Bovine somatotropin: review of an emerging animal technology

Growth hormone alters lipid composition and increases the abundance of casein and lactalbumin mRNA in the MAC-T cell line

The MAC-T cell line has been used extensively to investigate bovine mammary epithelial cell function. A lactogenic phenotype is generally induced in this cell line by a combination of dexamethasone, insulin and prolactin and has typically been assessed by milk protein production. Few studies have focused on identifying other factors that may affect milk protein synthesis in the MAC-T cell line, and none have considered the lipid class distribution of MAC-T cells as a component of the lactogenic phenotype. Growth hormone (GH) has been shown to increase milk protein synthesis both in vivo and in mammary cell models, and has been shown to alter the lipogenic profile of mammary explant models. We tested the hypothesis that MAC-T cells would respond directly to GH and that the response would include alterations to the lipid class distribution as well as to milk protein gene expression, leading to a more appropriate model for mammary cell function than treatment with dexamethasone, insulin and prolactin alone. Differentiated cells expressed GH receptor mRNA, and addition of GH to the differentiation medium significantly induced production of alpha-s1 casein and alpha-lactalbumin mRNA. GH also significantly affected the proportion of triacylglycerol and sphingomyelin. These results indicate that GH is an important factor in inducing a lactogenic phenotype in the MAC-T cell line, and support the possibility of a direct effect of GH on milk synthesis in vivo.

Effect of Bromocryptine on hormones and milk secretion in Murrah buffaloes ( Bubalus bubalis)

An experiment was carried out on 10 advance pregnant Murrah buffaloes to determine the role of hormones in milk secretion around parturition. Experimental animals were administered with a single injection of bromocryptine, @ 100 μg/kg BW, for 5 days before expected calving, whereas control group buffaloes were injected with placebo injections. Blood samples collected before parturition (-5,-4,-3,-2,-1 days), on day of parturition (day-0) and on day 1, 2, 3, 4, 5, 10 and 15 post partum were analyzed for growth hormone (GH), insulin like growth factor-I (IGF-I) and prolactin (PRL) by radioimmunassay methods. Milk samples were collected daily for 5 days and on day 10 and 15 after parturition. Milk fat, protein, lactose, citric acid, non-esterified fatty acids (NEFAs) and somatic cell counts (SCCs) were determined in milk samples. Bromocryptine treatment significantly (P < 0.01) decreased pre partum PRL and increased GH levels (P < 0.01) on day of parturition in experimental buffaloes without influencing plasma IGF-I level. Milk yield was significantly lower (P < 0.01) in experimental than in control group. Further, effect of bromocryptine on milk yield was only for a week. Milk yield increased (P < 0.01) gradually and was similar to control group on day 15 post partum. Bromocryptine treatment significantly increased milk SCC (P < 0.01) and protein content (P < 0.01) but there was no effect of treatment on fat, lactose, citric acid, glucose, milk and plasma NEFA concentration. It was concluded that prepartum suppression of PRL by bromocryptine impairs milk secretion temporarily in ensuing lactation. The significant rise in GH level before parturition and on day of parturition suggests a role of it in milk secretion of buffaloes.

Quantitative determination of recombinant bovine somatotropin in commercial shrimp feed using a competitive enzyme-linked immunosorbent assay

Recombinant bovine somatotropin (rbST), also known as growth hormone, is used to enhance production and development of animals within the agriculture and aquaculture industries. Its use is controversial because of its potential effects on human and animal health. To screen for rbST in shrimp feed, a competitive enzyme-linked immunosorbent assay (ELISA) with an inhibition step was developed. Sample and rbST antibody (rabbit anti-rbST) were incubated at room temperature for 30 min. Subsequently, this competitive reaction was transferred to a microplate coated with rbST, using goat antirabbit IgG linked with horseradish peroxidise as the secondary antibody. Substrates for peroxidise were added, and the absorbance at 410 nm was determined. The applicability of the method was assessed using rbST extracted from "spiked" shrimp feed samples. The assay was reproducible and linear with R(2) values greater than 0.98 over the standard curve range of 20-500 microg/g. The intra- and interday precisions expressed as relative standard deviations were 3.4 and 5.3%, respectively. The mean recovery from 15 spiked feed samples was 105%. This assay will be a valuable tool for quantitative detection of rbST by both governments and commercial companies and can be modified for other types of feed.

An analytical strategy for identification of a somatotropin-like bioactive peptide by ion trap liquid chromatography/electrospray ionization tandem mass spectrometry after immuno-affinity purification from buffalo serum

The use of growth hormones, such as native and recombinant somatotropins, is forbidden in the European Union (EU), but is legal in the USA. The misuse of recombinant bovine somatotropin in Italy is suspected for enhancing milk production, thanks to its availability on the illegal market. A synthetic bioactive peptide of 27 amino acids derived from bovine somatotropin was successfully tested in France and in southern Italy for scientific purposes, to stimulate milk production, both in cows and buffaloes. This somatotropin-like peptide (PEP-ST), suspected for illegal use in southern Italy, was synthesized by linking the 104-113 sequence of bovine somatotropin to the 323-339 sequence of ovalbumin. Herein, a method for detection and identification of the PEP-ST in buffalo serum is described; our strategy was based on the production of IgG anti-PEP-ST, used to synthesize an immuno-affinity column for peptide purification from buffalo serum, prior to analysis by ion trap liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI-MS/MS). The immuno-affinity column was successfully used to purify in a single step the bioactive PEP-ST from buffalo serum samples spiked at 20, 50 and 200 microg/mL for confirmatory analysis. Ion trap LC/ESI-MS/MS identification was based on detection of a multi-charged molecular ion and its characteristic fragmentation pattern. No significant matrix interference was observed, accounting for method specificity. We consider this strategy to be a basic approach that could be improved in the perspective of the official control of illegal use of somatotropin and somatotropin-like compounds in buffalo breeding.

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.

The environmental impact of recombinant bovine somatotropin (rbST) use in dairy production

The environmental impact of using recombinant bovine somatotropin (rbST) in dairy production was examined on an individual cow, industry-scale adoption, and overall production system basis. An average 2006 U.S. milk yield of 28.9 kg per day was used, with a daily response to rbST supplementation of 4.5 kg per cow. Rations were formulated and both resource inputs (feedstuffs, fertilizers, and fuels) and waste outputs (nutrient excretion and greenhouse gas emissions) calculated. The wider environmental impact of production systems was assessed via acidification (AP), eutrophication (EP), and global warming (GWP) potentials. From a producer perspective, rbST supplementation improved individual cow production, with reductions in nutrient input and waste output per unit of milk produced. From an industry perspective, supplementing one million cows with rbST reduced feedstuff and water use, cropland area, N and P excretion, greenhouse gas emissions, and fossil fuel use compared with an equivalent milk production from unsupplemented cows. Meeting future U.S. milk requirements from cows supplemented with rbST conferred the lowest AP, EP, and GWP, with intermediate values for conventional management and the highest environmental impact resulting from organic production. Overall, rbST appears to represent a valuable management tool for use in dairy production to improve productive efficiency and to have less negative effects on the environment than conventional dairying.

Greenhouse gas mitigation in agriculture

Agricultural lands occupy 37% of the earth's land surface. Agriculture accounts for 52 and 84% of global anthropogenic methane and nitrous oxide emissions. Agricultural soils may also act as a sink or source for CO2, but the net flux is small. Many agricultural practices can potentially mitigate greenhouse gas (GHG) emissions, the most prominent of which are improved cropland and grazing land management and restoration of degraded lands and cultivated organic soils. Lower, but still significant mitigation potential is provided by water and rice management, set-aside, land use change and agroforestry, livestock management and manure management. The global technical mitigation potential from agriculture (excluding fossil fuel offsets from biomass) by 2030, considering all gases, is estimated to be approximately 5500-6000Mt CO2-eq.yr-1, with economic potentials of approximately 1500-1600, 2500-2700 and 4000-4300Mt CO2-eq.yr-1 at carbon prices of up to 20, up to 50 and up to 100 US$ t CO2-eq.-1, respectively. In addition, GHG emissions could be reduced by substitution of fossil fuels for energy production by agricultural feedstocks (e.g. crop residues, dung and dedicated energy crops). The economic mitigation potential of biomass energy from agriculture is estimated to be 640, 2240 and 16 000Mt CO2-eq.yr-1 at 0-20, 0-50 and 0-100 US$ t CO2-eq.-1, respectively.

Greenhouse gas mitigation in agriculture

Agricultural lands occupy 37% of the earth's land surface. Agriculture accounts for 52 and 84% of global anthropogenic methane and nitrous oxide emissions. Agricultural soils may also act as a sink or source for CO2, but the net flux is small. Many agricultural practices can potentially mitigate greenhouse gas (GHG) emissions, the most prominent of which are improved cropland and grazing land management and restoration of degraded lands and cultivated organic soils. Lower, but still significant mitigation potential is provided by water and rice management, set-aside, land use change and agroforestry, livestock management and manure management. The global technical mitigation potential from agriculture (excluding fossil fuel offsets from biomass) by 2030, considering all gases, is estimated to be approximately 5500-6000Mt CO2-eq.yr-1, with economic potentials of approximately 1500-1600, 2500-2700 and 4000-4300Mt CO2-eq.yr-1 at carbon prices of up to 20, up to 50 and up to 100 US$ t CO2-eq.-1, respectively. In addition, GHG emissions could be reduced by substitution of fossil fuels for energy production by agricultural feedstocks (e.g. crop residues, dung and dedicated energy crops). The economic mitigation potential of biomass energy from agriculture is estimated to be 640, 2240 and 16 000Mt CO2-eq.yr-1 at 0-20, 0-50 and 0-100 US$ t CO2-eq.-1, respectively.

Supplementing Holstein cows with low doses of bovine somatotropin prepartum and postpartum reduces calving-related diseases

The objective of this study was to evaluate whether supplementing Holstein cows with bovine somatotropin (bST; 142.8 mg/14 d), beginning at 21 d (+/-3 d) before expected calving and continuing through 42 d in milk (+/-3 d), affected the incidence rates of retained fetal membranes (RFM), metritis (MET), clinical mastitis (MAS), digestive problems (DIG), ketosis (KET), milk fever (MF), displaced abomasum (DA, left or right), lameness (LAM), or number of sick cows during the first 60 d in milk. Data for multiparous Holstein cows from 3 separate trials were merged for analyses (n = 437). Cows in the bST-supplemented group (n = 162) received biweekly subcutaneous injections of Posilac, whereas control cows (n = 166) and a group of cohorts (n = 109) were not supplemented. Incidences of disease were collected from the herd health records. Across all treatment groups, the incidence rates (number of diseased cows divided by the total number of cows) for RFM, MET, MAS, DIG, KET, MF, DA, and LAM were 8.47, 18.31, 16.02, 4.35, 4.35, 3.66, 3.20, and 3.66%, respectively. The incidence rates of RFM, MET, MAS, DIG, KET, MF, DA, and LAM for cows in the bST-supplemented, control, and cohort groups were 6.79, 7.83, and 11.93%; 16.05, 7.47, and 22.94%; 10.49, 18.07, and 21.10%; 1.23, 5.42, and 7.34%; 1.23, 6.02, and 6.42%; 2.47, 4.22, and 4.59%; 2.47, 3.61, and 3.67%; and 3.70, 3.61, and 3.67%, respectively. The percentages of sick cows (number of cows having one or more cases of disease divided by the total number of cows) in the bST-supplemented, control, and cohort groups were 33.95, 43.37, and 49.54%, respectively. Significant chi-squared values were detected between the bST-supplemented and control groups for MAS, DIG, and KET, with a greater number of healthy cows in the bST-supplemented group. No differences in incidences of diseases or sick cows were detected between the control and cohort groups. Results indicated that a low dose of bST supplemented to Holstein cows for 3 wk prepartum through 60 d in milk reduced the incidences of some calving-related diseases compared with nonsupplemented controls or cohorts. Importantly, no negative effects of bST supplementation on postpartum calving diseases were detected compared with nonsupplemented cows.

Perspectives on ruminant nutrition and metabolism. II. Metabolism in ruminant tissues

The discovery of the dominance of short-chain fatty acids as energy sources in the 1940s and 1950s, as discussed in part I of this review (Annison & Bryden, 1998) led to uncertainties concerning the interrelationships of glucose and acetate in ruminant metabolism. These were resolved in the following decade largely by use of14C-labelled substrates. Although only small amounts of glucose are absorbed in most dietary situations, glucose availability to ruminant tissues as measured by isotope dilution was shown to be substantial, indicating that gluconeogenesis is a major metabolic activity in both fed and fasted states. Studies with14C-labelled glucose and acetate revealed that in contrast to non-ruminants, acetate and not glucose is the major precursor of long-chain fatty acids in ruminant tissues. Interest in the measurement of energy metabolism in livestock grew rapidly from the 1950s. Most laboratories adopted indirect calorimetry and precise measurements of the energy expenditure of ruminants contributed to the development of new feeding systems. More recently, alternative approaches to the measurement of energy expenditure have included the use of NMR spectroscopy, isotope dilution and the application of the Fick principle to measure O2consumption in the whole animal and in defined tissues. The refinement of the classical arterio-venous difference procedure in the study of mammary gland metabolism in the 1960s, particularly when combined with isotope dilution, encouraged the use of these methods to generate quantitative data on the metabolism of a range of defined tissues. The recent introduction of new methods for the continuous monitoring of both blood flow and blood O2content has greatly increased the precision and scope of arterio-venous difference measurements. The impact of data produced by these and other quantitative procedures on current knowledge of the metabolism of glucose, short-chain fatty acids and lipids, and on N metabolism, is outlined. The role of the portal-drained viscera and liver in N metabolism is discussed in relation to data obtained by the use of multi-catheterized animals. Protein turnover, and the impact of stress (physical, social and disease related) on protein metabolism have been reviewed. The growth of knowledge of mammary gland metabolism and milk synthesis since the first quantitative studies in the 1960s has been charted. Recent findings on the regulation of amino acid uptake and utilization by the mammary gland, and on the control of milk secretion, are of particular interest and importance.

Molecular cloning, characterization, and expression studies of water buffalo (Bubalus bubalis) somatotropin

Cloning, high-level expression, and characterization of the somatotropin (ST) gene of an indigenous Nili-Ravi breed of water buffalo Bubalus bubalis (BbST) are described. Coding, non-coding, and promoter regions of BbST were amplified and sequenced. Sequence analysis revealed several silent and two interesting point mutations on comparison with STs of other vertebrate species. One interesting variation in the BbST sequence was the replacement of a conserved glutamine residue by arginine. A plasmid was also constructed for the production of BbST in Escherichia coli BL21 (RIPL) CodonPlus, under the control of IPTG-inducible T7-lac promoter. High-level expression could be obtained by synthesizing a codon-optimized ST gene and expressing it in the form of inclusion bodies. The inclusion bodies represented over 20% of the E. coli cellular proteins. The biologically active conformation of purified BbST was confirmed by its efficient growth promoting activity in Nb2 cell proliferation assay. The expression system and purification strategy employed promise to be a useful approach to produce BbST for further use in structure-function studies and livestock industry.

Genetic parameters for yield traits of cows treated or not treated with bovine somatotropin

The objective of this study was to estimate genetic correlations between yield traits of cows treated with bovine somatotropin (bST) and the same yield traits of untreated cows. Lactation records from registered Holstein cows were divided by parity into 3 data sets: 1, 2, and 3 through 5. Approximately 10% of the records in each data set were from cows treated with bST. The numbers of records of treated and untreated cows in the data sets were 4,337 and 48,765; 3,730 and 37,796; and 3,645 and 33,957. Two-trait animal models (records for cows treated or not treated) were used to estimate genetic parameters for milk production traits and somatic cell score (SCS). Estimates of heritability for milk yield for records of treated and untreated cows for the 3 data sets were 0.13, 0.16, and 0.09, and 0.18, 0.18, and 0.14, respectively, with estimates of repeatability of 0.50 and 0.41 for data set 3. Estimates of heritability for fat yield for records of treated and untreated cows were 0.31, 0.16, and 0.12, and 0.27, 0.21, and 0.16. Estimates of repeatability were 0.50 and 0.43 for data set 3. Heritability estimates for protein yield for records of treated and untreated cows were 0.13, 0.17, and 0.12, and 0.20, 0.23, and 0.16, with estimates of repeatability of 0.52 and 0.47. Estimates of heritability for SCS for treated and untreated cows were 0.08, 0.15, and 0.13, and 0.11, 0.13, and 0.13 with repeatability estimates of 0.52 and 0.45. Estimates of genetic correlations between milk yields with and without bST treatment in lactations 1, 2, and 3 to 5 were all 0.99. Estimates of genetic correlations for fat and protein yields were 0.96 for all data sets. Estimates for SCS were 0.99. Estimates of genetic correlations between records of treated and untreated cows were large enough to conclude that records of treated and untreated cows could be considered to be one trait, with treatment as a fixed effect to account for differences in means.

An approach to identify dairy cows being responsive to recombinant bovine somatotropin

Forty-eight primiparous and pregnant Holstein cows at 202 (+/-59) days in milk and average daily milk production (DMP) of 22 (+/-5.3) kg at the beginning of the trial were used to study the possibility of identifying animals that are more responsive to recombinant bovine somatotropin (rbST). Animals were housed in free-stall barns, milked three times a day and fed a total mixed ration. Animals were injected with one dose (500 mg each) of rbST every 21 days during a 105-day total period (five doses in all). Daily milk production was recorded to measure average apparent response (AAR) and peak of apparent response (PAR). Average apparent response was defined as the average increase in milk production, expressed as kilogram per cow per day, for days 0-18 after dosing, as compared to the average production calculated for days -1, -2, -3, 19, 20 and 21 after dosing. Peak of apparent response was calculated as the increase in milk production for each day from 0 to 18 days after dosing as compared to the average production for days -1, -2 and -3. There was a positive linear correlation (r = 0.608; p = 0.0001) between AAR for the first 21 days and AAR for the total 105-day period (AATR). A correlation coefficient was calculated between each individual PAR value and AATR. The highest correlation coefficient (r = 0.511; p = 0.0002) was observed for days 8, 9 and 10, and therefore these days were considered the best estimates for calculating AAR when DMP records are not available. Also, high somatic cells count had a negative impact on milk yield response to treatment (p = 0.0162).

Selection on predicted breeding value for milk production delays ovulation independently of changes in follicular development, milk production and body weight

Two studies were conducted to investigate the effect of selection on predicted breeding value (PBV) for milk production, and its associated metabolic and endocrine milieu, on follicular development and ovulation in the postpartum period. A total of 71 cattle from lines selected to differ in their PBV were used in two consecutive years. In Study 1 the first ovulation and commencement of normal luteal function occurred significantly earlier in low (L) line cows than high (H) line cows. In Study 2 average daily milk production during the study period did not differ (P>0.10) between cows in either the H (=31.0+/-1.5kg/day) or L (=30.2+/-1.7kg/day) PBV lines although, 305 days milk production was significantly different (P<0.01; H=6880+/-164kg versus L=5795+/-317kg). As in Study 1, first ovulation postpartum in Study 2 occurred earlier (P<0.01) in the L (day 19) versus the H line (day 28). Circulating concentrations of glucose and insulin were significantly lower, whilst concentrations of GH and BOHB were higher in cows from the high PBV line. No differences in gonadotrophin concentrations were seen between lines. Both changes in body weight and patterns of follicle development did not differ between lines. By day 15 postpartum all cows had follicles of all three-size categories (small, medium-sized and large). Small (P<0.07) and medium-sized follicle numbers increased (P<0.01) with day postpartum. However, the inclusion of predicted changes in body weight as a covariate in the analysis, demonstrated that changes in number of small and medium-sized follicles were associated with changes in body weight. In conclusion, selection on PBV for milk production is associated with a longer interval from parturition to first ovulation, independent of changes in follicular development, milk production and body weight implicating other factor(s) associated with genetic selection.

Pre-pubertal measurements of the somatotrophic axis as predictors of milk production in Holstein-Friesian dairy cows

This study investigated possible relationships between measurements of the somatotrophic axis in pre-pubertal dairy calves and subsequent milk yields. Endogenous growth hormone (GH) release was measured through a fed and fasted period in fifty 6-month-old Holstein-Friesian heifers and they were then challenged with growth hormone-releasing factor (GRF) to assess their GH release pattern. Insulin-like growth factor-I (IGF-I), insulin and glucose concentrations were measured in relation to time of feeding. Cows were subsequently monitored through their first three lactations to record peak and 305-day milk yields. In the first lactation, milk energy output for the first 120 days of lactation was also calculated. The mean 305-day milk yield increased from 7417 +/- 191 kg in the first lactation (n=37) to 8749 +/- 252 kg in the third (n=25). There were no significant relationships between any measures of GH secretion and peak or 305-day yield in any lactation. A highly significant positive relationship was established between the GH peak measured 10 min post-GRF challenge and 120-day milk energy values in the first lactation. This relationship was, however, only present in the sub-population of 12 cows culled after one or two lactations and was absent in the 25 animals remaining for the third lactation. There were no significant relationships between pre-pubertal IGF-I and fed or fasted insulin or glucose concentrations and any subsequent measurement of yield. The usefulness of GH secretagogue challenges in calves as a predictive test for future milk production is thus limited but may have some bearing on nutrient partitioning and longevity.

Growth hormone-releasing hormone (GHRH) polymorphisms associated with carcass traits of meat in Korean cattle

BACKGROUND

Cold carcass weight (CW) and longissimus muscle area (EMA) are the major quantitative traits in beef cattle. In this study, we found several polymorphisms of growth hormone-releasing hormone (GHRH) gene and examined the association of polymorphisms with carcass traits (CW and EMA) in Korean native cattle (Hanwoo).

RESULTS

By direct DNA sequencing in 24 unrelated Korean cattle, we identified 12 single nucleotide polymorphisms within the 9 kb full gene region, including the 1.5 kb promoter region. Among them, six polymorphic sites were selected for genotyping in our beef cattle (n = 428) and five marker haplotypes (frequency > 0.1) were identified. Statistical analysis revealed that -4241A>T showed significant associations with CW and EMA.

CONCLUSION

Our findings suggest that polymorphisms in GHRH might be one of the important genetic factors that influence carcass yield in beef cattle. Sequence variation/haplotype information identified in this study would provide valuable information for the production of a commercial line of beef cattle.

Reducing phosphorus runoff from dairy farms

Phosphorus (P) runoff from manure can lead to eutrophication of surface water and algae growth. This study evaluates the impacts of alternative P reduction practices on dairy farm net returns and on potential P runoff. The P control practices include dairy herd nutrient management, crop nutrient management, and runoff and erosion control. Four farms representative of dairies in the Virginia Shenandoah Valley are simulated including dairies with and without supplementary broiler enterprises and with average and below average land area. A mathematical programming model was developed to predict farm production and net returns and the GLEAMS model was used to predict potential P runoff. The farms are evaluated under four scenarios: Scenario 1, no constraint on P runoff with access to crop nutrient, runoff and erosion control strategies but no access to dairy herd nutrient control strategies; Scenario 2, no constraint on P runoff with access to all crop and dairy herd nutrient control strategies; Scenario 3, constraint on P runoff with access to crop nutrient, runoff and erosion control strategies but no access to dairy herd nutrient control strategies; and Scenario 4, constraint on P runoff with access to all crop and dairy herd nutrient control strategies. Under Scenario 2, the herd nutrient control strategies increase milk output per cow and net returns on both farms and reduce P content of manure and P runoff. Under Scenario 3, limiting P runoff reduces farm returns by 1 and 3% on the average and small farms, respectively. Under Scenario 4, the P runoff constraint is less costly, reducing returns by less than 1% on both farms. Animal nutrient control strategies should be an important part of pollution control policies and programs for livestock intensive watersheds.

Efeito da somatotropina bovina recombinante (rBST) sobre o desempenho produtivo e reprodutivo de vacas da raça Holandesa

Avaliaram-se os efeitos da aplicação de rBST sobre o desempenho produtivo e reprodutivo de vacas da raça Holandesa no início da lactação. Foram avaliadas 41 vacas, dos 60 aos 150 dias de lactação, distribuídas em um delineamento inteiramente ao acaso, em três tratamentos: 1- sem aplicação de rBST (controle); 2- aplicação de rBST 60 dias após o parto (rBST-60); 3- aplicação de rBST 100 dias após o parto (rBST-100). A aplicação de rBST aumentou a produção de leite e a produção de leite corrigida a 4% de gordura em 14,0 e 13,2%, respectivamente, quando administrada aos 60 dias pós-parto. Não se observou efeito da aplicação de rBST sobre a porcentagem e a produção de gordura do leite nem sobre o período de serviço, número de serviços por concepção e taxa de gestação aos 150 dias de lactação. O uso do rBST também não afetou o ganho de peso dos animais durante o período avaliado. A aplicação de rBST aos 60 dias de lactação proporcionou maiores pico de produção e persistência da lactação, sem, no entanto, influenciar o desempenho reprodutivo. A aplicação de rBST aos 100 dias de lactação não aumentou a produção de leite e o desempenho reprodutivo das vacas.

Comparisons of Serum Somatotropin, 3,5,3′-Triiodothyronine, Thyroxine, Total Protein and Free Fatty Acid Levels in Newborn Sakiz Lambs Separated from or Suckling Their Dams

OBJECTIVE

To determine the effects on serum somatotropin, 3,5,3'-triiodothyronine (T(3)), thyroxine (T(4)), free fatty acids (FFAs) and total protein levels of different feedings and age in Sakiz sheep that have a high twin-bearing rate supported by estrous synchronization.

METHODS

20 newborn lambs were used in the study. Lambs were divided into 2 equal groups. The lambs in 1 group were separated from their dams following parturition, and those in other group were kept together with their dams. Separated lambs were fed commercial cow's milk for 2.5 weeks. After that, they were fed a milk substitute, hay and concentrated supplement for 2 months, and from the end of the 2 months they were fed hay and concentrated supplement. The lambs in other group were kept together with their dams only during the day and in addition were fed hay and concentrated supplement. After 2 months, they were maintained feeding only on hay and concentrated supplement. Blood samples were taken from vena jugularis of lambs at 12 and 24-48 h, and 14, 28, 42 and 56-90 days after parturition. Serum samples were analyzed for somatotropin by enzyme immunoassay, for T(3) and T(4) by radioimmunoassay, and for total protein and FFA by a spectrophotometric method.

RESULTS

Serum somatotropin levels were insignificantly different between the lambs with and without their dams. Serum T(3) levels were generally lower in the separated lambs than those in other group. Serum T(4) levels were significantly lower in the separated lambs 48 h and 90 days after parturition than those in other group. Serum FFAs were insignificantly different between 2 groups. Serum total protein concentrations were lower in the separated lambs than lambs kept together with their dams (significantly at 12 and 48 h and 14 days).

CONCLUSION

Ingestion of colostrum and dam milk markedly affected serum total protein levels, but body weight and serum somatotropin levels were insignificantly affected. Also serum T(3) and T(4) levels markedly decreased with advancing age. Serum FFA levels were not affected by the trial.

Correlation of blood and milk components with the milk yield response to bovine somatotropin in dairy cows

Our aim was to correlate the individual variation in the milk yield response (MYR) of Holstein dairy cows to bovine somatotropin (bST), with changes in milk plasmin and plasminogen activities as well as with plasma hormone and metabolite levels. Thirty-two housed multiparous Holstein cows (90 +/- 3.8 days post partum) received daily subcutaneous injections of saline for 1 week followed by subcutaneous injections of 20 mg/day of bST for 2 weeks. Blood samples were taken at approximately 4h intervals over 24 h at the end of the saline and bST treatment periods. Milk samples were also taken at the end of the saline and bST treatment periods. The difference in milk yield between the saline and the second week of bST treatment (MYR) varied considerably between animals (from -0.2 to +8.6 kg/day, relative to the saline treatment week). Low milk yield before bST treatment was associated with a high MYR. The plasma growth hormone response to treatment was negatively correlated with MYR. Plasma insulin-like growth factor-1 response to treatment was positively correlated with MYR. Furthermore, a high MYR to bST was associated with a lower milk plasminogen level before treatment and a greater reduction in the level of plasminogen in milk following treatment.

Bovine Somatotropin and Rumen-Undegradable Protein Effects in Prepubertal Dairy Heifers: Effects on Body Composition and Organ and Tissue Weights

The objectives of this study were to determine the effect of recombinant bovine somatotropin (bST) and added dietary rumen undegradable protein (RUP) on organ and tissue weights and body composition in growing dairy heifers. Thirty-two Holstein heifers were in the experiment, 8 killed initially at 3 mo of age, with the remaining 24 Holstein heifers randomly assigned to treatments (n = 6) consisting of 0.1 mg/kg of body weight per day of bST and 2% added dietary RUP (dry matter basis) applied in a 2 x2 factorial design. A total of 6 heifers per treatment group (3 each at 5 and 10 mo of age), were slaughtered to determine body composition and organ masses. Feed intake measured from group intakes were increased by 0.25 and 0.35 kg/d with bST and RUP, respectively. Administration of bST tended to increase the weights of visceral organs including heart, kidney, and spleen by 16, 16, and 38%, respectively. At 10 mo of age, there was a trend for increased empty body weights (EBW) and non-carcass components for heifers treated with bST, but there were no effects of RUP. Body components and organ weights, expressed as a percentage of BW were not affected by RUP or bST. Somatotropin increased ash weight at 10 mo without affecting amounts of protein, fat, and energy. Rates of ash deposition between 3 and 10 mo of age were increased 7 and 4 g/d by bST and RUP, respectively. There were no treatment effects on rates of body fat, protein, and energy deposition. Bovine somatotropin and RUP altered the metabolism of growing heifers in a manner that was consistent with increased rates of skeletal growth. This suggests that nutritional and endocrine manipulations could increase growth rates of skeletal tissues without increasing fat deposition in prepubertal dairy heifers.

Individual variation in the milk yield response to bovine somatotropin in dairy cows

The objective was to relate the short-term milk yield response (MYR) following use of exogenous bovine somatotropin (bST) to changes in plasma concentrations of metabolites and hormones. Twenty-four Holstein cows (52 +/- 4.1 d postpartum) received daily subcutaneous injections of saline for 1 wk followed by subcutaneous injections of 33 mg/d of bST for 2 wk (Trial 1). The difference in milk yield between wk 1 and 3 for each cow was used to determine the 5 cows with the highest (HR) and 5 with the lowest responses (LR) to bST. These 10 cows were then used in 3 further trials of the same design (Trials 2, 3, and 4, conducted at 122, 181, and 237 +/- 7.6 d postpartum, respectively). Blood samples were taken 2 h after the administration of bST on d 1, 3, 5, 15, 17, and 19 of each trial. The HR group had consistently greater MYR to bST than the LR group throughout their lactation. The LR group had a higher milk yield and lower plasma insulin like growth factor-I (IGF-I) concentrations during the saline treatment in all trials. The increase in plasma somatotropin concentrations following injections of bST was greater for the LR group, whereas the difference in plasma IGF-I level between wk 1 and 3 was greater for the HR group. The HR group had lower levels of 3-hydroxy-butyrate and nonesterified fatty acids before bST treatment. Low short-term response to bST was associated with plasma concentrations of hormones and metabolites that indicate negative energy balance, although other factors may be involved.

Induced Lactation in Nonpregnant Cows: Profitability and Response to Bovine Somatotropin

Significant culling of high-producing cows with low fertility reduces profitability of dairy farms as those cows are replaced with heifers. Induced lactation of nonpregnant cows may be a management alternative to reduce culling and increase profits. The objectives of this study were to evaluate the efficacy of bovine somatotropin (bST) to increase milk production in cows induced into lactation with estrogen plus progesterone, and to determine the profitability of inducing cows into lactation vs. using replacement heifers entering the herd as first-lactation cows. Parity 1 or greater, nonpregnant, healthy Holstein cows (n = 28) were induced into lactation by administration of estradiol-17beta (0.075 mg/kg of body weight [BW] per d) and progesterone (0.25 mg/kg of BW per d) for 7 d. Milking began on d 18. Cows were randomly assigned to control or bST treatment groups on d 37 +/- 20 of milking, and milk production was compared for 70 d. After the 70-d comparison, all cows received bST for the duration of lactation. Cows receiving bST produced more milk (28.4 kg/d) than controls (24.1 kg/d), with variable yields among cows. For the economic analysis, induced cows were compared to first-lactation cows in the same herd using fair market value for costs and multiple component pricing for milk. Net present value for an induced cow (1966 dollars) was significantly greater than that for a first-lactation cow (1446 dollars). Our data suggest that bST use in induced cows is profitable. If a reliable method were developed and approved by the FDA, inducing nonpregnant cows into lactation could be used by dairy producers to increase profitability.

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.

Bovine Somatotropin Increases Hepatic Phosphoenolpyruvate Carboxykinase mRNA in Lactating Dairy Cows,

Somatotropin (ST) increases milk production and through coordinated changes in hepatic glucose synthesis and amino acid metabolism in dairy cows. The objective of this study was to determine the effects of ST on hepatic mRNA expression for phosphoenolpyruvate carboxykinase (PEPCK) and pyruvate carboxylase (PC), enzymes that are critical to the synthesis of glucose in liver and hepatic mRNA expression for carbamylphosphate synthetase I (CPS-I), argininosuccinate synthetase (AS), and ornithine transcarbamylase (OTC), critical enzymes of the urea cycle. Eighteen cows were randomly allocated to 2 treatment groups and received either recombinant bovine ST (Posilac; Monsanto, St. Louis, MO) or saline injections at 14-d intervals during a 42-d period. Expression of mRNA was determined using Northern blot analysis. Nuclei, isolated from liver biopsy samples, were used to determine effects of ST on transcription rate of PEPCK. Milk production was increased with ST (37.3 vs. 35.1+/-0.6 kg/ d). Plasma NEFA was increased with ST (299 vs. 156+/-34 microM). There were no differences in the expression of CPS-I, AS, and OTC mRNA with ST. Expression of PEPCK and IGF-I mRNA were increased with ST but PC mRNA was unchanged. The data indicate increased PEPCK mRNA in cows given ST and indicates a greater capacity for gluconeogenesis from gluconeogenic precursors that form oxaloacetate. The effects of ST to elevate PEPCK mRNA expression require chronic administration and involve increased transcription of the PEPCK gene.

Low Doses of Bovine Somatotropin During the Transition Period and Early Lactation Improves Milk Yield, Efficiency of Production, and Other Physiological Responses of Holstein Cows

The objectives of this experiment were to determine whether low doses of bovine somatotropin (bST) during the transition period and early lactation period improved dry matter intake (DMI), body weight (BW), or body condition score (BCS); provoked positive changes in concentrations of somatotropin, insulin, insulin-like growth factor-I (IGF-I), glucose, nonesterified fatty acids, and Ca; or improved milk yield (MY) response without obvious adverse effects on health status. Eighty-four multiparous Holstein cows completed treatments arranged in a 2 x 3 x 2 factorial design that included prepartum and postpartum bST, dry period (30 d dry, 30 d dry + estradiol cypionate, and 60 d dry), and prepartum anionic or cationic diets. Biweekly injections of bST began at 21 +/- 3 d before expected calving date through 42 +/- 2 d postpartum (control = 0 vs. bST = 10.2 mg of bST/d; POSILAC). At 56 +/- 2 d in milk, all cows were injected with a full dose of bST (500 mg of bST/14 d; POSILAC). During the prepartum period and during the first 28 d postpartum, no differences in mean BW, BCS, or DMI were detected between the bST treatment group and the control group. During the first 10 wk of lactation, cows in the bST treatment group had greater mean MY and 3.5% fat-corrected milk yield and lower SCC than did cows in the control group. When cows received a full dose of bST, an increase in milk production through wk 21 was maintained better by cows in the bST group. Mean concentrations of somatotropin, IGF-I, and insulin differed during the overall prepartum period (d -21 to -1). During the postpartum period (d 1 to 28), cows in the bST group had greater mean concentrations of somatotropin and IGF-I in plasma. Concentrations of Ca around calving did not differ because of bST treatment. Results suggest that changes in concentrations of blood measures provoked by injections of bST during the transition period and early lactation period resulted in improved metabolic status and production of the cows without apparent positive or negative effects on calving or health.

Responses of Holstein Cows to a Low Dose of Somatotropin (bST) Prepartum and Postpartum

Objectives were to evaluate the effects of a low dose of bovine somatotropin (bST) injected prepartum and postpartum on body condition score (BCS), body weight (BW), and milk yield (MY) in cows as well as somatotropin insulin, insulin-like growth factor-I (IGF-I), glucose, and nonesterified fatty acids (NEFA) in plasma. Holstein cows nearing second or later parities were assigned randomly to control (CON = 98) or bST-treated (TRT = 95) groups. Biweekly injections of bST began 21 +/- 3 d before expected calving and continued through 42 d postpartum (CON vs. TRT; 0 vs. 10.2 mg of bST/ d). From 42 to 100 d postpartum, no cows received bST. During yr 1, somatotropin, IGF-I, insulin, NEFA, and glucose were measured in plasma samples from 82 cows. During yr 2, effects of bST on BCS and BW of 111 cows were evaluated, but no blood samples were collected. Milk yields through 100 d of all 193 cows were analyzed. Prepartum treatment with bST resulted in greater prepartum plasma concentrations of somatotropin, insulin, and numerically greater NEFA but did not affect glucose or IGF-I. Postpartum bST increased mean plasma concentrations of somatotropin and NEFA, but not INS, IGF-I, or glucose. Mean BCS of cows did not differ prepartum, around parturition, or postpartum. Although mean BW did not differ prepartum or around calving, cows receiving bST maintained greater BW postpartum. Cows receiving bST tended to have higher MY (6.6%) in the first 60 d of lactation, but differences did not persist through 100 d, including approximately 40 d when no cows received bST. Number of cows that were culled due to health (CON = 3 vs. TRT = 2) or died (CON = 3 vs. TRT = 1) were not affected by treatment. Low doses of bST in the transition period resulted in higher postpartum BW, quicker recovery of body condition during lactation, and significantly more milk during treatment.

Effects of amino acid nutrition on the responses of dairy cows to milking more frequently with or without injection of growth hormone

The influence of amino acid nutrition on the response to milking more frequently, with or without injection of growth hormone, was examined in eight dairy cows in two 4 x 4 Latin squares with 28-d periods. The four treatments were a diet adequate in amino acids with or without injection of growth hormone and a diet inadequate in amino acids with or without injection of growth hormone. For all four treatments, during the last 14 d of each period, one half of the mammary gland was milked three times a day (3x), while the other half remained on twice-daily milking (2x). Both diets were based on grass silage given ad libitum and 4 kg/d of sugar beet pulp together with a supplement containing either fish meal (adequate diet) or feather meal (inadequate diet) as the only protein feeds. The diet containing feather meal is known to be deficient in His, Met, and Lys. On the fish meal diet, the cows responded positively to growth hormone and to milking more frequently and the responses to both treatments were additive. On the feather meal diet, however, even though injection of growth hormone increased the yield of milk protein by around 10%, milking more frequently did not affect milk production. It is concluded that milking more frequently has a weaker effect on the partitioning of amino acid use between body and udder than does growth hormone treatment.

Factors affecting application of milk allantoin as an estimator of microbial protein flow to the duodenum under commercial conditions

Three experiments were conducted to determine the effect of diet change, milk sampling technique, and bovine somatotropin (bST) on allantoin output in milk and the use of allantoin as a practical, noninvasive method for estimating microbial protein flow in dairy cattle. In experiment 1, four lactating Holstein cows were used in a 2 x 2 Latin square design with two treatments (ratio of forage to concentrate) and two periods. In experiment 2, six Holstein cows were used in a completely randomized design, and milk was collected by 1) a strip sample collected immediately before milking, 2) a strip sample collected 3 min from start of milking, and 3) a composite sample taken with an autosampler. In experiment three, 10 cows were used in a randomized block design to determine the effect of bST on milk allantoin. Milk samples were taken daily for 21 d, 7 d before, and 14 d after bST administration. In experiment 1, allantoin output (mmol/d) was significantly greater for cows fed the higher ratio of concentrate to forage, and there was a significant change in the amount of allantoin in milk 12 h (first subsequent milking) after a diet change. There was no difference in milk yield or dry matter intake between treatments. In experiment 2, no difference was detected in milk allantoin concentration among the three sampling methods. In experiment 3, milk yield, allantoin concentration, and total allantoin output was significantly increased after bST administration even though dry matter intake (DMI) remained unchanged. During the first 14 d following bST administration, estimates of microbial protein production derived from milk allantoin may be inaccurate due to increased milk production without an increase in DMI.

Reproductive performance in Ohio dairy herds in the 1990s

The objective of this study was to evaluate trends in reproductive performance in Ohio dairy herds during the 1990s. Stringent criteria for herd inclusion were applied to DHI records to ensure high quality and reliability of the data. The final data set contained 44,425 monthly herd summary records from 1772 herds from years 1992, 1994, 1996 and 1998. Outcomes of interest were calving interval length, calving-to-conception interval, days to first breeding, services per conception and first service conception rate. PROC MIXED in SAS (version 8.1) was used and the monthly records were treated as repeated measures nested within years and herds. First-order autoregressive covariance structure was used to model the covariance between the repeated measures within herds. The data were analyzed for the entire herd as well as for the first lactation cows separately. During the 1990s reproductive performance declined in Ohio dairy herds. Herd average calving interval lengthened from 13.6 to 14.1 months and calving-to-conception interval increased from 136 to 150 days between 1992 and 1998, respectively. Days to first service and number of services increased while first service conception rate declined on a herd level. The reproductive performance of first lactation cows, however, remained constant during this same period. Overall herd reproductive performance was associated with herd size and fat-corrected rolling herd average milk production (FCM). As milk yield increased, first service conception rate decreased and services per conception increased. Larger herds had lower first service conception rate and needed more services per conception, but they started breeding their cows earlier resulting in a slightly shorter calving interval and calving-to-conception interval compared to smaller herds.

Effects of gossypol from cottonseed on hematological responses and plasma alpha-tocopherol concentration of dairy cows

The effects of feeding whole cottonseed (WCS) and bovine somatotropin (bST) administration on hematological responses and plasma alpha-tocopherol concentrations of lactating dairy cattle were examined. After parturition, multi and primiparous Holstein cows (n = 159) were assigned randomly to a 2 x 2 factorial arrangement of treatments consisting of (0 or 15% WCS and 0 or 208 mg of bST injected every 2 wk starting within 7 d after calving. Blood samples were collected from a subset group of 64 cows at 14, 28, 42, and 56 d postpartum. Blood was collected from all cows (n = 159) at 75, 96 and 120 d postpartum. Blood samples were analyzed for alpha-tocopherol and total and (+)- and (-)-gossypol in plasma. Erythrocyte osmotic fragility, hemoglobin and hematocrit also were determined in blood. The mean concentrations of alpha-Tocopherol, total, and (+)- and (-)-gossypol were higher in cows fed WCS regardless of bST administration and plateaued by d 75 postpartum. Hematocrit and hemoglobin concentrations were not affected by treatments. Erythrocyte osmotic fragility was higher in cows fed WCS, but the increase was attenuated when bST was injected (diet x bST interaction). No clinical signs of gossypol toxicity were observed in the cows consuming the WCS.

Effects of whole cottonseed diet and recombinant bovine somatotropin on ovarian follicles in lactating dairy cows

The effects of whole cottonseed (WCS) in the diet and the administration of bovine somatotropin (bST) on ovarian follicular dynamics and plasma progesterone (P4) concentrations were examined in cows during a period of synchronized follicular growth. Lactating Holstein cows (n = 28) were randomly assigned to treatments in a 2 x 2 factorial arrangement. Diets consisted of WCS (15% of dry matter) or no WCS, and bST at a dose of 0 or 208 mg/14 d. Dietary treatments began within 24 h of calving and bST treatments began within 7 d postpartum. Cows received GnRH at 65 +/- 3 d postpartum (d 0), PGF2alpha, (d 7), a second dose of GnRH (d 9), and were inseminated 16 h later (d 10). Ovarian changes were monitored daily by ultrasonography from d 0 to 9. On d 9,93% of cows had a preovulatory follicle and 86% ovulated. For Class 2 (6 to 9 mm) follicles, a diet x bST interaction was detected, with bST stimulating Class 2 follicles in cows fed WCS, but not in cows on the control diet. Neither diet nor bST affected numbers of Class 1 (2 to 5 mm) or Class 3 (> or = 10 mm) follicles or sizes of the subordinate and dominant follicles. During the luteal phase of the cycle, lactating cows fed WCS tended to have elevated concentrations of plasma P4, whereas bST was without effect. Plasma concentrations of high-density lipoprotein cholesterol were increased in cows fed WCS. Number and diameter of corpora lutea did not differ among treatments.

Endocrine profiles of cows undergoing extended lactation in relation to the control of lactation persistency

We conducted an experiment in dairy cows investigating the effects of calving season, milking frequency and nutrition on lactation persistency. Cows calved in the Spring (n=12) or Winter (n=12). Commencing in lactation week 9 one udder-half of each cow was milked thrice-daily and half of each calving group received additional concentrate at a fixed rate of 3kg per day above that of the control cows. As reported elsewhere, between lactation weeks 9 and 33 persistency (measured as the slope of decline in milk yield) was significantly improved by frequent milking (P<0.001), by calving in the Winter (P<0.001) and by additional concentrate (P<0.05). The cows were rebred after week 33. When analysis of persistency was extended up to week 20 of the recurring pregnancy only the frequency effect remained significant. Persistency was unaffected by the pregnancy up until pregnancy week 20 but was then greatly reduced (P<0.001). In this paper we report hormone concentrations. GH was unaffected by nutrition but was consistently elevated in the Winter calving group relative to the Spring. IGF1 and prolactin were both unaffected by nutrition and calving season, IGF1 tended to increase as lactation progressed but changes in prolactin were related to time of year more than stage of lactation. Insulin was not affected by nutrition and was lower in Winter calvers, but only during early lactation. Prior to rebreeding, lactation persistency was correlated (slightly) with [GH] but not with [IGF1] or [insulin] and was correlated significantly with changes in GH, IGF1 (both positive) and insulin (negative). In conclusion, whilst bovine lactation persistency is plastic and amenable to beneficial manipulation, the details of its endocrine control remain to be elucidated.

Timing of onset of somatotropin supplementation on reproductive performance in dairy cows

The objective of this field trial was to determine whether delaying the start of recombinant bovine somatotropin (rbST) supplementation from 9 to 10 wk postpartum to 17 to 18 wk postpartum would improve reproductive performance in lactating dairy cows. Cows from nine herds (n = 798 cows; 766 Holsteins, 32 Jerseys) were assigned at random to receive rbST supplementation at 14-d intervals beginning during wk 9 to 10 (n = 399) or wk 17 to 18 (n = 399) after calving. Effects of herd, season of calving, parity, and onset of rbST supplementation (9 to 10 wk vs. 17 to 18 wk) on days to first service and days open were determined. In primiparous but not multiparous cows, there tended to be fewer days to first service and fewer days open when onset of rbST supplementation was delayed. Percentages of cows pregnant at 150, 200, and 250 d postpartum were also examined. Time of onset of rbST did not affect percentages of multiparous cows pregnant at 150, 200, and 250 d postpartum. However, there appeared to be a slight tendency for percentages of pregnant primiparous cows to be greater at 200 and 250 d postpartum for those receiving rbST supplementation beginning at 17 to 18 wk compared to those receiving rbST starting at 9 to 10 wk. In conclusion, delaying the start of rbST supplementation to wk 17 to 18 postpartum had no beneficial effect on reproductive performance of multiparous cows but tended to improve some measures of reproductive performance in primiparous cows.

Lactation and gestation in dairy cows: flexibility avoids nutritional extremes

The modern dairy cow has been selectively bred to produce large amounts of milk. Partly as a result, food consumption is considerably less than milk energy output in early lactation. It is only at 2 months or more postpartum that intake increases to the point where positive energy balance is regained, the initial production being achieved by a substantial mobilisation of body reserves. These reserves are laid down before parturition, but it is certainly not the case that the pregnant cow will accumulate adipose tissue recklessly; in the last third of pregnancy well-fed cows in good body condition exhibit reduced, not increased, appetite. There is a fine balancing act to perform. Excessive body condition at parturition quickly leads to metabolic problems such as ketosis, but cows who subsequently become too thin have increased risk of metabolic diseases such as mastitis and lameness. The biological mechanisms regulating output of milk are reasonably well understood, those controlling appetite less well so, and there has been little attempt at systematic integration of the two. The transition from pregnancy to lactation represents a major challenge to homeostasis, made more complicated in multiparous cows by the fact that much of gestation is concurrent with lactation. Herein lies the potential for nutritionally-entrained flexibility. In the wild, concurrent pregnancy and lactation only occur when nutritional conditions are favourable. If conditions are poor, rebreeding will be delayed and lactation will continue, at an energetically-sustainable level, for much longer than its 'normal' duration. In this way the twin energetic burdens of pregnancy and lactation are separated, and extremes are avoided. Given the increasing public concern about stresses suffered by intensively-managed dairy cows, this case may be one where commercial dairying could learn useful lessons from nature.

Concentração plasmática de colesterol total e lipoproteína de alta densidade em novilhas mestiças doadoras de embriões tratadas com somatotropina bovina recombinante

O objetivo do experimento foi o de estudar as concentrações plasmáticas de colesterol total e lipoproteína de alta densidade (HDL) em novilhas mestiças tratadas com somatotropina bovina recombinante (rbST). Coletas de sangue foram feitas durante dois ciclos estrais, normal e superovulado, em 26 fêmeas distribuídas em dois tratamentos: T1 = aplicação de 500mg de rbST no terceiro dia do ciclo estral utilizado para a superovulação e T2 = controle. Análises dos metabólitos sangüíneos foram feitas utilizando-se o método enzimático, cujas concentrações médias plasmáticas de colesterol total e de HDL durante o ciclo estral normal não foram diferentes (P>0,05) entre os dois tratamentos: 87,9 e 25,8mg/dl e 85,9 e 26,7mg/dl para T1 e T2, respectivamente. O ciclo estral utilizado para a superovulação foi dividido em três períodos: P1 = do estro à inseminação artificial (0 ao15º dia), P2 = da inseminação artificial até a coleta de embriões (15º ao 21º dia) e P3 = da coleta até o final do período experimental (21º ao 27º dia). As concentrações plasmáticas de colesterol total e HDL no P1 não diferiram entre os tratamentos (P>0,05). Em P2 e P3 houve diferença nas concentrações de HDL e colesterol total entre os dois tratamentos: 29,0 e 88,5mg/dl (T1) e 27,1 e 81,8mg/dl (T2) no P2; e 30,4 e 88,0mg/dl (T1) e 26,6 e 80,5mg/dl (T2) no P3, respectivamente (P<0,01).

Pituitary adenylate cyclase-activating polypeptide induces secretion of growth hormone in cattle

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a hypothalamic neuropeptide that stimulates release of growth hormone (GH) from cultured bovine anterior pituitary gland cells, but the role of PACAP on the regulation of in vivo secretion of GH in cattle is not known. To test the hypothesis that PACAP induces secretion of GH in cattle, meal-fed Holstein steers were injected with incremental doses of PACAP (0, 0.1, 0.3, 1, 3, and 10 microg/kg BW) before feeding and concentrations of GH in serum were quantified. Compared with saline, injection of 3 and 10 microg PACAP/kg BW increased peak concentrations of GH in serum from 11.2 ng/ml to 23.7 and 21.8 ng/ml, respectively (P < 0.01). Peak concentrations of GH in serum were similar in steers injected with 3 or 10 microg PACAP/kg BW. Meal-fed Holstein steers were then injected with 3 microg/PACAP/kg BW either 1 hr before feeding or 1 hr after feeding to determine if PACAP-induced secretion of GH was suppressed after feeding. Feeding suppressed basal concentrations of GH in serum. Injection of PACAP before feeding induced greater peak concentrations of GH in serum (19.2 +/- 2.6 vs. 11.7 +/- 2.6 ng/ml) and area under the response curve (391 +/- 47 vs. 255 +/- 52 ng. ml(-1) min) than injection of PACAP after feeding, suggesting somatotropes become refractory to PACAP after feeding similar to that observed by us and others with growth hormone-releasing hormone (GHRH). We concluded that PACAP induces secretion of GH and could play a role in regulating endogenous secretion of GH in cattle, perhaps in concert with GHRH.

Effects of sustained release bovine somatotropin (sometribove) on animal health in commercial dairy herds

The health of dairy cows given bovine somatotropin (bST) for one lactation was evaluated in 28 commercial herds located in four regions of the United States. At least six herds were in a region and at least one herd/region contained fewer than 60 cows. Cows (n = 1213) were assigned randomly to control or bST groups and were treated beginning in wk 9 to 10 of lactation and every 14 d until dry-off or d 400 of lactation. Management was according to site practices. Cows were observed for health-related signs by farm personnel daily and by the herd veterinarian biweekly. Average 305-d test-day milk yields were 932 kg greater for bST-treated cows. Pregnancy rates, days open, twinning, cystic ovaries, or abortions were unaffected by treatments. Supplementation of cows with bST had no effect on total mastitis cases, total days of mastitis, duration of mastitis, or the odds ratio of a cow to develop mastitis. Cows supplemented with bST used more medications for health events other than mastitis. This usage was associated primarily with treatments for disorders of the foot and hock. Supplemented cows had a slight increase in foot disorders. There was no effect of supplementation with bST on culling from the herd or removal from study. Overall, the results confirm that label directions for bST are adequate for safe use under field conditions. All clinical signs observed in this study occur normally in dairy herds and were managed in cows supplemented with bST.