Parasites and Protein

Young growing lambs have a high demand for protein: for body maintenance, lean tissue and wool growth and a healthy immune system. Going into summer, worm burdens can place an additional protein demand on lambs, often coinciding with declining pasture quality, legumes making up a lower proportion of the sward, weaning, or a reduction in milk intake as ewe production drops.

A worm burden affects the lamb by:

• reducing appetite, limiting the total intake the lambs are achieving

• direct damage to the gut lining resulting in reduced protein uptake

• additional losses as the gut ‘leaks’ protein.

If lambs are already on a marginally adequate diet (low protein, low available energy or overall lack of feed), then the effect of the parasite burden can significantly reduce feed intake and growth rates over this critical period. Immunity will also suffer, and lambs will be less able to resist a parasite burden or infection (e.g. pneumonia).

Smaller lambs have the highest protein demand, and will be most affected by a heavy parasite burden. Lambs under 35kg should be a priority group for access to any higher quality feed available such as chicory, herbs or brassicas. These feeds have the added advantage of tending to have lower levels of larval contamination than grass dominant pasture. It is the daily ingestion and development of larvae within the lamb that cause the majority of production losses. In a 1982 study, it was shown that undrenched lambs grazed on low contamination pastures grew faster than lambs that were drenched regularly on high contamination pastures.

Depending on the season and available pasture, lambs may already be on the back foot as ewe’s milk production drops and pasture that is available may not have adequate legume content. It is therefore important to maintain good parasite control as to not add additional stress to the growing lambs, and where possible, prioritise feeding cleaner higher quality feeds such as brassicas or herb and legume-based pastures.