A big influence on lamb growth rate from birth to weaning has already been set. The ewe body condition at lambing and the ewe feeding level coming into lambing for multiple ewes both impact on lactation. If there is still time to intervene the most important action is to lift the feeding level of multiple ewes.
The other big area of influence on lactation is the level of feeding of the multiple ewes when they are reaching peak lactation. That starts around three to four weeks after lambing began. At that time ewes can eat more than at any other time of year. This is a hard feed supply to be in control of because it depends so much on the spring pasture growth rates. Last spring the pasture growth rates decreased at that critical time and even though there was feed later in the spring lamb weaning weights were back. Being aware of when the multiple ewes have this huge feed demand could enable some intervention to give those ewes more room at that time. Usually though at that time feed is short.
Animal health interventions from lambing to weaning mostly give more comfort to the operator than benefit to the lamb. A very common one is Vitamin B12. There is no question that lambs that are deficient in this vitamin will grow slower. But only if they are deficient. Most B12 deficiencies occur in the summer when cobalt levels at their lowest. For them to be low enough in the spring is confined to specific areas and is not widespread. Expectations of a response to injecting with B12 far out way any actual response.
Drenching suckling lambs is very common and is poorly supported by science. Not to say that there is not a response but it is highly variable. Combine that with our constant need to limit exposing the worms to drench and a potential cost to yarding ewes and lambs this action needs to be carefully considered. We know that milk gives lambs a lot of protection against the impact of worms. Within the flock there will be a big range in how much lambs are getting. Ewe age, ewe condition and feed levels are all variables which probably influence any response to a lamb drench. If it is to be done the need to ensure some refugia applies just as it does to any other drenches. Don’t do them all in a mob.
Once multiple ewes are past peak lactation their lamb’s growth rate is increasingly sensitive to the quality if the pasture that they are eating. Managing that quality is always a challenge but an important one if weaning weights are to be maximised. That then impacts on an appropriate weaning date should also be very sensitive to pasture quality.