Influence of Saponins on Alfalfa Utilization by Rats, Rabbits and Swine

Alfalfa samples with low (.4%) and high (1.7%) saponin contents were evaluated in diets for rats, rabbits and swine. In two experiments, with 40 and 60% dietary alfalfa, growth of rats was greater (P<.05) with low saponin than with high saponin alfalfa. Freeze-dried vs air-dried alfalfa of the two types were compared; the saponin effect was unrelated to drying temperature. Rats pair-fed low saponin alfalfa at the same level of intake as voluntarily consumed by rats fed a high saponin alfalfa diet ad libitum had similar growth rates, suggesting that saponin affects growth mainly by limiting feed intake. In a series of feed preference trials, rats preferred low saponin alfalfa to the high saponin material. An alfalfa-free diet was preferred over both types of alfalfa, even with a level of alfalfa as low as 2.5%. Rabbits preferred high saponin alfalfa at low (20% or less) dietary levels, while at 35% or higher, the low saponin type was preferred. Rabbits preferred an alfalfa-free diet when alfalfa levels of 20% or higher were used. Young pigs (22 kg initial weight) had similar gains on an alfalfa-free diet and a 15% low saponin alfalfa diet, and lower (P<.05) gains with a 15% high saponin alfalfa diet. These results indicate that low saponin alfalfa supports a higher growth rate of rats and swine than high saponin material; the pair-feeding experiment and the feed preference trials suggest that increased palatability is the major factor involved.