A comparison of the requirements and intake of selected minerals on beef finishing units

The results of mineral audits indicated that on every farm in the study the basal diet (before the inclusion of minerals) required mineral supplementation. This requirement varied between pasture finished and grass finished cattle. On all pasture finishing farms, grazing alone met the macro-mineral requirement, with a significant dietary excess of potassium. However micro-mineral deficits of two or more minerals were present on four of the seven farms. This was the result of either inadequate, or the absence of, mineral supplementation  and the low herbage content of micro-minerals.

Table 1. Percentage of farms where a mineral audit indicated individual dietary mineral content below requirement

Slaughterhouse samples were collected from 84 cattle, 43% of indoor finished cattle had liver copper analyses classed as above normal, indicating a degree of over supplementation on a number of indoor finished farms. In contrast 24 cattle (of the 42 finished at pasture) had liver copper values classed as below normal, with 8 of these cattle having a deficient value. The majority of these cattle were finished on farms with no previous history of a copper deficiency.

Table 2. Results of analyses of abattoir samples for liver copper content and GSHPx activity, a measure of selenium status (based on NUVetNA reference ranges)

Dietary audits provide valuable information about mineral content and the likelihood of any imbalance and should be used in ration formulation. The analysis of liver and blood collected at slaughter is valuable, particularly for farms where it is thought antagonism may be an issue or there has been a history of a previous mineral deficiency.

The Problem:

Evidence from other sectors has indicated that minerals are frequently being fed in excess with possible environmental and animal health implications. In a study of 50 dairy farms, Sinclair and Atkins (2014) demonstrated that most farms were feeding excess quantities of minerals. A comparative study from beef finishing systems appears lacking and incomplete.

Aims and Objectives:

The primary aim of this project was to examine mineral intake against requirement, and in particular assess if evidence exists that minerals are being fed in excess, on beef finishing systems and whether a difference exists  between cattle that are finished indoors and those that are finished at pasture. It also demonstrated how to undertake a mineral audit on farm and the value of doing so to farmers.

Approach:

The study required a farm visit to allow collection of feed samples for analysis on a minimum of 14 farms (6 from each type of system – grass finishing versus indoor finishing), but also the completion of a brief questionnaire seeking to explore the decisions taken around ration formulation, particularly with respect to the inclusion of minerals, previous history of any mineral deficiency and current levels of production. Dietary macrominerals assayed included calcium, phosphorus, magnesium, sodium, potassium and sulphur. Microminerals consisted of copper, iron, zinc, molybdenum, selenium and manganese.

Liver and blood samples from 6 animals from each farm were collected immediately post slaughter. Liver mineral analysis consisted of copper, selenium, manganese and cobalt. Blood sample analysis included plasma copper concentration, super oxide dismutase activity, caeruloplasmin activity, plasma selenium concentration, erythrocyte glutathione peroxidase activity, plasma zinc concentration, plasma cobalt concentration, haemoglobin concentration and packed cell volume.

Data was fed back to individual participating farms.

Liver tissue and blood can be collected for analysis in a relatively straightforward manner post slaughter.