Reproductive Performances of Holstein Cows with Different Milk Fat to Protein Ratio during Successive Stages of Lactation

Abstract

Aim of study was to determine relationship between the energy status of cows, expressed through different milk fat to protein ratio values (FPR<1.0, 1.0-1.3 and >1.3), and their reproductive performances (interval from calving to first artificial insemination; calving to conception interval; insemination index; pregnancy duration; intercalving interval) during succesive stages of lactation (day 15^th to 45^th; day 46^th-75^th; day 76^th-105^th; day 106^th to 135^th of lactation). The study included a total of 350 fresh calved Holstein cows (121 primiparous, 115 secundiparous and 114 cows which calved three or more times), kept and fed in usual farm conditions. Milk samples were taken during morning milking, and FPR value was calculated from concentrations of milk fat and protein for all milk samples. Reproductive parameters were calculated from farm data. Values of all reproductive parameters, except pregnancy duration, had generally increasing trend in all groups during successive stages of lactation. During successive stages of lactation, cows with optimal FPR values had generally better reproductive performances, compared to cows with increased or decreased FPR values, which indicates importance of FPR monitoring during early lactation for timely detection of cows predisposed for poor reproductive results.