Étude sur le terrain de cinquante-cinq cas de torsion utérine chez des vaches laitières. Deux cent soixante-treize animaux ont été enrôlés dans cette étude cas-cas comparant les torsions utérines à d’autres types de dystocies. Le but de l’étude était de décrire les torsions utérines et leur résolution et de les comparer avec d’autres types de dystocies rencontrées sur le terrain, et d’évaluer l’effet des saisons et du logement sur la fréquence des torsions. Cinquante-cinq cas de torsions utérines ont été rencontrés, représentant 20 % du total des dystocies. La plupart des torsions utérines ont été corrigées et suivies de la naissance d’un veau vivant par voie naturelle. Lorsqu’on les compare à d’autres types de dystocies, les vaches étaient plus à risque que les taures (OR = 5,2; P < 0,0001), et les animaux souffrant de disproportion foeto-pelvienne ou portant des jumeaux étaient moins à risque (OR = 0,05; P < 0,0001 et OR = 0,09; P = 0,007, respectivement). Les primipares étaient moins à risque lorsqu’elles vêlaient seules dans un enclos de vêlage plutôt qu’attachées dans une logette (OR = 0,2; P = 0,04). Aucun effet de la saison sur le risque de torsions utérines n’a pu être démontré.

(Traduit par les auteurs)

The etiology of the condition is not well understood. It generally occurs during late 1st stage or early 2nd-stage labor (8), but there are some reports of prepartum uterine torsions (9). The instability of the gravid uterus is certainly the most important predisposing factor in bovine uterine torsions. Each uterine horn is supported in a dorsolateral direction by the broad ligaments, which are attached to the ventral surface of the uterus. The greater curvature of the uterus is dorsal and, in advanced pregnancy, the uterus is positioned beyond the relatively stable area of attachment, resting on the abdominal floor and being supported by the rumen, viscera, and abdominal wall (10). In addition, the manner in which the cow lies down, with the forequarters going down first, and rises, by elevating the hindquarters first, implies that each time the cow lies down or rises, the gravid uterus is suspended in the abdominal cavity. Therefore, a sudden slip or fall could cause torsion of the unstable gravid uterus. However, there must be some contributory factors in addition to instability that occur during 1st-stage labor, otherwise uterine torsion would also be seen frequently in late gestation, which is not the case (8). Many authors suggest that the increased fetal movements that occur during 1st-stage labor in response to the contraction of the myometrium may be the precipitating parturient factor. Other factors that have been mentioned are a sudden push from another cow, decreased amounts of uterine fluid, a flaccid uterine wall, a small non-gravid horn, and excessive fetal weight (7,9,11). In the report of 1 study, pastured animals were more at risk (12), but in that of another study, uterine torsions were 3 times more frequent when animals were confined in stables for long periods (13). Twin pregnancy, on the other hand, tends to prevent torsion, because the bicornual nature of most cases of bovine twins stabilizes the gravid uterus (2).

Most commonly, the torsion extends caudally beyond the cervix, such that the vaginal wall is involved in the rotation (2,8,10). In our study, vaginal involvement was obvious in most cases, consistent with the fact that two-thirds of the torsions were diagnosed by vaginal examination alone. In all the other cases, a transrectal examination was performed, either as the sole diagnostic method or in addition to a vaginal examination, reinforcing the point made by Frazer et al (9) that the presence of a uterine torsion should not be ruled out unless a transrectal palpation has been performed.

Most authors agree that counterclockwise torsions are more frequent (between 63% and 75% of torsions) than clockwise torsions (4,7,9), in agreement with results of this study. In general, the gravid horn rotates over the nonpregnant horn (10). A counterclockwise torsion would then be found mostly in cases of right horn pregnancy, in line with the reported frequency of 60% to 68% right horn pregnancy in dairy cattle (7,8,15). In his report of 115 torsions, Desliens (12) describes a majority of counterclockwise torsions, but with almost three-quarter of the pregnancies in the left horn. This discrepancy between Desliens’s study and those reported by others is difficult to explain.

The degree of torsion varies considerably from 1 study to another, and there is a marked difference between referral and field cases (4,7,9,10). Almost all the referral cases are torsions of at least 180°, with approximately 25% of these being greater than 270°. In our field study, 75% of the torsions were 180° or less. Torsions of less than 45° probably do not cause dystocia and many dystocias where the fetus is in dorsoileal or dorsopubic position are actually uterine torsions of low magnitude (13).

We found fewer posterior presentations with uterine torsions than with control dystocias, where posterior presentations are over-represented compared with a normal population (10). Compared with the expected proportion of posterior births among all calvings, which is around 5% (7,9), it seems that uterine torsions could be more common with the calf in posterior presentation.

Several methods can be used to correct a uterine torsion and are well described in obstetrics textbooks: manual detorsion or rotation of the fetus and uterus per vagina, rolling the cow, use of a detorsion rod, and cesarean section (2,8,10,17). Some authors mention that manual correction of a torsion is impossible when the torsion does not involve the cervix (8,9). In our study, 8 out of 18 torsions that were manually reduced did not present vaginal folds, which could indicate that the torsion did not involve the cervix. However, 6 of those 8 torsions were 180° or less, so vaginal involvement may not have been noted because of the low magnitude of the torsion. All reported attempts at manual detorsion were successful, and followed by vaginal delivery of the calf in our study. Other authors have reported success rates of manual correction varying between 24% and 96%, with the rate being higher when correction per vagina is attempted as a 1st choice in field cases (4,7,9,10). Rolling the cow has been reported to be successful in 34% to 100% of cases (10,17,18). Because Schaffer’s method for rolling the cow with a plank (8) seemed more successful than without a plank in this and another study (18), it is probably advisable to use a plank, if one is available. Also, some cows need to be rolled more than once before the torsion is corrected and, according to some authors, rolling should be attempted 4 or 5 times before failure is admitted and another technique is tried (2). Looking at the distribution of the methods of correction by clinic (data not shown), it was clear, although not statistically significant, that the method of correction was more the personal preference of the attending clinician, the availability of assistance, and the convenience of location to roll the cow than the severity of the torsion. The only exception was cesarean section, which was never performed as a 1st choice, only after all other attempts at detorsion had failed (n = 1) or because of failure of cervical dilatation after detorsion (n = 5).

According to various authors, the cervix is incompletely dilated following 20% to 52% of successful detorsions (5,7,9); in most of those cases, vaginal delivery is impossible and a cesarean section has to be performed. However, some cases described as incompletely dilated could still have a partial torsion, especially if a transrectal examination was not done after correcting the torsion. In our study, the cervix failed to dilate properly in two-thirds of the uterine torsion cases, but only 5 of those cases required a cesarean section to deliver the calf. Interestingly, none of the 5 uterine torsions had been resolved by manual detorsion prior to the surgery. Likewise, fewer than a quarter of the uterine torsions had an undilated cervix following manual correction of the torsion, compared with half when other correction methods were used. We hypothesize that the manipulations through the cervix to correct the torsion can help to effectively dilate the cervix. Although some authors mention that oxytocin might be used to induce cervical dilation (2,10), no drug has consistently proven efficient in inducing cervical dilatation in cattle. The cervix seldom dilates if the fetus is already dead; even when the fetus is alive, the cervix may fail to dilate following a torsion (9). It would thus be advisable to proceed immediately to a cesarean section when vaginal delivery of a dead fetus is impossible because of an undilated cervix. Otherwise, if the fetus is alive, one may elect to wait a few hours to see if labor will naturally proceed to 2nd stage. However, this occurs in only a minority of cases and delay beyond 3 h is pointless and even dangerous, especially if the fetal membranes have already ruptured (7).

Approximately 30% of uterine torsions happen in heifers and 70% in cows. This is generally thought to be a reflection of the number of animals at risk (2,7,10). However, heifers are more at risk of dystocia than are cows (2,8,10). In our study, 47% of dystocias were seen with heifers, but cows accounted for 78% of the uterine torsions, making them at 5.2 greater odds than heifers of having a uterine torsion. One author who observed uterine torsion more commonly in cows than in heifers suggested that it could be because cows have a larger abdominal cavity than heifers, decreased uterine tone, and a stretched mesometrium (2).

Excessive fetal weight appears to be a predisposing factor for uterine torsion (7,9). Accurate data on calf weight in this study were insufficient to evaluate its role as a risk factor for uterine torsion. However, we determined that uterine torsion was rare when fetopelvic disproportion was present. Forty percent of the heifers had fetopelvic disproportion and none of them had uterine torsion. For multiparous cows, the odds of having a uterine torsion with fetopelvic disproportion were approximately 11 times lower than the odds without fetopelvic disproportion. Excessive fetal weight may be a predisposing factor for uterine torsion, but small size of the dam could be a protective factor.

The odds of a uterine torsion were higher in heifers that had received calcium than in those that had not. However, milk fever is rare in primiparous animals, and only 2 of the 16 heifers that received calcium after a dystocia had clinical signs of milk fever. The other 14 animals probably received calcium because the owner or the veterinarian perceived that the animal was not looking well, and heifers that suffered from a uterine torsion might have been looking worse than heifers with a control dystocia. We were not able to show an association between milk fever and uterine torsion in multiparous cows.

In some textbooks, it is mentionned that uterine torsions are more frequent in cows confined in stables for long periods, and it is hypothesized that insufficient exercise leads to slackness of the abdominal musculature, which may increase the risk of uterine torsion (2,10), in which case, where cows go outside, uterine torsions would be more common at the end of winter, after months of confinement. On the other hand, it is reported in the same textbooks that in most cases, uterine torsion is possibly precipitated by a mechanical factor such as a fall, walking up a steep slope, or being pushed by another cow, all of which are more likely to happen when cows are out on pasture or in a free-stall barn rather than in a tie-stall barn. Our data did not enable us to show a significant effect of season on the incidence of uterine torsion. Few cows in our study had access to pasture, and most cows housed in a tie-stall barn were stabled all year round, so more uterine torsions were not expected at the end of the winter due to slackness in the abdominal muscles. The odds of a uterine torsion were lower in primiparous cows that calved alone in a pen than in a tie-stall. Dairy heifers are often raised in loose housing and then moved to the tie-stall barn just before calving. Some of these animals may have difficulty lying down and rising up in a tie-stall, if they are not accustomed to it, thereby increasing the chance of slipping or falling, and increasing the risk of uterine torsion. Even for animals that were tied before calving, the increased weight of the fetus in late gestation, as well as the increase in udder size in the days before calving, could make it more difficult for them to get up and down in their stall. We did not find any significant association between calving location of cows and uterine torsion, although cows that were housed in a group tended to be more at risk for uterine torsion than were cows that calved in a tie-stall barn. This could reflect the fact that cows in group housing can be bumped on the side by another cow, which is obviously not the case in a tie-stall barn.

There were 3 main limitations to our study. The first 2 are inherent to the study design: uterine torsions were compared with control dystocias instead of normal calvings. This was done for a practical reason: normal calvings are usually not attended by veterinarians. Obtaining detailed information on all normal calvings for all the farms in the study would have been nearly impossible. A matched case-control study design could have been used, but that would have required more input from the clients than could reasonably be expected: they would have had to attend the next normal calving of a cow of the same parity, and fill in a detailed questionnaire for that particular cow. When interpreting the results of such a case-case study, one needs to be aware of the 2 problems that can arise from this design (19). First, the “control-cases” might not be representative of exposures in the population from which they originated. Therefore, the comparisons between the cases and controls cannot be used to make inferences about the general population. For example, an increase in control-cases associated with any study factors (more fetomaternal size mismatch for heifers) can introduce an association of that factor with uterine torsion, even if the true incidence in the population is not affected by the factor. Also, the exposures that are associated with both comparison groups will not be identified, or might be underestimated. The third limitation of our study is the relatively small number of animals enrolled (especially case animals) and the fact that some combinations of the variables were nonexistent when the data were stratified by parity, making it impossible to use a multivariable model.