The analysis of factors affecting the calving difficulty in Slovak Spotted cattle

© Slovak University of Agriculture in Nitra Faculty of Agrobiology and Food Resources


Introduction
Reproduction makes the greatest contribution to genetic gain in cattle measured in economic units.Reproduction can be as much as four times more economically important than end-product trait.In Slovak Spotted cattle, the calving ease can be regarded as one of the most important reproduction traits from the point of view of its breeding objective Slovak Simmental Breeders Association, 2018).
The calving difficulty can be affected by various genetic and non-genetic factors.Non-genetic factors include the sex of calf, the age of dam, the parity, and the season of calving, nutrition condition of dam before calving, and environmental conditions.On the other hand, the length of gestation, breed type and maternal dimensions of the dam are considered as genetic factors (Záhradková, 2009).
An indicator that greatly affects animal welfare, the livestock economy and the amount of farm work is the calving difficulty.The calving difficulty is influenced by direct and maternal genetic components.Animal selection and breeding strategies can optimize the accuracy of genetic evaluations and correctly highlight the calving difficulty in the multi-tagged indexes that provide estimates of genetic parameters (Strapák et al., 2011).Slovak Spotted is autochthonous breed which belongs to the Simmental group of cattle.The Simmental is among the oldest and most widely distributed across of all breeds in the world.The Slovak spotted cattle as an important dual-purpose breed with a long tradition of breeding in Slovakia has excellent dairy as well as beef production.Slovak spotted was created by the crossbreeding of several breed (grey-brown Carpathian cattle, red Carpathian cattle and grey Steppe cattle) and it is recognized as one of autochthonous officially accepted as breed in 1958.This breed is typical of a good balance between milk and meat production and is characterized by a larger body frame, symmetrical body stature, good sex expression and good musculature.They are known for their gentle nature, impressive stature and excellent dairy qualities.(Kadlečík et al., 2013, Strapák et al., 2013, Shevhuzhev and Belik, 2017, Bogdányi et al., 1996).
The aim of this study was to analyse several genetic and non-genetic factors that can affect the calving difficulty in Slovak Spotted cattle and to observe their statistical significance.

Material and methods
A total of 417030 calving difficulty records from 174795 dams were used in this study.The calving difficulty records were collected from the first to the sixth lactation during the parturition course from 2001 to 2017.All of records were provided by the Breeding Services of the Slovak Republic, s. e.Any additional information including pedigree data were obtained in cooperation with the Slovak Simmental Breeders Association.The impact of factors affecting the calving difficulty was analysed by using General Linear Models (GLM) procedure implemented in SAS 9.3 (SAS Institute Inc., 2011).The effects of the herd, year of calving, the sex of a calf, breed type, month of calving, parity and sire were tested.To prevent inaccuracy, the effect of year, month and herd were analysed separately and not as combined "contemporary groups".The impact of the individual factor was analysed based on multifactor analysis of variance using following linear model: where: Yijklmn o -a calving difficulty HERD i -fixed effect of the herd (i = 802) YEAR j -fixed effect of a year of calving (j = 17) MONTH k -fixed effect of a month of calving (k = 12) SL l -fixed effect of the parity (l = 6) SEX m -fixed effect the sex of calf (m = 4) BREED n -fixed effect of the breed type (n = 3) SIRE o -fixed effect of the sire (o = 1852) e ijklmno -represents random effect of the residual

State code of the sex of calf
For identification of sex in the data were used specific codes from animal recording used in Slovak republic: code 1 (bulls); code 2 (heifers); code 16 (live -born but calf died); code 61 (stillbirth).

Analysis of a calving difficulty by years of calving
In this study overall 417030 calving difficulty records of Slovak Spotted cattle, collected during the season from 2001 to 2017, were evaluated.All of collected records for 174795 dams were complete.A total of 87% parturitions occurred easy, while only 0.03% required medical intervention.The value of determinant coefficient for the evaluated effect is R 2 = 3.5%.Table 1 shows the number of observations within each evaluated class of calving score.

Analysis of calving difficulty by the month of calving
Within the evaluation of calving difficulty, we found the highest occurrence for the spontaneous calving during months March and April (97.60%).The lowest occurrence was found for calving requiring the caesarean section during month May and June (0.06%).The value of determinant coefficient for the evaluated effect is R 2 = 0.03%.Table 2 shows the number of observations within each evaluated class of calving score by the month of calving.
By comparing the results from Soltner (1978) for Charolais cows occurred the calving ease during months March and April with value 76.06%.Vavrišínová (2007) observed for Charolais cows highest occurrence of difficult calving during months January, February, and from September to December.Results from Johanson and Berger (2003) suggest that calf born during winter has higher weight and then has higher possibility of occurrence difficult calving of up to 15%.

Analysis of calving difficulty by the breed type
The results demonstrated in this section match state of calving difficulty for three breed types.Minimal value of Slovak spotted cattle within group S0 is 87.5% in genotype, breed type S1 has proportion of Slovak spotted cattle 75-87.5% and breed type S2 has proportion of Slovak spotted cattle 50-75%.
From in total of 417030 records, 225832 came from group of S0 cows, 73709 from the group of S1 cows and 117483 records was from the group of S2 cows.Compared to other factors tested in this study, the analysis proved that the breed type is significant effect on calving difficulty.Each of analysed groups showed approximately the same level of calving difficulty.Differences between breed types were negligible, therefore the effect of breed type was not considered in the model equation.The value of determinant coefficient for the evaluated effect was R 2 = 0.002%.Table 3 shows the number of observations

Analysis of calving difficulty by the sex of calf
During the calving of cows and heifers was recorded almost the same frequency between the calving difficulty of live-born bulls 46.4% and live-born heifers 46.2%.The proportion of live-born calf but calf died was 2.2% and the proportion of stillbirth was 5.2%.The value of determinant coefficient for the evaluated effect is R 2 = 6.11%.Detailed results are presented in Table 4.
The results from Vavrišínová et al. (2007) reported the frequency of stillbirth for Charolais breed as follows: spontaneous calving 0.9%, easy calving 1.5%, and difficult calving 26.8% and for caesarean section 37.7%.Olson (2009) observed in his study the frequency of difficult calving for Holstein breed 19.98% and for Jersey breed 5.73%.Authors dealing with evaluation of calving difficulty (Vavrišínová et al., 2007;Olson, 2009) confirmed the highest frequency of difficult calving for sex with code 61 (stillbirth) and confirmed the easiest calving for sex with code 2 (heifers).

Analysis of calving difficulty by the parity
The multiparous cows were observed the highest occurrence of spontaneous calving.More frequent occurrence of dystocia has heifers.This is mainly because of their incomplete physical development and the reduced space of the pelvic.
The analysis proved that the most calving difficulty was occurred in the heifers.In the second lactation calving difficulty was noticeably reduced compared to the first lactation.The value of determinant coefficient for the evaluated effect is R 2 = 1.04%.Maternal effect was not part of the analysis.Detailed results presented in Table 5 shows the number of observations within each evaluated class of calving score by the sequence of lactation.
Results of Gaafar et al. (2010) showed the frequency of the difficult calving 7.7% stating that the age has an impact to the calving difficulty.Juozaitiene et al. ( 2017) observed for Lithuanian black and white dairy cows from 559,304 records that 48.75% of calving were evaluated as easy, 13.43% had slight problems, 34.71% of cows needed assistance, 2.87% needed considerable and 0.24% of cows had a difficult parturition, the majority difficult calvings were recorded in heifers or in cows between 6 and 8 lactations.Graesbøll et al. (2015) in his study monitored the influence of selected factors on milk production.One of the factors was the calving difficulty, where they observed that spontaneous calving has the consequence on the higher milk production and observed a significant impact of the difficulty of the first calving.Schaeffer ( 2003) studied the application of random regression models and one of the examined factors was the application to fertility in dairy cattle and proposed a model with parity, and he reported that the result of such an analysis would be a different genetic value for each animal for each parity.

Analysis of calving difficulty by the sire
The sire affects the length of gestation, calving weight and proportions of calf.Effect of sire is one of the possible sources of calving difficulty.Each sire is unique and can affect calving difficulty in different way.
In the dataset of Slovak spotted cattle were in total 1803 sires used in breeding.For the evaluation were used only 14 most important sires, which influenced the results.In the population of Slovak spotted cattle were the most used sire with the state register code HAT001 (Name: Xirno, line: Haxist) and the highest occurrence of difficult calving was observed by sire DIK005 (Name: GS Dionis, line: Dirteck).The value of determinant coefficient for the evaluated effect is R 2 = 5%.Table 6 shows the number of observations within each evaluated class of calving score by the sire.

Analysis of the all factors involved in calving difficulty
The influence of the selected factors was verified based on General Linear Models (GLM) under ANOVA.From the short review above, key finding emerges: the overall explanatory effect of all factors on the variability of the calving difficulty was highly statistically significant and reached the value of the determinant coefficient (R 2 = 25.5%).The determinant coefficient (R-square) of 0.254796 means that 25.5% variability of calving difficulty is explained by the effects examined, and the remaining 74.5% variability of calving difficulty can be explained by other reasons than the linearity between the variables.Cumulative value of determinant coefficient of all factors observed by one-way analysis was 30.282%.This leads us to conclusion that other interactions between factors should be considered in future analysis.

Conclusions
Based on the results of the analysis we recommend continuing to use the recording of calving difficulty for the purposes of evaluation of effect of sire on inheritance.The results confirm the statistical proficiency between calving difficulty and selected factors.For the Slovak spotted cattle were the most significant and highly statistically significant factors: the sex of calf (R 2 =

Table 1
Calving difficulty in the analysed population Strapák et al. (2011)9),Eaglen and Bijma (2009)reported for Holstein cows only 42.07%calving occurred spontaneous, easy calving 50.17%, difficult calving 7.46% and caesarean section 0.29%.Overall our findings are in accordance with findings reported byStrapák et al. (2011), he reported lower frequencies of easy calving of Slovak spotted cattle in 66.48% for heifers and cows had 75.46% of spontaneous calving, the frequencies of easy calving for heifers 20.1% and for cows 12.83% of Slovak spotted cattle.Ryba (2010) demonstrated similar values for all breeds of cattle within the range from 13.94% to 20.05%.Reached conclusion by Kotásek (2012) was the frequencies of easy calving for Holstein breed within the range from 15.62 to 17.34%, the frequencies of difficult calving for all breeds of cattle is little bit higher within the range from 2.05 to 3.36%, the frequencies of calving difficulty for Holstein breed within the range in compared with our results we have more proportion of spontaneous calving.Inoue et al. (2017)describes the calving difficulty for Japanese black cattle in five-point scale from 1,850 records: 1.No problem or unobserved http://www.acta.fapz.uniag.sk© Slovak University of Agriculture in Nitra Faculty of Agrobiology and Food Resources

Table 2
Frequencies of calving difficulty by the month of calving /www.acta.fapz.uniag.skwithin each evaluated class of calving score by the breed type.Due to assignation to the breed type is specific within each Herd book there is no direct comparison of the results.Breed type has usually low proportion on total variance, but significant as proved by our results.

Table 4
Frequencies of calving difficulty by the sex of calf

Table 6
Frequencies of calving difficulty by the sires