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The purpose of this clinical-diagnostic study was the evaluation of the serum myeloperoxidase (MPO) activity in conjunction with the white blood cell count (WBCC) during the puerperium of the mare as well as the assessment of the reliability as a diagnostic marker for the breeding soundness and the subsequent pregnancy rate in the foal heat.
Sixteen Haflinger mares from 5 to 17 years of age were included in the study. All of them were in good breeding condition living in the same stud. Blood samples were collected daily starting the first day post partum until the day after the last breeding. A uterine swab for bacteriological and cytological examination was collected from the mares in heat once before the first breeding. All mares were bred naturally to five different stallions, which all fulfilled the fertility requirements according to the test results. The absolute values of the WBC, neutrophils, lymphocytes and total serum protein were used for the analysis of the blood samples.
Of the 16 mares 75 % (n=12) showed signs of foal heat and were bred whereas in 25 % (n=4) no foal heat was observed. The onset of the foal heat ranged from 5 to 14 days (9,25±2,49) post partum and the duration varied from 4 to 8 days with an overall average of 6±1,5 days. An early onset was followed by a longer duration in comparison to the later starting foal heats. The pregnancy rate achieved by using the first heat post partum (58,3 %, n=7) was in accordance with the results published by other authors, due to inadequate uterine involution, bacterial contamination and hormonal imbalances. The pregnancy rates of the mares showing a later post partum ovulation were higher than the ones achieved by the mares ovulating sooner presumably. During this study, all mares which displayed signs of the foal heat before day 8 post partum failed to conceive (n=3). A presumptive cause for this observation is thought to be an inadequate clearance and subsequent bacterial colonization of
The results of the bacteriological examination of the uterine swabs (after enrichment) showed a moderate to high detection of pathogenic germs in 83,3 % (n=10). Uterine cytology confirmed all mares to be in oestrus. The number of neutrophils within the endometrium was ≤2 %. All of the mares with swabs negative in the bacteriological examination (n=2) and half of the ones with positive results (n=5) were in foal. Insufficient uterine clearance and a bacterial contamination during foal heat may result in a diminished fertility.
The leucocyte count of almost all mares was within the normal reference value (7,94±1,52 x109/l). Mares without a foal heat (8,62±1,41 x109/l, n=4) tended to have higher WBC values before and during breeding as well as the non-pregnant (8,36±1,39 x109/l, n=5) in comparison to the pregnant mares (7,55±1,19 x109/l, n=7, p<0,05: D-3, D-1, D0, D1).
Except for two test results (0,97 and 1,99 x109/l), the measured neutrophil counts were within the normal reference value (4,49±1,12 x109/l). The values of mares not in foal heat (4,82±1,02 x109/l, n=4) were higher than the ones of mares which were bred during foal heat (4,38±1,13 x109/l, n=12, p≥0,05). Again, non-pregnant mares displayed higher values (4,86±1,17 x109/l, n=5) than pregnant mares (4,22±0,98 x109/l, n=7, p<0,05: D1).
An increased MPO-activity in the blood was measured on the first day post partum (0,97±0,65 U/ml) as well as on several consecutive days during the puerperium and sporadic after breeding (D1: 0,99±0,86 U/ml). Mares without foal heat (n=4) seem to have higher MPO-activity (1,26±1,04 U/ml) than the ones with distinct signs of foal heat (0,62±0,48 U/ml, n=12, p<0,05: D-5, D-4, D-3, D-2, D4). During the time of breeding (D-1 till D7), a significantly increased MPO-activity was also measured in mares, which failed to conceive (0,85±0,59 U/ml, n=5). Mares in foal (n=7) measured an average MPO-activity of 0,45±0,19 U/ml (p<0,05: D1, D3). Additionally, a negative bacteriological examination was related to lower MPO-activity (0,29±0,19 U/ml), whereas a positive bacteriological examination showed a higher MPO-activity level (0,65±0,23 U/ml). Mares in foal with a positive bacteriological examination (n=5) measured an average MPO-activity of 0,50±0,20 U/ml and non-pregnant mares (n=5) measured a level of 0,79±0,56 U/ml.
Despite the small number of test animals, the present study shows first evidence that high MPO-activity caused a higher rate of non-pregnancy and an absence of foal heat, whereas mares with lower values tended to conceive more frequently. The significance of myeloperoxidase serving as a reliable marker for breeding soundness during foal heat especially with a concurrent positive bacteriological uterine swab has to be confirmed in further prospective studies with both, a considerably higher number of mares and a larger breeding area with more representative breeding mare population.