Pre-weaning treatments can be crucial


In Livestock10 Minutes

When it comes to lamb performance at this time of year, I commonly get asked one of two questions;

  • Should I give my lambs a Vitamin B12 injection?
  • Should I drench my lambs before weaning?

I’m addressing these not because I see them as the most important considerations for the season but because these are the two topics farmers question me about the most.

The most important driver of lamb performance in the spring is high feed quality. This is possible with more legume and herb content in pastures. Also maintaining pastures in a vegetative growth phase.

Importance of vitamin B12

Vitamin B12 plays a very important role in energy metabolism in animals. Without sufficient B12 the liver stops being able to convert the products of food digestion into utilisable energy.

Feed intake drops, energy levels decline, and growth rates suffer. Humans source their Vitamin B12 from eating animal products (meat, eggs, milk, fish) or from B12 supplements. Ruminant animals (sheep, cattle, deer), source their B12 from the bacteria that digest feed in their rumen. For these bacteria to make enough B12 they need a source of cobalt, a trace element found in soil and plants.

There are regions of New Zealand where there is an absolute deficiency in soil cobalt. The most widely-known being the bush-sickness band of volcanic country that extends north from the centre of the North Island, through the King Country.

Through other regions, while the soil may contain sufficient cobalt it can be ‘locked-up’ and therefore unavailable for plants to take up through their roots. The common soil factors that will reduce cobalt availability are: high manganese levels, high iron, high aluminium, acidic soil pH, low soil moisture content.

Different plants will take up dramatically different amounts of cobalt when grown on the same soils. Legumes (clovers, lucerne) and the pasture herbs (plantain and chicory) will have far higher cobalt content than common pasture grass species.

Given the large number of factors, how do I untangle this mess to reach a recommendation?

  • Look at the soil test data you already have. Soils with good cobalt levels, low manganese content and a solid liming history are less likely to result in B12-deficient lambs. Soils with low cobalt levels, high manganese content, or an acidic soil test are more likely to result in deficiency.
  • Pastures dominated by grass with little clover and herb content are more likely to result in deficiency than clover rich pastures or herb stands. There are numerous reasons why a sheep breeding
  • operation should strive to see the clover content of their hill country pastures lift, and improved B12 status is one.
  • A large amount of data is behind the relationship between liver B12 concentration and lamb growth rates in NZ. Collecting liver samples from lambs prior to supplementation will confirm or alleviate your concerns about different classes of country. Many farms I have worked with have had intermittent trace element samples taken. Very few have had a robust, well-planned out survey on which their supplementation programmes are based.
  • On most properties you cannot look at your farm as a single block with one recommendation for all lambs. Harder hill country with more acidic soils and lower clover content to pastures will require more direct animal supplementation than easy, fertile flats.If stock are deficient, what options do you have for supplementation?


  • Cobalt chip in fertiliser. This can be an effective option where an absolute lack of soil cobalt is the cause of the problem. On soils where manganese lockup is occurring, cobalt chip will only give very short-term benefits. I rarely recommend this method as I have not been convinced it is cost-effective on North Canterbury soil types.
  • Short-acting water-soluble B12 (Hydroxocobalamin) injection. This is the cheap, red, watery B12 injections sold by every vet and farm supplies store. It will boost animal B12 levels for four-to-six weeks but on farms with more severe deficiency they may find themselves injecting lambs at every drench. This is also the type of B12 present in mineralised five-in-one vaccines.
  • Long-acting B12 injection (Smartshot) – more costly per dose but a single dose can provide up to six months B12 supplementation in sheep. Particularly useful in less-intensive systems where young sheep are infrequently yarded. Lower doses can be used for shorter periods of supplementation.
  • On paddock country with reticulated water systems the water supply can be dosed with trace elements.
  • *Boluses – I am aware of long-acting trace element boluses for adult sheep in NZ but am unaware of any bolus options for lambs.

    Pre-weaning drenching
  • When it comes to drenching lambs prior to weaning there is no ‘one size fits all’ answer to this question. When I work through this question on a farm the top point I have in my head is that most oral combination drenches given to these lambs will only kill the worms already present in the gut. To justify giving a pre-weaning drench I should be confident the lambs will have a worm burden at the time my drench is administered and that this burden is large enough to justify wiping out. What factors are likely to impact this?
  • High sheep-to-cattle ratios – farms with high sheep numbers and very few cattle will frequently see large worm burdens in lambs, earlier in the season. Cross-grazing is a critical principle to understand in a world where we need to focus on fewer chemical inputs.
  • Low covers – tight feed supply will result in lambs grazing lower, where we know more parasite larvae will be present. Increased competition for food and nutritional stress will make animals less resistant to parasites, resulting in higher faecal egg counts, resulting in more pasture contamination with parasites.
  • Previous farm history – pre-weaning egg counts from previous seasons, results of pre-weaning growth rate trials, farmer experience of leaving lambs un-drenched in previous seasons. This is all valuable information.
  • Paddock/block history – areas of the farm that grazed lambs the previous autumn or winter are likely to have higher parasite challenge than areas of the farm that haven’t seen a lamb/hogget since last weaning. A comment like, ‘the hoggets fell to pieces here last autumn’ raises a flag for me that lambs are likely to be challenged the next spring and that earlier drenching should be scheduled.
  • Onfarm trials – they don’t help you this year because the result comes in too late to help with your decision, but comparing the growth rate of drenched versus un-drenched lambs under your management brings huge value in making decisions for years to come.

    What about a tailing drench?
  • Not useful. If you are following good practice welfare standards and are tailing lambs at an appropriate age they will not have a worm burden that will justify a drench. Young lambs are also at far higher risk of toxicity and because of this you are limited to drench options that are ineffective on a large number of NZ farms.Ben Allott is a North Canterbury veterinarian.