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Effects of plant saponins on forage digestion and performance of grazing beef cattle

ProQuest Dissertations and Theses, 2011
Dissertation
Author: Casey Paul Mcmurphy
Abstract:
The inclusion of Micro-Aid® (MA) in protein supplements improved rumen DM and NDF degradability via a decrease in rumen particulate passage rate, but was not successful at improving apparent total tract digestibility. This improvement in rumen digestion may have the potential to increase the supply of nutrients to the small intestine for subsequent improvements in animal performance. Micro-Aid ® successfully suppressed protozoa after continuous administration, over 20 days, suggesting that complete adaptation to saponins by protozoa was not observed. Also, the reduction in protozoa has been shown to increase microbial efficiency (Veira, 1986) which would be beneficial to lactating cows that have a greater metabolizable protein requirement than cannulated steers or even gestating cows. The inclusion of MA did not impact performance of stocker steers or beef cows during the supplementation period. However, MA did improve calf performance when supplementing cows during early lactation. This advantage was lost due to compensatory gain after supplementation ceased, but could prove to be of great importance to a fall-calving cow herd, consuming low-quality forage for its entire lactation period. There was a non-significant increase in milk yield of 2.4% during early lactation, similar to other findings. Feeding frequency of MA needs to be evaluated as a potential role in animal performance. These performance studies intermittently supplied MA as opposed to a continuous supply. This may negatively impact the microflora populations intermittently and never sustain a stable environment. It would also be beneficial to evaluate the use of MA in combination with non-protein nitrogen. With the rising costs of feed protein, this may be an economical option to upgrade the use of non-protein nitrogen in grazing cow diets. More research needs to be conducted to determine the impact of daily provision of MA and its interaction with diet on performance of grazing animals.

  TABLE OF CONTENTS

Chapter Page

I. INTRODUCTION ......................................................................................................1

II. REVIEW OF LITERATURE....................................................................................3

Background of Saponins ..........................................................................................3 Saponins for the Feed Industry ................................................................................4 Saponins Role on Rumen Fermentation ..................................................................5 Fate of Saponins in the Rumen ................................................................................9 Saponins on Intake and Digestibility .......................................................................9 Saponins on Animal Performance .........................................................................10 Protein Supplementation ........................................................................................11 Urea Supplementation ............................................................................................11 Protein Supplementation on Animal Performance ................................................13 Conclusions ............................................................................................................15 Literature Cited ......................................................................................................16

III. EFFECT OF MICRO-AID ® ON HAY INTAKE AND UTILIZATION BY BEEF CATTLE ................................................................................................................25

Abstract ..................................................................................................................26 Introduction ............................................................................................................27 Materials and Methods ...........................................................................................28 Experiment 1: In Situ Digestibility ........................................................................29 Experiment 2: Metabolism .....................................................................................31 Results and Discussion ..........................................................................................34 Experiment 1: Intake and Passage Rate .................................................................34 Experiment 1: In Situ Digestibility ........................................................................36 Experiment 2: Intake and Digestibility ..................................................................37 Experiment 2: Rumen Fermentation and Blood Urea Nitrogen ............................38 Implications............................................................................................................40 Literature Cited ......................................................................................................42

 

Chapter Page

IV. EFFECTS OF INCLUDING MICRO-AID ® IN A PROTEIN SUPPLEMENT ON PERFORMANCE OF GROWING STEERS AND SPRING-CALVING COWS ................................................................................................................................53

Abstract ..................................................................................................................54 Introduction ............................................................................................................55 Materials and Methods ...........................................................................................56 Experiment 1: Stocker Steer Performance .............................................................56 Experiment 2: Spring-Calving Cow Performance .................................................58 Experiment 3: Milk production, Intake and Digestibility ......................................62 Results and Discussion ..........................................................................................65 Experiment 1 Forage Quality .......................................................................................................65 Steer Performance ..................................................................................................65 Experiment 2 Cow BW and BCS .................................................................................................67 Calf Performance ...................................................................................................68 Cow Reproductive Performance ............................................................................68 Experiment 3 Milk Yield and Composition .................................................................................69 Intake and Digestibility ..........................................................................................69 Implications............................................................................................................70 Literature Cited ......................................................................................................72

APPENDICES .............................................................................................................85

Institutional Animal Care and Use Committee Approval ......................................86

EFFECTS OF IMPLANT TYPE AND PROTEIN SOURCE ON GROWTH OF STEERS GRAZING SUMMER PASTURE .........................................................87 Abstract ..................................................................................................................88 Introduction ............................................................................................................89 Materials and Methods ...........................................................................................90 Results and Discussion ..........................................................................................94 Implications............................................................................................................98 Literature Cited ......................................................................................................99

  LIST OF TABLES

Table Page

CHAPTER I

1. Saponin-containing plants used for feed additives in ruminant diets ................23

2. Effects of commercial Yucca schidigera extract products on protozoa, ammonia and propionate concentrations in rumen contents in vitro and in vivo ..................24 CHAPTER II 1. Supplement composition and amount of nutrients supplied daily .....................48

2. Effect of supplement on feed intake and passage rate in steers consuming low- quality prairie hay in Exp. 1 ...................................................................................49

3. Effect of supplement on in situ digestibility kinetics of low-quality prairi e hay in Exp. 1 .....................................................................................................................50

4. Effect of supplement on DMI, total tract apparent digestibility, and nitroge n balance in steers consuming low-quality prairie hay in Exp. 2 .............................51

5. Effect of supplement on rumen fermentation, blood urea nitrogen and protozoa counts in steers consuming low-quality prairie hay in Exp. 2 ...............................52

CHAPTER III 1. Supplement composition and amount of nutrients supplied daily for stocker steers grazing late summer native range (Exp. 1) ............................................................76

2. Supplement composition and amount of nutrients supplied daily during gestation and lactation (Exp. 2 and 3) ...................................................................................77

3. Composition of tallgrass native range during summer supplementation from late

July until early October, 2009 (Exp. 1)..................................................................78

  4. Effect of supplement on performance of steers grazing native range in la te summer and early fall in Exp. 1 ...........................................................................................79

5. Effect of winter supplement on cow BW and BCS in Exp. 2 ............................80

6. Effect of winter supplement for spring-calving cows on calf performance in Exp. 2 .....................................................................................................................81

7. Effect of winter supplement on cow reproductive performance in Exp. 2 ........82

8. Effect of winter supplement on beef cow milk production and composition during early and late lactation in Exp. 3 ............................................................................83

9. Effect of supplement treatment during early and late lactation on hay intake a nd apparent total tract digestibility of dietary components (DM basis) Exp. 3 ..........84

APPENDICES

1. Composition of old world bluestem and tallgrass native range forages during late summer supplementation from late July until early October during 2008 and 2009. ..............................................................................................................................102

2. Ingredients and chemical composition of cottonseed meal (CSM) and dried distillers grains with soluble (DDGS) supplements .............................................103

3. Effects of protein source on performance of steers grazing summer warm-s eason grass pastures during 2008 and 2009 ...................................................................104

4. Effects of the type of single dose, moderate term implant on performance of ste ers grazing summer warm-season grass pastures during 2008 and 2009 ..................105

5. Ear palpation score ~95 d and 126 d post implantation with Ralgro ® (R) or Component TE-G ® (TEG) ...................................................................................106

  LIST OF FIGURES

Figure Page

CHAPTER I

1. Spiro-furostanol saponin ....................................................................................22

APPENDICES

1. Economic evaluation of implanting and supplementing summer stocker steers ..............................................................................................................................107

  CHAPTER I

INTRODUCTION

Micro-Aid ® has been shown to improve microbial efficiency and fiber digestibility in dairy diets, as well as feed conversion and microbial effici ency in feedlot diets. In the U.S., approximately 30 million beef cows graze pasture year around, whi le roughly 20 million growing cattle graze for some period of time after being w eaned and before entering the breeding herd or entering the feedlot for finishing. Li mited data suggests that Micro-Aid ® improves performance of grazing cattle while improving nitrogen utilization and reducing methane and urea emissions. Further study is nec essary to determine if the inclusion of Micro-Aid ® in supplements for forage-fed cattle is a cost effective practice. Addition of Micro-Aid ® to forage-fed cattle supplements could result in improved forage utilization, improved performance of forage-fed cattle or reduce d amount of protein supplement required. It is estimated that on an annual basis, the approximate 50 million head of grazing cattle in the U.S. are supplemented for an average of 120 days. Therefore, at the inclusion rate of 1 gram of Micro-Aid ® per head per day during the supplementation period alone would result in a total market potential of 6,000 metric tons of Micro-Aid ® annually. Micro-Aid ® improved feed to gain an average of 4.7% in fifteen independent studies of cattle at three different locations. In vitro work suggests that at least a portion

  of this response can be attributed to improved microbial efficiency when cattle a re supplemented with Micro-Aid ® . Similarly, addition of Micro-Aid ® to a dairy ration improved in vitro digestibility of ADF, microbial growth and microbial efficiency. In the Southern Great Plains, sta nding forage supplies adequate nutrients to maintain beef cows and (or) allow for we ight gain in cows and growing cattle three to six months of the year. Said another way, for age is of low quality in six to nine months when supplemental protein and (or) energy are not required. Previous work suggests that Micro-Aid ® and other Yucca Schidigera -based surfactants have defaunating properties (Hristov et al., 2004). For example, inclusion of Yucca Schidigera

resulted in a reduction in rumen protozoa and an increase in rumen bacteria and fungi (Hristov et al., 1999). Therefore, in high roughage diets the defaunating effects of Micro- Aid ® could potentially increase fiber digestion and improve microbial nitrogen supply to the

small intestine. Addition of Micro-Aid ® to forage-fed cattle supplements could result in improved forage utilization, improved performance of forage-fed cattle or reduced a mount of protein supplement required. Therefore, the purpose of this dissertation was to dete rmine if Micro-Aid ® can improve forage utilization and ultimately impact animal performance of growing cattle and spring-calving cows consuming a forage based diet.

  CHAPTER II

REVIEW OF LITERATURE

Background of Saponins

Micro-Aid ® is an all-natural, dry or liquid feed additive for use in animal feeds. It is manufactured from a purified extract of the Yucca schidigera plant that grows in the Southwest United States and Mexico. Micro-Aid ® is thought to have surfactant like properties because it contains saponins. By definition, saponins are glucosides that oc cur in plants and are characterized by the property of producing a soapy lather (M erriam- Webster, 2010). Saponins are either triterpenoids or steroids in nature and have a dydrophobic aglycone, more commonly named sarsapogenin (Figure 1), attached to a sugar (Wina et al., 2005). Steroidal saponins from Yucca schidigera and Quillaja saponaria plants are the most commonly used commercial saponins. Yucca extract has a concentration of 4.4% steroidal saponins (Wina et al., 2005). The actual role of steroidal saponins in nature is not known, but has been suggested that they may inhibit mold (antimicrobial) and protect plants from insects (Francis et al., 2002) or even provide a source of monosaccharides for the plant (Barr et al., 1998). The draw to saponin technology can be attributed to their known lytic action on erythrocyte membrane s. This action is believed to be due to their affinity to membrane sterols, particularly c holesterol (Glauert et al., 1962). When treated with saponins, cell membranes from human erythrocytes developed pores 40-50  in diameter (Seeman et al., 1973). The interaction

  between saponins and membrane lipids seems to be complicated, but it is thought that yuc ca saponins are effective at suppressing rumen protozoa by reacting with choles terol in the protozoal cell membrane, causing it to lyse (Cheeke, 2000). Saponins form micelles with sterols when the sapogenin (the hydrophobic portion) lipophilically binds with the hydrophobic sterol nucleus (Oakenfull and Sidhu, 1989). These characteristics allow saponins to bind to cholesterol membranes of protozoa and lyse them. A reduction in protozoa should increase the rate of fermentation in high roughage diets via the subs equent increase in bacterial and fungal populations.

Saponins for the feed industry The primary saponin-containing plants that have potential use as feed additives for

ruminants are listed in Table 1. The plant itself is not typically used as a feeds tuff, rather the extracted saponins from the plant. The process for obtaining yucca extract sta rts with the harvest of the trunk of the plant “yucca logs” which are macerated and then either ground or pressed to produce yucca powder or juice, respectively (Cheeke, 2000). Some commerci al uses for saponins include surfactants for mining and ore separation, emulsions for photographic films and in cosmetics (Cheeke, 2000). However, these extracts are currently being used as dietary feed additives for livestock, primarily for the control of ammonia and odor (Cheeke, 2000). It is thought that the effects of saponins on nitrogen metabolism are caused by the non-butanol-extractable fractions which contains primarily car bohydrates (Cheeke, 2000), but in ruminants it is thought that yucca extracts reduce rumen ammoni a concentrations as a consequence of suppressing rumen protozoa concentrations (Hrist ov et al., 1999). This potential use as a defaunating agent has led to the investigation of saponins a s

  feed additives over the past few decades (Goetsch and Owens, 1985; Wilson et al., 1998; Hristov et al., 2004). The consequences from defaunating the rumen include but are not limited to, decreased bacterial proteolysis, improved nitrogen conservation, decre ased methanogenesis, and a shift in VFA production toward propionate which all aid in the improvement in overall animal efficiency. These benefits to animal effici ency may be a domino effect or they might be independent results of steroidal saponins.

Saponins Role on Rumen Fermentation First, the data shows sufficient support that there is a reduction in rumen protozoa with the inclusion of saponins in ruminant diets (Valdez et al., 1986; Lu and Jorge nson, 1987; Wallace et al., 1994; Klita et al., 1996; Hristov et al., 1999). This reduction in rumen protozoa may ha ve several positive associative effects including improved nitrogen metabolism eff iciency, a reduction in methane emissions, shift’s in bacterial and fungal populations and a potent ial increase in bacterial protein flow to the lower gastrointestinal tract (Wallace et al., 19 94). The addition of 0.1% Yucca schidigera to rumen fluid inhibited the motion of the cilia of entodiniomorphs and the contraction of holotrichs, while decreasing the rate of breakdown of [ 14 C] leucine-labeled Selenomonas ruminantium (Wallace et al., 1994). This impairment can eventually lead to protozoal cell lysis and consequently provide a competitive advantage for some bac teria (i.e., S. ruminantium ) and fungi as well as reduce intrarumen nitrogen cycling and potentially improve microbial synthesis. One of the primary benefits from the use of saponins and a potential result of rumen defaunation is the impact on nitrogen metabolism. It has been well documented that an improvement in nitrogen retention can be expected as a response to rumen defaunation (Williams and Coleman, 1997). Summarized data from Wina et al. (2005) showed that

  ammonia was decreased in 50% of the reviewed studies while protozoa concentrations we re decreased in 70% of the studies (Table 2). This discrepancy may be due to method of determination of one concentration or the other or there may not be a linear rel ationship between reduced protozoa concentrations and reduced ammonia. It may also be due to the independent ability of yucca saponins to bind ammonia, reducing the rumen ammonia concentrations or the subsequent reduction in rumen proteolysis (Wallace et al., 1994). It has also been suggested that when rumen ammonia concentrations are high, yucca ex tract can bind ammonia-N and release it when concentrations are low (Hussain and Cheeke, 1995). Makkar et al. (1999) also demonstrated this rumen nitrogen conservation when urea- supplemented straw was fed. Another method of action on nitrogen metabolism in ruminants is via blood and milk urea

concentrations. There are some instances where no effect has been se en on blood urea nitrogen (Hristov et al., 1999; Wilson et al. 1998), but more often it has been cited to r educe blood urea nitrogen (Hussain and Cheeke, 1995; Hussain et al., 1996; Killeen et al., 1998a; Ki lleen et al., 1998b). Wilson et al. (1998) also found that it had no effect on milk urea nitrogen in la ctating dairy cows. It seems pretty evident that saponins interact with protein metabolism in the rumina nt, but diet or stage of production may be of great importance to the overall impact.

Another positive associative effect of rumen defaunation is the potential to reduce methanogens associated with protozoa. Methane is a hydrogen sink in the rumen and is not only a loss of carbon and hydrogen, but it is harmful to the environment. Therefore, a reduction in methanogensis would be beneficial to the whole system of beef cattle

production. Nevertheless, when Yucca extract was included in a high roughage diet or to a mixed diet of hay and barley grain there was no effect on methane production in a rumen simulation system (Sliwinski et al., 2002). Other studies have conversely demonst rated a

  reduction in methane production (Santoso et al., 2004; Hu et al., 2005). Sanotoso et al. (2004) also calculated a reduction in energy losses through methane as a percent of gross energy when Yucca schidigera was included in the diet. These results may be independent of rumen defaunation and rather a direct inhibition of methane producing bacteria. A source of ruminal ammonia is from the proteolysis of bacterial protein by protozo al ingestion. Not only are bacteria engulfing protozoa decreased by saponins, but s terols are absent on bacterial membranes (Cheeke, 2000), and therefore should be able to proliferate in the presence of saponins. Wallace et al. (1994) observed an increase in Prevotella ruminicola

growth, no affect on Selenomonas ruminantium , suppressed growth of Streptococcus bovis , and complete inhibition of Butyrivibrio fibrisolvens when Yucca schidigera was introduced to the medium at 1%. Prevotella ruminicola is a gram-negative bacteria and it is suggested that yucca extract is more potent to gram-positive bacteria (Wang et a l., 2000), which could lead to a subsequent increase in gram-negative bacteria. Antibiotics such as m onensin also decreases gram-positive bacteria, leading to an increase in propionate p roduction, a decrease in passage rate and an improvement in overall efficiency (Perry et al., 1976). Wang et al. (2000) also reported a suppressing effect on Streptococcus bovis , but they also saw a substantial reduction in cellulytic bacteria and fungi. Effects on certain ty pes of bacteria may be saponin or product specific and may be dependent on diet (i.e., high fiber vs. high concentrate). Potential for increases in fungal populations may also be due to the decrease in protozoa concentrations (Hsu et al., 1991), and fungi are an important component of fiber digestion in the rumen. Francis et al. (2002) observed that Sapindus rarak actually decreased fungal RNA concentration in rumen liquor in an in vitro fermentation experiment. Howeve r,

  Francis et al. (2002) also presented data from Diaz et al. (1993) demonstrating inc reased fungal populations in sheep fed 25-30 g of Sapindus saponaria for 30 days. There are inconsistent results pertaining to saponins effects on fungal populations and there is little knowledge as to which fungi are important to ruminant digestion. It is thought that a decrease in protozoa should decrease microbial engulfment, increasing microbial protein synthesis and bacterial protein flow to the sm all intestine. Again, results have been varied. Lu and Jorgensen (1987) reported a decrease in microbial pr otein concentration while Goetsch and Owens (1985) reported a contradictory improvement in efficiency of protein synthesis by 36%. Hu et al. (2005) also showed an improvement in microbial protein (mg/mL) when tea saponins were included in vitro at 6 and 8 millig rams. With respect to Lu and Jorgensen (1987), even if there is a decrease in microbial prote in concentration there may not be a decrease in microbial protein flow to the small i ntestine because bacterial nitrogen is more easily washed out of the rumen than protozoa l nitrogen (Abe et al., 1981) In addition, shifts in volatile fatty acid profiles have been reported in the prese nce of saponins. In this case there is typically a shift toward propionate production, res ulting in a decrease in the acetate to propionate ratio (Hristov et al., 1999) which is consiste nt with a decrease in protozoa numbers (Williams and Coleman, 1992). This shift is seen when ionophores are fed (Perry et al., 1976). In most cases a shift in propionate leads to a shif t in rumen pH. However, this has not consistently been reported with the use of saponins. Hristov et al. (1999) observed a numerical decrease in pH from the control diet when yucca extract was added at 20 and 60 g/day (6.28 vs. 6.18 and 6.19), whereas others have observed no differences in pH with yucca extract (Valdez et al., 1986; Wilson e t al., 1998).

  Conversely, there have also been reports of increased pH values (Hussain and Cheeke , 1995; Zinn et al., 1999). Regardless of pH changes, data suggests that an increase in propionate c an be expected when saponins are added to the rumen.

Fate of Saponins in the Rumen As for degradation of saponins in the ruminant, most are merely degraded in the rumen to derivatives of the sarsapogenin and are poorly absorbed (Oakenfull and Sidhu, 1989). Wang et al. (2000) recorded a decrease in Yucca saponins when added to the pure culture of Fibrobacter succinogenes . It is thought that because some bacteria can fully degrade dietary saponins that rumen adaptation could occur and that the results obtained from the administration of saponins may be transient. Therefore it has been sugges ted that feeding saponins intermittently might be more effective and alleviate bac terial adaptation (Cheeke, 2000). Thalib and others (1995) actually observed that a feeding frequency of 3 days per week was an effective means of supplying saponins with successful suppre ssion of protozoa and ammonia concentrations. However, the appropriate feeding regimen and complete metabolism of saponins in the ruminant needs to be further investigated.

Saponins on Intake and Digestibility Most reports suggest that the inclusion of saponins in the diet has no eff ect on dry matter intake (Valdez et al., 1986; Wilson et al., 1998; Hristov et al., 1999). Again, there have been inconsistent results with regard to digestibility. It has been shown that d efaunation resulted in a decrease in apparent organic matter, nitrogen, neutral detergent f iber and acid detergent fiber digestion (Koenig et al., 2000). However, Santoso et al. (2004) saw no effect on appar ent organic matter, nitrogen, neutral detergent fiber and acid detergent f iber digestibility in sheep fed

  orchardgrass silage and concentrates, and Hristov et al. (1999) saw no dif ferences in in situ dry matter disappearance, or total tract digestibility when fed to heifers. Conver sely, Goetsch and Owens (1985) saw an improvement in apparent total tract organic matter digest ibility. Hristov et al. (2004) did report an increase in the immediately soluble dry matter portion of corn, enabling it to have an increase in in situ rumen dry matter degradability when a yucca extra ct product was fed. As for passage rate, there have been no reports that saponins have any effect on parti culate passage rate (Goetsch and Owens, 1985; Hristov et al., 2004). Nitrogen conservation might be improved due to consequences previously mentione d. However, when evaluating nitrogen digestibility and retention there hav e been mixed results reported. Hristov et al. (1999) reported an increase in urinary nitrogen excretion of 5%, re sulting in a slight decrease in nitrogen retention when yucca saponin was included in the diet at 60 g/day. As for nitrogen digestion, Lu and Jorgensen (1987) observed a decrease in digesti bility when high levels of alfalfa saponins were provided in a forage-based diet. Similar findings have been reported for a 35% reduction in apparent nitrogen digestibility (Valdez et al., 1986).

Saponins on Animal Performance There have been very few studies evaluating animal performance in the pr esence of yucca extracts. In a study with dairy cows, Wilson et al. (1998) reported a tendency for reduced crude protein and true protein in the milk ( P = 0.13 and 0.07, respectively), but no difference in daily milk yield. Coinciding data from Valdez and others (1986) also showed no impact on body weight change, milk yield or composition of the milk. However, Valdez et al. (1986) sugges ted that there was a consistent improvement in milk production by 1 to 3% with the inclusion of sarsaponin. M ader and Brumm (1987) evaluated the replacement of soybean meal with urea in a ste er supplement and observed an improvement in rate of body weight gains from steers consuming the urea containing supplement with saponin as compared to urea only as the source of degradable p rotein. More research needs to be conducted to evaluate animal performance when providing dietar y plant saponins.

 

Protein Supplementation The potential for saponins to benefit grazing cattle is due to the fact that from l ate summer until early spring, tall-grass prairie forage is poor in quality and r umen ammonia is first limiting, reducing forage intake and digestibility (McCollum and H orn, 1990). Therefore it is essential to provide a supplement with enough crude protein to alleviate this rume n nitrogen deficit. McCollum and Horn (1990) outlined numerous studies that unveiled the increase in performance by supplementing low levels of protein when cattle gr aze low quality forage. The “Oklahoma Gold” program developed at Oklahoma State University was established on the basis that providing 0.45 kg of a high protein supplement (38 to 40% crude protein) three times/wk will improve performance of grazing steers b y 0.20 kg/d (Lalman and Gill, 2010). Additionally, in the Southern Great Plains it is a common practice to supply either a 40% crude protein cube three times/wk during the winter months to spring-c alving cows and a 30% cube to fall-calving cows four times/wk due to their increased ener gy demand. These protein cubes are typically formulated with cottonseed meal and whea t middlings as the primary ingredients. The crude protein in cottonseed meal is mode rate to high in rumen degradability (57 to 78%; NRC, 1996; Winterholler et al., 2009) and serves as a good source of nitrogen for rumen bacteria.

Urea Supplementation Alternative options to alleviate rumen ammonia deficiency in grazing catt le diets are to include non-protein nitrogen sources, which have the potential to decrease feed costs . Farmer et al (2004) concluded that incorporating urea up to 30% of rumen degradable protei n

  did not have a negative effect on performance of dry-pregnant cows when utiliz ed in an alternate day feeding system, but did decrease the acetate to propionate rat io compared to no dietary urea. They observed supplement refusals when urea was included at 45% of supplemental rumen degradable protein (30% CP; 188 g/d of urea). Farmer et al. (2004) went on to conclude that when feeding gestating cows on alternate days it would be s afe, without supplement refusal, to include urea at a level equivalent to 3.1% of the diet or 22% of crude protein in a 40% crude protein supplement delivered at 119 g urea/feeding. In concurr ing literature, Koster et al (2002) supplied 60% of the supplemental rumen degradable prote in via urea (103 g/d). Similarly, Koster et al (1997) supplied 100% of supplemental rumen degradable protein through urea (132 g/d) and Forero et al. (1980) supplied 62.5% of the supplemental crude protein with urea (108 g/d) and saw no palatability or toxici ty issues. Therefore it seems reasonable to conclude that urea could be included at levels ne ar 100 g/d regardless of its percentage of the crude protein or rumen degradable protei n. However, there is little information on maximum urea levels for lactating cows. In most fal l-calving systems feed is delivered four times per week at a common rate of 2.06 kg/day or 3.61 kg/feedi ng. This has to be considered when including urea as a substitute for a natural protein. I n a fall- calving system an inclusion rate of 2.6% urea (101 g/feeding) or urea included at 25% of crude protein or 37% of rumen degradable protein should result in no supplement refusals. When substituting a natural protein source with a slow-release urea product, pal atability issues have not been an issue. Owens et al. (1980) determined from observed ammonia level s that toxicity would not occur until urea intake reached 900 g/day. High inclusion rates of urea in supplements for cattle consuming a forage based diet have decreased total organic matter intake, decreasing performance as comp ared to natural

  protein supplements. Performance losses when substituting natural protein with ure a (Rush and Totusek, 1975) may be due to a metabolizable protein deficiency (NRC, 1996) or an increase in removal of urea from the kidneys and excretion in the urine. As previous ly mentioned, data suggests that saponins may have the potential to conserve this nitrog en and improve performance (Mader and Brumm, 1987). Correction of rumen ammonia deficiency could be arguably the most important mechanism, yet the most controversial in relation to animal performance. It i s the classic example of the chicken and the egg. The primary reason for the controversy is due to the fa ct that supplemental protein typically increases intake and digestibility, but in s ome instances digestibility is increased without a subsequent increase in dry matter intake . This has been the focus of several studies, primarily due to the fact that non-protein nitroge n (i.e., urea) has increased microbial synthesis similar to plant protein, but has been less effec tive at improving dry matter digestibility (Rush et al., 1976; Kropp et al., 1977). If rumen ammoni a deficiency was the sole mechanism of improving performance a source of non-prote in nitrogen should prove to be as effective as plant proteins. The fact that non-protein nit rogen is not as effective as plant protein has established the foundation for further me chanisms. Plant protein has been shown to be more effective at improving digestion of dry matte r and organic matter due to bypass of some of the feed protein to the small intestine (Kr opp et al., 1977).

Full document contains 119 pages
Abstract: The inclusion of Micro-Aid® (MA) in protein supplements improved rumen DM and NDF degradability via a decrease in rumen particulate passage rate, but was not successful at improving apparent total tract digestibility. This improvement in rumen digestion may have the potential to increase the supply of nutrients to the small intestine for subsequent improvements in animal performance. Micro-Aid ® successfully suppressed protozoa after continuous administration, over 20 days, suggesting that complete adaptation to saponins by protozoa was not observed. Also, the reduction in protozoa has been shown to increase microbial efficiency (Veira, 1986) which would be beneficial to lactating cows that have a greater metabolizable protein requirement than cannulated steers or even gestating cows. The inclusion of MA did not impact performance of stocker steers or beef cows during the supplementation period. However, MA did improve calf performance when supplementing cows during early lactation. This advantage was lost due to compensatory gain after supplementation ceased, but could prove to be of great importance to a fall-calving cow herd, consuming low-quality forage for its entire lactation period. There was a non-significant increase in milk yield of 2.4% during early lactation, similar to other findings. Feeding frequency of MA needs to be evaluated as a potential role in animal performance. These performance studies intermittently supplied MA as opposed to a continuous supply. This may negatively impact the microflora populations intermittently and never sustain a stable environment. It would also be beneficial to evaluate the use of MA in combination with non-protein nitrogen. With the rising costs of feed protein, this may be an economical option to upgrade the use of non-protein nitrogen in grazing cow diets. More research needs to be conducted to determine the impact of daily provision of MA and its interaction with diet on performance of grazing animals.