Understanding the efficacy of organic trace minerals has been increasingly important over the past few years as a result of increased customer awareness of their benefits and the increase in the number of commercial products available to the customer. Organically bound trace minerals of interest in animal nutrition specifically include iron, zinc, manganese, copper, cobalt, and selenium. These elements have been shown to improve reproductive efficiency as measured by conception rate, alleviated calving, and reduced placenta expulsion rate. Additional benefits include improved growth performance of calves. The field trials in the period of 2005 – 2007 with Charolais breed beef cattle cows and calves verified efficacy of the premix PROTRACE G containing Fe, Zn, Cu, Mn, and Co chelates, Se-amino acid (selenomethionine), potassium iodide, and vitamins A, D3 and E. Average calving rate of experimental group cows fed diet with added premix was 20 – 30 min, placenta expulsion time - 28 – 31 min, but in control group fed only basal diet - 2 h 21 min and 1 h 30 min – 2 h 09 min (p is less than 0.05) respectively. Live weight gain of calves and heifers of the experimental group was on 35 – 39% higher (p is less than 0.05) than that in the control group.

The research was conducted in Latvia University of Agriculture Research and Study Farm ‘Vecauce’ in 600 dairy cows herd, in the period from 2009 to 2013. Within the framework of the research, growth indicators (from birth till the first delivery) of 102 dairy cow calves were analysed. Live weight and hip height of the heifers were found out at birth, at the age of 6 and 12 months, at first insemination and first calving. Heifers born to primiparous cows in both breed groups had notably lower live weight (42.0 and 42.4 kg), as compared to the 4th group heifers born to mature cows (p is less than 0.05). At the age of one year, the greatest weight among the red breed animals was recorded for the 4th group heifers born to mature cows (on average 354.8 ± 7.09 kg), while in Holstein breed those were heifers born to mothers calving on average for the 2nd time (on average 363.0 ± 6.47 kg). The 4th group heifers born to mature Holstein cows had notably greater hip height at birth – on average 78.1 ± 0.9 cm (p is less than 0.05). Heifers of red and Holstein breeds on average were inseminated at the age of 14.6 – 14.8 months as they reached live weight 395 – 396.5 kg. Heifers of red breeds on average calved at the age of 25.8 months, whereas Holstein heifers - of 26.4 months. The research aimed at analysing growth rates of heifers born to dairy cows at different age.