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Summary.

Thirty-eight does were double mated to two bucks whose offspring were distinguishable from each other. The interval between mating to the first buck and mating to the second buck was ½ 1 or 2 hr. The first buck was mated 10, 9, 8, 7, 6, 5 or 4 hr before ovulation. The first buck sired 86% of the offspring when the interval between bucks was 2 hr. When the interval between males was shortened, the first male sired the majority of offspring but the proportion was less than that after a 2-hr interval. It was concluded that spermatozoa that have resided in the genital tract of the doe have a competitive advantage over other spermatozoa that have spent less time in the female. The advantage did not disappear after the 6 hr residence, usually thought to be adequate for capacitation, but extended to at least 10 hr. Capacitation (maturation) may possibly be a quantitative phenomenon as well as a qualitative one.

Summary. Spermatozoa from a Columbian (C) and a Leghorn (L) cock were stored at 4°C for 4 h before mixing in equal numbers for insemination. When hens were inseminated with either 100 × 10⁶, 200 × 10⁶ or 300 × 10⁶ spermatozoa, the proportion of chicks sired by Cocks C and L was not affected (P > 0·05) by the total number of spermatozoa inseminated or the interval from insemination to oviposition (2–16 days). Cock C sired 61% of the chicks after the 4-h storage period. In a concurrent study Cock C was found to sire 34% of the offspring when fresh semen was used, indicating that the relative fertilizing ability of spermatozoa from different males does not change during storage in vivo, but may do so during storage in vitro.

Ringer's solution (R) was compared to Locke's solution (O) in its ability to maintain the fertilizing ability of spermatozoa. Spermatozoa from Cocks C and L were stored in either R or O and then mixed in a 1:1 ratio in the four combinations: CR + LR, CO + LO, CR + LO, and CO + LR. When the same extenders were used for both cocks, i.e. CR + LR and CO + LO, differences between groups were not significant (P > 0·05) for the number of eggs collected, the % of eggs fertilized and the proportion of chicks sired by each cock. With the combinations CR + LO and CO + LR, the number of eggs collected, the % of eggs fertilized, and the number of chicks in the two groups were similar. The CR + LO combination resulted in 57% of the chicks being sired by Cock C, but the proportion of chicks sired by this cock rose significantly (P < 0·005) to 77% when the CO + LR combination was used. This 20% increase was presumably due to the advantage of storage in the O extender and indicates that appropriate heterospermic inseminations are more sensitive than homospermic insemination for evaluating treatments applied to semen.

Summary. When hens were inseminated with an equal number of spermatozoa from one of 3 Leghorn (L) and one of 3 Columbian (C) cocks in the 9 possible L and C combinations, a hierarchy of fertility was established based on the proportion of chicks sired by each cock. A similar hierarchy was established for 3 Duroc (D) and 3 Yorkshire (Y) boars by mating gilts in rapid succession to one D and one Y boar. A second hierarchy of fertility was established by inseminating hens with 40 × 10⁶ spermatozoa from only one cock or by mating gilts to only one of the boars. The hierarchies for the cocks and boars were essentially the same for each method. Minor discrepancies were observed for males which appeared to be nearly equally fertile when used alone or in combination with another male. After homospermic insemination, the hierarchy of cocks was identical whether the ranking was based on the percentage of eggs fertilized or on hatchability of fertilized eggs. Similarly, the boars ranked highest in fertility by double mating had higher conception rates, higher embryonic survival rates and larger litter sizes when used alone. Heterospermic insemination and double mating appear to be more efficient and sensitive than methods of estimating fertility which depend on homospermic insemination of high or low numbers of spermatozoa, single matings or the examination of various characteristics of semen. The method of heterospermic insemination or double mating offers a simple and effective method of assessing the relative fertility of males.

Summary.

Autografts and allografts of skin were transplanted into the uteri of ewes to determine the influence of ovariectomy and hormone replacement on survival of the grafts. The fate of the grafts in sheep differed from that previously reported for the rat. Autografts were accepted in the uteri of ovariectomized ewes. Intrauterine allografts were rejected, however, when oestrogen and progesterone were given to the hosts in doses sufficient to maintain pregnancy.

Summary.

Pilocarpine (50 mg) administered to the boar 20 min before semen collection had no detectable effect on either ejaculation or semen composition. However, the volume of fluid semen, the total volume of semen, and the time required for ejaculation differed significantly (P<0·01) between breeds of boars.

The capacity of follicular oocytes for normal fertilization has been tested in hamsters (Barros & Austin, 1967), sheep (Woody, Alliston & Ulberg, 1961) and rabbits (Noyes, 1952; Chang, 1955). Follicular oocytes of rabbits and hamsters were fertilized at a reduced rate but no sheep oocytes developed. Dziuk & Dickmann (1965) have proposed that the block to polyspermy develops concomitantly with oocyte maturation. The following experiments were conducted to test whether pig follicular oocytes could be fertilized normally and what proportion would become polyspermic.

In Trial I, eight cyclic gilts were injected with 500 i.u. hcg during late prooestrus to induce ovulation. Ovulation was assumed to occur 40 to 42 hr after hcg (Hunter & Polge, 1966; Baker, Dziuk & Norton, 1967). Each gilt was artificially inseminated about 20 hr after hcg and then,

Summary.

When semen is collected from boars 30 min after a single injection of 25 to 50 mg atropine sulphate, the volume of the ejaculate is reduced to about one-fourth, and hardly any gel is present. The ejaculate from an atropine-treated boar has less chloride, but a higher concentration of spermatozoa, organically-bound acid-soluble phosphate, fructose, ergothioneine, and citric acid, than normal semen. These changes are thought to be due to the inhibiting action of atropine on the parasympathetic stimuli which normally reach the urethral and bulbo-urethral glands at the time of ejaculation. In consequence, the urethral glands no longer contribute the watery, chloride-rich fluid, and the bulbo-urethral glands fail to provide the gel. Atropine does not interfere either with epididymal function, in so far as the output of spermatozoa and acid-soluble phosphate (mainly glycerylphosphorylcholine) is concerned, or with the secretory output of fructose, ergothioneine and citric acid, by the seminal vesicles. Thus, being made up to a large extent by the epididymal and vesicular contributions, the semen voided by the atropine-treated animal resembles the so-called spermrich or middle portion of a normal ejaculate.

A degree of control of oestrus in cattle by progestagens is possible by either injection (Nellor & Cole, 1956), implantation (Dziuk, Cmarik & Greathouse, 1966) or feeding (Dhindsa, Hoversland & Smith, 1967). Following withdrawal of the progestagen, heat occurs in 2 to 9 days and each cow can be mated or artificially inseminated according to signs of heat (Hansel, Donaldson, Wagner & Brunner, 1966). In some instances, treated cows may ovulate but not show the characteristic manifestations of oestrus and thus are not inseminated (Van Blake, Brunner & Hansel, 1962). The objectives of the current study were two-fold: first, to determine if ovulation in the cow could be controlled precisely, and second, by insemination at some predetermined time to eliminate detection of oestrus, to determine if the eggs could be fertilized.

The forty-seven cows

Summary. Cocks were fed diets containing 0, 0·025, 0·05, 0·075 or 0·1% caffeine during a 14-day treatment period. The number of spermatozoa produced by cocks fed 0·075 or 0·1% caffeine declined sharply at 12 days after onset of treatment. Hens were inseminated with a constant number of spermatozoa from individual cocks. The fertility of cocks fed 0·05, 0·075 or 0·1% caffeine declined during the 17-day post-treatment period and then returned to pretreatment levels.

Cocks whose offspring were distinguishable were paired and relative fertility was assessed in a heterospermic test. One cock in each pair was fed 0·05% caffeine during the treatment period. Hens were inseminated with semen mixed within pairs. The proportion of chicks sired by cocks fed caffeine decreased during treatment and remained at that level until 17 days after treatment, when it increased to pretreatment levels. The percentage of total eggs hatched declined concomitantly with the reduction in the proportions of chicks sired by treated cocks.

These results indicate that the effect of low levels of a toxin could be detected by reduced numbers of eggs hatched after heterospermic insemination with semen of normal appearance.

Summary.

The influence of four post-ovulatory ages of egg on the proportion of eggs penetrated by spermatozoa was studied in the pig. The time of ovulation was controlled by an injection of human chorionic gonadotrophin (hcg) given during pro-oestrus. Gilts in oestrus were inseminated 0, 4, 8 or 12 hr after the estimated time of ovulation, and eggs recovered from the oviducts in vivo either 2 or 3 hr later. Eggs were examined from thirteen gilts in each of the four insemination groups.

A total of 515 eggs was recovered, giving an overall recovery rate of 86%. Spermatozoa were found attached to or in the zona pellucida of twenty-eight of 117 eggs (24%) recovered 2 hr after insemination and in the perivitelline space of four of these eggs, but none was fertilized. Of 398 eggs recovered from forty animals 3 hr after insemination, 208 eggs (52%) from thirty-one animals had spermatozoa attached to or in the zona pellucida. Twenty-four of these eggs had spermatozoa in the perivitelline space, and 143 (36%) were fertilized.

These findings demonstrate that boar spermatozoa can reach and penetrate the zona pellucida of pig eggs within 2 hr of insemination, and can enter the ooplasm and cause resumption of meiosis within 3 hr of insemination. There was no indication that post-ovulatory age as such influenced the number of spermatozoa in the zona pellucida or the proportion of eggs fertilized.