C.Y. Lin, A.J. McAllister, T.R. Batra, A.J. Lee, G.L. Roy, J.A. Vesely, J.M.., Wauthy, K.A. Winter, “Effects of early and late breeding of heifers on multiple lactation performance of dairy cows,” Journal of Dairy Science, vol. 71, pp. 2735-2743. 1988.
 J. Hultgren, C. Svensson, “Heifer rearing con-ditions affect length of productive life in Swedish dairy cows,” Preventative Veterinary Medicine, vol. 89, pp. 255-264. 2009.
 R.D. Evans, M. Wallace, D.J. Garrick, P. Dillon, D.P. Berry, V. Olori, “Effects of calving age, breed fraction and month of calving on calving interval and survival across parities in Irish spring-calving dairy cows,” Livestock Science, vol. 100, pp. 216-230. 2006.
 J. S. Cooke, Z. Cheng, N. E. Bourne, D. C. Wathes, “Association between growth rates, age at first calving and subsequent fertility, milk production and survival in Holstein-Friesian heifers,” Open J. of Animal Sc., vol.3, no.1, pp. 1 – 12, 2013.
 Z. Riecka, J. Candrák, “Analysis of relationship between production and reproduction traits of Holstein cattle population in the Slovak Republic,” Animal Science and Biotechnologies, vol 44, no 1, pp. 332 – 336, 2011.
 Consultative Committee of Farm Animal Genetic Resources, State of the Animal Genetic Resources of Latvia, Ministry of Agriculture of Latvia, Rīga, pp.49. 2003.
 J.F. Ettema, J.E.P. Santos, “Impact of age at calving on lactation, reproduction, health, and income in first-parity Holsteins on commercial farms,” Journal of Dairy Science, vol. 87, pp. 2730-2742. 2004.
 M.A. Nilforooshan, M.A. Edriss, “Effect of age at first calving on some productivity and longevity traits in Iranian Holsteins of the Isfahan province,” Journal of Dairy Science, vol. 87, pp. 2130-2135. 2004.
 G. Pirlo, F. Miglior, M. Speroni, “Effect of age at first calving on production traits and on difference be-tween milk returns and rearing costs in Italian Holsteins,” Journal of Dairy Science, vol. 83, pp. 606-608. 2000.
 J.S. Brickell, N. Bourne, M.M. McGowan, D.C. Wathes, “Effect of growth and development during the rearing period on the subsequent fertility of nulliparous Holstein-Friesian heifers,” Theriogenology, vol. 72, pp. 408-416. 2009.
 L. Cielava, D. Jonkus “First Calving Age Effect on the Longevity of Cows and Milk Productivity,” Ražas svētki Vecaucē – 2013, nov. 2013.
 Y. Grohn P.J. Rajala-Schultz, “Epidemiology of reproductive performance in dairy cows” Animal Reproduction Science. vol. 60–61. pp. 605–614. 2000.
 P.R. Tozer, A.J. Heinrichs,) “What affects the costs of raising replacement dairy heifers: A multiple- component analysis,” Journal of Dairy Science, vol. 84, pp. 1836- 1844. 2001.
 M.C.M. Mourits, D.T. Galligan, A.A. Dijkhuizen, R.B.M. Huirne, R.B.M. “Optimization of dairy heifer man-agement decisions based on production conditions of Pennsylvania,” Journal of Dairy Science, vol. 83, pp. 1989-1997. 2000.
 M. Janžekovič, M. Ocepek, T. Virk, D. Škorjanc, “Comparison of longevity and production traits of Holstein and Simmental cows of different origin in Slovenia,” Mljekarstvo, vol. 59. no. 4. pp. 336 – 342. 2009.
 A. Chegini, A.A. Shadparvar N. Ghavi Hossein‐Zadeh, “Genetic trends for milk yield, persistency of milk yield, somatic cell count and calving interval in Holstein dairy cows of Iran,” Iranian J. of App. Animal Sc. vol. 3, pp. 503 – 508. 2013.
 L. Šernienė, A. Kabašinskienė, “Analysis of reproductive performance, milk composition and quality of indigenous cows: Lithuanian Light Gray and White Backed,” Vet Med Zoot, vol. 72, no. 94, pp. 30 – 36. 2015.
 A.P. Gulinski B. Giersz G. Niedziałek K Młynek, “First age calving and its importance for milk productivity of primiparous cows remaining in eastern Mazovia farms from years 1977-2000,” Acta Scientiarum Polonorum Zootechnica. vol. 2. pp. 31–41. 2003.
 A. Chegini, A.A. Shadparvar, N. Ghavi Hossein‐Zadeh, “Genetic parameter estimates for lactation curve parameters, milk yield, age at first calving, calving interval and somatic cell count in Holstein cows” Iranian J. of App. Animal Sc. vol. 5. no. 1. pp. 61 – 67. 2014.
 D.P. Berry A.R. Cromie, “Associations between age at first calving and subsequent performance in Irish spring calving Holstein-Friesian dairy cows,” Livest. Sci. vol. 123, pp. 44-54. 2009.
 J. Miciński, M. Maršálek, J. Pogorzelska, A. Vrbová, W. Sobotka, G. Zwierzchowski, P. Matusevičius, “The comperative analysis of milk performance in Czech Pied cattle rised in the Czech Republic versus Polish Holstein – Friesian, Simental and Czech Pied cattle rised in Polland,” Vet Med Zoot. vol. 67. no. 89. pp. 75 – 80. 2014.