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Abstract [Objectives] The aim was to improve and stabilize the estrus synchronization of local sheep in Xinjiang during the breeding season and non-breeding season. [Methods] The data of estrus rate and estrus concentration time were analyzed by different hormone treatment programs. [Results] eding season， whether PMSC was used did not affect the estrus of sheep when sponge and PG were used （P>0.05）. Estrus was concentrated in 36-48 h after sponge plugs were removed， and the estrus rate in this period accounted for 74.19% of the total. In non-breeding season， the estrus rate in the sponge plug plus PGF treatment was only 56.12%， significantly lower than that （90.43%） in the sponge plug plus PG plus PMSG treatment （P<0.01）. The estrus was also concentrated in 36-48 h after sponge plugs were removed. The estrus rate at this stage was 67.42%， accounting for 82.8% of the total. In breeding season， the estrus rate in sheep injected with 333 IU of PMSG （81.96%） was significantly lower than those of sheep injected with 500 （90.25%） and 750 IU （95.3%） （P<0.05）. [Conclusions] This study provides a theoretical basis for the production enterprises to save a lot of manpower and material resources.
Key words Altay sheep； Estrus synchronization； Estrus rate； Breeding season； Non-breeding season
Altay sheep， a native variety in Xinjiang has a long history. It is an excellent local variety in Altay， bred by the Kazakh herdsmen in Fuhai County after thousands of years of hard work. This breed of sheep is tolerant to roughage and cold， good at trek， and suitable for grazing. It is well known for its high physical fitness and high meat fat production performance[1-2]. Altay sheep are kept in large numbers in Xinjiang and a good embryo transfer recipient material. However， with the improvement of living standings， people consume less and less fat. Huge tail fat of Altay sheep is no longer suitable for market demand， and it needs to be improved. The technology of estrus synchronization can provide technical support for it. The technology of estrus synchronization allows a group of ewes to rut and ovulate within a relatively short period of time by using drugs or management methods[3-5]. Combination of estrus synchronization with artificial insemination and embryo transfer makes concentrated mating and childbearing possible to improve reproductive efficiency and facilitate production management， thus saving a lot of manpower and material resources for the production companies[6-7]. Materials and Methods
Experimental materials
This study was conducted at the Sheep Breeding Experimental Base of the China-Australia Sheep Breeding Research Center of Xinjiang Academy of Animal Husbandry and the sheep farm of Qitai Central Group of Changji City. The Altay sheep with robust physique and no apparent reproductive disease were selected as experimental sheep， which were divided into groups randomly. The sponge plugs were purchased from New Zealand. PG and PMSG were produced by Ningbo Sansheng Pharmaceutical Co.， Ltd. Terramycin powder was produced by Shijiazhuang Huashu Shanhe Pharmaceutical Co.， Ltd.
Programs for estrus synchronization
Before treatment， appropriate amounts of terramycin powder were sprinkled on the sponge plugs. Only about 7 cm of the fine lines was retained， and the excess was cut off. Each ewe was fixed and sterilized with diluted potassium permanganate solution in the vulva. One sponge plug was held with long tweezers and placed in vagina of the sheep. After 12 d， the sponge plugs were removed. According to the experimental design， different doses of PG and PMSG were injected to the sheep. After 24 h of the removal of sponge plugs， one ram with a test cloth was used to examine whether the ewes were in estrus， and the examination was carried once every 12 h. If the ewes stood still and accepted the climb， they were considered in estrus. The examination was conducted at each morning and evening till 72 h after the removal of sponge plugs. The number of rutting ewes was counted for calculation of estrus rate.
Statistics and analysis
All the data were statistically analyzed using the t-test module of SPSS 13.0 statistical software， and the results were expressed as mean ± standard deviation.
Results and Analysis
Effects of estrus synchronization programs on estrus in sheep in breeding season
In September-October， 826 Altay sheep were randomly and evenly divided into three groups， sponge plug vaginal implant plus PG intramuscular injection after removal of sponge plug [0.1 mg （1 ml）] plus PMSG intramuscular injection after removal of sponge plug （333 IU） （sponge plug + PG + PMSG）， sponge plug vaginal implant plus PG intramuscular injection after removal of sponge plug （sponge plug + PG） and sponge plug vaginal implant plus PMSG intramuscular injection after removal of sponge plug （sponge plug + PMSG）. The estrus rate in sheep of the three groups were 96.96% （sponge plug + PG + PMSG）， 92.62% （sponge plug + PG） and 95.44% （sponge plug + PMSG） respectively （Table 1）， and no significant differences were found in estrus rate of sheep among the three treatments （P>0.05）. In breeding season， under the condition of sponge plug vaginal implant， whether PG or PMSG was injected did not affect the estrus of Altay sheep. Concentrated time of estrus in Altay sheep in breeding season
During the breeding season， 275 Altay sheep were subjected to the treatment of sponge plug vaginal implant plus PMSG intramuscular injection. Within 24-48 h after the removal of sponge plugs， the estrus rate reached 82.18% （Table 3）. The estrus was mainly concentrated at 36-48 g after the removal of sponge plugs， and the estrus rate accounted for 68.52%. The estrus rate 36 h after the removal of sponge plugs was significantly higher than those in the other periods （P<0.01） （Table 2）， accounting for more than 50% of the total estrus rate （93.09%）.
During May-June， 730 Altay sheep were subjected to the three estrus synchronization programs. The results showed that in the non-breeding season， the estrus rate of sheep in the sponge plug + PG treatment group was only 56.12%， significantly lower than those in the other two groups （P<0.01）. There was no significant difference in estrus rate of sheep between sponge plug + PG + PMSG （333 IU） and sponge plug + PMSG treatment groups （P>0.05） （Table 3）.
Concentrated time of estrus in Altay sheep in non-breeding season
In the non-breeding season， the number of rutting sheep in the sponge plug + PMSG （330 IU） treatment group at different time after the removal of sponge plugs was recorded. The statistical analysis showed that in the non-breeding season， the estrus of Altay sheep was also concentrated in 36-48 h after the removal of sponge plugs， and the estrus rate was 67.42%， accounting for 72.32% of the total rutting sheep. The estrus rates 36 and 48 h after the removal of sponge plugs were significantly higher than those at other time points （P<0.01）. The total estrus rate was 81.42% （Table 4）.
Estrus rate of Altay sheep under different dose of PMSG in non-breeding season
During May-June， the estrus synchronization program of sponge plug plus PMSG was used. After removing the sponge plugs， 333， 500 and 750 IU of PMSG were injected to total 714 Altay sheep， respectively. After the examination， the situation of estrus synchronization was analyzed. The results showed that the estrus rates of sheep injected with 500 and 700 IU of PMSG were significantly higher than that of sheep injected with 333 IU （P<0.05）， and there was no significant difference in estrus rate of sheep between the 500 IU and 700 IU treatments （P>0.05） （Table 5）.
Conclusions and Discussion
Studies have found that the main factors influencing sheeps estrus synchronization effect are variety， season， age and treatment methods. Different hormone treatment methods and doses are the key factors affecting the estrus synchronization effect. There are a wide variety of sheep kept in China. According to the production performance， they can be divided into multiparous sheep， meat sheep， wool sheep and fur sheep[8]. Different sheep breeds have different reproductive function. Therefore， estrus synchronization program may also be different for different breeds of sheep. Altay sheep is a local breed in Xinjiang， with clear estrus season. The key to estrus synchronization is to control the growth and development of the corpus luteum of the female animal. There are two ways to control the growth and development of the corpus luteum： progesterone treatment to produce artificial luteal phase and intramuscular injection of PGF and the like to eliminate the corpus luteum[9-10]. The hormonal treatment scheme commonly used for sheep estrus synchronization is the combination of vaginal suppository with progesterone， PG and PMSG. This study compared the effects of three treatment options： sponge plug + PG + PMSG， sponge plug + PG and sponge plug + PMSG on the estrus synchronization effect of Altay sheep. The results showed that during the breeding season， there were no differences in total estrus efficiency among the three treatment options， and the estrus rates in sheep of the two treatment options with PMSG intramuscular injection were both above 95%. This is similar to the study result of Thomas et al.[4]， and is also similar to the finding of Wang Liqin et al.[11] on the estrus rate of transplanted embryonic recipients. Therefore， during the breeding season， estrus examination can be omitted under the use of sponge plug plus PMSG， thus reducing the workload of personnel and reducing the amount of ram stock.
However， in the non-breeding season， the estrus rate in the sponge plug + PG treatment group was significantly lower than those of the other two groups （P<0.01）， only 56.12%. Estrus synchronization was not achieved， so it cannot be used in production. In the sponge plug + PMSG treatment group， the estrus of Altay sheep was concentrated in 36-48 h after the removal of sponge plugs， and the estrus rate was 67.42%； and the estrus rates of Altay sheep 36 and 48 h after the removal of sponge plugs were similar. Therefore， in the non-breeding season of Altay sheep， estrus synchronization can be conducted 36 or 48 h after the removal of sponge plugs. Considering the synchronized estrus data of Altay sheep in both breeding and non-breeding seasons， the combination of sponge plug and PMSG can be used in any season to achieve the purpose of synchronized estrus[12].
In the premise of sponge plug vaginal implant， the effects of different doses （333， 500 and 750 IU） of PMSG on estrus of Altay sheep in the non-breeding season were compared. The statistical results showed that after removing sponge plugs， intramuscular injection of 500 or 750 IU of PMSG could significantly improve the estrus efficiency. The estrus rate in the 750-IU PMSG treatment group even reached the level of breeding season. The average estrus was above 95%. Therefore， in the non-breeding season， the estrus synchronization program of sponge plug plus PMSG （750 IU） can be used to save manpower and reduce the number of used rams. References
[1] ZHANG M， ZHENG WX， GAO WM， et al. Quality analysis of Altay sheep down[J]. Acta Ecologae Animals Domastici， 2017， 38（06）， 24-29.
[2] WEI YG. Effect analysis of different estrus synchronization methods for Altay sheep[J]. Xinjiang Xumuye， 2015（11）： 23-24.
[3] OOSTHUIZEN N， FONTES PLP， SANFORD CD， et al. Estrus synchronization and fixed-time artificial insemination alter calving distribution in Bos indicus influenced beef heifers[J]. Theriogenology， 2017， 106： 210-215.
[4] THOMAS JM， LOCKE JWC， BISHOP BE， et al. Evaluation of the 14-d CIDR-PG and 9-d CIDR-PG protocols for synchronization of estrus in Bos indicus-influenced and Bos taurus beef heifers[J]. Theriogenology， 2017， 92， 190-196.
[5] ROSALES-TORRES AM， López-Cedillo ZB， Hernández-Coronado CG， et al. Short-term dietary concentrate supplementation during estrus synchronization treatment in beef cows increased IGF-I serum concentration but did not affect the reproductive response[J]. Tropical Animal Health and Production， 2017， 49（1）： 221-226.
[6] MCLEAN KJ， DAHLEN CR， BOROWICZ PP， et al. Technical note： A new surgical technique for ovariohysterectomy during early pregnancy in beef heifers[J]. Journal of Animal Science， 2016， 94（12）： 5089-5096.
[7] Victoria de Brun， Ana Meikle， Andrea Fernández-Foren， et al. Failure to establish and maintain a pregnancy in undernourished recipient ewes is associated with a poor endocrine milieu in the early luteal phase[J]. Animal Reproduction Science， 2016， 173： 80-86.
[8] WANG HH， ZHAO FP， ZHANG L， et al. The geographical distribution and multivariate analysis of Chinese indigenous sheep breeds and their meat-related traits[J]. Scientia Agricultura Sinica， 2015， 48（20）： 4170-4177.
[9] Johannes Handler， Sabine Sch nlieb， Hans-Otto Hoppen， et al. Seasonal effects on attempts to synchronize estrus and ovulation by intravaginal application of progesterone-releasing device （PRID） in mares[J]. Theriogenology， 2005， 65（6）： 1145-1158.
[10] Jackson CG， Neville TL， Mercadante VRG， et al. Efficacy of various five-day estrous synchronization protocols in sheep[J]. Small Ruminant Research， 2014， 120（1）： 100-107.
[11] WANG LQ， CHEN T， LIN JP， et al. Factors influencing the pregnancy rate of embryo-transferred transgenic sheep[J]. Acta Agriculturae Boreali-occidentalis Sinica， 2012， 21（8）： 6-9.
[12] FENG KM. Estrus synchronization of sheep during non-breeding seasons. Grass-Feeding Livestock， 2006， 3： 43-44.
Key words Altay sheep； Estrus synchronization； Estrus rate； Breeding season； Non-breeding season
Altay sheep， a native variety in Xinjiang has a long history. It is an excellent local variety in Altay， bred by the Kazakh herdsmen in Fuhai County after thousands of years of hard work. This breed of sheep is tolerant to roughage and cold， good at trek， and suitable for grazing. It is well known for its high physical fitness and high meat fat production performance[1-2]. Altay sheep are kept in large numbers in Xinjiang and a good embryo transfer recipient material. However， with the improvement of living standings， people consume less and less fat. Huge tail fat of Altay sheep is no longer suitable for market demand， and it needs to be improved. The technology of estrus synchronization can provide technical support for it. The technology of estrus synchronization allows a group of ewes to rut and ovulate within a relatively short period of time by using drugs or management methods[3-5]. Combination of estrus synchronization with artificial insemination and embryo transfer makes concentrated mating and childbearing possible to improve reproductive efficiency and facilitate production management， thus saving a lot of manpower and material resources for the production companies[6-7]. Materials and Methods
Experimental materials
This study was conducted at the Sheep Breeding Experimental Base of the China-Australia Sheep Breeding Research Center of Xinjiang Academy of Animal Husbandry and the sheep farm of Qitai Central Group of Changji City. The Altay sheep with robust physique and no apparent reproductive disease were selected as experimental sheep， which were divided into groups randomly. The sponge plugs were purchased from New Zealand. PG and PMSG were produced by Ningbo Sansheng Pharmaceutical Co.， Ltd. Terramycin powder was produced by Shijiazhuang Huashu Shanhe Pharmaceutical Co.， Ltd.
Programs for estrus synchronization
Before treatment， appropriate amounts of terramycin powder were sprinkled on the sponge plugs. Only about 7 cm of the fine lines was retained， and the excess was cut off. Each ewe was fixed and sterilized with diluted potassium permanganate solution in the vulva. One sponge plug was held with long tweezers and placed in vagina of the sheep. After 12 d， the sponge plugs were removed. According to the experimental design， different doses of PG and PMSG were injected to the sheep. After 24 h of the removal of sponge plugs， one ram with a test cloth was used to examine whether the ewes were in estrus， and the examination was carried once every 12 h. If the ewes stood still and accepted the climb， they were considered in estrus. The examination was conducted at each morning and evening till 72 h after the removal of sponge plugs. The number of rutting ewes was counted for calculation of estrus rate.
Statistics and analysis
All the data were statistically analyzed using the t-test module of SPSS 13.0 statistical software， and the results were expressed as mean ± standard deviation.
Results and Analysis
Effects of estrus synchronization programs on estrus in sheep in breeding season
In September-October， 826 Altay sheep were randomly and evenly divided into three groups， sponge plug vaginal implant plus PG intramuscular injection after removal of sponge plug [0.1 mg （1 ml）] plus PMSG intramuscular injection after removal of sponge plug （333 IU） （sponge plug + PG + PMSG）， sponge plug vaginal implant plus PG intramuscular injection after removal of sponge plug （sponge plug + PG） and sponge plug vaginal implant plus PMSG intramuscular injection after removal of sponge plug （sponge plug + PMSG）. The estrus rate in sheep of the three groups were 96.96% （sponge plug + PG + PMSG）， 92.62% （sponge plug + PG） and 95.44% （sponge plug + PMSG） respectively （Table 1）， and no significant differences were found in estrus rate of sheep among the three treatments （P>0.05）. In breeding season， under the condition of sponge plug vaginal implant， whether PG or PMSG was injected did not affect the estrus of Altay sheep. Concentrated time of estrus in Altay sheep in breeding season
During the breeding season， 275 Altay sheep were subjected to the treatment of sponge plug vaginal implant plus PMSG intramuscular injection. Within 24-48 h after the removal of sponge plugs， the estrus rate reached 82.18% （Table 3）. The estrus was mainly concentrated at 36-48 g after the removal of sponge plugs， and the estrus rate accounted for 68.52%. The estrus rate 36 h after the removal of sponge plugs was significantly higher than those in the other periods （P<0.01） （Table 2）， accounting for more than 50% of the total estrus rate （93.09%）.
During May-June， 730 Altay sheep were subjected to the three estrus synchronization programs. The results showed that in the non-breeding season， the estrus rate of sheep in the sponge plug + PG treatment group was only 56.12%， significantly lower than those in the other two groups （P<0.01）. There was no significant difference in estrus rate of sheep between sponge plug + PG + PMSG （333 IU） and sponge plug + PMSG treatment groups （P>0.05） （Table 3）.
Concentrated time of estrus in Altay sheep in non-breeding season
In the non-breeding season， the number of rutting sheep in the sponge plug + PMSG （330 IU） treatment group at different time after the removal of sponge plugs was recorded. The statistical analysis showed that in the non-breeding season， the estrus of Altay sheep was also concentrated in 36-48 h after the removal of sponge plugs， and the estrus rate was 67.42%， accounting for 72.32% of the total rutting sheep. The estrus rates 36 and 48 h after the removal of sponge plugs were significantly higher than those at other time points （P<0.01）. The total estrus rate was 81.42% （Table 4）.
Estrus rate of Altay sheep under different dose of PMSG in non-breeding season
During May-June， the estrus synchronization program of sponge plug plus PMSG was used. After removing the sponge plugs， 333， 500 and 750 IU of PMSG were injected to total 714 Altay sheep， respectively. After the examination， the situation of estrus synchronization was analyzed. The results showed that the estrus rates of sheep injected with 500 and 700 IU of PMSG were significantly higher than that of sheep injected with 333 IU （P<0.05）， and there was no significant difference in estrus rate of sheep between the 500 IU and 700 IU treatments （P>0.05） （Table 5）.
Conclusions and Discussion
Studies have found that the main factors influencing sheeps estrus synchronization effect are variety， season， age and treatment methods. Different hormone treatment methods and doses are the key factors affecting the estrus synchronization effect. There are a wide variety of sheep kept in China. According to the production performance， they can be divided into multiparous sheep， meat sheep， wool sheep and fur sheep[8]. Different sheep breeds have different reproductive function. Therefore， estrus synchronization program may also be different for different breeds of sheep. Altay sheep is a local breed in Xinjiang， with clear estrus season. The key to estrus synchronization is to control the growth and development of the corpus luteum of the female animal. There are two ways to control the growth and development of the corpus luteum： progesterone treatment to produce artificial luteal phase and intramuscular injection of PGF and the like to eliminate the corpus luteum[9-10]. The hormonal treatment scheme commonly used for sheep estrus synchronization is the combination of vaginal suppository with progesterone， PG and PMSG. This study compared the effects of three treatment options： sponge plug + PG + PMSG， sponge plug + PG and sponge plug + PMSG on the estrus synchronization effect of Altay sheep. The results showed that during the breeding season， there were no differences in total estrus efficiency among the three treatment options， and the estrus rates in sheep of the two treatment options with PMSG intramuscular injection were both above 95%. This is similar to the study result of Thomas et al.[4]， and is also similar to the finding of Wang Liqin et al.[11] on the estrus rate of transplanted embryonic recipients. Therefore， during the breeding season， estrus examination can be omitted under the use of sponge plug plus PMSG， thus reducing the workload of personnel and reducing the amount of ram stock.
However， in the non-breeding season， the estrus rate in the sponge plug + PG treatment group was significantly lower than those of the other two groups （P<0.01）， only 56.12%. Estrus synchronization was not achieved， so it cannot be used in production. In the sponge plug + PMSG treatment group， the estrus of Altay sheep was concentrated in 36-48 h after the removal of sponge plugs， and the estrus rate was 67.42%； and the estrus rates of Altay sheep 36 and 48 h after the removal of sponge plugs were similar. Therefore， in the non-breeding season of Altay sheep， estrus synchronization can be conducted 36 or 48 h after the removal of sponge plugs. Considering the synchronized estrus data of Altay sheep in both breeding and non-breeding seasons， the combination of sponge plug and PMSG can be used in any season to achieve the purpose of synchronized estrus[12].
In the premise of sponge plug vaginal implant， the effects of different doses （333， 500 and 750 IU） of PMSG on estrus of Altay sheep in the non-breeding season were compared. The statistical results showed that after removing sponge plugs， intramuscular injection of 500 or 750 IU of PMSG could significantly improve the estrus efficiency. The estrus rate in the 750-IU PMSG treatment group even reached the level of breeding season. The average estrus was above 95%. Therefore， in the non-breeding season， the estrus synchronization program of sponge plug plus PMSG （750 IU） can be used to save manpower and reduce the number of used rams. References
[1] ZHANG M， ZHENG WX， GAO WM， et al. Quality analysis of Altay sheep down[J]. Acta Ecologae Animals Domastici， 2017， 38（06）， 24-29.
[2] WEI YG. Effect analysis of different estrus synchronization methods for Altay sheep[J]. Xinjiang Xumuye， 2015（11）： 23-24.
[3] OOSTHUIZEN N， FONTES PLP， SANFORD CD， et al. Estrus synchronization and fixed-time artificial insemination alter calving distribution in Bos indicus influenced beef heifers[J]. Theriogenology， 2017， 106： 210-215.
[4] THOMAS JM， LOCKE JWC， BISHOP BE， et al. Evaluation of the 14-d CIDR-PG and 9-d CIDR-PG protocols for synchronization of estrus in Bos indicus-influenced and Bos taurus beef heifers[J]. Theriogenology， 2017， 92， 190-196.
[5] ROSALES-TORRES AM， López-Cedillo ZB， Hernández-Coronado CG， et al. Short-term dietary concentrate supplementation during estrus synchronization treatment in beef cows increased IGF-I serum concentration but did not affect the reproductive response[J]. Tropical Animal Health and Production， 2017， 49（1）： 221-226.
[6] MCLEAN KJ， DAHLEN CR， BOROWICZ PP， et al. Technical note： A new surgical technique for ovariohysterectomy during early pregnancy in beef heifers[J]. Journal of Animal Science， 2016， 94（12）： 5089-5096.
[7] Victoria de Brun， Ana Meikle， Andrea Fernández-Foren， et al. Failure to establish and maintain a pregnancy in undernourished recipient ewes is associated with a poor endocrine milieu in the early luteal phase[J]. Animal Reproduction Science， 2016， 173： 80-86.
[8] WANG HH， ZHAO FP， ZHANG L， et al. The geographical distribution and multivariate analysis of Chinese indigenous sheep breeds and their meat-related traits[J]. Scientia Agricultura Sinica， 2015， 48（20）： 4170-4177.
[9] Johannes Handler， Sabine Sch nlieb， Hans-Otto Hoppen， et al. Seasonal effects on attempts to synchronize estrus and ovulation by intravaginal application of progesterone-releasing device （PRID） in mares[J]. Theriogenology， 2005， 65（6）： 1145-1158.
[10] Jackson CG， Neville TL， Mercadante VRG， et al. Efficacy of various five-day estrous synchronization protocols in sheep[J]. Small Ruminant Research， 2014， 120（1）： 100-107.
[11] WANG LQ， CHEN T， LIN JP， et al. Factors influencing the pregnancy rate of embryo-transferred transgenic sheep[J]. Acta Agriculturae Boreali-occidentalis Sinica， 2012， 21（8）： 6-9.
[12] FENG KM. Estrus synchronization of sheep during non-breeding seasons. Grass-Feeding Livestock， 2006， 3： 43-44.