Follicular dynamics during the non-reproductive season jennies of the Miranda donkey breed
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2017-08-17
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A raça Asinina de Miranda teve a sua origem na zona do planalto Mirandês, no território mais a nordeste de Portugal. Esta raça encontra-se atualmente na lista de raças autóctones em risco de extinção pelo que estudos têm vindo a ser realizados no sentido da sua melhor caracterização e proteção.
É comum a aplicação de estudos realizados em éguas a burras, no entanto, o gradual aumento de estudo em asininos tem vindo a demonstrar que, nomeadamente a nível reprodutivo, existe um considerável número de diferenças. A época reprodutiva é sem dúvida o principal alvo de estudo da maior parte dos trabalhos publicados. Observações como a sazonalidade menos marcada das burras e a necessidade de otimização dos resultados reprodutivos, particularmente de espécies em risco de extinção, leva ao interesse no estudo da época não reprodutiva.
Este estudo visou a medição dos diâmetros foliculares presentes em ambos os ovários de quinze burras mirandesas durante os meses de setembro a abril durante dois anos consecutivos e a caracterização da dinâmica folicular durante este período. Confirmou-se a sazonalidade menos marcada das burras. No entanto, foi observado um maior número de animais que demonstraram efeitos sazonais que o publicado em estudos anteriores. Os resultados da caracterização dos períodos interovulatórios concordou com a bibliografia disponível. Quando comparados com a época reprodutiva, os ciclos apresentaram-se mais longos, assim como os períodos de estro e os folículos ovulatórios atingiram maiores dimensões no início da época reprodutiva e na época de transição da primavera. As burras que passaram por um período de anestro foram também os animais que registaram diestros mais curtos. Duas das 15 burras a estudo apresentaram diestros sistematicamente mais longos. Os períodos de anestro registados foram mais longos que o publicado em estudos anteriores. Foram registados três folículos anovulatórios, todos em burras que passaram por um período de anestro (dois ocorreram durante a época de transição de primavera e um durante a época de transição de outono.
As ovulações no ovário esquerdo foram mais frequentes. Foi medido um maior número de folículos no ovário direito em todas as burras ao longo de todo o período de estudo em todas
as ecografias realizadas. A burra que apresentou um corpo lúteo persistente foi também a que apresentou um menor número de medições por ecografia.
Ao analisar os perfis foliculares, foi encontrada uma área de ambiguidade que não permitiu a distinção entre folículos em regressão de folículos em crescimento.
Um menor nível de atividade ovárica e menores dimensões foliculares parecem ter estado presentes já que foi encontrada uma grande percentagem de folículos menores que 18 mm e uma grande concentração de folículos de maiores dimensões nos períodos de estro.
Ondas menores foram significativamente mais frequentes durante os períodos de anestro. A emergência de ondas menores consecutivas foi o padrão mais frequente em burras que entraram em anestro. Nas restantes burras a emergência de apenas uma onda com um ou dois folículos ovulatórios foi o padrão mais frequente. O diâmetro máximo do maior folículo de ondas menores foi inferior ao diâmetro à divergência dos maiores folículos das ondas maiores. O diâmetro máximo registado em ondas maiores secundárias foi inferior ao diâmetro máximo registado em ondas maiores primárias.
Foram identificadas ondas primárias e secundárias menores e maiores. Burras que não entraram em anestro apresentaram um maior, mas não significativamente maior, número de ondas foliculares. Verificou-se uma ovulação múltipla em que os folículos derivaram de duas ondas foliculares distintas.
The Miranda donkey breed had its origin in the most northeast of the Portuguese country and it is considered in risk of extinction. Studies on this breed have been done towards its better characterization and protection. It is common the use of mare studies on jennies. However, the increasing number of donkey studies shows that their reproductive characteristics are distinct. The breeding season is with no doubt the most studied reproductive period in mares and jennies. Less seasonal effects in jennies and the necessity of better breeding results, particularly in endangered breed, leads to the interest in studying the non-breeding season. The follicular diameters existent in both ovaries of fifteen Miranda jennies were measured from September to April, during two consecutive years and the characterization of the follicular dynamics during this period was done. The less marked seasonality of jennies was confirmed. However, a higher rate of seasonal effects, than what was found in literature, was found among our study population. Results on basic characterization of cycle lengths agree with the available literature. When comparing to the breeding season, longer interovulatory intervals were found, as well as longer estrus lengths and larger ovulatory follicles at the onset of the breeding season and spring transition. Diestrus periods were shorter among the group of Miranda jennies that underwent periods of anestrus. Two of the fifteen jennies consistently presented longer diestrus during both breeding and non-breeding season. Anestrus periods lasted longer than what has been previously published. Three anovulatory follicles were recorded, two during spring transition and one during vernal transition – all in jennies that underwent an anestrus period. Ovulations from the left ovary were more frequent. More follicles were measured in the right ovary than in the left one during the entire considered period of time. The jenny that presented a persistent CL was the one that presented less follicles per ovary per ultrasound examination. When observing follicular profiles of consecutive waves, an “area of ambiguity” was found that did not allow the distinction between regressing and developing follicles. Indications of lower ovarian activity and smaller follicular diameters during the non-breeding season were corroborated by considerable high rate of follicles under 18 mm in diameter and a higher rate of larger follicles during estrus periods. Minor waves were significantly more frequent among jennies that underwent an anestrus period. The emergence of consecutive minor waves during anestrus was the most frequent pattern in this group of jennies. Among the remaining jennies, the most common wave pattern was the emergence of only one follicular wave with either one or two ovulatory follicles. The diameter of the largest follicles of minor waves was generally lower than the diameter at divergence of major waves. Also, mean maximum diameter of the largest follicles of major secondary waves was smaller than the maximum diameter of the largest follicles of major primary waves. It was found the presence of both major and minor secondary waves in all groups of jennies. Jennies that did not present an anestrus period presented, though not significantly, a higher number of follicular waves per cycle. Multiple ovulations with the ovulatory follicles being originated from different follicular waves were also found.
The Miranda donkey breed had its origin in the most northeast of the Portuguese country and it is considered in risk of extinction. Studies on this breed have been done towards its better characterization and protection. It is common the use of mare studies on jennies. However, the increasing number of donkey studies shows that their reproductive characteristics are distinct. The breeding season is with no doubt the most studied reproductive period in mares and jennies. Less seasonal effects in jennies and the necessity of better breeding results, particularly in endangered breed, leads to the interest in studying the non-breeding season. The follicular diameters existent in both ovaries of fifteen Miranda jennies were measured from September to April, during two consecutive years and the characterization of the follicular dynamics during this period was done. The less marked seasonality of jennies was confirmed. However, a higher rate of seasonal effects, than what was found in literature, was found among our study population. Results on basic characterization of cycle lengths agree with the available literature. When comparing to the breeding season, longer interovulatory intervals were found, as well as longer estrus lengths and larger ovulatory follicles at the onset of the breeding season and spring transition. Diestrus periods were shorter among the group of Miranda jennies that underwent periods of anestrus. Two of the fifteen jennies consistently presented longer diestrus during both breeding and non-breeding season. Anestrus periods lasted longer than what has been previously published. Three anovulatory follicles were recorded, two during spring transition and one during vernal transition – all in jennies that underwent an anestrus period. Ovulations from the left ovary were more frequent. More follicles were measured in the right ovary than in the left one during the entire considered period of time. The jenny that presented a persistent CL was the one that presented less follicles per ovary per ultrasound examination. When observing follicular profiles of consecutive waves, an “area of ambiguity” was found that did not allow the distinction between regressing and developing follicles. Indications of lower ovarian activity and smaller follicular diameters during the non-breeding season were corroborated by considerable high rate of follicles under 18 mm in diameter and a higher rate of larger follicles during estrus periods. Minor waves were significantly more frequent among jennies that underwent an anestrus period. The emergence of consecutive minor waves during anestrus was the most frequent pattern in this group of jennies. Among the remaining jennies, the most common wave pattern was the emergence of only one follicular wave with either one or two ovulatory follicles. The diameter of the largest follicles of minor waves was generally lower than the diameter at divergence of major waves. Also, mean maximum diameter of the largest follicles of major secondary waves was smaller than the maximum diameter of the largest follicles of major primary waves. It was found the presence of both major and minor secondary waves in all groups of jennies. Jennies that did not present an anestrus period presented, though not significantly, a higher number of follicular waves per cycle. Multiple ovulations with the ovulatory follicles being originated from different follicular waves were also found.
Descrição
Dissertação de Mestrado Integrado em Medicina Veterinária
Palavras-chave
Folículo ovariano , Anestro , Ultrassonografia , Raça Asinina de Miranda , Reprodução animal , Ondas foliculares , Burras