Saponins may increase lamb growth rates

By Sarah Guy

Study results show that the growth rate of female lambs given feed drenched with Agave extract or Quillaja saponaria - both of which contain saponins - increased over 2 months, indicating they may act as natural defaunating agents.

"There is an increasing interest to replace probiotics with natural compounds to beneficially manipulate the rumen, thus to improve livestock performances," say the researchers, who explain that the saponins in Agave could improve feed efficiency and meet this end.

In a study of 30 lambs whose feed was drenched with varying amounts of saponin supplement (n=25) or nothing (n=6), those that received the supplement had a significantly higher daily gain in weight, particularly during the first 30 days of the growth trial.

However, the agents had no effect on lambs' diet intake, nutrient digestibility, or nitrogen balance, note S Nasri and Hichem Ben Salem (Université de Carthage, Ariana, Tunisia).

The pair randomly assigned 30 lambs to five groups that received food drenched with Agave extract at either 120 mg (n=6), 240 mg (n=6), or 360 mg (n=6) saponin per kilogram of dry matter (DM) intake, Q. saponaria solution, containing 120 mg saponin/kg DM intake, or to a control group with no drenching. Lambs were weighed on the first and last day of the trial as well as at 15-day intervals.

The researchers report no effect of the supplements on hay or nutrient intakes or water consumption among the animals, while nutrient digestibility was statistically similar among the different groups of lambs. The animals' nitrogen balance and microbial N flow were also unaffected by the saponin agents.

By contrast, lambs' daily weight gain increased on average in the extract groups compared with control groups, with weak statistical significance. The effect was more pronounced at the 30- than the 60-day evaluation, at 81.1, 85.5, 93.3, 97.8 versus 63.3 g/day in the Agave 120, 240, 360, Q. saponaria, and control groups, respectively.

Lambs fed Agave- or Q. saponaria-drenched feed also had lower blood cholesterol and glucose concentrations than control-fed lambs; it is "well established" that saponins form insoluble complexes with cholesterol and reduce blood glucose, remark Nasri and Ben Salem.

"Further studies are warranted to evaluate the effect of these two saponins' sources on digestion in lamb receiving high concentrate diets," they conclude in Livestock Science.

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