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
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
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.
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.
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.
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.
Nogalski Z. (2003). Relations between the course of parturition, body weights and measurements of Holstein-Friesian calves. Czech J. Anim. Sci., 48: 51-59
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.
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.
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.
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.