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.