Changes in hormones, metabolites, and milk after treatment with sometribove (recombinant methionyl bST) in Deutsches Fleckvieh and German black and white cows

The Promise and Challenges of Determining Recombinant Bovine Growth Hormone in Milk

Recombinant bovine growth hormone (rbGH) is produced in large quantities and widely used in a number of countries worldwide to stimulate milk production in dairy animals. The use of this compound in animal production is strictly regulated by food safety directives in force, in particular in the European Union (EU). Although analytical strategies for the detection of rbGH in blood have been successfully reported over the past 15 years, they do not fully answer the expectations of either competent authorities or industrials that would expect measuring its occurrence directly in the milk. As a matrix of excretion but also of consumption, milk appears indeed as the matrix of choice for detecting the use of rbGH in dairy animals. It also allows large volumes to be collected without presenting an invasive character for the animal. However, rbGH detection in milk presents several challenges, mainly related to the sensitivity required for its detection in a complex biological matrix. This review article presents the specific difficulties associated with milk and provides an overview of the analytical strategies reported in the literature and whether they concern indirect or direct approaches to the detection of rbGH administration to animals, with applications either for screening or confirmation purposes.

Current trends in mass spectrometry of peptides and proteins: Application to veterinary and sports-doping control

Detection of misuse of peptides and proteins as growth promoters is a major issue for sport and food regulatory agencies. The limitations of current analytical detection strategies for this class of compounds, in combination with their efficacy in growth-promoting effects, make peptide and protein drugs highly susceptible to abuse by either athletes or farmers who seek for products to illicitly enhance muscle growth. Mass spectrometry (MS) for qualitative analysis of peptides and proteins is well-established, particularly due to tremendous efforts in the proteomics community. Similarly, due to advancements in targeted proteomic strategies and the rapid growth of protein-based biopharmaceuticals, MS for quantitative analysis of peptides and proteins is becoming more widely accepted. These continuous advances in MS instrumentation and MS-based methodologies offer enormous opportunities for detection and confirmation of peptides and proteins. Therefore, MS seems to be the method of choice to improve the qualitative and quantitative analysis of peptide and proteins with growth-promoting properties. This review aims to address the opportunities of MS for peptide and protein analysis in veterinary control and sports-doping control with a particular focus on detection of illicit growth promotion. An overview of potential peptide and protein targets, including their amino acid sequence characteristics and current MS-based detection strategies is, therefore, provided. Furthermore, improvements of current and new detection strategies with state-of-the-art MS instrumentation are discussed for qualitative and quantitative approaches.

Monolith immuno-affinity enrichment liquid chromatography tandem mass spectrometry for quantitative protein analysis of recombinant bovine somatotropin in serum

The use of recombinant bovine somatotropin (rbST) to enhance milk production is approved in several countries, but it is prohibited in the European Union. According to EU legislation, it is necessary to confirm positive screening results prior to enforcement. Although adequate screening assays are available nowadays, development of liquid chromatography tandem mass spectrometry (LC-MS/MS) confirmatory methods to detect low levels of rbST is still a challenge. Here, we present a novel approach using immuno-affinity enrichment on monolithic micro-columns in combination with state-of-the-art ultra-high pressure LC-MS/MS (UHPLC-MS/MS) detection. The developed approach enables detection and confirmation of rbST in serum at a decision limit (CCα) concentration of 0.8 ng mL⁻¹. Furthermore, the method is easy to handle, robust and reproducible. We successfully applied the confirmatory method to serum samples from rbST treated cows that were found suspect after immunoassay-based screening. The use of rbST could be confirmed over 1 week after treatment, and the developed method demonstrated the sensitivity needed for effective control.

Graphical Abstract

Production of polyclonal antibodies directed to recombinant methionyl bovine somatotropin

The administration of recombinant methionyl bovine somatotropin (rMbST) to dairy cows to increase milk yield remains a common practice in many countries including the USA, Brazil, Mexico, South Africa and Korea, whereas it has been forbidden within the European Union (EU) since 1999. A rapid screening immunoanalytical method capable of the unequivocal determination of rMbST in milk would be highly desirable in order to effectively monitor compliance with the EU-wide ban for home-made or imported dairy products. For decades, the production of specific antibodies for this recombinant isoform of bovine somatotropin (bST) has remained elusive, due to the high degree of sequence homology between both counterparts (e.g. methionine for rMbST in substitution of alanine in bST at the N-terminus). In this study, we compared several immunizing strategies for the production of specific polyclonal antibodies (pAbs), based on the use of the full-length recombinant protein, an rMbST N-terminus peptide fragment and a multiple antigen peptide (MAP) which consists of an oligomeric branching lysine core attached to the first two N-terminus amino acids of rMbST, methionine and phenylalanine (MF-MAP). The immunization with KLH-conjugated MF-MAP led to the production of the pAb with the highest rMbST/bST recognition ratio amongst the generated battery of antibodies. The pAb exhibited a specific binding ability to rMbST in a competitive antigen-coated ELISA format, which avidity was further improved after purification by rMbST N-terminus peptide-based affinity chromatography. These results suggest that immunodiscrimination between structurally related proteins can be achieved using immuno-enhanced immunogens such as MAPs.

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.

Growth-related hormones in plasma of bulls, steers and heifers given food with two different energy levels

Concentrations of growth hormone (GH), insulin-like growth factor (IGF-1), insulin and glucagon were determined in the plasma of growing bulls, steers and heifers (no. = 138 in total, German Simmental breed). The animals were offered either a high level or a low level of energy resulting in relatively high and low average daily gain. Trials were subdivided into two experimental series and started at approximately 3 months of age at an average live weight of 110 kg. The animals were slaughtered at different body weights from 200 to 510 kg (heifers) or 660 kg (bulls, steers). Blood samples (needle puncture) were collected at biweekly intervals. Frequent samples time-course analysis of GH were taken by catheter from nine animals in total. Concentrations of GH declined during growth in steers and heifers as well as in bulls in blood samples collected by means of a catheter. IGF-1 and insulin concentrations increased from the start of the trial onwards up to different ages among the groups. Concentrations of glucagon constantly decreased from the start of the trial until slaughter. Significant differences (P < 0·05) in concentrations ofGH, IGF-1 and insulin could be observed between sexes and levels of nutrition, with the highest GH and IGF-1 levels in bulls followed by steers and heifers. In contrast insulin values were highest in heifers followed by steers and bulls. A high level of nutrition increased concentrations of IGF-1 and insulin in all sexes.

On the alterations in serum concentration of somatotropin and insuline-like growth factor 1 in lactating cows after the treatment with a little studied recombinant bovine somatotropin

A study was performed to delineate bST and IGF-1 variation, over a whole lactation, in cows treated with a nowadays widely commercialised but little studied sustained release formulation of recombinant bST. Total bST levels were found to be exceptionally high in the first days after administration, but decreased rapidly in the second week after injection. The increase in the IGF-1 serum concentration was significant for almost the entire biweekly cycle. Based on this study, the peaks of ST (often above 100 ng/ml) are considered particularly unlikely to be found in non-treated bovines, even under pathological conditions, especially when detected in a number of animals within a herd. Notwithstanding the great heterogeneity of results on this topic, these data suggest that tests against fraud involving the use of rbST in dairy products may be regarded as a feasible possibility.

Direct determination of recombinant bovine somatotropin in plasma from a treated goat by liquid chromatography/high-resolution mass spectrometry

Recombinant bovine somatotropin (rbST) is used in dairy cattle to enhance milk production. Despite the ban on this hormone in some countries, especially in Europe, there is so far no method available for the direct detection of rbST either in milk or in plasma. An analytical strategy has been developed to analyze rbST in plasma, including a purification procedure based on a precipitation with ammonium sulphate, followed by a solid-phase extraction (SPE)-based clean-up on C4 sorbent and precipitation with cold methanol. The hormone was then digested with trypsin and analyzed by liquid chromatography/high-resolution mass spectrometry (LC/HRMSn) on a linear ion trap coupled with an Orbitrap. The tryptic N-terminal peptide, specific to the difference between the endogenous and recombinant form of the somatotropin, was fragmented and product ions were analyzed at high mass resolution. Applying this approach to goat plasma allowed the direct detection of 10 ng mL(-1) of rbST in fortified samples. It also showed the presence of rbST in plasma collected from a goat treated with the hormone, even 2 days after administration. These results are of a great interest in the field of somatotropin control and undoubtedly constitute a first step in the development of a method for the detection of rbST not only in bovine plasma, but also in other biological matrices such as milk.

Elimination kinetic of recombinant somatotropin in bovine

Bovine somatotropin (bST), also called growth hormone is a protein hormone produced by the pituitary gland and responsible directly or indirectly for various effects on growth, development and reproductive functions. Its recombinant bovine somatotropin form (rbST) is used in dairy cattle to enhance milk production. Even if the effects of treatment with rbST have been largely studied, until now analytical methods able to detect rbST were limited to immunoassays, which suffer from the impossibility to distinguish between the endogenous and the recombinant form. In this study, a sample preparation procedure based on different precipitation steps, extraction on solid phase and enzymatic digestion was used to purify rbST from serum. The detection was performed by liquid chromatography coupled to tandem mass spectrometry in positive electrospray ionization mode (LC-ESI(+)-MS/MS) allowing the unambiguous identification and quantification of rbST in serum. Samples collected from a cow treated with recombinant bovine somatotropin were analysed and for the first time, the elimination kinetic specific to recombinant somatotropin has been characterized in serum. Detection of rbST was possible from 4h 30min to 4 days after administration and concentration was found up to 10ngmL(-1) during the kinetic.

Relationship of Thermal Status to Productivity in Heat-Stressed Dairy Cows Given Recombinant Bovine Somatotropin

The responses of lactating Holstein cows to daily administration of bovine somatotropin (bST) were measured at thermoneutrality (Tn) and under both constant and cycled heat-stress conditions to determine the relationship between thermal status and bST-induced shifts in milk production. All tests included a 5-d acclimation period at Tn (18 degrees C), followed by a 2-d increase in ambient temperature to 28.5 degrees C. After d 3, ambient temperature was cycled between 28.5 (day) and 25.5 degrees C (night) for 4 d. Daily injections with either 31 mg of bST or saline began on d 1 of the experiment. Milk production, feed intake, and respiratory rate (RR) were measured daily. Intraperitoneal, telemetric temperature transmitters were used for a continuous measure of core body temperature (T(core)). Blood samples were collected during each phase to evaluate the changes in serum chemistry in response to bST and heat stress. Following a 15-d recovery, cows were switched across injection treatments and the study was repeated. Milk production decreased by approximately 18.4% below the initial yield at Tn by the end of 7 d of heat challenge. Although a reduction in milk production occurred during heat stress in both groups, milk production was higher in bST-treated cows compared with control cows during periods of constant and cyclic heat. Likewise, bST treatment during the entire period increased the milk-to-feed ratio over the control level by approximately 11.3%. Plasma insulin-like growth factor 1 and serum nonesterified fatty acids accompanied the increased growth hormone level with bST treatment (approximately 122.0 and 88.8%, respectively), whereas plasma urea nitrogen was reduced by approximately 13.3% to reflect the shift to lipid metabolism. There was no difference in T(core) of the treatment and control groups at Tn. Both bST and control cows increased RR and T(core) above the Tn level by approximately 94.8 and 2.9%, respectively, during constant heat, with a greater increase in T(core) of bST-treated compared with control cows (approximately 0.6%). The increase in RR during heat stress preceded T(core) by 1 d for both groups. During cyclic heat, T(core) decreased by approximately 0.4% compared with constant heat in both the control and bST-treated groups. Bovine somatotropin treatment increased milk production similarly during the Tn and heat-stress periods, approximately 8.3% over the control; however, the bST-induced increase in milk-to-feed ratio was greatest during the continuous and cyclic heat-stress phases, approximately 16.2%. This increase occurred together with the elevation in T(core).

Effect of dietary beta-carotene on the early embryonic development and uterine fluid composition of gilts

The role of beta-carotene in reproduction was investigated in gilts assigned to three dietary supplementations: VA (4000 IU vitamin A); VA + VA (4000 IU + 8300 IU); VA + BC (4000 IU + 100 mg beta-carotene) per kg diet for 14 weeks. Gilts were slaughtered at day 12 of gestation. In the VA + BC group, number of corpora lutea was lowest, but the number of embryos was greatest, resulting in a non-significant decreased prenatal mortality (p<0.07). The proportion of less developed spherical and tubular embryos compared with filamentous was greatest in the VA + BC group (p<0.01). No differences were observed for vitamin A and retinal binding protein (RBP) in the uterine fluid. When animals were grouped according to the development of blastocysts, vitamin A and RBP levels were higher in the VA + BC group with only filamentous embryos (p<0.01). This indicates that the supplementation of beta-carotene to gilts might affect embryonic losses possibly because of slower alterations in the uterine environment, resulting in a higher and less variable number of embryos, despite an apparently more heterogeneous development.

Hormonal and Lactational Responses to Growth Hormone-Releasing Hormone Treatment in Lactating Japanese Black Cows

Ten multiparous lactating Japanese Black cows (beef breed) were used to evaluate the effects of bovine growth hormone-releasing hormone (GHRH) analog on milk yield and profiles of plasma hormones and metabolites. The cows received 2 consecutive 21-d treatments (a daily s.c. injection of 3-mg GHRH analog or saline) in a 2 (group) x 2 (period) Latin square crossover design. The 5 cows in group A received GHRH analog during period 1 (from d 22 to 42 postpartum) and saline during period 2 (from d 57 to 77 postpartum), and those in group B received saline and GHRH analog during periods 1 and 2, respectively. Mean milk yield decreased in saline treated compared with that during the 1-wk period before treatment 7.4 and 19.1% during periods 1 (group B) and 2 (group A), respectively. Treatment with GHRH analog increased milk yield 17.4% (period 1, group A) and 6.3% (period 2, group B). Treatment with GHRH analog induced higher basal plasma concentrations of growth hormone (GH), insulin-like growth factor-1 (IGF-1), insulin, and glucose compared with saline-treated cows. In glucose challenge, the GHRH analog-treated beef cows had greater insulin secretion than the saline-treated beef cows. In insulin challenge, however, there were no significant differences in the areas surrounded by hypothetical lines of basal glucose concentrations and glucose response curves between GHRH analog- and saline-treated cows. These results demonstrate that GHRH analog treatment facilitates endogenous GH secretion in lactating Japanese Black cows, leading to increases in milk yield and plasma concentrations of IGF-1, insulin, and glucose.

Purification of bovine IGFBP-3 and the development of an enzyme immunoassay for the protein

Insulin-like growth factor binding protein-3 (IGFBP-3), the most prominent IGF-binding protein in serum, has been demonstrated to modulate the effects of the IGFs but also to exert IGF-independent actions. Quantification of IGFBP-3 in livestock species, in particular ruminants, is commonly limited to blotting methods in spite of the importance of these species. Here we describe the development of a specific homologous enzyme-linked immunosorbent assay (ELISA) to measure bovine IGFBP-3 in bovine plasma, serum and milk. IGFBP-3 purified from bovine serum was used both as standard and also for tracer synthesis. A specific antiserum was raised in rabbits using a synthetic peptide based on the sequence of bovine IGFBP-3. The measuring range of the assay was between 50 and 1000 ng IGFBP-3 per milliliter of plasma or milk. Mean recovery was 97.3% for plasma and 100.1% for milk. Intra- and interassay coefficients of variation were 6.2% and 9.3%, respectively. For the biological verification of the assay, IGFBP-3 was determined in plasma obtained from 12 dairy cows before and after being injected with a depot-formulated growth hormone (GH) preparation. GH, a well-characterized stimulator of IGFBP-3, led to a 1.3-fold increase of basal IGFBP-3 concentrations during days 3 to 19 after the injection. The availability of an ELISA procedure which permits precise and sufficiently sensitive quantification of bovine IGFBP-3 and which can be used on large sample numbers thereby avoiding the need for radioactive labels, should facilitate further research studies.

Expression of growth hormone and its transcription factor, Pit-1, in early bovine development

During bovine embryogenesis, bovine growth hormone (bGH) contributes to proliferation, differentiation, and modulation of embryo metabolism. Pituitary-specific transcription factor-1 (Pit-1) is a transcription factor that binds to promoters of GH, prolactin (PRL), and thyroid-stimulating hormone-beta (TSHbeta) encoding genes. A polymorphism in the fifth exon of the bGH gene resulting in a leucine (Leu) to valine (Val) substitution provides an Alu I restriction site when the Leu allele is present. To determine the onset of embryonic expression of the bGH gene, oocytes derived from ovaries homozygous for Leu alleles were fertilized in vitro with spermatozoa obtained from a Val homozygote. For each developmental stage examined, three separate pools of embryos composed of approximately 100 cell samples underwent RNA isolation, reverse transcription to cDNA, and amplification by nested PCR (nPCR). Bovine GH gene transcripts were identified at 2- to 4-cell (n = 162), 8- to 16-cell (n = 73), morulae (n = 51), and blastocyst (n = 15) stages. Likewise, transcripts for Pit-1 were detected at 2-cell (n = 125), 4-cell (n = 114), 8-cell (n = 56), 12-to-32-cell (n = 32), morulae (n = 68), and blastocyst (n = 14) stages. After digestion with Alu1, bGH cDNA was genotyped by restriction fragment length polymorphism (RFLP) analysis. Bovine GH mRNA was present in all pools of stages examined. Both Leu and Val alleles (maternal and paternal) were only detected in pools of embryos that had reached 8- to 16-cell stage. Results suggest that transcription of the bGH gene begins at the 8- to 16-cell stage in bovine embryos, possibly under control of the transcription factor, Pit-1, and that RFLP analysis of the bGH gene can be used to determine parental origin of transcripts in early embryonic development.

Bovine somatotropin dose titration in lactating dairy ewes. 3. Treatment interval

Seventy-four lactating dairy ewes were injected with recombinant bovine somatotropin (bST; sometribove) in a sustained-release formulation. Ewes received 0, 80, 160, or 240 mg of bST/14 d at the end of 2, 4, and 6 wk postlambing, after which injections were withheld for a 28-d period. Response of milk production to bST presented a positive linear contrast and a negative quadratic contrast. After the final injection of bST (d 0), an increase in daily milk production was observed until d +9. A continuous decrease followed with milk production returned to control levels on d +11, +18, and +20, for 80, 160, and 240 mg of bST/14 d. Milk protein content decreased gradually until d +8 before it returned to control levels on d +12, +14 and +14, for 80, 160, and 240 mg of bST/14 d. Levels of bST and IGF-I in plasma presented positive and highly significant linear contrasts and negative quadratics which were significant only for bST. Relative to the evolution of milk production, the evolution of IGF-I levels in plasma was more similar than that of bST, although the correlation of each measure with milk production was high and highly significant. It was concluded that the period between successive injections should be shorter the lower the dose employed; however, a 14-d period seemed to correspond correctly for the dosages and hormone formulation tested.

Growth hormone treatment of breeding bulls used for artificial insemination improves fertilization rates

To evaluate new therapeutical concepts for male subfertility, we tested the effects of exogenous recombinant bovine growth hormone (rbGH) on various endocrine and metabolic parameters both in blood and in seminal plasma of bulls. Sperm quality was assessed morphometrically and by monitoring the number of successful artificial inseminations (AIs) defined as non-return rates (NRR). Aliquots of 450 semen samples were used from each bull and each experimental period (4 wk before, 14 weeks during and 6 wk after treatment). Six out of ten sires (average age 8.4 years) were treated every two weeks with 640-mg depot formulated rbGH (Eli Lilly). Four bulls received vehicle only. Blood plasma bGH, IGF-I, insulin and glucose concentrations were increased with rbGH treatment. In seminal plasma there was no effect of rbGH treatment on fructose and citrate or on testosterone concentrations. With one exception, rbGH-treated bulls had greater IGFBP-3 concentrations in seminal plasma. Motility of spermatozoa after freezing and thawing was increased compared with pretreatment rates. Most interestingly, the number of successful AIs was increased by an average of 6.0% NRR when ejaculates from rbGH-treated bulls were used.

Seasonal levels of metabolic hormones and substrates in male and female reindeer (Rangifer tarandus)

Seasonal levels of cortisol, growth hormone (GH), insulin like growth factor 1 (IGF-1), glucose, triiodothyronine (T3), free T3, thyroxine and free fatty acids (FFA) were measured every 3 weeks for 54 weeks in the plasma of five adult bulls, and four barren and five pregnant Alaskan reindeer (Rangifer tarandus) cows. Three consecutive samples were taken from each animal. Cortisol levels exhibited wide seasonal variation (9-45 ng/ml) [corrected] without any peak or difference in levels among groups. Rising levels were detected between the 3 consequent samples. Peak GH levels, detected during January and February, were higher in the non-pregnant group (54 ng/ml) than the pregnant (26 ng ml-1) and the male (27 ng ml-1) groups. Low GH levels (2-10 ng ml-1) were recorded between May and September. IGF-1 reached peak levels (715 ng ml-1) in males in August, in non-pregnant females in September (677 ng ml-1), and in the pregnant females in October (505 ng ml-1). Seasonal minima (404 in males, 172 and 93 in pregnant and non-pregnant groups) were detected in February. Glucose was fairly stable throughout the year (100-200 mg/100 ml). A rising levels were found between the three consecutive samples. Triiodothyronine (T3) (2.16-2.30 ng ml-1) peaked in all three groups during the spring and early summer, and minimal levels (0.61-0.97 ng ml-1) were detected from October to January. Conversely, thyroxine or free T3 did not exhibit seasonal variation. FFA fluctuated widely (97-1076 nmol l-1) throughout the year. Only in pregnant females were concentrations more stable (150-460 nmol l-1). Perhaps, because of ad libitum supply of food in captive reindeer, only T3 and GH exhibited pronounced seasonal fluctuations which could be related to the metabolic changes expected during the annual cycle.

Effect of exogenous estradiol on plasma concentrations of somatotropin, insulin-like growth factor-I, insulin-like growth factor binding protein activity, and metabolites in ovariectomized Angus and Brahman cows

To determine the effect of breed and estradiol-17 beta on selected hormones and metabolites, ovariectomized (> or = 3 mo) Angus (n = 14) and Brahman (n = 12) cows were paired by age and body weight and randomly assigned as either nonimplanted controls (CON) or implanted with estradiol (E2) for 45 d. After Day 7 and through Day 42, plasma concentration of somatotropin was greater for E2 than CON cows (treatment x day, P < 0.05). During an intensive blood sampling on Day 36, E2 cows tended (P < 0.10) to have greater somatotropin pulse amplitudes than CON cows, but other parameters of somatotropin release were not affected (P > 0.10) by E2 treatment. The effect of breed was apparent on Day 36 as Brahman cows had greater (P < 0.05) somatotropin pulse amplitude, basal secretion, and mean concentration than Angus cows. Overall, plasma concentration of IGF-I was greater (P < 0.01) for E2 than CON cows (158.3 vs. 104.2 ng/ml) and was greater for Brahman than Angus cows (164.1 vs. 98.4 ng/ml). However, there was a trend (P < 0.10) for a treatment x breed x day interaction for IGF-I (i.e., the magnitude of increase in IGF-I concentration was greater in E2-Angus than E2-Brahman cows). After Day 7 and through Day 42, total plasma IGF binding protein (IGFBP) activity was greater (P < 0.01) for E2 than CON cows. Ligand blotting revealed at least five forms of IGFBP activity, and E2 cows had greater (P < 0.05) binding activity of IGFBP-3 and the 30- and 32-kDa IGFBP than CON cows. Brahman cows had greater (P < 0.05) IGFBP-3 and the 32-kDa IGFBP than Angus cows. After Day 14 and through Day 42, concentration of urea nitrogen (PUN) was greater (P < 0.001) for CON than E2 cows (treatment x day, P < 0.001). Brahman had greater (P < 0.01) PUN than Angus cows (16.6 vs. 14.2 mg/dl). Plasma concentration of glucose was greater (P < 0.01) for E2 than CON cows (78.9 vs. 76.4 mg/dl) but was not affected (P > 0.10) by breed. In summary, these data suggest that some, but not all, of the positive effects of estradiol on peripheral concentration of IGF-I and IGFBP activity can be attributed to increased somatotropin. Moreover, breed influenced basal and E2-induced secretion of somatotropin and IGF-I such that differences between Brahman and Angus cows in plasma IGF-I concentrations were abated within 3 wk of estradiol implantation. Thus, breed influences the metabolite and hormonal response of cattle to estrogenic implants.

Effect of slow-release somatotropin on the pattern of milk yield between and within injection intervals

Thirty-six Alpine goats (10 primiparous and 26 multiparous) were used to study the milk yield response induced by recombinant bST administered in a sustained-delivery vehicle. Eighteen goats were injected with recombinant bST at 4-wk intervals from about 7 wk postpartum for 12 wk. Patterns of milk yield were highly affected by injection of recombinant bST. Milk yield of treated goats increased from day of injection, peaked between d 3 to 5 after treatment, and then decreased progressively. This pattern of response was well fitted by a curve containing two exponential terms: Yi = A x [exp(-k1di - exp(-k2di)], where Yi = daily relative response of treated goats to recombinant bST, computed as a deviation of least squares means of milk yield at day i (i = 0,..., 26) of the treatment interval from least squares means of milk yield at d 27 of the treatment interval; A = constant; k1 and k2 = response rate parameters; and di = day from treatment (i = 0,..., 27). Administration of recombinant bST also improved persistency of lactation, and the overall milk yield response to exogenous hormone was 300 g/d (13.9%) higher than the yield of untreated goats. This response was due to both the short-term response immediately after injection (53%) and the medium-term effect on lactation persistency.

Growth hormone and insulin-like growth factor I concentrations in bulls of various growth hormone genotypes

A leucine/valine substitution at amino acid position 127 was identified by the polymerase chain reaction and restriction fragment length polymorphism in the bovine growth hormone gene. Genotyping was performed in 84 AI bulls of three different breeds, in which plasma concentrations of growth hormone (GH) and insulin-like growth factor I (IGF-1) were also measured. Gene frequencies of variants L (leucine) und V (valine) were 0.80/0.20 (Black and White), 0.90/0.10 (Brown), 0.71/0.29 (Simmental). Hormone concentrations were measured during different physiological conditions (normal feeding, fasting, realimentation) in the majority of animals. Generally, genotype LL was associated with higher concentrations of GH than LV. This difference was significant in Black and White bulls (P < 0.05). In contrast, IGF-1 concentrations were higher in LV than in LL animals. This was most pronounced in mature, realimented Simmental bulls. We conclude that the various GH alleles influence the circulating concentrations of GH and IGF-1.

Modeling response to slow-releasing somatotropin administered at 3- or 4-week intervals

The purpose of this study was to develop a time-dependent model to account for the effects of recombinant bST in a slow-release formulation on short-term (between two consecutive injections) and long-term (baseline of the lactation curve) response of milk yield and composition. Observations on milk yield (n = 8234) and on milk composition (n = 1509) of 196 Holstein Friesian cows were recorded over 1 yr of trial. Treated cows were injected with somidobove at 3- or 4-wk intervals. Data were analyzed according to a model that included effect of treatment, parity, interaction, and the random effect of cow; two time-dependent covariables, obtained by the splitting of DIM, were included in the model to account for the effects of bST on short- and long-term responses of milk traits. Cyclical variations of milk yield, protein, and SCC content in the interval between two consecutive injections were detected. Recombinant bST administration also influenced the persistency of milk yield and protein content. Treatment of cows at 3- and 4-wk intervals increased yield by 20.6 and 12.6% over those of untreated cows. Nearly 60% of this increment was due to the short-term effect of bST. Milk composition response to bST was less noticeable.

Identification of antigenic differences of recombinant and pituitary bovine growth hormone using monoclonal antibodies

For characterization and determination of recombinant bovine GH (rbGH) eight monoclonal antibodies (MAb) were produced against rbGH from Monsanto. The various MAb showed different affinities to rbGH, pituitary bovine GH (pbGH), and pituitary ovine GH (poGH). With epitope analysis several MAb were shown to recognize different epitopes of rbGH. The MAb MUC-rbGH-3A11 and MUC-rbGH-1E5 were used to develop a Sandwich ELISA. By checking the specificity of the assay no cross reactivity was found with pituitary porcine GH, pituitary human GH, bovine or ovine prolactin and little cross reactivity with poGH could be found. The Sandwich ELISA detected various rbGH (Monsanto, Elanco, Cyanamid) with different N-terminal amino acids and discriminated between rbGH and pituitary bovine GH by an affinity factor of 2.0. The detection level was 2 ng rbGH per ml PBS buffer. The recovery was about 86% in bovine serum. It might therefore be possible to detect rbGH-treated cows using a Sandwich ELISA, but this would need a field study.

Effect of recombinant bovine somatotropin (rBST) on follicular IGF-I contents and the ovarian response following superovulatory treatment in dairy cows: A preliminary study

Somatotropin and FSH act synergystically on insulin-like growth factor-I (IGF-I) synthesis in ovarian follicles; IGF-I regulates several granulosa cell specific functions and may thereby be beneficial in bovine superovulation. In a series of 3 experiments we investigated the effects of recombinant bovine somatotropin (rBST) on several parameters of the superovulatory response in dairy cows. A total of 81 Holstein Friesian crossbred dairy cows received either 640 mg rBST or the vehicle (controls) on Day 4 or 13 of the superovulation schedule. Superovulation was induced with 2500 IU PMSG on Day 9. The cows were artificially inseminated on Day 13. In Experiment 1, on Days 4, 8, 11, 13 and 17 4 to 5 animals each were slaughtered to obtain follicular fluid, endometrium and plasma. The rBST application increased IGF-I contents in plasma and follicular fluid on Days 8, 11 and 13 (P<0.05) in the treated cows when compared with that of the controls. Plasma and follicular IGF-I contents were correlated closely (rBST: r=0.90, n=10; control: r=0.94, n=9). The number of antral follicles increased following rBST treatment, and on the day of artificial insemination (AI) twice as many follicles>4 mm were counted in the rBST treated animals than in the control group. In Experiment 2, the flushing of 38 donors on Day 7 after AI resulted in more transferable embryos in the rBST group than in the control group (4.2+/-1.0 vs 2.5+/-0.7; P<0.05). In contrast, in Experiment 3 involving 21 animals when rBST was administered at the time of AI the superovulation response was not altered. It is concluded that rBST increases follicular and plasma IGF-I contents and thereby has profound effects on follicular and early embryonic development.