Improvement of the measurement and prediction of forage ingestibility in sheep by taking into account the variations of their intake capacity using astandard forage.

Sheep present important variations of their intake capacity that are relate d, for example, to the photoperiod, This makes it difficult to estimate the ingestibility of conserved forages, because they may be fed at different p eriods of the year. A method is proposed to standardise the measure of this forage ingestibility and to make it independent of the main factors influe ncing the intake capacity. Thus, the ingestibility of 51 forages was measur ed on 1- to 2-year-old Texel wethers. To correct the effect of different fa ctors ( the photoperiod and the group effect) which influence the intake ca pacity of these animals, a standard hay was fed before and after all sequen ces of measurements. The evolution of intake capacity was estimated with th is hay, for each group of six sheep, for each period of measurement, by lin ear interpolation between two measures concerning the standard hay. Under t hese conditions, it appears that: 1) the intake capacity of wethers leads t o an under-estimation of forage ingestibility in December-January and to a overestimation in May-September; 2) the proposed correction is well justifi ed; indeed, the relationship between ingestibility and NDF content, a class ical prediction criteria, gives a residual standard deviation of 9.9 g DM.k g(-1) light weight (LW)(0.75) before correction, and to 5.2 after correctio n; 3) the correction makes it possible to conclude that ingestibility of we ll-cured hays and silages is nearly equivalent to initial fresh forages. It is proposed to use this method of correction each time, when measurements of ingestibility are achieved on sheep, at different seasons, and/or with d ifferent group of animals, and when the results have to be pooled. ((C) Els evier / Inra).