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4 Use of Other NPN Products for Protein Replacement UREA-CARBOHYDRATE COMBINATIONS Several new products containing urea combined with carbohydrate feeds have recently been marketed for use in ruminant diets. These products differ from earlier ones in that manufacturing procedures usually in- clude a process step or the addition of an ingredient designed to slow down the rate of ammonia release from urea while the product is in the rumen. One such product makes use of heat and pressure generated by forcing mixtures of urea and air-dry cereal grain through an extruder die. Another product relies on a different process, in which water is added to the air-dry cereal grain before the mixture is passed through the extruder die. Two other new products make use of molasses-urea mixtures to which a material is added for purposes of slowing down ammonia release. These new products usually contain from 10 to 20 percent urea and are free-flowing with good handling and storage characteristics, allowing them to be mixed into diets with minimal segregation. Although the principal claimed benefits of these products over earlier mixtures are assumed to be improved efficiency and greater utilization of urea- nitrogen via slower-released ammonia from diets fed twice daily, this assumption may not be entirely valid based upon recent research results such as those by Knight and Owens (1973). Instead, the manufacturing procedures imposed may bring about alterations within the mixtures other than slower-released ammonia demonstrated by Helmer et al. 30
Use of Other NPN Products for Protein Replacement 31 (1970a), which may be responsible for some and possibly the major part of the claimed benefits. For example, some of the extruded products take on a dark amber appearance following processing, which suggests alterations in the organic constituents of the cereal grains as a result of processing. Such alterations might increase palatability of the new product, and increased feed (energy) consumption by cattle or sheep might be the more important explanation for the claimed im- proved urea utilization. Insufficient research data have been reported for appraising the validity of this palatability hypothesis; however, the negative results reported by Harris et al. (1973) and the positive results reported by Helmer et al. (1970b) and Stiles et al. (1970) are supportive. This is a worthy area for additional research, since greater energy consumption is known to increase urea-nitrogen conversion into microbial protein as shown by Bloomfield et al. (1964) and used by Satter and Roffler (1973). Four recent growth trials reported by Thompson et al. (1972) and Schmidt et al. (1974), comparing an ex- truded urea-grain product with urea failed to demonstrate appreciable palatability differences between the two products; and cattle perfor- mance, likewise, did not differ appreciably. Despite these recent trials, greater palatability and increased energy intake resulting from the use of any new type of urea product would be a useful feature in ruminant diets, especially in the high-producing cow, young growing calf and lamb, and feedlot cattle and lambs starting on feed when energy con- sumption is lowest. The future prospect of these new NPN- or urea-carbohydrate com- binations being as beneficial as oilmeals in supplements incorporated into cattle and sheep diets would appear to be better when the diet contains less natural protein than about 13 percent of its dry matter content. When feedstuffs contain larger amounts of natural protein and there is a need for protein supplementation, oilmeal-type supplements would be expected to out-perform NPN supplements. Although these new urea-carbohydrate products may have slower ammonia release rates than former mixtures, this feature should not be regarded as safety insurance against their misuse in feeding practice. Where a decision has been made to use these products, they should be fed in accordance with good feeding-management practices, as recom- mended by manufacturers. AMMONIATED PRODUCTS Ammonium salts have also been fed to ruminants as nitrogen sources. There have been attempts to ammoniate molasses and other carbo-
32 Urea and Other Nonprotein Nitrogen Compounds in Animal Nutrition hydrate sources in order to increase their nitrogen content. Millar (1942) and Stiles (1952) have developed procedures for ammoniating industrial and agricultural by-products. It was suggested that the nitrogen from these compounds could be used by ruminants (Millar 1941, 1944). AMMONIUM SALTS Ammonium salts of organic and inorganic acids have been tested as nitrogen sources for ruminants. Belasco (1954) and Hale (1956) demonstrated that the nitrogen of several ammonium salts, especially the organic salts, was used to a greater extent than that in urea. Belasco (1954) suggested that the organic component of these com- pounds was well utilized by the rumen microflora and that this stim- ulated rapid nitrogen uptake. Ammonium sulfate (Burroughs et al, 1950; Acord etal, 1966), ammonium chloride (Acord et al, 1966), ammonium acetate (Repp et al, 1955a,b; Kay etal, 1967a,b; Varner and Woods, 1970), ammonium bicarbonate (Kirsch and Jantzon, 1934; Hart et al, 1939; Hudman etal, 1953), ammonium propionate (Repp etal, 1955a,b; Varner and Woods, 1970), ammonium lactate (Allen and Henderson, 1972; Dutrow et al, 1974), ammonium butyrate (Var- ner and Woods, 1970), ammonium carbonate (King and Hale, 1955), ammonium formate (Repp et al, 1955a,b), monoammonium phosphate (Acord et al, 1966), diammonium phosphate (Cowman and Thomas, 1962;Lassitere/a/., 1962; Russell etal, 1962; Oltjen etal, 1963; Schaadt et al, 1966; Klosterman et al, 1967), and ammonium poly- phosphate (Colenbrander et al, 197 la,b) have been studied as nitrogen sources for ruminants in vivo and/or in vitro with varying degrees of success. Some ammonium salts, as would be expected, have been shown to be relatively toxic to ruminants (Repp et al, 1955a). Anhydrous am- monia has also been used directly as an additive for corn forage at en- siling, either in aqueous solution (Huber et al, 1973) or as a condensed liquid (Kjelgaard and Anderson, 1974). In an excellent review of the world literature on ammonium salts, Loosli and McDonald (1968) concluded that they are well used by ruminants. However, urea is the most widely used source of NPN, mainly because of economics. AMMONIATED MOLASSES Molasses is high in readily available carbohydrates; consequently, it is an attractive source of energy in solution that can be impregnated with
Use of Other NPN Products for Protein Replacement 33 ammonia. In vitro tests have suggested that only the "free" ammonia from these products is used by rumen microorganisms, while "bound" nitrogen is not significantly used (Stallcup, 1954; Davis etal, 1955; Hershberger et al., 1955). Indeed, in vivo digestion trials have shown that ammoniated molasses is of limited value as protein replacement in ruminant diets (Tillman and Swift, 1953; Tillman et al., 1955, 1957a,b;Kinge/a/., 1957). When fed at the rate of approximately 10 percent of the diet, ammoniated molasses has supported growth rates similar to that of urea and/or preformed protein in dairy heifers (Knodt etal, 1950, 1951; Frye e/a/., 1954; Parham etal, 1955) and feedlot cattle (Tillman and Kidwell, 1951; McCall and Graham, 1953). However, other work has demonstrated that the nitrogen from ammoniated mo- lasses was not well used as evidenced by growth trials with beef cattle and sheep (Tillman etal, 1957a,b) and dairy calves (Davis etal, 1955; Bartlett and Broster, 1958). It has been reported that ammoniated molasses causes nervous symp- toms in cattle and sheep (Richardson et al, 1954; Rusoff etal, 1954; Tillman et al, 1957a,b). Feeding high levels of ammoniated molasses has caused cattle to run wildly and to injure themselves (Tillman et al, 1957a) and caused endocardial hemorrhages in sheep (Tillman et al, 1957b). Production of toxic 4-methylimidazole has been observed in the ammoniation of molasses and other agricultural products (Wiggins, 1956; Nishie et al, 1970). It is possible that this compound is respon- sible for the toxic symptoms found in cattle and sheep. AMMONIATED RICE HULLS Recently, products of the milling industry have been ammoniated for use as ruminant feed. Several trials have been conducted to evaluate ammoniated rice hulls (ARM) as a feed source. ARH improved the di- gestibility of low-energy diets (Eng and Riewe, 1963; Eng, 1964), but had no effect on the nitrogen digestibility in high-energy diets when fed at levels less than 10 percent of the total diet (Furr and Carpenter, 1967). Feeding diets containing 20-40 percent ARH decreased the nitrogen digestibility in high-concentrate diets (White, 1966). Feeding less than 10 percent ARH did not affect performance of feedlot cattle fed high-concentrate diets (Furr and Carpenter, 1967; Tillman et al, 1969). The combination of urea and rice hulls, fed to be isonitrogenous to the ammoniated rice hulls, promoted gains and efficiencies equal to those obtained with the ammoniated product (Tillman et al, 1969). The urea-containing diets were more economical. Digestive distur- bances were noted, and performance was decreased when 20 and 40 per-
34 Urea and Other Nonprotein Nitrogen Compounds in Animal Nutrition cent ARH were fed to cattle fed high-concentrate diets. ARH have been shown to be less toxic than urea when fed to sheep (Eng and Riewe, 1963). AMMONIATED BEET PULP AND CITRUS PULP Citrus pulp and sugar beet pulp are agricultural by-products that are commonly used as energy sources in ruminant diets. Their nutritive value can be enhanced by ammoniation (Millar, 1944). However, Ferguson and Neave (1943) concluded that ammoniation of sugar beet pulp decreased the utilization of nitrogen and seriously lowered the nutritive value of the nonnitrogenous portion of the beet pulp when fed with a low-energy diet. Later studies with diets containing some concentrate have also demonstrated the utilization of nitrogen from ammoniated beet pulp to be low, but when fed at adequate levels they could supply the supplemental nitrogen needs of dairy cows with- out adverse effects (Broster et al., 1960). Ammoniated beet pulp and citrus pulp, containing no more than 20 percent crude protein equiva- lent, can be fed to beef cattle and dairy cattle in diets containing some concentrate and no more than 30-40 percent ammoniated pulp without adversely affecting intake or performance (Connell et al, 1944; Davis et al., 1946, 1952; McCall and Graham, 1953). The feeding of levels in excess of 40 percent of the diet generally results in a decrease in intake and performance (Kirk et al, 1954, 1957), especially with younger cattle (Davis et al, 1952). BIURET Earlier in this volume, urea was described as being soluble and quickly hydrolyzed to ammonia by urease. For efficient utilization, released ammonia must be used by rumen bacteria as it becomes available. Am- monia production greatly exceeding that utilized by bacteria is readily absorbed and, if sufficiently high, causes toxicity. Compounds resulting from the condensation of urea consist primarily of biuret with some cyanuric acid, triuret, and others-all considerably less soluble than urea. Crude biuret contains variable levels of biuret (about 70 percent) together with some 10 percent each of urea and moisture, with the remainder being other condensation products of urea. At high dietary levels and in high-roughage diets, biuret is more readily accepted by the ruminant and is less toxic than urea (Berry et al, 1956; Hatfield et al, 1959). It is also more stable in ensiled mixtures
Use of Other NPN Products for Protein Replacement 35 (Condon et al, 1969). Biuret is not currently approved by the Food and Drug Administration for feeding to animals producing milk for human consumption because of the possibility of carry-over into milk. The safety of biuret for ruminant animals is due to a relatively slow degradation in the rumen resulting in slow release of ammonia (Gaither etal, 1955;Hatfielde?a/., 1955; Meiske etal, 1955; Repp et al, 1955a; Berry et al., 1956; and Clark et al, 1965). Ewan etal. (1958) and Hatfield et al. (1959) reported that utilization of biuret nitrogen was similar to that of urea by sheep, but that an adaptation period was needed before rumen microorganisms were able to utilize biuret nitro- gen efficiently. An adaptation period of 3 weeks for sheep (Tomlin et al, 1967) and for steers (Oltjen et al, 1969) has been suggested. How- ever, Clark et al. (1963) observed that maximum nitrogen retention was obtained only after 6-8 weeks of feeding biuret to sheep. Variations in reports about adaptation periods to biuret appear to be related to the nitrogen status of the experimental animals and the level of protein in the basal diet to which biuret was added. The adaptation period may be shortened by the addition of readily available energy to a low- protein diet (Gilchrist et al, 1968). The mechanism of adaptation seems to involve an increase in the numbers of biuretolytic microorganisms present in the rumen (Ewan et al, 1958; Gilchrist et al, 1968; Slyter et al, 1968; Schroder and Gilchrist, 1969). Results of utilization studies involving supplementation of low- quality roughages available for range livestock have been promising when biuret was compared to urea (Ammerman et al, 1972; Pick et al, 1973). Release of energy from such roughages is relatively slow, conforming to the slow release of ammonia from biuret (Tiwari et al, 1973a,b). An increase in the consumption of low-quality hay by sheep fed a crude biuret supplement was observed by MacKenzie and Altona (1964). Their observations have been supported by the studies of Oltjen et al. (1969) and Raleigh (1969). Biuret has been used success- fully as a nitrogen supplement under range conditions for cattle (Meis etal, 1967) and for sheep (Tomlin et al, 1967). Lactating cows, calves, and finishing steers fed low-quality roughage supplemented with feed-grade biuret performed as well as with urea supplementation (Pickard and Lamming, 1968; Toilet et al, 1969; Clanton and Brown, 1971). In feeding trials with wintering calves, Thomas et al. (1969) observed that feed-grade biuret promoted faster gains than urea, but not as good as with soybean meal. Feed-grade biuret proved an effective, readily acceptable, NPN supplement for long-term feeding of beef cows (Thomas et al, 1971). Supplementation of low-energy diets with biuret under range-grazing conditions appears
36 Urea and Other Nonprotein Nitrogen Compounds in Animal Nutrition to be more suitable than supplementation with urea from the point of view of animal safety and acceptability. When biuret was withdrawn from the diet in a "deadaptation" test, Schroder and Gilchrist (1969) found that there was an abrupt decrease in biuretolytic activity, irrespective of diet. More importantly, a prac- tical consideration is the fact that "readaptation" must start over again once biuret is withdrawn, and readaptation does not take place at a rate faster than the original adaptation. Clemens and Johnson (1973) re- ported that sheep fed poor-quality hay free choice plus biuret at 4-day intervals could not maintain rumen biuretolytic activity compared to feeding biuret at 1 - or 2-day intervals. The rate of adaptation to biuret by ruminal microbes is enhanced by feeding low levels of starch and moderate quantities of biuret (Clemens and Johnson, 1974). Thomas and Armitage (1972) reported essentially equal gains from steers on range and fed a biuret supplement either at a rate of 0.9 kg daily or 1.8 kg every other day. Biuret in silage is relatively stable and usually has a higher feeding value for lambs, ewes, and cattle than urea in silage (Karr et al., 1965a,b; Albert^ al, 1967; Owens et al, 1967; Meiske et al, 1968; Condon et al, 1969). Urea hydrolysis produces ammonia, which neutralizes silage acids prolonging fermentation, whereas biuret remains stable during fermentation. Addition of biuret does not diminish palatability of the silage, and there is no loss of biuret nitrogen. Mild fungistatic action of pure biuret (Garrigus, 1970) may temporarily reduce losses in silage ex- posed to aerobic oxidation. Biuret-supplemented finishing diets for lambs and cattle appear to be about as well used as similar finishing diets supplemented with urea (Gaithere/a/., 1955; Hatfield et al, 1955, 1959; Meiske etal, 1955; Karr et al, 1965b; Meis et al, 1967; Thomas et al, 1969; Hooper and Mudd, 1971). However, biuret supplementation of diets for full-fed ruminants on high-energy diets does not appear to be superior to urea when fed in similar diets (Oltjen et al, 1974). While slow release of ammonia is probably not advantageous under feedlot conditions, it does provide safety from ammonia toxicity. CYANURIC ACID Some cyanuric acids and triuret results from the controlled pyrolysis of urea to produce feed-grade biuret. Cyanuric acid appears to be used by sheep at an efficiency similar to biuret (Garrigus et al, 1959; Boston et al, 1966). Clark et al. (1965) found nitrogen retention from urea, biuret, triuret, and cyanuric acid to be essentially equal by sheep fed a low-protein roughage diet.
Use of Other NPN Products for Protein Replacement 37 Because urea, biuret, cyanuric acid, and triuret each has an ammonia release rate that differs from the others, there is need for more research on the value of specified mixtures of two or more of these compounds in ruminant diets. SUMMARY AND CONCLUSIONS Many of the ammonium salts, both organic and inorganic, have been fed to ruminants as nitrogen sources. Also, there are procedures available for ammoniating molasses and other feeds to increase their nitrogen content. Many of these have been tested in feeding and metabolism trials, and the following conclusions appear to be justified: 1. The ammonium salts of both organic and inorganic acids are well utilized by ruminants as nitrogen sources. 2. The nitrogen of ammoniated molasses is not well utilized by rumi- nants. Also, toxic compounds are produced in the ammoniating of mo- lasses, and these compounds may cause nervous symptoms in sheep and cattle that result in high death losses. 3. Ammoniating beet or citrus pulp appears to increase feeding value when they are incorporated in small amounts in diets containing some grain. 4. When ammoniated rice hulls are fed at low levels in cattle diets, the nitrogen appears to be well utilized. The major condensation products of urea are biuret and cyanuric acid. Biuret, in basic metabolism and practical feeding trials, offers much promise as a nitrogen supplement for ruminants consuming low- protein roughages supplemented intermittently. Biuret is slowly hy- drolyzed and is less toxic than urea. Biuretase, which hydrolyzes biuret to ammonia, is an induced enzyme and requires variable periods of time, depending upon dietary factors, to reach a peak activity. Also, animals have to consume biuret regularly to maintain biuretase activity. The adaptation period may be reduced by the addition of readily fer- mentable carbohydrate, and the activity of biuretase can be maintained by frequent feedings. Although biuret is more expensive per unit of nitrogen than urea at this time, it may find use in situations where urea feeding presents special management problems involving animal safety. Biuret is not currently cleared by the Food and Drug Administration for feeding to cows producing milk for human consumption.
