Reproduction, Fertility and Development Reproduction, Fertility and Development Society
Vertebrate reproductive science and technology
RESEARCH ARTICLE

Overview of the response of anoestrous ewes to the ram effect

R. Ungerfeld A D , M. Forsberg B and E. Rubianes C
+ Author Affiliations
- Author Affiliations

A Departamento de Fisiología, Facultad de Veterinaria, Universidad de la República, Montevideo, Uruguay.

B Department of Clinical Chemistry, Swedish University of Agricultural Sciences, Uppsala, Sweden.

C Departamento de Producción Animal, Facultad de Agronomía, Universidad de la República, Montevideo, Uruguay.

D To whom correspondence should be addressed. email: piub@internet.com.uy

Reproduction, Fertility and Development 16(4) 479-490 https://doi.org/10.1071/RD04039
Submitted: cfArticle2ecfc1997462761$funcRECEIVEDDATE@8783057  Accepted: 23 March 2004   Published: 6 July 2004

Abstract

The present review summarises knowledge of the reproductive response of anoestrous ewes to the introduction of rams – in other words, the ram effect. The ovarian and endocrine response, the factors that determine whether ewes will respond or not (associated with both the stimulus and the receptivity of the ewes) and some aspects of practical management are discussed. Information on the use of the ram effect to stimulate post-partum, prepubertal and cyclic ewes is also given. New insights are provided on ovarian response patterns, including recently collected information on luteal responses. The existence of delayed ovulation (5–7 days after the introduction of the rams) followed by luteal phases of normal or short length, luteal cysts and luteinised follicles is reported after scanning the ovaries with ultrasound. Endocrine parameters for depth of anoestrus, such as LH pulsatility and FSH concentrations, and how the concentrations of these hormones should be considered are discussed. Particular attention is paid to the observation of spontaneous, higher LH pulsatility and higher FSH concentrations in anoestrous ewes that respond to rams with luteal phases than in those that fail to respond. The use of progestogen priming and single progestogen administration and the possible advantages for synchronisation of oestrus are also discussed. Other factors that should be considered before the ram effect is applied, such as the strength of the stimulus and some practical considerations, are also included.

Extra keywords: biostimulation, pheromones, sheep, seasonal anoestrus.


Acknowledgments

We are indebted to our co-authors, Andrea Pinczak, Bettina Carbajal, Gonzalo Suárez, Laura Dago, Leticia Silva and Mariana Laca; and to Milton Pintos and Alejandro Salina for animal handling. Thanks are extended to Ignacio Videla Dorna, from Syntex S.A. (Buenos Aires, Argentina), for continuous collaboration. Financial support was received from the CSIC (Universidad de la República, Montevideo, Uruguay), the CIDEC (Facultad de Veterinaria, Montevideo, Uruguay), the Department of Clinical Chemistry (Swedish University of Agricultural Sciences, Uppsala, Sweden) and FNI (CONICYT, Montevideo, Uruguay).


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