Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
PRODUCTION Potent potassium by Anelle Wabeke Potassium is the third-most abundant mineral element in the body after calcium and phosphorus. It is essential for life as it is involved in the osmotic regulation of tissue fluids and the acid-base balance that exists between potassium, sodium, calcium and magnesium. The highest potassium concentration in the body is found within the muscle cells and comprises about 5% of the total mineral content of the body. THE DAIRY MAIL • OCTOBER 2014 63 PRODUCTION Ruminants need more Ruminants have a higher requirement for potassium than monogastric animals, as it is essential for rumen microorganisms. The requirements are estimated to be between 0,5 and 0,8% of the diet, which increases under stress conditions. The optimal level of dietary potassium in high-production dairy cows under heat stress can increase to approximately 1,1%. Less potassium (0,65%) is recommended for dry cows, heifers and calves. High levels of potassium in the last three to four weeks before calving should be avoided as this may increase the probability of milk fever and retained placentas, which could lead to reduced milk production. The maximum potassium quantity allowed in a dry cow ration depends on the use of anionic salts. It is recommended that fertilised pastures should be avoided during this stage. The effect of heat stress of potassium • • • • • aintain water balance M Maintain osmotic pressure Maintain acid-base balance Activate enzymes Help metabolise carbohydrates and proteins • Regulate neuromuscular activity (along with calcium) • Help regulate heartbeat UPPE A11198/DM Heat stress leads to reduced feed intake and production, as well as a loss of sodium and potassium through sweat. This requires an increased dietary supply of minerals during hot days. Many responses to heat stress such as increased water intake, respiration and sweating rates are survival strategies to maintain normal body temperature. This compromises the optimum efficiency and maximum production of lactating cows. Potassium is the main mineral in sweat and, as the temperature rises, cows Functions 11:20 AM THE DAIRY MAIL • OCTOBER 2014 65 lose more potassium through sweating, panting and urination. In addition to sweat loss, lactating cows also lose additional potassium via milk, which contains 0,15% potassium. A cow producing 20 kg milk and consuming 20 kg dry matter containing 0,8% potassium will secrete about 19% of her daily potassium intake in milk. In addition to potassium loss through sweat and milk, meeting the animal’s requirement may be complicated by suppressed dry matter intake, reducing the total amount of potassium and other nutrients consumed. // A cow producing 20 kg milk and consuming 20 kg dry matter containing 0,8% potassium will secrete about 19% of her daily potassium intake in milk. ” Deficiency signs Potassium deficiency is uncommon in grazing dairy cows, as green forages are excellent sources of potassium (1 to 4%). 66 THE DAIRY MAIL • OCTOBER 2014 • • • • • • • • epressed growth D Muscular weakness Stiffness Decreased feed intake Intracellular acidosis Nervous disorders Reduced heart rate Abnormal electrocardiograms PRODUCTION Potassium in the ration Studies have shown that supplementing dietary potassium during hot summer days to Holstein cows increased feed intake and milk yield curvilinear to dietary potassium, although this response is lower for Jersey cows and animals under shade. The maximum tolerable concentration according to the National Research Council (NRC) has been set at 3% for cattle, but cattle grazing lush spring pastures often consume more than this with no adverse effects except for reduced absorption of magnesium causing grass tetany (this can be countered by giving extra magnesium). Pasture with an excess of 5% potassium can increase the occurrence of bloat and infertility. Excess potassium can also aggravate a sodium deficiency, which is associated with impaired reproduction. Potassium deficiency is uncommon in grazing dairy cows, as green forages are excellent sources of potassium (1 to 4%), especially lush spring pastures. But cows on a total mixed ration (TMR) are often deficient in potassium, as TMRs consist mostly of ingredients low in potassium such as cereals, hay and silage (although molasses and seed oils are good sources). Potassium can be supplemented by potassium chloride, potassium carbonate or potassium sulphate if necessary. When potassium chloride is used, the total chloride levels should be no more than 0,3 to 0,35% in the total dry ration. When potassium is increased in a ration, other minerals should be kept in mind too, as minerals have a significant number of interactions. Many of these interactions are between potassium, sodium, chloride and magnesium. Additional magnesium is required when a ration is fed which contains more that 1% potassium. Potassium supplementation may inhibit magnesium uptake from the rumen and could result in hypomagnesaemic tetany. Other adjustments nutritionists can make are to use high-quality forage to reduce heat production during digestion and adding water to the total mixed ration if dry matter intake drops significantly. This can sometimes increase dry matter intake substantially. Feeding a higher fat ration (up to 5 to 7% of the total ration) is also an option if a feed intake of 90% of normal intake can’t be maintained to increase ration energy without increasing the heat of rumen fermentation. Increasing bypass protein levels to account for the decline in dry matter intake is another option. Additives that have been effective in some studies such as niacin (vitamin B3), fat-soluble vitamins (A, D, and E), probiotics containing Aspergillus oryzae, dried brewer’s yeast and yeast cultures, live cell yeast or essential oil extracts can also be used to alleviate the effects of heat stress. Beating the heat Nutritionists can formulate feed to decrease the effect of heat stress on animals but this is only a tool dairy farmers can use together with good management practices. Some of these practices include providing most of the ration during the cooler periods of the day to minimise heat production at higher temperatures. Other practices include providing shade and extra air movement, and supplying clean and abundant drinking water. Based on this data, the recommended concentration of potassium in lactating dairy cows should be between 1,1 and 1,5% during heat stress to improve feed intake and to maintain a good electrolyte balance in the cow. Work with your nutritionist to ensure that the ration delivers the nutrients needed for peak performance in hot weather and put some management practices in place to decrease the effect of heat stress on your animals. Anelle Wabeke is a nutritionist specialising in ruminant nutrition at ADVIT Animal Nutrition. Contact her at [email protected] for more information. TDM THE DAIRY MAIL • OCTOBER 2014 67