New Approach to Transition Feeding Favoured

New Zealand dairy farmers are urged to tip their thinking about calcium supplements and wintering on its head to get the most out of their herd’s production into spring time and beyond.

Dr Joe McGrath, Asia-Pacific is the manager for nutrition company DSM and adjunct senior lecturer in ruminant nutrition at the University of New England in Australia. Dr McGrath’s research focuses on the critical relationship between macro minerals, primarily calcium, and health.

 “Typically what happens is the cow will experience a natural decline in feed intake from two weeks out before calving, over that transition period. That period requires good management to balance that tendency, ensuring she continues to get sufficient energy, minerals and vitamins as she approaches a very high stress period,” he said.

Dr McGrath said most dairy farmers will know something about the transition period being important, but not all may be aware how managing it effectively can bring on going benefits beyond calving, and well into lactation.

Deficiencies in calcium over that period culminate in impaired immune function, causing problems including retained placenta and ketosis.

Post calving metabolic problems like milk fever, or hypocalcaemia, can also be more common in cows poorly managed over transition.

Lowered calcium levels result from the significant demand for calcium to supply colostrum production post calving.

“A cow producing 10 litres of colostrum may lose 23g of calcium in one milking alone”.

At those demand levels a calcium deficit can quickly develop, and the resulting “down cow” can bring a cascade of secondary problems taxing her own health, and the time of herd managers in trying to rectify them over a busy time of the year.

But Dr McGrath cautions it is also the cows that don’t go down, but are still sub-clinically hypocalcaemic that lurk in a herd like the unseen bulk of an iceberg. For every clinical cow there can be up to 10 times the number in sub-clinical cows.

“If you add in the effect of high potassium, nitrate and ammonia intake from ingesting young green grass, magnesium absorption is reduced, and the cow’s ability to mobilise calcium will be reduced even further.”

Often farmers will adopt a transition programme to lower the dietary cation-anion difference (DCAD) into a “negative” or acidic level by feeding anionic salts. This improves the cow’s ability to mobilise calcium.

It activates the movement of calcium from her skeleton in preparation for the high demand colostrum production will place upon her calcium reserves.

“But with low DCAD diets, mobilising those levels of calcium can also run the risk a cow suffers from excessive bone wastage every lactation, furthermore a negative DCAD diet is almost impossible to achieve in New Zealand’s grass based systems.”

Sourcing calcium from somewhere other than her skeleton would appear a good option.

But farmers also risk worsening milk fever by feeding a calcium based supplement over the transition period.

“Over several lactations the continual draw down on her skeleton’s calcium, and that risk of traumatic events, make life hard for cows over this stressful period.

“Even when she is optimally fed, a cow will be in a calcium deficit for the first six to nine weeks post calving, typically losing skeletal mass post calving, and only regaining some of it back over the late lactation-dry period.”

Published data indicates that during early lactation a cow can lose between .3kg-1.5kg of calcium from her bone structure. That can reduce her fertility, impact on her health, and ultimately reduce her longevity within the herd.

But absorption of calcium sourced from her diet, rather than just her skeleton requires adequate levels of activated vitamin D, to make it available.

“However her vitamin D levels will be lowest over late winter-spring, the same time her calcium demand is greatest.”

Phosphorous rich spring grass will also further inhibit a cow’s ability to activate sufficient levels of vitamin D post calving.

As a result of the cow’s failure to metabolise that dietary calcium properly, they can suffer from milk fever.

To help manage the critical transition period DSM developed Tranzsol to provide cows with a metabolisable, safe source of dietary calcium.

Tranzsol contains limeflour, and a patented form of activated vitamin D (Hy-D). The presence of Hy-D with the lime-flour ensures effective, safe levels of calcium for the cow over the transition period.

“A cow’s ability to get sufficient calcium is usually compromised by a complex interaction between available calcium, magnesium levels, phosphorous levels and vitamin D.

“The presence of Hy-D in Tranzsol enables her to absorb the supplied dietary calcium. In New Zealand based studies this has lifted calcium blood concentrations by 30%, compared to when only feeding anionic salts usually used in DCAD diets.”

Dr McGrath said using Tranzsol in a transition program gave the cow a pathway to use the calcium in her diet, rather than relying solely upon mobilising her valuable skeletal calcium.

“This idea of supplying calcium in her diet before calving, using Tranzsol, is not common practice in NZ. But overseas farmers have used it effectively for years, better managing milk fever risk, and giving cows a healthier start to their lactation, without drawing down on their bone calcium which is what happens to Kiwi cows, year in, year out.

  Ultimately this may result in them leaving the herd too soon, on the grounds of health or fertility issues resulting from poor health.”