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The cow has been specifically selected for lactational performance. It has no lactational anoestrus and the simultaneous reproductive ability and milk yield have not only scientific interest but economic importance too. We have no evidence of a luteotrophic action of prolactin (Hoffmann, Schams, Bopp, Ender, Giménez & Karg, 1974) in this species such as has been shown in some others. Furthermore, mammary cancer, one motivation for the increasing amount of work devoted to studies on prolactin in man, has not been recorded in the cow.

Summary. Progesterone, LH and FSH were measured in the plasma of 4 female roe deer (2 kept with the buck, 2 separated from the buck to prevent mating) from July until the end of September or October, i.e. including the rutting season from the middle of July to the middle of August. At least two distinct peaks of LH and FSH were observed before the first small progesterone increase lasting for about 5 days in late July. The next clear LH peak and, with slight individual variations, FSH peak occurred exactly when progesterone values had fallen and before they rose again in a major elevation, i.e. after ovulation. LH and, with some variations, FSH values were generally basal while progesterone was high during the rest of the study. There were no obvious differences in hormone pattern in pregnant and non-pregnant animals.

Summary.

Levels of lh were determined by radioimmunoassay and those of progesterone by a competitive protein-binding technique. Blood samples from eight cows, representing two complete pregnancies (including post-partum periods), and from one cow in the first trimester and another around the time of parturition, were collected. The samples were withdrawn at intervals of 6 hr for lh and every 4 to 5 days for progesterone determination. Levels of lh were consistently low (1·0 to 1·6 ng/ml plasma) with a few single peaks occurring irregularly in individuals during the first 110 days. Distinct lh peaks were observed between Days 7 and 20 post partum. The decrease of progesterone from high levels during pregnancy (plateau between 5 and 9 ng/ml plasma with individual differences) before parturition and the low level following was not reflected in the lh concentration. In an experiment with one animal, an injection of 5 mg flumethasone near term caused a partial decrease in the progesterone concentration, and a larger dose of 10 mg induced parturition. This was preceded by a marked decrease of progesterone similar to that observed before a normal delivery.

Summary.

The luteotrophic properties of endogenously secreted LH and prolactin were studied by measuring CL function after neutralization of circulating LH and prolactin by the administration of highly specific antisera against these hormones on the 11th and 12th day of the oestrous cycle. In addition, the effect of a prolactin inhibitor (CB-154), which reduced prolactin concentration in peripheral blood by 80 to 90% was studied. A hysterectomized heifer carrying a persistent CL was treated with CB-154, a combination of CB-154 and prolactin antiserum and then with LH antiserum. In all animals treated with the LH antiserum, CL function ceased or was quantitatively inhibited. No change in circulating progesterone was seen after treatment with the prolactin antiserum or the prolactin inhibitor. It is concluded that LH is the dominant luteotrophic factor in the bovine species while prolactin has little or no activity.

Summary.

The growth of the pituitary and of the reproductive tract of Suffolk rams from birth to 168 days of age has been studied. Pituitary icsh and fsh concentrations were determined by bio-assay. The pattern of testicular androgen production has been examined using chemical and histological techniques and the relationship to spermatogenesis studied. Pituitary gonadotrophin content increased sharply from 42 days of age but was only weakly correlated with other parameters measured. The androstenedione : testosterone ratio was at its narrowest at birth; however, testosterone was the predominant androgen from birth onwards. Androgen concentration fluctuated but the total content increased with increase in testicular weight. Fructose was present in the seminal vesicles from birth and citric acid from 14 days; citric acid concentration was about one-tenth that of fructose. There was a significant correlation between testicular androgen content and the fructose and citric acid concentration and content of the seminal vesicles. Seminiferous tubule diameter was significantly correlated with most of the parameters measured. Testicular weight increased sharply from 42 days of age. Androgen production was present at birth and preceded spermatogenesis which began when testis weight exceeded 10 g, which was after 56 days of age. Spermatozoa were present in the seminiferous tubules at 112 days of age.