Evaluating the effect of calcium, magnesium and sodium supplementation of Merino ewes on their lambs' growth.

Our study aimed to investigate responses to supplementation of calcium (Ca), magnesium (Mg) and sodium (Na) to lactating ewes and lambs grazing barley forage from lamb marking to weaning. A 10-ha paddock sown to barley was subdivided into eight plots as four replicates of two treatments. Merino ewes (n = 104) with lambs at foot were stratified to the eight plots (13 ewes and 21 lambs/plot) based on number of lambs (twin or single) and ewes' weight. Supplemented groups had access to mineral supplements (30 g/ewe/day) supplying 12 g/ewe/day ground limestone, 12 g/ewe/day Causmag® and 6 g/ewe/day coarse salt in a ratio of 2: 2: 1 by weight (as fed) from day 0 (a day before lamb marking) after sample collection. Control groups were not supplemented with minerals. Blood, milk and urine samples from ewes and blood from lambs were collected at different time points, namely, a day prior to lamb marking (day 0), 14 days after the commencement of study (day 14), and 28 days after the commencement of study (day 28). Weight of the lambs was also recorded at each time point. We found that the concentration of the forage minerals (Ca, Mg and potassium (K)) was lower on day 28 than on day 0 (P < 0.025). Liveweight gain was greater in the first 14 days compared with the second weight gain period (P < 0.001). The interaction of time and treatment was significant for liveweight (P < 0.001). Due to the improvement in weight gain of supplemented lambs, we recommend that mineral supplementation during late lactation is beneficial considering the low cost of minerals, even though the mineral content of the forage was not deficient.

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

The purpose of this study was to test whether supplementation with K improves bone mineral density (BMD) in older cows so that by parturition their bone is better able to mobilize Ca. Twenty-four Holstein Friesian cows (6 mo pregnant, lactating, and in their third or later lactation) were allocated to 2 equal groups and individually fed twice daily a total diet comprising low K oaten hay plus a pelleted concentrate fortified with or without K(2)CO(3) to achieve 3.12% K/kg of DM in the total diet of the K-supplemented (KS) cows compared with 1.50% K/kg of DM for the control cows. The cows were fed their respective diets from the beginning of their sixth month of pregnancy until 2 wk before the expected date of parturition. The strategy was to use K to stimulate a mild increase in extracellular pH to potentially improve BMD well before parturition, when high K contents in the diet are considered safe, but cease supplementing in the few weeks prepartum, when high intakes of K are known to be problematic. The expectation was that the effect of the denser bone would carry through to benefit the cow's plasma Ca, P, and Mg status at parturition. Prior to the period of K supplementation, the cows were part of a commercial pasture-based herd, to which they were returned at the end of the supplementation period and treated as 1 group from at least 11 d prepartum until the end of the study at d 42 of the next lactation. Supplementation with K successfully induced a sustained increase of urinary pH throughout late lactation and into the dry period, as expected. The KS cows consistently averaged a urine pH 0.25+/-0.10 U higher than the controls. However, there was no significant effect of K supplementation on BMD, bone mineral concentrations, plasma osteocalcin, urinary deoxypyridinoline:creatinine plasma Ca, or plasma P concentrations during or immediately after the cessation of supplementation, nor where there any carryover effects during parturition or by d 42 of lactation. Instead, there was an unexpected decrease in the concentration of Mg in plasma of the KS cows compared with the control cows that extended from 0.5 to 2.5 d postpartum. The timing of the decline in plasma Mg was paralleled by declines in plasma concentrations of 1,25 dihydroxy-vitamin D(3) and urinary excretion of Ca and Mg, whereas urinary excretion of P increased; all changes were consistent with a hypomagnesemia that could increase the risk of hypocalcemia. These data suggest that, in addition to the well-documented negative effects of K when fed immediately at parturition, the effects of high dietary K diets can carry over for at least 11 d to trigger a mild hypomagnesemia at parturition. Because K supplementation did not improve BMD prepartum, it was not possible to conclude for or against an ability of denser bone to reduce the risk of hypocalcemia in older cows at parturition.

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.