Composition and flavor of milk and butter from cows fed unsaturated dietary fat and receiving bovine somatotropin.

Composition and flavor of milk and butter were evaluated from cows divided into four treatments including a control, control with bST, added dietary fat from sunflower seeds with bST, or added dietary fat from safflower seeds with bST. Feeding added unsaturated dietary fat resulted in lower concentrations of short-and medium-chain and higher concentrations of long-chain fatty acids in milk fat and butter. Milk fat unsaturated fatty acid concentrations were 25.0, 28.4, 39.6, and 37.9%, and butter unsaturated fatty acid concentrations were 23.0, 26.9, 37.8, and 36.2% for control, control with bST, sunflower seeds with bST, and safflower seeds with bST, respectively. Sensory evaluations indicated that butters from the bST with sunflower seed and bST with safflower seed treatments were equal or superior in flavor to the control butter. Milk from cows receiving bST or fed added unsaturated dietary fat and receiving bST was no more susceptible to oxidized off-flavors than control milk. Butters from sunflower seed and safflower seed treatments with bST contained higher concentrations of unsaturated fatty acids, were softer at 4 and 20 degrees C, and possessed acceptable flavor and processing characteristics compared with butters from control and control with bST.     

Hormonal responses to bovine somatotropin and dietary protein in early lactation dairy cows

The effects of bST injection and dietary protein level on blood hormone and metabolite concentrations were examined in four mature Holstein cows in a double crossover design. Cows were assigned at d 5 to 9 postpartum to receive daily injections of either a control (saline) solution or 20.6 mg of bST. Four 3-wk periods were used during which one cow from each group was fed a medium protein diet (17.1% CP), and the other received a high protein diet (23.6% CP). Injections of bST or control solutions began on d 0 of the second period. Intakes of DM were not influenced by dietary protein or bST injection. Milk yield tended to increase with increased CP level but was not affected by bST injection. Based on the rate and extent of decline in milk production after cessation of bST injection, the cows assigned to bST had lower milk production potential than control cows. Thus, the effect of bST injection apparently was to enhance milk yield to levels similar to those of controls. There were no significant CP level or bST injection effects on glucose, FFA, somatostatin, or somatotropin concentrations. Glucagon concentrations were higher in bST-treated cows. Concentrations of insulin-like growth factor-I were increased with increased CP level and also with bST injection. Significant effects of days on bST were observed for insulin, insulin-like growth factor-I, glucose, and FFA. Cows given bST injections and producing equal amounts of milk as control cows did not show major physiological differences in hormones and metabolites with the exception of insulin-like growth factor-I.     

Effect of added dietary fat and bovine somatotropin on the performance and metabolism of lactating dairy cows

Four early lactation Holstein cows (44 to 105 d postpartum) were used in a 4 X 4 Latin square experiment in a 2 X 2 factorial arrangement of treatments to study effects of added dietary fat and/or bovine somatotropin on performance and metabolism. Treatments were: 1) control diet plus placebo injection; 2) 5% added dietary fat (hydrolyzed blend of animal and vegetable fat) + placebo injection; 3) control diet + 50 IU bovine somatotropin/d; and 4) 5% added dietary fat + 50 IU bovine somatotropin/d. Dietary fat reduced dry matter intake (21.6 vs. 22.7 kg/d) and elevated plasma triglycerides (34.7 vs. 29.2 mg/100 ml). Injection of somatotropin lowered blood urea nitrogen, increased plasma free fatty acids, and increased plasma somatotropin. Milk production, milk fat percent, and 4% FCM production were increased by the injection of somatotropin. Milk protein percent was decreased (3.30 vs. 3.44%) with added fat and tended to be lower with somatotropin. The percentage of short-chain fatty acids (C6 to C14) in milk fat decreased with added fat while the percentage of stearic and oleic acids in milk fat increased. Production responses for fat plus somatotropin and somatotropin treatments were similar. Under the conditions of this study, the addition of dietary fat with injection of somatotropin had little effect on production parameters compared with that found with somatotropin alone.     

Lactational response of dairy cows to increased dietary crude protein with added fat.

Thirty-six Holstein cows were assigned to one of three diets containing soybean meal (16% CP), added fat from extruded soybeans (16% CP), and added fat and protein from extruded soybeans plus soybean meal (18% CP) to determine whether feeding additional protein would prevent the depression in milk protein percentages usually experienced when cows are fed additional fat. Total mixed diets containing 25% corn silage, 25% alfalfa hay, and 50% of respective concentrate mixtures were fed individually wk 4 through 16 postpartum; pretreatment (wk 3 postpartum), milk production, and composition data were used as covariates. Milk production (33.0, 35.8, and 34.2 kg/d) was higher for cows fed added fat. Milk protein (2.92, 2.88, and 2.83%) and casein (2.16, 2.13, and 2.09%) tended to decrease for cows fed added fat and did not increase with higher dietary protein. Dry matter intakes (20.9, 20.7, and 19.8 kg/d) and BW were similar for all diets. Supplementing additional CP to a diet containing added fat did not prevent depression in milk protein percentage.     

Effect of fish meal and expeller-processed soybean meal fed to dairy cows receiving bovine somatotropin (sometribove).

Forty-eight multiparous cows were blocked by calving date and milk production and assigned randomly to a TMR formulated to contain 68 or 55% of dietary CP as ruminally degradable CP. Diets contained corn silage, alfalfa haylage, and ground corn. Supplemental CP was soybean meal for the control diet or a combination of soybean meal, expeller-processed soybean meal, and fish meal for the low degradable protein diet. Two 10-wk phases began on d 31 +/- 3 (phase 1) and 110 +/- 7 postpartum [phase 2, all cows received subcutaneous implantations of pelleted (400 mg) bST (sometribove) every 14 d]. Dietary energy, CP, ruminally degradable CP, NDF, and ADF were similar between dietary treatments. Production of FCM increased in response to bST but was not affected by dietary treatment. Cows fed the expeller-processed soybean meal and fish meal TMR produced milk that contained less milk fat in phase 1 and less milk protein content in both phases. The DMI, BW, and body condition scores were not affected by diet. Hematocrit, plasma urea N, albumin, total protein, creatinine, glucose, and serum insulin were similar between dietary treatments. Replacing soybean meal with expeller processed soybean meal and fish meal did not affect ruminal degradation of protein or milk production but decreased milk fat and protein contents.     

Use of bovine somatotropin in lactating dairy cows receiving timed artificial insemination

Objectives of the research were to examine the effect of bovine somatotropin (bST) on pregnancy rates to a timed artificial insemination protocol and to test a resynchronization system with two consecutive synchronized services. Lactating Holstein cows (n = 403) were assigned to the following treatments: bST treatment (500 mg) was initiated at 63 +/- 3 d postpartum concomitantly with initiation of the timed artificial insemination protocol or bST treatment was initiated at 105 +/- 3 d postpartum. At 63 +/- 3 d postpartum, all cows received GnRH (100 microg), an injection of PGF2alpha (25 mg) 7 d later, and a GnRH injection at 48 h after PGF2alpha and were inseminated 16 to 20 h later. Cows were reinseminated at detected estrus or resynchronized with a GnRH injection at 20 d after insemination. At 27 d after insemination, cows were examined for pregnancy. Resynchronized cows diagnosed nonpregnant received an injection of PGF2alpha and were inseminated at detected estrus or received an injection of GnRH at 48 h after PGF2alpha and inseminated 16 to 20 h later. Cows pregnant at d 27 were reexamined for pregnancy at 45 d after insemination. First-service pregnancy rates at d 45 were increased in cows not resynchronized that initiated bST treatment at 63 +/- 3 d postpartum, compared with cows initiating bST treatment at 105 +/- 3 d postpartum (37.7 +/- 5.8% and 22.1 +/- 4.2%, respectively), but the effect of bST treatment was not observed when cows were resynchronized (25.6 +/- 4.3% and 25.8 +/- 5.5%, respectively). Thus, bST increased pregnancy rates to a timed artificial insemination protocol.     

Lactation response of dairy cows receiving bovine somatotropin and fed rations varying in crude protein and undegradable intake protein

Our experiment evaluated lactation and metabolic responses of Holstein cows injected with somidobove (recombinant bST) and fed one of four isocaloric rations containing either 14 (low) or 17% (high) CP and undegradable intake protein of 33 (low) or 40% (high) of CP. Multiparous cows (n = 37) in early lactation, averaging 37 kg/d of milk, received somidobove (640 mg per injection) at 28-d intervals for 112 d and one of four protein rations: low-low, low-high, high-low, and high-high. Nine other multiparous controls were fed low-low ration with no somidobove. On the low-low ration, somidobove significantly increased milk yield by 2.3 kg/d, but not 3.5% FCM (1.7 kg/d), intakes of DM or CP, or milk composition. Milk and 3.5% FCM increased by 1.7 and 2.1 kg/d in cows fed high undegradable intake protein but there was no effect on milk composition, BW, or DM intake. Ration CP had no effect on production variables in cows receiving somidobove. Serum urea was higher in cows fed high CP rations; undegradable intake protein was without effect. Plasma leucine was higher in cows fed high undegradable intake protein. Administration of somidobove to cows fed low-low rations reduced plasma methionine, serum albumin, hemoglobin, and albumin:globulin ratio. Milk production of high producing dairy cows receiving somidobove may be limited by the amount of protein available at the small intestine.     

Responses of dairy cows in early lactation to bovine somatotropin and ruminally inert fat

Bovine somatotropin (0 or 41.2 mg/d bST) and calcium salts of long-chain fatty acids (0 or .77 kg/d Ca-LCFA) were administered to 16 Holstein cows in early lactation. Cows remained on 0 or 41.2 mg/d bST for the entire 10 wk and received 0 or .77 kg/d Ca-LCFA in one of two 5-wk periods. Production data were recorded daily, milk fatty acids, and blood metabolites were determined once each period. Treatments did not affect feed intake. Fat-corrected milk (kg/d) and percentage of milk fat for cows receiving no supplementation, fatty acids alone, bST alone, and fatty acids and bST together were 33.8, 3.2; 33.5, 3.1; 37.4, 3.4; and 40.8, 3.5. Milk fatty acids below C16 were reduced with either bST or dietary fatty acids; C16 fatty acids were lower with bST but higher with dietary fatty acids; C18:0 fatty acids were reduced with dietary fatty acids; and C18:1 fatty acids were higher with either bST or dietary fatty acids. Blood acetoacetate concentrations were higher with both bST and dietary fatty acids, beta-hydroxybutyrate was not different, and FFA and insulin concentrations increased with bST. In this experiment, the energy supplied by Ca-LCFA acids enhanced the lactogenic effect of bST.     

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.     

Metabolic and production responses to dietary protein and exogenous somatotropin in late gestation dairy cows.

Forty-three multiparous Holstein cows were used in a completely randomized design to evaluate the effects of protein supplementation and the use of bovine somatotropin (bST; Posilac, Monsanto Co., St. Louis, MO) in late gestation on animal metabolism and productivity in the periparturient period. Treatments were initiated 28 d prior to expected calving date and continued through parturition. Diets contained either 13.3 or 17.8% crude protein and were formulated to be similar in profile of protein fractions. Within each dietary treatment, cows were assigned to receive either 0 or 500 mg of sustained released bST once every 14 d until parturition. Following parturition, all cows were subjected to the same management and dietary treatments, and production measurements were followed until 42 d in milk. The use of bST increased plasma glucose and decreased plasma nonesterified fatty acids and beta-hydroxybutyrate prior to calving. Despite these changes in metabolism, bST did not affect concentrations of fat and triglyceride in the liver prepartum or postpartum. Feeding the 17.8% protein diet failed to stimulate glucose metabolism and tended to elevate plasma beta-hydroxybutyrate in late gestation. Cows treated with bST produced 3.3 kg/d more milk than did controls across the first 42 d of lactation; the difference was 4.6 kg/d in wk 6 of lactation. The use of bST in late gestation has considerable promise to alter cow metabolism positively. The results of these and other possible periparturient responses to somatotropin may increase milk production in early lactation.     

Lactation response of dairy cows receiving bovine somatotropin via daily injections or in a sustained-release vehicle

Three experiments were conducted to characterize metabolic and milk production responses of dairy cows receiving recombinantly derived bovine somatotropin administered either by daily injection or in a sustained-release vehicle. In Experiment 1, somatotropin (25 mg/d) purified by two methods was given by daily injection for 14 d and resulted in 3.5 and 3.8 kg/d more milk than controls. Percentages of fat and total solids in milk were also increased by somatotropin. Eleven hematology indices and 12 metabolites, minerals, and enzyme activities in serum were unaffected by somatotropin. In Experiments 2 and 3, somatotropin was administered in a sustained-release vehicle during an 84-d treatment period. In Experiment 2, administration of 960 mg of somatotropin at 28-d intervals increased milk and SCM yields by 4.1 and 3.3 kg/d compared with yields of controls. There were no significant differences in other production parameters. In Experiment 3, 320, 640, and 960 mg somatotropin were each administered in the sustained-release vehicle at intervals of 14, 21, and 28 d. An uninjected group served as control. Cows receiving somatotropin averaged 3.5 to 5.9 kg/d more milk than controls across all injection intervals. Among doses, milk yield was greater at 960 mg than at 320 or 640 mg. There were no significant differences in milk or SCM among injection groups. These experiments demonstrate the comparable efficacy of somatotropin when given by daily injections or in a sustained-release vehicle.     

Lactational performance of high producing dairy cows fed diets containing salmon meal and urea.

Thirty Holstein cows were used in a 12-wk trial to study the effects of salmon meal and urea on lactational performance. Two experimental diets, one containing 5.6% salmon meal and the other 5.2% salmon meal plus .42% urea, were compared with a soybean meal control diet. Salmon meal and urea replaced a portion of the soybean meal. Dietary undegraded intake protein levels (expressed as percentage of CP) were 28.8, 35.6, and 32.4% for soybean meal, salmon meal, and salmon meal plus urea. Total mixed diets (average 17.3% CP, 17.6% ADF) consisting of 60% concentrate mixture and 40% bromegrass silage (DM basis) were fed twice daily. Total DMI was lower with salmon meal compared with soybean meal (20.2 versus 22.2 kg/d); salmon meal plus urea (21.2 kg/d) was intermediate. Actual milk production was similar for all diets (average 41.1 kg/d). Percentage milk fat and 4% FCM yield were lower with salmon meal (2.56%, 31.6 kg/d) and salmon meal plus urea (2.50%, 31.4 kg/d) than with soybean meal (3.03%, 35.9 kg/d). Gross efficiency (weight FCM/weight DMI) was higher for soybean meal than for salmon meal and salmon meal plus urea. Acetate: propionate tended to be higher with the soybean meal diet. The use of a high oil fish meal to provide a source of rumen undegraded intake protein, alone or in combination with urea, resulted in a decrease in milk fat percentage and yield without any beneficial effects on milk production or lactational efficiency.     

Lactational response of Jersey cows to bovine somatotropin administered daily or in a sustained-release formulation.

Twenty-four Jersey cows were administered either 0 or 15.5 mg of bST/d or 310 mg of bST/14 d to determine the effect on milk yield, milk composition, feed intake, and body weight. Administration of bST was from wk 14 through 42 postpartum. Cows were housed in a tie-stall barn and fed for ad libitum intake a TMR adjusted to one of two energy protein densities according to milk yield. Milk yield of cows administered bST daily or by sustained-released vehicle increased 27.6 and 24.7%, respectively, over that of control cows; FCM increased by 30.3 and 26.7%. Percentages of fat and protein in milk were unaffected by bST treatment. Dry matter intake of cows administered bST was greater than that of control cows, whether expressed as kilograms per day or as a percentage of body weight. Apparent efficiency of yield increased in cows administered bST. No significant change in body weight occurred; however, cows administered bST had lower body condition scores at 42 wk postpartum. This trial demonstrated comparable effects of bST on lactational performance when administered daily or in a 14-d sustained-release vehicle.     

Production responses of dairy cows when fed supplemental fat in low- and high-forage diets

Intake of net energy for lactation (NE_L) is often the limiting factor for milk production and is affected by stage of lactation and dietary concentrations of forage and fat. Because of the mechanisms involved, interactions are likely between those 2 diet components and stage of lactation. We conducted an experiment with 72 Holstein cows starting at 21 and ending at 126 d in milk (DIM). Cows were fed diets (dry matter basis) with 40 or 60% forage (67% corn silage, 33% alfalfa silage) each with 0 or 2.25% added saturated free fatty acids. The high- and low-forage diets contained 25 and 17% forage neutral detergent fiber and 30 and 33% total neutral detergent fiber, respectively; the low-forage diets contained several byproducts. Diets with and without fat contained approximately 5.2 and 3.2% long-chain fatty acids, respectively. Feeding fat or low-forage diets increased NE_L intake, but no interaction was observed. The increase in NE_L intake by cows fed low-forage diets was caused by increased dry matter intake, and the increase in NE_L intake by cows fed fat was caused by increased energy density of the diet. Interactions between fat and forage were observed for energy utilization. When high-forage diets were supplemented with fat, the increased NE_L intake went toward body energy reserves as measured by higher body condition scores with no change in milk yield. However, when low-forage diets were supplemented with fat, milk yield increased (2.6 kg/d) with no change in body condition. The differential partitioning of NE_L may have been caused by nutrients other than NE_L limiting milk production in cows fed the high-forage diets. With low-forage diets, intake of other nutrients was greater (i.e., greater dry matter intake). At 35 DIM, dietary treatments had little effect on milk fatty acids composition but in later lactation (125 DIM), feeding supplemental fatty acids or feeding low-forage diets increased long-chain fatty acids and decreased short-chain fatty acids. However, treatment did not have marked effects on concentrations of total fat or protein in milk. The amount of forage in a diet influences cow responses to supplemental fat and should be considered when diets are formulated.     

Effect of dietary energy and previous bovine somatotropin on milk yield, mastitis, and reproduction in dairy cows.

Thirty multiparous lactating Holstein cows were blocked according to time of calving and assigned to a 2 x 3 factorial arrangement of treatments in a randomized complete block design to evaluate the effects of two dietary energy concentrations either without or with bST (20.6 mg/d per cow) administered to cows that had not or had received bST during the preceding lactation. Subcutaneous injection of bST began 28 to 35 d postpartum and continued for 39 wk. The dietary energy concentration x bST interaction was not significant for any response variable. Compared with DMI of control cows, DMI was higher for cows receiving bST, being 1.6 and 2.4 kg/d higher for cows receiving bST for one and two lactations, respectively. Milk, fat, and protein yields were higher for cows receiving bST than for controls. Those receiving bST for a second lactation also produced more milk than controls until wk 20; thereafter, milk yields were similar to those of controls. Somatotropin administration had no adverse effect on udder health. Cows receiving bST tended to ovulate less regularly than controls, which may be attributed to their higher milk yield. However, BW gains during lactation were similar for all treatments, indicating that bST-treated cows built energy reserves for the subsequent lactation. Although energy concentrations of the diets had no significant impact on yield, the higher energy diet tended to depress milk fat concentration. Administration of bST to dairy cows for a second, consecutive lactation yielded responses similar for the first 20 wk of the study to those receiving bST for the first time. However, after wk 20, milk yield was less than that by cows receiving bST for the first lactation but similar to that of control cows.     

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 dietary fat supplementation on methane emissions from dairy cows fed wheat or corn

Diets that contain high proportions of either wheat or supplementary fat have been individually reported to reduce enteric methane production. The objective of this research was to determine the effect of dietary fat supplementation on methane emissions and milk yield from cows fed diets containing either corn or wheat grains. It was hypothesized that cows fed a diet containing wheat would produce less methane and have lower methane yield (methane per kg of dry matter intake; MY) than cows fed a diet containing corn and that methane mitigation from fat supplementation would occur irrespective of the type of grain in the basal diet. The experiment involved 32 Holstein-Friesian dairy cows allocated to 1 of 4 treatment groups (n = 8) and individually fed different diets restricted to approximately 90% of their mean ad libitum intake measured during a covariate period. All animals were offered 11.5 kg of dry matter/d of alfalfa hay, 1.8 kg of dry matter/d of solvent-extracted canola meal, and 1 of 4 dietary supplements. Dietary supplements were 8 kg of dry matter/d of either corn or wheat, or these same treatments with the addition of 0.8 kg of canola oil. In this 5-wk experiment, d 1 to 7 served as the covariate period, d 8 to 14 as the transition period, d 15 to 28 as the adaptation period, and d 29 to 35 as the experimental period. Cows were fed their full treatment diets from d 15 to 35 during which time milk production and feed intake were measured daily. During d 29 to 35, methane production was measured for individual cows daily using the sulfur hexafluoride tracer method. The resulting averages for milk production and feed intake were analyzed by analysis of covariance with factorial grain by fat as treatment structure, animal as the unit within blocks, and the corresponding milk production or feed intake covariate averages as principal covariate. Data on milk fatty acids, ruminal fluid data on pH, ammonia, volatile fatty acids, protozoa, and methane were analyzed by ANOVA using the same treatment and blocking structures excluding the principal covariate. Cows fed a diet containing wheat had greater MY than cows fed a diet containing corn. Irrespective of the type of grain in the diet, increasing the fat concentration from 2 to 6% dry matter reduced MY. It is concluded that the grain component in the basal diet does not affect the mitigating effects of dietary fat supplements on MY.     

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

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

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

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