The mismatch between energy demand and dietary energy supply leads to a negative energy balance in high-yielding dairy cows during early lactation. Therefore, to offset the energy deficit, and maintain lactation, the cows will catabolism a considerable amount of body fat. However, excessive mobilization of body fat leading to fatty liver syndrome and ketosis and also impairs reproductive performance. Several management strategies arising from the extensive research on lipid mobilization, which include feeding lipogenic and glucogenic diets, have been shown to limit body fat mobilization. The aim of this study was to evaluate the effects of the timing of initiation of glucogenic diet on dry matter intake (DMI), body condition score (BCS), and milk yield and composition in transition Holstein dairy cows. Holstein cows (n=36) were randomly assigned to 1 of 3 treatments (GGG and GGL or GLL). Cows were fed a glucogenic diet from 3 wk prepartum. Postpartum animals continued to receive glucogenic diet until 49 DIM (GGG) or shifted to a lipogenic diet at either 21(GGL) or 1(GLL) DIM and remained on said diet until 49 DIM. Diets were isocaloric and isonitrogenous. NDF and fat content in lipogenic and glucogenic diets were 465 and 408, and 57 and 31 g/kg DM in prepartum and 403 and 324, and 79 and 36 g/kg DM in postpartum, respectively. Diets were prepared and fed as a total mixed ration (TMR) in ad libitum amounts twice daily to allow for 10% refusal in the prepartum and postpartum periods, respectively. Body weights and body condition scores (BCS) were recorded weekly on all cows throughout the trial at the same time on the same day each week. Individual cow milk yields were recorded daily. Milk samples were collected from all cows on 3 consecutive milking, once a week and analyzed for fat, true protein, and lactose. Data were analyzed by using a mixed model (Proc Mixed, SAS 2001) for a completely randomized design with repeated measures. Overall effect of treatment was tested using cow within treatment as the error term. For all analyses, least square means were calculated. Diets had no effect on dry matter intake (DMI) in prepartum and body condition score (BCS) in prepartum and postpartum. The GGL diet increased DMI compare with GLL (P<0.05) in postpartum. The effect of time was significant (P<0.001) and DMI was increased over the time. The BCS was decreased by 6 week of experiment (P<0.001). Milk production and milk fat, protein and lactose content were not affected by diets. Diets had no effect on fat-to-protein ratio. Milk protein yields were increased by the GGG and GGL diets compared with GLL (P<0.05). The results of this study demonstrated that glucogenic diet feeding should be continuing until 21 DIM and the lipogenic diet can be feed after that. This pattern of feeding could be better in terms of reducing the diet expenses and it would have increasing effect on cow performance.

Keywords