Flaxseed is that obtained as a result of grinding flax seeds; it is rich in omega-3; contains between 6 and 10% of saturated fatty acids are unsaturated and the rest being the majority α linolenic acid; It has been confirmed that supplementation with fat before lambing, decrease the period of anoestrus or the time it will take to regain their reproductive cycle cow after giving birth. The objective of this research was to evaluate the effect of applying oil flaxseed on follicular dynamics and decreasing the effects of BEN. three (3) study groups called group A (control), Group B (treatment 1) and Group C (treatment 2) were established; They were included (11) simmental cows and F1 Simmental x zebu with a history of low return to estrus; fastest growing follicles and corpora lutea present in the ovaries were measured daily for 24 days, using transrectal ultrasound; during this time the oil Flaxseed was applied for four times with interval of 8 days and parallel weighing of the animals was made. Data were collected, tabulated and analyzed with the statistical package version 2008. Infostat oil flaxseed produced few effects on cyclicity, a low rate of return to estrus was obtained and no improvement was evident body condition.