Effects of different levels of vitamin A supply on production and blood parameters of transition cows

Melissa Rodriguez
Graduate (MS)
Chanhee Lee
Animal Sciences

Negative energy balance after calving promotes body fat mobilization and excessive mobilization can increase risk of hyperketonemia. Evidence exists that vitamin A (VA) is closely associated with adipose fat metabolism in non-ruminant species. This study investigated whether low or high VA supply to transition cows affected production and fat mobilization from blood indicators. Sixty-three prefresh Holstein cows in a complete randomized block design were assigned to: CON, a transition diet with supplemental VA (75 kIU/d) to meet requirement (NRC 2001); LO, no supplemental VA; HI, receiving supplemental VA (190 kIU/d) 2.5 times greater than the requirement. Periods were prepartum (14 d before calving), postpartum (30 d after calving) and carryover (31 to 58 DIM; cows were fed a common diet). Cows were fed a diet with no supplemental VA in the far-off period. Milk yield (MY) and DMI were recorded daily, and blood plasma was collected to measure cholesterol, nonesterified fatty acids (NEFA), and beta-hydroxybutyrate (BHB). Whole blood was collected at 5 DIM to determine blood differential counts. Data were analyzed using PROC MIXED of SAS (block, random effect; diets, repeated wk and their interaction, fixed effects). Treatments did not affect DMI during the pre- (ave. 10.6kg/d) and postpartum (18.8 kg/d) periods. There was no difference in MY in postpartum (ave. 37.1 kg/d) and carryover period (43.6 kg/d) among treatments. Milk fat content increased linearly (4.49 to 5.12%; P=0.02) as VA increased (i.e., from LO to HI) but yield did not differ. Cholesterol, NEFA and BHB were not affected pre- and postpartum by treatments (average 21% incidence of hyperketonemia based on postpartum BHB > 1200 umol/L). Increasing VA supply linearly decreased (P=0.01) segmented neutrophil (%) and linearly increased (P=0.01) lymphocyte (%). In conclusion, providing VA lower or higher than the requirement to transition cows did not affect milk production and likely had no impact on body fat mobilization and hyperketonemia. However, we found excessive VA supply may negatively affected resistance or susceptibility to disease.