Effects of dietary ratios of fish and blood meals on sites of digestion, small intestinal amino acid disappearance and growth performance of meat goat wethers

Small Ruminant Research 64 (2006) 255–267

Effects of dietary ratios of fish and blood meals on sites of digestion, small intestinal amino acid disappearance and growth performance of meat goat wethers S.A. Soto-Navarro, R. Puchala, T. Sahlu, A.L. Goetsch ∗ E (Kika) de la Garza American Institute for Goat Research, Langston University, P.O. Box 730, Langston, OK 73050, USA Received 5 October 2004; received in revised form 4 April 2005; accepted 28 April 2005 Available online 9 June 2005

Abstract Six yearling Boer × Spanish wether goats (37 ± 1.6 kg initial live weight; LW) and 24 growing Boer × Spanish and 24 Spanish wethers (21 ± 3.1 and 20 ± 2.6 kg initial LW, respectively) were used to determine the effects of total CP and two supplemental protein sources (fish meal, FIM; blood meal, BLM) in a 70% concentrate diet on sites of digestion, small intestinal amino acid disappearance and growth performance. Diets were formulated to be 12 or 15% CP (DM basis), with predicted ruminally undegraded intake protein (UIP) from FIM and BLM of 1.2 and 3.0% DM, respectively, achieved from FIM supplying 100, 67 and 33% and BLM 0, 33 and 67%, respectively (100F, 67F and 33F, respectively). True ruminal OM and N digestibilities were greater (P < 0.05) for 12% versus 15% CP and decreased linearly (P < 0.05) as level of FIM decreased. Duodenal flows of both microbial and non-microbial, non-ammonia (feed plus endogenous) N were greater (P < 0.05) for 15% than for 12% CP and increased linearly with decreasing FIM level in the diet. Correspondingly, small intestinal disappearance of essential amino acids was greater (P < 0.05) for 15% versus 12% CP and increased (P < 0.05) with decreasing FIM. In an 18-week growth experiment, DM intake (935 g/day versus 783 g/day), average daily gain (ADG; 145 g versus 108 g) and ADG:DM intake (155 g/kg versus 138 g/kg) were greater (P < 0.05) for Boer × Spanish compared with Spanish wethers. Regardless of genotype, neither level of total CP nor of FIM influenced growth performance. In conclusion, with diets relatively high in concentrate and a CP level of 12%, amino acid requirements of common genotypes of growing meat goats in the US may be satisfied by basal dietary ingredients, with little or no potential to enhance performance by addition of feedstuffs high in UIP regardless of amino acid profile. © 2005 Elsevier B.V. All rights reserved. Keywords: Meat goats; Crude protein; Amino acids

1. Introduction ∗ Corresponding author. Tel.: +1 405 466 3836; fax: +1 405 466 3138. E-mail address: [email protected] (A.L. Goetsch).

0921-4488/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.smallrumres.2005.04.026

Ruminants do not usually have dietary requirements for essential amino acids. Ruminal fermentation is

256

S.A. Soto-Navarro et al. / Small Ruminant Research 64 (2006) 255–267

accompanied by production of microbial protein that provides most amino acids absorbed in the small intestine. However, when microbial protein synthesis is limited or amino acid requirements are high, the sum of microbial protein and feed protein escaping ruminal degradation may not meet animal requirements (NRC, 1985). Consequently, the high growth potential of Boer goats compared with other meat goat genotypes might be accompanied by an increased demand for essential amino acids. Richardson and Hatfield (1978) found that methionine was first-limiting when the only source of amino acids available to growing Holstein steer calves was of microbial origin, and lysine and threonine were the second and third most limiting amino acids. For lambs, methionine and lysine limited N retention when microbial protein was the only source of amino acids (Storm and Ørskov, 1984). The amino acid composition of tissue protein is similar to animal requirements (Wolfrom and Asplund, 1979). In this regard, goat muscle has been reported to contain approximately 10% less methionine and lysine and 12% more arginine compared with sheep and cattle (Buttery and Foulds, 1985). Therefore, it is possible that amino acids most limiting to growth by goats could differ from other ruminant species. The quantity and quality of amino acids reaching the small intestine of ruminants can be altered by influencing microbial protein synthesis and use of various available supplemental protein sources not extensively degraded in the rumen (Titgemeyer et al., 1988). In the present experiment, different dietary ratios of two supplemental protein sources high in protein escaping ruminal degradation with unique amino acid profiles and two dietary levels of CP were used to determine potential influences on sites of digestion, small intestinal disappearance of amino acids and growth performance of meat goat wethers.

2. Materials and methods 2.1. Digestion experiment 2.1.1. Animals and treatments The protocol for this experiment was approved by the Langston University Animal Care Committee. Six yearling Spanish × Boer wether goats (37 ± 1.6 kg

initial live weight; LW) with ruminal, duodenal and ileal cannulas were used in an experiment with a 2 × 3 factorial arrangement of treatments and a 6 × 6 Latin square design with 14-day periods. Wethers were adapted to a high concentrate diet and metabolism crates for 3 weeks prior to the experiment, vaccinated for clostridium organisms (Ultra bac/7 way; Pfizer Animal Health, Exton, PA) and treated for internal parasites (Valbazen; SmithKline Beecham Animal Health, West Chester, PA). Six diets were formulated to be 12 or 15% CP (DM basis; Table 1). For each level of CP and UIP, there were three combinations of fish meal (FIM) and blood meal (BLM). Based on composition listings of NRC (1996), FIM supplied 100, 67 and 33% of supplemental ruminally undegraded intake protein (UIP), with corresponding contributions of UIP from BLM of 0, 33 and 67%, respectively (designated as ratios of 100F, 67F and 33F, respectively). UIP from FIM and BLM was estimated as 1.18 and 3.03% DM for 12 and 15% CP, respectively. The estimated (NRC, 1996) dietary concentration of ruminally undegraded methionine (i.e., reaching the small intestine intact) was 0.068, 0.062, 0.055, 0.125, 0.108 and 0.090, and the corresponding level of lysine was 0.148, 0.157, 0.166, 0.305, 0.329 and 0.351% for 12% CP-100F, 12% CP-67F, 12% CP-33F, 15% CP-100F, 15% CP-67F and 15% CP-33F, respectively. Therefore, methionine from supplemental protein sources reaching the small intestine decreased and lysine increased as dietary levels of FIM and BLM decreased and increased, respectively. Urea was included in diets to achieve a ratio of ruminally degraded intake protein (DIP):TDN of 0.10–0.11. Diets were 70% concentrate and based on ground corn with additional fiber provided by low-CP prairie hay to maximize UIP from supplemental protein sources Prairie hay used in the experimental diets was obtained from a single source and consisted of a mixture of big bluestem (Andropogon gerardii), little bluestem (Schizachyrium scoparium), indiangrass (Sorghastrum nutans) and switchgrass (Panicum virgatum). After removing and weighing feed refusals, wethers were fed twice daily at 08.00 and 20.00 h at approximately 110% of consumption on the preceding 3 days. 2.1.2. Samples and analyses Following a 10-day treatment adjustment period, ruminal, duodenal, ileal and fecal samples were col-

S.A. Soto-Navarro et al. / Small Ruminant Research 64 (2006) 255–267

257

Table 1 Composition of diets consumed by Boer × Spanish wethers Item

12% CPa (DM basis)

15% CPa (DM basis)

100F

67F

33F

100F

67F

33F

Ingredient composition (% DM) Prairie hay Ground corn Fish meal Blood meal Urea Molasses Dicalcium phosphate Limestone Vitamin premixb Trace mineralized saltc Ammonium chloride Deccoxd Potassium chloride Sodium sulfate Salt Chromic oxide

30.00 57.02 3.00 0.00 0.26 5.00 0.00 0.82 0.50 0.50 1.00 0.05 0.10 0.35 1.00 0.40

30.00 57.19 2.00 0.54 0.31 5.00 0.16 0.88 0.50 0.50 1.00 0.05 0.11 0.36 1.00 0.40

30.00 57.39 1.00 1.08 0.36 5.00 0.31 0.93 0.50 0.50 1.00 0.05 0.12 0.37 1.00 0.40

30.00 52.10 7.66 0.00 0.37 5.00 0.00 0.86 0.50 0.50 1.00 0.05 0.07 0.49 1.00 0.40

30.00 53.16 5.11 1.37 0.48 5.00 0.00 0.82 0.50 0.50 1.00 0.05 0.09 0.52 1.00 0.40

30.00 54.11 2.56 2.75 0.60 5.00 0.07 0.81 0.50 0.50 1.00 0.05 0.11 0.55 1.00 0.40

Analyzed composition CP (% DM) OM (% DM) NDF (% DM)

11.8 92.3 35.0

11.8 92.2 33.2

12.4 92.3 33.4

14.9 91.5 32.4

15.3 91.5 32.0

15.5 92.2 31.8

Calculated composition CP (% DM)e ME (MJ/kg DM)e Ca (% DM)e P (% DM)e K (% DM)e TDNe,f (% DM) DIPg (% DM) DIP (% TDN)

12.1 10.8 0.62 0.31 0.51 69.1 6.21 10.6

12.1 10.8 0.62 0.31 0.51 69.0 6.05 10.2

12.1 10.8 0.62 0.31 0.51 68.8 6.18 10.2

15.0 10.6 0.88 0.44 0.51 68.6 7.74 10.8

15.0 10.6 0.73 0.37 0.51 68.1 7.48 10.7

15.0 10.6 0.61 0.31 0.51 68.1 7.45 10.7

a

100F, 67F and 33F = 100, 67 and 33% of supplemental ruminally undegraded intake protein from fish meal and 0, 33 and 67% from blood meal, respectively. b Contained 2200 IU/g Vitamin A, 1200 IU/g Vitamin D3 and 2.2 IU/g Vitamin E. c Contained 95–98.5% NaCl and at least 0.24% Mn, 0.24% Fe, 0.05% Mg, 0.032% Cu, 0.011% Co, 0.007% I and 0.005% Zn. d Rhone–Poulenc, Atlanta, Ga; 6% decoquinate. e NRC (1996). f TDN, total digestible nutrients; based on Preston (2000). g DIP, ruminally degraded intake protein.

lected twice daily for 4 days. The time sequence for sampling was day 1, 07.30 and 13.30 h; day 2, 09.00 and 15.00 h; day 3, 10.30 and 16.30 h; and day 4, 12.00 and 18.00 h. Individual samples consisted of approximately 200 ml of ruminal contents, 80 ml of duodenal digesta, 50 ml of ileal digesta and 20 g (wet basis) of feces. Ruminal contents were mixed in a blender with an equal volume of saline for approximately 1 min and strained through eight layers of cheesecloth; particulate

matter was discarded and strained fluid was composited by animal and period and stored at 4 ◦ C for isolation of ruminal bacteria. Samples of feces were from excreta that had accumulated since the last collection. Duodenal, ileal and fecal samples from each wether and within each period were composited (equal weight, wet basis) for analysis. During the final day of each collection period, ruminal fluid (20 ml) was collected by the ruminal cannula from each wether at 2, 4, 6, 8, 10 and

258

S.A. Soto-Navarro et al. / Small Ruminant Research 64 (2006) 255–267

24 h after feeding and pH was measured with a pH electrode (Model 88; Markson, Phoenix, AZ). Upon completion of each collection period, ruminal bacteria were isolated via differential centrifugation (Bergen et al., 1968). Microbial isolates were prepared for analysis by oven-drying at 55 ◦ C and grinding with a small commercial coffee grinder. Duodenal, ileal and fecal samples were prepared for analysis by freeze-drying and then grinding in a Wiley Mill to pass a 1-mm screen (Thomas Scientific, Swedesboro, NJ). Feed, duodenal, ileal and fecal samples were analyzed for DM, OM (AOAC, 1990), CP (Technicon Instrument, Tarrytown NY) and NDF concentrations (filter bag technique; ANKOM Technology, Fairport, NY). Bacterial samples were analyzed for DM, OM and CP. Purine concentration was determined in duodenal and bacterial samples (Aharoni and Tagari, 1991) using 2 M HClO4 as recommended by Creighton et al. (2000). Duodenal digesta (0.5 g) was reconstituted with 5 ml of 0.1 N HCl and then centrifuged at 10,000 × g for 10 min; the supernatant was analyzed for ammonia N concentration by the procedure of Broderick and Kang (1980). Ruminal fluid samples were analyzed for ammonia N as described by Lu et al. (1990). Microbial OM and N leaving the abomasum were calculated using purines as a microbial marker (Zinn and Owens, 1986). The ratio of purines to N in bacterial samples was similar among treatments (P > 0.10); therefore, the average ratio and concentrations of DM, OM and N in bacterial samples were used to estimate microbial OM and N flows to the duodenum. To determine duodenal and ileal digesta amino acid profiles, samples were hydrolyzed with 6 N HCl using a MDS-2000 microwave system (CEM, Matthews, NC). The concentrations of amino acids in duodenal and ileal digesta were determined as described by Puchala et al. (1995) using an AminoQuant 1090 system (Hewlett Packard, San Fernando, CA), precolumn derivatization with o-phthalaldehyde and 9-fluorenylmethyl-chloroformate and UV detection. 2.1.3. Statistical analysis Data were analyzed with a repeated measures design using mixed model procedures of SAS (Littell et al., 1996). Fixed effects were CP level, supplemental protein source (mixture of FIM and BLM), period (repeated measure) and the CP level × protein source

interaction, and the random effect was wether. Because influences of dietary treatments relative to feed intake were of interest, DM intake was included as a covariate. A compound symmetry covariance structure was employed. Differences between CP level and among CP source main effect means and CP level-source interaction means were determined by least significant difference with a protected F-test (P < 0.05). In order to facilitate possible use of these data by future researchers combining data from several experiments, means for individual treatment combinations were presented regardless of significance of the interaction (JAS, 2002). Ruminal pH and ammonia-N concentration were analyzed as noted above, but with a repeated measure of period × sampling time. Interactions involving sampling time were non-significant and dropped from the model. Small intestinal amino acid disappearance was regressed against amino acid flow at the duodenum to determine true digestibility in the small intestine and endogenous amino acids passing from the small intestine (NRC, 1985); quadratic effects of duodenal amino acid flow were non-significant. 2.2. Growth performance experiment 2.2.1. Animals and treatments Procedures of this experiment were approved by the Langston University Animal Care Committee. Twenty-four weaned Boer × Spanish and 24 Spanish wether goats (21.4 ± 3.06 and 19.9 ± 2.56 kg initial LW, respectively; 3.5–4.5 months of age at the start of the experiment) were used. Wethers were weaned 1 month before the experiment and were vaccinated for clostridium organisms (Bar Vac CD/T; Boehringer Ingelheim Vetmedica, St. Joseph, MO) and treated for internal parasites (Valbazen; Smithkline Beecham Animal Health, West Chester, PA) before the experiment began. Between weaning and the experiment, wethers were adjusted to a high concentrate diet. During the 18-week experiment, wethers were maintained in 3.1 m × 15.3 m pens (four wethers per pen) equipped with automatic waterers. Diets were the same as those used in the digestion experiment with the exception of additional corn replacing chromic oxide. Animals were fed once daily at 08.00 h and consumption was ad libitum, with feeding at approximately 110% of consumption on the preceding 3 days.

S.A. Soto-Navarro et al. / Small Ruminant Research 64 (2006) 255–267

2.2.2. Measurements, samples and analyses Wethers were weighed at the beginning of the experiment and at 3-week intervals. Feed and refusal (10%) samples were taken once weekly and composite samples were formed over 3-week periods. Ruminal fluid was obtained via stomach tube in weeks 7 and 12, 4 h after feeding. Feed samples were analyzed as described for the digestion experiment. Ruminal fluid samples were analyzed for VFA as described by Lu et al. (1990). 2.3. Statistical analyses Because there was one pen per treatment combination of dietary CP level, ratio of FIM:BLM and genotype, data were first analyzed with three separate models by general linear models procedures of SAS (1990): (1) dietary CP level, ratio of FIM:BLM and their interaction; (2) dietary CP level, genotype and their interaction; (3) ratio of FIM:BLM, genotype and their interaction. Interactions were not significant; therefore, the final model consisted of the three main effects. Ruminal VFA data, with pen as the experimental unit, were first analyzed as a split-plot in time, with a subplot of period. Because period did not have significant effects or interact with other factors, data were averaged over period. Differences among means were determined by least significant difference with a protected F-test (P < 0.05).

259

decreased with decreasing FIM level, and true ruminal N digestion was lower for 15% than for 12% CP (P < 0.05). Small intestinal N digestion increased with decreasing FIM level (P < 0.05). Total tract N digestion was greater (P < 0.05) for 15% versus 12% CP but was similar among FIM levels. Microbial efficiency was greater for 15% than for 12% CP and increased with decreasing FIM level in the diet (P < 0.05). Duodenal, ileal and fecal NDF were greater for 15% versus 12% CP and increased with decreasing FIM (P < 0.05; Table 2). Ruminal and total tract digestibilities likewise were lower for 15% than for 12% CP and decreased with decreasing FIM (P < 0.05), although a quadratic effect of FIM level on total tract digestibility occurred (P < 0.05). Ruminal starch digestibility decreased linearly with decreasing FIM (P < 0.05), although total tract starch digestion was not affected by level of FIM. Ruminal pH was greater (P < 0.05) for 15% versus 12% CP (P < 0.05) and not affected by FIM level (Table 2). Ruminal pH was influenced (P < 0.05) by sampling time (6.04, 5.94, 5.97, 5.92, 6.14 and 6.34 at 2, 4, 6, 8, 10 and 12 h after feeding, respectively; S.E. = 0.060). Ruminal ammonia-N concentration was not affected by levels of CP or FIM, but did vary (P < 0.05) with sampling time (3.3, 2.5, 3.1, 4.1, 3.8 and 3.2 mg/dl at 2, 4, 6, 8, 10 and 12 h, respectively; S.E. = 0.83). 3.2. Amino acids

3. Results 3.1. Digestion and microbial growth Flow of total, microbial and non-microbial OM at the duodenum and OM passing to the ileum and in feces was greater for 15% than for 12% CP diets and linearly increased (P < 0.05) as dietary level of FIM decreased and that of BLM increased (Table 2). Apparent and true ruminal and total tract OM digestibilities were less for 15% versus 12% CP and decreased with decreasing FIM level (P < 0.05). Small intestinal OM digestion tended (P < 0.06) to increase with decreasing FIM concentration in the diet. Flow of all fractions of N to the duodenum and ileum was greater (P < 0.05) for 15% than for 12% CP, although fecal N was similar among treatments. Apparent and true ruminal N digestibilities

For nearly all amino acids, flow at the duodenum and ileum was greater for 15% versus 12% CP and increased linearly with decreasing FIM and increasing BLM levels (Table 3). Similarly, small intestinal disappearance in g/day of nearly all amino acids was greater for 15% than for 12% CP and increased with decreasing FIM level. Apparent small intestinal disappearance as a percentage of amino acids at the duodenum was not affected by CP or FIM level except for two amino acids; disappearance of methionine and leucine was greater (P < 0.05) for 15% versus 12% CP (Table 4). True small intestinal digestibility of amino acids and endogenous amino acid flow from the small intestine are presented in Table 5. There were not large differences among amino acids in true digestibility, although values were slightly lower for histidine and valine and

260

S.A. Soto-Navarro et al. / Small Ruminant Research 64 (2006) 255–267

Table 2 Effects of dietary CP level and supplemental ruminally undegraded intake protein from different ratios of fish and blood meals on site and extent of digestion and ruminal fluid characteristics in Boer × Spanish wethers Item

OM Intake (g/day) Duodenum (g/day) Total Microbial Non-microbial Ileum (g/day) Feces (g/day)

12% CP (DM basis)a

15% CP (DM basis)a

100F

67F

33F

100F

67F

33F

1001

938

979

979

958

935

428 151 278 207 190

501 162 332 260 253

517 169 357 282 247

495 159 333 263 240

566 196 372 294 268

647 203 435 345 295

S.E.

Effectb (P <) CP

L

Q

CP × L

CP × Q

2.6

0.01

0.01

0.01

0.01

0.01

28.4 11.7 22.9 20.7 17.8

0.01 0.01 0.01 0.01 0.01

0.01 0.01 0.01 0.01 0.01

0.66 0.38 0.97 0.88 0.15

0.30 0.24 0.66 0.88 0.92

0.54 0.54 0.55 0.49 0.22

Digestion (% intake) Apparent ruminal True ruminal Small intestine Hindgut Total tract

58.4 72.9 21.5 1.6 81.4

47.1 65.0 25.3 0.4 73.0

48.4 64.5 23.4 3.7 75.3

50.2 66.6 22.9 2.6 75.7

41.5 61.8 28.2 2.7 72.3

32.0 54.7 31.1 5.3 68.5

2.89 2.28 2.42 1.57 1.77

0.01 0.01 0.06 0.23 0.01

0.01 0.01 0.05 0.13 0.01

0.26 0.55 0.35 0.21 0.03

0.19 0.50 0.23 0.88 0.71

0.24 0.29 0.72 0.76 0.04

Intake (g/day)

17.3

19.5

17.1

23.4

22.0

22.1

0.48

0.01

0.08

0.05

0.25

0.01

Duodenum (g/day) Total Microbial Non-microbial, nonammonia Ammonia Ileal (g/day) Feces (g/day)

19.7 12.2 6.3 1.2 5.8 2.4

23.4 13.0 9.0 1.4 6.7 2.4

23.7 13.4 9.1 1.3 7.5 2.4

24.3 12.8 9.9 1.5 6.8 2.3

28.7 15.7 11.3 1.8 7.7 2.4

33.0 16.1 14.8 2.1 9.0 2.4

1.17 0.89 0.98 0.09 0.50 0.08

0.01 0.01 0.01 0.01 0.01 0.34

0.01 0.02 0.01 0.01 0.01 0.62

0.38 0.35 0.89 0.37 0.79 0.99

0.07 0.24 0.33 0.04 0.50 0.99

0.48 0.51 0.23 0.37 0.79 0.83

−13.4 63.2 79.8 4.5 64.2 17.0

−17.7 54.1 84.8 −0.3 65.1 22.9

−45.5 44.2 99.7 5.8 65.4 21.4

−3.0 58.0 73.9 2.3 71.4 21.1

−34.2 46.1 98.0 3.6 71.6 28.0

−50.2 33.4 108.6 5.4 69.2 34.5

7.31 4.41 6.04 2.07 1.89 1.84

0.48 0.04 0.24 0.78 0.01 0.01

0.01 0.02 0.02 0.23 0.72 0.01

0.69 0.91 0.85 0.09 0.45 0.24

0.24 0.54 0.21 0.64 0.22 0.03

0.11 0.99 0.27 0.17 0.21 0.34

346 156 121 115

326 178 156 162

316 185 158 152

362 205 153 154

316 214 179 169

336 248 214 194

0.01 0.01 0.01 0.01

0.01 0.02 0.01 0.01

0.01 0.84 0.67 0.15

0.39 0.63 0.44 0.91

0.01 0.47 0.46 0.08

3.85 4.56 3.71 3.29

0.01 0.20 0.61 0.01

0.01 0.50 0.49 0.01

0.36 0.85 0.41 0.01

0.86 0.99 0.79 0.95

0.76 0.60 0.29 0.19

3.9 9.4 2.5 1.8

0.01 0.76 0.19 0.03

0.04 0.01 0.44 0.66

0.12 0.29 0.66 0.85

0.47 0.62 0.49 0.48

0.01 0.63 0.70 0.70

N

Digestion (% intake) Apparent ruminal True ruminal Small intestine Hindgut Total tract Microbial efficiencyc NDF Intake (g/day) Duodenum (g/day) Ileum (g/day) Feces (g/day) Digestion (% intake) Ruminal Small intestine Hindgut Total tract Starch Intake (g/day) Duodenum (g/day) Ileum (g/day) Feces (g/day)

56.7 8.5 2.1 67.5 380 54 7 5

45.4 8.6 −3.4 50.2 379 69 10 6

42.5 5.9 3.6 52.6 390 68 8 6

43.3 14.0 0.2 57.5 341 51 8 4

33.6 10.2 3.1 47.0 360 64 5 3

27.6 11.6 3.6 42.3 346 71 9 3

2.0 14.1 15.1 11.5

S.A. Soto-Navarro et al. / Small Ruminant Research 64 (2006) 255–267

261

Table 2 (Continued ) Item

Digestion (% intake) Ruminal Small intestine Hindgut Total tract Ruminal fluid pH Ammonia-N (mg/dl)

12% CP (DM basis)a

15% CP (DM basis)a

100F

67F

33F

100F

67F

33F

86.5 11.7 0.7 98.8

82.9 14.8 0.8 98.6

83.0 14.5 1.1 98.5

85.5 12.5 1.1 99.1

82.5 15.9 0.9 99.2

79.7 18.0 1.2 99.0

6.04 3.3

6.07 3.3

5.91 3.0

6.15 3.2

6.09 3.5

6.10 3.6

S.E.

Effectb (P <) CP

L

Q

CP × L

CP × Q

2.54 2.15 0.30 0.45

0.20 0.13 0.38 0.04

0.01 0.01 0.44 0.40

0.42 0.31 0.54 0.76

0.46 0.36 0.64 0.54

0.57 0.70 0.88 0.63

0.060 0.83

0.05 0.37

0.14 0.94

0.63 0.59

0.53 0.22

0.25 0.96

a 100F, 67F and 33F = 100, 67 and 33% of supplemental ruminally undegraded intake protein from fish meal and 0, 33 and 67% from blood meal, respectively. b CP, dietary CP level; L and Q, linear and quadratic effects of levels of supplemental ruminally undegraded intake protein from fish and blood meals, respectively; CP × L and CP × Q, interaction between CP level and linear and quadratic effects of levels of fish and blood meals, respectively. c Grams of microbial N per kg of OM truly fermented in the rumen.

greater for methionine, lysine and tyrosine compared with other amino acids. 3.3. Performance There were no effects of dietary levels of FIM and BLM on measures of performance or levels of ruminal VFA (Table 6). The dietary level of CP did not influence performance but increased the concentration of acetate in ruminal VFA and decreased that of propionate (P < 0.05). DM intake, ADG and ADG:DM intake were greater (P < 0.05) for Boer × Spanish versus Spanish wethers.

4. Discussion 4.1. Digestion and microbial growth The extent to which true ruminal OM digestibility was lower for 15% versus 12% CP diets and decreased with decreasing level of FIM were greater than anticipated based on differences in ingredient composition and assumed digestibilities. The ratio of truly digested ruminal N to assumed TDN intake decreased as level of FIM in the diet decreased, with values approximately 0.07 for 33F compared with 0.10 or greater for 100F. Hence, ruminal availability of nitrogenous compounds could have limited ruminal digestibilities of OM and NDF with 67F and to a greater extent with 33F. How-

ever, ruminal fluid ammonia-N concentrations do not indicate that adequacy of ammonia availability varied among dietary treatments, with values in the range at which limitations of microbial growth or digestion could but would not necessarily occur (Miller, 1973; Satter and Syter, 1974). Chen et al. (1992) characterized the influence of DM intake relative to LW of sheep on efficiency of microbial protein synthesis. Other than microbial efficiency for 100F with 12% CP, observed values in the present experiment were in the range of ones reported by Chen et al. (1992) for diets with similar ratios of DM intake to LW. That the ammonia-N concentration in the present experiment did not differ with FIM level and an increasing magnitude of difference between N intake and duodenal N flow as dietary level of FIM increased imply an increasing extent of ruminal N recycling as the level of FIM and ratio of intake of ruminally degraded N to TDN decreased. A reason for the effect of decreasing FIM level on ruminal digestion perhaps more likely than an ammonia limitation is decreasing availability of amino acids or peptides, which are relatively more important sources of N for amylolytic compared to fibrolytic bacteria (Van Soest, 1994). It was expected that duodenal flow of non-microbial, non-ammonia N (i.e., feed plus endogenous) would not differ among dietary FIM levels, since diets were formulated to be similar in UIP concentration based on assumed ruminal digestibilities of FIM and BLM protein. That this was not observed, with true ruminal

262

S.A. Soto-Navarro et al. / Small Ruminant Research 64 (2006) 255–267

Table 3 Effects of dietary CP level and supplemental ruminally undegraded intake protein from different ratios of fish and blood meals on amino acid flow (g/day) at the duodenum and ileum in Boer × Spanish wethers Item

Duodenum Histidine Threonine Arginine Valine Methionine Isoleucine Leucine Lysine Phenylalanine Tyrosine Aspartate Glutamine Serine Glycine Alanine Proline Essential Non-essential Total Ileum Histidine Threonine Arginine Valine Methionine Isoleucine Leucine Lysine Phenylalanine Tyrosine Aspartate Glutamine Serine Glycine Alanine Proline Essential Non-essential Total

12% CP (DM basis)a

15% CP (DM basis)a

100F

100F

67F

2.5 6.9 19.7 3.4 8.2 4.8 5.9 13.6 3.9 6.1 16.0 21.2 7.3 6.9 1.3 5.2 68.8 64.2

2.8 8.2 24.0 3.9 9.4 6.0 6.6 16.4 4.6 7.2 19.2 24.0 8.8 7.7 1.7 5.8 81.8 74.3

133.0

156.2

1.0 1.8 6.0 1.0 1.9 1.2 1.2 3.4 1.0 1.6 4.2 4.9 1.9 1.8 0.3 1.6 18.6 16.5 35.1

33F 2.9 8.6 24.2 3.8 9.9 5.8 7.16 16.4 4.7 6.3 19.7 25.6 9.0 8.3 1.9 5.9 83.4 76.8

67F

S.E.

33F

Effectb (P <) CP

L

Q

CP × L

CP × Q

2.9 8.7 25.5 4.1 10.3 6.3 7.5 17.1 4.9 7.5 20.4 25.7 9.0 8.7 1.6 6.2 87.2 79.1

4.0 9.7 27.8 4.4 12.5 7.3 8.2 19.7 5.3 8.3 23.0 28.3 10.2 9.9 1.7 7.4 99.0 88.7

4.1 11.9 33.1 5.4 14.3 8.5 10.0 22.6 6.4 10.8 27.3 33.5 12.0 11.8 2.1 8.5 116.4 106.0

0.19 0.49 1.71 0.29 0.69 0.44 0.49 1.20 0.31 0.82 1.14 1.63 0.50 0.44 0.14 0.39 5.53 4.41

0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.12 0.01 0.01 0.01

0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.06 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01

0.12 0.90 0.86 0.82 0.61 0.48 0.68 0.56 0.89 0.91 0.82 0.80 0.79 0.68 0.82 0.80 0.78 0.99

0.07 0.15 0.41 0.22 0.12 0.21 0.21 0.30 0.25 0.10 0.21 0.33 0.24 0.08 0.93 0.06 0.23 0.15

0.28 0.30 0.29 0.33 0.93 0.33 0.50 0.52 0.31 0.27 0.32 0.55 0.30 0.65 0.51 0.88 0.43 0.38

160.1

166.3

187.7

222.5

9.60

0.01

0.01

0.88

0.18

0.39

1.1 2.2 6.2 1.1 2.4 1.4 1.5 3.8 1.2 1.8 4.7 5.4 3.9 2.0 0.3 1.9 20.8 18.2

1.3 2.4 7.8 1.3 2.6 1.6 1.6 4.4 1.4 2.1 5.6 6.9 2.3 2.5 0.4 2.1 24.5 22.1

1.1 2.1 7.4 1.2 2.2 1.5 1.3 4.1 1.3 2.0 5.3 5.8 2.4 2.3 0.3 1.9 22.3 20.0

1.5 2.6 8.1 1.5 2.9 1.8 1.8 4.9 1.5 2.5 6.2 7.1 2.7 2.8 0.4 2.3 26.4 24.0

1.4 2.8 9.8 1.5 2.7 1.6 1.6 5.2 1.7 2.7 6.8 7.6 3.3 2.9 0.5 2.4 26.9 26.1

0.07 0.16 0.44 0.11 0.19 0.11 0.12 0.29 0.09 0.14 0.32 0.42 0.67 0.12 0.04 0.15 1.46 1.28

0.01 0.01 0.01 0.01 0.07 0.01 0.13 0.01 0.01 0.01 0.01 0.01 0.90 0.01 0.02 0.01 0.01 0.01

0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.03 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.01

0.31 0.71 0.14 0.66 0.22 0.74 0.16 0.89 0.80 0.84 0.92 0.90 0.63 0.98 0.50 0.59 0.99 0.97

0.86 0.93 0.52 0.51 0.60 0.89 0.56 0.77 0.99 0.31 0.99 0.85 0.39 0.89 0.48 0.81 0.85 0.86

0.06 0.56 0.96 0.63 0.17 0.31 0.13 0.37 0.71 0.30 0.43 0.25 0.91 0.19 0.93 0.55 0.46 0.35

39.0

46.6

42.3

50.5

54.8

2.72

0.01

0.01

0.99

0.85

0.40

a 100F, 67F and 33F = 100, 67 and 33% of supplemental ruminally undegraded intake protein from fish meal and 0, 33 and 67% from blood meal, respectively. b CP, dietary CP level; L and Q, linear and quadratic effects of levels of supplemental ruminally undegraded intake protein from fish and blood meals, respectively; CP × L and CP × Q, interaction between CP level and linear and quadratic effects levels of fish and blood meals, resepctively.

S.A. Soto-Navarro et al. / Small Ruminant Research 64 (2006) 255–267

263

Table 4 Effects of dietary CP level and supplemental ruminally undegraded intake protein from different ratios of fish and blood meals on amino acid disappearance in the small intestine of Boer × Spanish wethers Item

Grams per day Histidine Threonine Arginine Valine Methionine Isoleucine Leucine Lysine Phenylalanine Tyrosine Aspartate Glutamine Serine Glycine Alanine Proline Essential Non-essential

12% CP (DM basis)a

15% CP (DM basis)a

100F

100F

67F

33F

67F

S.E.

33F

Effectb (P <) CP

L

Q

CP × L

CP × Q

1.5 5.1 13.7 2.4 6.3 3.5 4.7 10.2 2.9 4.4 11.8 16.3 5.3 5.1 1.0 3.7 50.3 47.7

1.7 6.0 17.8 2.8 7.0 4.6 5.2 12.5 3.3 5.4 14.4 18.5 6.6 5.6 1.4 3.9 59.3 55.0

1.7 6.2 16.4 2.6 7.2 4.2 5.5 12.1 3.3 4.3 14.2 18.9 6.5 5.8 1.4 3.8 60.9 55.8

1.7 6.5 18.1 2.9 8.1 4.8 6.2 13.0 3.6 5.5 15.1 19.8 6.7 6.4 1.2 4.3 64.5 59.0

2.5 7.1 19.7 2.9 9.6 5.5 6.5 14.9 3.9 5.8 16.8 21.2 7.4 7.1 1.3 5.1 72.6 64.8

2.6 9.1 23.3 3.7 11.6 6.6 8.4 17.3 4.8 8.1 20.5 25.7 8.9 8.9 1.7 6.0 87.4 79.7

0.16 0.48 1.84 0.30 0.67 0.45 0.48 1.20 0.30 0.91 1.07 1.60 0.51 0.42 0.14 0.37 5.45 4.37

0.01 0.01 0.01 0.03 0.01 0.01 0.01 0.01 0.01 0.02 0.01 0.01 0.01 0.01 0.29 0.01 0.01 0.01

0.01 0.01 0.04 0.10 0.01 0.02 0.01 0.02 0.01 0.16 0.01 0.02 0.01 0.01 0.01 0.03 0.01 0.01

0.18 0.80 0.62 0.80 0.87 0.48 0.43 0.59 0.94 0.93 0.82 0.80 0.70 0.65 0.93 0.94 0.78 0.99

0.05 0.16 0.51 0.31 0.08 0.23 0.15 0.35 0.23 0.12 0.20 0.34 0.37 0.07 0.98 0.96 0.25 0.16

0.61 0.25 0.32 0.26 0.64 0.25 0.29 0.45 0.34 0.20 0.23 0.44 0.32 0.43 0.46 0.74 0.36 0.29

98.0

169.9

114.1

124.0

137.4

167.3

9.73

0.01

0.01

0.88

0.20

0.31

Percentage of flow at the duodenum Histidine 59.0 60.9 Threonine 73.9 73.5 Arginine 69.2 73.3 Valine 69.8 71.7 Methionine 76.0 75.1 Isoleucine 73.7 76.8 Leucine 79.2 78.0 Lysine 73.9 76.0 Phenylalanine 72.5 73.3 Tyrosine 72.4 74.6 Aspartate 73.4 74.9 Glutamine 76.3 76.7 Serine 72.6 75.4 Glycine 72.9 73.6 Alanine 76.2 81.8 Proline 66.9 66.7 Essential 72.4 74.2 Non-essential 73.8 75.2

56.9 71.8 68.0 67.7 73.2 72.0 77.1 73.6 70.6 64.4 71.6 73.7 72.5 70.1 78.0 64.7 70.9 71.4

56.1 72.5 67.7 68.5 76.4 74.3 80.7 73.4 70.8 71.2 71.8 74.5 71.3 71.5 75.8 66.5 71.5 72.5

62.7 73.3 70.9 67.3 77.0 75.1 78.4 75.4 72.7 70.0 72.7 74.7 73.1 72.1 76.8 68.7 73.4 72.8

63.5 75.5 69.6 70.9 80.1 76.6 83.1 75.7 73.3 73.1 74.6 76.2 73.3 74.7 76.3 69.6 74.5 74.6

2.63 1.98 2.47 3.30 1.80 2.22 1.54 2.36 2.23 3.52 1.73 2.05 2.45 1.72 2.98 2.30 2.15 1.88

0.40 0.57 0.70 0.75 0.03 0.50 0.04 0.87 0.94 0.72 0.84 0.80 0.62 0.69 0.32 0.26 0.68 0.92

0.31 0.70 0.87 0.96 0.85 0.88 0.89 0.63 0.90 0.33 0.77 0.82 0.66 0.92 0.67 0.85 0.77 0.94

0.18 0.78 0.13 0.97 0.99 0.26 0.28 0.36 0.57 0.43 0.46 0.78 0.37 0.75 0.43 0.65 0.39 0.55

0.09 0.22 0.53 0.53 0.09 0.35 0.15 0.57 0.34 0.15 0.20 0.29 0.67 0.09 0.81 0.27 0.32 0.24

0.91 0.53 0.69 0.43 0.36 0.25 0.13 0.68 0.87 0.18 0.33 0.56 0.70 0.37 0.68 0.89 0.51 0.35

71.1

72.1

73.1

74.5

1.99

0.86

0.91

0.45

0.28

0.43

Total

Total

73.1

74.7

a 100F, 67F and 33F = 100, 67 and 33% of supplemental ruminally undegraded intake protein from fish meal and 0, 33 and 67% from blood meal, respectively. b CP, dietary CP level; L and Q, linear and quadratic effects of levels of supplemental ruminally undegraded intake protein from fish and blood meals, respectively; CP × L and CP × Q, interaction between CP level and levels of fish and blood meals, respectively.

264

S.A. Soto-Navarro et al. / Small Ruminant Research 64 (2006) 255–267

Table 5 True small intestinal digestibility of amino acids and endogenous amino acid flow from the small intestine of goats consuming concentrate-based dietsa Amino acid

Endogenous (g/day) Mean

Histidine Threonine Arginine Valine Methionine Isoleucine Leucine Lysine Phenylalanine Tyrosine Aspartate Glutamine Serine Glycine Alanine Proline Essential Non-essential Total a

R2

True digestibility (%) S.E.

Mean

S.E.

0.306 0.849 2.183 0.126 1.108 0.574 0.725 1.679 0.292 0.994 1.437 1.913 0.492 0.562 0.071 0.788 7.617 5.597

0.1046 0.2463 0.7519 0.1682 0.3178 0.1782 0.2036 0.4706 0.1308 0.2393 0.4930 0.6500 0.2380 0.1895 0.0484 0.1921 2.3318 1.9531

70.82 83.73 78.98 72.60 87.83 84.59 90.03 85.25 78.61 85.56 80.77 83.34 78.75 79.37 81.80 80.90 82.24 80.89

3.1181 2.612 2.7832 3.814 2.806 2.636 2.558 2.539 2.505 2.915 2.242 2.346 2.427 2.034 2.679 2.801 2.483 2.286

93.8 96.8 96.0 91.4 96.7 96.8 97.3 97.1 96.7 96.2 97.5 97.4 96.9 97.8 96.5 96.1 97.0 97.4

13.061

4.2683

81.51

2.380

97.2

Estimated by regressing amino acid disappearance in the small intestine against flow at the duodenum, n = 36.

Table 6 Effects of dietary CP level and supplemental ruminally undegraded intake protein from different ratios of fish and blood meals on DM intake, ADG, gain efficiency (ADG:DM intake) and ruminal VFA concentrations of growing Boer × Spanish wethers in an 18-week experiment Item

DM intake (g/day) ADG (g/day) ADG:DM intake (g/kg) Total VFA (mM) Molar (%) Acetate Propionate Isobutyrate Butyrate Isovalerate Valerate Acetate:propionate

Protein sourcea

S.E.

100:0

67:33

33:67

880 132 149 67.2

866 130 148 69.8

832 119 142 74.4

48.8 28.9 0.49 17.2 2.34 2.26 1.86

47.3 30.4 0.54 17.7 2.18 1.76 1.86

49.4 29.4 0.43 16.5 2.27 1.93 1.99

25.6 6.3 4.9 3.27 2.29 0.88 0.055 1.98 0.289 0.226 0.143

CP level (% DM) 12

15

844 122 143 68.9

875 131 150 72.0

51.9b 27.2a 0.46 16.1 2.39 1.90 2.16b

45.1a 32.0b 0.51 18.2 2.13 2.07 1.64a

S.E.

20.9 5.1 4.0 2.67 1.87 0.72 0.045 1.62 0.236 0.184 0.117

Genotypeb

S.E.

BS

S

935b 145b 155b 70.5

783a 108a 138a 70.4

48.1 29.8 0.52 17.2 2.35 2.04 1.89

49.0 29.3 0.45 17.1 2.17 1.93 1.91

20.9 5.2 3.4 2.67 1.87 0.72 0.045 1.62 0.236 0.184 0.117

Within a row and FIM:BLM, CP level or genotype grouping, means without a common superscript letter (a and b) differ (P < 0.05). a 100F, 67F and 33F = ratios of supplemental ruminally undegraded intake protein from fish meal and blood meal of 100:0, 67:33 and 33:67, respectively. b BS, Boer × Spanish; S, Spanish.

S.A. Soto-Navarro et al. / Small Ruminant Research 64 (2006) 255–267

N digestion decreasing as dietary FIM decreased, indicates that ruminal digestion of FIM protein was greater than presumed or that of protein in BLM was less. This may be attributable to variability in feedstuff manufacturing processes that can influence UIP concentration, particularly for FIM (Hussein and Jordan, 1991). Although, increased ruminal outflow of microbial OM and N as FIM in the diet decreased and BLM rose is counter to expectations based on the earlier postulate that ruminal digestibilities of OM and NDF were limited by availability of nitrogenous compounds such as amino acids or peptides with 67F and 33F diets. As a result of change in both ruminal digestibility and microbial N synthesis, microbial efficiency increased with decreasing FIM, to a greater extent for 15% than 12% CP. The only apparent explanations for these changes involve a decrease in the proportion of energy used by microbes for cell maintenance compared to growth or replication. Recycling of N to the rumen and the accompanying availability in the rumen of nitrogenous compounds other than ammonia (amino acids or peptides) with diets including BLM were adequate to support high microbial growth but not digestion of OM or NDF. Effect of decreasing dietary level of FIM on microbial use of energy for maintenance or growth could have been associated with the decrease in ruminal fiber digestion that increased physical effects of fibrous particles, which caused the rate of ruminal outflow of digesta to rise by increased stimulation of ruminal motility and saliva flow with increased rumination. 4.2. Amino acids Although most interactions between dietary CP level and the linear effect of level of FIM in small intestinal disappearance of amino acids in g/day were not significant, numerically effects of FIM with 12% CP were considerably less than with 15% CP. Significant interactions might have been expected because of smaller differences in ingredient composition of 12% than 15% CP diets, and could have been noted with a larger number of observations. Similar effects among amino acids of dietary levels of CP and FIM on flow to the duodenum and ileum and disappearance in the small intestine in g/day agree with dietary treatment effects on duodenal flow of both feed plus endogenous and microbial N rather than expected change only in response to differences between FIM and BLM in the

265

amino acid profile of protein escaping ruminal digestion. True amino acid digestibility in the small intestine was in most cases slightly greater than observed by Soto-Navarro et al. (2005) with diets 13 and 19% in CP. Soto-Navarro et al. (2005) also estimated true amino acid small intestinal disappearance for each dietary CP level, with values greater based on observations with goats consuming 13% versus 19% CP diets. Values in the present experiment are in closer agreement with those for the 13% CP diet, and it was suggested that the 19% CP diet values were low because amino acid flow might have exceeded digestive and (or) absorptive capacity. Thus, most appropriate suggested true small intestinal amino acid disappearance for goats, derived by averaging values of the present experiment and ones for the 13% CP diets of Soto-Navarro et al. (2005), are: histidine 81.3%, threonine 82.9%, arginine 87.5%, valine 82.0%, methionine 84.3%, isoleucine 91.3%, leucine 89.0%, lysine 82.2%, phenylalanine 79.1%, tyrosine 81.1%, asparatate 82.9%, glutamine 82.8%, serine 78.6%, glycine 79.3%, alanine 82.8%, essential 83.7%, non-essential 79.9% and total 81.7%. Estimates of endogenous small intestinal flow of some amino acids were greater than noted by SotoNavarro et al. (2005) but were lower for others. The total endogenous amino acid flow of 13.1 g/day was slightly greater than that of 10.1 g/day reported by Soto-Navarro et al. (2005). Endogenous amino acid N relative to N intake and duodenal N flow is fairly similar to values noted by Soto-Navarro et al. (2005). Endogenous amino acid N was 8.2 and 10.3% of duodenal N and N intake, respectively. 4.3. Performance No performance benefits from the 15% dietary CP level relative to 12% or from various levels of FIM and BLM, coupled with small intestinal amino acid disappearance, indicate that amino acid requirements for growth by both goat genotypes were met by all diets. This is in agreement with findings of Soto-Navarro et al. (2004) with diets containing protein sources varying in extent of ruminal protein degradation and amino acid profile. Diets of the present experiment did not apparently result in amino acid absorption excessive to an extent that performance was limited because of high-energy use in urea excretion or marked amino acid

266

S.A. Soto-Navarro et al. / Small Ruminant Research 64 (2006) 255–267

imbalances. Similarly, these results support those of Soto-Navarro et al. (2003) in that the DIP requirement of goats appears less than for other ruminant species because of greater ruminal N recycling (Silanikove, 2000). Diets in the present experiment were formulated to have a DIP:TDN ratio of at least 0.10, although results of the first experiment suggest an actual ratio lower.

5. Summary and conclusions Cereal grain-based diets with 15% CP resulted in greater small intestinal amino acid disappearance in goats than diets with 12% CP, and partial substitution of BLM for FIM increased small intestinal amino acid disappearance. However, these treatments did not influence performance of growing Boer × Spanish or Spanish wethers. There does not appear potential to enhance performance of common genotypes of growing meat goats of the US by dietary manipulation to increase intestinal amino acid absorption above basal levels with diets moderate to high in corn and with a CP concentration of 12%.

Acknowledgments This research was supported by USDA Grant No. 98-38814-6240. Appreciation is expressed to members of the research crew and analytical laboratory for assistance.

References Aharoni, Y., Tagari, H., 1991. Use of nitrogen-15 determinations of purine nitrogen fraction of digesta to define nitrogen metabolism traits in the rumen. J. Dairy Sci. 74, 2540–2547. AOAC, 1990. Official Methods of Analysis, 15th ed. Association of Official Analytical Chemists, Washington, DC. Bergen, W.G., Purser, D.B., Cline, J.H., 1968. Determination of limiting amino acids of rumen-isolated microbial protein fed to rat. J. Dairy Sci. 51, 1698–1700. Broderick, G.A., Kang, G.A., 1980. Automated simultaneous determination of ammonia and total amino acids in ruminal fluid and in vitro media. J. Dairy Sci. 63, 64–75. Buttery, P.J., Foulds, A.N., 1985. Amino acid requirements of ruminants. In: Haresing, W., Cole, D.J.A. (Eds.), Recent Advances in Animal Nutrition. Butterworths, London, UK, pp. 257–271.

Chen, X.B., Chen, Y.K., Franklin, M.F., Ørskov, E.R., Shand, W.J., 1992. The effect of feed intake and body weight on purine derivative excretion and microbial protein supply in sheep. J. Anim. Sci. 70, 1534–1542. Creighton, K.W., Mass, R.A., Klopfenstein, T.J., 2000. Modification of purine assay to increase accuracy and precision. J. Anim. Sci. 78 (Suppl. 1), 121. Hussein, H.S., Jordan, R.M., 1991. Fish meal as a protein supplement in ruminant diets: a review. J. Anim. Sci. 69, 2147–2156. JAS, 2002. Journal of Animal Science style and form (Revised 2002). J. Anim. Sci. 80, 279–293. Littell, R.C., Henry, P.R., Ammerman, C.B., 1996. Statistical analysis of repeated measures data using SAS procedures. J. Anim. Sci. 76, 1216–1231. Lu, C.D., Potchoiba, M.J., Sahlu, T., Fernandez, J.M., 1990. Performance of dairy goats fed isonitrogenous diets containing soybean meal or hydrolyzed feather meal during early lactation. Small Rumin. Res. 3, 425–434. Miller, E.L., 1973. Evaluation of foods as source of nitrogen and amino acids. Proc. Nutr. Soc. 32, 79–84. NRC, 1985. Ruminant Nitrogen Usage. National Academy Press, Washington, DC, pp. 46–52. NRC, 1996. Nutrient Requirements of Beef Cattle, sixth ed. National Academy Press, Washington, DC, pp. 16–21. Preston, R.L., 2000. Typical composition of feeds for cattle and sheep. Beef 36 (10), 10–20. Puchala, R., Sahlu, T., Pierzynowski, S.G., Hart, S.P., 1995. Effects of amino acids administered to a perfused area of the skin in Angora goats. J. Anim. Sci. 73, 565–570. Richardson, C.R., Hatfield, E.E., 1978. The limiting amino acids in growing cattle. J. Anim. Sci. 46, 740–745. SAS, 1990. SAS User’s Guide, Version 6, fourth ed., vol. 2. SAS Inst. Inc., Cary, NC. Satter, L.D., Syter, L.L., 1974. Effects of ammonia concentration on ruminal microbial protein production in vitro. Br. J. Nutr. 32, 199–208. Silanikove, N., 2000. The physiological basis of adaptation in goats to harsh environments. Small Rumin. Res. 35, 181– 194. Soto-Navarro, S.A., Goetsch, A.L., Sahlu, T., Puchala, R., 2004. Effects of level and source of supplemental protein in a concentrate-based diet on growth performance of Boer × Spanish wether goats. Small Rumin. Res. 51, 101–106. Soto-Navarro, S.A., Goetsch, A.L., Sahlu, T., Puchala, R., 2005 Effects of level and source of supplemental protein in a concentrate-based diet on sites of digestion and small intestinal amino acid disappearance in Boer × Spanish wether goats. Small Rumin. Res., in press. Soto-Navarro, S.A., Goetsch, A.L., Sahlu, T., Puchala, R., Dawson, L.J., 2003. Effects of ruminally degraded nitrogen source and level in a high concentrate diet on site of digestion in yearling Boer × Spanish wether goats. Small Rumin. Res. 50, 117– 128. Storm, E., Ørskov, E.R., 1984. The nutritive value of rumen microorganisms in ruminants. 4. The limiting amino acids of microbial protein in growing sheep determined by a new approach. Br. J. Nutr. 52, 613–620.

S.A. Soto-Navarro et al. / Small Ruminant Research 64 (2006) 255–267 Titgemeyer, E.C., Merchen, N.R., Berger, L.L., Deetz, L.E., 1988. Estimation of lysine and methionine requirements of growing steers fed corn silage-based diets. J. Dairy Sci. 71, 421–434. Van Soest, P.J., 1994. Microbes in the gut. In: Nutritional Ecology of the Ruminant, second ed. Cornell University Press, Ithaca, NY, pp. 253–280.

267

Wolfrom, G.W., Asplund, J.M., 1979. Effect of amino acid patterns and level of intravenously and intraruminally infused sheep. J. Anim. Sci. 49, 752–763. Zinn, R.A., Owens, F.N., 1986. A rapid procedure for purine measurements and its use for estimating net ruminal protein synthesis. Can. J. Anim. Sci. 66, 157–166.