[Andreu - VázquezC., Garcia - Ispierto I., López - Gatius F. (2012 a). Photoperiod length and the estrus synchronization protocol used before AI affect the twin pregnancy rate in dairy cattle. Theriogenology, 78: 1209-1216.10.1016/j.theriogenology.2012.05.01422898015]Search in Google Scholar
[Andreu- Vázquez C., Garcia - Ispierto I., Ganau S., FrickeP.M., López - Gatius F. (2012 b). Effects of twinning on the subsequent reproductive performance and productive lifespan of high-producing dairy cows. Theriogenology, 78: 2061-2070.10.1016/j.theriogenology.2012.07.02723043948]Search in Google Scholar
[Azzam S.M., Kinder J.E., Nielsen M.K., Werth L.A., Gregory K.E., Cundiff L.V., Koch R.M. (1993). Environmental effects on neonatal mortality of beef calves. J. Anim. Sci., 71: 282-290.]Search in Google Scholar
[Bicalho R.C., Galvao K. N., CheongS.H., Gilbert R.O., Warnick L.D., Guard C.L. (2007). Effect of stillbirth on dam’s survival and reproduction performance in Holstein dairy cows. J. Dairy Sci., 90: 2797-2803.]Search in Google Scholar
[Davis M.E., Haibel G.K. (1993). Use of real-time ultrasound to identify multiple foetuses in beef cattle. Theriogenology, 40: 373-382.]Search in Google Scholar
[Des Coteaux L., Gnemmi G., Colloton J. (2010). Practical atlas of ruminant and camelid reproductive ultrasonography. Blackwell Publishing, pp. 1-244.]Search in Google Scholar
[Echternkamp S.E., Thallman R.M., CushmanR.A., Allan M.F., Gregory K.E. (2007). Increased calf production in cattle selected for twin ovulations. J. Anim. Sci., 85: 3239-3248.]Search in Google Scholar
[Gregory K.E., Echternkamp S.E., Dickerson G.E., Cundiff L.V., Koch R.M., Van Vleck L.D. (1990). Twinning in cattle: III. Effects of twinning on dystocia, reproductive traits, calf survival, calf growth and cow productivity. J. Anim. Sci., 68: 3133-3144.]Search in Google Scholar
[Gregory K.E., Echternkamp S.E., Cundiff L.V. (1996). Effects of twinning on dystocia, calf survival, calf growth, carcass traits, and cow productivity. J. Anim. Sci., 74: 1223-1233.]Search in Google Scholar
[JohansonJ.M., BergerP.J. (2003). Birth weight as a predictor of calving ease and perinatal mortality in Holstein cattle. J. Dairy Sci., 86: 3745-3755.]Search in Google Scholar
[Johanson J.M., BergerP.J., Kirkpatrick B.W., Dentine M.R. (2001). Twinning for North American Holstein sires. J. Dairy. Sci., 84: 2081-2088.]Search in Google Scholar
[Kuźma R., Kuźma K. (1994). The occurrence of multiple calving in dairy cows under natural conditions and their impact on parturition, postpartum period and fertility (in Polish). Prz. Hod., 9: 1-6.]Search in Google Scholar
[Kuźma R., Kuźma K., Malinowski E. (1998). Occurrence and effect of multiple births on the health and fertility of cows (in Polish). 45th Anniversary Symposium of the Department of Animal Science, AR Kraków, pp. 89-90.]Search in Google Scholar
[Lopez - Gatius F., Hunter R.H. (2005). Spontaneous reduction of advanced twin embryos: its occurrence and clinical relevance in dairy cattle. Theriogenology, 63: 118-125.]Search in Google Scholar
[Max A. (1996). Twin pregnancy in cattle (in Polish). Med. Weter., 89: 5-6.]Search in Google Scholar
[Max A. (2001). Pregnancies in heifers after induced poly-ovulation (in Polish). Med. Weter., 57: 433-436.]Search in Google Scholar
[Nałęcz - Tarwacka T., Palińska K., Grodzki H. (2011). Influence of multiple pregnancy on delivery complications and calf mortality (in Polish). Med. Weter., 67: 409-411.]Search in Google Scholar
[Nogalski Z. (2003). Relations between the course of parturition, body weights and measurements of Holstein-Friesian calves. Czech J. Anim. Sci., 48: 51-59]Search in Google Scholar
[Nogalski Z. (2009). Perinatal mortality of calves in dairy herds (in Polish). Pr. Mat. Zoot., 67: 167-176.]Search in Google Scholar
[Nogalski Z., Mordas W. (2012). Pelvic parameters in Holstein-Friesian and Jersey heifers in relation to their calving. Pakistan Vet. J., 32: 507-510.]Search in Google Scholar
[Pogorzelska P., NogalskiZ. (2010). Calving difficulty in cows and heifers of the Polish dairy cattle population in 2007-2008. Rocz. Nauk. PTZ, 6, 3: 103-110.]Search in Google Scholar
[Raboisson D., Delor F., Cahuzac E., Gendre C., Sans P., Allaire G. (2013). Perinatal, neonatal, and rearing period mortality of dairy calves and replacement heifers in France. J. Dairy Sci., 96: 2913-2924.]Search in Google Scholar
[Sawa A. (1994). Influence of twin pregnancy on usefulness of cows (in Polish). Zesz. Nauk. ATR Bydgoszcz, Zoot, 26: 7-14.]Search in Google Scholar
[Sawa A. (2001). Effect of birth type on performance, fertility and culling of Black-and-White cows. Ann. Anim. Sci., 1: 13-24.]Search in Google Scholar
[Sawa A., Bogucki M., Krężel - Czopek S. (2012). Reproduction performance of cows with single, twin and triplet calves. Acta Vet., Brno, 81: 347-352.]Search in Google Scholar
[Skrzypek R., Baraniak R., Grycz J. (1989). Influence of twin pregnancy on milk productivity, breeding and culling of cows and calves born alive (in Polish). Rocz. AR Poznań, Zoot., 38: 83-94.]Search in Google Scholar
[SYMLEK http://www.pfhb.pl/?strona=symlek_polaczenie.htm ]Search in Google Scholar
[Wielgosz - Groth Z., Cieślak S., KijakZ., Cichocki M. (1999). The incidence of various types of deliveries, and the relationship between the type of calving and milk production (in Polish). Zesz. Nauk. PTZ, 44: 249-256. ]Search in Google Scholar