Prevalence of bovine subclinical endometritis 4 h after insemination and its effects on first service conception rate
Introduction
The key for excellent fertility in dairy herds is a healthy uterine environment, optimal estrus detection efficiency and ideal timing for breeding. This study focuses on the uterine environment at the time of breeding. The incidence and impact of clinical and subclinical endometritis (SE) in the postpartum period has been the objective of several studies [1], [2], [3], [4], [5].
A case definition for clinical endometritis based on the risk of impaired fertility was introduced by LeBlanc et al. [1]. Clinical endometritis was characterized by a cervical diameter >7.5 cm and the presence of purulent or mucopurulent vaginal discharge after 20 days postpartum (dpp). Affected cows were 30% less likely to become pregnant at first service and 70% more likely to be culled for reproductive failure [1].
Recent studies have focused on a more sophisticated diagnosis of endometrial alterations beyond clinical signs of endometritis. New techniques have been described for the diagnosis of subclinical endometritis (SE). The inflammation of the endometrium is characterized by the proportion of polymorphonuclear cells (PMN) in a cytological sample taken from clinically healthy cows. Cytological samples can be obtained by flushing the uterine lumen [3], [6], [7] or by using the cytobrush technique [2], [8], [9]. This latter technique uses a small brush that is inserted into the uterus to collect endometrial cells and to determine the proportions of PMN in the sample.
Studies on SE found a prevalence of SE in the range between 12% and 94% [2], [3], [4], [8], [10], [11]. Different study designs and inconsistent definitions for SE hinder a valid comparison of the results of these studies. The time of examination in these studies varied from 21 to 60 dpp. Furthermore, different threshold values of PMN were used for the definition of SE. For example, Hammon et al. [4] used a threshold value of >25% in the cytological sample at 28 (±3) dpp whereas Kasimanickam et al. [10] found >18% PMN at 20–33 dpp as indicative of SE. Other authors [3], [8], [9], [11] set the threshold at 5% or 8% PMN. All cited studies, except [12], found negative effects of SE on reproductive performance, i.e. decreased first service conception rate and/or prolonged days open. Subclinical endometritis in the postpartum period, however, can resolve before insemination. Gilbert et al. [3] found decreasing proportions of cows with SE from 2 weeks postpartum (100%) to 8 weeks postpartum (41%). In contrast, cows without SE at the end of the postpartum period can be positive for SE later in lactation. Of 152 cows identified as healthy 21–27 dpp (≥5% PMN), 12.5% were identified with SE and 14.5% with clinical endometritis 14 days later [8]. It remained unclear in that study, if subclinical and clinical endometritis were caused by the cytological examination itself. In the cited studies, however, cytological examinations were conducted at the end of the postpartum period, not in the breeding period. To our knowledge there are few studies that investigated the impact of cytological evidence of inflammation immediately prior to insemination on fertility in dairy cows [13]. Although not statistically significant, the cited researchers did notice a negative relationship between uterine inflammation and conception.
The objective of the current study was to investigate the prevalence of bovine subclinical endometritis 4 h after AI and its effect on first service conception rate (FSCR). To evaluate an effect of the diagnostic technique itself, conception rates of cows included in the study were compared with conception rates of cows not examined for SE.
Section snippets
Study farm
The study was conducted between December 2005 and July 2006 on a commercial dairy farm in Germany. Cows were housed in a free-stall barn with slotted floors and cubicles, lined with rubber mats. Herd average milk yield was 9259 kg (4.08% fat, 3.48% protein) per cow per year. Cows were fed a total mixed ration.
Study design
The voluntary waiting period was set at 65 dpp. Estrus detection was performed by the herd manager and the staff of the farm by visual observation of signs of estrus. The cows were visually
Results
A total of 201 Holstein-Friesian cows were enrolled in the study. No effect on FSCR was found for the collection of endometrial sample with the cytobrush technique. First service conception rate was 43.3% for 201 cows examined with the cytobrush technique and 41.7% for 103 cows with no sample taken after AI (P > 0.05).
Cows in group Medium had higher FSCR than cows in groups Zero and High, respectively (57.6% vs. 39.1% and 29.6%, P < 0.05). The difference between Zero and High was found not
Discussion
The finding that collection of samples with the cytobrush technique had no effect on FSCR indicates that this technique is suitable for endometrial examination 4 h after AI.
Studies in various species reported that natural breeding or AI is followed by an immigration of leukocytes into the lumen and tissue of the uterus [14], [15], [16], [17], [18]. Semen induces a neutrophil response in the uterus of the mare after insemination [14]. Post-breeding inflammatory reaction in the horse peaked
Conclusion
This study demonstrated that cows with high proportions of endometrial PMN (>15% PMN) after AI have a decreased FSCR, which might be indicative of SE. Further analyses showed that results were affected by parity. In multiparous cows the proportion of PMN had no effect on conception rates. In primiparous cows, FSCR was highest for cows with PMN >0–15%.
Furthermore, the results of the current study show that the cytobrush technique is an appropriate method for the collection of endometrial samples
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2021, Journal of Dairy ScienceCitation Excerpt :Hence, several studies might have underestimated the condition. Individuals with clinical endometritis have generally been excluded in studies of subclinical endometritis, due to the interference between the definition of the conditions (Kasimanickam et al., 2004; Kaufmann et al., 2009; Plöntzke et al., 2010). In some studies that investigated CYTO (Dubuc et al., 2010a; Pascottini et al., 2017a), the higher prevalence of positive animals might be explained by inclusion of individuals with opaque vaginal discharge.