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The effect of exogenous bovine recombinant somatotropin (bST) on the recruitment of follicles and quality of oocytes was investigated in the bovine. Single injections of recombinant depot form of bST were given to nine heifers and seven cows at the time of synchronized estrus (day 0). Nine heifers and six cows served as controls. Three days after bST injection the animals were slaughtered, their ovaries dissected and follicles separated into two categories according to diameter (2–5 and 5–10 mm). A total of 196 (53.2%) healthy oocyte-cumulus complexes (OCC) was isolated and selected from 369 follicles (diameter 2–5 mm) of bST treated heifers and 137 (49.8%) OCC from 275 follicles of bST treated cows. After 25–28 h of culture, 164 (44.4%) and 124 (45.1%) oocytes from follicles of heifers and cows, respectively, had developed to the metaphase of the second meiotic division (MII). From control heifers, 122 (35.5%) OCC derived from 344 follicles (2–5 mm) and from control cows 87 (39.7%) OCC derived from 219 follicles were similarly selected for maturation in vitro and 109 (31.7%) and 78 (35.6%) oocytes in control heifers and cows, respectively, developed to the MII stage. The numbers of follicles developed in the experimental and control groups were similar (P > 0.05) but differences were evident in the healthy OCC and oocytes maturing in the treated versus control groups of heifers and cows (χ2 detected at 1% and 5% levels, respectively). The injection of bST resulted in significantly increased levels of growth hormone (GH) in peripheral blood and follicular fluid (FF), the GH levels in blood plasma correlating with the levels in FF. The level of insulin-like growth factor I (IGF-I) in sera from bST treated animals was significantly higher than in sera from control animals (353.6 vs. 155.5 ng ml−1). In conclusion, recombinant bST positively affected (at day 3) the proportion of OCC and oocytes maturing to MII.

Milk production, plasma bovine somatotropin (bST) and insulin-like growth factor I (IGF-I) were measured in dairy cows following a single subcutaneous injection of a slowly released preparation of either recombinant enterokinase linker bST (somidobove: 640 mg) or recombinant methionyl bST (sometribove: 500 mg). There was a 3-7-fold increase in plasma bST concentrations during the first three postinjection hours in cows treated with both sometribove (from 3.4 +/- 0.8 to 11.2 +/- 3.0 ng ml-1) or somidobove (from 2.3 +/- 0.3 to 17.5 +/- 2.6 ng ml-1). In the next 8 days the bST concentration in the bST-treated cows varied, but was still significantly increased above the controls. In the following days, the concentrations of bST did not differ from the controls. Plasma concentrations of IGF-I increased nearly 2-fold as early as 24 h following recombinant bST administration and then continued to rise so that by 48 h postinjection they were nearly four times higher (control 16.2, bST-treated 61.7 ng ml-1). From 48 h after sometribove injection, IGF-I concentrations remained at a plateau (varying between 60.4 and 85.7 ng ml-1) till day 11. Then it decreased slowly, but still remained higher on day 14 than those in placebo-treated cows (44.4 +/- 17.8 ng ml-1 in bST-treated animals; 12.2 +/- 7.5 ng ml-1 in the controls). Although IGF-I level was increasing in all bST-treated animals, the absolute IGF-I increase was not related to the increase in milk production.

The effects of administration of recombinantly derived bovine somatotropin (somidobove) in a sustained-release vehicle on the profiles of concentrations of bovine somatotropin (bST) in the blood plasma and on the milk yield of dairy cows of three herds were examined. Cows (36-87 days post partum) were treated subcutaneously with recombinant bST at 28-day intervals. In control animals, basal concentrations of bST averaged 1.4 ng.ml-1 in first-calf heifers and 1.5 ng.ml-1 in multiparous cows. In somidobove treated first-calf heifers, the concentration of bST was increased to 10.7, 14.5, and 27.0 ng.ml-1 at 24 h postinjection and in multiparous cows to 6.6, 11.0, and 11.7 ng.ml-1 on day 2 postinjection of 320, 640, and 960 mg of somidobove, respectively. On day 8 postinjection the average plasma bST levels of both parity groups are similar (on the average 3.4, 8.6, and 12.5 ng.ml-1 for three doses of somidobove respectively) and for the two highest doses being still significantly increased. During the 2nd week postinjection plasma bST concentration declined returning to control levels on day 15 postinjection. Somidobove-treated first-calf heifers produced 10.9, 16.7 and 17.9% and multiparous animals 25.5, 24.2 and 32.5% more milk than the controls when given 320, 640 and 960 mg somidobove, respectively. The cyclic pattern in milk yield within each 28-day injection interval was observed consistently in all herds. The milk yield increased to a maximum between day 4 to 8 postinjection and then slowly declined. Milk composition was not affected by somidobove treatment.

Publisher Summary This chapter describes the blood constituents and subcutaneous adipose tissue metabolism of dairy cows after administration of recombinant bovine somatotropin (bST) in a prolonged release formulation. In the first experiment 25 primiparous and multiparous dairy cows were randomly assigned to bST treatments. Blood samples were collected at day 1, 8, 14, and 22 postinjection and plasma was analyzed tor bST concentration and for clinical parameters. Plasma glucose, free fatty acids and serum Ca, Na and K were not affected by treatment. In the second experiment the profiles of bST in the plasma from the intensive sampling on five multiparous crossbred cows showed that as early as during 1 h after the subcutaneous hormone administration. bST concentration in plasma increased to 22 ng/ml and then varied between 17 to 24 ng/ml during the first 5 days post injection. The suppression of lipogenesis in adipose tissue of bST treated cows support the concept that bST partitions ratty acids from adipose tissue and circulation for preferential use by mammary tissue.

SUMMARY A method for the bioassay of oxytocin in the lactating rat mammary gland in vitro is described. The changes in transparency induced by oxytocin in a flat segment of the gland are recorded by means of a CdS photoresistor and a simple Wheatstone bridge. The sensitivity of the assay in routine use is about 0·5–10 μu. oxytocin, the index of precision being about 0·1.

Goat placental lactogen was partially purified from a medium collected after placental tissue incubation. The data obtained by disc electrophoresis and isoelectric focusing experiments, as well as by means of radioreceptor assay methods, provide evidence of the similarity between the goat and ovine placental lactogen.