secreted bioactive components: (1) only mammary disposal, (2) mammary cell regulation, and (3) neonatal function [gastrointestinal tract (GIT) or systemic]. Traditionally, it was assumed that the development of the GIT is preprogrammed and not influenced by events occurring in the intestinal lumen. However, a large volume of research has demonstrated that colostrum (or milk-borne) bioactive components can basically contribute to the regulation of GIT growth and differentiation, while their role in postnatal development at physiological concentrations has remained elusive. Much of our current understanding is derived from cell culture and laboratory animals, but experimentation with agriculturally important species is taking place. This chapter provides an overview of work conducted primarily in neonatal calves and secondarily in other species on the effects on neonates of selected peptide endocrine factors (hormones, growth factors, in part cytokines) in colostrum. The primary focus will be on insulin-like growth factors (IGFs) and IGF binding proteins (IGFBPs) and other bioactive peptides, but new interest and concern about steroids (especially estrogens) in milk are considered as well.

Relationship of Inflammatory Cytokines, Growth Hormone, and Insulin-Like Growth Factor-I to Reduced Performance During Infectious Disease

Abstract Production of inflammatory cytokines and concentrations of growth hormone and insulin-like growth factor-I (IGF-I) were studied during experimental Escherichia coli mastitis to determine their potential involvement in reduced animal performance during infectious disease. During the first 10 to 14 hr after intramammary infusion of E. coli, bacteria multiplied to maximum levels of 104-109 cfu/ml of milk with no clinical signs of mastitis. A rapid and intense inflammatory response, characterized by udder swelling, increased bovine serum albumin (BSA) and somatic cell count (SCC) in milk of infected glands, and elevated rectal temperature and serum cortisol concentration, began at approximately 12 hr after challenge. Lactational performance was reduced greatly at 24 hr, and the maximal decrease averaged 76% and 63% among infected and uninfected glands, respectively, of challenged cows; three cows became temporarily agalactic in all glands. By 6 days, all cows had nearly or completely eliminated the E. coli, and milk production had partially recovered. Milk composition showed an initial decrease in fat percentage followed by an increase thereafter. Protein percentage was increased and lactose content was reduced during most of the mastitic episode. High concentrations of tumor necrosis factor (TNF) and interleukin-1 (IL-1) were detected in milk of infected glands, and their appearance preceded or coincided with development of the mammary inflammation, systemic reaction, and hypogalactia. Serum growth hormone concentration was higher among challenged cows, whereas serum IGF-I concentrations changed little during the mastitic episode. Concentrations of IGF-I in milk whey increased from 5.0 to 12.2 ng/ml among infected glands and from 4.4 to 8.5 ng/ml among contralateral, uninfected glands; IGF binding proteins also increased in the milk of infected glands. These data demonstrate that (I) reduced lactational performance is not caused by reduced concentrations of growth hormone or IGF-I and (II) inflammatory cytokines are produced at a time consistent with a possible role in the inhibition of milk synthesis.

Colostrogenesis: Mass transfer of immunoglobulin G1 into colostrum

Bovine IgG(1) is thought to be specifically transported by a process of transcytosis across the mammary epithelial cells during colostrogenesis. Mammary IgG(1) appearance in cow colostrum has typically been reported as a concentration and shows IgG(1) concentration to be extremely variable because of animal variation, colostrum milking time, and water dilution effects. To identify animal IgG(1) transfer capacity and separate it from the other effects, our objective was to determine first colostrum IgG(1) total mass. We collected 214 samples of totally milked first colostrum with recorded colostrum weights from 11 Pennsylvania dairy farms that participated in Pennsylvania Dairy Herd Improvement Association, analyzed colostrum for IgG(1) by ELISA, and calculated total IgG(1) mass. Median and mean concentrations of IgG(1) were 29.4 mg/mL and 37.5+/-30.2 mg/mL, respectively, with a range of 9 to 166 mg/mL. However, total mass of IgG(1) had a median of 209.1g, mean of 291.6+/-315.8 g, and a range of 14 to 2,223 g. Colostrum IgG(1) concentration showed no relationship with colostrum volume, but IgG(1) mass had a positive relationship with volume. Colostrum IgG(1) mass was related to IgG(1) concentration (R(2)=0.58). Using DHIA records for 196 animals, we established milk production for these animals to a 15-d equivalent. An established milk secretion relationship to mammary parenchyma tissue (secretory tissue) was calculated and showed no relationship of IgG(1) mass with mammary parenchyma tissue. In addition, we show that approximately 10% of the sampled animals had IgG(1) mass greater than 1 standard deviation above the mean (high mass transfer) and represented all parities tested (1-7). Whereas first-lactation animals showed less overall calculated parenchyma tissue when compared with other parities, approximately 10% of the first-lactation group animals were capable of high mass transfer, with one transporting 2,029 g into first colostrum. Concentration variance of IgG(1) can be attributed to water inclusion, whereas mass transfer provides a clear indication of animal IgG(1) transfer capacity. The specific mechanism of bovine mammary IgG(1) transfer is not clear, but secretory tissue mass does not explain the variation observed. We hypothesize that the animal variation is attributable to endocrine regulation or genetic variation of the transporter(s).

Signal Relay by Retinoic Acid Receptors α and β in the Retinoic Acid-induced Expression of Insulin-like Growth Factor-binding Protein-3 in Breast Cancer Cells

Neither retinoic acid receptor-β (RARβ) nor insulin-like growth factor-binding protein-3 (IGFBP-3) is expressed in breast cancer cell line MCF-7. The expression of both proteins can be induced in response to all-trans-retinoic acid (atRA). By using an RARα-selective antagonist (Ro 41-5253), we demonstrated that RARβ expression was induced by atRA through an RARα-dependent signaling pathway and that RARβ induction was correlated with IGFBP-3 induction. However, MCF-7 cells transfected with sense RARβ cDNA expressed IGFBP-3 even in the presence of the RARα-selective antagonist Ro 41-5253. On the other hand, antisense RARβ cDNA transfection of MCF-7 cells blocked atRA-induced IGFBP-3 expression, indicating that RARβ is directly involved in the mediation of IGFBP-3 induction by atRA. Induction of IGFBP-3 expression by atRA occurs at the transcriptional level, as measured by nuclear run-on assays. Finally, we showed that atRA-induced IGFBP-3 is functionally active in modulating the growth-promoting effect of IGF-I. These experiments indicate that RARα and RARβ, both individually and together, are important in mammary gland homeostasis and breast cancer development. By linking IGFBP-3 to RARβ, our experiments define the signal intersection between the retinoid and IGF systems in cell growth regulation and explain why loss of RARβ might be critical in breast cancer carcinogenesis/progression.

Short communication: Heritability of gross feed efficiency and associations with yield, intake, residual intake, body weight, and body condition score in 11 commercial Pennsylvania tie stalls

The objectives of this study were to calculate the heritability of feed efficiency and residual feed intake, and examine the relationships between feed efficiency and other traits of productive and economic importance. Intake and body measurement data were collected monthly on 970 cows in 11 tie-stall herds for 6 consecutive mo. Measures of efficiency for this study were: dry matter intake efficiency (DMIE), defined as 305-d fat-corrected milk (FCM)/305-d DMI, net energy for lactation efficiency (NELE), defined as 305-d FCM/05-d NEL intake, and crude protein efficiency (CPE), defined as 305-d true protein yield/305-d CP intake. Residual feed intake (RFI) was calculated by regressing daily DMI on daily milk, fat, and protein yields, body weight (BW), daily body condition score (BCS) gain or loss, the interaction between BW and BCS gain or loss, and days in milk (DIM). Data were analyzed with 3- and 4-trait animal models and included 305-d FCM or protein yield, DM, NEL, or CP intake, BW, BCS, BCS change between DIM 1 and 60, milk urea nitrogen, somatic cell score, RFI, or an alternative efficiency measure. Data were analyzed with and without significant covariates for BCS and BCS change between DIM 1 and 60. The average DMIE, NELE, and CPE were 1.61, 0.98, and 0.32, respectively. Heritability of gross feed efficiency was 0.14 for DMIE, 0.18 for NELE, and 0.21 for CPE, and heritability of RFI was 0.01. Body weight and BCS had high and negative correlations with the efficiency traits (-0.64 to -0.70), indicating that larger and fatter cows were less feed efficient than smaller and thinner cows. When BCS covariates were included in the model, cows identified as being highly efficient produced 2.3 kg/d less FCM in early lactation due to less early lactation loss of BCS. Results from this study suggest that selection for higher yield and lower BW will increase feed efficiency, and that body tissue mobilization should be considered.

Genetic parameters of feed intake, production, body weight, body condition score, and selected type traits of Holstein cows in commercial tie-stall barns.

The objectives of this study were to determine the feasibility of measuring feed intake in commercial tie-stall dairies and infer genetic parameters of feed intake, yield, somatic cell score, milk urea nitrogen, body weight (BW), body condition score (BCS), and linear type traits of Holstein cows. Feed intake, BW, and BCS were measured on 970 cows in 11 Pennsylvania tie-stall herds. Historical test-day data from these cows and 739 herdmates who were contemporaries during earlier lactations were also included. Feed intake was measured by researchers once per month over a 24-h period within 7 d of 6 consecutive Dairy Herd Information test days. Feed samples from each farm were collected monthly on the same day that feed intake was measured and were used to calculate intakes of dry matter, crude protein, and net energy of lactation. Test-day records were analyzed with multiple-trait animal models, and 305-d fat-corrected milk yield, dry matter intake, crude protein intake, net energy of lactation intake, average BW, and average BCS were derived from the test-day models. The 305-d traits were also analyzed with multiple-trait animal models that included a prediction of 40-wk dry matter intake derived from National Research Council equations. Heritability estimates for 305-d intake of dry matter, crude protein, and net energy of lactation ranged from 0.15 to 0.18. Genetic correlations of predicted dry matter intake with 305-d dry matter, crude protein, and net energy of lactation intake were 0.84, 0.90, and 0.94, respectively. Genetic correlations among the 3 intake traits and fat-corrected milk yield, BW, and stature were moderate to high (0.52 to 0.63). Results indicate that feed intake measured in commercial tie-stalls once per month has sufficient accuracy to enable genetic research. High-producing and larger cows were genetically inclined to have higher feed intake. The genetic correlation between observed and predicted intakes was less than unity, indicating potential variation in feed efficiency.

Secretion of insulin-like growth factors in milk and their effect on the neonate

Abstract Many hormones and growth factors appear in milk and colostrum. Interest and research concerning these factors has recently been revitalized to study their role in both mammary and neonatal development. Colostrum is rich in insulin-like growth factor-I (IGF-I), IGF-II and IGF binding proteins (IGFBPs). The appearance of IGFs in colostrum is specific and the pattern of appearance is similar to that of immunoglobulins. Blood concentrations of IGF-I are significantly altered by the cessation and initiation of lactation. Increasing blood IGF-I concentrations by somatotropin treatment results in increased mass appearance of IGF-I into colostrum during the prepartum period with only modest increases at parturition. Because local production of IGF-I is low and not epithelial in origin, and because blood flux has been demonstrated, it is likely that most colostrum IGF-I is of blood origin. Conversely, mammary tissue epithelial cells synthesize and secrete IGFBPs. Peak secretory IGF-I and IGFBP colostrum concentrations are 10–30-fold that of blood concentrations. Two possible mechanisms of appearance are described. Because of the occurrence of IGFs in colostrum, the dietary effects of IGF-I on the newborn were of interest. Both intestinal and systemic changes were hypothesized. Calves were fed dietary treatments of: (1) milk replacer (MR), (2) pooled colostrum for four feedings, followed by MR, and (3) MR supplemented with 750 ng/ml of recombinant human (rh) IGF-I for one week. The dietary treatments had no effect on circulating neonate IGFBP profiles, yet IGFBPs changed with neonate age. Blood insulin and prolactin concentrations, but not IGF-I were altered initially. A latent increase in blood IGF-I concentrations in IGF-I-fed animals appeared after 4 to 5 days of feeding. At slaughter, there was more growth in intestinal proximal regions in rhIGF-I-fedanimals than in the colostrum-fed controls. Thermodynamic analysis of the IGF type I and II receptors of intestinal mucosal microsomes indicated that IGF-I feeding up-regulated (increased binding capacity) the type I IGF receptor, whereas dietary colostrum down-regulated the type II IGF receptor. These data support the concept of a physiological effect of colostrum-borne IGFs on the neonate.