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In the first Hammond Memorial Lecture, presented by Dr McMeeken, he reviewed the rôle of science in animal industry on a global basis and discussed in general terms its application in the future.
In this second lecture, I would like to deal with some of the more specific fields of research in which Sir John was interested and to attempt to project into the future the potentialities of some of the more recent work.
INCREASED PRODUCTION THROUGH ARTIFICIAL INSEMINATION
Throughout his whole life in research, Sir John's primary interest was in methods of increasing production in domestic animals and it is almost certainly true to say that his intense interest in reproduction and growth was secondary to this aim. It is, therefore, quite understandable that, when asked what he considered the most important way in which he had influenced this objective, he replied, 'by the introduction of artificial insemination'.
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A.R.C. Unit of Reproductive Physiology and Biochemistry, Cambridge
(Received 12th November 1974)
In sheep, the transfer of two- to four-cell eggs from the oviduct of donors to the uterus of recipients results in a poor conception rate, while uterine transfers of Day-3 (eight-cell) eggs (Day 0 = day of oestrus) give a satisfactory conception rate (Averill & Rowson, 1958). Moore & Shelton (1964) found that transfers to the oviduct were more successful than those to the uterus, but Trounson & Moore (1974) found that the site of transfer of Day-3 eggs had no effect upon their subsequent survival. In sheep, most eggs are present in the uterus 66 hr after ovulation (Holst, 1974), whereas in the cow, which ovulates about 12 hr after the end of standing oestrus, Hamilton & Laing (1946) could find no eggs in the uterus before 96 hr after the end of oestrus. Thus, although the
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Several authors have recently demonstrated the luteolytic action of exogenous prostaglandin F2α (PGF2α) in various laboratory and domestic animals and there is now ample evidence that PGF2α is the uterine luteolytic hormone which terminates the life of the CL in many species (McCracken, 1972; McCracken, Carlson, Glew, Goding, Baird, Gréen & Samuelsson, 1972). In cattle, Rowson, Tervit & Brand (1972) showed that an intrauterine (i/u) infusion of PGF2α on 2 successive days at any time between the 5th and 16th day of the cycle, induces oestrus 3 days later; they found that for 0·5 mg PGF2α to be strongly luteolytic in the cow, the substance must be placed in the uterine horn which is ipsilateral to the ovary containing the active CL. This observation is in accordance with the experiments of Moor & Rowson (1966), Harrison, Heap & Linzell (1968) and others, which have indicated
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Summary.
Morulae and blastocysts obtained from ewes 5, 7 and 9 days after oestrus were transferred to 120 recipients whose oestrous cycles were either synchronized or ± 2 or 3 days out of phase relative to the onset of oestrus in the donors.
When synchronization was exact 75% of all recipients became pregnant. A high proportion of pregnancies were, in general, also obtained where the onset of oestrus in the recipient differed from that of the donor by ±2 days. With a difference of ±3 days, however, only 8 % of ewes became pregnant. The survival of 5-day morulae transferred to 7-day recipients was lower than when 9-day blastocysts were transferred to 11-day recipients.
The results are discussed with reference to possible factors associated with early embryonic mortality.
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Summary.
The ovary not containing the corpus luteum was removed from each of fifty-two ewes on Day 8 of the cycle. These animals were then allocated to one of the following groups. Group 1 : (control) received no further treatment. Group 2: the contralateral uterine horn, i.e. located on the side opposite to the corpus luteum, was removed. Group 3 : the ipsilateral uterine horn, i.e. located on the same side as the corpus luteum, was removed.
Neither unilateral ovariectomy alone (Group 1) nor the removal of the contralateral horn (Group 2) affected the length of the post-operative oestrous cycles. In contrast, extirpation of the ipsilateral uterine horn (Group 3) resulted in a significant extension of the oestrous cycle and thus of the life-span of the corpus luteum. The results suggest that the ovaries of the cyclical sheep are probably affected by the uterus in a local manner.
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Despite repeated attempts by many workers to transfer eggs to the cow by non-surgical methods, no success was achieved until the recent report of a single pregnancy by Mutter, Graden & Olds (1964). Subsequently, Sugie (1965) using a technique involving the puncture of the anterior wall of the vagina and the inflation of the uterus with carbon dioxide reported two more successful transfers; one of which however was followed by abortion.
The difficulty inherent in the technique of non-surgical transfer of cow eggs was attributed by Rowson, Lamming & Fry (1953), Harper, Bennett & Rowson (1961) and Bennett & Rowson (1961) to at least two causes (i) uterine infection, and (ii) expulsion of the eggs via the cervix, the two factors acting either singly or in conjunction with each other. Our efforts to overcome these
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Summary.
The administration of chlormadinone acetate to pubescent lambs suppressed the growth of the reproductive tract as a whole, reduced both ejaculate volume and fructose concentration and delayed the appearance of spermatozoa. Following a period of suppression, a `rebound' effect was seen with fructose levels exceeding those of the controls for a short period and then returning to normal.
Sperm production and motility were reduced and the number of dead and abnormal spermatozoa increased.
Treatment was least effective after the onset of spermatogenesis and the inhibitory effect was counteracted by injection of pituitary gonado-trophin (icsh). There was no effect on growth rate.
Intravenous injection of methallibure appeared to have no effect on testicular growth, and did not delay the first appearance of spermatozoa, but fructose secretion by the seminal vesicles was increased. There was an increase in the number of spermatozoa produced and also in the numbers of dead and abnormal forms. Methallibure did not affect the growth rate.
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Early cleavage stage (one-cell to eight-cell sheep ova cultured by Tervit, Whittingham & Rowson (1972) in a synthetic oviduct fluid medium (SOF) with an atmosphere of 5% CO2/5% O2/90% N2 cleaved readily during culture and twelve ova, which had been cultured for 3 to 6 days, developed to viable Day-13 or Day-14 conceptuses in recipient animals. Similar cleavage-stage ova had previously been reported to undergo only limited development during culture (Wintenberger, Dauzier & Thibault, 1953; Hancock, 1963; Kraemer, 1966; Tervit & McDonald, 1969; Moore, 1970; Moor & Cragle, 1971; Moore & Spry, 1972) and to be viable after culture for 1 or 2 days (Hancock, 1963; Tervit & McDonald, 1969; Moore, 1970; Schwartz & Ulberg, 1972; Schwartz, Thompson, Goode & Ulberg, 1972). This communication describes the birth of lambs after the culture of early cleavage-stage ova for up to 6 days.
Welsh Mountain ewes were
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Summary.
A technique of cannulation of the epididymis of the bull with the subsequent establishment of a patent fistula is described, which allows for the repeated collection of epididymal spermatozoa and secretions from the living animal.
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Summary.
Following the daily intra-uterine infusion of a homogenate prepared from frozen and thawed tissue of 14- or 15-day sheep embryos the length of the oestrous cycle was significantly prolonged. A single intra-uterine infusion, however, had only a slight effect on oestrous cycle length.
The substance derived from the embryonic tissue, which presumably must be of a chemical nature, probably acts on the endometrium in an `anti-luteolytic' manner, that is by counteracting the action of the endometrium which otherwise would have resulted in the regression of the corpus luteum.
Unlike homogenate prepared from 14- or 15-day sheep embryos similar material obtained from 25-day sheep embryos did not increase cycle length. This indicates that the effect is dependent on the stage of development of the embryo in relation to the uterus.
Homogenate prepared from 14-day pig embryos infused into sheep uteri was unable to maintain the corpus luteum, which suggests that the embryonic factor may be species-specific. Repeated intra-uterine infusions of control material consisting of frozen and thawed saline, serum or serum plus white blood cells had no effect on cycle length. Transfer into the sheep uterus of a whole but heat-inactivated 12-14days sheep embryo had no effect on the cycle length.
