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.     

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 bovine somatotropin on milk yield and composition, body weight, and condition score of Holstein and Jersey cows

Forty cows (20 Holstein, 20 Jersey) were administered 0, 5, 10, 15, or 20 mg of recombinantly derived bST daily to determine the effect on milk yield, milk composition, body weight, and body condition score. Administration of bST was from 75 +/- 7 d through 305 d postpartum. A total mixed diet of 45% corn silage and 55% of a concentrate mixture (dry basis) was provided for ad libitum intake. Milk yield of Holstein and Jersey cows administered 20 mg of bST increased 25.3 and 22.8%, respectively, over controls. Fat-corrected milk from Holsteins and Jerseys that were administered 20 mg of somatotropin increased 32.2 and 18.7% over controls, but Jersey response was greatest when 15 mg of bST were administered (27.1% over controls). Dry matter intake of the 20 mg bST group was 13.5% greater than DM intake of controls. Apparent efficiency of production increased linearly with increasing somatotropin. There was no significant change in body weight, but body condition score declined linearly with increasing somatotropin. Most milk composition measures were unaffected by somatotropin. Jersey and Holstein milk yield increased quadratically and linearly, respectively, with somatotropin dose.     

Effect of somatotropin on kinetics of nonesterified fatty acids and partition of energy, carbon, and nitrogen in lactating dairy cows

The utilization of energy, carbon, and nitrogen, and irreversible loss rates of nonesterified fatty acids were examined in lactating cows during treatment with bovine somatotropin. Six multiparous Holstein cows at approximately 62 d postpartum received daily intramuscular injections of somatotropin (29.4 mg/d) or excipient during two 21-d treatment periods in a crossover experimental design. Milk yield was increased 11% (37.1 versus 41.3 kg/d), whereas intake and digestibility of DM, energy, nitrogen, and carbon were not affected. Cows remained near zero net energy balance during both treatments (1.31 versus -1.52 Mcal/d for control and somatotropin, respectively). The major effect of somatotropin was to partition net energy into milk while tissue energy accretion was reduced. Postabsorptive use of nitrogen and carbon was altered by somatotropin as reflected by greater secretion in milk. Urinary losses of nitrogen and tissue use of carbon were reduced. Plasma concentrations and irreversible loss rates of nonesterified fatty acids did not differ between treatments. Somatotropin treatment of lactating cows results in partitioning of nutrients away from tissue deposition toward milk synthesis. The extent to which different metabolic processes are altered depends upon the energy balance of the somatotropin-treated animal.     

Effects of prepartum somatotropin and monensin on metabolism and production of periparturient Holstein dairy cows

Fifty-five multiparous Holstein dairy cows were used to evaluate the singular and combined effects of somatotropin and monensin treatments during the late dry period on postpartum metabolism and production. Treatments were 1) control (C); 2) injection of exogenous bovine somatotropin (bST); 3) TMR top dressed with 300 mg of monensin/day (M); and 4) monensin and somatotropin in combination (bST+M) during the last 28 days before expected parturition. A 500-mg subcutaneous injection of sustained release somatotropin was administered adjacent to the tail head at d -28 and -14 relative to expected calving. Diet and management were the same for all cows after parturition. Production and intake were measured daily until 63 d in milk. Milk composition, blood metabolites, and body weight and condition score were measured weekly. Prepartum glucose, nonesterified fatty acid, and blood urea nitrogen concentrations were not different among treatments. Cows on the M treatment tended to have greater dry matter intake postpartum than those on the C treatment and 30% lower plasma nonesterified fatty acid concentrations during wk 1 postpartum than all other treatments. Milk yield and milk fat yield were not different among treatments, but milk fat percent tended to be lower for the bST+M treatment than the C treatment. Changes in plasma amino acid concentrations were consistent with mobilization of skeletal muscle protein, possibly for use in gluconeogenesis. Results from this study provide evidence that prepartum feeding of monensin reduced plasma nonesterified fatty acid concentrations and may improve glucose metabolism of the periparturient dairy cow.     

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 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.     

Effects of abomasal or intravenous administration of arginine on milk production, milk composition, and concentrations of somatotropin and insulin in plasma of dairy cows

Holstein cows just past peak lactation were used in a 3 x 3 Latin square design to determine the effects of arginine infusion on concentrations of somatotropin and insulin in plasma, milk production, and milk composition. Treatments were: 1) control; 2) arginine injection into jugular vein, and 3) arginine infusion into abomasum. Concentrations of arginine and ornithine in plasma were increased by injection of arginine into the jugular vein compared with the control. The concentration of ornithine in plasma was increased shortly after injection of arginine into the jugular vein, and both arginine and ornithine concentrations in plasma decreased rapidly. Abomasal infusion of arginine significantly increased concentrations of arginine, ornithine, and urea in plasma compared with concentrations in the control treatment. Injection of arginine into the jugular vein increased concentrations of somatotropin and insulin in plasma, but the increase did not persist for more than 30 min. A secondary peak in plasma somatotropin concentration occurred approximately 1 h after the initial peak. Arginine infusion into the abomasum did not alter plasma concentrations of either somatotropin or insulin. Dry matter intake, milk production, and milk composition were not affected by treatments. Lack of changes in milk production and milk composition suggest that acute increases in somatotropin with concomitant increases in insulin are not sufficient to stimulate synthesis of milk and milk components by cows during established lactation.     

Effects of recombinant bovine somatotropin on milk production, body composition, and physiological parameters

Twenty-eight multiparous Holstein cows were utilized to determine effects of long-term administration of recombinant bovine somatotropin on lactational performance, body condition, body composition, hormones, blood constituents, and physiological parameters. Treatments were 0 (control), 10.3, 20.6, and 41.2 mg recombinant bovine somatotropin administered daily as subcutaneous injections beginning 4 to 5 wk postpartum and continuing for 38 wk. A total mixed diet of 28% corn silage, 22% alfalfa hay cubes, and 50% corn-soybean meal-based grain mixture was fed. Fat-corrected milk yields were increased 12 to 25% for cows treated with somatotropin as compared with controls (29.9 kg/d). Milk composition was similar among treatments. Cows receiving somatotropin consumed 4 to 10% more feed and were 11 to 17% more efficient than controls for conversion of feed to milk. Body weight changes were not significantly different among treatments, but cows receiving somatotropin gained 4 to 10% less weight than controls. Body fat (kg) of cows receiving 20.6 and 41.2 mg/d was less than that of cows receiving 10.3 mg/d or no somatotropin. Estimated weights of body protein and mineral, most blood constituents, respiratory rates, and body temperature were not affected by somatotropin administration. Plasma fatty acids were elevated and hematocrit values were reduced. Plasma insulin, serum somatotropin, and heart rate increased concurrently with somatotropin administration.     

Bovine somatotropin dose titration in lactating dairy ewes. 3. Treatment interval.

Seventy-four lactating dairy ewes were injected with recombinant bovine somatotropin (bST; sometribove) in a sustained-release formulation. Ewes received 0, 80, 160, or 240 mg of bST/14 d at the end of 2, 4, and 6 wk postlambing, after which injections were withheld for a 28-d period. Response of milk production to bST presented a positive linear contrast and a negative quadratic contrast. After the final injection of bST (d 0), an increase in daily milk production was observed until d +9. A continuous decrease followed with milk production returned to control levels on d +11, +18, and +20, for 80, 160, and 240 mg of bST/14 d. Milk protein content decreased gradually until d +8 before it returned to control levels on d +12, +14 and +14, for 80, 160, and 240 mg of bST/14 d. Levels of bST and IGF-I in plasma presented positive and highly significant linear contrasts and negative quadratics which were significant only for bST. Relative to the evolution of milk production, the evolution of IGF-I levels in plasma was more similar than that of bST, although the correlation of each measure with milk production was high and highly significant. It was concluded that the period between successive injections should be shorter the lower the dose employed; however, a 14-d period seemed to correspond correctly for the dosages and hormone formulation tested.     

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.     

Somatotropin and lactation

Somatotropin, which can now be produced by biotechnology, could have an enormous impact on the dairy industry. Milk yield has been increased up to 40% with daily injections of somatotropin. Cows adjust their nutrient intake to support this increase. Somatotropin does not adversely affect cows' health, although all studies to date have been for less than one complete lactation. The search for a single biochemical or physiological event to account for the effects of somatotropin on milk production is elusive. Coordinated changes in many tissues and physiological processes occur to support the increases in the synthesis of lactose, fat, and protein in the mammary gland. Changes in the irreversible loss and oxidation rates of two key metabolites, glucose and free fatty acids, can quantitatively account for increases in lactose and milk fat during the short-term administration of somatotropin. Similarly, feed intake and live weight changes can account for increases in milk production in the longer experiments. Parallels between physiological changes that occur during somatotropin administration and differences between genetically high and lower yielding cows are highlighted, and the rates of improvement that can be expected from various new technologies are quantified. Existing data on the safety of somatotropin to both the consumer and the animal are evaluated.     

Long-term evaluation of a prolonged-release formulation of N-methionyl bovine somatotropin in lactating dairy cows

Eighty Holstein cows (first, second, or third lactation) were used to evaluate the efficacy of a prolonged-release formulation for sometribove (n-methionyl bovine somatotropin). Cows were fed ad libitum a complete mixed diet and milked twice daily. Cows were allocated randomly by parity to two treatment groups receiving 500 mg sometribove in a prolonged release formulation or excipient at 14-d intervals starting at 60 +/- 3 d postpartum and continuing for 36 wk. Treatment with sometribove increased FCM yield to a similar extent (11.4%, +3.1 kg/d) in primiparous and multiparous animals. Milk content of lactose, fat, ash, and Ca was not affected, but protein and phosphorous were slightly greater (less than 5%) in milk from sometribove-treated cows. Within a 14-d injection interval, animals treated with sometribove displayed a cyclic pattern in milk yield, but a similar pattern was not evident in feed intake.     

Treatment of dairy cows with recombinant bovine somatotropin: genetic and phenotypic aspects

Thirty-four multiparous and primiparous Holstein cows were utilized to examine the association between the response to long-term administration of recombinant bovine somatotropin and the cow's phenotypic and genetic production potential. Cows representing a range of phenotypic and genetic production potentials were assigned to one of four treatment groups: 0, 12.5, 25.0, or 50.0 mg recombinant bovine somatotropin daily. They were injected daily for 266 d beginning on d 24 to 35 postpartum. Pretreatment milk and fat yields were used to predict daily yields over the lactation and allowed treatment groups to serve as their own controls. Actual minus predicted yield estimated the response to treatment for milk, fat, and FCM for each cow. Milk composition (fat, protein, and lactose percentage) was not significantly affected by treatment. Response in yield for milk, fat, and FCM was significant during the treatment period (266 d). Milk yield increased by 18.5, 19.9, and 21.4%; fat yield increased by 13.4, 20.3, and 18.1%; and FCM increased by 16.3%, 19.7%, and 21.1% after receipt of 12.5, 25.0 and 50.0 mg recombinant bovine somatotropin, respectively. Differences in response were not significant. The dramatic effect recombinant bovine somatotropin has on production requires that alternative approaches be adopted in the future for accurate genetic evaluation of sires and dams if somatotropin is discriminantly used in the national herd.     

Effect of experimental design on responses to 2 concentrations of metabolizable protein in multiparous dairy cows

The objective of this research was to characterize the implications of changing between diets formulated to be adequate (ADMP) or low (LOMP) in metabolizable protein in a Latin square (LSq) design or of feeding the same diets continuously in a randomized complete block experimental design (RCBD). Fifty-four multiparous early-lactation cows (initial average ± SD; parity 2.8 ± 0.9, 85.8 ± 31 d in milk, 715 ± 63 kg of body weight, 29.1 ± 2.7 kg of dry matter intake/d, and 57.7 ± 5.7 kg of milk yield/d) were blocked by parity and days in milk and were then randomly assigned to experimental design, with 16 cows assigned to LSq and 38 cows assigned to RCBD. Cows within blocks in LSq were randomly assigned to sequence in a 4-sequence, 4-period, 2-treatment LSq balanced for the effects of previous treatment carryover. Cows within blocks in RCBD were randomly assigned to dietary treatment, which was fed over the same four 28-d periods as the cows in LSq. Treatment diets were formulated to be similar in composition with the exception of exchanging an equal quantity of expeller soybean meal from ADMP (16.5% crude protein; 28.4% ash-free, amylase-treated neutral detergent fiber organic matter) for soybean hulls in LOMP (14.6% crude protein; 31.1% ash-free, amylase-treated neutral detergent fiber organic matter). Cows were individually fed treatment diets in a tiestall barn once daily for ad libitum consumption, milked 3 times daily, and administered recombinant bovine somatotropin every 14 d. Milk yield and feed offered and refused were measured daily; BW was recorded on 2 consecutive days each week; milk composition was measured at 6 consecutive milkings each week; and spot samples of feces, urine, and blood were collected during the last week of each period and a covariate period. Experimental designs were analyzed separately using results from wk 4 of each period with mixed effects modeling. Dry matter intake and milk fat yield were not affected by diet in either design, whereas milk and protein yields were greater for cows fed ADMP in both designs. Milk fat and protein percentage responses and milk energy output inferences were different between designs. Milk fat yield and percentage responses were affected by previous treatment carryover in LSq. Metabolic and digestibility inferences were very similar between designs. Under the conditions of this experiment, inferences on N metabolism and the majority of production measurements were not affected by experimental design, with the principal exceptions of milk fat and protein percentage and milk energy output.     

Induced lactation in pubertal heifers: efficacy, response to bovine somatotropin, and profitability

Heifer rearing represents one of the largest costs of commercial dairying because these animals do not begin to produce milk until approximately 2 yr of age. The objectives of this study were to characterize milk production, growth, reproduction, and herd life after induced lactation in healthy 15-mo-old heifers. We further wanted to quantify their lactation response to bovine somatotropin (bST), and compare survival rate and profitability of heifers induced into lactation to that of heifers reared using traditional methods. Holstein heifers (n = 32) were induced into lactation by administration of estradiol-17β (0.075 mg/kg of body weight per d) and progesterone (0.25 mg/kg of body weight per d) for 7 d. Milking began on experimental d 18. Heifers were paired based on milk production, and one in each pair was assigned randomly to bST or control treatment groups; treatments began on 25 ± 7 d of lactation, and milk production was compared for 70 d. Heifers treated with bST produced 14.7% more milk than did controls. After the 70-d comparison period, all heifers received bST for the remainder of their lactations. Throughout the induced lactation, heifers gained 0.69 kg/d, averaged 1.8 services/pregnancy, and 27 heifers calved for a second lactation. For the herd life and economic analyses, heifers induced into lactation were compared with similarly aged heifers in the same herd reared by traditional management methods. The animals induced into lactation had a 62.7% chance of remaining in the herd as long as the peer cohorts, but both groups had similar productive lifespans. Net present value for an induced animal ($2,459) was not different from that of a traditionally raised peer ($3,137). In summary, heifers hormonally induced into lactation with estrogen and progesterone were healthy, grew normally, had a mean daily milk production of 18 kg with normal composition, and had good reproductive performance. Based upon the assumptions and prevailing financial environment of this experiment, hormonally induced lactation of 15-mo-old heifers, as a routine management tool, was not more profitable than traditional management practices.     

Effects of rumen-protected Capsicum oleoresin on productivity and responses to a glucose tolerance test in lactating dairy cows

The objective of this experiment was to investigate the effects of rumen-protected Capsicum oleoresin (RPC) supplementation on feed intake, milk yield and composition, nutrient utilization, fecal microbial ecology, and responses to a glucose tolerance test in lactating dairy cows. Nine multiparous Holstein cows were used in a replicated 3 × 3 Latin square design balanced for residual effects with three 28-d periods. Each period consisted of 14 d for adaptation and 14 d for data collection and sampling. Treatments were 0 (control), 100, and 200 mg of RPC/cow per day. They were mixed with a small portion of the total mixed ration and top-dressed. Glucose tolerance test was conducted once during each experimental period by intravenous administration of glucose at a rate of 0.3 g/kg of body weight. Dry matter intake was not affected by RPC. Milk yield tended to increase for RPC treatments compared to the control. Feed efficiency was linearly increased by RPC supplementation. Concentrations of fat, true protein, and lactose in milk were not affected by RPC. Apparent total-tract digestibility of dry matter, organic matter, and crude protein was linearly increased, and fecal nitrogen excretion was linearly decreased by RPC supplementation. Rumen-protected Capsicum oleoresin did not affect the composition of fecal bacteria. Glucose concentration in serum was not affected by RPC supplementation post glucose challenge. However, compared to the control, RPC decreased serum insulin concentration at 5, 10, and 40 min post glucose challenge. The area under the insulin concentration curve was also decreased 25% by RPC. Concentration of nonesterified fatty acids and β-hydroxybutyrate in serum were not affected by RPC following glucose administration. In this study, RPC tended to increase milk production and increased feed efficiency in dairy cows. In addition, RPC decreased serum insulin concentration during the glucose tolerance test, but glucose concentration was not affected by treatment.     

Effect of a prolonged-release formulation of N-methionyl bovine somatotropin (sometribove) on milk fat.

Nine Holstein cows were injected bi-weekly with a prolonged-release formulation of N-methionyl bST, and 9 cows were injected with excipient. Intramuscular injections began at 60 +/- 3 d postpartum and continued at 14-d intervals for the full lactation. Administration of bST increased production of milk, total fat, and all milk fat components measured. Average fatty acid composition of milk fat was not influenced by bST treatment. Stage of lactation had a large influence on production and percentage of individual fatty acids in milk fat from both bST-treated and control cows. The stage of lactation impact on the fatty acid composition of milk fat reflected changes in the relative contributions of body fat mobilization and de novo synthesis of milk fat components in response to changes in energy balance. Initiation of bST treatment caused some transient changes in milk fatty acid composition that were related to energy balance. These changes were small compared with the normal changes because of stage of lactation in all cows. Phospholipid and cholesterol content of milk also changed with stage of lactation but were not influenced by bST treatment. Melting properties of milk fat were influenced greatly by stage of lactation. Bovine somatotropin did not cause any changes in composition or physical properties of milk fat that were outside the range of normal variation.     

Effects of sodium sesquicarbonate on dry matter intake and production of milk and milk components by Holstein cows

Forty-six multiparous Holstein cows were used to investigate the effects of sodium sesquicarbonate on dry matter intake, body weight, and production and composition of milk during a 308-d lactation. Diets contained alfalfa silage, corn silage, and concentrate. Composition of diets was changed twice during the 308-d lactation experiment. Diets fed during d 1 to 175 and d 176 to 245 were formulated to contain more rumen-undegradable protein and fat, and less forage than that fed during d 246 to 308. Sodium sesquicarbonate did not affect yields of milk, 4% fat-corrected milk, and components in milk, or percentages of components in milk during the complete 308-d lactation or during d 1 to 175 or d 176 to 245. However, from d 246 to 308, cows fed sodium sesquicarbonate produced more milk, 4% fat-corrected milk, fat, protein, and solids-not-fat than did control cows. Milk composition was not altered. These data suggest that composition of the diet has a significant effect on the response to dietary buffers by lactating dairy cows.     

Effects of long daily photoperiod and bovine somatotropin (Trobest) on milk yield in cows.

Bovine somatotropin (bST) and exposure to long daily photoperiod increase milk yield of dairy cattle. We tested the hypothesis that long daily photoperiod and bST treatment would increase milk yield in an additive manner in lactating cows. At winter solstice, 40 lactating cows were started on a 140-d experiment; cows were greater than 70 d in milk (DIM) and were balanced for uniformity of DIM and milk yield within parity. Cows were randomly assigned to one of four treatments (10/treatment): 1) natural photoperiod, 2) natural photoperiod + bST (14 mg/d Trobest i.m.), 3) long daily photoperiod (18 h of light and 6 h of darkness/d), or 4) long daily photoperiod + bST. Long daily photoperiod increased fat-corrected milk (FCM) yield 1.9 kg/d versus natural photoperiod. Treatment with bST increased FCM 5.7 kg/d versus natural photoperiod, and long daily photoperiod + bST increased FCM 5.8 kg/d versus long daily photoperiod. Long daily photoperiod + bST was additive, increasing FCM 7.7 kg/d versus natural photoperiod. Serum somatotropin increased with bST, but not photoperiod, and bST increased serum insulin-like growth factor-I. Long daily photoperiod tended to increase prolactin; bST had no effect. Long daily photoperiod + bST increased dry matter intake (DMI) relative to natural photoperiod and natural photoperiod + bST; long daily photoperiod increased DMI relative to natural photoperiod + bST. Photoperiod had no effect on net energy balance; however, bST decreased net energy balance. Generally, body weight and milk composition did not differ among treatments. In conclusion, combination of bST with long-daily photoperiod tended to amplify the increases in milk yield observed with either treatment individually.