Using Yucca Schidigera in Pig Diets: Effects on Nitrogen Metabolism

Extracts and preparations of the desert plant Yucca schidigera Roezl ex Ortgies (Mohave yucca), family Lillaceae, have a variety of beneficial effects when included in the diets of humans and domestic animals. Such effects include reduced gastrointestinal and faecal ammonia levels. Y. schidigera is the principal active component of De-Odorase (Alltech).

The objective of the recent studies discussed in this review was to investigate metabolic changes associated with performance benefits of Y. schidigera extract supplementation. The first animal study was carried out using rats. Thirty-two male Wistar rats were allocated to four dietary treatment groups: control, control plus 200 ppm total Y. schidigera, control plus 200 ppm butanol (BuOH) extractable fraction and control plus 200 ppm non-BuOH extractable fraction. Rats were weighed at 10 day intervals and samples of urine and faeces were collected at 20 day intervals for analysis.

The second study was carried out using pigs. Twenty-four Large White x (Large White x Landrace) pigs (12 male and 12 female, 25–30 kg) were allocated to three dietary treatments. Treatment consisted of a control, control plus 120 ppm De-Odorase (Y. schidigera extract) and control plus 250 ppm Y. schidigera. Pigs were fed a grower diet for weeks 1–4 of the trial and a finisher diet from week 4 to slaughter. The diets contained 25% crude protein which was in excess of requirements. Male pigs were removed from the test house on two occasions during the trial and were placed in metabolism crates to allow collection of urine and faeces.

Addition of Y. schidigera extract to rat diets had no significant effect on whole body weights. Although both BuOH and non-BuOH fractions stimulated growth when fed together (as total Y. schidigera extract), they interacted significantly to apparently cancel each other out.

Addition of De-Odorase extract to the pig diets significantly increased whole body weight on weeks 2–7 and again on week 10 (P<0.05). Average daily weight gain was 52 g/day higher for animals supplemented with De-Odorase.

Serum urea levels were up to 21% lower when rats were given Y. schidigera. No significant effect was observed in rat serum ammonia levels. Plasma urea and ammonia also tended to be lower in response to Y. schidigera, although significant reductions in plasma ammonia were noted only at week 6 of trial. Decreases of up to 36% in urine ammonia concentration were observed in both metabolism studies for pigs treated with 120 ppm De-Odorase.

The most notable result from the pig trials was a 14% reduction in P2 backfat thickness (P<0.05) was also observed. These data add support to previously published results which suggest that addition of De-Odorase extract has beneficial effects on nitrogen metabolism which is reflected in improved biological performance and reduced ammonia production performance benefits.


Introduction

People living in the arid deserts of the Americas have long used extracts and preparations of the flowers, seed pods and stalks of Yucca schidigera Roezl ex Ortgies (Mohave yucca), family Lillaceae. Extracts have been approved by the United States Food and Drug Administration as additives for human consumption (Oser, 1966) and they are commonly used as flavouring or foaming agents in foods.

More recently, such preparations have been effectively applied to the treatment of human diseases such as arthritis, hypercholesterolaemia, hypertension and elevated triglyceride levels (Bingham et al., 1978). Improved performance and health in livestock, resulting from inclusion of Y. schidigera preparations in feeds at 100 to 250 g/tonne, have also been reported (Table 1).

Although the beneficial effects of Y. schidigera have been extensively reported, a specific mode of action remains unresolved. Since investigations of the effects of Y. schidigera began and sales of commercial preparations of the extract became substantial, work has continued to elucidate a possible mode of action. Suggested modes of action of Y. schidigera include: a) direct steroidal stimulus, b) gut urease inhibition, c) ammonia binding, and d) modulation of selected microbes.

Initial work centred around the study of the sapogenins of Y. schidigera as growth stimulants, but no biological effect through steroid hormone activity could directly be attributed to these compounds (Hale et al., 1961). Headon et al. 1991 suggested Y. schidigera bound ammonia and acts in much the same way as oxystarch (Sparks et al., 1971) and ion exchange resins (Holtzman and Visek, 1965).

Another hypothesis proposed in the early 1980s was that Y. schidigera directly inhibits urease in the hindgut of animals (Preston et al., 1985b). However studies on the inhibition of bacterial urease from Bacillus pasteurii concluded that the low levels of inhibition observed could not account for the in vivo effects of effects of Y. schidigera at normal feed inclusion levels (Killeen et al., 1994). Another suggested mode of action is possible alterations of the indigenous microbial populations of the gastrointestinal tract.

Y. schidigera is predominantly used as an ammonia control agent because of its known effects on gastrointestinal and faecal ammonia (Rowland et al.,1976; Gibson et al., 1985). However as discussed below, additional effects have been noted which suggest beneficial effects on nitrogen metabolism in animals.


Table 1. Some examples of the effects of Y. schidigera extract supplementation on performance and health of livestock in the literature.


NS = no significant effects observed.
NR = no statistical significance reported.
* P<0.05.



Recent animal studies

Two animal studies have recently been conducted at the National University of Ireland Galway, Ireland and at the University of Plymouth, England. The first study used rats as the test animal as they have well-studied metabolism and biochemistry, they are easily and cost effectively maintained and they are large enough to yield samples of tissue, digesta and excreta.

Thirty-two male Wistar rats were allocated to four groups: control, control plus 200 ppm total Y. schidigera extract, control plus 200 ppm butanol extractable fraction (BE) and control plus 200 ppm non-butanol extractable fraction (NBE). Rats were weighed at 10 day intervals and samples of urine and faeces were collected at 20 day intervals for analysis of nitrogen metabolites. Also at slaughter samples of serum, liver and muscle were taken for analysis.

Both NBE and BE supplements stimulated growth. However, in the total Y. schidigera extract the two fractions appeared to interact significantly and cancel each other out (Figure 1). This observation suggests that Y. schidigera extract therefore contains at least two active constituents with quite different mechanisms of action, one of which is butanol extractable and one of which is not.




Figure 1. Influence of feed supplementation with Y. schidigera and fractions thereof on rat growth.



Serum urea levels were significantly reduced by Y. schidigera supplementation. The total Yucca schidigera extract, NBE and BE treatment groups reduced serum urea by -21%, -15% and -16%, respectively (Table 2). This is consistent with reductions of blood and plasma urea concentrations reported in rats (Preston et al., 1985a), poultry (Balog et al., 1994) and steers (Hussain and Cheeke, 1995).


Table 2. Influence of feed supplementation with Y. schidigera and fractions thereof on serum variables.


TOT = Total Y. schidigera extract.
BE = butanol extractable fraction.
NBE = non-butanol extractable fraction.
INT = interaction .
SE = standard error of difference.



Although up to -36% numerical reductions in serum ammonia concentrations were observed in the groups supplemented with NBE and BE, differences failed to reach significance. No effect was observed on serum glucose, protein or cholesterol in this experiment. Serum creatinine was 29% (P<.0.02) lower in the BE group than the control. However, although the NBE fraction had no significant effect on its own, it interacted significantly with BE in the recombined total Yucca schidigera extract treatment group to actually increase serum creatinine.

Creatinine is a waste product of muscle metabolism which is released into the bloodstream. Since it is known that creatinine levels increase in proportion to muscle mass (Vander, 1994), these changes in serum creatinine may indicate differences in muscle mass. Serum insulin levels were significantly increased by Yucca schidigera extract and NBE by +195% and +135%, respectively. Insulin promotes fuel storage, protein synthesis and increased nitrogen balance, that is increased muscle mass and reduced urea synthesis rate (Vander, 1994).

As a consequence of the encouraging results from the rat study, a second trial was conducted using pigs as the test animal. Using pigs it was possible to carry out metabolism studies.

Twenty-four Large White Cross (Large White x Landrace) pigs, 12 male and 12 female, were allocated postweaning (25–30 kg) to three dietary treatment groups. Treatments consisted of a control, control plus 120 ppm Y. schidigera and control plus 250 ppm Y. schidigera. The Y. schidigera extract source used in this experiment was De-Odorase (Alltech, Inc.). Pigs were fed a grower diet for weeks 1–4 and a finisher diet for weeks 4 to slaughter. Both the grower and finisher diets were designed to provide 25% more crude protein than was needed for maintenance and production, consequently, both diets contained 25% crude protein.

Male pigs were removed from the test house on two occasions during the trial (week 6 and week 10) and placed in standard metabolism crates for a period of 8 days. Three days were allowed for acclimatisation to the new environment and for the following 5 days both urine and faeces were collected from each animal over a 24 hour period. Serum samples were collected from male animals on 3 occasions during the trial, at the end of week 6, 8, and 10, and from both sexes at slaughter. At slaughter, samples of liver, muscle, backfat and caecal contents were taken for analysis.

Weight, weight gain, feed conversion ratios and dry matter intake were also measured for each animal.

Addition of De-Odorase to the diet increased daily liveweight gains by 52 g/day in the 120 ppm supplemented animals (Table 3). This result supports findings in previous trials of enhanced performance in animals supplemented with De-Odorase (Table 1). Although no significant difference in feed intake was observed, the tendency forward improvement in both would account for the observed increase in gain.

Animals were sent to slaughter one week after reaching 85 kg. The number of days required for supplemented animals to reach slaughter weight was reduced by 7 days when compared to control animals (Table 3).

A significant decrease in P2 backfat thickness, measured using ultrasonic techniques, was observed (P<0.05, Figure 2) in response to De-Odorase supplementation. Such a decrease in backfat thickness has not been reported previously.


Table 3. Effect of De-Odorase supplementation on pig performance.





Decreases in urine ammonia concentrations of 12–36% were observed in both metabolism studies for pigs supplemented with 120 ppm De-Odorase (Figure 3); however due to the small scale of the study numbers failed to reach significance.

Serum urea and ammonia tended to be lower in response to De-Odorase (120 ppm), with significant reductions in serum ammonia noted at week 6 (Table 4).

Serum creatinine was significantly increased on all three sampling occasions during the trial in the animals receiving diets supplemented with 120 ppm De-Odorase (P<0.01, Figure 4).




Figure 2. Effect of De-Odorase supplementation on P2 backfat thickness.





Figure 3. Effect of De-Odorase supplementation on urine ammonia.





Figure 4. Effect of De-Odorase supplementation on serum creatinine concentration.



Since total urinary and faecal excreta were collected and total dry matter intake was recorded it was possible to calculate percent apparent nitrogen digestibility and percent nitrogen retention. There was a numerical increase in both of these parameters in animals supplemented with De-Odorase (Table 5).

Further evidence to support this contention is starting to accumulate from in vitro studies. A recent experiment investigated effects of De-Odorase on ammonia generation from the caecal contents of pigs. Caecal contents were collected from pigs at slaughter and incubated with buffer (control) or buffer containing 200 ppm De-Odorase. Ammonia production over time was then measured by the Chaney and Marbach method (Chaney and Marbach, 1962) This experiment showed a significant decrease in ammonia production in samples treated with De-Odorase (P<0.05, Figure 5) after 36 and 48 hours incubation.


Table 4. Effect of De-Odorase supplementation on serum ammonia and urea concentrations.





Table 5. Effect of De-Odorase supplementation on apparent nitrogen digestibility and percent nitrogen retention at week 10.







Figure 5. Effect of De-Odorse on caecal ammonia production.

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