EFFECT OF ZINC INTAKE DURING TRANSITION PERIOD ON ZINC AND CALCIUM IN MILK OF SUBCLINICAL HYPOCALCEMIA DAIRY COWS

Mayasari, Novi, Nurjanah, Laela Tien, Setyowati, Endang Yuni, Salman, Lia Budimulyati

Abstract
   In early lactation, high producing cows frequently suffer from negative energy balance and mineral imbalances. Negative energy balance is associated with immune suppression and some diseases like a hypocalcemia. Zinc (Zn) is known as immune stimulator, able to increase immune response to diseases. The objective of this study was to study the effect of supplemental Zn intake in dairy cows at 4 weeks prior to calving (dry period) on Zn and calcium (Ca) content in milk and subclinical hypocalcemia. Twenty-two dairy cows (Holstein Friesian) were randomly allocated to either a dry cow ration with or without Zn supplementation (40 ppm Zn in the diet). The cows received a roughage mixture ad libitum and concentrates were fed individually. Post-partum, cows were milked twice daily and throughout the experiment animal health was monitored daily. Blood and milk samples were taken at week 1 after calving. Data were statistically analyzed with SAS. A cow was considered a case of subclinical hypocalcemia when blood calcium lowered below 8.0 mg/100 ml. The results showed the percentage incidence of clinical and subclinical hypocalcaemia (1.5% vs. 31%). Zn and Ca content in milk were not affected by dietary Zn content in diet. In conclusion, feeding above Zn requirements during 4 weeks before calving does not seem to reduce the incidence of clinical milk fever nor subclinical milk fever. Zn supplementation may improve the immune system but its form and absorption must be considered.

Key words: subclinical hypocalcemia, transition cow, zinc supplementation