Supplementing your stock and managing your minerals

With drench resistance on the rise, many farmers are looking to use summer forages to reduce their reliance on drenches – a positive trend. However, oral anthelmintics often contain minerals, so reducing drench use can result in deficiencies. Managing your mineral supplementation is relatively easy and helps maximise stock performance. 

Selenium (Se), an antioxidant, influences immune responses and regulates thyroid metabolism. Signs of deficiency include, ill-thrift, low liveweight gains, decreased fertility through embryonic mortality, and, in severe cases, white muscle disease. Much of New Zealand is Se deficient, and the uptake is lower in some forages, like kales and swedes, compared to pastures. While adding Se to fertilisers is successful for pastures, the addition of Se, Cobalt (Co) and Copper (Cu) fertiliser on swede and kale crops does not correct deficiencies. Oral worm drenches and oral mineralised products provide five to six weeks of supplementation, short acting injections four to seven weeks. It is important to remember; too much Se is toxic. The rapid absorption of the injectable forms makes them the riskiest, so avoid using two selenised products at the same time.

Cobalt is an intrinsic part of the production of Vitamin B12 in the rumen. Blood samples indicate if the current feed is deficient, while liver test shows the state of Co reserves. Low growth rates and a watery eye discharge are signs of deficiency. Regular monitoring is advised as Co availability varies. Fertilisers may provide up to 10 weeks supplementation in pastures. A short acting injection works for one-month while oral mineralised products (containing seven mg Co) last for one week. Oral drenches containing Co have little effect.

Brassicas, including bulb crops, can be low in Iodine (I). They also contain goitrogens which interfere with thyroid metabolism and leads to goitres. Because goitrogens are present in so many plants, including white clover, sampling herbage is not a good predictor. While common to supplement pregnant stock grazing these forages, little is known about how the summer grazing of these forages impacts on growth rates. We do see a reduction of 40 to 50 percent in wool growth. Because salt blocks and water supplementation are not effective in supplementing sheep with iodine, it is recommended to oral dose ewes with 200 mg of Potassium Iodide (KI) which lasts four to six weeks.

Copper (Cu) is required for nerve, bone immune, and growth functions of the body. Compounds in forage brassica prevent absorption of Cu in the gut, leading to deficiency. Reducing worm burden can increase Cu absorption in sheep. Grazing forage brassicas and bulb crops for extended periods, many months, may result in low Cu. This can be monitored by liver analysis at the freezing works.

Introducing summer forages into your farm systems can result in higher growth rates, lower worm burdens, and reduces the need for drench which in turn slows the development of drench resistance. It is important to regularly monitor your stock’s trace element levels, to ensure deficiencies are not resulting in lower stock performance.

For help managing mineral supplements in your stock, contact your PGG Wrightson Technical Field Representative.

Managing mineral deficiencies in grazing livestock. Grace N, Knowles S, Sykes A | Occasional Publication No. 15 (2009) | New Zealand Society of Animal Production