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

Effects of misty-fan cooling and supplemental rbST on rumen function and milk production of crossbred Holstein cattle during early, mid and late lactation in a tropical environment

Two groups of five crossbred 87.5% Holstein cattle were housed in normal shade only (NS) as non-cooled cows and in shaded housing with misty-fan cooling (MF) as cooled cows. The cows were treated with recombinant bovine somatotropin (rbST) in early, mid and late lactation with three consecutive injections of rbST in every 14 days. Ambient temperatures and the temperature humidity index in the NS barn were significantly higher than those of the MF barn, whereas relative humidity in MF was higher than that of NS barn. The DMI of cooled cows were higher than those of non-cooled cows, and cooled cows exhibited more response to rbST treatment. Exogenous rbST significantly increased milk yield throughout lactation. The rbST-treated cows had higher total ruminal fermentation products as volatile fatty acid and ammonia nitrogen than the non-rbST treated cows and associated changes were greater in cooled animals in all stages of lactation. Exogenous rbST increased the concentrations of milk urea nitrogen in both groups. These results suggest that the changes in ruminal fermentation with greater production of total VFA and NH(3)N in response to rbST in crossbred cows whether under misty-fan cooling or not, is in part through an increase in feed intake, thereby making more substrate available to the mammary gland for milk synthesis.

Responses of Holstein Cows to a Low Dose of Somatotropin (bST) Prepartum and Postpartum

Objectives were to evaluate the effects of a low dose of bovine somatotropin (bST) injected prepartum and postpartum on body condition score (BCS), body weight (BW), and milk yield (MY) in cows as well as somatotropin insulin, insulin-like growth factor-I (IGF-I), glucose, and nonesterified fatty acids (NEFA) in plasma. Holstein cows nearing second or later parities were assigned randomly to control (CON = 98) or bST-treated (TRT = 95) groups. Biweekly injections of bST began 21 +/- 3 d before expected calving and continued through 42 d postpartum (CON vs. TRT; 0 vs. 10.2 mg of bST/ d). From 42 to 100 d postpartum, no cows received bST. During yr 1, somatotropin, IGF-I, insulin, NEFA, and glucose were measured in plasma samples from 82 cows. During yr 2, effects of bST on BCS and BW of 111 cows were evaluated, but no blood samples were collected. Milk yields through 100 d of all 193 cows were analyzed. Prepartum treatment with bST resulted in greater prepartum plasma concentrations of somatotropin, insulin, and numerically greater NEFA but did not affect glucose or IGF-I. Postpartum bST increased mean plasma concentrations of somatotropin and NEFA, but not INS, IGF-I, or glucose. Mean BCS of cows did not differ prepartum, around parturition, or postpartum. Although mean BW did not differ prepartum or around calving, cows receiving bST maintained greater BW postpartum. Cows receiving bST tended to have higher MY (6.6%) in the first 60 d of lactation, but differences did not persist through 100 d, including approximately 40 d when no cows received bST. Number of cows that were culled due to health (CON = 3 vs. TRT = 2) or died (CON = 3 vs. TRT = 1) were not affected by treatment. Low doses of bST in the transition period resulted in higher postpartum BW, quicker recovery of body condition during lactation, and significantly more milk during treatment.

Southeastern pasture-based dairy systems: housing, posilac, and supplemental silage effects on cow performance

This experiment tested performance and physiological responses to evaporative cooling, bovine somatotropin (bST), and supplemental silage of lactating cows grazing bermudagrass (Tifton 85; Cynodon dactylon x C. nlemfuensis cv.) pastures. Multiparous (n = 32) cows (196 d in milk) were assigned one of five treatments arranged in two replicates. Treatments were 1) cows maintained continuously on pasture with access to shade, 2) treatment 1 + bST, 3) night housing on pasture, then free-stall housing with fans and misters from 0730 to 1630 h, 4) treatment 3 + bST, and 5) treatment 4 + corn silage fed at 0.5% of body weight (dry matter basis) in the barn. A grain supplement was fed at a rate of 0.5 kg/kg of milk produced. Time spent grazing ranged from 4 to 7.2 h/d, with cows fed corn silage spending the least amount of time. Cows given bST grazed 45 min/d longer than controls, but intake of bermudagrass was unchanged. Intake of bermudagrass ranged from 7.4 to 9.5 kg/d of organic matter, with the lowest intake by cows fed corn silage. With the exception of cows fed corn silage, cows kept in a cooling barn during the day ate equivalent amounts of pasture as those given unlimited access to pasture. Production of 4% fat-corrected milk was greater by cows injected with bST (17.7 vs. 15.8 kg/d) compared with controls and tended to be greater for cows given daytime cooling compared with cows on pasture continuously (17.2 vs. 16.3 kg/d). Cows provided evaporative cooling did not lose weight compared with continually pastured cows (6.3 vs. -10.9 kg/24 d). Cows injected with bST compared with controls maintained their body weight better (2.5 vs. -7.1 kg/24 d). Cows given bST had increased concentration of plasma insulin-like growth factor-I (142 vs. 89 ng/ml), insulin (0.60 vs. 0.56 ng/ml), and nonesterified fatty acids (318 vs. 239 mEq/L). Cows given bST and those continually on pasture had greater diurnal body temperatures. Use of barn cooling systems and bST treatments as management tools provided limited improvement in performance of midlactation cows managed in pasture-based systems.

Interactions of energy and bovine somatotropin with heat stress

Heat stress, resulting when dairy cows are exposed to hot or to hot and humid environmental conditions, reduces DMI and milk yield and increases maintenance costs of the cow. Decreased DMI may help to maintain homeothermy through reduced metabolic heat production. The high yielding cow has greater metabolic activity and produces more body heat than those with lower yields; thus, greater milk yield may increase heat stress if the cause of that stress is not mitigated. Use of bST increases milk yield, and, during hot or hot and humid environmental conditions, bST increased milk yield with or without noticeable effects on heat stress, depending on the study. The use of bST does not change maintenance requirements or partial efficiencies of milk yield. Thus, the greater heat stress that occurred in some studies probably was related to the increased metabolic activity and heat production associated with milk yield and to the difficulties of cows in dissipating the additional body heat from environmental conditions. Cows that are administered bST are subject to heat stress as are other high yielding cows if sufficient metabolic heat is not dissipated. Management to minimize effects on the cow of environments conducive to heat stress and strategies that improve DMI are necessary to sustain the high milk yield potential offered by technologies, including bST.

Interactions of heat stress and bovine somatotropin affecting physiology and immunology of lactating cows

During summer, 34 cows received daily injections of placebo or 25 mg of bST and were placed in a thermoregulated or a heat stress environment. Heat stress increased rectal temperatures, respiration rates, and plasma cortisol concentrations and decreased milk yield. Four of 9 bST-treated cows and none of 8 control cows became atactic on the 1st d of heat stress. When exposed to heat stress, cows treated with bST experienced higher rectal temperatures throughout the trials than cows treated with placebo. Nonetheless, bST increased milk yields in both environments. The major effect of heat stress on immune function was decreased migration of leukocytes to the mammary gland after chemotactic challenge. This effect of heat stress was not altered by bST. In summary, hyperthermia induced by heat stress and associated changes were greater for cows treated with bST. Detected effects of heat stress on the immune system were few and were not alleviated by bST. Use of bST during summer in subtropical climate zones requires careful management to avoid overexposure of bST-treated cows to heat stress.

[Concentrations of metabolites and hormones in the blood plasma of lactating dairy cows during treatment with recombinant bovine somatotropin (BST)]

Sixteen lactating dairy cows were submitted to six injections in a four-week interval of either 640 mg prolonged release bST or of 640 mg saline (control, n = 8). The bST-treated animals were pair fed to the control cows, which were fed according to requirements. Fourteen days after each injection, blood samples were derived and analysed for metabolites and hormones. Plasma contents averaged 0.16 mmol/l non esterified fatty acids (NEFA), 2.69 mmol/l glucose, 0.43 mmol/l beta-hydroxybutyrate, 0.024 mmol/l acetoacetate, 78.8 g/l protein, 4.6 mmol/l urea, 0.81 micrograms/l insulin, 44.4 ng/l thyroxine (T4) and 1.41 ng/l triiodothyronine (T3). The bST-application was without effect on the analysed plasma contents.

Effect of sometribove on rumen fermentation, rate of passage, digestibility, and milk production responses in dairy cows

Six ruminally and duodenally fistulated Holstein cows 60 d postpartum were assigned randomly to each of two treatments in a single reversal design. Treatments consisted of placebo or 25 mg of sometribove (bST) injected daily. Treatments were initiated at 60 d +/- 7 postpartum and maintained for 6 wk with a 3-wk adjustment between treatment periods. All cows received a TMR consisting of 16% CP and 1.67 Mcal of NE I/kg of DM. Influence of bST on rumen fermentation characteristics, digesta rate of passage, apparent nutrient digestibility, and milk production was evaluated. Milk yield of treated animals was 4.0 kg/d higher than controls. The 3.5% FCM and milk production efficiency (3.5% FCM/DMI) were significantly higher in treated animals than in controls (29.0 vs. 25.4 kg/d and 1.38 vs. 1.21 kg/kg, respectively). Percentage of rumen cellulolytic bacteria (of total viable bacteria) was not significantly different for bST-treated animals (6.4 vs. 3.4%). Total number of rumen protozoa tended to be higher (7.25 vs. 6.55 x 10(3)/ml) in bST-treated animals. Ruminal percentages of CP, NH3 N, alpha-amino N, VFA, and pH were unaffected by treatment. Sometribove treatment did not significantly affect liquid dilution or solids turnover rates. Percentages of CP, alpha-amino N, and NH3 N content in duodenal samples were unaffected by treatment. Total tract apparent digestibility of nutrients and mean daily DMI were unaffected by treatment.

Control of growth and differentiation of the mammary gland by growth factors

Mammary gland development is a complex process regulated by various steroid and polypeptide hormones. Although the systemic importance of hormones, such as estrogen, progesterone, prolactin, and growth hormone, in the growth of the mammary gland has been well documented, these hormones are virtually incapable of stimulating mammary cell growth in vitro. Thus, the growth stimuli for mammary cells requires clarification. In recent years, a number of growth factors have been discovered; this has prompted interest in examining possible involvement of these biologically active agents in the process of mammary gland development. Results presented herein indicate that several growth factors including epidermal growth factor, transforming growth factor alpha and beta, basic fibroblast growth factor, insulin-like growth factor-I, and mesenchyme-derived growth factor participate in the regulation of mammary cell growth and differentiation.

Effects of somatotropin on milk yield and physiological responses during summer farm and hot laboratory conditions

The effects of bST on performance and physiological responses of lactating cows was studied under farm summer and laboratory heat conditions. Twelve cows, 90 to 50 d postpartum, were injected with either bST or vehicle solution for 30 d under farm summer and 10 d under either laboratory thermoneutral or heat conditions. Somatotropin increased milk yield by 6.1 (21%), 8.1 (32%), and 7.3 kg (35%) under the farm summer, laboratory thermoneutral, and heat conditions, respectively. Somatotropin also increased milk fat by 15 and 19% and dry matter intake by 16 and 18% under laboratory thermoneutral and heat conditions, respectively. Somatotropin increased the efficiency of feed conversion into milk without any significant changes in body weight and temperatures. Somatotropin reduced plasma concentrations of triiodothyronine and cortisol and had no effect on plasma prolactin and insulin concentrations. Somatotropin did not increase water intake; however, hematocrit was decreased. The results suggest that stimulatory effects of bST on milk production are still observed on heat-stressed cows without any significant indications of additional heat stress.

Effects of bovine somatotropin on physiologic responses of lactating Holstein and Jersey cows during hot, humid weather

Thirty-one lactating Holstein and Jersey cows were used to determine the effects of daily injections of 0 or 20 mg of recombinant bST on physiologic responses during hot, humid weather. Body temperature was determined by measuring milk temperature at each milking. Jugular blood was sampled for serum analysis of selected hormones, blood metabolites, and fatty acids, and arterial blood was sampled for blood pH and blood gas analysis. Milk was characterized for fatty acid composition. Blood pH was unchanged, but partial pressure of blood CO2, blood bicarbonate, base excess, and total CO2 declined with administration of bST. Serum triglycerides increased 89% in cows receiving bST. Blood urea nitrogen tended to decline in cows receiving bST. Serum cortisol, triiodothyronine, and thyroxine did not change, but insulin-like growth factor-1 increased 128% with bST use. Reduced milk short-chain fatty acids, increased milk long-chain fatty acids, and increased blood serum C18:1 fatty acid content occurred in cows administered bST and probably reflected tissue mobilization. Cows administered bST in hot weather had higher milk temperatures. Alterations in physiologic and metabolic measures in association with higher milk temperature suggest an interaction of bST use with hot, humid weather and reflect the need to minimize the effects of heat stress.

Effects of bovine somatotropin on dry matter intake, milk yield and body temperature in Holstein and Jersey cows during heat stress

Thirty-one lactating Holstein and Jersey cows were used to determine the effect of daily injections of 0 or 20 mg of recombinant bST in hot, humid weather. The comparison period lasted 80 d, from mid-June through August. The maximum and minimum ambient temperature and relative humidity averaged 34.6 and 22.2 degrees C and 100 and 59.8%, respectively. Body temperatures of somatotropin-treated Holsteins were elevated over controls by .2 and .3 degrees C at the a.m. and p.m. milkings, respectively, whereas corresponding treatment effects for Jerseys were .5 and .6 degrees C, thus demonstrating a breed by treatment interaction. The response of milk and FCM yields and apparent efficiency of production to somatotropin administration depended on the level of production prior to treatment. Cows at low pretreatment production increased milk and FCM yields to a greater degree than did cows at higher production. A breed by treatment interaction showed that Holsteins increased milk and FCM yields more than Jerseys upon administration of somatotropin. Intake of DM was not affected by treatment. Cows administered bST lost BW and condition score. Greater heat stress was associated with the higher milk production of cows administered bST.

Model to describe and alleviate milk protein depression in early lactation dairy cows fed a high fat diet

The depression of milk protein percentages for cows fed high fat diets in early lactation is a major problem facing the dairy industry. In order to describe more fully the mechanism involved, data involved 97 cows observations were summarized. Cows were fed diets containing corn-soybean meal or additional fat in the form of whole oilseeds as the main ingredients in the concentrate mix. Blood samples from the tail artery and subcutaneous abdominal vein were taken approximately 6- to 8-wk postpartum for amino acid analyses. Production of milk during the week of blood sampling was increased (36.9 and 39.6 kg/d) approximately 7.3% but milk protein percentages (2.91 and 2.79) were reduced for cows fed added fat. Intake of DM (21.1 and 21.4 kg/d) and BW (605 and 608 kg) were similar. Uptake of amino acids by the mammary gland, as measured by arteriovenous differences, was numerically lower for all essential amino acids and significantly reduced for histidine, isoleucine, leucine, phenylalanine, threonine, valine, and total essential amino acids for cows fed added fat. It is proposed that added fat inhibits somatotropin release from the anterior pituitary, thereby reducing mammary gland uptake of amino acids because of the role of somatotropin in aiding amino acid uptake. Administration of exogenous somatotropin with added fat diets may alleviate milk protein depression associated with such diets.

Effects of bovine somatotropin on milk yield and composition, dry matter intake, and some physiological functions of Holstein cows during heat stress

Thirteen Holstein cows (46 to 106 d postpartum) were assigned to a partially balanced incomplete block experiment to evaluate effects of bovine somatotropin (20.6 mg monomer/d) and environment (shade and no shade) on milk yield and composition, feed intake, rectal temperature, respiration rate, and concentrations of hormones in plasma. Two treatment periods were 29 d each, preceded by 10-d preliminary periods. Water and cotton-seed hull-based diet were available ad libitum. Mathematical model for statistical analyses included cow, period, treatment, environment, day, and estimable interactions. Black globe temperature and respiration rate and rectal temperature of cows were higher in no shade. Milk and 3.5% FCM yields and feed intake of cows in no shade were approximately 9.5 and 16% less than for cows in shade. Much of the effect of heat stress was associated with reduced DM intake. The 3.5% FCM, but not milk yield, was increased by injections of bovine somatotropin. Dry matter intake was unaffected, but milk, 3.5% FCM, and component yields were increased by bovine somatotropin when adjusted for DM intake. Response of cows to bovine somatotropin was not different in the two environments, except cows injected with bovine somatotropin had slightly higher body temperature and respiration rate. Increased production responses of heat-stressed cows due to bovine somatotropin were less than in cows injected under more temperate conditions.