Responses by lactating cows in commercial dairy herds to recombinant bovine somatotropin

Effect of two formulations of recombinant bovine somatotropin on milk production and body condition of cattle under intensive management in Peru

The effect of recombinant somatotropin (rbST) application in cattle has been demonstrated in temperate climate but very limited studies are available in tropical regions. The objective of this study was to compare the effect of the application of two different formulations of rbST on the milk yield and body condition of dairy cattle in a commercial herd under intensive production in Peru. We evaluated the application of 500 mg of active rbST in a zinc sesame oil (ZSO-rbST; n = 44) or vitamin E lecithin (VEL-rbST; n = 45) vehicle while control cows (n = 42) did not receive any application. The application of rbST was performed by every 14 days for 12 cycles, for a total of 168 days. The application of rbST increased the milk production of primiparous and multiparous cows by 3 and 3.2 kg/day for the VEL-rbST formulation respectively when compared with control cows (p < 0.01) and no difference in milk production was observed between the ZSO-rbST formulation and the control group (p > 0.05). However, no significant difference on milk production was observed between the rbST formulations evaluated. The effect of rbST per injection cycle indicated differences in milk production and economic return for the 12 cycles between rbST and control in primiparous group, while in multiparous, no differences were found between ZSO-rbST and control (p > 0.05), but differences were observed between VEL-rbST and control in 41% of the cycles (p < 0.05). No differences in body condition were found between the two rbST formulations and the control group during the evaluation. In conclusion, the application of rbST promoted higher milk production of cattle which had a positive impact on the economic income of the farmer.

Meta-analysis of the effects of sometribove zinc suspension on the production and health of lactating dairy cows

OBJECTIVE

To provide an updated evaluation of the efficacy and safety of sometribove zinc suspension (rbST-Zn), a form of recombinant bovine somatotropin, in lactating dairy cows.

DESIGN

Meta-analysis.

SAMPLE

26 studies published in peer-reviewed journals or reviewed by a regulatory agency.

PROCEDURES

To be included, a study had to involve the use of the rbST-Zn formulation available to US producers in accordance with the label instructions for treatment initiation (57 to 70 days postpartum), dose (500 mg, q 14 d), and route (SC).

RESULTS

For cows treated with rbST-Zn, mean milk, 3.5% fat-corrected milk, fat, and protein yields were increased by 4.00, 4.04, 0.144, and 0.137 kg/d (8.8, 8.89, 0.32, and 0.30 lb/d), respectively; however, the concentration of milk components did not change. Pregnancy proportion for the first 2 breeding cycles was increased by 5.4%, and pregnancy proportion for the duration of the trial was reduced by 5.5% for rbST-Zn-treated cows, compared with proportions for untreated cows. Mean body condition score (1 to 5 scale) was reduced by 0.06 points during the period of rbST-Zn use for treated cows. Administration of rbST-Zn had no effect on milk somatic cell count, the number of days to pregnancy, or inseminations per pregnancy; rates of fetal loss, twins, cystic ovaries, clinical lameness, lameness lesions, or traumatic lesions of the integumentary system; and odds of clinical mastitis or culling.

CONCLUSIONS AND CLINICAL RELEVANCE

Results indicated that rbST-Zn administration to dairy cows effectively increases milk production with no adverse effects on cow health and well-being.

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).

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.

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.

Dairy herd management practices that impact nitrogen utilization efficiency

Improving the efficiency of feed N utilization by dairy cattle is the most effective means to reduce nutrient losses from dairy farms. The objectives of this study were to quantify the impact of different management strategies on the efficiency of feed N utilization for dairy farms in the Chesapeake Bay Drainage Basin. A confidential mail survey was completed in December 1998 by 454 dairy farmers in PA, MD, VA, WV, and DE. Nitrogen intake, urinary and fecal N, and efficiency of feed N utilization was estimated from survey data and milk analysis for each herd. Average efficiency of feed N utilization for milk production by lactating dairy cows (N in milk/N in feed x 100) was 28.4% (SD = 3.9). On average, farmers fed 6.6% more N than recommended by the National Research Council, resulting in a 16% increase in urinary N and a 2.7% increase in fecal N. Use of monthly milk yield and component testing, administration of bovine somatotropin (bST), and extending photoperiod with artificial light each increased efficiency of feed N utilization by 4.2 to 6.9%, while use of a complete feed decreased efficiency by 5.6%. Increased frequency of ration balancing and more frequent forage nutrient testing were associated with higher milk production, but not increased N utilization efficiency. Feeding protein closer to recommendations and increasing production per cow both contributed to improving efficiency of feed N utilization.

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.

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.

Modeling milk production and labor efficiency in modernized Wisconsin dairy herds

The 1999 Wisconsin Dairy Modernization Project was conducted to examine variation in milk production and labor efficiency among herds that had recently expanded. Data were obtained from a sample of Wisconsin herds that expanded between 1994 and 1998. Using rolling herd average milk production in 1998 as the dependent variable in the milk production model, milking frequency, bovine somatotropin use, sprinkler use, average linear somatic cell score, average age at first calving, average days dry, and rolling herd average milk production in 1994 predicted 69% of the variation in milk production. Milking three times daily, using bovine somatotropin, using sprinklers to cool cows, and decreasing linear somatic cell score, age at first calving, and days dry were associated with increased milk production. Each of these variables supports previous research from designed experiments with on-farm results. Variation in milk production is determined primarily by differences in management ability and management practices employed by the dairy producer. Using cows per full-time equivalent as the dependent variable in the labor efficiency model, acres per cow, number of people involved in the milking operation, milking system type, herd size, and interactions between milking system types and herd size predicted approximately 43% of the variation in labor efficiency. As expected, labor efficiency increased with larger herd sizes, fewer acres per cow, and fewer people involved in the milking process. Parallel milking parlors were associated with the highest cows per full-time equivalent followed by herringbone parlors, flat barns, and stall barns.

The impact of somatotropin, milking frequency, and photoperiod on dairy farm nutrient flows

Three technologies that increase milk production per cow and that are available to dairy producers are bovine somatotropin, three times daily milking, and extended daily photoperiod. Dairy herds fed according to National Research Council requirements were simulated to predict the impact of these technologies on N losses to manure and to water resources. Because Dairy Herd Improvement Association total lactation records (n = 93,080) revealed a positive linear relationship between 305-d milk production and calving interval, calving intervals were predicted to increase with the use of technologies and to result in a change in the ratio of lactating cows to growing heifers in a herd. Compared with a herd using no technologies, the use of bovine somatotropin, three times daily milking, or extended photoperiod were predicted to reduce herd N excretion per unit of milk by 7.8, 7.0, and 3.6%, respectively. When the use of all three technologies was simulated, N losses to manure were decreased by 15.7% when assuming calving interval increases from the technologies or 15.4% without accounting for calving interval increases. Reductions in feed N requirements and manure N losses with these three technologies were predicted to reduce environmental N loading by up to 16%.

Production responses to bovine somatotropin in northeast dairy herds

The commercial response to bovine somatotropin was examined in northeast dairy herds from 1990 to 1998 (4-yr preapproval and 4-yr postapproval). With DHI records and Monsanto customer files, a control group (never purchased Posilac) and a bovine somatotropin (bST) group (used on at least 50% of cows) were identified. A total of 340 herds were involved and, over the 8-yr period, there were over 80,000 cows, 200,000 lactations, and 2 million test days. Herd management comparisons demonstrated the response to bST was relatively constant each year of the postapproval period. Assuming 100% of cows were supplemented, response to bST over a 305-d lactation equaled 894 kg of milk, 27 kg of milk fat, and 31 kg of milk protein. Comparisons of lactation curves were used to identify where the bST response occurred in the lactation cycle. Analysis demonstrated the responses in milk, milk fat, and protein yield were minimal in the early phase of lactation, and then gradually increased until reaching a plateau over the last half of the lactation cycle. Persistency of lactation was also improved by bST, indicating the opportunity exists to extend lactation with combined use of bST and altered reproductive management. Average age and days in milk did not differ between control and bST herds. Thus, stayability and herd-life of animals were not altered by bST treatment. Somatic cell count (SCC) linear scores were minimally affected in herds utilizing bST and the pattern of SCC over the lactation cycle was unaffected. Overall bST improved lactation yield and persistency consistently over the 4-yr postapproval period with no effects on cow stayability and herd-life.

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

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

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 sustained-release somatotropin on performance and grazing behavior of ewes housed at different stocking rates

This study evaluated the effects of recombinant bovine somatotropin (bST; one injection of 320 mg per ewe) on milk production and composition and on the grazing behavior of multiparous ewes in the third to fourth lactation. Forty Comisana lactating ewes were divided into four groups: 1) untreated, grazing on natural pasture (botanical composition: 35% of Graminaceae, 49% of Fabaceae, 6% of Cruciferae, 10% of other families) at a low stocking rate (16 m2/d); 2) untreated, grazing at a high stocking rate (8 m2/d); 3) treated with bST, grazing at a low stocking rate; and 4) treated with bST, grazing at a high stocking rate. The diets of the ewes were supplemented with vetch and oat hay (500 g/d) and with concentrate (500 g/d). Treatment increased milk production (923.8 vs. 669.5 g/d) but had little effect on fat and protein contents. Administration of bST significantly increased herbage intake; the effect on intake was more marked at the high stocking rate. Under these grazing conditions, the treated ewes reduced selective intake behavior and, thus, achieved good feed intake despite the low biomass availability.

Response of Brazilian crossbred cows to varying doses of bovine somatotropin

The effect of n-methionyl bovine somatotropin (bST) on milk yield was evaluated in crossbred cows (40 1/2 Bos indicus x 1/2 Bos taurus and 18 1/4 B. indicus x 3/4 B. taurus) in Brazil. Cows were randomly assigned to treatments within stage of lactation [stage 1 = 56 to 100 d in milk (DIM); stage 2 = 101 to 199 DIM] and breed groups (1/2 vs. 1/4 B. indicus blood). Treatments were 250 or 500 mg of bST administered every 14 d. Cows in the control group did not receive bST or a placebo. Treated cows received bST injected subcutaneously in the postscapular region, alternating between the left and right sides. The 26-wk experiment consisted of 2 wk of pretreatment and 24 wk of treatment. Cows were housed in an open lot with regulated access to pasture. Cows were milked twice daily and scored for body condition at 2-wk intervals. Compared with controls, milk yield increased equally (22%) for cows receiving 250 or 500 mg of bST. Milk yield response to bST was higher and persisted longer during stage 1 of lactation than during stage 2 of lactation. No difference in response to bST was noted between cows with 1/2 or 1/4 B. indicus blood. Cows treated with 500 mg of bST tended to have more mastitis, but no other adverse health effects were observed. The potential use of 250-mg doses of bST at 14-d intervals in crossbred cattle in Brazil and other subtropical regions throughout the world is suggested, particularly before about 220 DIM.

Recombinant bovine somatotropin and clinical mastitis: incidence, discarded milk following therapy, and culling

Holstein cows (n = 555) from four Michigan dairy farms were randomly assigned to receive bovine somatotropin (bST) or to serve as untreated controls. Bovine somatotropin (500 mg) was administered every 14 d beginning at 63 to 69 d of lactation and continuing until approximately 21 d prior to dry-off or until the cow was removed from the herd. Trial objectives were to determine the effect of bST on the incidence of clinical mastitis, number of days that milk was discarded because of therapy for clinical mastitis, and culling for mastitis. A total of 127 (22.9%) cases of clinical mastitis occurred during lactation. In the pretrial period (before 63 to 69 d of lactation), 42 (33.1%) cases occurred, and 85 (66.9%) cases occurred during the trial. Of the 42 pretrial cases, 57.1% occurred in control cows, and 42.9% occurred in treated cows. Of the 85 trial cases 47.1% occurred in control cows, and 52.9% occurred in treated cows. Using logistic regression, the odds ratio for the occurrence of clinical mastitis in treated cows was 1.06 (95% confidence interval = 0.62 to 1.81). The number of days that milk was discarded following therapy for clinical mastitis and the culling rate for mastitis did not differ between study groups.

Responses of dairy cows supplemented with somatotropin during weeks 5 through 43 of lactation

Beginning at wk 5 of lactation, 136 cows (34 per treatment) were supplemented daily for 38 wk with 0, 10.3, 20.6, or 41.2 mg of recombinantly derived bST monomer. Cows were obtained from University of Kentucky, University of Minnesota, University of Pennsylvania, and The Ohio State University. Nine cows (4 at 0 mg/d, 1 at 10.3 mg/d, 1 at 20.6 mg/d, and 3 at 41.2 mg/d) did not complete the experiment because of health problems. Data from these cows were included in the reproduction and health databases but not in the production database. Cows supplemented with bST produced more milk, consumed more feed, had lower rates of BW gain, and had improved efficiencies of milk production (conversion of feed and NEL to milk). Additional increases in productivity were modest at 20.6 and 41.2 mg/d versus productivity at 10.3 mg/d of bST. Concentrations of fat, protein, and TS in milk were unaffected. At 10.3 mg/d, bST did not adversely affect reproduction or health.

Clinical mastitis in cows treated with sometribove (recombinant bovine somatotropin) and its relationship to milk yield

Effect of sometribove (methionyl bovine somatotropin) on mastitis in 15 full lactation trials (914 cows) in Europe and the US and 70 short-term studies (2697 cows) in eight countries was investigated. In full lactation studies, sometribove (500 mg/2 wk) was given for 252 d, commencing 60 d postpartum. Although herds varied considerably, incidence of clinical mastitis within a herd was similar for cows receiving control and sometribove treatments. Relative risk analyses indicated no treatment effect, and percentage of mastitis during treatment was similar for control and sometribove groups. A positive linear relationship existed between peak milk yield and mastitis incidence (percentage of cows contracting mastitis or cases per 100 cow days); sometribove treatment did not alter this relationship. Increases in mastitis related to milk yield increase from sometribove or related to genetic selection were similar. When expressed per unit of milk, mastitis incidence declined slightly as milk yield increased; this relationship was not altered by sometribove. No effect on clinical mastitis was observed in 70 commercial herds utilizing sometribove for 84 d. However, effects were significant for stage of lactation and milk yield. Overall, studies represented a wide range of research and commercial situations demonstrating that sometribove had no effect on incidence of clinical mastitis during the lactation of treatment. Furthermore, sometribove did not alter typical relationships between milk yield or herd factors and incidence of clinical mastitis.

Production performance of dairy cattle administered recombinantly derived bovine somatotropin (USAN, Somavubove) daily: a dose range study

Herds (n = 9) were used on which cattle (n = 598) received 0, 4.3, 8.6, 12.9 or 17.2 mg of recombinant bovine somatotropin (rbST; USAN, Somavubove) daily from about 75 d postpartum until lactation end. Minimum effective dose to increase (3.5% fat corrected milk) FCM of cows (multiparous) compared with controls is 2.0 mg rbST/d and maximum is 16.6 mg/d. Minimum effective dose to increase FCM of heifers (primiparous) is 5.0 mg rbST/d while the maximum is 16.7 mg/d. Dosing of 4.3 to 13.2 mg rbST/d enhances efficiency of FCM production in cows. Milk fat, protein, calcium and phosphorus were not effected by rbST except for instances of transient changes. Lactose was greatest in heifers given 12.9 mg rbST/d. Days of lost milk, incidents of mastitis, and somatic cell counts were not affected by rbST. Cows given 12.9 or 17.2 mg of rbST had reduced pregnancy and conception rates, whereas heifers did not. Total services, first service conception rate, services per conception, days open and days to first AI (artificial insemination) were not affected by rbST. Days between AI were greater in cows given 17.2 mg rbST/d. Restoration of body weight and condition occurred at slower rates in rbST-dosed cows. Heifers given 8.6 or 12.9 mg rbST/d gained more weight than controls. Net energy and protein balance was reduced (less so in heifers) near start of rbST but recovered as intakes increased. Cattle given rbST produce more milk than controls and should be managed accordingly.

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.

Dose titration of sustained-release recombinant bovine somatotropin in lactating dairy cows

Lactating dairy cows (n = 264) were used in seven dose titration experiments at four geographic locations in the United States. A sustained-release formulation of recombinant bST was evaluated for a 30-wk treatment period that began 14 wk postpartum. The first series of four experiments evaluated doses of 0, 140, 350, or 700 mg of bST/14 d (series A); the second series evaluated doses of 0, 56, 140, or 350 mg of bST/14 d (series B). Milk yield, DMI, milk composition, body condition, health, and reproductive parameters were measured. Multiparous cows in series A that were administered 700 mg of bST/14 d yielded 3.0 kg/d more milk and 3.5% FCM than control cows. When all seven experiments were combined, multiparous cows that were administered 350 mg of bST/14 d yielded 2.7 and 2.6 kg/d more milk and 3.5% FCM than control cows. Dry matter intake was not significantly affected by bST administration. In series A, an increase in milk yield with no increase in DMI resulted in lower adequacy of dietary NEL and CP to meet maintenance and yield requirements among multiparous cows administered 700 mg of bST/14 d. Primiparous cows that were administered bST in series A and both parity groups in the combined seven experiments were not different from control cows in the adequacy of dietary NEL or CP to meet maintenance and yield requirements. No adverse effects of bST on health parameters were significant, and doses of 350 mg of bST/14 d or less caused no changes in reproductive parameters. Conception rate was decreased by administration of 700 mg of bST/14 d. These data suggest that 350 mg of bST/14 d increased yields of milk and FCM with no adverse effects on DMI, health, or reproduction in dairy cows.

Milk yields and hormone concentrations of Holstein cows in response to sometribove (somatotropin) treatment during the dry period

Holstein cows (n = 135) under commercial management were used to determine whether sometribove (recombinant methionyl bST, 25 mg/d) administered during the dry period affected milk yield during the ensuing lactation. Cows scheduled to begin lactations (greater than or equal to 2) during January to March were assigned randomly to treatments of sodium bicarbonate excipient (n = 67) or bST (25 mg/d, n = 68). Subcutaneous injections were given for 14 d, corresponding to d -21 to -7 relative to expected calving date. Days dry prior to first injection (64.0, 60.2) and number of injections received (13.9, 13.8) were similar for control and treatment groups, but days from last injection to calving (8.8, 7.1) differed. No differences in incidence of dystocia or udder edema were detected. Previous lactation yields were 8251 and 7952 kg, and yields for lactations following treatment were 8328 and 7852 kg, based on complete lactation data. Mean test date 3.5% FCM yields for control and treated groups during experimental lactation differed before (30.3 vs. 28.1 kg) but not after (29.5 vs. 28.4 kg) covariance adjustment for previous total lactation milk yield. Test of heterogeneity of regression provided no evidence that respective curves for FCM yield during lactation were not parallel or of different magnitude. Elevation of serum bST during 2 wk of the dry period resulted in no apparent increase in extent of mammogenesis or lactogenesis that was translated into an increase in milk yield.