1 December 1995

Sluggish lactations put down to high potassium levels

By Sue Rider and

Jessica Buss

FRESHLY calved cows are having difficulty "getting going" in early lactation on some units.

Keenan nutritionist Tony Hall suspects the unusually high potassium and nitrogen in this autumns grass is to blame. He has analysed grass samples taken in the midlands and discovered crude proteins over 24% in the dry matter.

"More importantly, with the flush of grass that we have had, we have seen very high potassium levels, with some as high as 6% compared with an average of 2.5-3%," he says.

Blood samples have reflected these high potassium and nitrogenlevels. "These two elements can depress the amount and availability of magnesium and calcium present, so that blood levels fall – which has also been shown in blood tests."

The upset mineral metabolism could increase the risk of staggers and milk fever. But Mr Hall says the effects are more likely to be sub-clinical, with an increased incidence of difficult calvings, retained cleansings and poor appetite.

Mr Hall advises producers get dry cows off pasture and take control of their diets by offering restricted grass silage at about 20kg a cow a day, with 4kg a cow a day of chopped straw and 0.75kg a cow a day of a protein supplement.

Extra magnesium should be given, especially when a high magnesium dry cow mineral has not been fed. Cows need about 60g (2oz) a day of a calcined magnesite during the high risk period.

He also recommends adding anionic salts such as ammonium chloride to freshening cow rations to redress the cation/anion balance. This will ensure high potassium (cation) diets become more acidic (anionic).

An energy stimulant such as mono-propylene glycol offered to fresh calvers at 200ml a cow a day could help boost their metabolism. "This is a very handy feed for cows struggling in early lactation."

He says some producers have also had success feeding 100-200g of protected-fat Megalac as a concentrated energy source.

Mr Hall also cautions that silages are much lower in crude protein material than anticipated. "It is a rare animal to find a grass crude protein over about 14% these days," he says.

Could target wrong level

"Unless producers are made aware of silage protein by analysis they could target the wrong level of crude protein in the diet."

&#8226 Independent Wiltshire-based consultant Mike Tame also reports that some cows are failing to reach their expected peak yields. "These are animals that lost weight at the end lactation due to the hot, dry summer and during the dry period, and they are now continuing to lose weight in early lactation.

"We know from other years that cows losing weight early in lactation are likely to have infertility problems later on," he says.

"It is too late to reclaim the situation completely when this has occurred. But ensure the energy density of the diet is sufficient and that there is adequate protein to balance it."