WINTER KALE FOR DRY COWS. Mineral Point of View

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1 WINTER KALE FOR DRY COWS Mineral Point of View Copper requirements for dry cows on Kale Cows are at greater risk of copper deficiency on Kale than sheep, due to the relatively higher requirement for copper by cattle. Pregnant cows in late gestation are at particular risk of copper deficiency because the calf preferentially accumulates liver copper reserves during the last few weeks of pregnancy. Kale is more likely to induce copper deficiency in cows than nonbrassica feeds. Kale contains low concentrations of copper, typically ranging from 3-8 mg/kg DM (Table 1). High sulphur levels in Kale (Table 1) further challenge uptake of copper from the gut. The formation of insoluble complexes between dietary copper and sulphur reduces the absorption of dietary copper by the cow. The ingestion of soil during winter grazing further depletes the copper reserves of pregnant cows. Soil contains high concentrations of iron, and iron interferes with copper uptake from the gut of the cow. To avoid potential problems of copper deficiency through the winter, the copper status of cows should be assessed, preferably by liver biopsy, before dry off (typically during May). Copper status may be topped up at dry off with supplementation through the dry period through in-line dispensers, Peta-dispensers or using dry cow licks. Zinc requirements for dry cows on Kale In Zinc deficiency soils, the supplementation of it will be very important for cows on Kale. The reason is, again, the low content of Zinc in Kale (Table 1) and, like copper, formation of insoluble complexes with sulphur, and high concentration of iron, interferes with zinc absortion. Selenium requirements for dry cows on Kale Selenium is essential for an enzyme, glutathione peroxidase (GSH-px). This enzyme plays an important role in reducing or preventing the effects of red water in cows feeding on brassica crops. Red water (haemoglobinuria) is caused by the SMCO toxin, described later.

2 A sub-optimal selenium and GSH-Px status may increase the susceptibility of the cow to the effects of SMCO. Brassica crops do not typically contain high levels of selenium (Table 1), however levels depend on soil selenium status. The use of selenium fertilisers can increase the selenium concentration of the brassica plant. Low selenium status may also compromise the iodine status of cattle. As for copper, selenium status of cows going onto brassica crops should be checked before drying off using liver selenium or serum selenium levels. Selenium can be topped up using supplementation. Follow the recommendations of your veterinarian or nutritionist. Iodine requirements for dry cows on Kale Dry cows eating winter Kale crops may suffer from either a primary iodine deficiency (not enough iodine in the feed) and/or secondary iodine deficiencies (caused by compounds called goitrogens blocking the uptake of iodine by the cows thyroid gland). Kale contains low levels of iodine (Table 1) and can contain high levels of goitrogens. In the absence of goitrogens, 0.5 mg iodine/kg DM is considered sufficient to meet the iodine requirements of all classes of ruminants, but in the presence of goitrogens iodine requirements may increase to 2 mg iodine/kg DM (Grace, 1994). Iodine deficiency may extend the duration of pregnancy and increase risk of stillbirths and poor viability of newborn stock. Iodine supplementation is the only practical supplementation option. Typical rates are mg iodine/cow/day, however check with your veterinarian or nutritionist for rates suitable for your situation. Dilution of anti-nutritional factors Kale contains compounds including nitrates, glucosinolates (goitrogens) and SMCO. These compounds may reduce cow performance and increase risk of health problems. Feeding silage and hay in addition to brassicas will dilute the total dietary concentration of anti-nutritional factors and reduce potential challenges to cow productivity and health. Try to keep no more that 6 kg DM per cow per day of Kale.

3 Springing dairy cows Cows should be taken off the Kale crop when transferred to the springer mob to minimise risk of rumen fermentation change at the point of calving. Calcium and phosphorus mineral profile Calcium Leaf material of forage brassicas can contain high concentrations of calcium (up to 40 g/kg DM; Table 1). These levels are high relative to a cow s calcium requirement in the last 2-3 weeks before calving. If brassicas must be fed to springer cows, feeding low calcium feeds with the brassica can reduce calcium intake. Low calcium feeds include cereal grains and straws and/or legume free hay, however the best option is to avoid the feeding of brassicas to springers. Phosphorus In contrast to calcium levels, brassica concentrations of phosphorus (P) are considered marginal (2-4 g/kg DM) for dry cows, particularly if the diet includes other low P feeds (e.g. cereal straws, poor quality hay). KALE contains low levels of magnesium Low magnesium during the transition diet can cause hypomagnesemia (low blood magnesium) and hypocalcaemia (low blood calcium). Both conditions will increase the risk of metabolic disease and poor milksolids production in early lactation. Low concentrations of magnesium and high concentrations of potassium in Kale (Table 1) will increase risk of metabolic disease, particularly during the last 4 weeks of pregnancy. Standard recommendations for the supplementation of magnesium for dry cows on brassica crops include magnesium oxide or alternatively, magnesium chloride or sulphate.

4 Dietary Cationic Anionic Difference (DCAD) of KALE The low DCAD makes forage brassicas a potentially good springer feed if DCAD were the only factor under consideration. However, the previously discussed challenges of brassicas for springer cows (change in diet from springer to milker diet; high calcium, low phosphorus and low magnesium) are likely to reduce any perceived benefits of the relatively low dietary DCAD levels. Table 1: The nutritional and mineral characteristics of Kale Analysis Mean Range DM % OM % OMD % CP % WSC % NDF % ADF % MJ ME N (g) Ca (g) P (g) S (g) Mg (g) K (g) Na (g) Cl (g) * * Cu (mg) Zn (mg) * Mn (mg) * Fe (mg) * Co (mg) Se (mg) I (mg) Bo (mg) Mo (mg)

5 THE IDEAL MINERAL SUPPLEMENT FOR DRY COWS ON KALE LIKE PRINCIPAL FEED: TOPMIX PLUS WC (winter crop): A combination of inorganic and organic minerals for dairy cattle. Zinc, copper and selenium 50% from organic sources to enhanced absortion. 5 g dose: 10 mg Cobalt, 200 mg Copper, 15 mg Iodine, 4.5 mg Selenium, 400 mg Zinc.