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J. D. SKINNER and J. BOWEN

Relatively little is known about the time when the stallion reaches puberty. In the Anglo-Norman breed the testes have been shown to increase gradually in weight from the 11th month onwards, and then more rapidly from the 16th month (Nishikawa & Horie, 1955). Large amounts of testosterone have been found in the spermatic vein blood of mature stallions (Lindner, 1959, 1961). It has also been postulated that the rise in urinary oestrogen excretion accompanies sexual maturation at 20 months (Zondek, 1934; Pigon, Lunaas & Velle, 1961). The object of the present experiment was to study sexual development in living pony stallions from birth until the time when spermatozoa appear in ejaculates, and to define the time relationship between the onset of androgenic and gametogenic testicular functions. In addition, a study was made of the effects of season on

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J. C. Haigh and G. Bowen

Summary. Semen collected from wapiti (Cervus elaphus) in Canada in 1983 was frozen in two extenders. In 1988, the semen was used to inseminate 200 red deer hinds on 2 farms in New Zealand. Oestrus was synchronized in the hinds with progesterone-impregnated intravaginal devices (CIDR); 200 iu pregnant mares' serum gonadotrophin was given to each hind on Day 11. The CIDRs were removed on Day 12 at 20/h, as the numbers of the hinds were recorded. On Day 14, 54–56 h after CIDR removal, the hinds were brought into the yards in the same batches and laparoscopically inseminated. Semen from three sires was used. The overall conception rate was 51%. Gestation length ranged from 239 to 247 days. One hind was lost at calving, 3 calves had to be hand raised and there were 2 neonatal calf deaths.

Keywords: Cervus elaphus; artificial insemination; red deer; wapiti; North American elk; cross breed; laproscopic; oestrus synchronization

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AI Odeh, JJ Dascanio, T Caceci, J Bowen and LA Eng

Phospholipids are an essential component of all mammalian cells; platelet activating factor (PAF=1-O-alkyl-acetyl-sn-glycero-3-phosphocholine) is a signalling phospholipid that has many biological properties in addition to platelet activation. PAF receptors have been detected on stallion spermatozoa; therefore, the aim of this study was to evaluate the effect of synthetic PAF on the motility, capacitation and the acrosome reaction of stallion spermatozoa. Treatment of ten stallion semen samples with 10(-4)-10(-13) mol PAF l(-1) resulted in significant differences in motility and capacitation (r(2)=0.81 and 0.83, respectively). Statistical analysis indicated that PAF also has an effect on acrosome reaction (r(2)=0.20). PAF concentrations, incubation time and their interaction had a highly significant (P<0.01) effect on motility. After capacitation in vitro with PAF, and induction of the acrosome reaction by progesterone, transmission electron microscopy was conducted on the spermatozoa of three stallions to detect the true acrosome reaction. Differences in PAF concentrations were highly significant (r(2) for intact: 97.2; reacted: 89.8; and vesiculated: 98.1). The results indicate that a lower concentration of PAF enhances motility and induces capacitation of stallion spermatozoa, whereas a higher concentration of PAF induces the acrosome reaction.

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J. F. Hasler, R. A. Bowen, L. D. Nelson and G. E. Seidel Jr

Summary. Progesterone concentrations in systemic blood were determined by radioimmunoassay in crossbred cattle used as recipients in an embryo transfer programme. An embryo was transferred surgically to the uterine horn of 528 females which were in oestrus within one half-day of the donor. Jugular blood was obtained at the time embryos were transferred (3–7 days after oestrus) and again from most females between Days 9 and 14. Pregnancy was determined by rectal palpation 45– 65 days after oestrus. There were no significant differences between serum progesterone levels of females which remained pregnant and those which did not. Out of 177 pregnant recipients, none had serum progesterone levels <0·5 ng/ml on Days 10, 11, or 12 but in 8, values were <1·0 ng/ml. Blood samples were also taken on Days 20, 21, or 22 from 113 of these recipients. The mean ± s.e.m. concentration of progesterone in the pregnant females (5·14 ± 0·34 ng/ml) was significantly higher (P < 0·001) than in the non-pregnant females (1·17 ± 0·25 ng/ml). The correlation coefficients between progesterone levels on Days 3, 4, 5 or 6 and 10–12 ranged from 0·18 to 0·37 (all P < 0·02). Progesterone levels were not related to length of the previous cycle, the time of day an animal was first noticed in oestrus or the side of the corpus luteum. However, cows with a short oestrus had higher progesterone levels on Days 3–7 (P < 0·01) than those in oestrus for a longer time.