Increased secretion of insulin-like growth factor I into milk of cows treated with recombinantly derived bovine growth hormone

Plasma Proteomic Profiling Reveals the Regulatory Factors of Milk Protein Synthesis in Holstein Cows

Simple Summary

We aimed to determine the plasma bio-markers of cows with high long-term milk protein concentration and investigate the mechanism of plasma proteins in milk protein synthesis. Some plasma proteins are considered to be related to milk protein synthesis. However, the characteristics of these proteins with different long-term milk protein concentrations are not fully elucidated. In this study, we collected milk protein concentration data of Holstein cows for 10 months on a commercial farm. Three groups of cows (n = 10 per group) with low, medium, and high milk protein concentrations were selected. We found that cows with high milk protein concentration had higher glucose, insulin-like growth factor 1, prolactin, insulin, and growth hormone concentrations than cows with low milk protein concentration. A total of 91 differentially expressed proteins were identified between cows with high and low milk protein concentrations by plasma proteomic. Furthermore, β-casein level and mammalian rapamycin target protein pathway in bovine mammary epithelial cells were enhanced by insulin-like growth factor 1 treatment. Our findings revealed that the differences in plasma proteins in cows with different milk protein concentrations and determined that β-casein synthesis was increased via the mammalian rapamycin target protein pathway following IGF-1 treatment in vitro.

Abstract

Milk protein concentrations in dairy cows are considered to be related to some plasma biomolecules. However, the characteristics of plasma biomolecules in dairy cows with different long-term milk protein concentrations are not fully elucidated. This study was conducted to understand the mechanism of plasma proteins in milk protein synthesis by the comparative analysis of the plasma proteomics of cows with different milk protein concentrations. Three groups of Holstein cows (per group = 10) with low (LMP), medium (MMP), and high long-term milk protein concentrations (HMP) were selected for the experiment to determine plasma hormones, biochemical parameters, and proteome. We found that HMP cows had higher concentrations of plasma insulin-like growth factor 1 (IGF-1), glucose, prolactin, insulin, and growth hormone than LMP cows. Additionally, plasma proteomic identified 91 differential proteins, including IGF-1 between the LMP and HMP groups, and the mTOR pathway was enriched. In vitro, IGF-1 treatment increased β-casein expression and simultaneously activated S6K1 and mTOR phosphorylation in bovine mammary epithelial cells. Taken together, these data demonstrate the differences in plasma hormones, biochemical parameters, and proteome of cows with different milk protein concentrations and indicate that IGF-1 enhanced milk protein synthesis, associated with activation of the mTOR signaling pathway.

Production-related contaminants (pesticides, antibiotics and hormones) in organic and conventionally produced milk samples sold in the USA

OBJECTIVE

Consumption of cow's milk, which is associated with diet and health benefits, has decreased in the USA. The simultaneous increase in demand for more costly organic milk suggests consumer concern about exposure to production-related contaminants may be contributing to this decline. We sought to determine if contaminant levels differ by the production method used.

DESIGN

Half-gallon containers of organic and conventional milk (four each) were collected by volunteers in each of nine US regions and shipped on ice for analysis. Pesticide, antibiotic and hormone (bovine growth hormone (bGH), bGH-associated insulin-like growth factor 1 (IGF-1)) residues were measured using liquid or gas chromatography coupled to mass or tandem mass spectrometry. Levels were compared against established federal limits and by production method.

SETTING

Laboratory analysis of retail milk samples.

RESULTS

Current-use pesticides (5/15 tested) and antibiotics (5/13 tested) were detected in several conventional (26-60 %; n 35) but not in organic (n 34) samples. Among the conventional samples, residue levels exceeded federal limits for amoxicillin in one sample (3 %) and in multiple samples for sulfamethazine (37 %) and sulfathiazole (26 %). Median bGH and IGF-1 concentrations in conventional milk were 9·8 and 3·5 ng/ml, respectively, twenty and three times that in organic samples (P < 0·0001).

CONCLUSIONS

Current-use antibiotics and pesticides were undetectable in organic but prevalent in conventionally produced milk samples, with multiple samples exceeding federal limits. Higher bGH and IGF-1 levels in conventional milk suggest the presence of synthetic growth hormone. Further research is needed to understand the impact of these differences, if any, on consumers.

Analysis of the IGF-system in milk from farm animals - Occurrence, regulation, and biomarker potential

IGFs and IGF-binding proteins (IGFBPs) are abundantly present in milk and in dairy products. Compared to the IGFs, the IGFBP have received less attention in milk, although truncated IGFBPs and IGFBP-glycosylation have been described in milk. Thereby, complex control of local IGF-effects can be assumed on the levels of IGFBPs, proteases, and protease inhibitors. The present review collects the current knowledge both on presence and regulation of IGFs and IGFBPs in milk particularly from dairy animal species. As a rule higher levels of IGF-I, IGF-II, and IGFBPs are measured around parturition if compared to later time-points of lactation. In all farm animal species included in this review, it is found that the relative abundancies of IGFBPs in milk and serum are similar, with IGFBP-3 and -2 characterized by higher concentrations if compared to IGFBP-4 or -5. The concentrations of IGFs and IGFBPs in milk or dairy products can be altered by hormones, dairy processing, or fermentation. Because milk can be used for non-invasive biomarker research, quality management, and health monitoring, we discuss novel directions of IGF-analysis and potential on-site biomarker research in milk.

Increased milk protein synthesis in response to exogenous growth hormone is associated with changes in mechanistic (mammalian) target of rapamycin (mTOR)C1-dependent and independent cell signaling

The objective of this study was to determine if increased milk protein synthesis observed in lactating dairy cows treated with growth hormone (GH) was associated with mechanistic (or mammalian) target of rapamycin complex 1 (mTORC1) regulation of downstream factors controlling nucleocytoplasmic export and translation of mRNA. To address this objective, biochemical indices of mammary growth and secretory activity and the abundance and phosphorylation status of mTORC1 pathway factors were measured in mammary tissues harvested from nonpregnant lactating dairy cows 6 d after treatment with a slow-release formulation of GH or saline (n=4/group). Treatment with GH increased mammary parenchymal weight and total protein content and tended to increase ribosome number and cell size, whereas protein synthetic efficiency, capacity, and cell number were unchanged. Cellular abundance of the mTORC1 components mTOR and (phosphorylated) mTOR(Ser2448) increased, as did complex eukaryotic initiation factor 4E:eukaryotic initiation factor 4E binding protein 1 (eIF4E:4EBP1), whereas no change was observed for mTORC1-downstream targets 4EBP1, 4EBP1(Ser65), p70/p85(S6K) and p70(S6K)Thre389/p85(S6K)Thre412. Changes in activation were not observed for any of the targets measured. These results indicate that GH treatment influences signaling to mTORC1 but not downstream targets involved in the nucleocytoplasmic export and translation of mRNA. Increased eIF4E:4EBP1 complex formation indicates involvement of the mitogen-activated protein kinase (MAPK) pathway. Abundance of MAPK pathway components eIF4E, eIF4E(Ser209), eIF4E:eIF4G complex, MAP kinase-interacting serine/threonine-protein kinase 1 (MKNK1), MKNK1(Thr197202), and ribosomal protein S6 kinase, 90kDa, polypeptide 1 (RPS6KA1) increased significantly in response to GH, whereas relative activation of the proteins was unchanged. Expression of IGFBP3 and IGFBP5 increased, that of IGF1R decreased, and that of IGF1 remained unchanged in response to GH. PatSearch analysis of the milk caseins αS1-casein, αS2-casein, and β-casein, MAPK signaling target RPS6KA1, and proliferation gene IGFBP3 mRNA indicated that all contained putative eIF4E-sensitivity elements. In response to GH, these genes were all upregulated, suggesting that increased abundance of eIF4E and eIF4E(Ser209) plays a role in mediating their nucleocytoplasmic export. We propose that, in response to GH, the IGF1-IGF1R-MAPK signaling cascade regulates eIF4E-mediated nucleocytoplasmic export and translation of mRNA, whereas mTOR controls cell renewal, cell turnover, and rRNA transcription through an alternative signaling cascade.

Hormone variations in serum and milk of buffaloes (Bubalus bubalis) as potential indicators of treatment with recombinant bovine somatotropin

Recombinant bovine somatotropin (rbST) is used to increase milk yield in cows, but it has been forbidden in some countries and in the EU. However, rbST misuse represents a concern in both bovine and buffalo dairy production. A number of studies on rbST treatment have been performed on bovines, but there are few data on buffaloes. In this study, we treated eight lactating buffaloes with biweekly injections of a slow-release formulation of rbST, for five cycles of administration, and analysed total ST and insulin-like growth factor 1 (IGF-1) variations in serum and IGF-1 in milk. The aim was to assess their power as potential indicators of rbST-treatment. Blood was collected on days 2, 5, 9 and 14 of each cycle, and milk on days 2, 9 and 14 of cycles 2 and 5. Results showed an extraordinary increase in ST levels on day 2 in treated animals, followed by a rapid decrease over the following days, while a significant increase in IGF-1 was observed both in serum and in milk throughout most of each cycle. These results suggest that serum ST levels are a good indicator of treatment. However, the rapid decrease after the peak limits the useful period of sample collection.

Variation in selected blood plasma constituents during the post-partum and breeding periods in dairy cows

Concentrations of insulin-like growth factor-I, albumin, beta hydroxybutyrate, glucose and urea were measured in 12 plasma samples collected over 9 weeks from mid-August from each of 40 cows in four seasonal herds which calved from mid-July. These herds comprised Jersey or Holstein-Friesian animals, with each breed grazed at two stocking rates. Daily dry matter intakes (kg dry matter/cow/day), which were estimated from pasture assessments before and after grazing, ranged from 4% (low stocked Jersey herd) to 38% (high stocked Friesian herd) below recommended intakes for each breed of cow in peak lactation. Stocking rate was associated with a 4% reduction in liveweight for cows in the high stocked herds and a 20% reduction in daily milk production (as a proportion of the low stocked herds' liveweight and milk production). Eight cows produced at least one blood sample with a beta hydroxybutyrate concentration of more than 1.0 mmol/l. There were 42% of samples with glucose concentrations greater than 4.1 mmol/l. These two concentrations were the maximum values classified as normal for these two metabolites by the Ruakura Animal Health Laboratory. No concentrations of the other metabolites were outside their respective normal ranges. Breed, age and individual animals usually had greater effects on the average metabolite concentrations than did stocking rate. The greatest effect was associated with sample day, especially for insulin-like growth factor-I and urea. A significant breed x stocking rate x sample day interaction in urea concentrations indicated that changes in the feeding value of the grazed pastures available to each herd were sufficient to produce separate fluctuating patterns in the daily average concentrations. These results showed that frequent sampling on a herd basis would be necessary to identify the significance of factors which may be contributing to sample day variation in the concentration of metabolites in the plasma of pasture-fed cows.

Promoting effects of milk on the development of 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumors in rats

To assess the effect of milk on the development of 7,12-dimethylbenz(a)anthracene (DMBA)-induced mammary tumors, 48 female Sprague-Dawley rats treated with DMBA were divided into 3 groups and given 1 of 3 test solutions for 20 weeks as their drinking liquid: milk, estrone sulfate solution or tap water. The milk group showed a significantly great incidence (75%) in tumor development compared with the water group (38%) and was comparable to the estrone sulfate group (69%). Mean tumor number per rat in the milk group was significantly higher than that in the water group (p=0.009). We classified the mammary tumors into three histological types: intraductal papilloma, fibroadenoma, and adenocarcinoma. Although the percent of intraductal papilloma and fibroadenoma was almost same among the three groups, malignant tumor was found only in the milk and estrone sulfate groups. In conclusion, our results indicate that milk as well as estrone sulfate promotes the development of DMBA-induced mammary tumors in rat and could be associated with the occurrence of adenocarcinoma.

Consumption of dairy products and the risk of breast cancer: a review of the literature

Differences in eating patterns and breast cancer rates across countries suggest that several dietary components, including dairy products, could affect breast cancer risk. However, dairy products are a diverse food group in terms of the factors that could potentially influence risk. Some dairy products, such as whole milk and many types of cheese, have a relatively high saturated fat content, which may increase risk. Moreover, milk products may contain contaminants such as pesticides, which have carcinogenic potential, and growth factors such as insulin-like growth factor I, which have been shown to promote breast cancer cell growth. In contrast, the calcium and vitamin D contents of dairy products have been hypothesized to reduce breast cancer risk. We reviewed the current epidemiologic literature on the relation between dairy product intakes and breast cancer risk, focusing primarily on the results of cohort and case-control studies. Most of the studies reviewed showed no consistent pattern of increased or decreased breast cancer risk with a high consumption of dairy products as a whole or when broken down into high-fat and low-fat dairy products, milk, cheese, or butter. Measurement error may have attenuated any modest association with dairy products. The available epidemiologic evidence does not support a strong association between the consumption of milk or other dairy products and breast cancer risk.

Lack of effect of 10 kV/m 60 Hz electric field exposure on pregnant dairy heifer hormones

Sixteen pregnant Holstein heifers weighing 521 +/- 46 kg, at 3.3 +/- 0.7 months of gestation and 2.2 +/- 2.0 months of age were confined to wooden metabolism cages and were exposed to a vertical electric field (EF) of 10.0 +/- 0.4 kV/m and an artificial light cycle of 12 h light-12 h dark. The heifers were divided into two replicates of eight each. Each replicate was divided into two groups of four animals each, one group becoming the non-exposed and the second, the EF exposed group. The exposed group were housed in metabolism cages in an area where EF were generated, and the non-exposed group, in metabolism cages located in the adjacent area where the EF was less than 2% of that present in the exposed area. The test animals were subject to the different treatments for 4 weeks continuously. After 4 weeks, the animals switched treatment, the exposed group becoming the non-exposed group and vice-versa. Then the treatment continued for 4 more weeks. Catheters were inserted into the jugular vein of the animals, and blood samples were collected on twice a week to estimate the serum concentration of progesterone (P4), melatonin (MLT), prolactin (PRL), and insulin-like growth factor-1 (IGF-1). Feed consumption was measured daily and feed samples were collected twice a week. The results indicated that exposure of dairy cattle to EF similar to those encountered directly underneath a 735 kV high tension electrical power line carrying a maximum load of current, cannot be associated with any variation in the experimental variables mentioned above. An exception to this, is the variation in MLT, which was associated with the EF exposure. Due to the inconsistency of the MLT response in the different replicates, caution should be exercised in the interpretation of this phenomenon.

Mammary blood flow does not limit milk yield in lactating goats

There is a close relationship between mammary blood flow (MBF) and milk production, but whether MBF is limiting milk yield has not been determined. Five lactating goats received close arterial (external pudic) infusion of PBS or the nitric oxide donor diethylamine NONOate (0.5 mg/h; NONate) for 6 h, according to a crossover design. Goats were hand milked (with oxytocin) every 2 h starting 2 h before and ending 6 h after the end of the infusion. In one goat, a transit time flow probe was implanted around the infused and noninfused artery, whilst in another goat a flow probe was implanted around the infused artery only. Infusion of PBS did not affect MBF or milk production. As with previous results (Lacasse et al., 1996), NONate induced a rapid increase (up to 250% of preinfusion level) in MBF in the infused gland only. Mammary blood flow was still above the preinfusion level at the end of the infusion period. Despite this increase in MBF, NONate did not affect milk production. Milk yield ratio (infused/noninfused gland) averaged 1.20, 1.12, and 1.17 for the preinfusion, infusion and post infusion periods, respectively. Similarly, protein, fat and lactose yields were not affected by PBS or NONate infusion. These results provide no support to the contention that increasing MBF can enhance milk production.

Effect of electric and magnetic fields (60 Hz) on production, and levels of growth hormone and insulin-like growth factor 1, in lactating, pregnant cows subjected to short days

Electric and magnetic fields (EMF) are generated by the transmission of electricity through high tension lines traversing rural areas. Previous studies showed increased dry matter intake (DMI) and fat corrected milk in dairy cows exposed to EMF. Because EMF exposure has been shown to suppress pineal release of melatonin in some species, it was hypothesized that EMF effects resemble those of exposure to long days. Previous studies have shown that DMI and milk production increase in dairy cattle in response to long day photoperiods, and this has been observed in association with increased circulating insulin-like growth factor 1 (IGF-1), but not growth hormone (GH). The hypothesis that EMF act by modifying the response to photoperiod was tested by subjecting dairy cows to controlled EMF exposure while keeping them under short-day conditions. Sixteen lactating, pregnant Holstein cows were exposed to a vertical electric field of 10 kV/m and a horizontal magnetic field of 30 microT in a crossover design with treatment switchback. Two groups of eight cows each were exposed to EMF for 16 h/d in either oftwo sequences. Each sequence consisted of three consecutive 28-d periods. All animals were maintained under short day conditions (8 h light, 16 h dark) during the trial. DMI and plasma IGF-1 were increased (P < 0.01) during EMF exposure (17.03 vs.16.04 kg/d, SE = 0.4; 137 +/- 6 ng/ml vs 126 +/- 6, respectively). The mean GH concentration was not affected, but a treatment x hour interaction was detected, with GH lower for the EMF exposed animals during the first 16 h of the sampling period, and higher for the last 8 h. Overall, the yield of milk or its components was not affected by EMF exposure, but milk yield was significantly higher for the exposed animals during wk 4 of treatment.

Effects of insulin, recombinant bovine somatotropin, and their interaction on insulin-like growth factor-I secretion and milk protein production in dairy cows

This trial was designed to test the effects of insulin, recombinant bovine somatotropin (rbST), and their interaction on milk protein and selected blood parameters in dairy cows. Eight Holstein cows (86 +/- 10 d in milk) were divided in two groups and used in two replicates of a Latin square design with four animals, four periods, and four treatments: 1) intravenous infusion of saline, 2) infusion of saline and subcutaneous administration of 40 mg of rbST per day, 3) intravenous infusion of 12 mg of insulin per day coupled with glucose infusion, and 4) rbST administration combined with insulin and glucose infusion. The glucose infusion rate was adjusted to maintain euglycemia. Each experimental period lasted 14 d: treatments were administered during the first 6 d, and no treatment was administered during the following 8-d resting phase. The average daily amount of glucose infusion needed to avoid hypoglycemia was 2.8 kg/cow when only insulin was infused as opposed to 2.2 kg/cow when both insulin and rbST were administered, indicating that either rbST causes a peripheral resistance to insulin or rbST increased liver gluconeogenesis or both. Data from the last 3 d of infusion were analyzed by using the SAS system for mixed models. Percent protein of milk tended to be lower (2.84 vs. 2.79%) and milk urea content was lower (16.6 vs. 14.8 mg/dl) during rbST administration, regardless of insulin infusion. Insulin infusion increased percent protein (2.78 vs. 2.85%) and percent casein (2.36 vs. 2.46%) and decreased milk urea content (17.1 vs. 14.3 mg/dl) regardless of rbST administration. For milk yield, protein yield, casein yield, lactose percent, and lactose yield, there were significant interactions between insulin and rbST administration. For example, casein yield averaged 1.17, 1.12, 1.20, and 1.28 kg/d for saline, insulin, rbST, and insulin combined with rbST, respectively. Similarly, there was a significant interaction between insulin and rbST on IGF-I levels, which were 122.5, 181.3, 342.3, and 492.2 ng/ml for saline, insulin, rbST, and insulin combined with rbST, respectively. In conclusion, these results clearly demonstrated that insulin interacts with bST in early lactation to improve milk protein synthesis and yield in dairy cows. These effects are probably mediated through a combination of bST nutrient mobilization, bST-induced gluconeogenesis, bST-induced insulin peripheral resistance, and bST/insulin synergism on insulin-like growth factor-I secretion and on mammary epithelial tissue.

Comparison of a conventional immunoassay (ELISA) with a surface plasmon resonance-based biosensor for IGF-1 detection in cows' milk

Recombinant bovine somatotropin (rBST) treatment is adopted in dairy cows to augment milk yield. Previous studies showed that insulin-like growth factor-1 (IGF-1) is present in milk from cows treated with rBST. Since IGF-1 is a suspected carcinogen, its presence in milk for human consumption is potentially a health hazard. Therefore rBST use, still authorized in the United States, has been revoked in Canada and is under evaluation in the EU. The rising attention on IGF-1 presence in alimentary milk focused the necessity to develop specific, sensitive and rapid IGF-1 detection systems. We have developed a solid phase enzyme-linked immunoassay (ELISA) and also an automated surface plasmon resonance-based biosensor system (BIA-technology) for evaluating IGF-1 in fresh cow's milk. Hyperimmune polyclonal anti-IGF-1 antibodies were characterized with respect to their specific binding capacity to IGF-1. The results obtained with these two methods have been compared. This study shows the potential usefulness of the biosensor technology for biomolecular interaction analysis. The features of this technology (fully automated, measures in real time, sharpened yes/no response) offer several advantages compared to ELISA in the detection of compounds in fresh cows' milk (MURST 40%; CNR P.F. MADESS 2).

Modulation of the inflammatory reaction and neutrophil defense of the bovine lactating mammary gland by growth hormone

This review is focused on the possible interactions of prolactin and somatotrope hormone in the modulation of inflammation of the mammary gland. Several different models are examined: Escherichia coli, Streptococcus uberis, and endotoxin mastitis. Subsequently, the release of growth hormone and insulin-like growth factor during fever and mastitis, the immunophysiological effects of GH on E. coli mastitis, S. uberis and endotoxin mastitis, the galactopoietic action of rBST on healthy and mastitis cows as well as the immunologic effects of GH on leukocytes in healthy and diseased cows are discussed. It can be concluded that the underlying regulation of the neuro-endocrine network is fundamental in the normal function of the immune system.

Presence of thyroxine deiodinases in mammary gland: possible modulation of the enzyme-deiodinating activity by somatotropin

Thyroid hormones (TH) and somatotropin (ST) play critical role in lactation. One explanation of their multiple physiological actions is based on the functional interrelationships among ST, TH, and thyroxin deiodinase (5'D). This enzyme is present in the mammary tissue, milk cellular components, and whole milk and is responsible for intramammary production of triiodothyronine (T3). In rats in which the 5'D isozymes in the mammary gland and in the liver are similarly of type I (5'D-I), an enhancement of mammary 5'D-I causes a reduction of hepatic 5'D-I activities. This opposite rearrangement in the mammary and hepatic deiodinating activities is thought to be a factor of a homeorhetic response characterized by an increased and compartmentalized energy expenditure of the mammary gland. In the cow, the mammary 5'D is the type II (5'D-II) deiodinase. The 5'D-II, owing to its high catalytic efficiency, secures T3 production, making tissues relatively independent from the circulatory levels of TH and from variations in the hepatic 5'D-I activity. No significant alterations of 5'D-II isozymes were found during a low T3 syndrome. Location of tissue deiodinases in the cow, the 5'D-II in the mammary gland, and the 5'D-I in the liver make it so that T3 production in these two tissues can be dissociated in time to secure better local requirement for T3 supporting lactation. To date, attempts to evidence that the alterations in iodothyronines blood levels and in tissues' 5'Ds activity during lactation are due to ST action have not received clear experimental support in either cows or rats.

Effect of recombinant bovine somatotropin on milk production and composition of cows with Streptococcus uberis mastitis

The protective effect of bovine somatotropin (bST) during experimental Streptococcus uberis mastitis in cows was studied. The left quarters of 10 cows were infected with 500 cfu of S. uberis O140J. Five cows were subcutaneously treated with 500 mg of recombinant bST 7 d before and after infection, and 5 control cows received the excipient. In the treated cows, total milk production significantly increased after the first and second bST treatments. After infection, milk production decreased 24 and 40% in the infected quarters, 6 and 14% in the uninfected quarters, and 15 and 28% overall for treated and control cows, respectively. In the bST group, milk production was completely restored after 3 wk, but, in the control group, total production and the production of the infected quarters remained lower than preinfection production. The increase in somatic cell count occurred earlier and more rapidly in the control group, and the return to normal values was also more rapid in these cows. The amount of bacteria in milk was higher in the control cows. Changes in milk composition, such as lactose, protein, fat, Na+, K+, and Cl-, were significantly more pronounced in the control cows. Also, clinical symptoms were more prominent in the control cows. Somatotropin protected the mammary gland from excessive production losses and compositional changes during a subsequent episode of experimentally induced Streptococcus uberis mastitis and significantly improved the normalization of production and composition, which indicates a beneficial effect on the restoration of the integrity of the blood-milk barrier.

Effect of bovine somatotropin on neutrophil functions and clinical symptoms during Streptococcus uberis mastitis

The effect of recombinant bovine somatotropin (bST) on the chemiluminescence, diapedesis, and expression of adhesion receptors (CD11a, CD11b, CD18) of isolated polymorphonuclear leukocytes was studied. The plasma concentrations of insulin-like growth factor-I (IGF-I), bST, cortisol, and alpha-lactalbumin were also monitored. In addition, general and local clinical symptoms and the differentiation of circulating leukocytes were also studied during experimentally induced Streptococcus uberis mastitis in cows. Ten cows were infected with 500 cfu of S. uberis O140J in both left quarters. Five cows were subcutaneously treated with 500 mg of recombinant bST 7 d before and after infection, and 5 control cows received the excipient. General (fever, tachycardia, inappetance, and depression) and local symptoms (swelling, pain, firmness, and flecks in milk) were more acute, severe, and longer-lasting in control cows. Treatment with bST had no effect on chemiluminescence and diapedesis of circulating polymorphonuclear leukocytes and no effect on the expression of adhesion receptors. Recombinant bST induced significantly higher IGF-I and bST concentrations in plasma. The leukopenia observed after infection was less pronounced in the bST-treated cows, and the number of circulating band neutrophils and metamyelocytes was significantly lower in the treated group. The concentration of cortisol did not differ between both groups, but the blood concentration of alpha-lactalbumin significantly increased in both groups from 6 d after infection. These results showed that treatment with recombinant bST improves animal welfare by protecting the cows from severe local and general clinical symptoms during subsequent S. uberis mastitis, but that it has no effect on chemiluminescence, diapedesis, and the expression of adhesion receptors of circulating polymorphonuclear leukocytes.

The effect of bovine somatotropin and diet on somatotropin binding sites in hepatic tissue of lactating dairy cows

In the lactating cow, galactopoiesis is stimulated by treatment with recombinant bovine somatotropin (bST) and by an improved plane of nutrition. The present study determined the interaction between these variables and examined whether a positive galactopoietic effect was accompanied by a change in hepatic binding sites for bST. Lactating dairy cows received one of three diets with increasing nutrient density; diet 1, 150 g/kg of dry matter (DM) of crude protein (CP) and 10.5 MJ/kg of DM of metabolizable energy; diet 2, 170 g/kg of DM of CP and 11.3 MJ/kg of DM of metabolizable energy; and diet 3, 190 g/kg of DM of CP and 12.1 MJ/kg of DM of metabolizable energy. At 90 d after calving, half of the cows in each dietary group were treated with bST every 14 d for the rest of the lactation. Both nutrient density and administration of bST increased milk yield significantly in mid and late lactation; there was no significant treatment by diet interaction. Treatment with bST significantly increased plasma concentrations of insulin-like growth factor (IGF)-I compared with IGF-I concentrations in controls in both mid and late lactation. Comparisons within diet revealed that concentrations of IGF-I were significantly higher in cows fed diet 3 than in cows fed diets 1 and 2 at both stages of lactation. Increases in plasma insulin were confined to cows in late lactation, and no changes were observed for nonesterified fatty acids. Liver biopsies showed that concentrations of hepatic binding sites for bST were not affected significantly by bST treatment but were increased in midlactation for cows fed diet 3. Concentration of hepatic binding sites per unit weight of tissue were greater for cows in midlactation than for cows in late lactation. In summary, exogenous bST treatment and increased nutrient density were associated with elevated plasma IGF-I concentrations and increased milk yield; however, only nutrient density in midlactation increased the number of hepatic binding sites for bST. Exogenous bST treatment had relatively little effect on the concentration of hepatic bST receptors compared with nutrient density.

Dairy products and breast cancer: the IGF-I, estrogen, and bGH hypothesis

Research on the role of dietary factors in breast cancer causation has focused predominantly on fat intake. While some studies have examined associations between breast cancer rates and consumption of whole milk, there has been less attention given to dairy products in general. Dairy products contain both hormones and growth factors, in addition to fat and various chemical contaminants, that have been implicated in the proliferation of human breast cancer cells. This literature review evaluates the epidemiological and mechanistic evidence linking dairy consumption with breast cancer risk.

Effects on nutrient and hormonal profile of long-term infusions of glucose or insulin plus glucose in cows treated with recombinant bovine somatotropin before peak milk yield

Ten Holstein cows were treated with 30.9 mg.d-1 of recombinant bST from 15 to 41 d of lactation. The Latin square design included three infusion periods of 6 d each with 3 d of rest between infusion periods. Infusions were physiological saline, glucose (50 g.h-1), and insulin plus glucose (12.5 IU.h-1 + 50 g.h-1). Blood was collected continuously during the last 24 h of each infusion period. Statistical analyses of data for energy balance, milk yield, and DMI were performed on the last 3 d of each infusion period. Production data before and after infusions (i.e., no recombinant bST) estimated that recombinant bST increased milk yield of cows infused with glucose and saline by 3.1 and 3.6 kg.d-1, respectively. Net energy intake was not affected by infusion, but glucose infusion resulted in higher BW loss than did saline infusion (2.33 vs. 0.08 kg.d-1, respectively), and insulin plus glucose infusion resulted in BW gain (0.65 kg.d-1). Milk yield was 39.9, 39.6, and 37.6 kg.d-1 for cows infused with saline, glucose, and insulin plus glucose, respectively. The insulin plus glucose infusion increased milk protein 11 and 14% compared with response to saline and glucose infusions, respectively; no change occurred in the proportion of casein and whey proteins. Serum bST was increased 109% with exogenous recombinant bST. Serum IGF-I was lower for cows infused with glucose than for those infused with saline (21.03 vs. 27.44 ng.ml-1) and increased to 46.55 ng.ml-1 for cows infused with insulin plus glucose. Serum concentrations of insulin and glucose were 13.7 and 56.7, 18.5 and 61.9, and 30.5 muIU.ml-1 and 39.4 mg.dl-1 for cows infused with saline, glucose, and insulin plus glucose, respectively. The results of this study suggest that low concentrations of plasma insulin in early lactation may limit the IGF-I response to recombinant bST (uncoupling). Despite higher IGF-I, milk yield was lower, probably as a result of low blood glucose. These results suggest that, in early lactation, insulin is still anabolic because the BW gain of cows increased. However, milk yield was still higher than that for cows in late lactation with similar insulin concentrations.

Insulin-like growth factors in milk and mammary gland

Milk contains insulin-like growth factor I and II (IGF-I and IGF-II) and four IGF binding proteins (IGFBP). Their concentrations are highest prepartum and early postpartum, coinciding with maximal proliferation of mammary cells and the time when the infant gut is the least developed. This has lead to the suggestion that IGFs may be important for the growth and development of the mammary gland and that IGFs in milk play a role in promoting development of the gastrointestinal tract of the newborn. IGF-I and, to a lesser extent, IGF-II can stimulate milk yield and blood flow in goats when infused directly into the mammary gland, suggesting they may also be important in supporting established lactation. Thus IGFs may have a dual function in the mammary gland, establishing and maintaining the maternal mammary system and, once secreted into milk, supporting gastrointestinal development in the newborn.

Unlabeled milk from cows treated with biosynthetic growth hormones: a case of regulatory abdication

Levels of insulin-like growth factor-1 (IGF-1) are substantially elevated and more bioactive in the milk of cows hyperstimulated with the biosynthetic bovine growth hormones rBGH, and are further increased by pasteurization. IGF-1 is absorbed from the gastrointestinal tract, as evidenced by marked growth-promoting effects even in short-term tests in mature rats, and absorption is likely to be still higher in infants. Converging lines of evidence incriminate IGF-1 in rBGH milk as a potential risk factor for both breast and gastrointestinal cancers.

Effect of milking frequency and somatotropin on the activity of plasminogen activator, plasminogen, and plasmin in bovine milk

Six pairs of identical twin cows during late lactation (213 d) were used to study the effect of milking frequency (twice vs. once daily) and bST during once daily milking on the activity of plasminogen activator, plasminogen, and plasmin in milk. Less frequent milking increased the activity of plasminogen, plasmin, and plasminogen activator in milk. The ratio of plasminogen to plasmin, a measure that is independent of milk volume, decreased during less frequent milking, suggesting that at least part of the increase in activity of plasmin was due to the accelerated conversion of plasminogen to plasmin. Changes in the activity of plasminogen and plasmin in milk were positively correlated with increases in the concentrations of milk BSA and plasma lactose, both of which are indicators of disruption of tight junctions between mammary epithelial cells, indicating that paracellular leakage may have contributed to increased protease activity in milk during less frequent milking. No correlation existed between changes in plasminogen activator and indicators of tight junction disruption, suggesting that increased activity of plasminogen activator in milk was not due to leakage across the mammary epithelium, but rather to increased local production in the mammary gland. Administration of bST during once daily milking did not significantly affect milk protease activity.

Somatotropin and insulin-like growth factor-I concentrations in plasma and milk after daily or sustained-release exogenous somatotropin administrations

Effects of daily injectable or sustained-release bovine somatotropin (bST) administrations on plasma and milk bST and insulin-like growth factor-I (IGF-I) concentrations were monitored in 74 lactating cows through early, mid- and late lactation. Treatments beginning at wk 4 of lactation were excipient (CO, 24 cows) at 2 wk intervals, daily injections of 10.3 mg bST (DI, 25 cows) and 350 mg sustained-release bST at 2 wk intervals (SR, 25 cows). The duration of treatments was 40 wk. Data were first analyzed for the overall mean concentrations covering the 40 wk treatment period. Overall mean plasma bST, milk bST and plasma IGF-I concentrations were significantly increased by both bST treatments (p < 0.05). On the other hand, milk IGF-I concentrations were significantly increased (p < 0.05) only in the DI group. Next, data were analyzed according to stage of lactation. The bST treatments resulted in significant increases (p < 0.05) in plasma and milk bST concentrations for all early, mid- and late lactation periods. Even though plasma IGF-I concentrations were higher (p < 0.05) in all lactation periods for bST treatment groups, higher milk IGF-I concentrations (p < 0.05) occurred only in mid- and late lactation periods for the DI group. The patterns of bST and IGF-I concentrations in milk follows those of the plasma after bST treatments.

Recombinant bovine and porcine somatotropin: safety and benefits of these biotechnologies

This article reviews the literature about the safety and benefits of two recombinantly derived proteins, bovine somatotropin (bST) and porcine somatotropin (pST), that likely will be used in animal agriculture in the future. When administered to dairy cows, bST increases milk production per cow approximately 15% to 20% and improves productive efficiency approximately 10%. Administration of pST to growing pigs reduces carcass fat content by as much as 70% to 80% and improves productive efficiency 15% to 35%. Because meat is a major source of total fat and saturated fatty acids in the diets of human beings, pST will allow consumers to include leaner, more nutrient-dense pork in their diets and still meet current dietary guidelines. Although these biotechnologies have not yet received regulatory approval from the Food and Drug Administration (FDA) for commercial use, information published by the FDA, the National Institutes of Health, the US Congress Office of Technology Assessment, and the American Academy of Pediatrics, as well as an extensive body of scientific evidence, indicate that these products are safe for the consumer. Nonetheless, it is important that consumers understand the benefits and safety of these biotechnologies. Dietitians can play an important role in providing information to consumers about the safety and benefits of bST and pST.

Factors affecting insulin-like growth factor-I concentration in bovine milk

To establish the naturally occurring range of insulin-like growth factor-I concentrations in bovine milk, samples from individual cows (n = 409) managed on five Missouri dairy herds were assayed. Parity, stage of lactation, and farm affected milk insulin-like growth factor-I concentration. Milk insulin-like growth factor-I concentration was higher in early lactation than mid and late lactation with concentrations in multiparous cows exceeding those in primiparous cows. Insulin-like growth factor-I concentration was negatively correlated to milk production the day of sample collection (r = -.15) and not correlated to predicted 305-d milk yields. Unprocessed bulk tank milk samples (n = 100) from a commercial processing plant had a mean concentration of insulin-like growth factor-I in milk of 4.32 ng/ml with a range of 1.27 to 8.10 ng/ml. This distribution was similar to the range detected in samples from individual cows, but values were lower than those reported for human milk. Concentration of insulin-like growth factor-I in milk was not altered by pasteurization (at 79 degrees C for 45 s). However, insulin-like growth factor-I was undetectable in milk heated to temperatures (121 degrees C for 5 min) required for infant formula preparation or in commercially available infant formula. These data indicated that insulin-like growth factor-I is a normal but quantitatively variable component of bovine milk that is not destroyed by pasteurization but is undetectable in infant formula. Concentration of insulin-like growth factor-I in bovine milk is lower than concentrations reported for human milk yet similar to those reported for human saliva.(ABSTRACT TRUNCATED AT 250 WORDS)

Control of growth and differentiation of the mammary gland by growth factors

Mammary gland development is a complex process regulated by various steroid and polypeptide hormones. Although the systemic importance of hormones, such as estrogen, progesterone, prolactin, and growth hormone, in the growth of the mammary gland has been well documented, these hormones are virtually incapable of stimulating mammary cell growth in vitro. Thus, the growth stimuli for mammary cells requires clarification. In recent years, a number of growth factors have been discovered; this has prompted interest in examining possible involvement of these biologically active agents in the process of mammary gland development. Results presented herein indicate that several growth factors including epidermal growth factor, transforming growth factor alpha and beta, basic fibroblast growth factor, insulin-like growth factor-I, and mesenchyme-derived growth factor participate in the regulation of mammary cell growth and differentiation.

Changes in concentrations of insulin-like growth factor 1, insulin and growth hormone in bovine mammary gland secretion ante and post partum

Concentrations of insulin-like growth factor 1 (IGF-1), insulin and growth hormone were measured in the secretion of the bovine mammary gland from day 70 ante partum until 6 d post partum. Highest levels were found during the last 2 weeks ante partum followed by a rapid decrease during the first milkings post partum. The association of IGF-1 with its binding proteins in milk was analysed and striking differences were found in the distribution of bound and free IGF-1. IGF-1 appeared mainly in the bound form (91%) at days 40-2 ante partum. Free IGF-1 preponderated in the first milkings post partum (73%) and changed again to about 85% in the bound form after day 4 post partum. A slightly acidic pH (6.3) of the secretion was correlated with high amounts of free IGF-1. Gel filtration experiments revealed a possible pH-dependent mechanism for the binding of IGF-1 to its binding proteins in milk.

bSTH and IGF-I levels in blood and milk of black and white dairy cows before and after application of recombinantly derived bovine somatotropin

In an 8 week trial period six black and white dairy cows were injected with Optiflex, a slow release formulation of recombinantly derived bovine somatotropin (BST). Three cows each were injected at two-weeks (BST-14) or four weeks (BST-28) intervals. The dosage was 640 mg BST per injection. Average milk yield increased by 18.3% and 13.8% in groups BST-14 and BST-28 respectively. Blood plasma levels of bSTH and IGF-I increased till day 10 post-injection; thereafter they declined, except IGF-I levels in group BST-14 which persisted continuously elevated with minor variations. No bSTH above detection level could be assayed in the milk of treated animals. The IGF-I level in milk was slightly elevated after BST-application but stayed within the normal range.