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C. NOVOA

Summary.

Sexual activity in Camelidae appears to be acyclic and ovulation is induced by copulation. The duration of sexual activity is variable. When a rutting season exists, it is probably elicited by influences similar to those which induce the advent of oestrus in the female. The pattern of the reproductive cycle appears to relate to the harsh environment in which the camel progenitors evolved. Only calves born in a restricted period of the year had any chance of survival. Selection has, thus, been towards a type of animal with a breeding season coinciding with the most favourable time of the year. In areas with better environmental conditions, sexual activity does not follow such a restricted pattern.

Fertility rate is low compared with other domestic mammals.

Mating behaviour follows a fairly complex pattern of olfactory and/or visual stimuli.

All Camelidae have a similar type of placenta. It is diffuse and epithelio-chorial in nature, much as in the horse.

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S. FERNANDEZ-BACA, D. H. L. MADDEN and C. NOVOA

Summary.

The ovulation response following different mating stimuli was studied in 177 adult female alpacas killed 72 hr after mating. Ovulation rates in females that received a mounting stimulus alone, either by aproned males or other females, were low and did not significantly differ from those controls which did not receive any stimulus. Single services by intact, or vasectomized males caused ovulation in 77 to 82% of the females, a significant increase over the previous treatments. Increasing the number of services by intact males to three within 24 hr, or interrupting services 5 min after their initiation, did not significantly affect ovulation or fertilization rates, as compared to single or uninterrupted services. Single hcg injections to females in oestrus induced ovulation in all cases. Results indicate that mounting accompanied by penile intromission is necessary to provide an adequate stimulus for lh release and subsequent ovulation in the alpaca.