Several experiments have shown (see Armstrong and Ross, 1968) that the addition of fats to ruminant diets can lead to a reduction in the digestibilities of forage cell walls due to adverse effects on the rumen microflora. Jenkins and Palmquist (1982) showed in vitro that the in situ formation of calcium soaps in the rumen could prevent this problem. Subsequently Jenkins and Palmquist (1984) have provided evidence that the feeding of preformed calcium soaps of tallow and soya oil fatty acids to dairy cows allowed normal rumen digestion of cell walls whereas non-saponified tallow fatty acids caused cell wall digestibility to be reduced.

Givens et al (1988) reported that a calcium soap of palm fatty acids (Protector, UFAC-UK Ltd) did not cause any reduction in the digestibility of neutral detergent fibre (NDF) when fed to sheep at up to 152.4 gkg-1 of total diet dry matter (DM). Since it is believed that these beneficial effects of calcium soaps are due to their reduced rumen solubility, the present experiment has examined this aspect in further detail.