Seasonal reproductive patterns and effectiveness as teasers (ram effect) of Corriedale and Milchschaf rams
R. UngerfeldDepartamento de Fisiología, Facultad de Veterinaria, Universidad de la República, Montevideo, Uruguay. Email: rungerfeld@gmail.com
Animal Production Science 52(11) 1036-1041 https://doi.org/10.1071/AN12114
Submitted: 30 March 2012 Accepted: 15 June 2012 Published: 25 July 2012
Abstract
The first objective of this study was to compare the seasonal reproductive pattern of Corriedale and Milchschaf rams. Because seasonal patterns were similar, a second objective was to compare the effectiveness of rams from both breeds to induce oestrus in seasonally anoestrous Corriedale ewes using the ram effect. In the first experiment, the seasonal changes of bodyweight, scrotal circumference, testosterone concentrations, sexual behaviour towards oestrous ewes (ano-genital sniffing, lateral approaches, flehmen, mount attempts, mounts, and copulation), and semen characteristics (total spermatozoa in the ejaculate, mass motility, and percentage of alive and normal spermatozoa) were recorded during 13 months in five Corriedale and seven Milchschaf rams. All recorded variables changed through the year, with maximum reproductive patterns occurring in summer and autumn. Milchschaf rams were heavier than Corriedale rams, but no difference was observed in their reproductive patterns. Experiment 2 was performed during the non-breeding season with 169 Corriedale and Polwarth mulitparous ewes. All ewes were isolated from the rams so that they could not see, hear or smell them (minimum distance: 1000 m) from Day –40. They were primed over 8 days with an intravaginal sponge impregnated with 50 mg of medroxiprogesterone. Four Corriedale rams were introduced to 83 ewes, and four Milchschaf rams to the remaining 86 ewes at sponge withdrawal, and oestrus was recorded for 5 days. On Day 5, no ewe of the group bred with Milchschaf rams was marked. By contrast, 46 out of 83 (55.4%) of the ewes bred with Corriedale rams were marked (P < 0.0001). It was concluded that reproductive seasonal pattern of Corriedale and Milchschaf rams, including scrotal circumference, testosterone concentrations, sexual behaviour and semen characteristics, was similar. However, Corriedale rams were more effective than Milchschaf rams in inducing oestrus in anoestrus ewes (the ram effect).
Additional keywords: semen, sexual behaviour, socio-sexual signals, testicle, testosterone.
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