Thirty-two mature, white-faced western ewes were studied in a 22 factorial experiment of one estrous cycle duration. The factors studied were the feeding of glucose and the administration of triiodothyronine (T3). Both treatments were effective in elevating the blood glucose level. Treatment with T3 caused a loss in body weight; the greatest loss occurred in the T3-treated, glucose-fed ewes. The estrous cycle was longer for animals on T3 treatment. Both glucose alone and T3 alone appeared to depress follicular development. No difference in follicular activity from the controls was observed when both treatments were used together.

A total of 96 mature ewes was used in an experiment to determine the effect of longterm feeding a high-energy ration (grain) on ovarian and pituitary activity. The animals were studied at four stages of the estrous cycle (days 1, 4, 10 and 16). Grain-fed ewes, when compared with ewes receiving only hay, were heavier and had a higher plasma glucose level and lower concentration of plasma freefatty acids. The adrenal weight, pituitary weight and ovulation rate were greater for this group also. Follicular fluid weight and the number of large follicles were greater in grain-fed animals at all stages. Both follicular traits were greatest at day 10. Volume of the largest follicle was greatest at day 1. Luteal weight and progesterone content of the luteal tissue increased between days 4 and 10 and remained high at day 16. Although the bio-assays were not entirely valid, pituitary LH concentration appeared higher in grain-fed ewes at all stages of the cycle. LH concentration was lowest at day 1 and increased to day 16. FSH concentration also appeared to increase from day 1 to day 10 and then remain high through day 16. Feed had no apparent effect on FSH concentration. Rumen action on the high-energy ration presumably leads to an abundance of propionic acid, which through gluconeogenesis results in elevated plasma glucose levels. Probably less gluconeogenesis from protein is then required, allowing an increase in body protein. It is suggested that persistently elevated plasma glucose levels, via hypothalamic stimulation, lead to greater gonadotropin production and subsequent greater ovarian activity.

Studies were made to determine the hormonal requirements for the maintenance of early pregnancy in swine. Nine control and 27 treated gilts were used. Ovariectomy was performed on day-4 and autopsy on day-25 of pregnancy. Subcutaneous injections of progesterone and estrone at a ratio of 4000:1 were administered in three different dosage levels per pound body weight, daily: (1) 0.3 mg. progesterone plus 0.075 meg. estrone, (2) 0.6 mg. progesterone plus 0.15 mcg. estrone (3) 1.2 mg. progesterone plus 0.3 meg. estrone. Injections were started 72 hours after breeding and were continued to slaughter. The numbers of gilts out of nine that were pregnant at day-25 of gestation were 8, 8, 9 and 8 for the three treated and control groups, respectively. The average percentages of embryo survival (for all gilts per group) and the average numbers of live embryos (per pregnant gilt) in the three treated groups were significantly less than for the control group (17, 4.1; 45, 4.6; and 38, 5.2 vs. 86, 11.8). There were significantly greater average numbers of dead embryos at autopsy in the three treated groups than in the control group (3.6, 2.1 and 1.8 vs. 0). The group receiving the lowest hormone level also had a significantly greater average number of dead embryos as compared to the group receiving the highest hormone level (3.6 vs. 1.8). Embryo and membrane weights averaged 0.39, 5.9; 0.47, 7.8; 0.48, 7.7; and 0.51, 9.2 gm. for the three treated and control groups respectively. These means were not significantly different.

Four gilts (three open and one bred) were hysterectomized 7 days after the beginning of heat. The corpora lutea were marked with India ink. None of the gilts exhibited estrus before slaughter at 32, 71, 72 and 119 days post heat. The average individual corpus luteum weights and progesterone concentrations of the corpora lutea for the four gilts were 484 mg., 57 ug.; 486 mg., 79 ug.; 305 mg. (not determined); and 414 mg., 12 ug., respectively. Thus hysterectomy caused retention of the corpora lutea for prolonged intervals. Another experiment involving 32 market gilts was designed to study the effect of progesterone injections on maintenance of the corpora lutea in hysterectomized gilts. All animals were bred on the first day of estrus (day-0); hysterectomy was performed on day-7 and slaughter was on day-25. Progesterone was injected subcutaneously daily from day-10 to slaughter at the rate of 1 mg. per lb. body weight per day. Four groups of gilts were involved: pregnant, pregnant-injected-with-progesterone, hysterectomized, and hysterectomized-injected-with-progesterone. The average individual corpus luteum weights and progesterone concentrations of the corpora lutea from the four respective groups were 419 mg., 34 mcg.; 178 mg., 19 meg.; 421 mg., 42 mcg.; and 181 mg., 26 mcg. Progesterone treatment reduced the corpora lutea weight in both the hysterectomized and non-hysterectomized groups. There was no significant effect of hysterectomy or progesterone treatment on the mean progesterone concentration of the corpora lutea, but progesterone brought about a positive regression of concentration on corpus luteum weight. Local injections of 4 mg. of progesterone directly into the corpora lutea on the 18th day of pregnancy produced no measurable influence on the average individual corpus luteum weights in two gilts at the 25th day of pregnancy. Two progesterone-treated corpora lutea from each of the two gilts averaged 413 and 412 mg. as compared to an average of 471 and 407 mg. for six and ten untreated corpora lutea from the same gilts. Transplants of luteal or estrual phase uterine tissue into four gilts hysterectomized on day-7 or -11 of the cycle failed to cause regression of the corpora lutea. The average individual corpus luteum weights for the four gilts were 520, 475, 593 and 517 mg. at 24 to 30 days from their previous estrus. Another gilt in which the nerves associated with the middle uterine artery had been sectioned on day-7 of the cycle returned to heat 21 days post estrus. Evidence from these five gilts fails to demonstrate the role of the uterus in corpus luteum maintenance and regression.

Thirty-two Chester White-Poland China and 16 Chester White gilts were used in a study to determine the minimal flushing interval required to stimulate increased ovulation rate. Fifty-one Chester White gilts were used in two other experiments to demonstrate the effect of increased energy intake, only, on ovulation rate. Flushing for intervals of approximately 6, 10 or 14 days produced greater increases in ovulation rate from one estrual period to the next than occurred normally in unflushed gilts as a result of one estrual cycle increase in sexual age (increases of 2.8, 3.2 and 3.9 ova, respectively vs. an increase of 1.5 ova for unflushed gilts). There was a tendency for ovulation response to increase with greater length of the flushing period. Gilts fed glucose in addition to a basal ration for approximately 2 weeks prior to ovulation were found to shed a greater number of ova than gilts receiving only the basal ration (2.1 and 0.8 more ova in two different experiments, respectively). In the second experiment, gilts receiving a similar caloric intake furnished by lard were found to produce 1.9 more ova than the basal-fed gilts. The greatest response was obtained, however, when gilts were fed lard at approximately 150% of the caloric intake of those fed glucose—exceeding the ovulation rate of control gilts by 4.1 ova and the glucose and low fat gilts by 3.3 and 2.2 ova, respectively.

The effect of restricted feeding, crossbreeding and season of birth on age at puberty in swine was studied in six trials involving 368 gilts. Full-fed gilts grew more rapidly and attained puberty at an earlier age than restricted-fed gilts. Their earlier age at puberty appeared to be explainable on the basis of their greater growth rates. Poland China gilts grew more rapidly than Chester White gilts but no consistent differences in age at puberty were found for the two breeds. Reciprocal crossbred gilts of the two breeds attained puberty significantly earlier than either parent breed. The effect of season of birth on age at puberty was found to differ for the two breeds; spring-born gilts attained puberty earlier than fall-born gilts in the Chester White breed, while in the Poland China breed the fall-born gilts attained puberty earlier.

THE importance of progesterone in the establishment and maintenance _t of early pregnancy is well recognized (Allen and Corner, 1929). It is possible, however, that progesterone may not always be found at the appropriate level or in the proper ratio with other hormone levels for greatest reproductive efficiency. Progesterone therapy of "repeat-breeder" cows has shown a tendency to decrease the large amount of embryonic death by which these cows are characterized (Wiltbank et al., 1956; Herrick, 1953; Dawson, 1954). Pomeroy (1955) suggested from data collected by Perry (1954) that the greater proportion of embryonic death in larger litters of swine than in smaller may be traceable to the larger numbers of corpora lutea and a presumed excess of progesterone. Thus the existence of an optimal progesterone level may be implied.