Chapter 46 Maarten Drost College of Veterinary Medicine, University of Florida, Gainesville, Florida, USA The term “dystocia” means difficult birth. The economic impact of calving difficulties is significantly associated with increased morbidity and mortality of newborn calves, as well as the subsequent fertility of the dam. The etiology can be fetal or maternal. Early recognition of the delay in the calving process and intervention can ameliorate the economic impact. In a study conducted on three Colorado dairy farms, it was reported that 51.2% of first-calf heifers required assistance compared with 29.4% of pluriparous cows.1 Risks were greater for bull calves than for heifer calves, and for twins than singletons. Images of the various causes, anatomic relationships, and procedures are shown in this chapter and can also be viewed in the Bovine Reproduction Guide.2 The most common cause of dystocia is fetopelvic disproportion, when the fetus is too large and/or the maternal pelvis is too small. Other fetal causes are abnormal presentation, position or posture of the fetus, multiple offspring, and occasionally fetal monsters. Nearly all calves (95%) are delivered in anterior presentation (head first) (Figure 46.1). Retention of the head (Figure 46.2) and/or a leg increases the diameter of the calf. This abnormal posture is frequently the result of a weak fetus or dead fetus that fails to participate in the delivery process by keeping its head and neck extended. Figure 46.1 The calf is in anterior longitudinal presentation (head first), dorsosacral position (right side up), and has normal posture (both limbs and head and neck extended). Figure 46.2 The calf is in anterior longitudinal presentation, dorsosacral position, with its head deviated to the left (of its own body). While only 5% of calves are born in posterior presentation (tail first), only about half of these are born spontaneously. The blunt conformation of the hindquarters with the thin legs (Figure 46.3) is not as effective in dilating the birth canal and in eliciting the Ferguson reflex (straining, as the cone-shaped head rests on the forelimbs). An added risk of a posterior presentation is the impingement of the umbilical cord on the pubic brim, cutting off the oxygen supply to the fetus. Figure 46.3 This calf is in a posterior longitudinal presentation (backwards), dorsosacral position, and normal posture (both legs extended). Twins or triplets, while not too large individually, can create a problem by presenting extremities of two calves at one time, with or without the presence of a head. Conceptus development following transfer of embryos from in vitro production (IVP) or somatic cell nucleus transfer (SCNT) in cattle may lead to early embryonic death, fetal death, or overgrown calves (type IV abnormal offspring syndrome). The latter has also been referred to as large offspring syndrome. Abnormal phenotypes resulting from IVP and SCNT embryos are stochastic in occurrence. Therefore IVF recipient cows should be monitored closely near term, and a cesarean section should be anticipated.3 Fetal monsters and anomalies, while rare, are frequently disproportionate. Incomplete twins like a bicephalic calf (Figure 46.4), or conjoined calves, a schistosomus reflexus calf (Figure 46.5), or calves with ankylosed limbs do not conform to the birth canal and will require a partial fetotomy to be delivered per vaginam. In the case of fetal anomalies such as hydrocephaly (Figure 46.6) the body of the calf may be small but the fluid-filled skull is too large to enter the pelvic canal. Diagnosis can be a challenge, and the simple solution is to drain the thin cartilaginous skull (Figure 46.7). Hydrocephalus results from an accumulation of excessive fluid in the ventricular system of the brain. Figure 46.4 Term fetal monster with two asymmetrical heads and a parasitic (extra) pelvic limb. Figure 46.5 Schistosomus reflexus in a newborn Holstein calf. The vertebral column has doubled back on itself and is ankylosed. Recommended method of delivery is by fetotomy. Figure 46.6 Hydrocephalus in a Jersey calf. This is uncommon in calves and can be inherited and congenital. This calf also did not have a tail nor an anus, and had a septal defect of the heart. Figure 46.7 Severe hydrocephalus in a Guernsey calf. Note the membrane-like calvarium. The cause of uterine torsion remains open to speculation. Review of the hospital records of 164 cases from 24 North American veterinary schools4 showed that there was no effect of season. It was found that large fetuses appear to predispose a cow to uterine torsion. Brown Swiss cows were at significantly higher risk (P < 0.01), while Hereford, Angus, and Jersey cows were at lower risk compared with Holstein-Friesian cows, the largest breed population. Most cows (81%) were at term. Vaginal delivery was possible after manual correction (20%) or rolling of the cow (18%). Cesarean section was performed immediately in 35% of the cases, after failed detorsion attempts in 7%, and due to failure of the cervix to dilate following successful correction of the torsion in 20%. Calf birthweight exceeded breed means in 89% of the cases, and a significantly greater proportion (63%) was male. Fetal survival rate was 24% (14% of dead fetuses were emphysematous), and the cow survival rate was 78% (10 were euthanized). The ventral attachment of the broad ligament is along the lesser curvature of the uterus, leaving the greater curvature free, and predisposing the cow to torsion of the uterus during the third trimester. In Bos indicus cattle, the ventral attachment changes from ventral at the body to dorsal at the tip of the horn. As cows get up on their hindlegs first, the (gravid) uterus is temporarily suspended. The broad ligament is looser and longer in pluriparous cows. The abdomen is capacious, especially when the rumen is relatively empty. Strong fetal movements and poor maternal muscle tone further contribute to torsion of the uterus. There is evidence of abdominal pain and discomfort due to stretching of the broad ligament. Other signs, such as anorexia, rumen stasis, constipation, and increased pulse and respiration, are usually present. The diagnosis is based on a history of advanced pregnancy. On transrectal palpation the orientation of the broad ligaments is distinctly altered; depending on whether the torsion is to the left or to the right, the respective broad ligament is pulled tightly across the uterus (Figure 46.8
Dystocia and Accidents of Gestation
Introduction
Fetal causes
Abnormal offspring syndrome
Fetal monsters and anomalies
Maternal causes
Torsion of the uterus
Predisposition
Clinical signs
Diagnosis
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