The aim of this study was to evaluate the effects of vitamin or mineral supplement on conception rates of dairy heifers when replacing the last injection of GnRH with hCG in ovsynch protocol. Forty four heifers were randomly assigned into 3 groups. All of the groups were treated with an intramuscular injection of GnRH(day 0), PGF2α(day 7), hCG(day 9) and were inseminated on day 10, 12~16h after hCG injection. In group 1, the heifers were treated with an intramuscular injection of 5 ml of vitamin-ADE 500® (1 ml soulution contains 500,000 IU of Vit A, 75,000 IU of Vit D, and 50 IU of Vit E) and in group 2, the heifers were treated with an intramuscular injection of 30 ml of mineral supplement-LAPTOVET® (1 ml soulution contains 20 mg of calcium glycerophosphate, 50 mg of ferricⅢ glycerophosphate, 40 mg of magnesium-2,3-dihydroxypropylphosphate, 10 mg of disodium-1-glycerophosphate 5H2O, 0.2 mg of cobaltⅡ gluconate 2H2O, and 1.4 mg of manganeseⅡ chloride 4H2O), 2 times in a week interval, respectively. Nothing was treated in group 3. Pregnancy diagnosis was performed by ultrasonography. First service conception rates and average services per conception were recorded.

First service conception rates were 59%, 80%, 50% in the group 1, 2, 3, respectively. Average services per conception were 1.53±0.72, 1.27±0.59, 1.63±0.74 in the group 1, 2, 3, respectively. In summary, although many factors influence on conception rates, this study indicate that vitamin or mineral supplement with ovsynch protocol has positive effects on conception rates of dairy heifers.

Following survey for investigation of whether the estrus synchronization program in the heifer season effects on the conception rates after parturition or not, was conducted. The postpartum average services per conception were 1.55±0.82 and 2.17±1.47 in estrus synchronized(ES) group and non-ES group, respectively. The postpartum average days open were 116±56(n=11) and 197±93(n=12) in ES group and non-ES group, respectively. These results suggest that ES program in heifer season did not effect the following conception rates after parturition.