14 January 2000

More vitamin B needed for the modern heifer

SUPPLEMENTING dairy cows with two forms of vitamin B increased heifer milk yields by 2.5kg a day in a recent study.

But further work is required to assess supplementation costs.

Christiane Girard of Agriculture and Agri-Food Canada, Quebec, believes higher dietary vitamin B levels are necessary to keep pace with modern milk production.

"Most studies on ruminant B vitamin requirements were conducted 50 years ago and during these decades, milk production has more than tripled.

"Generally, there is no need to add B vitamins to dairy diets, as they are synthesised by rumen micro-organisms in sufficient amounts to avoid deficiency. But if the goal is to maximise animal performance rather than avoid deficiency, supplementing these vitamins is necessary."

A study carried out by Dr Girard showed that heifers supplemented with 3mg folic acid/kg body weight in their diet and a 10mg weekly injection of vitamin B12 produced an extra 2.5kg of milk a day. For cows the rise was lower, an extra 1.5kg a day.

"Heifers are poorer synthesisers of vitamin B12 than cows because their rumens are less primed to synthesise the vitamin. Therefore, they showed a greater response to supplementation."

Dr Girard plans to conduct further studies on in-feed vitamin B12 supplementation, which should be simpler to give than the injectable form.

"Producers believing their herds may benefit from supplementation couldould offer animals 2-4mg folic acid/kg bodyweight and should see a yield increase within a month. Where there is no effect, further supplementation with vitamin B12 may also be necessary," advised Dr Girard.