Rode et al (1997) reported a significant improvement in milk production and milk fat content when the ration was supplemented at the start of lactation with hydroxy-analogue of methionine (HMB) (DL,2 hydroxy 4 (methyl thio) butanoic acid. This could be explained either by the fact that HMB in the liquid form, in a manner similar to the calcium salt of HMB is used by the rumen microorganisms, resulting in the stimulation of the rumen microflora or that the HMB supplies by-pass methionine analogue to the duodenum. The objective of the present trial was to measure the effects of HMB in the rumen using a rumen simulation technique and to test the effect of different sources of methionine on the digestibility of the organic matter of maize silage.

Experiments were carried out using the in vitro rumen technique (Menke et al, 1988) (HFT). Different sources of methionine were tested : two sources of the hydroxy-analogue of methionine (HMB) : [A] AlimetTM (88,2%) (Novus Int Inc) and [B] RhodimetTM AT88 (88,9%) (Rhone Poulenc Animal Nutrition), [C] calcium salt of HMB (85,3%) [D] Rhodimet NP99 (99%) (DL methionine powder (RPAN)) [E] mineral sulphur in the form of sodium sulphate (99,5%).