Milk production in lactating buffalo receiving recombinantly produced bovine somatotropin

Thirty healthy Murrah buffalo (Bubalus bubalis) in their second to fourth lactations were selected from the herd at the National Dairy Research Institute, Karnal, Haryana, India, for use in a 35-d study to determine the effects of recombinantly produced bovine somatotropin on milk production, milk composition, and dry matter intake. Treatments were daily injections of 0, 25, or 50 mg somatotropin per animal for 14 d. All buffalo consumed green chopped fodder ad libitum plus a predetermined quantity of concentrate mixture to each animal, based on individual milk production during the 14-d pretreatment period. The quantity of concentrate mixture fed to each buffalo was not altered during the study. Net increase in milk volume for groups receiving 25 and 30 mg somatotropin was 16.8 and 29.5% over controls. Milk composition, DM intake, and body weights were not affected by treatment.     

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

Cows (890) in 15 US herds were assigned randomly in equal numbers to control or bST injections (500 mg in a prolonged-release form every 14 d for 12 wk) within three stages of lactation (57 to 100, 101 to 140, and 141 to 189 d postpartum) and two parity groups (primiparous and multiparous). Yield and milk composition were monitored 1 d/wk for 16 wk including 2 wk pretreatment and 2 wk posttreatment. Increases in milk and FCM due to bST injections were less at 57 to 100 d than at 101 to 189 d postpartum (milk 3.6 vs. 5.5; FCM 3.9 vs. 6.1 kg/d per cow), and increases in milk and FCM were more for multiparous than for primiparous cows (milk 5.5 vs. 4.2; FCM 6.0 vs. 4.7 kg/d cow). Temporarily, concentration of milk fat increased and protein decreased; later, concentrations for control and injected cows were similar. Postinjection milk fat concentration decreased, but milk protein concentration increased temporarily. The net increase in milk (and FCM) varied significantly among herds from 2.9 to 7.6 kg/d per cow (mean, 4.9 kg). Responses in FCM were similar over a wide range of pretreatment yields. A great variety of feed ingredients were fed as total mixed rations, and nutrient concentrations varied greatly. The SCC were similar before, during, and after treatment, but increase in FCM of injected cows exhibited a negative correlation with pretreatment SCC. Changes in body condition score of sometribove-injected cows varied among herds (.25 to -.45) and averaged -.02 compared with .07 for controls. There was no pattern in incidence of mastitis during sometribove injections.     

Milk yield and mammary function in goats during and after once-daily milking

Starting in week 5 of lactation, goats were milked unilaterally once daily for 4 1/2 weeks, then twice daily for 12 weeks and finally thrice daily for 2 weeks. The control gland was milked twice daily throughout. During less frequent milking, yield fell by 26%. There was a rapid and essentially complete recovery of milk yield on resumption of twice-daily milking, and five of the six goats subsequently responded to thrice-daily milking with a small increase in milk yield. Mammary function was assessed during each phase by determining enzyme activities and in vitro synthesis rates of lactose and casein in mammary biopsies. There was a trend towards reduced differentiation of secretory cells during infrequent milking, with very little recovery during twice-daily milking but complete recovery during thrice-daily milking. The differentiative state of the control gland remained unchanged throughout.     

Anti-idiotypic responses of lactating cows immunized with monoclonal antibodies against bovine somatotropin.

The objective of this study was to produce anti-idiotypic antibodies with bovine somatotropin (bST)-like activity by active immunization of lactating cows and to determine their effects on milk yield. Several monoclonal antibodies against bST were evaluated for their interaction with bST in a rat growth bioassay. Two bST-agonist monoclonal antibodies (1 and 2), and two bST-antagonist monoclonal antibodies (3 and 4) were selected. Cows were immunized with immunoglobulin G as a control (n = 12) or with one of the four anti-bST monoclonal antibodies (1, 2, 3, 4; n = 12) on d 3, 24, 45, 66, 87, 108, 129, and 150 of lactation. From wk 3 of lactation, all cows immunized with each of the four anti-bST monoclonal antibodies developed anti-idiotypes until wk 30 of lactation. Total lactation yields were not different among monoclonal antibodies 2, 3, and 4 and control cows (9299, 9321, 9733, and 9415 kg, respectively). However, cows immunized with anti-bST monoclonal antibody 1 had reduced lactation yield compared with cows on other treatments (8136 kg). Daily milk yield of cows immunized with monoclonal antibody 1 was decreased from wk 9 of lactation [36.2 vs. 40.9 kg/d (control)] until the end of lactation, concomitantly with decreased bST concentration from wk 9 of lactation. Cows immunized with anti-bST monoclonal antibody 4 had increased milk yield compared with that of controls during wk 3 to 6 and wk 18 to 21 of lactation. Therefore, anti-idiotypes directed against anti-bST 1 had bST-antagonistic effects on lactation performance; anti-idiotypes against anti-bST 4 transiently increased milk yield.     

Effect of increased milking frequency in early lactation with or without recombinant bovine somatotropin

Multiparous Holstein cows (n = 300) were assigned to 1 of 2 milking frequency treatments at parturition. Cows were either milked 6 times (6×) or 3 times (3×) daily to determine effects on early lactation milk yields and subsequent lactation persistency with or without use of recombinant bST (rbST). Treatments included a control group milked 3× and 3 groups milked 6× for either the first 7, 14, or 21 days in milk (DIM). Those 4 groups of cows all received rbST starting at 63 DIM. The fifth treatment group was also milked 6× for the first 21 DIM but those cows received no rbST during the entire lactation. All cows returned to 3× milking after their respective treatment periods ended. Cows milked 3× tended to produce more milk (43.2 vs. 41.5 and 41.0 ± 1.1 kg/d) during the first 9 wk of lactation compared with cows milked 6× for 7 or 21 DIM, respectively. Group milk yields after wk 9 averaged 38.3 ± 0.7 kg/d and did not differ among various groups assigned to an increased milking frequency in early lactation. Percentages of milk fat (3.8 ± 0.12%) and protein (2.9 ± 0.06%) did not differ among treatments during the first 9 wk after calving. Early lactation milk yield (41.9 ± 1.2 kg/d) did not differ between the 2 groups of cows milked 6× for 21 DIM. However, cows subsequently administered rbST (at 63 DIM) produced more milk (38.8 vs. 34.2 ± 0.9 kg/d) from wk 10 to 44. The number of cows sent to the hospital during the 305-d trial for mastitis (97), digestive disorders (14), respiratory issues (9), lameness (22), or retained placenta (16), were not affected by treatments (χ² = 0.49). Under the conditions of this commercial dairy herd in Arizona, increasing milking frequency to 6 times daily for 7 to 21 d at the start of lactation conditions did not increase milk yield nor improve lactation persistency.     

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

Recombinant bST at daily dosages of 0, 10.3, 20.6, and 41.2 mg/d were injected for 266 d into 8, 10, 9, and 9 Holstein cows, respectively. Treatment effects of recombinant bST were assessed for milk production traits, BW, blood components, and health and reproductive variables. Data reported compare controls to all bST-treated cows. There was an average increase of 18% in 3.5% FCM for bST versus control cows. This increase resulted in enhanced feed efficiency for bST cows, as their DM intakes were not elevated above those of the control cows. Recovery of BW was similar between control and bST groups. Milk composition was unaffected except for a slight decrease in protein percentage during the first 9 wk of treatment, and an elevated SCC between wk 19 and 28. Blood parameters were not different between control and bST cows, except for hematocrit, which decreased with bST treatment. The only health and reproductive parameters affected by bST were mastitis and days open, which were increased in the highest dosage groups.     

Contact sensitivity and systemic antibody responses in dairy cows treated with recombinant bovine somatotropin.

Effects of exogenous bST on humoral and cell-mediated immune responses in lactating dairy cows were determined. The systemic antibody response to human erythrocytes and the cutaneous sensitivity response induced by dinitrochlorobenzene were the immune responses investigated. Cows were treated with either 0, 10.3, or 20.6 mg of bST/d for 266 d starting between wk 4 and 5 of lactation. Systemic immunizations and contact sensitivity were initiated during midlactation, 22 wk after bST treatments began. Hemagglutinating antibody titers and areas under the response profiles were not statistically different for bST-treated versus control cows. The cutaneous sensitivity response was similarly not affected by bST administration. Present antibody titer results agreed with our previous observations that bST did not affect serum IgM concentrations, but the cutaneous sensitivity results were in contrast with our finding of augmented proliferative responsiveness of mitogen-stimulated peripheral blood lymphocytes in bST-treated versus control cows. It is possible that exogenous bST affects some immune processes and lymphocyte subsets and not others. Further research is required to determine the practical significance of the variable immunomodulation elicited by exogenous bST.     

Dose response to recombinant bovine somatotropin from weeks 15 to 44 postpartum in lactating dairy cows

Forty Holstein cows were used in an experiment to determine the response of cows to daily subcutaneous injections of 0, 10.3, 20.6, and 30.9 mg of recombinant bST. Injections began between 98 and 104 d postpartum and continued for 29 wk, up to 70 d prepartum, or a maximum of 400 d postpartum. Increasing recombinant bST increased milk yield and 3.5% FCM yield in a linear fashion and by 5.2 and 5.7 kg/d, respectively. Milk composition was not changed, and DM intake as a percentage of BW increased from 3.39 to 3.80% with increasing (30.9 mg/d) bST. Feed efficiency (3.5% FCM/DM intake) was increased from 1.35 to 1.64 with increasing dose, suggesting improved efficiency of use of DM intake, primarily by dilution of maintenance. Increasing bST reduced BW gain linearly from .46 kg/d for the control to .22 kg/d for the 30.9 mg/d bST. Calf birth weight, weight of cows at calving, and incidence of metabolic diseases during subsequent calving were not affected by bST. Somatotropin treatment resulted in somewhat smaller increased in milk yield than that reported in previous studies. Long-term health effects and effects on reproduction could not be determined from the relatively few cows used in this study.     

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.     

Effect of exogenous bovine somatotropin on mammary lipid metabolism and milk yield in lactating dairy cows

Eight lactating Holstein cows were used to study the effect of bovine somatotropin on mammary lipid metabolism, milk production, and milk composition. Eight cows were injected with either excipient (n = 4) or 50 IU somatotropin/d (n = 4). A 2-wk adjustment period preceded a 10-d period when treatments were administered. On d 9, serial blood samples were collected from 2 to 5 h post-injection to determine concentrations of somatotropin and metabolites in plasma. Mammary tissue biopsies were obtained 2 to 3 h after a.m. milking on d 10 to determine lipoprotein lipase activity and in vitro rates of acetate incorporation into fatty acids and acetate oxidation by mammary tissue slices. Activity of lipoprotein lipase in milk and mammary tissue and rate of acetate metabolism by mammary tissue were not affected by treatment. The following means for placebo and somatotropin, respectively, were: milk production (21.5 and 24.8 kg/d), milk fat (3.8 and 4.0%), and 4% FCM (20.7 and 25.1 kg/d). Plasma concentrations of somatotropin (3.0 and 43.4 ng/ml) and free fatty acids (105.6 and 219.5 mu eq/L) were significantly elevated with somatotropin. The injection of somatotropin into lactating dairy cows did not affect the mechanisms of fatty acid synthesis or metabolism evaluated in this study.     

Effects of recombinant bovine somatotropin on nutritional status and liver function of lactating dairy cows

Twenty-four high producing, multiparous Holstein cows were utilized to evaluate effects of long-term administration of sustained-release rbST on blood pH, gases, buffer capacity, circulating metabolites and hormones, and on liver lipid content and functions during lactation. Treatment, commencing 98 to 112 d postpartum and continued until d 305, consisted of a subcutaneous injection of a placebo or 350 mg of rbST every 14 d. Milk and 3.5% FCM were increased significantly by rbST, but milk fat and protein content, feed intake, energy balance, corrected feed efficiency for milk production, and body condition scores were unaffected. Somatotropin decreased blood pH and buffer capacity by decreasing bicarbonate without affecting blood partial pressures of oxygen or carbon dioxide. Concentration of plasma albumin was decreased and nonesterified fatty acids, glucose, insulin, rbST and insulin-like growth factor-I were increased by treatment. Total plasma proteins and cortisol, hemoglobin, and hematocrit were unaffected. Liver DM, total lipid and triacylglycerol contents, and plasma 3-hydroxybutyrate and glutamic oxalacetic transaminase were not affected by rbST, but the percentage of triacylglycerol in total lipids was increased. Results of this experiment suggest that rbST exhibited lipolytic and diabetogenic activities in lactating dairy cows in vivo and that these effects might be important for the increase in nutrient partitioning toward the mammary gland elicited by rbST.     

Effect of prepartum administration of recombinant bovine somatotropin on health and performance of lactating dairy cows

A double-blind, randomized clinical trial was conducted in 5 commercial dairy herds in southern Ontario with 1,362 cows enrolled to evaluate the effect of prepartum administration of recombinant bovine somatotropin (rbST) on health and performance. Cows were randomly assigned to receive either 325 mg of sometribove zinc suspension (n = 680) or a placebo injection (n = 682; control) subcutaneously every 14 d until calving. Treatments started 28 to 22 d before expected calving, with a maximum of 3 treatments per cow. Serum samples taken at the time of enrollment, 1 wk before calving, and weekly for 3 wk after calving were analyzed for nonesterified fatty acids (NEFA), β-hydroxybutyrate (BHBA), glucose, aspartate aminotransferase, calcium, and haptoglobin. Diseases were recorded by farm staff. Incidences of clinical ketosis, clinical mastitis, displaced abomasum, metritis, retained placenta, milk fever, and lameness were similar between groups. Body condition score was lower for treated than for control cows at 3 wk after calving (3.13 and 3.17, respectively). Serum NEFA tended to be higher for treated than for control cows by 0.01 mmol/L. Overall BHBA was not different between groups, but BHBA for treated cows was higher in wk 1 after calving (750 and 698 μmol/L, respectively) and tended to be higher in wk 2 after calving (779 and 735 μmol/L, respectively). Incidence of hyperketonemia was similar between groups. Treated cows had higher serum glucose compared with control cows (2.8 and 2.7 mmol/L, respectively). We detected no differences in serum aspartate aminotransferase, calcium, or haptoglobin between groups. Milk yield was recorded daily for each cow for 63 d, and did not differ between groups (37.1 ± 0.5 kg and 36.7 ± 0.5 kg, respectively) but we detected a tendency for treated cows to produce 0.8 kg/d more milk than control cows in wk 1 after calving. We observed no difference between groups in the time from calving to first insemination or the probability of pregnancy at the first insemination. Groups did not differ in the proportion of anovular cows at 53 ± 3 d in milk based on serum progesterone measured from a subset of cows (38.0 and 34.3%, respectively, for treated and control groups). We found no difference between groups in dry matter intake from 21 d before calving to 63 d after calving in a subset of cows (17.4 ± 0.4 and 17.5 ± 0.4 kg/d, respectively). Based on results of the current study, biweekly (every 14 d) administration of rbST before calving to prevent disease and enhance performance is not recommended.     

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.     

Recombinant bovine somatotropin with lactating cows fed diets differing in energy density

Sixty-four Holstein cows (32 primiparous) were assigned randomly at parturition to one of two diets differing in forage:grain ratio and were further assigned to either control or treatment with recombinant bST. A full lactation study was conducted. Total mixed rations consisted of alfalfa silage, high moisture ear corn, soybean meal, and vitamin and mineral supplements. Percentages of forage in the diet (dry basis) for the high and medium energy diets were wk 1 to 12, 38.2 and 58.2; wk 13 to 26, 48.2 and 68.2; and wk 27 to 44, 68.2 and 88.2. Injection of a saline placebo or 20.6 mg/d per cow of bST started at wk 13 and stopped at wk 43 of lactation. Administration of bST increased 305-d milk yield by 19.9 and 18.3% for multiparous cows fed high and medium grain diets and by 13.0 and 5.9% for primiparous cows fed the same diets. Body weight gain during lactation tended to be lower for cows treated with bST, and body condition scores were significantly lower for those treated with bST and fed the medium energy diets. Daily injection of bST did not change concentrations of glucose or urea in blood or beta-hydroxybutyrate in plasma. Multiparous cows had a transitory increase in plasma FFA concentration immediately after bST treatment started. Milk composition, health, and reproductive parameters observed were not adversely affected by bST administration. Cows fed low energy diets during bST administration in the first lactation did not produce as much milk as controls when compared during the first 10 wk of their second lactation.     

Short-term administration of bovine somatotropin to lactating dairy cows in a subtropical environment

Our objective was to evaluate response of lactating dairy cows to daily injections of bovine somatotropin during a subtropical summer. Ten Holstein cows, averaging 196 d in lactation, were used in a 30-d study. No treatment was imposed during d 1 to 10 (period 1) and d 21 to 30 (period 3). During d 11 to 20 (period 2), cows were injected daily with either 0 or 59 IU of pituitary-derived bovine somatotropin in 30 ml solution. Dry matter intake and milk yield and composition were measured daily. Jugular blood samples, taken on d 10, 15, 20, and 30, were analyzed for insulin, nonesterified fatty acids, urea nitrogen, and insulin-like growth factor-1. Body temperatures and respiration rates were measured at 1400 h on 4 or 5 d during each 10-d period. Data were analyzed using orthogonal contrasts. Contrast of period 1 plus period 3 vs. period 2 for treatment X days interaction was significant for milk yield, respiration rate, serum nonesterified fatty acids, and insulin-like growth factor-1. Under heat stress, cows injected with bovine somatotropin for 10 d produced 9.3% more milk than control cows with no change in feed intake. This increased production was accompanied by higher respiration rates (6%) and higher concentrations of serum nonesterified fatty acids (150%) and insulin-like growth factor-1 (222%).     

Effects of treatment of preweaning dairy calves with recombinant bovine somatotropin on immune responses and somatotropic axis

Weaning may be associated with negative energy balance and body weight loss when calves are still immunologically immature, predisposing them to infectious diseases. The aim of the present experiment was to investigate the effects of treatment of preweaning dairy calves with recombinant bovine somatotropin (rbST) on the somatotropic axis, selected immune parameters, and hematology of calves around weaning. Thirty-six Holstein female calves were randomly assigned to receive 1.5 to 1.8 mg of rbST (Posilac, Elanco Animal Health, Greenfield, IN) per kilogram of body weight or to receive injections of saline (saline solution 0.9%, Valley Vet Supply, Marysville, KS) every 7 d from 21 to 63 d of life. Calves were fed milk replacer ad libitum from birth to 38 d of age (d ?11), when progressive weaning started, and calves were weaned at 49 d of age (d 0). Calves were weighed at birth and weekly from 21 to 63 d of age, when wither height also was measured. Calves were vaccinated with 0.5 mg of ovalbumin on study d ?28 and ?7. Blood samples were collected on d ?28, ?25, ?21, ?11, 0, 3, 7, and 14. Polymorphonuclear leukocytes were isolated and challenged ex vivo with Escherichia coli to determine phagocytosis and oxidative burst capacity. Additionally, expression of cluster of differentiation (CD)62L and CD18 by granulocyte, lymphocyte, and CD14+ monocyte were determined. Blood samples were also used to determine hematological parameters and concentrations of growth hormone, insulin-like growth factor-1, insulin, glucose, fatty acids, β-hydroxybutyrate, haptoglobin, and anti-ovalbumin IgG. Calves treated with rbST had greater concentrations of growth hormone and insulin-like growth factor-1 from d ?25 to 14 than control calves, whereas insulin, fatty acid, and β-hydroxybutyrate concentrations did not differ. On d ?11, glucose concentration was greater for rbST-treated calves. Treatment did not affect polymorphonuclear lymphocyte phagocytosis and oxidative burst, but intensity of expression of CD62L and CD18 by granulocytes tended to be increased by rbST treatment. Treatment did not affect the concentration of anti-ovalbumin IgG in serum. Haptoglobin concentration was reduced in rbST treated calves on d 3 and we noted a tendency for hematocrit to be lower in rbST-treated calves. Treatment did not affect body weight, wither height, and average daily gain, despite the fact that rbST-treated calves had lower daily milk replacer intake. The relatively minor improvements in immune responses resulting from rbST treatment of weaning calves may not be sufficient to reduce the incidence of infectious diseases.     

Metabolic and lactational responses during recombinant bovine tumor necrosis factor-alpha treatment in lactating cows

This study examined the effects of recombinant bovine tumor necrosis factor-alpha (rbTNF) administration on metabolic and hormonal responses and lactational performance in dairy cows. Twelve lactating Holstein cows were injected subcutaneously with rbTNF (2.5 microg per kg per d) or saline (3 ml per head per d) at 1200 h daily for 7 d (d 0-6) and used in a crossover design. The rbTNF treatment induced increases in plasma haptoglobin, nonesterified fatty acid, cortisol, and growth hormone levels compared with the control levels. The rbTNF-treated cows had lower triiodothyronine and insulin-like growth factor-1 concentrations than control cows. In a somatoliberin challenge on d 6, the somatotropin response to somatoliberin (0.25 microg/kg) was smaller in the rbTNF group than in the control. The rbTNF treatment also produced increases of the nitrite plus nitrate concentration in plasma and milk during the period between d 1 and 7. Milk yield was reduced by rbTNF administration from d 1 to 8. The percentage of milk fat was increased on d 1-7 by rbTNF treatment, but milk protein content in the rbTNF group was decreased on d 5 and 7 as compared with that in the control group. These results support the possibility that tumor necrosis factor-alpha is responsible for the changes in hormone secretion, milk production and composition, and inflammatory parameters observed during coliform mastitis.     

Natural and recombinant bovine somatotropin: immunodetection with a sandwich ELISA

Bovine Somatotropin (bST) is a peptide hormone secreted by the anterior pituitary gland and its recombinant form (rbST) is used for artificially boosting milk yield in cows. Identification of rbST is difficult in that there is little difference from the pituitary bST (pbST). In this work, we further studied the possibility of immunologically discriminating between rbST and pbST. With this purpose, we produced mouse monoclonal antibodies using, as antigen, a peptide mimicking the N-terminus of rbST from Monsanto (rbST-M) conjugated to keyhole limpet haemocyanin (KLH) and polyclonal antibodies in rabbits immunized with the whole bST or rbST-M. Hence, we developed a sandwich ELISA with the obtained antibodies for detection and quantification of bST in serum and compared its performance on the two worldwide commercialized rbSTs: rbST-M and rbST from LG Life Science (rbST-LG). The lowest detection limit of the assay was 0.05 ng/ml for rbST-M, 0.10 ng/ml for rbST-LG and 0.15 ng/ml for pbST. Furthermore, the assay showed the capability to amplify the signal in the presence of rbSTs, recognizing more efficiently rbST-M and rbST-LG than pbST (ECn pbST/ECn rbST: 3 and 1.6 respectively). Its employment for measuring bST levels in sera from bovines administered with rbST LG allowed us to detect exceptional values due to the treatment itself and probably further increased as a consequence of the higher affinity for rbSTs of our monoclonal antibody.     

Lactational evaluation of recombinant bovine somatotropin with corn and barley diets

Forty-eight Holstein cows were randomly assigned to receive diets containing corn or barley as the primary energy concentrate from wk 4 through 44 postpartum. During wk 14, cows from each grain source group were randomly assigned to receive 0 (control), 10.3, 20.6, and 30.9 mg/cow per d of recombinant bST injected wk 15 through 44 postpartum. Grain source exerted no significant effect on production parameters and efficacy of bST, although milk production tended to be higher with corn diets. Milk production (24.2, 29.2, 31.7, and 29.5 kg/d) and 4% FCM (21.9, 26.2, 28.1, and 28.0 kg/d) were higher for cows injected with bST, and DM intakes (20.9, 22.8, 22.0, and 23.3 kg/d) increased slightly. Percentages of milk fat (3.47, 3.28, 3.39, and 3.52) and protein (3.48, 3.44, 3.44, and 3.38) varied. Lactose, SCC, and body weights were similar for bST and dietary treatments. Diet or bST had no detectable affect on health or reproduction. Injection of bST wk 15 through 44 increased milk production 21 to 31% relative to control animals. Limiting bST use to the latter two-thirds of lactation resulted in an 8 to 17% increase in total yield with only a 0 to 5% increase in lactational DM intake.     

Separate and additive stimulation of bovine milk yield by the local and systemic galactopoietic stimuli of frequent milking and growth hormone.

Lactating heifers were treated for 4 weeks with recombinant bovine growth hormone (bGH, n = 9) or were untreated (n = 9). In addition, two mammary glands of each heifer were milked four times daily rather than the normal twice daily for the same 4 weeks, and for the following 2 weeks. Over the 4 weeks, milk yield was increased 12.8% by bGH, 14.0% by frequent milking and 28.5% by the combined treatment. The effect of bGH as administered here was slower in onset than that of frequency, but eventually produced a higher peak yield. ANOVA revealed significant effects of each stimulus independently and an additive, but not synergic effect of the combined treatment. The effect of the combined treatment tended to persist beyond the end of treatment; most of this response was related to the milking frequency component rather than the bGH. Mammary differentiation was assessed in biopsies of mammary tissue obtained prior to and at the end of treatment. Mammary enzyme activities (expressed on a per cell basis) indicated minimal differentiative response to either treatment, but synthesis rates for lactose and casein determined in vitro were increased by bGH treatment. Histological examination revealed a stimulatory effect of milking frequency on epithelial cell size. The results indicate that these two galactopoietic stimuli operate through independent mechanisms, and neither stimulus alone is sufficient to maximize milk yield in dairy heifers.