Evaluation of an inexpensive needle test for the diagnosis of phosphorus deficiency and management of phosphorus supplementation for cattle: A multiple case study.

The needle test (NT) is a point-of-care test developed in Brazil to evaluate the Phosphorus (P) status in cattle. Based on bone resistance, the NT is a very inexpensive method which allows the diagnosis of any degree of P deficiency in a fast and simple way in vivo and directly on farm. The NT measures three levels of resistance in the transverse process (TP) of the lumbar vertebrae: a) TP that are impenetrable and result in warping of the needle (P healthy animals); b) TP offering some resistance to the penetration (animals with subclinical P deficiency); and c) TP which has minimal resistance to penetration (clinical P deficiency). This manuscript presents results from a series of case studies to evaluate the hypothesis that the NT could be used to assess P status in cattle and assesses the usefulness of results to support decision making on mineral supplementation strategies for grazing cattle. The NT was able to detect the changes in the resistance patterns of the TP, as there was reduction or elevation of P levels in the mineral mixtures. The NT was useful to assist in decision-making for adoption of mineral supplementation strategies better suited for each farm, helping farmers to save money and avoid unnecessary waste of P.

Bio-economic evaluation of a reduced phosphorus supplementation strategy for a cow-calf system in Brazil: a case study.

Fertility, weight of calves at weaning, and the economic aspects of a breeding herd receiving mineral supplements containing 75 or 12.5 g of phosphorus (P)/kg were measured from 2013 to 2016. No differences in reproduction parameters or weight at weaning were found before and after the adoption of the new scheme of mineral supplementation. Before the study, the annual cost with the formula containing more P was equivalent to 29.3 weaned beef calves; after the P reduction, the annual cost was equivalent to 2.2 to 6.8 weaned calves. After 3 years of supplementation with 12.5 g P/kg no signs of P deficiency were observed. The clinical-nutritional diagnosis of the herd indicated no cause-effect of P content of mineral supplements upon fertility or performance of healthy cows, demonstranting that the adequate forage allowance was enough to meet most P required by the cows.