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References 1. Alnimer M., De Rosa G., Grasso F., Napolitano F., Bordi A.: Effect of climate on the response to three oestrous synchronisation techniques in lactating dairy cows. Anim Reprod Sci 2002, 71, 157-168. 2. Arechiga C.F., Staples C.R., McDowell L.R., Hansen P.J.: Effects of timed insemination and supplemental β-carotene on reproduction and milk yield of dairy cows under heat stress. J Dairy Sci 1998, 81, 390-402. 3. Ayres H., Ferreira R.M., Cunha A.P., Araújo R.R., Wiltbank M.C.: Double Ovsynch in high-producing dairy cows: effects on progesterone

References Ansari Z., Dirandeh E., Rezaei Roodbari A. (2016). Effect of service number on resynchronization response in lactating dairy cows during heat stress. J. Agr. Sci. Tech., 18: 1153-1160. Astiz S., Fargas O. (2013). Pregnancy per AIdifferences between primiparous and multiparous high-yield dairy cows after using Double Ovsynch or G6Gsynchronization protocols. Theriogenology, 79: 1065-1070. Bello N.M., Steibel J.P., Pursley J.R. (2006). Optimizing ovulation to first Gn RHimproved outcomes to each hormonal injection of Ovsynch in lactating dairy cows. J

, W.W. (2001). Effects of presynchronization and bovine somatotropin on pregnancy rates to a timed artificial insemination protocol in lactating dairy cows. J Dairy Sci. 84(7): 1646-1659. https://doi.org/10.3168/jds.S0022-0302(01)74600-0 6. Stevenson, J.S., Pulley, S.L. (2012). Pregnancy per artificial insemination after presynchronizing estrous cycles with the Presynch-10 protocol or prostaglandin F 2α injection followed by gonadotropin-releasing hormone before Ovsynch-56 in 4 dairy herds of lactating dairy cows. J Dairy Sci. 95(11): 6513-6522. https

References Behrouzi A., López-Helguera I., Mapletoft R.J., Ambrose D.J, Colazo M.G. (2016). Plasma progesterone concentration at TAI in dairy cows: what is low enough? Proceedings of the 18th International Congress on Animal Reproduction, 26–30 June 2016, Tours, France. Brusveen D.J., Souza A.H., Wiltbank MC. (2009). Effects of additional prostaglandin F2α and estradiol-17β during Ovsynch in lactating dairy cows. J. Dairy Sci., 92: 1412–1422. Carvalho P.D., Fuenzalida M.J., Ricci A., Souza A.H., Barletta R.V., Wiltbank M.C., Fricke P.M. (2015). Modifications to

artificial insemination in lactating Holstein cows. J Dairy Sci 2018, 101, 1730–1736. 3. Bartolome J.A., van Leeuwen J.J., Thieme M., Sa Filho O.G., Melendez P., Archbald L.F., Thatcher W.W.: Synchronization and resynchronization of inseminations in lactating dairy cows with the CIDR insert and the Ovsynch protocol. Theriogenology 2009, 72, 869–878. 4. Bilby T.R., Bruno R.G., Lager K.J., Chebel R.C., Moraes J.G., Fricke P.M., Lopes G. Jr., Giordano J.O., Santos J.E., Lima F.S., Stevenson J.S., Pulley S.L.: Supplemental progesterone and timing of resynchronization on

References Bello N.M., Steibel J.P., Pursley J.R. (2006). Optimizing ovulation to first Gn RHimproved outcomes to each hormonal injection of Ovsynch in lactating dairy cows. J. Dairy Sci., 89: 3413-3424. Bridges P.J., Fortune J.E. (2003). Characteristics of developing prolonged dominant follicles in cattle. Domest. Anim. Endocrinol., 25: 199-214. Brusveen D.J., Souza A.H., Wiltbank M.C. (2009). Effects of additional prostaglandin F-2 alpha and estradiol-17 beta during Ovsynch in lactating dairy cows. J. Dairy Sci., 92: 1412-1422. Colazo M.G., Mapletoft R.J. (2014

Abstract

Science has been searching for a long time for a reliable method for controlling the sex of mammalian offspring. Recently, the application of specific modern cellular methodologies has led to the development of a flow cytometric system capable of differentiating and separating living X- and Y-chromosome-bearing sperm cells in amounts suitable for AI and therefore, commercialization of this sexing technology. The aim of this work was to present the first results of heifers that introduce bovine AI with sex sorted semen, for the first time in Macedonia. Insemination with sex sorted cryopreserved semen (2×106 spermatozoa per dose) imported from the USA was done at two dairy farms in ZK Pelagonija. In total, 74 heifers (Holstein Friesian) were inseminated. Inseminations were carried out in a timely manner following a modified OvSynch protocol. During the insemination, the sperm was deposited into the uterine horn ipsi lateral to the ovary where a follicle larger than 1.6 cm was detected by means of transrectal ultrasound examination. Pregnancy was checked by ultrasound on day 30 after the insemination. Overall, the average pregnancy rate in both farms was 43,24% (40,54% and 45,95%, for farm 1 and farm 2, respectively). All pregnant heifers delivered their calves following a normal gestation length (274,3 days in average) and of the 32 born calves, 30 (93,75%) were female. In conclusion, since the first results from inseminations with sex-sorted semen in dairy heifers in Macedonia are very promising, the introduction of this technique may bring much benefit to the local dairy sector. Average pregnancy rate seems similar with results obtained following ‘regular’ inseminations, notwithstanding the relatively low number of spermatozoa per insemination dose. Due to the latter, we however recommend inseminations only to be carried out by experienced technicians followinga TAI protocol and ultrasound examinations of the ovaries prior to insemination.

References 1. Barański W., Zduńczyk S., Janowski T.: Reproductive performance of cows with subclinical endometritis diagnosed by different cytological thresholds in the postpartum period. Tierärztliche Praxis Grottiere 2013, 1, 15-19. 2. Bartolome J.A., Silvestre F.T., Kamimura S., Arteche A.C.M., Melendez P., Kelbert D., McHale J., Swift K., Archbald L.F., Thatcher W.W.: Resynchronization of ovulation and timed insemination in lactating dairy cows. I. Use of the Ovsynch and Heatsynch protocols after non-pregnancy diagnosis by ultrasonography. Theriogenology 2005

References Bartolome JA., Silvestre F.T., Kamimura S., Arteche A.C.M., Melendez P. K e l bert D., McHale J., Swift K., Archbald L.F.,Thatcher W.W. (2005). Resynchroniza tion of ovulation and timed insemination in lactating dairy cows: I: use of the Ovsynch and Heatsynch protocols after non-pregnancy diagnosis by ultrasonography Theriogenology, 63: 1617-1627. Binelli M., Machado R. Bergamaschi M.A.C.M., Bertan C.M. (2009). Manipulation of ovarian and uterine function to increase conception rates in cattle. Anim. Reprod. 6: 125-134. Bisinotto R.S., Greco L

.C. (2003). Follicular size and response to ovsynch versus detection of estrus in anovular and ovular lactating dairy cows. J. Dairy Sci. 86, 3184 –3194. https://doi.org/10.3168/jds.S0022-0302(03)73921-6 5. Leblanc, S. (2010). Monitoring metabolic health of dairy cattle in transition period. J Repro Dev. 56, 23-35. https://doi.org/10.1262/jrd.1056S29 6. Dovenski, T., Kocoski, Lj., Trojacanec, P., Popovski, K., Mickovski, G., et al. (2000). Ultrasound diagnosis of functional ovarian disorders in dairy cows and its adequate treatment. Proceedings Symposium on veterinary