Overall efficacy of chronically administered recombinant bovine somatotropin to lactating dairy cows

The Impacts of Climate Change Mitigation Strategies on Animal Welfare

The objective of this review is to point out that the global dialog on reducing greenhouse gas emissions in animal agriculture has, thus far, not adequately considered animal welfare in proposed climate change mitigation strategies. Many suggested approaches for reducing emissions, most of which could generally be described as calls for the intensification of production, can have substantial effects on the animals. Given the growing world-wide awareness and concern for animal welfare, many of these approaches are not socially sustainable. This review identifies the main emission abatement strategies in the climate change literature that would negatively affect animal welfare and details the associated problems. Alternative strategies are also identified as possible solutions for animal welfare and climate change, and it is suggested that more attention be focused on these types of options when allocating resources, researching mitigation strategies, and making policy decisions on reducing emissions from animal agriculture.

Nano-islands integrated evanescence-based lab-on-a-chip on silica-on-silicon and polydimethylsiloxane hybrid platform for detection of recombinant growth hormone

Integration of nano-materials in optical microfluidic devices facilitates the realization of miniaturized analytical systems with enhanced sensing abilities for biological and chemical substances. In this work, a novel method of integration of gold nano-islands in a silica-on-silicon-polydimethylsiloxane microfluidic device is reported. The device works based on the nano-enhanced evanescence technique achieved by interacting the evanescent tail of propagating wave with the gold nano-islands integrated on the core of the waveguide resulting in the modification of the propagating UV-visible spectrum. The biosensing ability of the device is investigated by finite-difference time-domain simulation with a simplified model of the device. The performance of the proposed device is demonstrated for the detection of recombinant growth hormone based on antibody-antigen interaction.

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.

Development and Validation of a Simple Sensitive Enzyme Immunoassay (EIA) for GH Determination in Buffalo Plasma

A simple and highly sensitive enzymeimmunoassay (EIA) for GH determination in buffalo plasma on microtitreplates using biotin-streptavidin amplification system and the second antibody coating was developed. Biotin was coupled to GH and used to bridge between streptavidin-peroxidase and immobilized antiserum in competitive assay. The EIA was carried out directly in 100 microL buffalo plasma. The GH standards ranging from 0.05 ng/well/100 microL to 12.8 ng/well/100 microL were prepared in hormone free plasma collected from an aged (> 15 years) senile buffalo. The sensitivity of the EIA procedure was 50 pg/well GH. which corresponded to 0.50 ng/mL plasma; the 50% relative binding sensitivity was seen at 800 pg/well/100 microL. Plasma volumes for the EIA, viz., 25, 50, and 100 microL did not influence the shape of standard curve, even though a slight drop in the OD450 was seen with higher plasma volumes. For the biological validation of the assay, 12 Murrah buffalo calves were used. Six of these were administered synthetic bovine growth hormone-releasing factor (10 microg/100 kg body weight, i.v., and the remaining six animals were administered sterile normal saline and kept as controls. Jugular blood samples were collected at -60, -45, -30, -15, -10, -5, 5, 10, 15, and 30 min and, thereafter, at an interval of 15 min using an indwelling jugular catheter, beginning 1 h prior to GRF injection up to 8 h post treatment. In all animals, a peak of GH was recorded within 5 to 20 min of GRF administration, which confirms the biological validation of the EIA. To confirm homogeneity of buffalo GH with bovine GH, a parallelism test was conducted between the buffer standard curve of bovine GH and GH measured from serial dilution of buffalo plasma containing a high level of endogenous growth hormone.

Effects of BST on oviductal and uterine genes encoding components of the IGF system in lactating dairy cows

Lactating Holstein cows, averaging 80 d in milk, were used to examine effects of exogenous bovine somatotropin (bST) on oviductal and uterine genes encoding components of the insulin-like growth factor (IGF) system. About 12 h before expected ovulation in an Ovsynch protocol, cows were assigned randomly to receive bST (500 mg; n = 11) or serve as untreated controls (n = 10). Cows that ovulated (n = 9 bST, 8 control) were divided within treatment to be sacrificed on d 3 or 7 postovulation. Samples of oviductal and intercaruncular endometrial tissue from oviducts and uterine horns ipsilateral to the corpus luteum (CL) were collected and immediately frozen at -80 degrees C for subsequent mRNA analyses. Northern blots revealed mRNAs for IGF-II, IGF-binding protein-2 (IGFBP-2), and IGFBP-3 in all oviductal and endometrial tissues. Significant amounts of IGF-I and growth hormone receptor-1A (GHR-1A) mRNAs were detected in uteri but not in oviducts. The bST treatment had no effect on amount of IGF-I mRNA transcript in uterine endometrium. The mRNA encoding IGF-II was induced by bST in oviducts collected on both d 3 and 7 but was down-regulated in endometrium on d 7. Transcript of IGFBP-2 mRNA was greater in endometrial than oviductal tissues and did not differ between treatments. Both oviductal and endometrial IGFBP-3 mRNA concentrations increased between d 3 and 7 postovulation, with a tendency for greater endometrial IGFBP-3 mRNA in bST-treated cows on d 7. On d 7, concentrations of endometrial GHR-1A mRNA were 30% lower in bST-treated cows. Results indicate complex and tissue-specific regulation of the uterine IGF system components by exogenous bST. Some of those biological responses to bST may be important in early development of bovine embryos.

Recombinant bovine somatotropin: association with reproductive performance in dairy cows

A clinical trial was performed to determine the effect of bST on reproductive performance in dairy cows on 4 Michigan dairy farms when bST was used according to labeled directions. Holstein cows (n = 555) at 4 Michigan dairy farms were randomly assigned to receive bovine somatotropin (bST) or to serve as untreated controls. Bovine somatotropin (500 mg, s.c.) was administered every 14 d beginning at 63 to 69 d of lactation and continuing until approximately 21 d prior to the end of lactation or until the producer removed the animal from the herd. A total of 229 (42.57%) animals consisting of 112 (48.91%) controls and 117 (51.09%) bST-treated cows were not diagnosed pregnant and were considered as having reproductive failure by 150 d of lactation and 92 (17.10%) of the animals consisting of 45 (48.91%) controls and 47 (51.09%) bST-treated cows had reproductive failure at the end of their lactation. No significant difference in the incidence of reproductive failure existed between the study treatment groups during either time frame. Cows with cystic ovarian disease had more instances of reproductive failure at 150 d of lactation than cows without this disease. Cows with dystocia, twin births, metritis, displaced abomasum and cystic ovarian disease had more instances of reproductive failure by the end of lactation than cows without these diseases. The bST-treated cows developed more nonspecific off feed conditions during the study lactation and had more twin births at the calving following bST administration compared to control cows. No differences were found between the study treatment groups in calculations of reproductive parameters. Logistic regression analysis found no significant effect of bST on reproductive failure; the odds ratios for the bST treatment effect on reproductive failure at 150 d of lactation and reproductive failure at the end of lactation were 0.95 (95% CI 0.67 to 1.36) and 0.95 (95% CI 0.59 to 1.54), respectively. Overall, bST was not found to have a significant impact on reproductive performance in the herds studied.

Effect of exogenous somatotropin on hematological variables of lactating cows and their offspring

Eighty-two lactating Holstein cows in their first, second, or third lactation received either one, three, or five concurrent i.m. injections of a unit dose (0.6 g) of zinc methionyl bovine somatotropin (bST) or five doses of the vehicle. Injections were administered at 14-d intervals from 60 +/- 3 d postpartum until the end of lactation or until necropsy. Thirty-eight cows were continued on the treatment for a 2nd yr. Blood samples were collected at wk -2, -1, 3, and 7 relative to the start of treatment and then every 8 wk (yr 1) or 4 wk (yr 2) thereafter. Untreated cows that were included in a survey of the resident herd were bled at wk 7 or 8, wk 10 or 11, and wk 13 or 14 of lactation and every 4 or 8 wk thereafter. Calves were bled within 72 h of birth and at approximately 5 wk of age. Most parameters associated with erythrocytes were decreased mildly in cows that were treated with bST. However, data remained within generally accepted reference ranges, and changes were not of clinical importance. Decreased hematocrit was not associated with increased hemolysis, hemodilution, or clinical anemia. No morphological lesions related to treatment were noted in the bone marrow or spleen; bST did not affect the incidence of immature cell types. Energy and protein balances did not significantly affect the hematological results of the cows. Calves generally were unaffected by bST treatment of the dam, but heavier calves had higher parameters associated with erythrocyte and lymphocyte counts than did calves with lower body weight. Exogenous bST treatment caused predictable changes in hematological parameters of dairy cows.

Effect of bovine somatotropin administered to periparturient dairy cows on the incidence of metabolic disease

Thirty-eight dry, pregnant Jersey cows were assigned to diet and bST treatment in a 2 x 2 factorial design. During the dry period, half of the cows were fed a normal TMR (0.4% Ca; 0.3 to 0.4% P), and half of the cows were fed a high Ca TMR (1.5 to 1.6% Ca; 0.4 to 0.7% P). The high Ca diets were designed to induce milk fever and were relatively cationic (194 to 293 meq/kg) compared with the normal diets (-131 to 30 meq/kg). A standard dairy diet was fed to all cows postcalving. Cows received subcutaneous injections of either an oil-based excipient or 500 mg of bST in an oil-based excipient every 14 d from 28 d before expected calving until approximately 14 d postcalving. Peripartal bST treatment decreased the incidence of clinical mastitis, did not affect incidence of milk fever, and increased the duration, but not the incidence, of ketosis in mature Jersey cows. Blood data confirmed the clinical responses and indicated that treated cows mobilized more bone Ca than did controls, as was evidenced by increased hydroxyproline concentrations. Treatment with bST did not affect blood concentrations of 1,25-dihydroxyvitamin D, Ca, or Mg. High Ca diets increased the incidence of milk fever and downer cow syndrome compared with normal diets. The effect of bST on mastitis and milk production must be considered as preliminary given the small size of the study. Although bST treatment increased Ca mobilization, the effect was insufficient to prevent milk fever in this model.

Reproductive performance in high producing dairy cows treated with recombinant bovine somatotropin

The reproductive performance of 156 cows treated with recombinant bST for two consecutive lactations was assessed as part of a target animal safety study conducted in the San Joaquín Valley of central California. Daily intramuscular administration of 17.2, 51.6, and 86 mg of bST per cow started at d 70 postpartum and ended at dry-off or 305 d postpartum. The AI did not begin until d 70 postpartum. During the first lactation study, multiparous cows treated with bST had significantly decreased pregnancy rates, increased behavioral anestrus, and increased anestrus confirmed by palpation. Treated primiparous cows in first lactation had shorter mean days to first standing estrus. In the second lactation study, cows treated with bST had an increased rate of delayed uterine involution, cystic ovarian condition, behavioral anestrus, and anestrus confirmed by palpation. Progeny from the first lactation cows were evaluated for rates of growth, morbidity, mortality, and for reproductive performance; no difference was detected between the progeny from different groups.

Interval from calving to conception in high producing dairy cows treated with recombinant bovine somatotropin

Intervals from calving to conception in cows treated for two lactations with recombinant bST were ascertained using survival analysis methods. Daily intramuscular administration of placebo, 17.2, 51.6, or 86 mg of bST per cow started at d 70 postpartum and ended at culling or drying off. Breeding began at d 70 postpartum. Multiparous cows treated during the first lactation had significantly longer intervals from calving to conception. Cows treated during the previous lactation, but not during the second lactation, had significantly shorter intervals from calving to conception. Cox proportional hazards regression analysis was used with adjustment for the confounding effect of serum metabolites, milk production, energy balance, and body condition.

Interactions of energy and bovine somatotropin with heat stress

Heat stress, resulting when dairy cows are exposed to hot or to hot and humid environmental conditions, reduces DMI and milk yield and increases maintenance costs of the cow. Decreased DMI may help to maintain homeothermy through reduced metabolic heat production. The high yielding cow has greater metabolic activity and produces more body heat than those with lower yields; thus, greater milk yield may increase heat stress if the cause of that stress is not mitigated. Use of bST increases milk yield, and, during hot or hot and humid environmental conditions, bST increased milk yield with or without noticeable effects on heat stress, depending on the study. The use of bST does not change maintenance requirements or partial efficiencies of milk yield. Thus, the greater heat stress that occurred in some studies probably was related to the increased metabolic activity and heat production associated with milk yield and to the difficulties of cows in dissipating the additional body heat from environmental conditions. Cows that are administered bST are subject to heat stress as are other high yielding cows if sufficient metabolic heat is not dissipated. Management to minimize effects on the cow of environments conducive to heat stress and strategies that improve DMI are necessary to sustain the high milk yield potential offered by technologies, including bST.

Pregnancy incidence in high producing dairy cows treated with recombinant bovine somatotropin

Reproductive performance in cows exposed for two lactations to recombinant bST was measured using unconditional logistic regression. Intramuscular administration of 17.2, 51.6, and 86 mg of recombinant bST/d per cow started at d 70 postpartum and ended at dry-off or 305 d postpartum. Performance was measured as the cumulative incidence of cows becoming pregnant by 305 d post-partum. Within each parity group, cows treated with bST had higher total milk yield. During the first study lactation, the log odds of a cow becoming pregnant decreased linearly as dose increased, following adjustment for serum cholesterol, blood urea N, average daily milk yield, peak milk yield, net energy balance, and body condition score. However, differences in pregnancy incidence between treated and untreated cows were statistically significant only at the higher dose categories, the 51.6 and 86.0 mg of recombinant bST per cow. During the second study lactation, pregnancy rates were similar to those in the first lactation; rates reduced as recombinant bST dose increased. The singular exception was for cows exposed to recombinant bST during the previous lactation but not during the second. In the latter group, previously treated cows had higher pregnancy incidence than did the controls.

Multi-farm use of bovine somatotropin for two consecutive lactations and its effects on lactational performance, health, and reproduction

In a two-lactation study, 352 Holstein cows (124 primiparous) from six commercial dairy herds were assigned to daily injections of bST. Dosages were 0 (control), 5.15, 10.3, or 16.5 mg/d of bST; injections began 28 to 35 d postpartum. During yr 1, FCM production increased linearly as bST dose increased for primiparous and multiparous cows. However, FCM production for primiparous cows that were retained for yr 2 was not increased by bST, and the increase in FCM for multiparous cows was only 67% of that observed during yr 1 for doses of 10.3 and 16.5 mg/d. Milk SCC were not increased with the use of bST during either lactation. Days to conception of multiparous cows during yr 1 tended to increase linearly with increasing dose. Multiparous cows administered bST during yr 2 tended to have a lower conception rate than control cows (71 vs. 87%, respectively). Body condition was decreased linearly by bST dose at the end of yr 1 and 2. Prior to receiving bST during yr 2, bST-treated cows regained less body condition than control cows. Number of health disorders at parturition and assisted births of cows that received bST during yr 1 were unaffected by previous treatment. General health, ratio of single to multiple births, and BW gain of calves was similar among treatments.

Effects of recombinant bovine somatotropin under conditions of high production and heat stress

The effect of bST injection on milk production of Israeli Holsteins was tested under conditions of mean production > 9000 kg/yr and climatic stress; mean maximum and minimum summer temperatures are 38 and 25 degrees C, respectively, in the Jordan Valley, located 200 m below sea level. In 1989, 111 cows were injected, and 115 cows were recorded as controls. In 1990, 108 cows were injected, and 93 cows were included as controls. Fifty-nine of the cows injected in 1990 were also injected in 1989. Production records were corrected for parity, calving month, days to first injection, and days in milk. Injection with bST increased total lactation milk production by 12%, fat production by 15%, and protein production by 13%. Injection also resulted in slight increases in fat and protein percentages. Daily milk production during the injection period was increased by 4.4 kg. Injection during the previous lactation slightly decreased production of cows injected during the following lactation. Advancing the commencement of injection from the 4th to the 2nd mo in milk did not affect total lactation production. Weight gains and dry matter intake were higher for injected cows, but body condition score was higher for the control group. Injection had no discernible effect on fertility variables.

Enzyme immunoassay for the determination of bovine growth hormone using avidin-biotin-peroxidase complexes

The development of a competitive enzyme immunoassay for bovine growth hormone (bGH) is described. Antiserum, raised in rabbits and diluted 1/250,000, was preincubated with samples and free antibodies from the reaction mixture were immobilized using a microtiter plates coated with bGH. Bound antibodies remaining from the preincubation were visualized using a biotinylated second antibody as a bridge for subsequent amplification by an avidin-biotin-peroxidase complex. The measuring range was between 0.5 and 100 ng/ml. Cross-reactivity with other pituitary hormones was < 0.1%. The intra- and interassay coefficients of variations were 8.1 and 12.7%, respectively, and the recovery of added bGH was 110%. To validate the assay, two bull calves were treated with bGH-releasing factor. The response showed that there was an immediate rise in immunoreactive bGH which peaked after 5 and 15 min at 200 ng/ml and 60 ng/ml, respectively. This enzyme immunoassay is an economic and sensitive alternative to the established radioimmunoassay, and the first competitive enzyme immunoassay described for bGH.

Lactation, health, and reproduction of dairy cows receiving daily injectable or sustained-release somatotropin

Seventy-four Holstein cows (26 primiparous) were utilized to compare the efficacy and safety of sustained-release versus daily injectable formulations of recombinant bST. Twenty-four control cows were injected biweekly with oil microsphere; 25 cows were injected biweekly with 350 mg of bST microsphere; and 25 cows were injected daily with 10.3 mg of bST. Injections were initiated between wk 4 and 5 of lactation and continued for 280 d. Administration of bST caused a moderate increase in milk and FCM production and improved the efficiency of feed and energy conversions. Most health-related and reproduction-related variables did not differ among treatment groups. However, incidence of teat and udder disorders and feet and leg problems tended to be higher during the 40-wk injection period for the bST-treated cows than for the control cows. Incidence of GnRH therapy and number of days to first service were higher for daily bST-treated cows than for controls. No differences existed between sustained-release and daily bST-treated cows for any parameters monitored.

Effect on production traits of bovine somatotropin for up to three consecutive lactations

Thirteen (control) cows were injected daily with saline and 22 with bST (12 at 10.3 mg/d and 10 at 20.6 mg/d) through wk 5 to 42 of lactation. Nine of the treated cows had received bST in the previous lactation, and 7 cows received bST in the previous two lactations. All control cows and 6 treated cows had not previously received bST. Treatment with bST caused substantial increases in milk production, feed intake, and efficiency of feed conversion in the current lactation, which is consistent with previous trials. Increases in feed intake were established fully within 9 wk of starting bST administration, somewhat earlier than usually reported. Treatment with bST in one or two previous lactations caused a statistically significant 14% reduction in production and 8% reduction in efficiency of feed conversion during the first 9 wk of bST treatment in the current lactation; reductions observed later in lactation were not statistically significant. Differences for other traits were not statistically significant. In combination with earlier trials, these results suggest that, although bST has beneficial effects on production and efficiency traits, these benefits may be considerably lower in the second and subsequent lactations of bST use. However, carry-over effects on cows not receiving bST in the current lactation were not explored in this trial.

The effects of genetic and phenotypic production potential on response to recombinant bovine somatotropin

Evidence was sought for an interaction between both phenotypic and genetic production potential and response of milk production to administration of bST in three trials of 38, 43, and 35 cows. In each trial, bST was administered in doses of 0, 10.3, 20.6, and, in trial 1 only, 41.2 mg/d for 38 wk from wk 4 of lactation. Data were analyzed for each experiment separately and combined across experiments. Analyses included separate regressions for treated and untreated animals for milk production during the production period on pretreatment production and estimated breeding value for milk production. Breeding value was estimated as the sire's estimated transmitting ability plus one-half of the maternal grandsire's estimated transmitting ability. With the exception of regression on estimated breeding value in trial 1 and in combined data, differences between treated and untreated animals in the regression of milk production on pretreatment milk production or on estimates of breeding value were not statistically significant. However, regressions on pretreatment production were substantially lower for treated than for untreated animals in each of the three trials. Regressions on breeding value estimated from sire and maternal grandsire estimated transmitting abilities were substantially, but not significantly, lower for untreated than for treated animals in all three trials. The results suggest that cows with high production potential for nongenetic reasons may show diminished response to bST, whereas cows with genetically high production potential show enhanced response. However, borderline statistical significance argues for considerable further examination before drawing firm conclusions.

Milk yield of dairy cows receiving somatotropin (somavubove) daily with periodic 14-day interruption

Thirty multiparous (cows) and 15 primiparous (heifers) lactating Holstein cattle were used in a 112-d study to examine the effects of pattern of administration of recombinantly derived bST on 3.5% FCM yield. Ten cows and 5 heifers each received either no injection (controls), 14 mg of bST daily, or four repetitions of 14 mg of bST/d for 14 d followed by 14 d of no injection (intermittent bST). Because there was an interaction between treatment groups and parity, analyses were performed separately for cows and heifers. All cows and heifers produced more FCM when given bST than controls. Comparing FCM only during the last 7 d of each period of injection for the intermittent bST group with contemporary daily injected cattle indicated that cows produced equivalent amounts of milk at those times, whereas heifers given daily bST produced 3.4 kg/d more than intermittently injected animals. Furthermore, over each of the four repetitive periods, cows and heifers given daily or intermittent bST responded similarly, although heifers given continuous bST produced more FCM than the intermittent group during each of periods 2 through 4. We conclude that daily administration of bST lends itself to dosing termination during established lactation with concomitant decline of FCM; resumption of bST allows milk yields of cows to achieve levels comparable with those prior to short-term interruption.

Effects of sometribove on performance, carcass composition, and chemical blood characteristics of dairy calves

Ten intact male Holstein calves averaging 75 kg of BW and 59 d of age were used to study the effects of daily injections of 0 (control) or 10 mg of sometribove (recombinant methionyl bST) for 6 wk on performance, health, carcass composition, N metabolism, chemical blood characteristics, and hormone profiles. Average daily gain, feed intake, feed:gain ratio, and height at withers, hip, and hock were not influenced by bST. Carcasses from bST-treated calves contained 5% more protein and 36% less lipid than controls. Circulating concentrations of Ca, P, glucose, urea N, alkaline phosphatase, creatine phosphokinase, insulin-like growth factor-I, and insulin were not affected by bST. Packed cell volume was decreased about 7% (29.9 vs. 32.4%) in the bST calves. Hormone injection did not adversely affect health of the calves as measured by body temperature and by pulse and respiration rates. The most profound effects of sometribove were a reduction in carcass lipid and an increase in body proteins. These effects may be of some practical importance when leanness of carcass is desirable.

Influence of bovine somatotropin and nutrition on production and composition of milk from dairy cows

Forty-eight multiparous Holstein cows were used in an experiment with a 2 x 2 factorial arrangement of treatments to study interactions of bST and nutrient density during wk 5 through 20 postpartum. Main effects were bST (0 or 10.3 mg/d) and diet (control or high protein and energy). The control diet was formulated to contain 16.3% CP and 1.65 Mcal of NEL/kg of DM; the high protein and energy diet was formulated to contain 18% CP and 1.74 Mcal of NEL/kg of DM with additional energy as fat from extruded soybeans and calcium salts of fatty acids. Diet ratios were 50:25:25 for concentrate:alfalfa hay:corn silage (DM basis). Bovine somatotropin increased milk production (40.9 vs. 37.9 kg/d) and production of 4% FCM (35.7 vs. 32.3 kg/d). The high protein and energy diet increased milk production (40.3 vs. 38.5 kg/d); 4% FCM production was higher for high protein and energy plus bST (36.0 kg) than without bST (33.6 kg). Percentage of milk fat was not affected by treatment. Percentage of milk protein was reduced with the high protein and energy diet, presumably because of the added fat, but this reduction was less with high protein and energy plus bST. Dry matter intake was not significantly elevated by bST (23.1 vs. 22.8 kg/d) but was lower for high protein and energy (22.0 vs. 23.8 kg/d). Increased dietary protein and energy with bST augmented the total milk production response.

Serum immunoglobulin profiles of dairy cows chronically treated with recombinant bovine somatotropin

The objective of this study was to determine the effects of exogenous somatotropin on blood profiles of the major bovine Ig isotypes. Holsteins were treated with either 0, 10.3, or 20.6 mg recombinant bST/d. Subcutaneous injections were started between wk 4 and 5 of lactation and continued for 266 d. Blood samples were collected by coccygeal venipuncture throughout lactation for serum IgG, G1, G2, A, and M concentration determination. Cows treated with 10.3 mg of bST/d exhibited modest increases in mean blood concentrations of IgG (12.4%) and IgG2 (18.4%) relative to the other groups of cows. In addition, treated cows had 10.1% higher average concentration of IgA than controls. Somatotropin did not influence average lactational concentrations of IgG1 or IgM, although the group receiving 10.3 mg/d had higher late lactation concentrations of IgG1 than did the other two groups. However, treatment mean isotype concentrations were always within normal ranges, except for IgG2 from the 10.3 mg/d group, which were higher. The practical significance of elevated serum Ig concentrations observed in the present study is not known. However, the present data do show that bST administered at doses that increased milk yield had no apparent detrimental effect on humoral immunity as measured by blood concentrations of Ig.

Influence of exogenous bovine somatotropin on the responsiveness of peripheral blood lymphocytes to mitogen

Our objectives were to determine the effects of exogenous bovine somatotropin on peripheral blood lymphocyte responsiveness to mitogen and on concentrations of serum insulin-like growth factor-I and to determine whether a statistical relationship exists between these two variables. The cows on trial were treated with 0, 10.3, or 20.6 mg/d somatotropin, starting between wk 4 and 5 of lactation and continuing for 266 consecutive d. Lymphocyte proliferation (counts per minute) and concentration of insulin-like growth factor-I (nanograms per milliliter) were recorded from blood sampled at wk 3, 10, 26, 35, and 46 of lactation. The results showed that lymphocytes from the blood of treated cows responded to mitogen with higher proliferative responsiveness than cells from control cows, but that this effect required long-term treatment and adequate mitogen concentrations to be detected. The blood of treated cows also had elevated concentrations of insulin-like growth factor-I relative to that of control cows, but these were not statistically associated with the proliferative responsiveness of the peripheral blood lymphocytes to mitogen. Our results suggest that somatotropin has a role in the immune system of cows, but its mode of action and target tissues must be determined. Bovine somatotropin, injected at doses that increase milk yield, can augment cow immunity as judged by the proliferative responsiveness of peripheral blood lymphocytes in culture.

Use of recombinant bovine somatotropin for up to two consecutive lactations on dairy production traits

Fifteen (control) cows were injected with saline; 28 cows were treated with rbST (15 with 10.3 and 13 with 20.6 mg/d). Fourteen of the 28 treated cows had between injected with rbST in the previous lactation. A total of 29 cows in the present trial had not received rbST in previous lactation. Treatment injections were started between wk 4 and 5 of lactation and continued for 266 consecutive days. Milk production, fee intake and efficiency, and BW data were recorded for 3 wk before and 3 wk after a 38-wk rbST treatment period. Administration of rbST increased average FCM yields in the current lactation by 19%, increased feed energy intake by 7%, and decreased feed conversion (energy intake per unit FCM output) by 17%. Previous treatment with rbST did not significantly affect current milk production but caused a nonsignificant increase in feed intake and a significant, unfavorable, increase in feed conversion of 12%. The results suggest that the advantages of rbST in terms of increased milk yield are maintained for a second consecutive lactation of rbST administration. However, the advantages of rbST in terms of improved feed conversion may be substantially reduced in a second consecutive lactation of administration.

Health and reproductive performance of dairy cows treated for up to two consecutive lactations with bovine somatotropin

Forty-three purebred Holstein cows were put on an rbST milk production trial. There were 15 control cows (saline-injected), 15 cows injected with 10.3 mg rbST/d and 13 cows injected with 20.6 mg rbST/d. Injections were initiated between wk 4 and 5 of lactation and continued for 266 consecutive days. Fourteen of the rbST-treated cows were treated with one of three dosages of rbST in the previous lactation (10.3, 20.6, or 41.2 rbST/d). The objective of this study was to determine the health and reproductive efficiency of cows treated with rbST for up to two consecutive lactations relative to control cows. The incidence of 11 health-related variables before, during, and after the 38-wk injection period were not different among treatment groups. Previous treatment with rbST had no effect on reproductive variables; however, there was evidence that injections with the highest dosage of rbST in the current lactation resulted in lowered reproductive efficiency. It is possible that the effects of rbST on early lactation energy and nitrogen balance have confounding effects on the estrous cycle.