AABArchives Animal BreedingAABArch. Anim. Breed.2363-9822Copernicus PublicationsGöttingen, Germany10.5194/aab-64-83-2021Determining the factors affecting the gestational length in sheepDetermining the factors affecting the gestational length in sheepTozlu CelikHilalhilalcelik@odu.edu.trhttps://orcid.org/0000-0002-9744-7719AslanFatih AhmetKasko ArıcıYelizKahveciMetehan Eserhttps://orcid.org/0000-0002-3910-4195KiperİbrahimDepartment of Food Processing, Ulubey Vocational School, Ordu University, 52850 Ulubey, Ordu, TurkeyDepartment of Chemical and Chemical Processing Technologies, Ulubey Vocational School, Ordu University, 52850 Ulubey, Ordu, TurkeyDepartment of Basic Medical Sciences, Faculty of Medicine, Ordu University, 52000 Altınordu, Ordu, TurkeyVeterinary Department, Ulubey Vocational School, Ordu University, 52850 Ulubey, Ordu, TurkeyOrdu Sheep and Goat Breeders' Association, 52000 Altınordu, Ordu, Turkey
This research aimed to determine the effects of body weight, the body condition score
(BCS), body measurements, birth type (single offspring or twin birth), birth weight and sex on the gestational length in sheep
(n=111). Karayaka sheep raised on a private farm were used in the study. Progeny yield
characteristics in sheep were also determined (n=139). Estrus was monitored daily using teaser
rams from August to September 2016. According to our findings, the pregnancy rate, infertility rate,
fecundity, and twin and single birth rates were 93.52 %, 6.48 %, 93.52 %, 14.62 % and
85.38 % respectively. The effect of age on the BCS in sheep at mating was found to be significant
(P<0.05): BCS decreased as age increased. It was determined that there was a positive
association between the BCS and live weight during the mating period (P<0.001). The chest
circumference, front shin circumference and body length were found to be higher in sheep with a BCS ≥4.5 at mating time (P<0.01). The middle rump width was significantly affected by the BCS
(P<0.001). In this study, the lowest and highest gestational lengths were found to be 148.90
and 151.41 d respectively. The gestational length in sheep was
not found to be affected by age, the BCS, body measurements, sex or birth type (P>0.05); however, it was observed that the gestational lengths for male offspring and single offspring (non-multiple births) were longer. In
addition, it was detected that the gestational length was different in sheep with a BCS ≥4.5. The time spent in the womb is important with respect to obtaining a healthy lamb. For
profitable production, a BCS of between 2.5 and 4 is recommended in sheep. It
is thought that the use of body condition scoring, which is easy information for the breeder to utilize, will
have a positive effect on determining the bodily reserves of sheep and the reproductive efficiency as well as on
obtaining a healthy lamb. More studies on the gestational length in sheep are required.
Introduction
Karayaka sheep are usually bred in the Black Sea
region (Ordu, Giresun, Samsun, Sinop and Tokat provinces) and constitute 4.61 % of the total sheep population in Turkey (Turkish Statistical Institute, 2020). Karayaka
sheep are a breed with a low milk and offspring yield, a fine tail and a coarse mixed fleece. They are known to
have good-quality meat. In Karayaka sheep, the number of lambs at birth is 1.05 (Akcapınar
et al., 2002). For this reason, it is beneficial for breeders to increase the fertility rate in this breed via various breeding
methods (Cam et al., 2017). The period spend in the uterus
has an important effect on the development of the offspring. In Karayaka sheep, the pregnancy rate,
return rate, twinning rate and triplet rate of females from twin births mated with rams from twin births were determined
to be 100, 16.22, 52.25 and 3.60 respectively. Thus, the selective breeding of twin animals in Karayaka sheep may increase the
rate of twinning (Cam et al., 2017).
The body condition score (BCS) can vary depending on the environment and husbandry conditions
(Özdemir, 2008). The gestational length in sheep is influenced by the interaction of maternal
age, offspring sex, genotype, nutrition, environmental temperature, year, lambing season,
location of the enterprise and geographical location. It is stated that approximately two-thirds of
the variation seen among sheep breeds in terms of gestational length is caused by the genotype of
the fetus (Ates et al., 2003; Ahmad and Khan, 2008; Cedden, 2002; Koyuncu et al., 2001; Koyuncu and
Duru, 2003; Odabaşıoğlu et al., 1996). The average gestational length of Kari sheep in
Pakistan has been determined to be 110.2±1.10 d. It is stated that this situation is
caused by the genetic structure (Ahmad and Khan, 2008). The mean gestational length was found to be
150.6±0.64 d in Nigerian sheep and their crosses, and it was not affected by sex
or birth type (single offspring or twin birth; P>0.05). During pregnancy, nutrition, BCS, body measurements and body weight
affect the offspring, as does the number of ovarian cells in the mid-gestational period, although these
effects may decrease at the end of pregnancy (Asmad et al., 2015). It has been reported that the
gestational length was shorter in fertile breeds (Öztürk and Aktaş, 1996). A longer
gestational length was also found to increase the lamb birth weight (Ates et al., 2003). It was determined that the
gestational length in Kari sheep in Pakistan can vary between 3 and 5 months (Ahmad and Khan,
2008). It has been stated that the pregnancy rate is low in overweight sheep, whereas the abortion rate is high
(Staykova et al., 2013). The gestational length in Nigerian sheep was determined to be 151.6 d for
male offspring, 150.0 d for female offspring, 150.5 d for single offspring births, 151.0 d for twin births
and 150.6 d for the herd average (Iyiola-Tunji et al., 2010). It was determined that lambs with
high birth weights spent more time in the uterus (Öztürk and Aktaş, 1996).
The BCS is a method that can be easily applied by the breeder and gives information on the nutritional status of the
animals. At the same time, it is a system based on the grading of the differences that can be
observed in the fattening of the organism with the help of identifiable physical properties. Sheep
in good condition during the mating period show a higher value in terms of reproductive
efficiency. Determining the BCS of the herd and bringing it to an optimum level during the
mating period in sheep increases the number of lambs. The body weight and BCS at the time of mating have
positive effects on some reproductive traits, such as ovulation rate and the number of lambs born (Atti
et al., 2001; Vatankhah et al., 2012; Kandemir et al., 2013; Van Der Linden et al., 2014). At the
same time, the mother's bodily reserves have an effect on the lamb's feeding and on the mother's mammary glands after
birth (Van Der Linden et al., 2014). In Karya-type sheep, the average respective BCS and body weight values during the
mating period were found to be 1.85±0.06 and 42.95±0.66kg (Özdemir,
2008). The BCS in Caucasian Merino sheep was affected by the physiological condition. Pregnancy rates
were found to be higher in animals with a BCS between 2.5 and 3.5, and the abortion rate was higher in those with a BCS < 2 (Staykova et al., 2013). Fetal development was negatively affected in sheep that were malnourished
at the beginning of pregnancy, animals with a low body weight and animals carrying twin offspring (Asmad et al.,
2015). A BCS of between 2.5 and 3.5 during the mating period positively
affected the lambing rate (Staykova et al., 2013). Specifically, more efficient use of limited feed
resources, via utilization of the BCS, during the breeding season can increase the total income by increasing the
reproductive yield and the number of lambs obtained (Yılmaz et al., 2011; Sejian et al.,
2015). The BCS differs among diverse breeds and ages in sheep (Türkyılmaz et al., 2017). It is also
an important indicator of the milk yield of lactating ewes after birth and,
therefore, of adequate nutrition of the offspring. Nutrition during pregnancy is necessary for
both the development of the offspring and the needs of the mother. It is known that fertility in
Karayaka sheep is low; however, it can be improved by controlling environmental effects and by undertaking selective breeding studies
(Cam et al., 2017).
In this study, the effects of age, BCS, body weight and body measurements, birth weight, sex,
and birth type on the gestational length were examined. It is thought that the results obtained will contribute to expanding upon existing knowledge in the literature.
Material and methods
This study was carried out in accordance with the ethical principles and rules of decision number 1 of the
Ordu University Animal Experiments Local Ethics Committee dated 27 January 2016.
Data set
The research was carried out on Karayaka sheep raised on a private farm in Bolaman Gölbaşı village in the Fatsa district of Ordu. Animals were selected for the study, their ear tag
numbers and ages were recorded, and their reproductive yield records were evaluated
(n=139). Data were analysed for the factors (body condition score, age, live weight, body
measurements, birth type, sex and birth weight) affecting the gestational length of 111 pregnant ewes, according to the BCS values obtained during the mating period.
Animal management
The sheep were grazed in the hazelnut garden in the village of Bolaman and were taken to Çambaşı Plateau, Sinanlıobas, Ordu, as the weather got warmer. The animals were
grazed on the pasture between 06:00 and 13:00 LT and between 14:00 and 20:00 LT. During the
pregnancy period, approximately 600 g of a corn, barley and wheat mixture was given to each
female per day. After the sheep returned from the plateau, they were again grazed in the hazelnut
garden. The breeder did not intervene in the animals' nutrition. Lambs were weaned on the 90th
day after birth.
Mating
The mating period took place between 2 August and 9 September 2016. Four weeks before the mating
period, the sheep were weighed using an animal scale with a sensitivity of 100 g, and their
live weight was determined. Body condition scores and body measurements were also taken. Their body
condition was scored using the 0.5 scale (1 to 5 scale) defined by Russel et al. (1969). The ewes
were divided into four groups based on their BCSs: BCS≤2.5 (n=27),
BCS between 2.5 and 3.49 (n=42), BCS between 3.5 and 4.49 (n=32) and BCS≥4.5
(n=10). During the mating period, mating dates and the ear tag numbers and ages of the females
and rams were recorded. During the same period, certain body measurements were taken. The
gestational length was calculated by recording the mating dates of the ewes and the birth
dates of the lambs. Abortion was not detected during pregnancy. The lambs were weighed and ear-tagged
after birth. The birth type and sex of the lambs were recorded.
Statistical analysis
The data were tested for normality using a Kolmogorov–Smirnov test and for homogeneity of variance
using a Levene's test prior to the analyses. Categorical variables were analysed using the Pearson
χ2 test. Continuous variables were analysed with an independent sample t test or one-way ANOVA
followed by a Tukey post hoc test.
Results
Data on the reproductive efficiency characteristics of Karayaka sheep from this study are given in
Table 1. According to the findings, the pregnancy rate, infertility rate, fecundity, twinning rate,
single birth rate and survival rate of lambs during the weaning period were 93.52 %, 6.48 %,
93.52 %, 14.62 %, 85.38 % and 83.85 % respectively. The litter size at
birth and weaning were 1.00 and 0.78 respectively (Table 1).
Descriptive information on the reproductive traits the Karayaka sheep from this study.
TraitsnNumber of sheep during the mating period139Pregnant sheep130Pregnancy rate93.52 %Infertile sheep9Infertility rate6.48 %Aborted pregnancies0Lambs born130Fecundity93.52 %Number of twin births19Twinning rate14.62 %Number of single births111Single birth rate85.38 %Number of lambs born from each ewe that mated0.94Litter size at birth1.00Stillbirths6Number of lambs weaned109Percentage of lambs that survived the weaning period83.85 %Litter size at weaning0.78Number of weaned lambs per ewe that gave birth0.84
The results obtained during the mating period are given in Table 2. The effect of age on the BCS in
sheep was found to be significant (P<0.05): the BCS decreased as age increased. The increase in
sheep age caused a decrease in the BCS and live weight (LW). It was determined that there was a positive
association between the BCS and LW during the mating period (P<0.001). It was also determined that the
chest circumference (CC), front shin circumference (FSC) and body length (BL) were larger in females
with a BCS ≥4.5 during the mating period, and the effect of the BCS on the CC, FSC and BL was found to be
significant (P<0.01). The withers height (WH) and rump height (RH) were not affected by the BCS
(P>0.05). However, the middle rump width (MRW) was significantly affected by the BCS (P<0.001). The middle
rump widths of sheep with a BCS between 3.5 and 4.5 and >4.5 were different from sheep with a
BCS<2.5 and between 2.5 and 3.49. As the BCS increased, the middle rump widths increased. The gestational length was not
affected by BCS changes in Karayaka sheep (P>0.05). In this research, the lowest gestational length
was found to be 148.90 d, whereas the highest was found to be 151.41 d. It was determined that the single
birth rate of Karayaka sheep was higher than the twin birth rate. It was also
found that more than half of the offspring born were female. The lamb birth weight was not affected by
BCS during the mating period (Table 2).
Descriptive statistics and comparison results for breeding season variables in terms of the four BCS groups. The results are given as the mean ± SD (standard deviation).
VariablesBCS groups P<2.5 (n=27)2.5–3.49 (n=42)3.5–4.49 (n=32)≥4.5 (n=10)Sheep age4.44±2.06a3.67±1.46ab3.19±1.42b3.80±1.14ab0.031*Sheep body weight at mating54.46±5.10c57.24±4.61bc58.90±5.18b65.07±4.88a0.000***Chest circumference95.19±4.06c97.24±4.11bc98.34±4.52ab101.50±4.22a0.001**Front shin circumference12.00±0.62b12.29±0.67b12.22±0.79b13.00±1.05a0.005**Middle rump width23.67±1.39b24.38±1.03b25.22±1.50a26.30±1.70a0.000***Body length83.85±2.63b84.38±2.70b85.06±2.73ab87.30±2.26a0.005**Withers height67.52±2.7467.10±2.3267.09±2.1567.30±2.540.889NSRump height65.30±1.6464.86±2.5665.66±3.0865.70±1.830.528NSGestational length151.41±3.50151.26±5.46150.81±4.87148.90±6.280.548NSLamb birth weight4.14±0.884.10±0.674.03±0.544.44±0.520.504NS
* Statistically significant at the P<0.05 level. ** Statistically significant at the P<0.01 level. *** Statistically significant at the P<0.001 level. NS Statistically not significant (P>0.05). Means that do not share a letter are significantly different (Tukey test, P<0.05).
As seen in Table 3, the regression coefficients of all variables were not significant. Furthermore, the
regression equation was not found to be significant. The R2 value of the is very low. In this study, BCS, age, live
weight during the mating period, the various body measurements (chest circumference, middle rump width,
body length, wither height, rump height and front shin circumference), lamb birth weight and sex did not show a significant impact
on the gestational length of Karayaka sheep.
Regression coefficients for gestational length. SE refers to standard error, and VIF refers to the variance inflation factor.
Gender and birth type also did not affect the gestational length in this sheep breed. However, it was
observed that the gestational lengths of male offspring and animals from single offspring births were longer (Fig. 1). Gestational length was
determined as 151.11 d for male offspring, 150.81 d for female offspring (P=0.747),
151.04 d for single offspring (non-multiple births) and 150.53 d for twins (P=0.680).
Interval plot showing the confidence interval of the gestational length for sheep with respect to the
sex and birth type.
The distribution of the gestational length with respect to the BCS is shown in Fig. 2. It was
determined that BCS during the mating period did not affect the gestational length. However, as seen in
Fig. 2, the lowest gestational length was seen in animals with a BCS ≥4.5. With respect to the four BCS
groups, the gestational lengths were determined to be 151.4 d (BCS < 2.5),
151.3 d (BCS between 2.5 and 3.49), 150.8 d (BCS between 3.5 and 4.49) and
148.9 d (BCS≥4.5). This result shows that excessive fat during the
mating period may affect the gestational length in Karayaka sheep.
Individual value plot of gestational length for sheep in the four BCS groups.
Discussion
The finding that sex and birth type have no effect on the gestational length in Karayaka sheep is
consistent with the study by Asmad et al. (2015). However, the findings of this study did not concur with Cam et al. (2018), who reported that the length of gestation was positively affected
by the live weight and BCS of sheep. This divergence may be due to individual differences stemming from the farm, region and animals used in the studies.
In the province of Tokat, the rate of infertility, the birth rate, the twinning rate, the abortion rate and the number
of lambs of per ram and per ewe in Karayaka sheep were 22.7 %, 73.0 %, 3.3 %,
2.1 %, 0.75 and 1.03 respectively (Belgüzar, 2011). These values diverge
from the reports by Belgüzar (2011) and Cam et al. (2017), which may be due to
regional differences and breeding practices.
The findings in this study that the gestational length in sheep was not affected by age, BCS,
body measurements, sex, birth weight or birth type (P>0.05) were also different from what has been reported in many other studies in the literature (Ates et al., 2003;
Ahmad and Khan, 2008; Cedden, 2002; Koyuncu et al., 2001; Koyuncu and Duru, 2003; Odabaşıoğlu et al., 1996). The average gestational length of Karacabey Merino sheep was found to be
150.97±0.054 d. The duration of gestation was significantly affected (P<0.01) by
the year of gestation, the sex of the lamb and the mother's age, and the birth type was
significant (P<0.05). The gestational period of 6-year-old mothers was found to be longer than
the gestational length of 2-, 3-, 4- and 5-year-old mothers. The phenotypic correlation coefficient
between birth weight and gestational length was reported to be 0.077±0.028 (P<0.05) (Koyuncu
and Duru, 2003). The results of this study differ from those of Koyuncu and Duru (2003), and this difference may stem from genotype,
business, and regional differences.
The mean gestational length was 150.273±0.240 d in Morkaraman sheep and
148.604±0.300 d in crosses. The effect of birth type, maternal age and sex on the
duration of pregnancy was found to be insignificant (P>0.05) (Ateş et al., 2003). The mean
gestational period of Konya Merino sheep was found to be 152.7±0.25 d, and year, age of the
female, birth type and birth weight of the lamb affected the gestational length. It was determined
that the gestational length (153.7±0.73) was longer for triple births than for twins, and the gestational length for twin births
(152.8±0.16) was longer than for single births (151.6±0.22) (Öztürk and Aktaş,
1996). These results are similar to those reported by Ates et al. (2003), Öztürk and Aktaş (1996),
Iyiola-Tunji et al. (2010), and Öztürk and Aktaş (1996).
The effect of age on the BCS was significant (P<0.05) in Karayaka sheep in this study: the BCS decreased with
increasing age. This finding is not compatible with the publication by Türkyılmaz et al. (2017). It
has been reported that Karayaka sheep with a BCS between 2.5 and 4.0 during the mating period have high
reproductive performance (Cam et al., 2018), and our findings concur. The result obtained here regarding the BCS of sheep during the mating period was higher
than the value reported by Özdemir (2008). In our study, it was found that the BCS was related to the body weight
and chest circumference of animals, which was consistent with the findings of Worku (2019). The chest circumference
and the BCS can provide information about the bodily reserves available to the sheep. This information is then easily
utilized by the breeder. In Karayaka sheep, the findings regarding the BCS obtained before the mating period are
similar to those reported by Thompson and Meyer (1994).
The finding in this study that the effects of the
type of birth, the mother's age and the sex on the length of pregnancy were insignificant is consistent with the results of Ates et al. (2003).
Differences between the literature and the results of this study may be due to genotype, management,
animal nutrition, breeders' practices and regional differences.
Conclusions
It was determined that the length of pregnancy did not change according to physical
characteristics. However, it was observed that the gestational lengths of male and single offspring births were
longer. The lowest gestational length was seen in animals with a BCS ≥4.5. It was determined that
the BCS of the Karayaka sheep during the mating period was between 2.5 and 4.5. This result
shows that the bodily reserves are good. Thus, it is beneficial if the BCS of the sheep during the
mating period is between 2.5 and 4. Excessive fattening of sheep may cause difficulty during birth. It is
recommended that breeders apply body condition scoring regularly to ensure efficient use of feed sources in sheep
breeding. Controlling the BCS, which is an indicator of the bodily reserves of the sheep during the mating
period, can prevent reproductive efficiency problems that may arise from nutritional deficiencies.
Data availability
The data are available from the corresponding author upon request.
Author contributions
HTC and FAA were responsible for the study design. HTC, FAA, MEK and İK collected the data. YKA performed data analysis. HTC wrote the paper. All authors read and approved the final article.
Competing interests
The authors declare that they have no conflict of interest.
Acknowledgements
The authors would like to thank the ODU BAP unit for supplying the equipment used in the experiment (AR-1629).
Review statement
This paper was edited by Steffen Maak and reviewed by three anonymous referees.
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