SAC Research

Periparturient breakdown of immunity to parasites has long been recognised, but it remains unclear why it occurs and how it can be controlled. Research has shown that it is not necessarily associated with lambing per se, time of the year, or hormonal changes.

We have suggested that breakdown of immunity to parasites may be a consequence of limited protein supply (a situation that often occurs during the periparturient period). This could be the case because the available protein would be prioritised to lamb growth (i.e. milk production) over maintenance of immunity. If such a nutritional basis exists, then this opens the possibility to use nutritional management to reduce the degree of periparturient breakdown of immunity to parasites, and its consequences on pasture infectivity.

Recent research at SAC has shown that:

• Scarce protein supply is indeed directed towards milk production rather than to immunity to nematode parasites
• Twin-rearing ewes excrete more nematode eggs than their single-rearing counterparts
• Increased protein supply to twin-rearing ewes increases milk production and reduces nematode egg excretion within a matter of days
• The presence of body protein reserves reduces nematode egg excretion at times of limited protein supply from the diet.

The results of these studies support the view that breakdown of immunity to parasites has indeed a nutritional basis, and indicate that it is mainly the poorly conditioned, twin-rearing ewe that contributes to contamination of the pasture with parasite eggs.