Carryover effects of potassium supplementation on calcium homeostasis in dairy cows at parturition

Effect of dietary difructose anhydride III supplementation on bone mineral density and calcium metabolism in late-lactation dairy cows

The aim of the present study was to examine the effect of 28 days of dietary difructose anhydride (DFA) III supplementation on calcium (Ca) metabolism in late-lactation dairy cows. Twenty-four multiparous pregnant Holstein cows were divided into two groups. The DFA group was fed total mixed ration (TMR) supplemented with 40 g of DFA III, and the control group was fed TMR only. The replenishment of bone Ca reserves was evaluated by measuring bone mineral density (BMD) and blood biochemical bone markers. Serum Ca concentrations, urinary Ca-to-creatinine (Cre) (Ca/Cre) ratios, and milk Ca concentrations were also analyzed. The BMD of the 4th caudal vertebra in the DFA group was higher than in the control group on day 28. With respect to bone markers, the ratios of undercarboxylated osteocalcin (ucOC) to osteocalcin (OC) in the DFA group were significantly lower than those in the control group on days 21 and 28. Milk Ca concentrations in the DFA group were also higher than those in the control group on days 14, 21, and 28, whereas serum Ca concentrations and urinary Ca/Cre ratios were unchanged in both groups. These results suggest that dietary supplementation with DFA III increased BMD and decreased serum ucOC/OC ratios in late-lactation dairy cows; this indicates that the replenishment of bone Ca reserves may be enhanced by dietary DFA III supplementation.

Effect of dietary potassium supplementation on the calcium absorption capacity in the rumen and abomasum and fractional excretion of urinary minerals in sheep

The aim of this study was to determine the effect of potassium (K) supplementation on the calcium (Ca) absorption capacity from the rumen and abomasum of sheep. The Ca absorption capacity from the rumen and abomasum of sheep was measured using stable strontium (Sr) as a Ca-analogue tracer method. The sheep, cannulated at either the rumen or abomasum, were randomly allocated to one of two groups (control or K-supplemented) and fed in individual metabolism pens twice daily with a diet comprising oaten hay, lucerne chaff and barley fortified with or without potassium carbonate (K2CO3). The K content of the diet of the K-supplemented animals was 3.1% of dry matter compared with 1.4% for the control animals. The animals were fed their respective diets for a period of 2 weeks. The fractional absorption capacity (FC) of Ca was estimated before, during and after the treatment period. Supplementation with K decreased the FC of Ca in both the rumen and abomasum during treatment and increased the FC of Ca in the abomasum post-treatment. Supplementation with K also increased the fractional excretion of K in the urine, but decreased the fractional excretion of Ca and magnesium (Mg) (P < 0.05), showing that K supplementation significantly affected Ca and Mg metabolism. Results suggest that renal conservation of Ca and Mg is an important mechanism controlling the Ca and Mg pool for vital functions of the body. In times of high demand for these minerals during lactation and pregnancy, high K in the diets may predispose sheep to hypomagnesaemia and hypocalcaemia, which in turn will have a negative impact on productivity and economic returns.

Survey on the occurrence of milk fever in dairy cows and the current preventive strategies adopted by farmers in New South Wales, Australia

OBJECTIVE

The aim of this study was to investigate general and specific strategies adopted by New South Wales (NSW) farmers to prevent milk fever (MF) and its occurrence at calving within their dairy herds.

DESIGN AND METHODS

Of 300 dairy farmers in NSW randomly chosen and sent questionnaires, descriptive analysis of the returned data was performed for 102 questionnaires. To identify the various strategies used to prevent MF and its incidence, farms were classified as having a low (<3%) or high (>3%) incidence of MF. The data were analysed using a multivariable logistic regression model and backwards stepwise elimination to identify significant preventive strategies adopted by farmers having a low or high incidence of MF.

RESULTS

Based on the 102 responses, the median incidence of MF in the NSW dairy region was 3% (range 0-30%). The farms with low MF incidence practised specific MF control strategies, such as feeding dry cows separately, grain supplementation and feeding a low-potassium ration before calving and using a commercial ration mix immediately after calving. The time to first milking post-calving was on average 13.6 h on the low-incidence farms compared with 21.1 h on the high-incidence farms.

CONCLUSIONS

The low median incidence of MF (3%) in NSW was probably related in part to awareness of the importance of feeding a low-potassium, high-grain diet before calving. However, the incidence of MF was high on the farms not practising specific MF preventive methods.