Effects of dietary supplements of rumen-protected folic acid on lactation performance, energy balance, blood parameters and reproductive performance in dairy cows

• Dry matter intake increased with supplementary rumen-protected folic acid (RPFA).
• Milk yield, milk protein content and production increased with supplementary RPFA.
• Energy balance(MJ/cow/day) was improved by supplementary RPFA.
• Total conception rate and percentage of cows pregnant at 150 DIM were also improved by supplementary RPFA.

The objective of this study was to evaluate the effects of dietary supplements of rumen-protected folic acid (RPFA) on lactation performance, energy balance, reproductive performance and blood parameters of dairy cows. Ninety-six multiparous Holstein cows were assigned to four groups of 24 each according to their previous 305-days milk production. The treatments were: control, low RPFA (LRPFA), medium RPFA (MRPFA) and high RPFA (HRPFA) with 0–3 g RPFA/cow per day, respectively. Supplements of RPFA were top-dressed and manually mixed into the upper one third of the ration during the morning feeding from 3 weeks before the expected calving date to 15 weeks after parturition. Dry matter (DM) and net energy (NE) intakes, milk yield, milk protein content and production increased linearly (P < 0.05) with increasing RPFA supplementation, whereas milk fat content and production only tended to be linearly increased. Cows supplemented with RPFA showed a similar pattern (P < 0.05) of decreased loss of body weight (BW) and improved energy balance (expressed in MJ/cow/day) during the 105 days in milk (DIM) period. Concentrations of glucose in plasma, folate and methionine in serum increased linearly (P < 0.05), whereas concentrations of non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHBA) and serum homocysteine linearly (P < 0.01) decreased. Total conception rate and the percentage of cows pregnant at 150 DIM linearly increased (P < 0.05), DIM at first breeding and breeding per conception tended to change linearly with increasing RPFA supplementation. These results indicated that supplementary RPFA in cow diets had positive effects on feed intake and milk production, increased concentrations of plasma glucose and serum folates, decreased plasma concentrations of NEFA and BHBA and serum concentration of homocysteine, and improved energy balance and reproductive performance. These data suggest that RPFA improves lactation, energy balance and reproductive performance in a dose-dependent manner.