The Difference of the Rumen Microbial Population in Cyclic and Acyclic Grey Shirazi Ewes

So far, changes in the vaginal microbial population during the estrous cycle have been evaluated in several livestock species such as sheep. However, changes in the rumen microbial population have not been investigated during the estrous period in sheep. In a study, the results showed that the differences in the rumen microbial population in two reproductive seasons were due to the differences caused by the reaction to day length, and nutrition did not have much effect on it. It is possible that during the reproductive and non-reproductive seasons, the animal has a different microbial population in the digestive tract. The available evidence from clinical research in animals shows that microbes in the digestive system can alter brain activity and behavior through hormonal and neural pathways. Therefore, this study mainly aims to investigate changes in the rumen microbial population during the reproductive season in the estrous period in ewes with estrus and those without estrus for any reason or are so-called anestrus. The changes in the rumen microbial population during the breeding season in the estrous period were measured for the animals showing the occurrence of estrus and those not showing this trait or were anestrous.

This research was done at the same time as the non-breeding season (late spring-beginning of July). The ewes were of Grey Shirazi breed (2-3 years old). To investigate changes in the rumen fluid microbial population in the estrus cycle in estrus and non-estrus animals, two groups of 10 animals were formed from estrus and anestrus animals with the use of teaser rams, and rumen fluid samples were collected for microbial culture and other investigations in both groups once per four days (5 times) during 17 days (like estrus cycle days). The colonies were cultured and separated using general culture media with different growth factors for anaerobic bacteria colonies, such as plate count agar, MRS agar (de Man-Rogosa - Sharpe), and starch agar. The colonies were subtracted by subtractive cultures or different diagnostic tests to identify colonies. Data were analyzed using SAS software version 1/9. Means were compared with the least square procedure and adjusted for Tukey's test.

The population difference between the two groups at 5 different times showed that the population of lactic acid bacteria (LAB) on the day of estrus showed a higher value and a significant difference with other times than the anestrus group. Lipolytic bacteria were higher on the day of estrus than on all days in both groups, with a significant difference. The comparison of different groups showed that the estrous group from times 1 to 5 in the breeding season had the highest number compared to the other groups at different times of the study (p < 0.05). Anestrous groups also had the lowest number at all times (p < 0.05). The comparison of the two estrus and anestrus groups showed that heat and ninth days had higher values than the other times. In comparing the average number of lipolytic colonies in the estrus group, the highest and the lowest numbers belonged to the 1st and the 4th times, respectively, which were significantly different from the other times (p < 0.05). The population of proteolytic bacteria had the highest number of bacteria at time 1 and showed the next values at times 2, 5, 3, and 4, respectively, compared to the estrus group at time 5 (p < 0.05). Time 5 was not significantly different from times 2 and 3 (p < 0.05). In this season, the estrus group was the highest and the lowest at times 1 and 4, respectively (p < 0.05). Times 3-5 were no different significantly (p < 0.05). In the anestrus group, times 3 and 1 had the highest number vs. the lowest numbers in times 2 and 5  (p < 0.05). Based on the comparison of the average population resulting from the counting of total bacterial colonies in the examination of different groups, the estrous group had the highest number of the average microbial population in all 5 times (p < 0.05). The lowest number belonged to two anestrus groups (p < 0.05). The population difference between the two groups at 5 different times showed that the population of LAB had a higher value only on the day of estrus, with a significant difference compared to the anestrous group. The population of lipolytic bacteria in two groups of estrus and anestrus in the 5 studied times showed that the estrus group had a higher and significant value than the anestrus group in the 4th time, i.e. the day of estrus and days 5, 6, and 17. The results showed that the total bacterial population was higher in the estrus group at all times, with a significant difference. Furthermore, anaerobic bacteria increased significantly in certain days of estrus (days 1-9) compared to the anestrous group. The population difference between the two groups at 5 different times indicated that the population of LAB had a higher value only on the day of estrus, with a significant difference compared to the anestrous group. The population of lipolytic bacteria in the two estrus and anestrus groups in the 5 studied times revealed that the estrus group had a higher and significant value than the anestrus group in 4 times, i.e. days of estrus, 5, 6, and 17. The total bacterial population in the estrous group was higher and significant at all times.

In general, the colony population of amylolytic and lipolytic bacteria and the total colonies of anaerobic bacteria are significantly different on days of the estrus cycle, which may affect reproduction. Accordingly, it is better to provide more understandable results of rumen microbial effects on estrus in ewes by increasing analyses such as hormonal changes and molecular investigations, along with microbial culture in estrus crops.