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 Ruminant Research 65 (2006) 85–100

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 S.A. Soto-Navarro, A.L. Goetsch ∗ , T. Sahlu, R. Puchala 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 12 May 2005 Available online 6 July 2005

Abstract Twelve yearling Boer × Spanish wether goats fitted with ruminal, duodenal and ileal cannulae (34.5 ± 1.39 kg average BW) were used in an experiment with two simultaneous 6 × 6 Latin squares to determine effects of different supplemental protein sources on sites of digestion and small intestinal amino acid disappearance with concentrate-based diets moderate or high in CP concentration. Diets were formulated to be 13 or 19% CP (DM basis), with supplemental protein provided by blood (BLM), corn gluten (CGM), cottonseed (CSM), feather (FTM), fish (FIM) or soybean meal (SBM). Small intestinal disappearance of the sum of essential amino acids measured (i.e., histidine, threonine, arginine, valine, methionine, isoleucine, leucine, lysine and phenylalanine) was greater for BLM versus SBM (39.0, 33.4, 28.7, 33.1, 33.3 and 20.5 g/day for BLM, CGM, CSM, FTM, FIM and SBM, respectively). Small intestinal disappearance of some essential amino acids was similar among CP sources with 13% CP but different with 19% CP. With 19% CP, small intestinal disappearance of histidine and valine was greatest (P < 0.05) among sources for BLM (histidine: 6.1, 1.8, 2.1, 1.9, 1.5 and 1.1 g/day; valine: 7.1, 3.6, 3.0, 4.3, 4.7 and 2.1 g/day), for leucine was greater (P < 0.05) for BLM and CGM than for CSM, FTM and SBM (13.2, 13.1, 5.8, 8.5, 9.3 and 4.4 g/day), of lysine was greater (P < 0.05) for BLM versus CGM, CSM, FIM and SBM (8.2, 3.2, 3.9, 5.5, 4.1 and 2.9 g/day) and of phenylalanine was lowest among sources for SBM (6.6, 5.2, 3.8, 3.9, 3.7 and 2.2 g/day for BLM, CGM, CSM, FTM, FIM and SBM, respectively). Essential amino acids with small intestinal disappearance not influenced by protein source within CP level were threonine, methionine and isoleucine. However, small intestinal disappearance of threonine (2.5 and 3.8 g/day) and methionine (1.1 and 1.9 g/day for 13 and 19% CP, respectively) was greater (P < 0.05) for 19% versus 13% CP diets. In conclusion, use of different feedstuffs high in protein not extensively degraded in the rumen and with unique amino acid concentrations in diets of goats may have little influence on small intestinal absorption of select amino acids with dietary CP levels, such as 13%, although effects may occur with much higher levels of CP (e.g., 19%). © 2005 Elsevier B.V. All rights reserved. Keywords: Goat; Protein; Amino acids; Digestion

∗

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.2005.05.028

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1. Introduction

2. Materials and methods

The NRC (1981) publication on the nutrient requirements of goats expresses protein requirements on total and digestible protein bases. These dietary characteristics do not provide information about the quantity and quality of protein that reaches the small intestine for absorption. Most protein entering the small intestine is from microbial cells synthesized and feed not degraded in the rumen (NRC, 1996). Microbial protein synthesis is affected principally by ruminal concentrations of Ncontaining compounds (Hespell, 1979) and the quantity of carbohydrates fermented (Rohr et al., 1986). When amino acid requirements are high, such as for rapidly growing young ruminants, ruminally produced microbial protein may not meet amino acid needs of the host. Different sources of protein vary in susceptibility to ruminal degradation and amino acid composition. The average concentrations of ruminally undegraded protein (UIP) in blood, corn gluten, feather, fish, cottonseed and soybean meals is 80, 60, 75, 60, 39 and 36% of total CP content (Preston, 2000). Blood meal is relatively high in lysine and histidine but low in methionine; corn gluten meal is relatively high in methionine and leucine but low in lysine and arginine; feather meal is relatively high in arginine, isoleucine and valine but low in methionine and lysine; fish meal is relatively high in lysine and methionine; cottonseed meal is relatively high in arginine but low in methionine; soybean meal has moderate concentrations of most essential amino acids but is somewhat low in methionine (NRC, 1988). In addition to the potential value of influencing ruminal outflow of UIP and microbial protein, it is also desirable to know true digestibility of amino acids in the small intestine and the quantity of endogenous amino acids. Many estimates are available for cattle and sheep (NRC, 1985). However, AFRC (1998) and GfE (2003) highlighted the lack of similar determinations for goats and, thus, proposed extrapolation of apparent small intestinal digestibilities of non-ammonia N for cattle and sheep to goats. Therefore, objectives of this experiment were to determine effects of different supplemental protein sources on sites of digestion and small intestinal amino acid disappearance when feeding concentrate-based diets moderate or high in CP concentration using Boer × Spanish wether goats.

2.1. Animals and treatments The protocol for this experiment was approved by the Langston University Animal Care Committee. Twelve yearling Boer × Spanish wether goats (34.5 ± 1.39 and 30.3 ± 1.91 kg BW at the beginning and at the end of the experiment, respectively) with ruminal, duodenal and ileal cannulae were used in an experiment with a 2 × 6 factorial arrangement of treatments. There were two simultaneous 6 × 6 Latin squares for the two dietary CP levels and six supplemental protein sources. Periods were 14 days in length, and between periods 3 and 4, wethers were removed from metabolism crates and placed in 1.2 m × 1.2 m bedded pens for 2 weeks, during which time period 4 diets were fed. Wethers were weighed at the beginning of period 1 and end of period 6. Wethers were 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) before the experiment, and were adapted to a high concentrate diet and metabolism crates for 3 weeks prior to period 1. 2.2. Experimental diets Diets (Table 1) were fed in equal proportions at 08:00 and 20:00 h daily, with feed offered at approximately 110% of consumption on the preceding few days. Diets were based largely on ground corn, included 0.4% chromic oxide as an inert, external marker to estimate digestibility and nutrient flows, and were formulated following recommendations for avoidance of urinary calculi (2:1 calcium to phosphorus ratio, 1% ammonium chloride and 1.5% trace mineralised plus white salt). Diets were formulated to be 13 or 19% CP (DM basis), with supplemental protein sources of blood (BLM), corn gluten (CGM), cottonseed (CSM), feather (FTM), fish (FIM) or soybean meal (SBM). Urea was included in diets to achieve a minimum ratio of ruminally degraded intake protein (DIP) to total digestible nutrients (TDN) of 0.09 and to minimize differences among diets in the ratio. Dietary ingredients chosen were ones commonly used in beef cattle diets, so that DIP concentrations determined with beef cattle (Preston, 2000) might be employed here.

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Table 1 Composition of diets consumed by growing Boer × Spanish wether goats (DM basis) Item

Ingredient (%) Cottonseed hulls Ground corn Soybean meal (SBM) Blood meal (BLM) Fish meal (FIM) Corn gluten meal (CGM) Cottonseed meal (CSM) Feather meal (FTM) Urea Molasses Dicalcium phosphate Limestone Vitamin premixa Trace mineralised saltb Ammonium chloride Deccoxc Potassium chloride Sodium sulfate Salt Chromic oxide

13% CP

19% CP

BLM

CGM

CSM

FTM

FIM

SBM

BLM

CGM

CSM

FTM

FIM

SBM

30.00 57.96

30.00 57.12

30.00 55.02

30.00 58.17

30.00 57.70

30.00 54.58 5.99

30.00 48.17

30.00 43.65

30.00 33.24

30.00 49.22

30.00 44.22

30.00 39.19 21.87

1.52

11.24 2.54

17.32

2.67

17.50 5.08

0.99 3.00 0.85 1.29 0.50 0.50 1.00 0.05 0.32 0.63 1.00 0.40

0.86 3.00 0.79 1.34 0.50 0.50 1.00 0.05 0.30 0.46 1.00 0.40

0.73 3.00 0.60 1.44 0.50 0.50 1.00 0.05 0.17 0.51 1.00 0.40

27.43 1.60 0.97 3.00 0.81 1.30 0.50 0.50 1.00 0.05 0.31 0.39 1.00 0.40

0.87 3.00 0.45 1.15 0.50 0.50 1.00 0.05 0.28 0.57 1.00 0.40

0.42 3.00 0.70 1.36 0.50 0.50 1.00 0.05 0.07 0.44 1.00 0.40

0.47 3.00 0.86 1.19 0.50 0.50 1.00 0.05 0.39 1.22 1.00 0.40

3.00 0.52 1.49 0.50 0.50 1.00 0.05 0.28 0.11 1.00 0.40

3.00 2.22 0.50 0.50 1.00 0.05 0.66 1.00 0.40

11.81 0.31 3.00 0.61 1.26 0.50 0.50 1.00 0.05 0.34

3.00 1.03 0.50 0.50 1.00 0.05 0.15 0.83 1.00 0.40

1.00 0.40

3.00 0.34 1.46 0.50 0.50 1.00 0.05 0.69 1.00 0.40

Analyzed (%) Ash CP NDF

5.6 13.1 31.7

5.3 13.6 31.1

5.2 13.5 31.9

5.1 13.4 31.6

5.7 13.5 30.5

5.8 14.0 32.3

5.6 18.7 31.7

5.2 20.0 30.3

5.2 19.5 31.8

5.6 20.0 31.6

5.5 19.1 30.5

5.2 19.1 32.3

Calculatedd CP (%) ME (MJ/kg DM) Ca (%) P (%) K (%) TDN (%) DIPe :TDN

13.0 9.20 0.72 0.36 0.75 67.5 0.09

13.0 9.29 0.72 0.36 0.75 68.1 0.09

13.0 9.29 0.72 0.36 0.75 67.9 0.09

13.0 9.25 0.72 0.36 0.75 67.8 0.09

13.0 9.33 0.72 0.36 0.75 68.2 0.09

13.0 9.37 0.72 0.36 0.75 68.6 0.09

19.0 8.95 0.72 0.36 0.75 65.4 0.09

19.0 9.54 0.72 0.36 0.75 68.9 0.10

19.0 9.25 0.72 0.36 0.75 68.7 0.12

19.0 9.25 0.72 0.36 0.75 67.1 0.09

19.0 9.33 1.42 0.71 0.75 67.4 0.11

19.0 9.50 0.72 0.36 1.02 68.6 0.14

a b c d e

Contained 2200 IU/g Vitamin A, 1200 IU/g Vitamin D3 and 2.2 IU/g Vitamin E. 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. Rhone-Poulenc, Atlanta, Ga; 6% decoquinate. Based on Preston (2000). DIP, ruminally degraded intake protein.

2.3. Samples and analyses Following a 10-day treatment adjustment period, ruminal, duodenal, ileal and fecal samples were collected twice daily for 4 days. The time sequence for sampling wethers 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; day 4, 12:00 and 18:00 h. Individual samples consisted (wet basis) of approximately 200 ml of ruminal contents,

80 ml of duodenal digesta, 50 ml of ileal digesta and 20 g of feces. Ruminal contents from each wether and within each period were composited (equal weight, wet basis), 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 and was stored at 4 ◦ C for isolation of ruminal bacteria. Samples of feces were from excreta that had accumulated since the last

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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 via the ruminal cannula from each wether at 4 h after feeding and pH was measured with a pH electrode (Model 88; Markson, Phoenix, AZ). Ruminal fluid was strained through eight layers of cheesecloth. For ruminal ammonia analysis, 5 ml of ruminal fluid was added to 0.5 ml of 6N HCl. Upon completion of each collection period, ruminal bacteria were isolated via differential centrifugation (Bergen et al., 1968). Microbial isolates were prepared for analysis by ovendrying 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, ash (AOAC, 1990), CP (Technicon Instrument, Tarrytown, NY) and NDF concentrations (filter bag technique; ANKOM Technology, Fairport, NY). Bacterial samples were analyzed for DM, ash and CP, and 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 0.1N HCl and 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, ash 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 allowed to react with 3,3 -dithiodi-propionic acid to convert cysteine to stable cysteine-3-mercaptopropionic acid and hydrolyzed with 6N HCl using a MDS-2000 microwave system (CEM, Matthews, NC). 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 UV detection. 2.4. Statistical analysis Data were analyzed with a repeated measures design using mixed model procedures of SAS (Littell et al., 1998). Fixed effects were CP level, supplemental protein source, period and the CP level × supplemental protein source interaction; the random effect was wether within source of supplemental CP. A compound symmetry covariance structure was employed. Differences between CP level and among protein source main effect means and CP level–source interaction means were determined by least significant different 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). 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), which was performed with all data and separately for 13 and 19% CP diets; quadratic effects of duodenal amino acid flow were non-significant.

3. Results 3.1. DM and OM DM and OM intakes were not affected by CP level, supplemental protein source or their interaction (Table 2). Total duodenal OM was lowest among protein sources (P < 0.05) for SBM with 19% CP and also with 13% except for the CGM diet. With 19% CP, total duodenal OM was greater (P < 0.05) for FIM than for BLM, CGM and FTM. Microbial OM flow at the duodenum was greater (P < 0.05) for BLM, CSM and FIM than for SBM. Non-microbial OM at the duodenum within CP levels was lowest among protein sources (P < 0.05) for SBM and with 19% CP was greater (P < 0.05) for FIM versus FTM. Total OM at the ileum and in feces differed among CP sources in a manner similar to differences in duodenal OM.

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Table 2 Effects of dietary CP level and protein source on DM intake and OM intake and digestion in growing Boer × Spanish wether goats Sourcea

Item

CP level (% DM)

DM intake (g/day)

13 19 Mean

655 679 667

657 679 669

654 677 665

652 677 666

657 678 668

658 682 669

41.7

13 19 Mean

620 632 626

628 640 634

622 636 629

612 636 627

628 637 633

622 631 626

39.9

324b 387b

298ab 361b

330b 411bc

341b 357b

336b 432c

240a 214a

25.2

92 99 96b

80 70 75ab

105 95 100b

94 81 88ab

101 89 95b

78 66 72a

9.8

13 19

232b 288bc

218b 292bc

224b 315bc

247b 275b

235b 343c

163a 148a

19.3

Ileum (g/day)

13 19

226ab 281bc

230ab 232bc

237b 304c

238b 227b

238b 298c

160a 137a

20.2

Feces (g/day)

13 19

124ab 160bc

135b 144b

129ab 193c

146b 146b

132ab 183c

100a 81a

10.8

BLM

OM Intake (g/day)

Duodenum (g/day) Total Microbial

Non-microbial

13 19 13 19 Mean

Digestion (% intake) Apparent ruminal 13 19

S.E. CGM

CSM

FTM

FIM

SBM

29.5

28.2

6.9

48.4a 38.1a

52.7ab 43.5a

46.9a 35.4a

44.1a 43.4a

46.7a 32.3a

61.3b 66.2b

2.72

True ruminal

13 19

63.0a 54.2ab

65.4ab 54.5ab

63.6a 50.3ab

59.6a 56.3b

62.6a 46.4a

73.8b 76.6c

2.04

Small intestine

13 19 Mean

15.9 16.7 16.3b

10.7 20.3 15.5ab

15.6 16.6 16.1a

17.0 20.6 18.8b

15.3 20.7 18.0b

12.6 12.1 12.3a

1.99

13 19 Mean

16.0 19.8 17.9b

14.9 13.6 14.3ab

17.0 17.7 17.3b

15.2 13.1 14.2ab

17.1 17.9 17.5b

10.2 8.9 9.6a

13 19

80.3ab 74.6a

78.3a 77.3b

79.4a 69.6a

76.3a 77.1b

79.2a 70.9a

84.1b 87.2c

Hindgut

Total tract

1.41

CP level (% DM)

S.E.

13

19

655

678

41.7

623

635

39.7

92

83

6.8

14.5

17.8

1.13

15.1

15.2

1.17

2.11 1.53 1.20

a–c: Means within a row for CP source or level without a common letter differ (P < 0.05). Superscripts for CP level–source interaction means appear when the interaction between CP level and source was significant (P < 0.05); superscripts are not presented for interaction means of a CP level when there was not a significant difference among sources. Main effect means for CP level and CP source appear when an effect was significant (P < 0.05) and if the interaction between CP level and source was non-significant. a BLM, blood meal; CGM, corn gluten meal; CSM, cottonseed meal; FTM, feather meal; FIM, fish meal; SBM, soybean meal.

True ruminal OM digestion was greater (P < 0.05) for SBM than for other protein sources except for CGM with 13% CP and was greatest among all CP sources for SBM with 19% CP (Table 2). In accordance, small intestinal OM digestion was lower for SBM versus BLM, CSM, FTM and FIM. Hindgut OM

digestion was lower (P < 0.05) for SBM versus BLM, CSM and FIM. With 13% CP, total tract OM digestion was greater (P < 0.05) for SBM than for CGM, CSM, FTM and FIM, and with 19% CP total tract OM digestion ranked (P < 0.05) BLM, CSM and FIM < CGM and FTM < SBM.

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Table 3 Effects of dietary CP level and protein source on N intake and digestion in growing Boer × Spanish wether goats Item

CP level (% DM)

Sourcea BLM

Intake (g/day)

Duodenum (g/day) Total Microbial

S.E. CGM

CSM

FTM

SBM

13 19 Mean

13.6 20.6 17.1

13.7 20.7 17.2

13.6 20.6 17.1

13.6 20.6 17.1

13.7 20.6 17.1

13.7 20.7 17.2

1.03

13 19

13.2 25.7cd

14.0 19.7b

15.7 21.0b

16.7 21.1bc

15.4 27.3d

11.4 11.2a

1.51

5.8 5.8 5.8a

0.81

5.2 4.8a

1.21

0.6 0.7 0.6a

0.10

4.3 4.2a

0.73

4.4ab 7.7d

3.3a 2.7a

0.46

4.1ab −2.6ab −15.2a −23.9a −12.9ab −25.9ab 4.2b −3.3ab −3.6ab −30.8a

15.6b 45.7c

6.94

13 19 Mean

7.4 7.0 7.2ab

6.9 5.9 6.4ab

8.3 7.5 7.9b

7.4 6.2 6.8ab

5.0 18.0cd

6.6 13.0bc

6.6 12.4b

8.3 14.1bc

Non-ammonia and non-microbial

13 19

Ammonia

13 19 Mean

0.7 0.7 0.7ab

0.6 0.9 0.7ab

0.8 1.1 0.9b

0.9 0.8 0.9b

Ileum (g/day)

13 19

6.0 9.5bc

5.5 6.6ab

6.8 9.8cd

6.9 7.8bc

Feces (g/day)

13 19

4.4ab 6.5cd

4.4ab 4.8b

4.8b 7.3d

5.6b 5.1bc

Digestion (% intake) Apparent ruminal

FIM

13 19

7.8 6.5 7.1ab 6.9 20.0d 0.8 0.8 0.8ab 6.2 11.4d

0.73

0.57

0.07

True ruminal

13 19

62.6 12.8ab

51.8 37.1b

51.1 38.6b

38.7 30.8ab

49.0 5.1a

62.1 76.8c

5.57

Small intestine

13 19

52.3 79.8b

61.9 63.7b

65.6 55.2ab

71.8 66.0b

67.7 75.9b

51.7 34.0a

5.90

Hindgut

13 19 Mean

12.1 15.1 13.4ab

14.7 12.3 13.5ab

10.9 12.7 11.8ab

13.4 17.3 15.4b

8.3 7.3 7.8a

2.37

13 19

68.5bc 69.0ab

67.6b 76.7b

65.2ab 64.4a

58.8a 75.2b

68.4bc 62.4a

75.8b 87.1c

1.89

13 19 Mean

19.0 22.6 20.8b

16.6 17.2 16.9ab

20.8 23.6 22.2b

21.1 18.2 19.6b

19.7 22.3 21.0b

12.6 12.3 12.4a

2.57

Total tract Microbial efficiencyb

8.3 8.9 8.6ab

1.68

1.82

CP level (% DM)

S.E.

13

19

13.6a

20.6b

1.03

7.3

6.5

0.57

0.71

0.82

0.06

11.3

12.2

1.02

18.3

19.4

1.54

a–c: Means within a row for CP source or level without a common letter differ (P < 0.05). Superscripts for CP level–source interaction means appear when the interaction between CP level and source was significant (P < 0.05); superscripts are not presented for interaction means of a CP level when there was not a significant difference among sources. Main effect means for CP level and CP source appear when an effect was significant (P < 0.05) and if the interaction between CP level and source was non-significant. a BLM, blood meal; CGM, corn gluten meal; CSM, cottonseed meal; FTM, feather meal; FIM, fish meal; SBM, soybean meal. b Grams of microbial N/kg OM truly fermented in the rumen.

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Table 4 Effects of dietary CP level and protein source on NDF intake and digestion in growing Boer × Spanish wether goats Sourcea

Item

CP level (% DM)

CGM

CSM

FTM

Intake (g/day)

13 19

219ab 247c

216a 223b

222b 257d

220ab 259d

215a 212a

217ab 224b

14.2

Duodenum (g/day)

13 19

130b 129b

109ab 131b

118b 167c

123b 124b

125b 152bc

84a 74a

10.2

Ileum (g/day)

13 19

129ab 159bc

133b 133bc

133b 173b

133b 125b

135b 160bc

84a 71a

11.9

Feces (g/day)

13 19

72.8ab 91.8bc

80.3b 83.9b

74.7ab 106.8c

87.4b 83.5b

75.6ab 104.9c

56.8a 45.9a

6.42

Digestion (% intake) Ruminal 13 19

41.4a 47.6bc

49.4ab 41.2ab

46.4a 35.1ab

43.4a 52.1c

41.8a 28.8a

60.9b 67.6d

2.90

−6.1 −3.0 −4.6

−4.8 −0.7 −2.7

−4.5 −5.1 −4.8

−0.6 0.4 −0.1

4.22

3.97

BLM

Small intestine

13 19 Mean

0.3 −12.7 −6.2

S.E.

−11.2 −0.8 −6.0

FIM

SBM

Hindgut

13 19 Mean

25.5 27.7 26.6b

24.3 21.2 22.8b

26.2 26.2 26.2b

21.9 16.4 19.2ab

27.7 26.0 26.8b

13.4 11.4 12.5a

Total tract

13 19 Mean

67.2ab 62.7b 64.9b

62.5a 61.7b 62.1ab

66.3ab 58.5ab 62.4ab

60.5a 67.8b 64.1b

65.0ab 49.7a 57.3a

73.9a 79.4c 76.6c

CP level (% DM) 13

2.99

2.81

S.E.

19

−4.5 −3.6

2.81

23.2

2.19

21.5

2.22 1.58

a–c: Means within a row for CP source or level without a common letter differ (P < 0.05). Superscripts for CP level–source interaction means appear when the interaction between CP level and source was significant (P < 0.05); superscripts are not presented for interaction means of a CP level when there was not a significant difference among sources. Main effect means for CP level and CP source appear when an effect was significant (P < 0.05) and if the interaction between CP level and source was non-significant. a BLM, blood meal; CGM, corn gluten meal; CSM, cottonseed meal; FTM, feather meal; FIM, fish meal; SBM, soybean meal.

3.2. Nitrogen Supplemental protein source did not influence total N flow at the duodenum with 13% CP (Table 3). Conversely, with 19% CP, total N at the duodenum was lowest among protein sources (P < 0.05) for SBM and greatest (P < 0.05) for FIM versus CGM, CSM and FTM. Duodenal microbial N was lower (P < 0.05) for SBM versus CSM. Differences among protein sources in duodenal non-ammonia, non-microbial N and total N at the ileum were similar to those in duodenal flow of total N. Fecal N with 13% CP was lower (P < 0.05) for SBM versus FTM and with 19% CP was lowest among protein sources for SBM and greater (P < 0.05) for CSM and FIM than for CGM and FTM. True ruminal N digestion was similar among protein sources with 13% CP (Table 3). With 19% CP, true ruminal N digestion was greatest among treatments

(P < 0.05) for SBM. Small intestinal N digestion was greater among treatments (P < 0.05) for BLM and FIM. Hindgut N digestion was greatest (P < 0.05) for FIM versus SBM diets. Efficiency of microbial growth was lower (P < 0.05) for SBM versus BLM, CSM, FTM and FIM. 3.3. NDF Ruminal digestion of NDF was greater (P < 0.05) for SBM versus BLM, CSM, FTM and FIM with 13% CP, and was greatest among protein sources with 19% CP for SBM (Table 4). Small intestinal NDF disappearance was low as expected and similar among protein sources. Hindgut NDF disappearance was lower (P < 0.05) for SBM than for BLM, CGM, CSM and FIM. Total tract NDF digestion was similar among protein sources with 13% CP, but with 19% CP was highest among protein

92

S.A. Soto-Navarro et al. / Small Ruminant Research 65 (2006) 85–100

Table 5 Effects of dietary CP level and protein source on amino acid flow (g/day) at the duodenum and ileum in growing Boer × Spanish wether goats Item

CP level (% DM)

Sourcea BLM

Duodenum Histidine

S.E. CGM

CSM

FTM

FIM

SBM

13

13 19

2.1 8.0b

2.0 2.8a

2.2 3.5a

2.1 2.9a

2.1 2.7a

1.5 1.7

0.44

13 19 Mean

3.4 6.6 5.2ab

4.5 5.8 5.2ab

4.6 6.4 5.5b

4.6 6.9 5.7b

4.7 7.5 6.1b

3.4 3.8 3.6a

0.64

Arginine

13 19

5.5b 8.3bc

5.5b 5.7ab

5.3b 10.4c

6.2b 7.0ab

5.3b 9.8c

4.0a 4.0a

1.20

Valine

13 19

Methionine

13 19 Mean

Isoleucine

13 19 Mean

Threonine

3.6 10.4c

0.45

4.1 5.6ab

4.3 6.4ab

4.8 6.8ab

4.2 8.0b

3.3 3.3a

0.89

1.9 2.9 2.4ab

2.3 3.7 3.0b

2.3 3.4 2.9b

2.2 3.6 2.9b

2.2 3.0 2.6ab

1.7 1.8 1.7a

0.31

2.6 3.9 3.2ab

3.6 4.9 4.2ab

3.8 5.9 4.8b

4.1 5.6 4.8b

3.6 6.1 4.9b

2.9 2.8 2.9a

0.68

0.22

0.48

Leucine

13 19

7.2 18.4d

8.4 16.3cd

8.5 11.0ab

8.6 11.9bc

8.2 14.1bc

6.0 6.2a

1.18

Lysine

13 19

4.6 11.7c

5.1 5.3ab

5.4 8.2b

5.0 7.9ab

5.4 7.1ab

3.8 4.3a

0.82

Phenylalanine

13 19

3.9 9.6c

4.3 7.2b

4.6 7.2bc

4.5 6.4b

4.4 8.0bc

3.2 3.4a

0.65

Tyrosine

13 19 Mean

3.5 5.5 4.5b

4.2 6.3 5.3b

4.1 5.6 4.8b

4.2 5.5 4.8b

4.2 6.4 5.3b

3.1 3.3 3.2a

0.51

Aspartate

13 19

9.2 23.0c

9.9 14.0b

11.5 17.8bc

11.6 16.5bc

11.3 18.0bc

8.5 8.4a

1.29

Cysteine

13 19 Mean

0.2 0.3 0.2a

0.3 0.4 0.3ab

0.3 0.5 0.4b

0.2 0.6 0.4b

0.2 0.2 0.2a

0.06

Glutamine

13 19 Mean

10.1 19.4 14.7b

11.9 19.0 15.5b

12.3 21.5 16.9b

8.2 10.1 9.2a

1.89

Serine

13 19

4.8 8.7ab

5.4 8.1ab

5.5 8.0ab

6.0 9.5bc

5.5 13.8c

3.9 4.4a

1.05

Glycine

13 19

4.8 9.3bc

5.1 6.1ab

5.5 8.1bc

5.9 9.4cd

5.5 11.6d

4.0 4.1a

0.72

Alanine

13 19

5.8b 13.7c

6.8b 11.4bc

6.5b 9.0b

6.9b 9.7b

6.7b 10.5bc

4.9a 5.4

0.85

Essential

13 19

34.7 79.8b

39.4 56.8b

40.4 62.0b

42.1 58.6b

40.1 66.2b

29.5 31.2a

6.14

Non-essential

13 19

38.5b 79.8b

44.0b 71.1b

43.9b 72.0b

46.7b 70.0b

45.6b 82.4b

33.1a 35.9a

5.87

Total

13 19

73.3 159.7b

83.5 128.2b

88.7 128.9b

85.7 148.8b

62.6 67.2a

11.78

0.3 0.4 0.3ab 12.3 24.9 18.6b

12.2 23.2 17.7b

84.3 134.3

CP level (% DM)

0.36

0.04

1.34

S.E.

19

4.2a

6.2b

0.36

2.1a

3.1b

0.15

3.4a

4.8b

0.38

3.9a

5.4b

0.35

0.2a

0.4b

0.03

11.1a

19.7b

1.04

S.A. Soto-Navarro et al. / Small Ruminant Research 65 (2006) 85–100

93

Table 5 (Continued) Item

CP level (% DM)

Sourcea BLM

Ileum Histidine

S.E. CGM

CSM

FTM

FIM

SBM

CP level (% DM) 13

13 19

0.7 1.9c

0.8 0.9ab

1.0 1.4bc

0.9 1.0ab

0.9 1.2bc

0.6 0.6a

0.12

Threonine

13 19

1.4ab 2.4bc

1.7ab 2.0ab

2.1b 3.3d

2.0ab 2.3bc

1.8ab 3.0cd

1.2a 1.3a

0.21

Arginine

13 19

1.5ab 2.6cd

1.6ab 1.6ab

1.8ab 3.5d

1.9b 2.0bc

1.6ab 2.7cd

1.1a 1.1a

0.19

Valine

13 19

1.4 3.3c

1.6 1.9ab

2.2 3.4c

1.9 2.5bc

1.8 3.4c

1.2 1.2a

0.30

Methionine

13 19

1.0ab 1.2b

0.9ab 1.0ab

1.1ab 1.8c

1.1ab 1.2b

1.1ab 1.4bc

0.7a 0.6a

0.09

Isoleucine

13 19

0.9 1.7ab

1.1 1.5ab

1.3 2.6c

1.3 1.7ab

1.4 2.1bc

0.9 0.9a

0.18

Leucine

13 19

2.2 5.2d

2.5 3.2ab

3.2 5.2d

2.9 3.4bc

2.7 4.8cd

1.9 1.8a

0.37 0.37

Lysine

13 19

1.8a 3.5cd

1.9ab 2.1ab

2.4b 4.3d

2.1ab 2.4b

2.1ab 2.9bc

1.4a 1.4a

0.22

Phenylalanine

13 19

1.4 3.0bc

1.6 2.0ab

2.0 3.3c

1.8 2.6bc

1.8 3.4c

1.2 1.2a

0.27

Tyrosine

13 19

1.6ab 2.3ab

1.8ab 2.1ab

2.0bc 3.0bc

2.1bc 2.8bc

2.1c 4.4c

1.5a 1.3a

0.35

Aspartate

13 19

3.7 7.6cd

3.9 4.5ab

4.9 7.6c

4.6 6.1bc

4.3 8.1c

3.0 3.0a

0.50

Cysteine

13 19

0.1 0.2a

0.1 0.2a

0.1 0.2a

0.1 0.2a

0.1 0.3b

0.1 0.1a

0.02

Glutamine

13 19

5.0 7.4b

5.6 6.8b

6.7 10.7c

6.3 7.2b

6.0 9.0bc

4.0 3.6a

0.71

Serine

13 19

1.9 3.0bc

2.1 2.3ab

2.6 3.8cd

2.5 2.9bc

2.2 4.6d

1.5 1.4a

0.31

Glycine

13 19

1.9ab 3.2bc

1.9ab 2.3ab

2.5b 3.7cd

2.4ab 3.1bc

2.2ab 4.1d

1.5a 1.5a

0.24

Alanine

13 19

2.8 4.5cd

2.8 3.2b

3.2 4.9d

3.1 3.4bc

2.9 4.5cd

2.1 2.0a

0.30

Essential

13 19

16.6 35.7cd

19.9 25.3ab

22.2 36.5b

22.6 29.4bc

21.0 35.0cd

14.8 15.3a

2.65

Non-essential

13 19

17.1 28.0bc

18.3 21.3ab

20.1 33.9d

21.1 25.7bc

19.7 34.9cd

13.9 12.8a

2.23

Total

13 19

33.8 63.7bc

38.1 47.0ab

42.3 70.4d

43.7 55.0bc

40.8 69.8cd

28.8 28.1a

4.51

S.E.

19

a–c: Means within a row for CP source or level without a common letter differ (P < 0.05). Superscripts for CP level–source interaction means appear when the interaction between CP level and source was significant (P < 0.05); superscripts are not presented for interaction means of a CP level when there was not a significant difference among sources. Main effect means for CP level and CP source appear when an effect was significant (P < 0.05) and if the interaction between CP level and source was non-significant. a BLM, blood meal; CGM, corn gluten meal; CSM, cottonseed meal; FTM, feather meal; FIM, fish meal; SBM, soybean meal.

94

S.A. Soto-Navarro et al. / Small Ruminant Research 65 (2006) 85–100

Table 6 Effects of dietary CP level and protein source on amino acid disappearance in the small intestine of growing Boer × Spanish wether goats Item

CP level (% DM)

Sourcea BLM

Grams per day Histidine

S.E. CGM

CSM

FTM

FIM

SBM

CP level (% DM) 13

13 19

1.3 6.1b

1.2 1.8a

1.2 2.1a

1.3 1.9a

1.2 1.5a

1.0 1.1a

0.41

Threonine

13 19 Mean

2.3 4.2 3.3

2.8 3.8 3.3

2.5 3.1 2.8

2.6 4.6 3.6

2.8 4.6 3.7

2.2 2.6 2.4

0.58

Arginine

13 19 Mean

4.1 5.8 4.9ab

3.8 4.0 3.9ab

3.5 7.0 5.2b

4.4 5.0 4.7ab

3.7 7.0 5.4b

2.9 2.8 2.9a

1.14

Valine

13 19

2.2 7.1b

2.5 3.6a

2.2 3.0a

2.9 4.3a

2.4 4.7a

2.1 2.1a

0.78

Methionine

13 19 Mean

0.9 1.7 1.3

1.3 2.7 2.0

1.2 1.7 1.4

1.1 2.4 1.7

1.2 1.7 1.4

1.0 1.2 1.1

0.31

Isoleucine

13 19 Mean

1.7 2.2 1.9

2.5 3.4 3.0

2.4 3.2 2.8

2.8 3.9 3.4

2.3 3.9 3.1

2.1 1.9 2.0

0.67

0.41

0.81

0.22

0.47

Leucine

13 19

5.1 13.2c

5.9 13.1c

5.3 5.8ab

5.7 8.5ab

5.4 9.3bc

4.1 4.4a

1.02

Lysine

13 19

2.8 8.2b

3.2 3.2a

3.1 3.9a

3.0 5.5ab

3.3 4.1a

2.5 2.9a

0.77

Phenylalanine

13 19

2.5 6.6b

2.7 5.2b

2.6 3.8b

2.7 3.9b

2.6 3.7b

2.1 2.2a

0.52

Tyrosine

13 19 Mean

1.9 3.2 2.5

2.5 4.2 3.3

2.2 2.6 2.4

2.1 2.7 2.4

2.1 2.0 2.1

1.6 2.0 1.8

0.51

Aspartate

13 19

5.5 15.3b

6.0 9.5a

6.6 10.2ab

7.0 10.4ab

6.9 9.9ab

5.5 5.4a

1.15

Cysteine

13 19 Mean

0.1 0.2 0.2

0.1 0.3 0.2

0.1 0.2 0.2

0.2 0.4 0.3

0.2 0.3 0.2

0.2 0.2 0.2

0.05

Glutamine

13 19 Mean

5.1 12.0 8.5ab

6.6 18.1 12.4b

5.6 12.6 9.1ab

5.6 11.9 8.7ab

6.3 12.6 9.4ab

4.2 6.6 5.4a

1.70

Serine

13 19

2.9 5.7ab

3.3 5.8ab

3.0 4.3a

3.5 6.5ab

3.3 9.3b

2.4 3.0a

0.82

Glycine

13 19

2.9 6.2bc

3.2 3.8ab

3.0 4.3ab

3.5 6.4c

3.4 7.5c

2.5 2.6a

0.59

Alanine

13 19

3.0 9.2b

4.0 8.2b

3.4 4.1a

3.8 6.3ab

3.8 6.0ab

2.8 3.4a

0.78

Essential

13 19 Mean

22.9 55.1 39.0b

26.0 40.8 33.4ab

24.0 33.5 28.7ab

26.3 39.9 33.1ab

25.0 41.5 33.3ab

19.8 21.1 20.5a

5.46

0.36

0.03

1.20

3.86

S.E.

19

2.5a

3.8b

0.25

3.7

5.3

0.90

1.1a

1.9b

0.12

2.3

3.1

0.30

2.0

2.8

0.25

0.1a

0.2b

0.02

5.6a

12.3b

0.65

24.0a

38.6b

2.91

S.A. Soto-Navarro et al. / Small Ruminant Research 65 (2006) 85–100

95

Table 6 (Continued) Item

CP level (% DM)

Sourcea BLM

CGM

CSM

FTM

FIM

SBM

23.3 45.6

21.6 35.5

23.6 41.7

23.8 45.5

17.6 21.1

4.53

Non-essential

13 19 Mean

34.0b

34.5b

28.6ab

32.6b

34.7b

19.3a

3.52

Total

13 19 Mean

42.4 103.6 73.0b

49.3 86.4 67.9b

45.6 69.0 57.3ab

49.8 81.6 65.7ab

48.7 87.0 67.9b

37.4 42.2 39.8a

9.77

56.1 75.6 65.8

50.0 55.1 52.6

45.6 54.8 50.2

38.7 63.8 51.3

56.8 53.7 55.2

43.3 61.8 52.6

13.32

13 19 Mean

52.1 62.0 57.1

53.8 61.2 57.5

47.8 47.0 47.4

49.5 67.0 58.2

60.2 59.3 59.7

52.9 65.7 59.3

8.76

13 19 Mean

63.8 66.9 65.3

63.3 67.3 65.3

54.5 63.1 58.8

63.5 60.8 62.2

63.3 70.7 67.0

58.1 68.7 63.4

7.73

Valine

13 19 Mean

44.8 64.5 54.6

41.2 57.4 49.3

35.8 40.6 38.2

42.7 63.7 53.2

55.6 55.8 55.7

39.5 61.6 50.5

14.44

Methionine

13 19 Mean

34.7 55.2 44.9

50.7 70.9 60.8

45.7 47.4 46.6

40.3 67.4 53.8

50.0 47.8 48.9

46.9 63.8 55.3

9.03

13 19 Mean

44.2 50.9 47.5

50.9 60.1 55.5

47.6 44.9 46.3

52.0 70.4 61.2

62.2 62.5 62.3

47.2 65.0 56.1

15.24

Leucine

13 19 Mean

65.2 71.9 68.6b

66.6 79.6 73.1b

58.6 52.1 55.3a

64.0 71.6 67.8b

66.2 66.6 66.4b

62.1 70.1 66.1b

5.05

Lysine

13 19 Mean

52.7 69.1 60.9

58.7 57.7 58.2

49.6 44.6 47.1

50.2 68.1 59.2

60.8 56.1 58.5

55.1 63.9 59.5

8.13

13 19 Mean

60.5 68.6 64.5

59.1 71.3 65.2

52.8 52.5 52.7

56.4 60.7 58.6

59.1 59.0 59.0

56.5 63.9 60.2

5.77

13 19 Mean

46.5 56.6 51.5

53.5 64.7 59.1

46.9 45.5 46.2

44.7 51.0 47.8

50.5 30.8 40.6

46.6 62.8 54.7

8.40

Aspartate

13 19 Mean

42.9 67.0 54.9

55.3 66.6 60.9

55.1 56.9 56.0

56.5 63.2 59.8

61.4 55.0 58.2

58.8 63.8 61.3

6.79

Cysteine

13 19 Mean

52.0 52.5 52.2

44.0 55.0 49.6

42.8 52.6 47.7

54.3 63.4 58.8

56.7 53.3 55.0

61.7 65.5 63.6

Percentage of flow at the duodenum Histidine 13 19 Mean Threonine

Arginine

Isoleucine

Phenylalanine

Tyrosine

19.5 48.6

S.E.

6.91

9.42

6.19

5.47

10.21

6.39

10.78

3.57

1.54

4.08

5.94

4.80

CP level (% DM)

S.E.

13

19

21.6a

39.7b

2.22

45.6a

78.3b

5.11

48.4a

60.8b

2.28

52.7a

60.4b

1.60

61.1

66.3

3.98

43.3a

57.2b

2.73

44.7a

58.7b

1.81

50.7

59.0

2.77

63.7a

68.7b

1.37

54.5a

59.9b

1.54

57.4a

62.6b

1.51

48.1

51.9

3.37

55.0a

62.1b

1.49

51.9

57.0

2.68

7.72 5.46

96

S.A. Soto-Navarro et al. / Small Ruminant Research 65 (2006) 85–100

Table 6 (Continued) Item

CP level (% DM)

Sourcea BLM

Glutamine

S.E. CGM

CSM

FTM

FIM

SBM

CP level (% DM)

S.E.

13

19

42.7a

58.2b

2.22

13 19 Mean

42.1 56.9 49.5

50.0 64.9 57.5

36.1 50.0 43.0

37.7 61.6 49.6

47.3 51.9 49.6

43.2 63.7 53.4

13 19 Mean

57.1 65.0 61.1

59.1 70.4 64.7

52.8 53.2 53.0

57.1 68.3 62.7

60.0 66.1 63.1

57.4 66.3 61.8

2.91

57.3a

64.9b

1.25

13 19 Mean

58.1 66.1 62.1

58.9 61.0 60.0

53.6 53.5 53.5

58.3 67.8 63.0

60.3 64.3 62.3

59.2 62.0 60.6

4.06 4.06 2.87

58.1a

62.4b

1.28

Alanine

13 19 Mean

41.8 66.7 54.2

55.9 70.5 63.2

47.7 45.1 46.4

54.1 64.9 59.5

52.7 55.9 54.3

52.9 61.9 57.4

6.11 50.9a

60.8b

1.93

Essential

13 19 Mean

53.1 66.1 59.6

57.6 68.2 62.9

50.8 52.1 51.4

54.3 65.9 60.1

58.7 59.2 58.9

55.2 65.2 60.2

54.9a

62.8b

1.58

13 19 Mean

44.8 60.2 52.5

50.5 61.8 56.1

46.1 48.8 47.4

47.9 59.8 53.8

51.2 54.7 52.9

49.2 58.5 53.9

48.3a

57.3b

1.18

13 19 Mean

50.9 64.1 57.5

55.0 65.2 60.1

49.7 50.2 50.0

52.6 63.8 58.0

56.2 57.8 57.0

52.9 62.1 57.5

52.8a

60.5b

1.43

Serine

Glycine

Non-essential

Total

8.01 5.67 4.11

4.32 6.31 4.46 4.91 3.47 5.93 4.19

a–c: Means within a row for CP source or level without a common letter differ (P < 0.05). Superscripts for CP level–source interaction means appear when the interaction between CP level and source was significant (P < 0.05); superscripts are not presented for interaction means of a CP level when there was not a significant difference among sources. Main effect means for CP level and CP source appear when an effect was significant (P < 0.05) and if the interaction between CP level and source was non-significant. a BLM, blood meal; CGM, corn gluten meal; CSM, cottonseed meal; FTM, feather meal; FIM, fish meal; SBM, soybean meal.

sources for SBM (P < 0.05) and lower (P < 0.05) for FIM versus BLM, CGM and FTM. 3.4. Ruminal pH and ammonia N Ruminal pH was not influenced by CP source, but was slightly greater (P < 0.05) for 19% versus 13% CP (6.06 versus 5.86; S.E. = 0.05). Ammonia N concentration in ruminal fluid was similar between CP levels and among protein sources (17.6 and 18.7 mg/dl for 13 and 19% CP; S.E. = 1.2). 3.5. Amino acids Flows of amino acids at the duodenum and ileum are shown in Table 5, with corresponding small intestinal disappearance (i.e., apparent digestibility) in g/day and

percentage of amino acids entering the duodenum in Table 6. Histidine, threonine, arginine, valine, methionine, isoleucine, leucine, lysine and phenylalanine were considered essential amino acids. Small intestinal disappearance of most non-essential amino acids measured was similar among CP sources with 13% CP diets but differed with 19%, being or tending to be lowest among protein sources for SBM. Small intestinal disappearance in g/day of some essential amino acids was similar among CP sources with 13% CP but different with 19% (i.e., histidine, valine, leucine and lysine). With 19% CP, small intestinal disappearance of histidine and valine was greatest among treatments (P < 0.05) for BLM, whereas leucine disappearance was greater (P < 0.05) for BLM and CGM than for CSM, FTM and SBM. Disappearance of lysine was greater (P < 0.05) for BLM versus

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Table 7 True small intestinal digestibility of amino acids and endogenous amino acid flow from the small intestine of wether goats consuming concentratebased diets with 13 or 19% CP (DM basis)a Endogenous (g/day)

CP level (%)

S.E.

Mean

Histidine

13 19 Mean

0.634 0.485 0.457

0.1396 0.1011 0.0651

91.8 81.2 81.3

6.58 2.34 1.91

0.85 0.97 0.96

Threonine

13 19 Mean

0.900 0.363 0.518

0.2419 0.3414 0.1870

82.1 67.8 71.4

5.41 5.27 3.36

0.83 0.83 0.87

Arginine

13 19 Mean

1.332 0.466 0.847

0.1376 0.2441 0.1548

95.7 76.5 83.7

2.25 2.97 2.14

0.98 0.95 0.96

Valine

13 19 Mean

1.300 0.742 0.727

0.2544 0.3119 0.1842

91.4 71.9 73.5

5.78 4.15 2.99

0.88 0.90 0.90

Methionine

13 19 Mean

0.572 0.613 0.575

0.1581 0.2259 0.1193

80.8 81.3 80.4

7.05 7.01 4.30

0.79 0.80 0.83

Isoleucine

13 19 Mean

1.054 0.374 0.497

0.2225 0.2337 0.1647

97.9 72.6 77.9

5.93 4.43 3.60

0.89 0.89 0.87

Leucine

13 19 Mean

1.606 1.000 0.926

0.3813 0.6008 0.2979

87.9 77.5 77.8

4.66 4.33 2.61

0.91 0.90 0.93

Lysine

13 19 Mean

0.981 0.991 0.764

0.2643 0.3822 0.2126

82.0 76.0 74.8

5.06 4.75 3.12

0.89 0.88 0.89

Phenylalanine

13 19 Mean

0.735 0.060 0.217

0.2560 0.3270 0.1710

79.6 63.8 66.4

5.93 4.40 2.81

0.84 0.86 0.89

Tyrosine

13 19 Mean

0.913 0.517 0.012

0.4226 0.6886 0.3656

76.5 41.4 52.2

10.21 12.12 7.34

0.63 0.26 0.42

Aspartate

13 19 Mean

2.899 0.073 0.899

0.5423 0.7308 0.4115

88.9 62.6 68.4

5.01 4.27 2.87

0.90 0.86 0.89

Cysteine

13 19 Mean

0.021 0.016 0.016

0.0140 0.0187 0.0104

67.0 64.2 64.6

5.25 4.01 2.74

0.83 0.88 0.89

Glutamine

13 19 Mean

3.358 2.693 2.965

0.6022 1.0499 0.5004

81.1 76.2 77.5

5.01 4.95 2.90

0.89 0.87 0.91

Serine

13 19 Mean

0.974 0.485 0.666

0.3279 0.2811 0.1634

78.0 71.3 72.9

6.08 2.91 2.09

0.83 0.95 0.95

Mean

True digestibility (%)

R2

Amino acid

S.E.

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Table 7 (Continued) Endogenous (g/day)

CP level (%)

S.E.

Mean

Glycine

13 19 Mean

0.970 0.459 0.557

0.3073 0.2657 0.1605

78.7 69.1 70.5

5.76 3.08 2.24

0.85 0.94 0.93

Alanine

13 19 Mean

1.923 1.417 1.475

0.3214 0.5883 0.2753

85.6 76.4 77.6

4.87 5.64 3.16

0.90 0.84 0.90

Essential

13 19 Mean

9.052 3.024 4.309

1.8238 2.7084 1.4584

87.6 70.4 73.6

4.55 4.31 2.77

0.92 0.89 0.91

Non-essential

13 19 Mean

10.707 2.531 6.055

1.9369 2.9433 1.4457

76.9 61.6 66.4

4.42 4.09 2.43

0.90 0.87 0.91

Total

13 19 Mean

19.992 5.315 10.073

3.7270 5.6363 2.8727

82.3 65.5 69.5

4.45 4.19 2.56

0.91 0.88 0.91

Mean

True digestibility (%)

R2

Amino acid

S.E.

a

Estimated by regressing amino acid disappearance in the small intestine against flow at the duodenum. n = 36 for 13 and 19% CP and 72 for mean.

CGM, CSM and FIM and of phenylalanine was lowest among protein sources for SBM. Essential amino acids with small intestinal disappearance not influenced by protein source within level were threonine, methionine and isoleucine. However, small intestinal disappearance of threonine and methionine was greater (P < 0.05) for 19% versus 13% CP diets. As a result of varying treatment effects for the different amino acids, total essential amino acid disappearance in the small intestine was greater (P < 0.05) for diets with 19 than 13% CP and for BLM than for SBM diets. CP source influenced apparent small intestinal digestibility as a percentage of only one amino acid, leucine, with the value for CSM being lowest among sources (P < 0.05; Table 7). Apparent small intestinal digestibility of all amino acids was greater or tended to be so for diets with 19% CP than 13%. The magnitude of the difference was slightly greater for non-essential than for essential amino acids (18.6% versus 14.4%). However, estimates of true digestibility, except for methionine, were greater (P < 0.05) for 13% versus 19% CP. Correspondingly, most estimates of endogenous amino acids passing from the small intestine were greater for diets with 13% CP than 19%.

4. Discussion 4.1. Ruminal digestion and microbial growth Even though SBM diets were more extensively digested in the rumen than most other diets, microbial OM synthesis was not greater. This suggests that availability of nitrogenous compounds did not limit microbial growth with any diet, as is supported by ruminal ammonia N concentrations. In this regard, and in agreement with findings of Soto-Navarro et al. (2003, 2004), it appears that requirements of goats for DIP may be less than for other ruminant species, such as cattle (NRC, 1996), with results of the present experiment suggesting a DIP requirement no greater than 9% of TDN intake. In addition to ample ruminally available nitrogenous compounds, another factor that probably prevented greater ruminal OM digestion of SBM diets from being accompanied by increased microbial cell synthesis is that ruminal microbes derive little energy directly from degradation of protein in the rumen compared with carbohydrate. However, it appears that supplemental SBM stimulated fiber digestion in the rumen to a larger degree relative to other protein sources regardless of dietary CP level. Factors responsible for this finding are

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unclear, since a similar effect on microbial protein synthesis was not evident. Although variability was quite high, it appeared that extent of ruminal degradation of protein in BLM and FIM was low compared with protein in CGM, CSM and FTM. 4.2. Protein and amino acid requirements of goats In a companion 27-week experiment (Soto-Navarro et al., 2004) with the same treatments employed in this one except for omission of CSM diets, feed intake, rate of BW gain and gain efficiency by growing Boer × Spanish wether goats were similar among treatments. Hence, even with growing crossbred Boer wethers, it appears that protein requirements can be satisfied with the moderate dietary CP level of 13% and with much dietary protein from a feedstuff, such as SBM, with protein fairly extensively degraded in the rumen. Use of a diet higher in forage with protein more extensively degraded in the rumen than corn, which made up sizeable portions of these diets, could have yielded different results. However, foragebased diets can restrict energy intake and correspondingly lessen amino acid demands for protein synthesis. Small intestinal disappearance of many essential amino acids can be increased by use of CP levels in high concentrate diets above 13%, generally when additional protein is supplied by feedstuffs high in UIP rather than one, such as SBM, that is extensively degraded in the rumen. Blood meal was more efficacious than other protein sources relatively high in UIP in increasing small intestinal disappearance of the essential amino acids histidine, valine and lysine. However, because of differences among protein sources in amino acid composition and extent of ruminal N digestion, for some amino acids other protein sources elicited similar or greater change in small intestinal disappearance than BLM in 19% CP diets. For example, dietary supplementation with CSM and FIM slightly increased arginine disappearance relative to SBM, whereas other protein supplements only elicited tendencies for change. Also, leucine disappearance was greater for BLM and CGM versus CSM, FTM and SBM. However, disappearance of isoleucine was not significantly affected by supplementation with any of the protein sources or by dietary CP level.

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4.3. Small intestinal amino acid disappearance The mean apparent small intestinal amino acid digestibilities of 52.5 and 60.5% for 13 and 19% CP diets are slightly lower than most estimates reviewed by NRC (1985) and AFRC (1998), although ad libitum intake may result in lower values than with restricted intake (AFRC, 1998). The lower value for 13% versus 19% CP diets is in accordance with the difference in the estimate of endogenous amino acids flowing from the small intestine and the expected higher proportion of amino acids of endogenous than dietary origin with low than higher dietary CP levels. The mean true small intestinal digestibility value for total amino acids with the 13% CP level (i.e., 82.3%) is similar to the assumption of 85% for goats based on data from other ruminant species recommended by AFRC (1998), although that for the 19% CP level of 65.5% is considerably lower. The difference in true amino acid digestibility in the small intestine between essential and non-essential amino acids is in accordance with findings for other ruminant species (NRC, 1985). Also, results of this experiment do not suggest marked differences among essential amino acids in true digestibility in the small intestine (e.g., mean values ranging only from 71.4 to 83.7%). Factors responsible for differences among CP levels in estimates of endogenous amino acids passing from and true amino acid digestibility in the small intestine are unclear. As noted earlier, the relationship between amino acid disappearance in the small intestine and flow at the duodenum was not significantly curvilinear, although the differences in the estimates of endogenous flow and true digestibility for 13 and 19% CP diets suggest a curvilinear trend. Because of lower disappearance and flow for 13% CP diets, a more accurate estimate of endogenous amino acids than with 19% CP diets is anticipated, as is reflected in the observed S.E. Relatedly, no explanation for a lower endogenous amino acids loss with 19% versus 13% dietary CP is evident. The mean estimate of endogenous amino acids flowing from the rumen is equivalent to 1.5% of DM intake, 9.4% of N intake and 9.1% of total duodenal N flow, which are in accordance with values for other ruminant species (NRC, 1985). This estimate also represents an average of 22.8% of N flow at the ileum. Values based only on 13% CP diets result in estimates approximately twice

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as great, which are also within ranges noted by NRC (1985). One potential explanation for the greater estimate of true amino acid digestibility in the small intestine for 13% versus 19% CP is that small intestinal digestibility of microbial amino acids was greater than of supplemental protein sources, which provided more amino acids with 19% CP. However, this reasoning is not in accordance with findings for other ruminant species (ARC, 1980; NRC, 1985). It seems more plausible that amino acids entering the small intestine exceeded digestive and (or) absorptive mechanisms with 19% CP diets. Although, true digestibility for methionine and cysteine were similar between dietary CP levels, suggesting that such mechanisms were sufficient for flows incurred with 19% CP diets.

5. Summary and conclusions These results suggest that microbial requirements in goats for ruminally available nitrogenous compounds may be met with a dietary ratio of CP:TDN as low as 0.09. Use of different feedstuffs high in protein not extensively degraded in the rumen and with unique amino acid composition offers potential to increase small intestinal absorption of select amino acids by goats, but only with dietary CP levels greater than typically used in production settings.

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.

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