Date of Award:

5-1986

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Animal, Dairy, and Veterinary Sciences

Committee Chair(s)

Warren C. Foote

Committee

Warren C. Foote

Committee

Jay V. Call

Committee

Donald V. Sisson

Committee

Simon G. Riera

Abstract

This research was conducted at the La Raya experiment station, Cusco, Peru (4200 m elevation, 15°S latitude, and 70 °W longitude) using 60 Corriedale, and 60 Criollo ewes during three consecutive years (April 1981 - March 1984). Age, and weight at puberty, age at physical maturity, and the effects of breed, age (physically immature and mature), year, and month were measured on body weight, incidence of estrus, and incidence and rate of ovulation. There was a significant difference (P<.05) among breed, year, and the interactions for body weight at puberty. The mean age at puberty for 1982-83 was 693.6 days (23.1 months) for Corriedale and 483.3 days (16.1 months) for Criollo. The mean liveweight at puberty was 27.2 kg for Corriedale, and 25.3 kg for Criollo. Corriedale ewe lambs weighed more than Criollo, attained puberty seven months later than Criollo. At comparable age (15-17 months) at the Southern Peruvian Highlands 100 % of the Criollo reached puberty, compared to 58% of the Corriedale. Body weight, incidence of estrus and ovulation were affected (P<.01) by breed, age, year, month, and their interactions. Physical maturity was attained at 39 and 36 months of age for Corriedale, and Criollo, respectively. Weight changes during the year were associated with feed availability. The mean overall incidence of estrus was 45.4 % for Corriedale (43.6 in physically immature, and 47.2 % in mature ewes), and 67.1 % for Criollo ewes (66.3, in physically immature, and 68.7 % in mature ewes). The mean overall incidence of ovulation was 39.6 % for Corriedale (39.7, in physically immature, and 39.5 % in mature ewes), and 58.5 % for Criollo ewes (59.4, in physically immature and 56.7 % in mature ewes). Both breeds demonstrated seasonality of estrus and ovulation with the Corriedale being shorter than the Criollo. The incidence of ovulation in both breeds was less than that of estrus. The ovulation rate was 1.00 for Corriedale, and 1.03 for Criollo (P>.05). Even though Criollo ewes weighed less than Corriedale, they attained puberty earlier, and showed less seasonality in estrus and ovulated throughout the year than the Corriedale.

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