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BARBARA J. WEIR

In a recent paper, Rood & Weir (1970) suggested that oestrus in Galea muste-loides was induced by the male. Modification of oestrus by the male is known to occur in mice (Whitten, 1956) and in voles (Richmond & Conaway, 1969). Female mice in small groups will show regular oestrous cycles in the absence of a male, and in Mus (Marsden & Bronson, 1964) and Microtus ochrogaster (Richmond & Conaway, 1969), proximity of the male and exposure of the females to male excreta are sufficient stimuli to initiate oestrus. Richmond & Conaway (1969) have shown that in the prairie vole, change of cage type or social grouping can cause the female to respond but exposure to the male or his excreta is the best stimulus to induce oestrus. Similar factors do not

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BARBARA J. WEIR

Summary.

Plains viscacha were established in the laboratory to investigate their reproductive physiology. The species was found to have a mean oestrous cycle length of 45·0±1·2 days and a mean gestation period of 153·7±0·5 days. There was rarely an immediate post partum oestrus but if the young died at birth, oestrus occurred 17·1±3·6 days later. When the young suckled, the mother exhibited a lactation anoestrus of 55·9±3·7 days. The litter size was nearly always two, and these well-developed young were frequently of opposite sex. In captivity, births occurred throughout the year.

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BARBARA J. WEIR

Summary.

The anatomy of the reproductive organs of female plains viscacha was examined at various stages of the reproductive cycle. The ovary is peculiarly flat with deep and convoluted surface invaginations. The ripe follicle is 200 μm in diameter and spontaneous ovulation of up to 800 eggs at a time takes place. True and accessory corpora lutea may be formed but it is suggested that luteinization occurs only after copulation. About seven ova are fertilized and implant, but resorption of all except the most distally situated foetus in each uterine horn occurs by Day 90 of pregnancy. No changes were detected in the uterine histology at different stages of the cycle. The cervix is not muscular but there is a longitudinal vaginal septum which extends distal to the cervical openings, causing the copulatory plug which is formed at mating to be Y-shaped. The vaginal epithelium shows changes associated with ovarian activity.

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BARBARA J. WEIR

Summary.

Acouchis (Myoprocta pratti) were investigated in the laboratory for comparison of their reproductive characteristics with those of other hystricomorphs. In this colony, the oestrous cycle length averaged 42·7±2·5 days; there was some indication of the existence of a summer and a lactation anoestrus. The gestation period was 99 days. The ovaries and reproductive tracts of these animals, and from animals obtained post mortem, were studied to complement a previous report on the ovarian histology in the acouchi. The presence of numerous accessory corpora lutea was confirmed but little interstitial tissue was found. Several ovaries contained groups of'immature testis tubules'.

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BARBARA J. WEIR

Summary.

Agoutis (Dasyprocta aguti) were investigated in the laboratory for comparison of their reproductive characteristics with those of other hystricomorphs. A vaginal closure membrane was present and the length of the oestrous cycle averaged 34·2±2·1 days. The ovaries and reproductive tracts of these animals, together with specimens obtained post mortem were studied and some correlations with physiological condition attempted. The ovary of the agouti is characterized by the presence of large numbers of accessory corpora lutea and by the extensive interstitial tissue which appears to replace completely the stroma of other mammals. Patches of 'immature testis tubules' were found in the ovaries of several animals.

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BARBARA J. WEIR

Summary.

Further investigations were made in the chinchilla, Chinchilla laniger, on the induction of ovulation and oestrus. Chinchilla treated with exogenous gonadotrophins (PMSG and HCG) in various regimens came into oestrus (73%) and a mean number of 2·6 ova were ovulated per animal. Mating occurred in 18% and conception in 12% of the treated chinchilla. This response was considered promising for encouraging chinchilla to breed at all times of the year.

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P. HEALEY and BARBARA J. WEIR

During the search for a suitable medium in which to freeze spermatozoa of the chinchilla (Chinchilla laniger), samples taken from ten males by electro-ejaculation (Healey & Weir, 1967) were pooled and studied after treatment with different diluents. All the samples contained a large proportion of motile spermatozoa and no samples were discarded before treatment. One aliquot of undiluted semen was dropped into 2 % buffered osmium tetroxide at pH 7·4 (Palade, 1952) and other aliquots were diluted in 0·5 ml of Baker's fluid (Baker, 1931), normal Ringer (8·5 g sodium chloride, 0·42 g potassium chloride and 0·25 g calcium chloride/litre water), half-strength Ringer or double-strength Ringer. The undiluted semen solidified immediately in the fixative and only the outer layer was used. The sperm suspensions in the different diluents were left at room temperature
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P. HEALEY and BARBARA J. WEIR

This technique was standardized on chinchilla (Chinchilla laniger) as part of two wider projects: (a) to investigate a method for artificial insemination (Weir, 1966), and (b) an electron microscope study of the spermatozoa.

Dalziel & Phillips (1948) used unipolar lumbar-anal electrodes on both guinea-pigs and chinchillas, Scott & Dziuk (1959) reported success with bipolar rectal electrodes on rats, mice and guinea-pigs. Hillemann, Gaynor & Dorsch (1963) described an electro-ejaculation method in chinchilla, but gave no details of the electrode or of the voltage used (Table 1).

Some of the sixty-four chinchillas used were those already in our colony and the rest were kindly lent by two chinchilla ranchers. The electrode was a multiring type (Healey & Sadleir, 1966) 12 cm long × 6·5 mm in diameter with 2·5 mm brass rings separated by

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J. P. ROOD and BARBARA J. WEIR

Summary.

The breeding characteristics of three species of wild guineapig (F. Caviidae) are reported. Cavia aperea, Galea musteloides and Microcavia australis were studied in Argentina in the field and in outdoor pens, and laboratory colonies of the two former species were also established in England. Pens of domestic guinea-pigs (Cavia porcellus) and of C. aperea × C. porcellus hybrids were maintained in Argentina for comparisons with C. aperea.

C. aperea and G. musteloides gave birth in every month but there was a breeding peak in spring (September to December). Microcavia had a more restricted breeding season ; in the field study area, births occurred only between August and April. Gestation length in C. aperea was variable but the mode was at 61 days, while the modes of Galea and Microcavia were much shorter at 53 and 54 days, respectively. All three species exhibited a post-partum oestrus and Galea may experience a lactation anoestrus. Oestrous cycle lengths in C. aperea and Galea varied considerably but the mean length in Cavia was 20·6±0·8 days and in Galea it was 22·3±12·4 days; in the latter species, the presence of a male in the same cage was necessary for the induction of oestrus. Average litter size was 2·2 for C. aperea, 2·6 for Galea and 2·8 for Microcavia. In the Argentine colonies, the age at first conception in C. aperea and Galea varied with the time of year of birth, but this variation was not maintained under the more equable laboratory conditions.

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CHRISTINE M. ROBERTS and BARBARA J. WEIR

Summary.

Accurately dated pregnancies were obtained in order to determine the time and mode of implantation in the plains viscacha, Lagostomus maximus. Implantation was completely interstitial and occurred antimesometrially on Day 18 post coitum. From each animal, very large numbers of single-celled and fragmenting eggs and relatively few blastocysts were flushed from the uterus up to the time of implantation. They were found at the ovarian end of the uterine horns, indicating that the blastocysts do not become spaced until just before implantation. Up to five blastocysts implanted progressively in each horn from the cervical to the ovarian end.

No morphological or histological differences could be detected along the length of the uterus. The significance of these findings is discussed in relation to the fact that only those fetuses nearest the cervix in each uterine horn survive whilst the others are resorbed early in pregnancy.