The aim of this study was to evaluate productive, metabolic and ovarian responses of different timing to start lipogenic diet in dairy cows. Thirty-six multiparous cows were assigned randomly to 1 of 3 treatments in a completely randomized design. All cows were fed a similar glucogenic diet, 21 days before expected calving date. After parturition, they received a glucogenic diet until 42 days in milk (DIM; GGG) or shifted to a lipogenic diet at either 1 (GLL) or 21(GGL) DIM and remained on these diets until 42 DIM. After the day 42 postpartum, all cows returned to a common stall and received a mixed lipogenic and glucogenic (50:50) diet until 100 DIM. Postpartum dry matter intake (DMI) was lower (Po0.05) and body weight, body condition score, milk yield, milk protein, and milk lactose contents tended to be lesser (Po0.1) for the GLL group; however, negativity of energy balance, aspartate aminotransferase (AST), cholesterol, and urea concentrations were significantly higher (Po0.05). Glucose concentration and number of follicles Z10 mm diameter were significantly higher (Po0.05) but BHBA and NEFA concentrations were lower (Po0.05) for the GLL group compared to other two groups. For the GLL group days to ovulation and cervical diameter were significantly higher (Po0.05). The conclusion is that providing a lipogenic diet immediately after calving has negative effects on energy balance, metabolic status and follicular dynamics of dairy cows. However, offering a glucogenic diet during
21 to þ42 days relative to calving was more effective in improving animal performance and ovarian activity. This strategy may be enhancing the pregnancy rate.

Keywords