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C. A. Price, B. A. Morris, and R. Webb

Summary. Yearling heifers were actively immunized against 8 mg testosterone-3-carboxymethyloxime-ovalbumen in Non-Ulcerative Freund's Adjuvant, with or without the addition of Corynebacterium parvum (Groups A and B, respectively; N = 4 for each group). After the priming injection, Groups A and B were boosted twice at 4-monthly intervals. Control heifers (N = 9) were not injected. All treated animals except one gave a measurable antibody response, and all responding animals became anoestrous and displayed ovarian cysts after the first booster injection. There were no apparent differences between treatments, and so results for Groups A and B were pooled.

At 25 weeks after the second booster 3 of the 7 responding, anoestrous heifers resumed cyclicity; one with two consecutive double ovulations, and one with one double ovulation. The 3rd heifer showed 4 corpora lutea, then became anoestrous again. The 4 remaining acyclic heifers, and the control heifers, were intensively blood sampled; the anoestrous heifers showed significantly higher mean LH and significantly lower mean FSH concentrations and higher LH pulse frequency than did the control animals. These heifers remained anoestrous for 11 months after the second booster, at which point they were injected with GnRH and PGF-2α; only 1 heifer resumed ovarian cyclicity. These results indicate that it is possible to increase ovarian activity in cattle by active immunization against testosterone, but that there is a high incidence of anoestrus.

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M. J. Sauer, J. A. Foulkes, A. Worsfold, and B. A. Morris

Summary. A simple direct-addition microtitre plate enzymeimmunoassay (EIA) for progesterone in whole milk is described. The assay used antiserum raised against 11α-hydroxyprogesterone 11-hemisuccinate (progesterone 11-hemisuccinate) and a heterologous label prepared by conjugation of 11α-hydroxyprogesterone 11-glucuronide (progesterone 11-glucuronide) with alkaline phosphatase using an active ester procedure. The sensitivity, analytical recovery, linearity of response and precision of the assay compared favourably with radioimmunoassay (RIA). Results from EIA of milk samples were compared with determinations made after isolation of progesterone by HPLC (r = 0·910). Milk samples (200) were assayed by RIA at both the Milk Marketing Board and the Cattle Breeding Centre and the results were correlated with EIA performed at the Cattle Breeding Centre (r = 0·890 and r = 0·833 respectively). Calving data were obtained from a further 110 cows for which the milk progesterone EIA had provided a pregnancy test 24 days after AI; 46 cows were correctly identified as non-pregnant and 58 as pregnant and there were 4 false positive and 2 inconclusive results.

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R. B. Land, Marjorie Fordyce, I. K. Gauld, B. A. Morris, and R. Webb

Summary. The incidence of oestrus (6/46) and ovulation (14/46) in ewes given antisera to androstenedione, oestrone, oestradiol and testosterone either separately or as a mixture of these sera at the time of treatment with progestagen sponges alone or progestagen sponges followed by LH-RH was similar to that of control ewes (2/13 and 6/13 respectively). The number of corpora lutea (CL) recorded for those ewes that did ovulate was, however, greater in the antiserum-treated ewes (22 CL/14 ewes) than in the controls (6 CL/6 ewes) at the first ovulation after sponge withdrawal. This superiority persisted to the second ovulation (53 CL/42 treated ewes compared to 13 CL/13 controls). The results for groups treated with antisera did not differ amongst themselves.

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N. Pathiraja, W. R. Carr, Marjorie Fordyce, Janet Forster, R. B. Land, and B. A. Morris

Summary. The concentration of FSH and LH in peripheral plasma was studied in sheep from 8 h before to 17·5 h after injection (i.v.) with antisera to the steroids androstenedione, oestradiol, oestrone and testosterone. The fitted mean concentration of LH increases after all treatments and the increase was associated with a higher frequency of LH pulses. The greater concentration was evident for all groups by the period 3·5–6·5 h after injection, but by the end of the sampling period the concentration had returned to or towards the values in the controls. For FSH, significant change was limited to those animals given anti-oestrogen sera but it was more rapid than for LH, both groups receiving anti-oestrogen sera showing an increase during the period 0·5-3·0 h after injection.

The ovulation rate was increased by treatment and an effect close to 0·75 corpora lutea per ewe was maintained by treatment in subsequent oestrous cycles. This declined to 0·25 corpora lutea after two oestrous cycles without treatment.

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R. B. Land, B. A. Morris, G. Baxter, Marjorie Fordyce, and Janet Forster

Summary. Sera from sheep immunized against oestrone (Group E1), oestradiol (Group E2), androstenedione (Group A) and testosterone (Group T) were given to ewes singly or as a mixture (Group M) of all 4 types as a single intravenous injection at the time of the start of mating. The number of lambs produced, the numbers of eggs shed and the display of oestrus were recorded. The ovulation rates were 1·8 in Group E1, 2·1 in Group E2, 1·6 in Group A, 1·8 in Group T and 2·1 in Group M compared with 1·3 for the controls (P, variation among groups, < 0·001) in the first oestrous cycle. The effect persisted in those animals not conceiving to the first mating—1·3 in Group A, 1·8 in Group E1, 1·9 in Group E2 and 2·0 in Group M compared with 1·3 for the controls; all of the ewes in Group T conceived to mating at a single oestrus. The mean number of lambs born alive per ewe treated was 1·1 for Group A, 1·3 for Group E1, 1·3 for Group E2, 1·5 for Group T, 1·5 for Group M and 1·0 for the controls. The increase in the number of lambs born was due to a higher proportion giving birth to twins (P < 0·01); no ewe gave birth to triplets. High conception rates were recorded for all treatments.

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C. A. Price, B. A. Morris, T. O'Shea, and R. Webb

Summary. Yearling cross-bred heifers were injected with 0·4 or 4 mg total protein in non-ulcerative Freund's adjuvant (Groups A and C, respectively; N = 5 per group), or adjuvant with C. parvum (Groups B and D, respectively; N = 5 per group). Control heifers were not treated (N = 9). No antibodies were detected in heifers in Groups A and C and so these were excluded from the analysis. There was no effect of the treatment on Group B or D heifers after the priming or first booster injection. After a second booster injection one Group D heifer gave a triple ovulation, and two Group D heifers and one Group B heifer gave double ovulations, but for one oestrous cycle only. Group B heifers also showed a significant rise in FSH concentrations after the second booster injection. Group D heifers were given a third booster injection; there was an increase in the mean number of large follicles per heifer, and a decrease in oestrous cycle length, but no increase in ovulation rate.

These results indicate that a transient increase in ovulation rate can be induced by actively immunizing cattle against partly purified follicular fluid from sheep.

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N. Jenkins, P. G. Knight, C. M. Howles, B. A. Morris, and G. M. H. Waites

Summary. Passive immunization of male lambs against oestradiol-17β from 2 to 16 weeks of age significantly elevated androgen concentrations in plasma and depressed the median eminence content of dopamine. Removal of endogenous oestrogens had no significant effects on plasma FSH, LH or prolactin concentrations or on testicular growth and hypothalamic content of GnRH. These results suggest that endogenous oestrogens may indirectly suppress testicular androgen secretion by exerting a stimulatory influence on hypothalamic dopaminergic neurones, which in turn may inhibit GnRH secretion by the median eminence.