Responses of whole body protein synthesis and degradation to plantain herb in sheep exposed to heat.

An experiment including a [1-(13)C]leucine isotope dilution and a nitrogen balance were carried out to determine the effect of feeding plantain herb (Plantago lanceolata L.) on whole body protein synthesis (WBPS) and degradation in sheep kept at thermoneutral temperature (20 degrees C) or exposed to heat (30 degrees C). The animals were fed either mixed hay of orchardgrass and reed canarygrass (Hay-diet) or Hay-diet and plantain (9:1) (PL-diet) at maintenance level using a crossover design. Nitrogen intake was higher (p < 0.0001) for the Hay-diet than for the PL-diet, but N balance remained similar between diets and was higher (p = 0.003) during heat exposure than at thermoneutral temperature. The WBPS was numerically lower (p = 0.10) for the PL-diet than for the Hay-diet. The direction of the response to heat exposure differed (p = 0.04) between diets: after feeding the PL-diet the WBPS increased from 15.2-16.9 g x kgW(-0.75) x d(-1), whereas it decreased after feeding the Hay-diet from 17.5-16.6 g x kgW(-0.75) x d(-1). The present results suggest that the PL-diet may have a positive impact for WBPS during heat exposure, and could be used for rearing sheep as an alternative to the Hay-diet.