7.3. Milk yield

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

72 Ruminants - The Husbandry, Economic and Health Aspects

The mortality rate is four times higher in twin-born calves due to an increased dystocia and a

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 single-

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

reduced gestation length; furthermore, twin calves had a lower birth weight [6].

among triplets.

born calves [14].

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, respectively), which was in good concordance with results of another study [40]. In contrary to these reports, mothers of twins have been shown to be superior to mothers of single calves in terms of milk yield in a third investigation [30].

of all occurrences, heifers are not suitable for breeding because of freemartinism [67], causing infertility in the female calf born with a male twin. As fertile heifer calves are far more valuable

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

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

75

It has been shown [14] that multiple pregnancies considerably decreased the chance of survival until the next calving and increased the culling rate. When analyzing the reasons for culling cows from the herds, it was found that multiple births gave rise to a greater proportion of cows culled due to udder diseases, infertility, reproductive diseases, old age, metabolic and gastro-

The lifespan of 3581 cows that had never had twins and 386 cows that had twins at least once was examined [38]. On average, the total lifespan was 68 months. Whether or not the cows had twins had a significant impact on their lifespan (p < 0.001). The cows that never had twins reached on average 60 months (roughly 5 and a half years old), and cows that had at least one set of twins reached on average 76 months old (roughly 6 and a half years). The difference in life expectancy between these two groups was 15.8 months (a year and 3 months approxi-

Losses due to the higher incidence of abortions, ketosis (subclinical or clinical), reduced birth weight or stillbirths, mastitis, and problems related to dystocia are all more common in twin calvings. Multiparous cows with dead twins produced less milk than cows with live twins. Compared with dams with singleton birth, cows with twins were 0.78 times as likely to conceive and 1.42 times as likely to die or be culled. Cows with dead twins also had increased

This increased cost in the case of multiple births adds up to 40% per cow [64]. In the case of twinning, there is an elevated incidence of pregnancy loss and reduced milk yield along with

Total losses were on average \$171 – \$63 = \$108 per twin birth. Realistic changes in input variables could not change this negative outcome to a positive result. Therefore, it was concluded that it is not profitable to select to increase the number of twins in dairy cattle [68].

Dairy cattle breeders could develop strategies to manage twinning based, for example, on ultrasonic examination of corpus luteum and its direct use in selection. While it is obvious when cows give birth to twins, it is much less obvious when cows that would have twins suffer embryonic reduction of one of their embryos. An examination [69] of 770 pregnancies showed 13 cows with 3 or more corpora lutea and 757 with 2 corpora lutea. Of those with two corpora lutea, 464 were carrying twins and 293 were carrying single calves. Subsequently, 69 (23.5%) of the single pregnancies and 132 (28.4%) of the twin pregnancies lost one of the corpora lutea or one of the embryos before day 60. Of the 132 twin pregnancies, 34 (25.8%) lost a corpus luteum together with an embryo (corpus luteum reduction occurred in the ovary on the same side as the horn of the uterus that underwent embryo reduction). As dead embryos and their debris

than bull calves, this is an issue on dairy farms.

intestinal diseases, and diseases of the locomotor system.

7.6. Culling reasons and life span

7.7. Economic outcome and selection

time to conception, compared with live twins [63].

the number of fertile heifers' required for herd replacement [15].

mately).
