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.

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.

Effect of bovine somatotropin on neutrophil functions and clinical symptoms during Streptococcus uberis mastitis

The effect of recombinant bovine somatotropin (bST) on the chemiluminescence, diapedesis, and expression of adhesion receptors (CD11a, CD11b, CD18) of isolated polymorphonuclear leukocytes was studied. The plasma concentrations of insulin-like growth factor-I (IGF-I), bST, cortisol, and alpha-lactalbumin were also monitored. In addition, general and local clinical symptoms and the differentiation of circulating leukocytes were also studied during experimentally induced Streptococcus uberis mastitis in cows. Ten cows were infected with 500 cfu of S. uberis O140J in both left quarters. Five cows were subcutaneously treated with 500 mg of recombinant bST 7 d before and after infection, and 5 control cows received the excipient. General (fever, tachycardia, inappetance, and depression) and local symptoms (swelling, pain, firmness, and flecks in milk) were more acute, severe, and longer-lasting in control cows. Treatment with bST had no effect on chemiluminescence and diapedesis of circulating polymorphonuclear leukocytes and no effect on the expression of adhesion receptors. Recombinant bST induced significantly higher IGF-I and bST concentrations in plasma. The leukopenia observed after infection was less pronounced in the bST-treated cows, and the number of circulating band neutrophils and metamyelocytes was significantly lower in the treated group. The concentration of cortisol did not differ between both groups, but the blood concentration of alpha-lactalbumin significantly increased in both groups from 6 d after infection. These results showed that treatment with recombinant bST improves animal welfare by protecting the cows from severe local and general clinical symptoms during subsequent S. uberis mastitis, but that it has no effect on chemiluminescence, diapedesis, and the expression of adhesion receptors of circulating polymorphonuclear leukocytes.

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.

The effect of recombinant bovine placental lactogen on induced lactation in dairy heifers

The primary objective of this study was to determine whether bovine placental lactogen stimulated additional mammary growth as assessed by milk yield from a lactation induced by steroids. Pubertal, nonpregnant Holstein heifers (n = 23) were given daily subcutaneous injections of estradiol-17 beta (0.05 mg/kg) and progesterone (0.25 mg/kg) for 7 d to initiate mammary growth. Prolactin secretion was suppressed in all heifers via bromocriptine, which was administered until d 15. Heifers were treated with either placental lactogen (40 mg/d; n = 12) or water (control group; n = 11) for 18 d. Lactation was induced by daily injection of dexamethasone for 3 d and twice daily injections of recombinant bovine prolactin for 5 d starting on d 18. From 3 to 8 wk of lactation, milk yield of heifers treated with placental lactogen was numerically higher (22%) than the yield of control heifers, but the difference was not significant because of the high coefficient of variation. Daily injection of bovine somatotropin (d 57 to 66 of lactation) increased milk yield of both groups and stimulated a greater numerical increase in milk yield for heifers that were treated with placental lactogen. These results support the hypothesis that bovine placental lactogen is mammogenic and is one of the factors that regulates mammary growth during pregnancy.

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.

Stimulation of mammogenesis and lactogenesis by recombinant bovine placental lactogen in steroid-primed dairy heifers

A model of induced lactation was modified to examine the effects of bovine prolactin (bPRL) and bovine placental lactogen (bPL) on mammary growth and differentiation. Thirty-two peripubertal, non-pregnant Holstein heifers were given daily s.c. injections of oestradiol (0.05 mg/kg) and progesterone (0.25 mg/kg) for 7 days to initiate mammary growth. Treatment with bromocriptine (40 mg/3 days) reduced serum PRL concentrations to approximately 25% of pretreatment levels, for the duration of the study. On the day following the last steroid injection, groups of eight heifers were given twice daily s.c. injections of either saline (negative control), recombinant bPRL (rbPRL; 80 mg/day) or recombinant bPL (rbPL; 80 and 160 mg/day) for 7 days. At the end of this period (day 15), growth and differentiation of the mammary glands were assessed. Treatment with rbPL increased total mammary DNA above control value by 50 and 60% for the 80 and 160 mg/day doses respectively. However, total DNA was not different for the control and rbPRL-treated groups. The blood serum concentration of alpha-lactalbumin was measured daily throughout the study and used as an index of mammary differentiation. Both rbPRL and rbPL stimulated mammary differentiation (i.e. induction of milk synthesis), although rbPRL appeared to be more potent than rbPL. These results indicate that rbPL is lactogenic in vivo and strongly suggest that bPL is a mammary mitogen.

Pharmacokinetic and galactopoietic response to recombinant variants of bovine growth hormone

Two studies were designed to examine the pharmacokinetic and galactopoietic potency of three molecular variants of recombinant-derived bovine GH (rbGH): [Met1, Leu127]-bGH, [Ala1, Val127]-bGH and [Ala1, Val127, His133]-bGH. Histidine substitution for arginine at residue 133 of rbGH was shown to impart thrombin resistance. In a Latin square design, nine lactating Holstein cows received a 25 mg rbGH bolus infusion via the jugular vein followed by frequent blood sampling over the next 12 h. The serum GH concentration data were found to fit a two-compartment open model. Neither primary nor secondary kinetic parameter estimates differed significantly (P > 0.05) among the three rbGH variants. Thus, the disposition of GH concentration at time t was described by the equation C(t) = (1295.5 micrograms/l) (e-(0.11/min)(t)) + (317.3 micrograms/l)(e-(0.03/min)(t)). Overall averages were: area under the curve = 27.1 mg.min per l, clearance = 0.15 litres/min per 100 kg and volume of distribution of the central compartment = 2.59 litres/100 kg. The t 1/2 for the two compartments averaged 8.2 and 29.1 min. In the second study, 36 lactating Holstein cows received i.m. injections of one of four oil-based formulation treatments: control vehicle or 500 mg of one of the three rbGH variants every 14 days for 42 days. Average and maximum serum GH concentrations and area under the curve estimates were increased by approximately 3-6 micrograms/l, 5-15 micrograms/l and 40-90 micrograms.day per 1 respectively. Ala1, Val127 rbGH treatments elicited greater blood GH concentrations than [Met1, Leu127]-bGH when administered in an oil-based formulation. Blood GH responses did not directly translate into milk response differences, possibly due to differences in biopotency or receptor availability. Thrombin resistance resulting from substitution of histidine at position 127 of rbGH did not affect blood GH pharmacokinetic parameters or milk response over other rbGH variants.

Variants of somatotropin in cattle: gene frequencies in major dairy breeds and associated milk production

The amino acid sequence of bovine somatotropin (bST) varies at position 127 where either valine or leucine is found. The frequencies of leucine127 and valine127 bST gene alleles in cows (n = 302) and sires (n = 70) from major dairy breeds (Holstein, Brown Swiss, Guernsey, Jersey, and Ayrshire) were determined using DNA extracted from whole blood or spermatozoa. A 428 base pair fragment of the bST gene was amplified using polymerase chain reaction (PCR) and variants of the bST gene were detected as polymorphisms by Alu I restriction endonuclease digestion of PCR products. Restriction enzyme DNA fragments for the leucine127 variant were 265, 96, 51, and 16 base pair and for the valine127 variant were 265, 147, and 16 base pair as a polymorphism of bST was present in the 147 base pair DNA fragment. Frequencies of leucine127 and valine127 alleles for cows (n = 302) were 1.0 and 0 for Brown Swiss, .93 and .07 for Holstein, .92 and .08 for Guernsey, .79 and .21 for Ayrshire, and .56 and .44 for Jersey, respectively. In Holstein sires used for artificial insemination (n = 70), the frequency of leucine127 and valine127 alleles was .96 and .04. Estimates of transmitting ability for milk production tended to be greater for Holstein cows that were homozygous for leucine127 bST and Jersey cows that were homozygous for valine127 bST whereas Holstein sires with different bST genotypes were similar. In summary, frequencies of alleles for the bST gene were not similar in different dairy breeds and estimates of milk production were correlated with bST gene variant in cows but not sires.

Effect of high doses of a sustained-release bovine somatotropin on antibody formation in dairy cows

Eighty-two lactating Holstein cows received either one, three, or five concurrent, intramuscular injections of a unit dose (.6 g) of zinc methionyl bST (some-tribove) or five doses of the vehicle. Injections were administered at 14-d intervals from 60 d postpartum until the end of lactation or necropsy. Thirty-eight cows continued on the same treatment for a 2nd yr. Blood bST antibodies developed within the first 7 wk of treatment, and the number of cows with anti-bST binding generally declined with time. Thirteen out of 59 cows receiving bST developed binding activity > 25% (positives) during the 1st yr. At the .6-g dose level, no binding was detected after wk 15. Seven of the 13 positive cows were among the group randomly selected to continue on study during yr 2. In the 2nd yr, only 2 out of 24 bST-treated cows were positive. Binding activity was associated with the IgG fraction in serum. Binding capacities of antibodies ranged from .625 to 3.04 mg of bST/L, and affinities ranged from 1.14 x 10(8) to 3.14 x 10(8) L/mol. Cows considered to be clinically positive had performance similar to those of their herdmates having binding < 25%. No evidence of a pathologic effect of antibodies existed in treated cows, their calves, or fetuses. The presence of anti-bST antibodies did not affect milk production of the cow or growth of the calves conceived during bST treatment.

Ruminant placental lactogens: structure and biology

Ruminant placental lactogens (PL) are members of the somatotropin, prolactin gene family that are synthesized by trophectodermal binucleate cells. The structure and biology of PL has been studied in the cow, sheep, and goat. Ruminant PL have greater structural identity to prolactin than somatotropin, although they bind to both lactogenic and somatogenic receptors. The molecular weights of ovine and caprine PL are approximately 23,000, whereas bovine PL is larger (31,000 to 34,000) due to glycosylation. Placental lactogen is secreted into both the fetal and maternal circulations. The concentration of PL in the fetus decreases with advancing gestation, whereas PL concentration peaks in the maternal circulation during the last third of pregnancy then reaches a plateau. Furthermore, the maternal concentration of PL is 100- to 1,000-fold higher in sheep and goats than in cows. The precise factors that modulate secretion of PL are unknown, although placental mass and nutrition seem to play a role. Ruminant PL have both lactogenic and somatogenic biological activities and may also have unique activities mediated through a specific receptor. There is circumstantial evidence to suggest that PL plays a role in stimulating mammogenesis. Placental lactogen secreted into the fetal compartment may also help regulate fetal growth. Direct experimental data indicate that PL can regulate maternal intermediary metabolism. Thus, it may act as a partitioning agent to regulate nutrient supply for fetal growth. The precise biological function of PL in ruminants, therefore, still needs to be defined.

Stimulation of milk yield and feed intake by bovine placental lactogen in the dairy cow

A 6 x 6 Latin square design was used to test the effects of recombinant bovine placental lactogen on milk yield, milk composition, feed intake, and blood hormone and metabolite levels in nonpregnant lactating cows. The six treatments (5, 10, 20, and 40 mg/d of placental lactogen, water as negative control, and 20 mg/d of bST as positive control) were administered by subcutaneous injection twice daily for 9 d. Blood samples were taken during the last 5 d of the treatment period. The three highest doses of placental lactogen increased milk yield, and there was a linear dose effect, although placental lactogen was less potent than bST. Milk concentrations of lactose, protein, and fat were not altered by any of the treatments. Dry matter intake was increased by two of the doses of placental lactogen, but not by bST. Blood urea N concentration was decreased in a dose-dependent manner by placental lactogen and was also decreased by bST. Similarly, serum insulin-like growth factor-I was increased in a dose-dependent manner by placental lactogen and was also increased by bST. Plasma concentrations of NEFA and glucose were increased by bST, but placental lactogen had little or no effect on either of these parameters. Thus, placental lactogen appears to act, in part, as a weak somatotropin agonist; however, it also appears to have specific activities, e.g., stimulating feed intake.

Serum half-life and in-vivo actions of recombinant bovine placental lactogen in the dairy cow

The clearance rate of recombinant bovine placental lactogen (rbPL) from the blood serum of four lactating dairy cows was measured using a specific radioimmunoassay. Two animals were non-pregnant, while the other two were at approximately 120 days of gestation. The rbPL was administered as an i.v. bolus injection (4 mg total) via an indwelling jugular catheter. Blood samples were taken periodically for 180 min and assayed for rbPL. Analysis of the clearance curves for the bolus injection suggested a single-compartment model and a serum half-life of 7.25 min. In a second experiment with the same animals, following cessation of lactation, rbPL or bovine GH (bGH) were administered by s.c. injection (50 mg/day) for 5 consecutive days. Blood samples were taken twice per day during the treatment period and a 3-day pretreatment period. Samples were analysed for glucose, blood urea nitrogen (BUN), non-esterified fatty acids (NEFA), creatinine, insulin, insulin-like growth factor-I (IGF-I) and IGF-II, tri-iodothyronine (T3), progesterone and IGF-binding protein-2 (IGFBP-2) to determine whether rbPL mediates similar metabolic effects to those of bGH. Administration of bGH stimulated an increase in NEFA, glucose, T3 and insulin, whereas none of these variables was affected by rbPL. The plasma concentrations of IGF-I and IGF-II were both increased by treatment with rbPL but, to a lesser extent than occurred with bGH. Interestingly, BUN and IGFBP-2 concentrations were reduced equally by bGH and rbPL. These results suggest that rbPL does not necessarily act as a GH agonist but, rather, may have distinct effects on intermediary metabolism that could be mediated through another specific receptor.

Comparison of the galactopoietic response to pituitary-derived and recombinant-derived variants of bovine growth hormone

Two studies were designed to examine the differences in galactopoietic potency of molecular variants of pituitary- and recombinant-derived bovine GH (bGH). The recombinant bGH molecules included amino-terminal and position-127 amino acid substitutions which are representative of two of the four natural pituitary variants or of partially degraded bGH molecules. Amino-terminal variants of bGH included methionine (Met1), alanine (Ala1), serine (Ser1) or deletion of four amino acids (delta 1-4). The delta 1-4 variants were representative of degradation products previously isolated in pituitary bGH preparations. In the first study, 54 lactating Holstein cows received i.m. injections of a buffer solution (control), pituitary-derived bGH, or recombinant-derived [Met1,Leu127]-bGH, [Met1,Val127]-bGH, [Ala1,Leu127]-bGH, or [Ala1,Val127]-bGH. Cows received 25 mg bGH/day for 21 days. Substitution of the amino-terminal alanyl residue with methionine did not affect milk response. GH variants with Val127 elicited a greater milk response (8.5 kg/day) than Leu127 bGH variants (6.5 kg/day). The average milk response to the four recombinant bGH variants was 7.5 kg/day greater than controls compared with 4.4 kg/day for pituitary-derived bGH. In contrast, blood bGH concentrations were equivalent for pituitary and recombinant bGH treatments, approximately 20 micrograms/l more than control levels at 3 h after injection. Blood free fatty acid concentrations were increased, but insulin and glucose levels were unaffected by bGH treatment. In the second study, 54 lactating Holstein cows received i.m. injections of a buffer control solution or recombinant-derived [Met1,Leu127]-bGH, [Ser1,Leu127]-bGH, [Ser1,Val127]-bGH, [delta 1-4,Leu127]-bGH or [delta 1-4,Val127]-bGH. Cows received 25 mg bGH/day for 28 days. The milk response to full-length bGH variants was 6.6 kg/day greater than the response to the amino-terminal deletion variants (P less than 0.05). Substitution of valine for leucine did not affect milk response to either the deletion (delta 1-4) or full-length (Met1 or Ser1) bGH molecules. In conclusion, the lowered galactopoietic potency of pituitary bGH preparations was demonstrated, at least in part, to be due to the presence of amino-terminal amino acid deletions rather than differences in amino acid sequences of recombinant bGH. Ala1 bGH variants with valine at position 127 elicited a greater milk response than Leu127 variants.

Response of dairy cows to high doses of a sustained-release bovine somatotropin administered during two lactations. 2. Health and reproduction

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 (.6 g) of zinc methionyl bST (sometribove) or five doses of the vehicle. Injections were given at 14-d intervals from 60 +/- 3 d postpartum until the end of lactation or necropsy. Thirty-eight animals were continued on treatment for a 2nd yr. Sometribove did not affect the incidence of ketosis, milk fever, tetany, or pneumonia. Digestive disorders, primarily cows going off feed, were increased by bST during yr 1 only. The incidence of lameness was increased by bST in some time frames because of an increase in the 3.0-g bST group. Lameness was not associated with treatment-specific histopathologic changes or with abnormalities in cartilage or bone. Reproductive health generally was unaffected by treatment, but delayed conception and increased incidence of abortion were noted. Incidence of cystic ovaries was unaffected by bST. Pregnancy rates were decreased during the 100-d breeding interval of yr 1 but not during the 215-d interval of yr 2. The incidence of clinical mastitis was increased by bST, primarily at the 3.0-g dose. During the 2-yr study, 0, 3, 3, and 2 cows died or became moribund on 0, .6, 1.8, and 3.0 g of bST, respectively. Health issues identified for further evaluation included lameness and clinical mastitis for the 3.0-g group and early removal from the herd and decreased reproductive performance for all bST groups. Bovine somatotropin caused no treatment-specific toxic effects in dairy cows even at 3.0 g every 14 d.

Response of dairy cows to high doses of a sustained-release bovine somatotropin administered during two lactations. 1. Production response

This study evaluated the effect of sometribove (zinc methionyl bST) in a sustained-release formulation administered to lactating cows at concentrations up to 3.0 g every 14 d over two lactations. Eighty-two lactating Holstein cows in their first, second, or third lactation were assigned to the study. Cows received .6, 1.8, or 3.0 g of bST in one, three, or five intramuscular injections of a unit dose (.6 g) every 2 wk. Controls received five injections of the vehicle (equivalent volume to the 3.0-g treatment) every 2 wk. Injections were administered from 60 +/- 3 d postpartum until dry-off or necropsy. Thirty-eight animals were continued on treatment for a second consecutive lactation. During the 1st yr of treatment, bST increased mean 3.5% FCM by 7.2, 9.4, and 8.4 kg/d over control production (21.1 kg/d). During the 2nd yr, milk response to .6, 1.8, and 3.0 g of bST averaged 10.6, 3.6, and 4.9 kg/d over controls (24.8 kg/d). The incidence of clinical mastitis increased in the 3.0-g group relative to controls during the 2nd yr. Thus, salable FCM averaged 8.1, 9.1, and 6.2 kg/d above controls (yr 1) and 12.1, 4.7, and -2.8 kg/d (yr 2) for the .6-, 1.8-, and 3.0-g groups. Salable FCM was unaffected by mastitis at a proposed commercial dose (.6 g). Milk fat, protein, lactose, calcium, phosphorus, zinc, magnesium, and ash concentrations were unaffected by bST treatment. Calculated energy, calcium, phosphorus, and protein balances also were unaffected except for early decreases of up to 5 Mcal/d, and 40, 20, and 600 g/d, respectively, until feed intake increased. Milk serum bST concentrations greater than the assay limit of sensitivity (1 ng/ml) were routinely measurable only at doses of 1.8 and 3.0 g. Results confirmed that bST concentrations in milk serum are exceedingly small. Overall, supraphysiological doses of sometribove increased milk production with little effect on composition. No toxic effects of bST were observed.

Factors affecting insulin-like growth factor-I concentration in bovine milk

To establish the naturally occurring range of insulin-like growth factor-I concentrations in bovine milk, samples from individual cows (n = 409) managed on five Missouri dairy herds were assayed. Parity, stage of lactation, and farm affected milk insulin-like growth factor-I concentration. Milk insulin-like growth factor-I concentration was higher in early lactation than mid and late lactation with concentrations in multiparous cows exceeding those in primiparous cows. Insulin-like growth factor-I concentration was negatively correlated to milk production the day of sample collection (r = -.15) and not correlated to predicted 305-d milk yields. Unprocessed bulk tank milk samples (n = 100) from a commercial processing plant had a mean concentration of insulin-like growth factor-I in milk of 4.32 ng/ml with a range of 1.27 to 8.10 ng/ml. This distribution was similar to the range detected in samples from individual cows, but values were lower than those reported for human milk. Concentration of insulin-like growth factor-I in milk was not altered by pasteurization (at 79 degrees C for 45 s). However, insulin-like growth factor-I was undetectable in milk heated to temperatures (121 degrees C for 5 min) required for infant formula preparation or in commercially available infant formula. These data indicated that insulin-like growth factor-I is a normal but quantitatively variable component of bovine milk that is not destroyed by pasteurization but is undetectable in infant formula. Concentration of insulin-like growth factor-I in bovine milk is lower than concentrations reported for human milk yet similar to those reported for human saliva.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of acute challenge with an extreme dose of somatotropin in a prolonged-release formulation on milk production and health of dairy cattle

Eight pregnant Holstein cows were given weekly injections of 15 g of recombinant bST over a 2-wk period for a total dose of 30 g to determine signs of acute toxicity. Cows were monitored intensively throughout the study, and samples were taken for analyses of hormones, metabolites, chemistries, hematology, and urine analytes. Animal health throughout the study was generally excellent. Mean rectal temperatures were significantly higher in treated cows (38.7 vs. 39.2 degrees C). Least squares means for 3.5% FCM production were 15.9 and 23.0 kg/d, and net energy intakes were 29.4 and 26.9 Mcal/d for control and treated cows, respectively. Somatotropin concentrations reached more than 250 ng/ml on d 10 and remained above 200 ng/ml. Insulin and glucose concentrations were also increased but returned toward baseline values. Free fatty acid concentrations were higher in treated cows, but beta-hydroxybutyrate was not affected. Most hematological measurements were unaffected except for a reduction in erythrocyte number in treated cows and decreases in hematocrit and hemoglobin, but values were within clinically normal ranges. Although cows received in 2 wk a dose that was equivalent to the amount administered during more than 2 yr of continuous use, no signs of acute toxicity to bST were observed.

Effect of 188-day treatment with somatotropin on health and reproductive performance of lactating dairy cows

Health and reproductive performance were observed in a lactational study involving 188 d of treatment with bovine somatotropin. Treatments commenced 84 +/- 10 d postpartum and consisted of 27 mg/d of pituitary somatotropin and 0, 13.5, 27, and 40.5 mg/d of recombinantly derived somatotropin (six cows per treatment group). Cows were high yielding (greater than 9600 kg/305 d), and somatotropin increased milk yield by 16 to 41% depending on source and dose. Somatotropin had no discernible effect on mammary health based on somatic cell count and incidence of clinical mastitis. Cows receiving somatotropin averaged 96% conception rate, 2.0 services per conception, and 116 d open, which were comparable to controls. No subclinical or clinical evidence of ketosis or milk fever was observed. Thirty-two blood chemistry and physical examination variables were examined at several intervals during the study and no adverse treatment effects of physiologic importance for any of the variables were observed. Somatotropin treatment had no discernible effect on gestation length or birth weight and growth rate (first 28 d) of calves. Milk yields for the first 60 d postpartum were compared for the period just prior to start of treatment and the lactation subsequent to treatment; no treatment effects were observed. Overall, our results for a well-managed herd demonstrate somatotropin treatment did not cause any serious health effects. However, examination of subtle health effects will require large numbers of animals treated under a range of environmental and management conditions.

Effect of dose of bovine growth hormone on milk composition: alpha-lactalbumin, fatty acids, and mineral elements

Tissue-specific effects of bovine growth hormone on lactating dairy cows were examined by analysis of milk composition. Milk samples were from 6 cows that received subcutaneous injections of 0, 5, 10, 25, 50, and 100 IU/d of growth hormone in a Latin-square design. Samples from the last 5 d of each 10-d treatment period were pooled for analyses of milk components. Concentration of alpha-lactalbumin in milk increased progressively across the treatment range up to 32% above controls (1.30 mg/nl) at the 100 IU dose. Specific alpha-lactalbumin synthesis (expressed as a percent of total milk protein) was also increased. Secretion of de novo synthesized fatty acids (short and medium chain length) in milk was increased, but response plateaued between the 50 and 100 IU/d. Secretion of preformed (long-chain) fatty acids progressively increased across the entire dose range. Thus, the percentage of long-chain fatty acids in milk increased at the highest doses of hormone. Changes in fatty acid composition of milk were apparently related to energy status; the milk response to 50 and 100 IU/d of growth hormone caused cows to be in or near negative energy balance. Exogenous growth hormone did not affect the concentration of calcium, phosphorus, sodium, iron, copper, and manganese in milk. Results are consistent with growth hormone functioning in homeorhesis to coordinate the partitioning of all nutrients to support the increased secretion of milk and milk components.

Responses of high-producing dairy cows to long-term treatment with pituitary somatotropin and recombinant somatotropin

Thirty Holstein cows capable of high milk production were utilized to examine the effects of long-term administration of bovine somatotropin on lactational performance. Treatments were 0 (control), 13.5, 27, and 40.5 mg/day of recombinantly-derived bovine somatotropin and 27 mg/day of pituitary-derived bovine somatotropin. Hormone was injected intramuscularly, once daily beginning at 84 +/- 10 days postpartum and continuing for 188 days. Cows were fed ad libitum a total mixed diet throughout the lactation. Recombinant somatotropin treatments increased average fat-corrected milk yield in a dose-dependent fashion from 23 to 41% over the control production (27.9 kg/day. Pituitary somatotropin (27 mg/day) increased milk production by 16%. Milk lactose, protein, and fat composition was similar for all treatments. Control cows were in positive energy balance throughout the treatment period (4.7 Mcal net energy/day. Initially, the large increase in milk yield with somatotropin treatment caused cows to decrease in energy balance. However, voluntary intake gradually increased, and by week 10 of treatment all somatotropin treatment groups were in positive energy balance. Thus, the gain in body weight over the treatment period was similar for all groups, ranging from 17 to 22%. Gross lactational efficiency (milk per unit of net energy intake) was improved by exogenous somatotropin whether calculated as observed, corrected for body weight changes, or using the theoretical energy requirements for maintenance and milk production. Results are consistent with bovine somatotropin as a homeorhetic control that coordinates an array of physiological processes so that nutrients are partitioned for milk synthesis.

Effect of dose of bovine growth hormone on lactation of dairy cows

We administered bovine growth hormone to six Holstein cows in a Latin square design to study the relationship between dose of growth hormone and response of milk yield. Treatments were 0, 5, 10, 25, 50, and 100 IU/day of pituitary-derived bovine growth hormone administered in once-daily subcutaneous injections. Feed intake and yield of milk and milk components were measured for the last 5 days of each 10-day injection period. Yields of milk, protein, and fat increased in a dose-responsive fashion up to 32, 27, and 46% (for the 100 IU treatment) above control (26.7, .90, and .98 kg/day). Concentration of lactose in milk was not influenced by treatment, but at larger doses of growth hormone, milk fat percent was elevated and protein percent declined. As a result, milk energy secretion in response to 100 IU/day was increased 37% from control (19.2 Mcal/day). Both energy and nitrogen balance decreased with increasing growth hormone. Limited blood samples (timed to coincide with peak concentration of growth hormone postinjection) indicated treatment did not affect concentrations of glucose or insulin in blood plasma but increased concentration of growth hormone. Concentration of nonesterified fatty acids in blood plasma was increased slightly only at the 100 IU/day dose for which energy balance was negative.

Sources of variation and prospects for improvement of productive efficiency in the dairy cow: a review

In this review, "productive efficiency" in dairy cows is defined as the yield of milk obtained in ratio to the nutritional costs associated with maintenance, milk synthesis and loss of body condition during lactation. Improvements in efficiency could occur as a result of changes in digestion and nutrient absorption, maintenance requirement, utilization of metabolizable energy for production or nutrient partitioning. Digestibility can be greatly enhanced by appropriate dietary manipulation. Likewise, it may be possible to reduce maintenance requirements and improve the efficiency with which metabolizable energy is used for milk synthesis by manipulation of the pattern of nutrients presented to tissues. However, these factors apparently do not respond to selection for increased milk yield, and little variation is observed among cows. In contrast, individual cows differ substantially in feed intake and in the partitioning of nutrients among body tissues. Techniques associated with genetic engineering and the early prediction of genetic merit have the potential to improve productive efficiency by manipulation of these processes. However, changes in nutrient partitioning and feed intake during lactation are coordinated by a complex network of controls that accommodate the nutrient requirements of each tissue while maintaining homeostatic balance. Future improvements in productive efficiency will therefore depend on our ability to understand the manner in which these controls operate.

Influence of sodium bicarbonate on growth and health of young calves

Fifty-four Holstein and Jersey calves were assigned at 4 days of age within breed and sex to one of four treatments: control consisting of colostrum, milk replacer, and starter; buffered colostrum and replacer (.6% sodium bicarbonate) and starter (2% sodium bicarbonate); acidified colostrum (1% propionic), untreated replacer, and starter; and acidified, buffered colostrum (1% propionic, .6% sodium bicarbonate), buffered replacer (.6% sodium bicarbonate), and starter (2% sodium bicarbonate). The feeding regimen was colostrum once daily, day 4 to 14; milk replacer once daily, day 15 to 28; and calf starter ad libitum, day 4 to 84. Bull calves were fed for 42 days and heifers for 84 days. Calves fed acidified colostrum refused more feed and were less efficient from day 4 to 14 than calves fed buffered colostrum. Bulls were more sensitive to acidified colostrum than heifers. Starter intake, total dry matter intake, and average daily gains were similar for all calves during days 4 to 84. Rumen fluid from calves fed diets with sodium bicarbonate was higher in acetate and lower in propionate and lactate than that from calves fed diets without sodium bicarbonate. Sodium bicarbonate improved intake of acidified colostrum during the first 2 or 3 days of feeding but had no other effect on gain or feed intake.