7.2. Dystocia and perinatal mortality

Dystocia means a difficult or abnormal delivery that occurs more frequently with twin births than with single births. In any calving, dystocia can be due to fetopelvic disproportion, an oversized calf or a dam with incomplete development or incomplete cervical dilation or due to abnormal presentation of the calf. However, twin calvings have the added complication of both calves entering the birth canal at the same time. These are usually dealt with by some sort of intervention.

Multiple births can cause difficulties at parturition, if parts of more than one fetus enter the birth canal at the same time [42–48]. These abnormalities can occur when two of the fetuses are released from the uterine horns at the same time and meet in front of the pelvis [49].

The symptoms of dystocia are highly variable, since each of the fetuses may be presenting in the anterior or posterior positions with variable positioning of the head and legs [50]. Therefore, these presentation anomalies occur more regularly in twin births than in single births [28, 42, 43, 45, 46, 51–53].

The occurrence of posterior presentation in twin birth is approximately four times higher (10.7%) than in single births (2.5%) [54]. Abnormal presentation was the cause of dystocia in 15.3% of the singletons and 77.8% of the twins. However, this can be easily corrected in twins due to their relatively low body weight, but nevertheless these factors still can result in stillbirths when there is a lack of observation during parturition. Obstetrical intervention was implemented in 42.2% of twin births and 20.4% of single births [28].

Some studies in the USA have demonstrated that the incidence of calving difficulty has decreased within the last number of years [26], whereas conflicting studies have shown the opposite, that it has not changed [55]. In this period of time, a gradual increase of twinning and periparturient mortality was detected [26, 55].

An analysis of the relationship between multiple births and dystocia [56] data was drawn from the SYMLEK database and provided information on 148,385 calvings of Polish Black-and-White Holstein Friesian cows. The animals used for the study first calved in 2006 and were in use or had been culled by the end of 2012. All the data were classified in accordance with the SYMLEK database. The calving ease was classified as unassisted (natural, without human intervention), easy, difficult (using much more force than normal), very difficult (surgical procedure, injury to the cow or calf, embryotomy), or cesarean section. Calf mortality was classified as: live calf (normal live calf born), dead calf (stillborn calf or calf having died within 24 hours after birth), and the perinatal mortality. The goal is to investigate the relationship between the number of fetuses and gender of the fetuses on the outcome of the birth. The study found in the analyzed population there were 2.11% twin pregnancies and just 0.01% triplet pregnancies of the calves born. The proportion of unassisted parturitions was around 31% for single and twin births and only 7% when triplets were born. The proportion of difficult births increased from 4.3 to 28.6% with the increasing number of fetuses. Very difficult births and cesarean sections were sporadic and occurred with similar frequency when single calves and twins were born. For single calvings out of a total number of 145,241 calvings, 31.14% were unassisted, 64.35% were easy, 4.30% were difficult, 0.15% were very difficult, and 0.05% required a cesarean section. For twin calvings out of a total number of 3130 calvings, 30.96% were unassisted, 63.67% were easy, 5.21% were difficult, 0.10% were very difficult, and 0.06% required a cesarean section. For triplet births out of a total number of 14, 7.14% were unassisted, 64.29% were easy, and 28.57 were difficult with no births described as very difficult or requiring a cesarean section. Analyzing the gender ratio, most single calves were bull calves. In twin calvings, opposite sex twins were the most common, with bull calves being the least frequent. Opposite-sex calves were most common among triplets.

when one of the calves was alive and the other was dead, heifers tended to survive more often. The proportionally small number of triplet calvings (only 14 cases) and the various gender combinations in triplets made the results difficult to interpret. Examination of the results confirms that bull calves were more likely to die perinatally than heifers, and multiple pregnancies increase calves' risk of perinatal mortality. The increased calving difficulty associated with multiple births majorly increases the risk of perinatal mortality in calves. In calvings classed as very difficult, the risk of calves being born dead or dying within 24 hours after birth

Bulls + heifers 8 12.5 75.00 12.5 0 0

n Unassisted Easy Difficult Very difficult Cesarean section

Twin Calving and Its Connection to Other Economically Important Traits in Dairy Cattle

http://dx.doi.org/10.5772/intechopen.72905

73

Twin pregnancies have a higher risk of fetal death or abortion in the final months of gestation [57, 58]. The limited energy reserves and vitality of twin calves during and after pregnancy are seen as the primary reasons for the elevated proportion of stillbirths [59, 60]. The shorter

This is preventable by supplying a targeted diet with adequate nutrients to the dam in late pregnancy and also drying cows off early when twins are expected. The rate of stillbirth in twin calves was 19.0% and 12.9% and in single calves 5.0% and 4.1% [5, 28, 61]. Two different types of embryonic death can be distinguished [18]: "independent loss" describes the phase prior to implantation and in this phase, losing one or more embryos does not affect the rest, whereas in "dependent loss" the embryo dies after implantation, causing a loss of all other

At parturition, twin calves are at a higher risk of hypoxia if the umbilical cord becomes

A study in America [63] showed the effect of twin-birth calving on milk production. Primiparous and multiparous cows with singletons produced more milk than cows with live twins or at least 1 dead twin (primiparous, 33.1 vs. 31.9 vs. 31.2 l; multiparous, 36.5 vs. 35.7 vs. 35.0 l,

increased 10-fold, independent of gender, in relation to unassisted calving.

Table 4. Calving difficulty by number and gender of calves born [56].

Type of birth Sex of calf Parturition

Single Heifer 69,789 34.9 61.88 3.12 0.09 0.02

Twin Heifer + heifer 872 28.78 67.2 3.9 0.11 0 χ<sup>2</sup> = 13.54 Bull + bull 841 30.68 64.09 5.23 0 0

Triplet 3 Heifers 3 0 33.33 66.67 0 0 χ<sup>2</sup> = 3.61 3 Bulls 3 0 66.67 33.33 0 0

Bull 75,452 27.67 66.63 5.4 0.22 0.09

Heifer + bull 1417 32.46 71.26 6 0.14 0.14

intrauterine period is also thought to be a reason for the lower birth weight.

embryos due to the placental anastomosis.

entangled in a leg of the other fetus [62].

7.3. Milk yield

χ<sup>2</sup> = 1243.78 p < 0.01

The mortality rate is four times higher in twin-born calves due to an increased dystocia and a reduced gestation length; furthermore, twin calves had a lower birth weight [6].

Perinatal mortality is also a major factor related to parturition. Twinning-associated perinatal mortality was three times higher than that of pluriparous [51]. However, the number of calves born alive was higher among mothers of twins and triplets compared to mothers of singleborn calves [14].

Analysis of the results (Table 4) shows that heifer calves tend to be born more easily than bull calves; however, this relationship only was significant in single births (P ≤ 0.01). In twin births, when two heifers were born, they tended to be easier, whereas difficult births, very difficult births, and cesarean sections tended to be more frequent when a bull and a heifer calf were born. The results show a higher perinatal mortality in twins; however, even including the losses, on average 1.81 live calves were produced from twin calvings compared to only 0.92 from single calvings. When analyzing calf mortality's relationship to gender, in single calvings, the number of bulls and heifers born live was similar (46%). However, the percentage of stillborn bull calves was over 3 times that of heifer calves. Examination of twin births showed that the proportion of both calves being live-born was highest (39.84%) when twins were of opposite sex and lowest (22.81%) when twin bulls were born. Perinatal mortality tended to be highest (3.19%) when twin bull calves were born and over twice as low when twin heifer calves were born. When opposite gender twins were born, perinatal mortality was 2.65%, and


Table 4. Calving difficulty by number and gender of calves born [56].

when one of the calves was alive and the other was dead, heifers tended to survive more often. The proportionally small number of triplet calvings (only 14 cases) and the various gender combinations in triplets made the results difficult to interpret. Examination of the results confirms that bull calves were more likely to die perinatally than heifers, and multiple pregnancies increase calves' risk of perinatal mortality. The increased calving difficulty associated with multiple births majorly increases the risk of perinatal mortality in calves. In calvings classed as very difficult, the risk of calves being born dead or dying within 24 hours after birth increased 10-fold, independent of gender, in relation to unassisted calving.

Twin pregnancies have a higher risk of fetal death or abortion in the final months of gestation [57, 58]. The limited energy reserves and vitality of twin calves during and after pregnancy are seen as the primary reasons for the elevated proportion of stillbirths [59, 60]. The shorter intrauterine period is also thought to be a reason for the lower birth weight.

This is preventable by supplying a targeted diet with adequate nutrients to the dam in late pregnancy and also drying cows off early when twins are expected. The rate of stillbirth in twin calves was 19.0% and 12.9% and in single calves 5.0% and 4.1% [5, 28, 61]. Two different types of embryonic death can be distinguished [18]: "independent loss" describes the phase prior to implantation and in this phase, losing one or more embryos does not affect the rest, whereas in "dependent loss" the embryo dies after implantation, causing a loss of all other embryos due to the placental anastomosis.

At parturition, twin calves are at a higher risk of hypoxia if the umbilical cord becomes entangled in a leg of the other fetus [62].
