Cow metabolic status assessed from fat/protein ratio in milk affected ovarian response and number of transferable embryos after superovulation

This work aimed to evaluate the quantity and the quality of flushed embryos based on the metabolic status of dairy cows, lactation number, and size of the ovaries. Fifty-nine Holstein cows on 1^st to 5^th lactation were enrolled in the experiment. Monitoring took place during the period from October to November and from March to June. Cows with corpus luteum were included for the hormonal treatment – superovulation and timed insemination. The cow was inseminated, resp. re-inseminated, during the induced heat with insemination doses from one bull from the same batch. Embryo flushing was performed on the 7^th day after the first insemination. We isolated individual embryos after flushing, and morphologically evaluated them under a stereo microscope. The metabolic status of tested cows was determined based on the ratio between fat and protein in milk around the period of embryo flushing (< 1.1; 1.1–1.3; > 1.3). Data about fat and protein content were taken from milking parlour records. Data were evaluated in SAS v9.4 with GLM procedure. The results of our study showed that there is a significant relationship between the fat/protein ratio and the total number of flushed embryos, resp. the number of transferable embryos. The highest number of flushed and transferable embryos were collected from the group of cows with fat/protein ratio between 1.1–1.3. The fat/protein ratio within these values represents cows in an optimal metabolic state. We also observed a significant positive relationship between the size of the ovaries and the number of flushed and transferable embryos. Lactation number did not significantly affect monitored parameters. The assessment of the fat/protein ratio might become a useful tool for the evaluation of cows selected for embryo transfer. Our findings could be used to improve the efficacy of the superovulation system, with the aim to extract the maximum number of transferable embryos.