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Summary.Day 13–16 pig conceptus tissue was cultured for 24 h in medium containing [3H]leucine. The patterns of radioactively labelled proteins that were released into the medium during culture were analysed by SDS—polyacrylamide gel electrophoresis and fluorography. Day-13 conceptuses released two major radiolabelled proteins of Mr23 000 and 26 000 and Day 14–16 conceptuses released these as well as proteins of Mr14000, 19 000, 44000, 50 000 and 88 000. Various immunological and biological tests for a human chorionic gonadotrophin-like activity were performed on tissue extracts and on culture medium, but there was no evidence for its presence in the pig conceptus at Day 13–16 of gestation.

Three experiments have been carried out to investigate the mechanism by which glycerol reduces the fertilizing capacity of boar spermatozoa during storage, and any relationship between this effect and the relatively poor conception rates obtained with deep-frozen boar semen.The loss of fertilizing capacity in the presence of glycerol was shown to be temperature-dependent, Fertilizing capacity was significantly reduced after 6 hr of incubation at 20°C in the presence of 5 or 10% glycerol, although there was no detectable change in motility or morphology of the spermatozoa. By contrast, there was no effect on fertilizing ability after storage for 6 hr at 5°C or for 30 min at 20°C in the presence of these concentrations of glycerol. Removal of the seminal plasma and a large proportion of the free cytoplasmic droplets did not prevent the reduction in fertilizing capacity. When semen was frozen and thawed, attempts to minimize the exposure of spermatozoa to glycerol did not lead to fertilization when the thawed semen was inseminated through the cervix. It is suggested that at ambient temperature glycerol causes damage to boar spermatozoa which is exacerbated by the stress of freezing and thawing.

Summary.Occupied and unoccupied LH receptors in corpora lutea, and LH and progesterone concentrations in circulating plasma, were measured in non-pregnant gilts that had been treated with oestradiol-17β benzoate to prolong luteal function. Oestradiol benzoate (5 mg, administered on Day 12 after oestrus) delayed luteal regression and the decline in LH receptor levels at luteolysis and raised unoccupied receptor levels from 11·8 ± 1·14 fmol/mg protein on Days 10–15 after oestrus to 31·8 ± 3·26 fmol/mg protein on Days 15–21. There was no simultaneous rise in occupied receptor levels and occupancy decreased from 29·8 ± 3·01 to 11·5 ± 1·26%. Basal plasma LH concentrations were unchanged by oestradiol, but mean corpus luteum weight and plasma progesterone concentrations were slightly reduced. Oestradiol benzoate on Day 12 caused a similar increase in unoccupied receptor levels in gilts hysterectomized on Days 6–9 after oestrus, from 17·0 ± 5·83 to 34·5 ±6·00 fmol/mg protein, determined on Days 15–18. Plasma concentrations of LH and progesterone were unchanged by oestradiol. Unoccupied receptor levels in corpora lutea and plasma LH and progesterone were unaltered by hysterectomy in untreated gilts. Occupied receptor levels were not influenced by hysterectomy or oestradiol. It is concluded that oestradiol-17β raises luteal LH receptor levels by a mechanism independent of the uterus.

Reproductive efficiency is one of the most important components in the economy of animal production and it is well recognized that it can be influenced by many factors affecting different areas of the reproductive process. Fertilization is just one of the essential links in the whole chain of reproductive events leading to the production of offspring, but it is the link most closely associated with the efficiency of breeding by means of artificial insemination. Different techniques used in A.I., especially those concerned with methods of insemination or with the dilution and storage of semen, can therefore best be assessed by their effects on fertilization and these aspects will be emphasized in the present paper.

Summary.A reciprocal translocation, identified as t(6p+; 14q−), is described in a 38,XX intersex pig. It is the fourth reciprocal translocation to be reported for this species, whereas Robertsonian translocations, of frequent occurrence in cattle and sheep, are so far unknown in domestic pig breeds.

Summary.Methanol was examined as a cryoprotective additive that permits the direct transfer of frozen–thawed Day-4 mouse embryos to foster mothers without dilution of the cryoprotectant. Methanol permeated the embryos rapidly, was not toxic and exerted a cryoprotective action. The highest level of survival (50%) of embryos in vitrowas observed after equilibration in Medium PB1 containing 3·0 M-methanol, slow cooling (0·5°C/min) to a temperature between −30 and − 40°C, rapid cooling (800°C/min) and storage in liquid nitrogen ( − 196°C), rapid warming (800°C/min), and rapid dilution. A high rate of development in vivoto late-stage fetuses (up to 81%) was observed when cryopreserved embryos were transferred to pseudopregnant recipients immediately after thawing.

Summary.Mouse embryos (8-cell) fully equilibrated in 1·5 M-glycerol were cooled slowly (0·5°C/min) to temperatures between − 7·5 and − 80°C before rapid cooling and storage in liquid nitrogen (−196°C). Some embryos survived rapid warming (~500°C/min) irrespective of the temperature at which slow cooling was terminated. However, the highest levels of survival of rapidly warmed embryos were observed when slow cooling was terminated between − 25 and − 80°C (74–86%). In contrast, high survival (75–86%) was obtained after slow warming ( ~ 2°C/min) only when slow cooling was continued to − 55°C or below before transfer into liquid N2. Injury to embryos cooled slowly to − 30°C and then rapidly to −196°C occurred only when slow warming (~2°C/min) was continued to − 60°C or above.Parallel cryomicroscopical observations indicated that embryos became dehydrated during slow cooling to − 30°C and did not freeze intracellularly during subsequent rapid cooling ( ~ 250°C/min) to − 150°C. During slow warming (2°C/min), however, intracellular ice appeared at a temperature between −70 and − 65°C and melted when warming was continued to − 30°C. Intracellular freezing was not observed during rapid warming (250°C/min) or during slow warming when slow cooling had been continued to − 65°C.These results indicate that glycerol provides superior or equal protection when compared to dimethyl sulphoxide against the deleterious effects of freezing and thawing.

Treatment of cows or mares with prostaglandin (PG) F-2α as early as Days 4 or 5 of the oestrous cycle causes regression of corpora lutea (CL) and results in oestrus 2–4 days after treatment (Lauderdale, 1972; Rowson, Tervit & Brand, 1972; Douglas & Ginther, 1972; Allen & Rowson, 1973) However, the CL of pigs do not regress in response to PGF-2α until Days 11–12 of the cycle (Gleeson, 1974; Guthrie & Polge, 1976). Because the secretory activity of the CL in the pig declines rapidly by Days 14 or 15 of the cycle, the effective period for synchronization of oestrus by PGF-2α treatment is too short to be of practical use. Exogenous gonadotrophins induce the formation of accessory CL at any stage of the oestrous cycle of the pig (Neill & Day 1964; Day, Neill, Oxenreider, Waite & Lasley, 1965; Caldwell, Moor, Wilmut, Polge & Rowson, 1969) and the CL formed on Days 8, 10 or 16 delayed oestrus for at least 15 days (Caldwell et al., 1969). We therefore investigated the possibility of synchronizing oestrus in gilts by inducing accessory CL to delay oestrus and ovulation and then injecting PGF-2α analogues to regress the accessory CL at a predetermined time.

Pronuclear development was used to measure the effects on ovine oocytes of altering follicular steroidogenesis during maturation in vitro. Follicular steroid secretion was altered using enzyme inhibitors and exogenous steroid supplementation. Abnormalities induced during maturation were measured 24 h after transfer of oocytes to the oviducts of inseminated hosts. The presence throughout maturation of aminoglutethimide, an inhibitor of the conversion of cholesterol to pregnenolone, reduced steroid secretion to 7% of that in controls and decreased from 77% to 33% the number of normal oocytes. Abnormalities were substantially reduced by the addition of aminoglutethimide during the final 8 h of maturation only. The inhibition of 17 α -hydroxylase enzymes with SU10603 reduced oestrogen and testosterone secretion to about 10% of control levels but had no effect on progestin secretion. Only 13% of oocytes matured in the continual presence of SU10603 underwent normal fertilization. The number of oocytes undergoing normal fertilization was increased to about 50% by (i) delaying the addition of SU10603 until the last 8 h of the maturation period or (ii) adding exogenous steroids to follicles cultured with inhibitor from explantation. It is concluded that oocytes require a specific intra-follicular steroid environment for the completion of the full maturation process. Alterations to the steroid profile during maturation induce changes in the oocyte which are expressed as gross abnormalities at fertilization.

Sheep embryos, collected 1-8 days after oestrus, were placed in Dulbecco's phosphate-buffered saline medium (PBS). After treatment, the viability of the embryos was tested by temporary transfer to ligated rabbit oviducts. In Exp. 1, Days 5-8 embryos survived for at least 15 min at 0°C in the presence of 1·5 m-DMSO. In Exp. 2, 12/14 Days 5-8 embryos survived after being frozen in 1·5 m-DMSO at 0·3°C/min to temperatures ranging between −15° and −60°C and then thawed at 12°C/min. In Exp. 3, Days 5-8 embryos were frozen in 1·5 m-DMSO at 0·3°C/min to below −65°C before being transferred to liquid nitrogen (−196°C), and stored for 12 hr to 1 month. The embryos were thawed at 3°C/min, 12°C/min or 360°C/min and, after transfer to rabbit oviducts, 0/4, 10/36 and 1/4, respectively, developed normally. The 11 embryos which were considered normal when recovered from the rabbit oviducts plus 1 slightly retarded embryo were transferred to 7 recipient ewes. Four ewes subsequently lambed, producing 5 lambs. In addition, 8 embryos were transferred to 4 ewes directly after thawing. Three of these ewes subsequently lambed, producing 3 lambs.

Five true hermaphrodite pigs and two male pseudohermaphrodite pigs were studied. A 38XX sex chromosome constitution was found in peripheral leucocytes of three true hermaphrodites and in one male pseudohermaphrodite; XX/XY mixoploidy was present in the leucocytes of the remaining male pseudohermaphrodite. The occurrence of C19steroids, including 16-androstenes, in the testicular tissue and submaxillary gland of intersex pigs was of a similar pattern to that found previously in mature boars, and masculinization of the genital tract was related to the amount of testicular tissue present. It is postulated that in the absence of germ cells in the testicular tissue of intersex pigs the Sertoli cells may be involved in the metabolism of dehydroepiandrosterone to 5-androstenediol, a possible testosterone precursor in the pig. The high levels of 16-androstenes found in the submaxillary gland of intersex pigs indicates that these steroids are responsible for `boar taint' in these animals. In contrast to the boar, no consistent relationship was found between the occurrence of C19steroids and the degree of masculinization of the submaxillary gland; it is postulated that the predominantly female genetic constitution may have affected the response of the salivary gland to androgen.