HYDROLYZED FEATHER MEAL AS A PROTEIN SOURCE FOR GROWING CALVES. University of Nebraska, Lincoln ABSTRACT

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1 HYDROLYZED FEATHER MEAL AS A PROTEIN SOURCE FOR GROWING CALVES F. K. Goedeken2, T. J. Klopfenstein3. R. A. Stock3 and R. A. Britton3 University of Nebraska, Lincoln ABSTRACT Growth, digestion and in situ studies were conducted to determine the protein value of hydrolyzed feather meal (J?th) for growing ruminants. Dacron bags containing blood meal 0, Fth, corn gluten meal (CGM) and soybean meal (SBM) were suspended in the rumen of two steers for 12 h to estimate escape protein. The escape protein value for Fth, 69.1%, was less than that for BM (82.8%) and CGM (80.4%; P e.05) but greater than that for SBM (26%; P <.05). Apparent protein digestion by lambs was similar (P >.lo) for isonitrogenous diets containing urea 0, BM, Fth, CGM and SBM. Amino acid contents of the protein sources before vs after a 12-h ruminal in situ digestion were similar (P >.lo). In a growth study, a basal diet of 80% ensiled corncobs and 20% alfalfa was fed to 60 individually fed crossbred steers (215 kg BW). Steers were supplemented with U, BM, Fth, 1/2 BMlD Fth, 1/2 BM:1/2 CGM and 1/3 BMlB Fth:1/3 CGM (protein basis). Protein sources were fed at 30, 45 and 60% of the supplemental N with urea supplying the remainder. Protein efficiency was calculated using the slope ratio technique. Protein efficiency was similar (P >.lo) for BM- and Fth-supplemented calves. Protein efficiencies were similar (P >.lo) for BM:CGM, BMFth and BM:Fth:CGM combinations. These data indicate the Fth is a digestible high escape protein source that is useful in diets for growing ruminants. (Key Words: Degradable Protein, Amino Acids, Feather Meal, Blood Meal, Maize Gluten Meal, Beef.) Introduction Feather meal may be valuable as a protein source in ruminant diets. Jordan and Croom (1957) reported that gains of fattening lambs were slightly greater when feather meal replaced soybean meal. Perry et al. (1978) reported that performance of finishing cattle was similar when soybean meal or a combination of soybean meal and feather meal was fed. Protein digestibility of feather meal has been reported to be comparable to that of cottonseed meal (Aderibigbe and Church, 1983b) but less than that of soybean meal (Thomas and Beeson, 1977; Church et al., 1982). 'Published with the approval of the Director as Paper No Journal Sex.. Nebraslra Agric. Res. Div. *current address: purioa ill^, Dodge city, KS. kept. of ~nim. sci. Received June 14,1989. Accepted January 18, J. Anim. Sci : Feather meal protein may escape ruminal digestion. Thomas and Beeson (1977) reported that steers fed soybean meal had higher ruminal ammonia N concentrations and higher urinary N excretion than those fed feather meal. A similar reduction in ruminal ammonia concentrations was reported by Daugherty and Church (1982) for feather meal vs soybean meal. However, the proportion of ruminal escape protein supplied by feather meal has not been determined. The main objective of this research was to characterize ruminal escape and overall protein value of feather meal for growing ruminants. A secondary objective was to estimate the amino acid flow to the small intestine of calves fed feather meal diets. Materials and Methods Protein sources were analyzed for CP (AOAC, 1975), soluble protein in a phosphate

2 2946 GOEDEKEN ET AL. buffer (Poos-Floyd et al., 1985), acid detergent insoluble nitrogen (ADIN, Goering et al., 1972) and pepsin insoluble nitrogen (PIN, Goering and Van Soest, 1970). This feather meal (Fth) was commercially prepared from turkey feathers and had some blond addition (approximately 10% of DM). The blood was added prior to hydrolysis in a batch hydrolyzer. In Situ Study. Alfalfa was available ad libitum as a basal diet to two mature, ruminally cannulated Angus x Hereford steers; fresh feed was provided once daily for a minimum of 14 d before bag incubation. Approximately 2 g of soybean meal (SBM), blood meal (BM), Fth and corn gluten meal (CGM) were placed intran~minally in 7-cm x 12.7-cm dacr0n4 bags (50 micron pore size) for 12 h. Bags were sewn closed and attached to a nylon line with a sinker, which was attached to the ruminal cannula. Each protein source was placed in four bags within each steer. This procedure was replicated for three periods. After removal, bags were washed under flowing tap water until water leaving the bags was clear. Total N was determined for two bags for each steer and period (AOAC, 1975). The other bags were used for amino acid analysis. Amino acid and diaminopimelic acid (DAP) content were determined in BM, Fth, and CGM using samples composited within animal and period before and after 12 h of ruminal digestion. After lyopholization, samples were acid-hydrolyzed (AOAC, 1975). The amino acids in the hydrolysates were separated by ion exchange chromatography, derivatized postcolumn with 0-phthaldehyde and detected fluorometrically. In separate analyses, samples were oxidized with perfomate to convert methionine to methionine sulfone and cystine to cysteic acid prior to acid hydrolysis to determine methionine and cystine concentrations (AOAC, 1975). Complete oxidation was required because sulfur amino acids are partially oxidized during acid hydrolysis (Yamasake et al., 1982). Also, a separate analysis for tryptophan was conducted using a modified procedure based on the method of Lewis et al. (1976). The procedure was conducted manually rather than automatically. %iks Inc., Springfield, MO. AU analyses were conducted in duplicate and means of duplicates were analyzed statistically. The GLM procedure of SAS (1982) was used to statistically analyze the protein degradation data according to a randomized block design. Model effects included steer, period, protein source and the protein source x period interaction. The period x steer interaction was used as the error term even though the same two steers were used in each of the three periods. Least significant differences (SAS, 1982) were used to separate protein degradation means. For each protein source, each amino acid was compared before and after ruminal digestion. The model included effect of degradation time (0 vs 12 h) and period (3). Digestion Study. Thirty Suffolk x commercial white-face crossbred lambs (51 f 2.7 kg) were allotted randomly to protein treatments. Lambs were fed a basal diet of 76% ensiled corncobs, 12% alfalfa hay and 12% supplement OM; Table 1) that was balanced to be isocaloric (49% TDN) and isonitrogenous (11% CP). Protein sources were urea, SBM, BM, Fth and CGM and they supplied 30% of the diet protein. Diets were fed at 2.25% of BW daily for 10 d of precollection and 7 d of fecal collection. Feed, feces and orts were dried in a forced-air oven (55 C) and analyzed for N (AOAC, 1975). Data were analyzed according to the GLM procedure of SAS (1982) as a completely randomized design. Least significant difference (SAS, 1982) was used to separate protein source means. Growth Trial. Sixty growing Hereford x Angus 9-mo-old steers (215 f 4.7 kg) were individually fed protein supplements containing urea, BM, Fth, BM with CGM, BM with Fth and a combination of BM, Fth and CGM. Combinations of protein sources consisted of equal portions of protein from each source. Steers were blocked by weight and randomly allotted within blocks to treatments. The slope ratio technique was utilized to compare protein sources (Klopfenstein et al., 1985). Diets were formulated to contain 72% ensiled corncobs, 20% alfalfa (DM basis) and 8% protein supplement to balance for 11.5% CP, % Ca,.35% P and.13% S (Table 2). Diets containing natural protein sources were mixed with the urea control to obtain graded levels (30, 45 and 60%) of the supplemental protein from natural protein sources. Three or four animals were fed at each level. Diets were fed once daily at a constant percentage of BW

3 medient FEATHER MEAL FOR CALVES 2947 TABLE 1. SUPPLEMENT COMPOSITIOP FOR THE LAMB DIGESTION STUDY Treatment soybean Blood Feather Corn gluten Urea meal meal meal meal Soybean meal 77.0 Blood meal 35.9 Feather meal 34.9 Corn gluten meal 53.8 Urea salt Trace mineralsb A.4 vitamin premix' SUlfUrd A.4 Corn Dicalcium phosphate Analyzed CP 'Percentage of DM, fed as 12% of diet to obtain 11% CP, % Ca,.35% P and.13% S. blo% Mg, 6% Zn, 4.5% Fe, 2% Mn, 5% Cu, 1.3% I and.05% Co. '15,000 IU vitamin A, 3,000 Tu vitamin D and 3.75 IU vitamin E per gram of premix. %mental SUKW (99% s). for all treatments. Intake was altered to minimize orts (taken weekly) and maintained near ad libitum intake (2.22% BW). Initial and final weights were the average of three consecutive days' weights taken before the morning feeding. All steers were implanted with estradiol-17p at the beginning of the study. Postruminal digestible amino acid flows were calculated utilizing results obtained from the steer in situ study and the lamb digestion study. Composite samples of alfalfa and corncobs were analyzed for escape protein content using in situ incubation. Samples were ground through a 2-mrn screen and placed in dacron bags similar to the in situ study but were incubated for 20 h. The DAP content of the digested samples was used to adjust for microbial attachment. The amino acids provided in microbial protein were determined from a sample of ruminal contents obtained from a ruminally cannulated steer fed solka floc and nonprotein N. This was done to ensure that the amino acid profile of ruminal TABLE 2. SUP- COMPOSITION' FOR THE STEER GROWTH STUDY Ingredient Blood meal Feather meal Corn gluten meal Urea salt Trace mineralsb vitaminpremixb SUlfUrb Corn Dicalcium phosphate Analwed CP Blood Feather Urea meal meal Treatment 'Percentage of DM, fed as 8% of diet for 11.5% CP, % Ca..35% P and.13% S. bas in Table 1. Blood meal: Blood meal: feather meal: corn gluten corn gluten meal meal

4 2948 GOEDEKEN ET AL. TABLE 3. PROTEIN CHARACTERISTICS OF SOYBEAN MEAL. BLOOD MEAL, FEATHER MEAL. AND CORN GLUTEN MEAL USED IN IN SITU, DIGESTION AND GROWTH STUDJES Protein source Soybean meal Blood meal Feather meal Corn gluten meal 'Percentage of DM. bpercentage of protein. 'Soluble in phosphate buffer (Poos-Floyd et al., 1980). Acid Soluble detergent Pepsin cpa proteinbc insoluble Nb indiaestible Nb E microbes accounted for attached bacteria. The majority of reports that describe amino acid profiles of ruminal microbes used centrifugation to separate bacteria from digesta. This centrifugation technique does not include the attached bacteria from ruminal digesta (Akin and Barton, 1983) and, thus, assumes that amino acid compositions of attached bacteria are similar to those of free bacteria. Amino acid and DAP analyses followed procedures described in the in situ study. Intake and gain were compared using the GLM procedure of SAS (1982). Gain above the urea control and protein intake were subjected to nonlinear regression (NLIN procedure of SAS, 1982). This model forces a common intercept at the urea control. The slope derived from the non linear regression was used as the mean protein efficiency for each treatment. Mean protein efficiencies for each treatment were compared using a one tailed t-test (Steel and Tome, 1980). Results and Discussfon Protein Characteristics. Feather meal used in these studies appeared to have a soluble protein fraction similar to that of SBM and a relatively high content of ADIN and PIN compared with the other protein sources (Table 3). In Situ Study. After 12 h of incubation, protein degradation was highest for SBM and lowest for BM and CGM (P <.05). Degradations were 73.4, 17.2, 19 and 30.9 (f 2.8) for SBM, BM, CGM and Fth, respectively (data not shown). The degradation of Fth protein was higher (P <.05) than for BM or CGM but less (P <.05) than for SBM. The 12-h incubation appeared numerically equal to in vivo ruminal degradation for SBM the 73.4% degradation value was very similar to the mean ruminal degradation value of the in vivo data summarized in NRC (1985) for SBM (72.1%). Results of the current study indicate that Fth has 2 times the amount of ruminal escape protein of SBM. The ruminal degradation of these protein sources appeared to have minimal effect on the amino acid profile (Table 4), with the exception of tryptophan. Microbial contamination in hydrolysates was negligible; DAP content was less than.05% of DM. This work agrees with that of Weakley et al. (1984), who reported that the amino acid profile of SBM was not altered extensively during in situ incubation. These data suggest that the amino acid profile of the ruminal escape protein for BM, Fth and CGM was very similar to the amino acid profile that was fed. Digestion Study. The digestion study detected no differences (P >.20) in DM or total tract N digestibility when lambs were fed urea-, SBM-, BM-, Fth- or CGM-supplemented diets. True N digestibilities were 96.8, 94, and 96.5, respectively. True N digestibilities were calculated by difference from the urea control. We assumed that sufficient ammonia was supplied by urea and rumen degradable protein to meet the needs of the rumen microorganisms. We also assumed that apparent N digestibility of urea in the control above that needed by the microorganisms was 100%. Any decrease in apparent N digestibility in the diets containing test protein sources was assumed to be due to the indigestibility of the N in the test protein source. The true N digestibility was calculated as: (N digestibility of urea control diet - N digestibility of test protein diet) + protein source N as a percentage of total diet N. The similar N digestion of SBM and Fth

5 ~ ~~ FEATHER MEAL FOR CALVES 2949 TABLE 4. AMINO ACID COMPOSITION* OF PROTEIN SOURCES BEFORE AND AFl'ER 12 HOURS OF RUMINAL IN SITU INCUBATION Amino Blood meal Feather meal acids Undigested Digested Undigested Digested kg His Ile Leu LYS Met.8 1.o.8.8 Phe O Thr Trp 1.1.4b.7.4b Val Cys CP "Expressed as a percentage of CP in the respective digested or undigested sample. bigested amino acid content differs from undigested amino acid content (P <.05). Corn gluttn meal Undigested Digested b does not agree with previous data. Thomas and Beeson (1977) reported that N digestibility was reduced from 68% to 59% when Fth replaced SBM in the diet. Church et al. (1982) reported that protein digestibility was reduced 5.7 and 8.5 percentage units in two digestion studies when Fth replaced 70% of the SBM protein in the diet. In these studies, the replacement of SBM by Fth may have reduced the amount of protein degraded in the rumen and, thus, the ruminal ammonia concentration may have been reduced below the optimal level for maximal ruminal digestion. This could have increased the amount of digestion that occurred in the hind gut and, thus, increased the amount of fecal microbial N. Higher fecal microbial N would reduce the apparent N digestibility for any diet. The N digestibility of Fth compared to SBM in the current study also may be due to the method of processing of Fth. During processing, blood was added to the feathers. This addition may have increased digestibility of the product. Pressure and duration of hydrolysis also may influence digestibility (Aderibigbe and Church, 1983a). The higher content of ADIN and PIN of Fth than of the other protein sources did not Sect protein digestion. Other researchers also have reported that PIN and ADIN do not predict protein digestibility of Fth (Aderibigbe and Church, 1983a; Britton et al., 1986). Growth Study. Intake was similar (Table 5) because all treatments were fed at a constant percentage of BW. The steers consuming BM, Fth, BM:CGM, BM:Fth and BMCGM:Fth gained faster (P e.05) than did those fed the urea diet. Presumably, this was due to the ruminal escape protein supplied by these sources. Protein efficiency was similar for BM and Fth (Figure 1; P >.lo). The ruminal escape value of Fth was less than that of BM in the in situ study. Thus, less protein probably entered the small intestine from Fth than from BM, but protein efficiency was similar, perhaps indicating that the quality of Fth escape TABLE 5. PROTEIN RESPONSE OF CALVES FED UREA, BLOOD MEAL (BM). FEATHER MEAL 0 AND CORN GLUTEN MEAL (CGM) BMCGM Item Urea BM Fth BMFth BMCGM Fth SEM Daily intake", kg Daily gain", kg. 19b.3aC * 37c.4@.46=.3T.13 BExpressed as the average of levels fed. bcmeans in the same row with unlike letters in their superscripts differ (P c.05).

6 2950 u.4 \ CT) Y - 6 c a 3 a,.2 5 a, > a.- S a 0 GOEDEKEN ET AL. Maximal response (.31 kg/d) BM:CGM BM Fth CG M _ , ,..._.._ _. 1 I Protein intake above the urea control, kg/d Figure 1. Regression of gain on protein intake for the growth study. The resulting slopes (numbers on graph) are the protein efficiencies from the growth study. Standard errors of treatment means were.166 for blood meal (BM),.I68 for feather meal (Fa),.167 for BM:Fth,.388 for Bhtcom gluten meal (CGM) and.198 for BMFth:CGM. protein was at least comparable to the quality of BM escape protein in this study. When the combinations of BM:Fth or B:Fth:CGM were fed, protein efficiency increased numerically but not statistically (P >.lo). When combmations of BM and either Fth or CGM were fed, the BM may have supplied needed lysine, and Fth or CGM may have provided needed sulfur amino acids. The protein efficiency of BM: CGM was improved compared with BM or Fth (P <.05) but was similar to protein efficiency of BMFth and BM:Fth:CGM (P >.lo). Stock et al. (1981) reported a 28% improvement (P >.05) in protein efficiency when BM: CGM was fed compared with BM. In the current study, a 79% improvement in protein efficiency was observed for BM:CGM compared with BM. This large improvement in protein efficiency may be due to large animal variation. The 16% and 14.4% improvements for BM:Fth:CGM and BMFth compared with BM are near the expected responses. The level of blood added to Fth in this study is not known. Approximately 10% blood would be present if all the blood produced from poultry slaughter were added to the feathers. This added blood may have affected quality and possibly reduced the complementary effect of adding BM to the Fth protein. The amount of digestible ruminal escape protein and amino acids absorbed from the small intestine at maximal gain from supplemental protein sources was calculated using protein and amino acid degradation data from the steer in situ study and digestibilities from the lamb study. The gams of supplemental protein required for maximal gain was multiplied by its escape value and amino acid profile (after in situ digestion) to determine the supplement contribution to amino acid absorption. Ruminal microbial amino acid absorption (Table 6) from the small intestine was based on the conversion of 10.44% of TDN to digestible microbial CP (Burroughs et al.,

7 FEATHER MEAL FOR CALVES TABLE 6. AMINO ACID PROFILE OF RUMINAL CONTENTS FROM A STEER FED SOLKA FLOC ANDUREA Amino acid 968 Threonine Valine Cystine Methionine Isoleucine Leucine Tyrosine phenylalanine Lysine Histidine Arginine Tryptophan Diaminouimelic acid o ). This calculation is supported by the total duodenal CP flow data in the summary by Rohr et al. (1986). The resulting equation was: MAA = (P x DEP x PAA) x TDN x.lo44 x MPAA) + (BDI x EDP x BDAA), where MA4 = metabolizable amino acid supply; P = amount of protein source required for maximal gain; DEP = digestible escape protein of protein source; PAA = protein source amino acid composition after ruminal digestion; DMI = DM intake; MPAA = microbial protein amino acid profile; BDI = basal diet intake, EDP = escape of basal diet protein and BDAA = basal diet amino acid content. The amount of ruminal escape protein from alfalfa and ensiled corncobs was estimated by 20-h dacron bag degradation to be 3.28% of protein fed, with 16% of the escape protein in the form of ADIN. The amino acid profile of the alfalfa and ensiled corncobs escaping ruminal digestion was assumed to be similir to the composition that was fed. The 20-h in situ incubation time is an attempt to simulate slower passage from the rumen of forage than of these protein smes. The total amino acid profile absorbed at maximal gain (Table 7) then was compared to TABLE 7. EsTulIATED GRAMS OF AMINO ACIDS ABSORBED FROM THE SMALL INTES"J3, OBTAINED AT MAXlMAL STEER GAIN BASED ON IN SITU DEGRADATION Blood Feather BMFth Item meal meal BMFW BMCGM~ COW AVG~ cvf BWU@ Metabolizable test protein Microbialprotein Basal diet escape protein Thr Val Cys Met Ile Leu m Phe i LYS His h TrP TSAAh %ood meal and feather meal. %load meal and corn gluten meal. 'Blood meal, feather meal and corn gluten meal. daverage amount of each amino acid supplied by the average of all treatments. epercent of CP supplied by the average of all treatments. koefficient of variation for amino acids supplied across freatments. gburroughs et al. (1974) requiremeats reported as a percentage of beef tissue. %tal sulf~r amino acids. 'Expressed as a requirement for me plus TV.

8 2952 GOEDEKEN ET AL.. the requirements estimated by Burroughs et al. (1974). The amount of amino acids supplied for each protein source at maximal gain indicates that levels of threonine, methionine and tryptophan were very similar for all treatments. The CV among treatments for the amino acids was less than 20%, indicating that these amino acids were at or near the minimal level required for maximal gain and thus may be limiting in microbial protein and basal dietary escape protein. Other amino acids may have been fed in excess in some of the protein treatments, as indicated by the variability in their supply across treatments. Similarities in amounts also may be attributed to the low contribution of amino acids from the supplement relative to the amounts from microbial protein and other components of the diets. The requirement for any amino acid should be constant across the treatments. With the slope ratio technique, it was possible to determine how much protein from the test source was needed to meet the requirement for the first limiting amino acid. If a given amino acid was not first limiting or co-limiting, then it would be fed in excess in a given treatment. Some thirty-five to 40% of the metabolizable protein was supplied by the test proteins in these diets. Because of the large difference in amino acid patterns in these protein sources, different profiles of amino acids were presented to the small intestine on these different diets. If a specific amino acid, such as methionine, gave a similar value (low CV) across diet, then it was likely first limiting and the mea value may be indicative of the requirement. Conversely, if an amino acid such as lysine was not first limiting on a diet such as the blood meal diet, then the level supplied would be higher and a larger c"v across diets would result. For the BM diet, lysine may have been overfed, because the other treatments providing less lysine gave similar rates of gain. For BM to supply needed levels of sulfur amino acids, threonine, tryptophan and(or) isoleucine, lysine was fed at higher levels than the other treatments. Nimrick et al. (1970) and Richardson and Hatfield (1978) reported that methionine, lysine and threonine were limiting amino acids in microbial protein. Low variations in calculated amino acid flows from OUT study support that conclusion. Methionine and threonine appear to be at a minimal level for all treatments. With the exception of the BM treatments, lysine also may be at the minimal level. In swine diets, cystine may supply 50% of the sulfur amino acids, but a range of 40 to 70% cystine may not alter performance (ARC, 1981). Data from the current study indicate that the supply was near this presumed optimal ratio. Cystine supplied approximately 50% of the sulfur amino acids for BM, BMFth, BM: CGM and BM:Fth:CGM treatments and slightly more than 50% for the Fth treatment. During hydrolysis of feathers, lanthionine can be formed (Baker, 1986). The feather meal source used in this experiment contained 7.08% lanthionine prior to ruminal degradation and 4.0% following degradation. Some of the lanthionine may be utilized by nonruminants (Baker, 1986), but usefulness for ruminants has not been determined. We assumed no utilization because lanthionine was not included in total sulfur amino acids. Lysinoalanine was not detected in the samples. The average amount of each amino acid for each treatment, expressed as a percentage of total amino acids, can be compared to estimates of amino acid requirements of Burroughs et al. (1974) calculated as the percentage of protein present in beef tissue. The percentages of methionine, tyrosine, phenylalanine, lysine, histidine, arginine and tryptophan in beef tissue were quite similar to the calculated optimal amino acid percentages in the current study at maximal gain. Comparisons of these values also indicate that threonine, valine, cystine, isoleucine and leucine were in excess in the current study. However, using the amino acid profile of beef tissue as a standard for amino acid requirements does not consider metabolic needs and losses. Thus, the amino acid profile of beef tissue may not reflect fully the amino acid requirement for optimal growth. lmpllcations Feather meal contains over twice the ruminal escape protein of soybean meal. Feather meal protein appears to be as digestible as soybean meal, blood meal and corn gluten meal. When fed to calves, feather meal that contained some blood had a protein value similar to blood meal. Amino acid profiles indicate that feather meal may provide ruminal escape sulfur amino acids that may limit growth of ruminants.

9 FEATHER MEAI, FOR CALVES 2953 Literature Cited Aderibigbe, A. 0. and D. C. Church. 1983a. Feather and hair meals for ruminants. I. Effect of degree of processing on utilization of feather meal. J. Anim. Sci. 56:1198. Aderibigbe, A. 0. and D. C. Church. 1983b. Feather and hair meals for ruminants. II. Comparative evaluation of father and hair meals as protein supplements. J. Anim. Sci. 57:473. Akin. D. E. and F. E. Barton Rumen microbial attachment and degradation of plant cell walls. Fed. Proc AOAC Official Methods of Analysis (12th Ed.). Association of official Analytical Chemists, Washing- 104 DC. ARC The Nutrient Requirement of plps. Commonwealth Agricultural Bureaux, Slough, UK. Baker, D. H Utilization of isomers and analogs of amino acids and other sulfur-containing compounds. Prog. Food & Nutr. Sci. 10:133. Britton, R., T. J. Klopfenstein, R. Cleale, F. Goedeken and V. Wilkemn Methods of estimating heat damage in protein sources. Roc. Distillers Feed Cod. 41:66. Burroughs, W., A. H. Trenkle and R L. Vetter A system of protein evaluation for cattle and sheep involving metabolizable protein (amino acids) and urea fermentation potential of feedstuffs. Vet. Med. Small Anim. Clin. 69:713. Church, D. C., D. A. Daugherty and W. H. Kennick Nutritional evaluation of feather and hair meals as protein sources for h t s. J. Anim. Sci. 54:337. Daugherty, D. A. and D. C. Church In vivo and in vitro evaluation of feather and hair meals in combination with urea for ruminants. J. Anim. Sci Goering, H. K., C. H. Gordon, R. W. Hemken, P. J. Van Soest and L. W. Smith, Analytical estimates of nitrogen digestibility in heat damaged forages. J. Dairy Sci. 53:1275. Goering, H. K. and P. J. Van Soest Fora@ fiber analyses (apparatus, reagents, procedures, and some applications). Agric. Handbook 379. ARS, USDA, Washington, DC. Jordan, R. M. and H. G. Croom Feather meal as a source of protein for fattening lambs. J. Anim. Sci. 16: 118. Klopfenstein, T., R Stock and R. Britton Relevance of bypass protein to cattle feeding. Prof. Anim. Scientist 1:27. Lewis, A. J., P. J. Holden, R. C. Ewan and D. R. ti An automated fluorometric method for the measurement of hyptophan in plasma J. Agric. Food Chem. M1081. Nimrick, K. E., E. E. Hatfield, J. Kamimki and F. N. Owens Quantitative assessment of supplemental amino acid needs for growing lambs fed urea as the sole nitrogen source. J. Nutr. 100:1293. NRC Ruminant Nitrogen Usage. National Academy Press, Washington, DC. Perry, T. W., W. M. Bees04 M. I. Wray, M. T. Mohler and E. Barge Feather and hair meal and soybean meals as protein sources for beef cattle. Indiana Cattle Feeders Day Rep. Poos-Floyd M., T. Klopfenstein and R. A. Britton Evaluation of laboratory techniques for predicting ruminal protein degradation. J. Dairy Sci. 68:829. Richardson, C. R. and E. E. Wield The limiting amino acids in growing cattle. J. Anim. Sci. 46:740. Rohr. K., P. Lebzien, H. Schaft and E. Schulz Prediction of duodenal flow of non-ammonia nitrogen and amino acid nitrogen in dairy cows. Livest. Prod. Sci SAS SAS User s Guide: Statistics. SAS Inst, Inc., Gary, NC. Steel, RGD. and J. H. Tome Principles and Rocedures of Statistics. McGraw-Hill Book Co., New York. Stock, R., N. Mahen, T. Klopfenstein and M. Poos Feeding value of slowly degraded proteins. J. Anim. Sci. 53:1109. Thomas, V. M. and W. M. Beeson Feather meal and hair meal as protein sources for steer calves. J. Anim. Sci Weakley. D. C., F. N. Owens and W. L. Stockland Soybean meal digestion in the men: Amino acid changes. Oklahoma Agric. Exp. Sta. MP 116:179. Yamasaki, R. B., 0. T. Osuga aod R. E. Feeney Periodate oxidation of methionine in proteins. Anal. Bicchem