Milk fever (parturient paresis / hypocalcaemia) is a metabolic disorder that usually occurs near parturition and at the onset of lactation in high producing multiparous dairy cows. Milk fever can indirectly contribute to an increased incidence of several diseases in early lactation. This study was conducted to compare two different feeding strategies to prevent milk fever, namely (i) the established concept of feeding a diet with a negative DCAD and (ii) a feeding strategy combining a negative DCAD supplement with 25-hydroxyvitamin D3 (25-OH-D3). Thirty dairy cows were used in a randomized block design and were selected and blocked by parity (second parity and later), 305 day mature equivalent milk production in the previous lactation and expected calving date. Within each of the 15 blocks, the cows were allocated to two experimental groups named DCAD and DCAD + HyD. Fifteen animals in the DCAD + HyD group received a daily oral dosage of 3 mg of 25-OH-D3. Plasma samples were collected from day 21 prepartum to 10 days postpartum and were analysed for 25-OH-D3, 1,25-dihydroxyvitamin D3, total and ionized calcium, phosphorus and magnesium. Samples were collected on day 21, 14, 10 prepartum and every second day to calving, 4 and 6 h postpartum and every second day up to day 10 after calving. Urinary samples for determination of macro minerals (calcium and phosphorus) were collected via manual stimulation on day 21, 14, 8 and 4 prepartum and day 4 postpartum. These samples were used to ensure that mild metabolic acidosis was achieved in both treatment groups. The metabolic acidosis was demonstrated by decreased urinary pH. Milk samples were collected on day 1, 4 and 10 postpartum and used for macro mineral (calcium and phosphorus) determination. This study did not achieve all of the expected results observed in similar experiments. No treatment differences could be detected for plasma Ca2+ concentrations (P>0.05) and the mean plasma Ca2+ concentrations were [1.086a mmol/L ± 0.010 (DCAD treatment) and 1.083a mmol/L ± 0.010 (DCAD + HyD treatment)] respectively. Furthermore 1,25-(OH)2D3 plasma concentrations did not indicate any treatment differences (P>0.05). These results could be due to the fact that the experimental animals were not sufficiently challenged and therefore the combination of a low DCAD diet and Rovimix HyD did not influence the calcium homeostatic mechanisms as expected. A clear correlation between plasma 25-OH-D3 concentration and treatment duration was however demonstrated (P<0.001), indicating effective absorption of orally supplemented 25-OH-D3. Several authors demonstrated that feeding massive doses of vitamin D2 (30 million units) for extended periods led to clinical evidence of vitamin D toxicity. When 10 million IU of vitamin D3 were however administered intramuscularly within 10 days of parturition, a reasonable measure of protection against toxicity could be provided. It can be concluded from this study that longer feeding periods (± 21 days) than the proposed 10 days prior to calving can safely be implemented when feeding 3 mg 25-OH-D3 per animal per day (=240 mg Rovimix HyD 1,25%). Copyright
Dissertation (MSc(Agric))--University of Pretoria, 2012.