University of Guilan Caspian Journal of Environmental Sciences 1735-3033 24 3 2026 07 01 Effects of various protein levels in the ration of dairy heifers on their growth rate and biochemical status 701 711 9337 10.22124/cjes.2026.9337 EN Serimbek Abugaliev Agricultural Innovation and Technology Park, West Kazakhstan Innovation and Technology University, Uralsk 090009, Kazakhstan Darkhan Smagulov Agricultural Innovation and Technology Park, West Kazakhstan Innovation and Technology University, Uralsk 090009, Kazakhstan Stepan Batanov Scientific and Innovative Complex, Udmurt State Agricultural University, Izhevsk 426063, Udmurt Republic Yedige Nassambayev Agricultural Innovation and Technology Park, West Kazakhstan Innovation and Technology University, Uralsk 090009, Kazakhstan Elena Babich Breeding Animal Husbandry Laboratory, Research and Production Center "Agroinnovation", Kostanay 110000, Kazakhstan Journal Article 2026 01 04 When breeding dairy cattle, scientists and specialists focus special attention on their productive qualities (milk yield per lactation, fat and protein content, growth rate of young animals, etc.) and the influence of both genetic and paratypic factors on them. The impact of several dietary factors is especially relevant. Therefore, the purpose of this study was to determine the influence of dietary protein concentration, 20.87% (control), 23.49% (Mid), and 30.52%, on the growth of young dairy cattle bred in the northern region of Kazakhstan. The study involved 60 Holstein heifers, aged 90 days (± 5 days), with a body weight of 107.2 ± 0.48 kg. Their daily consumption of dry matter was 2.5 kg day^-1 which contained 10.10-10.60 MJ metabolizable energy, indigestible protein 14.4-17.8% and crude fiber 22.6-24.6%. The body weight of newborn calves in all groups did not differ and was 31.8-32.6 kg. At the age of 6 months, difference in body weight in the control, Mid, and High groups were 181.1 kg, 198.6 kg, and 200.8 kg respectively. The gain of calves in two experimental groups exceeded that of the control by 9.7% (<em>p</em> < 0.001) and 10.9% (<em>p</em> < 0.001), respectively. No differences in blood glucose were found. Highest AST values were observed in the control compared to Mid (5.14 U L^-1) and High (8.25 U L^-1). The Coefficient of Ritis value was within 2.74-3.11. Research indicates that a ratio in dry matter with an optimal proportion of indigestible protein 23.49% and degradable protein 70% was economically justified. https://cjes.guilan.ac.ir/article_9337_c1b02959da1beec3e6ecc9bbf9e2248f.pdf