The effect of virginiamycin in diets with adequate or reduced dietary calcium or nonphytate phosphorus for broilers1

The Effect of Virginiamycin in Diets with Adequate or Reduced Dietary Calcium or Nonphytate Phosphorus for Broilers1 T. O’Connor-Dennie and L. L. Southern2 Department of Animal Sciences, Louisiana State University Agricultural Center, Baton Rouge 70803 ABSTRACT Four experiments (EXP) were conducted to evaluate the effects of virginiamycin (Vm) in diets adequate or reduced in Ca or nonphytate P (nPP) levels on growth performance and bone response variables in chicks. All diets were corn-soybean meal (C-SBM) based, and all treatments were replicated 6 or 8 times with 5 or 6 chicks each. In EXP 1 and 2, the dietary treatments were 1) C-SBM with 1.00% Ca and 0.45% nPP (positive control; PC); 2) C-SBM with 0.80% Ca and 0.45% nPP (0.80Ca); 3) C-SBM with 1.00% Ca and 0.35% nPP (0.35nPP); and 4 to 6) Diets 1 to 3 with 11 (EXP 1) or 22 (EXP 2) ppm of Vm. In EXP 1, daily gain (ADG), feed intake (ADFI), bone breaking strength (BBS), milligrams of ash per gram of Ca intake (ASH/Ca), and BBS per gram of Ca (BBS/Ca) or nPP (BBS/nPP) intake were increased in chicks fed Vm (P < 0.04 to 0.07). Chicks fed the 0.35nPP diet with Vm had increased ADG, ADFI, BBS, milligrams of tibia ash (ASH), BBS/Ca, and BBS/nPP (nPP × Vm, P < 0.03 to 0.10). Chicks fed the 0.80Ca diet with Vm had increased ASH, milligrams of ASH per gram of nPP intake (ASH/ nPP), and ASH/Ca (P < 0.01 to 0.09). Tibia ash, BBS, gain:feed (G:F), BBS/nPP, and ASH/nPP were decreased in chicks fed the 0.80Ca diet (P < 0.01 to 0.07). Bone ash percentage (BAP), BBS, BBS/Ca, ASH, and ASH/Ca were decreased in chicks fed the 0.35nPP diets (P < 0.01); ASH/ nPP was increased (P < 0.01). In EXP 2, BAP, ASH, ASH/ Ca, and ASH/nPP were increased in chicks fed Vm (P <

0.02 to 0.07). Chicks fed the 0.80Ca diet had a decreased ASH/nPP (P < 0.04) but an increased BBS/Ca and ASH/ Ca (P < 0.01 to 0.02). Chicks fed the 0.35nPP diet had decreased ADG, ADFI, G:F, BBS, BAP, ASH, ASH/Ca, and BBS/Ca (P < 0.01 to 0.04), but BBS/nPP and ASH/ nPP were increased (P < 0.01 to 0.04). In EXP 3, the dietary treatments were 1) PC; 2) C-SBM with 0.70% Ca and 0.45% nPP (0.70Ca); 3) C-SBM with 1.00% Ca and 0.25% nPP (0.25nPP); 4 to 6) Diets 1 to 3 with 9 ppm of Vm. The addition of Vm to the 0.25nPP diet decreased BBS (nPP × Vm, P < 0.06), but Vm increased BBS in the 0.70Ca and PC diets (P < 0.02). Chicks fed the 0.25nPP diet had decreased ADG, ADFI, and BBS (P < 0.01), and chicks fed the 0.70Ca diets had reduced ADFI, BBS, and G:F (P < 0.03 to 0.10). In EXP 4, 4 levels of nPP (0.15, 0.25, 0.35, or 0.45%) and 3 levels of Vm supplementation (0, 11, or 22 ppm) in a 4 × 3 factorial arrangement were used. The addition of Vm increased ADG, BBS, ASH, ASH/Ca, and ASH/nPP only in chicks fed diets with 0.35 or 0.45% nPP (nPP × Vm, P < 0.05). Daily gain, ADFI, G:F, BBS, BAP, BBS/Ca, and ASH were increased as nPP levels were increased (P < 0.01), but BBS/nPP and ASH/nPP were decreased (P < 0.01) as nPP levels were increased. The results obtained from these EXP indicate that Vm, regardless of supplementation level, can partially overcome an nPP deficiency when nPP levels are = 0.35%.

(Key words: bone ash, chick, phosphorus, calcium, virginiamycin) 2005 Poultry Science 84:1868–1874

INTRODUCTION Virginiamycin (Vm) is a cyclic polypeptide antibiotic complex from Streptomyces virginiae of the streptogramin class of antibiotics. It is commonly used to treat infections from gram-positive organisms or as a growth promotant in cattle, swine, and poultry diets. The Vm complex consists of 2 major components, Vm factor m1 and s1, which

2005 Poultry Science Association, Inc. Received July 13, 2005. Accepted September 11, 2005. 1 Approved for publication by the director of the Louisiana Agricultural Experiment Station as manuscript number 2005-18-0316. 2 Corresponding author: [email protected]

act synergistically to prevent protein synthesis within bacteria (Cocito, 1979). It also has been suggested that antibacterial agents improve growth performance and nutrient utilization by either thinning the epithelium of the small intestine or by reducing the production of growth-

Abbreviation Key: ADFI = average daily feed intake; ADG = average daily gain; ASH = milligrams of tibia ash; ASH/Ca = milligrams of ash per milligram of Ca intake; ASH/nPP = milligrams of ash per milligram of nPP intake; BAP = bone ash percentage; BBS = bone breaking strength; BBS/Ca = kilograms of bone breaking strength per milligram of Ca intake; BBS/nPP = kilograms of bone breaking strength per milligram of nPP intake; C-SBM = corn soybean meal; EXP = experiment; G:F = gain:feed; nPP = nonphytate phosphorus; PC = positive control; Vm = virginiamycin.

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depressing toxins or metabolites by intestinal mircoflora (Cocito, 1979). Several researchers have reported the nutrient-sparing effects of Vm on CP, energy, Ca, Mn, and P in pigs and chickens. Pelura et al. (1980) reported that the addition of Vm to low CP diets improved BW gain and feed efficiency in pigs. Agudelo et al. (2003) reported that Vm improved P, Ca, and Zn digestibility and retention in pigs when compared with those fed the control diet. Cervantes et al. (2002) reported that the addition of Vm to marginally deficient P diets for broilers increased BW, improved feed conversion, and decreased mortality. These recent results agree with the findings of Buresh et al. (1985), who reported that the addition of Vm to diets with 0.47% total P or greater increased BW and P utilization. A significant proportion of the endogenous Ca and P in corn and soybean meal (C-SBM) is bound to phytate (Harland and Oberleas, 1999; Jang et al., 2003). The phytate-bound minerals have a reduced bioavailability to nonruminant animals, resulting in an increased need for inorganic P supplementation (Broz et al., 1994; Johnston and Southern, 2000). Moore et al. (1999) indicated that the biggest problem facing the poultry industry is P runoff into surrounding watersheds. If Vm can increase P utilization as indicated by Buresh et al. (1985) and Agudelo et al. (2003), then Vm could possibly reduce P runoff by increasing P bioavailability to the animal. Therefore, the objectives of these experiments (EXP) were to investigate the effects of Vm in diets with adequate or reduced levels of Ca and nonphytate P (nPP) on growth performance and bone response variables in broilers.

MATERIALS AND METHODS General The methods used in these EXP were approved by the Louisiana State University Agricultural Center Animal Care and Use Committee. Each EXP used female Ross × Ross broilers obtained from a commercial hatchery on d 0 post-hatching. The broilers were allotted, wing-banded, and placed in environmentally controlled brooder batteries (Petersime Incubator company, Gettysburg, OH) with raised wire floors for the duration of the 0- to 18-d EXP. The diets used for these EXP were C-SBM based and were formulated to provide 1.26% total Lys and 3,200 kcal of ME/kg of diet (Table 1). The diets met or exceeded the nutrient requirements suggested by the NRC (1994) except for Ca and nPP when appropriate. The reduced Ca and nPP levels were achieved by replacing limestone and monocalcium phosphate with sand. Throughout all EXP, the chicks, feed, and water were checked twice daily, and the feed in mash form and water were provided ad libitum. At the termination of each EXP, all broilers and feed were weighed for calculation of daily gain (ADG), daily feed intake (ADFI), gain:feed (G:F), Ca intake, and nPP intake. Calcium intake was calculated by multiplying the Ca content of the diet by ADFI. Nonphytate phosphorus intake was calculated in

1

Table 1. Percentage composition of the control diets Ingredient Corn Soybean meal (47.5% CP) Vegetable oil Monocalcium phosphate Limestone Salt Trace mineral premix2 DL-Methonine Choline chloride Vitamin premix3 Calculated composition ME, kcal/kg Ca, % P, % Nonphytate P, % Lysine, % Tryptophan, % Threonine, % TSAA, %

Experiments 1, 2, and 3

Experiment 4

52.46 37.96 5.33 1.65 1.51 0.50 0.25 0.24 0.05 0.05

52.46 38.03 5.31 1.65 1.51 0.50 0.25 0.19 0.05 0.05

3,200 1.00 0.73 0.45 1.26 0.28 0.86 0.91

3,200 1.00 0.73 0.45 1.26 0.28 0.86 0.91

1 Virginiamycin was added to the basal diet at 9, 11, or 22 ppm to make the respective diets for each experiment. Monocalcium phosphate and limestone were replaced by sand to create low Ca or nonphytate P diets for each experiment. 2 Provided (/kg of diet): copper (copper sulfateⴢ5 H2O), 7.0 mg; iodine (potassium iodate), 1.0 mg; iron (ferrous sulfateⴢ7 H2O), 50 mg; manganese (manganese sulfateⴢH2O), 100 mg; selenium (sodium selenite), 0.15 mg; and zinc (zinc sulfateⴢ7H2O), 75 mg. 3 Provided (/kg of diet): vitamin A (retinyl acetate), 8,000 IU; vitamin D3 (cholecalciferol), 3,000 IU; vitamin E (DL-alpha-tocopheryl acetate), 25 IU; menadione, 1.5 mg; vitamin B12 (cyanocobalamin), 0.02 mg; biotin, 0.1 mg; folacin (folic acid), 1 mg; niacin (nicotinic acid), 50 mg; pantothenic acid, 15 mg; pyridoxine (pyridoxineⴢHCl), 4 mg; riboflavin, 10 mg; and thiamin (thiamin mononitrate), 3 mg.

the same manner. After weighing, 3 (EXP 1 and 3) or 6 (EXP 2 and 4) broilers per replicate were randomly selected for bone analyses. The left tibia was collected, pooled by replicate, and then frozen until further analyses.

EXP 1 and 2 In EXP 1 and 2, 216 broilers per EXP were allotted to 6 treatments with 6 replications of 6 chicks each. The average initial and final BW for EXP 1 and 2 were 47 and 488, and 40 and 523 g, respectively. The treatments were as follows: Diet 1) C-SBM with 1.00% Ca and 0.45% nPP (positive control; PC); Diet 2) C-SBM with 0.80% Ca and 0.45% nPP (0.80Ca); Diet 3) C-SBM with 1.00% Ca and 0.35% nPP (0.35nPP); and Diets 4 to 6) as Diets 1 to 3 supplemented with 11 (EXP 1) or 22 (EXP 2) ppm of Vm (Stafac 20, Phibro, Fairfield, NJ).

EXP 3 In EXP 3, 240 broilers were allotted to 6 treatments with 8 replications of 5 chicks each. The average initial and final BW were 45 and 462 g, respectively. The treatments were as follows: Diet 1) C-SBM with 1.0% Ca and 0.45% nPP (PC); Diet 2) C-SBM with 0.70% Ca and 0.45% nPP (0.70Ca); Diet 3) C-SBM with 1.00% Ca and 0.25% nPP (0.25nPP); and Diets 4 to 6) as Diets 1 to 3 supplemented with 9 ppm of Vm.

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EXP 4 In EXP 4, 432 broilers were allotted to 12 treatments with 6 replications of 6 chicks each. The average initial and final BW were 37 and 432 g, respectively. Four levels of nPP (0.15, 0.25, 0.35, or 0.45%) and 3 levels of Vm (0, 11, or 22) were used in a 4 × 3 factorial arrangement.

GLM procedure of SAS (SAS Inst., Inc., Cary, NC). In all EXP, contrast statements were used to test the main treatment effects and any interactions of Ca, nPP, and Vm. The pen of chicks served as the experimental unit for all response variables. Treatment differences were considered significant at α ≤ 0.10.

RESULTS

Bone Analysis After thawing the bones, bone breaking strength (BBS) was determined (HD 250 Texture Machine, Texture Technologies Corporation, Scarsdale, NY) using a 3-point bend rig with a load cell capacity of 25 kg and cross-head speed of 100 mm/min. After determining BBS, fat was extracted from the tibias by a 36-h Soxhlet extraction in ethyl alcohol followed by a 36-h extraction with diethyl ether. The bones were dried at 110°C for 24 h and then weighed. The dry, defatted tibias were dry-ashed in a muffle furnace at 560°C for 24 h. Bone ash percentage (BAP) was not determined in EXP 3. After cooling, tibia ash was weighed for determination of ash weight, BAP, BBS per Ca intake (BBS/Ca), BBS per nPP intake (BBS/nPP), milligrams of tibia ash per chick (ASH), tibia ash per Ca intake (ASH/ Ca), and tibia ash per nPP intake (ASH/nPP) for EXP 1, 2, and 4. Bone breaking strength per Ca or nPP intake was calculated by dividing the kilograms of BBS by total Ca or nPP intake in grams. Tibia ash was calculated for each treatment by dividing the ash weight of the tibias by the number of tibias. Tibia ash was then divided by total Ca or nPP intake to calculate ASH/Ca and ASH/ nPP, respectively.

Statistical Analysis Data were analyzed by ANOVA procedures (Steel and Torrie, 1980) for completely randomized designs by the

EXP 1 Reducing dietary Ca decreased (P < 0.01 to 0.07) G:F, Ca intake, BBS, BBS/nPP, ASH, and ASH/nPP (Table 2). Reducing dietary nPP decreased (P < 0.01) nPP intake, BBS, ASH, BAP, BBS/Ca, and ASH/Ca, but it increased (P < 0.01) ASH/nPP. The addition of Vm increased (P < 0.04 to 0.09) ADG, ADFI, Ca intake, nPP intake, BBS, BBS/Ca, BBS/nPP, and ASH/Ca. The addition of Vm to the 0.80Ca diet increased (Ca × Vm interaction, P < 0.01 to 0.09) ASH, ASH/nPP, and ASH/Ca. The addition of Vm to the 0.35nPP diets increased (nPP × Vm interaction, P < 0.03 to 0.10) ADG, ADFI, Ca intake, nPP intake, BBS, BBS/Ca, BBS/nPP, and ASH.

EXP 2 Reducing dietary Ca decreased (P < 0.01 to 0.04) Ca intake and ASH/nPP, but it increased (P < 0.02) BBS/Ca and ASH/Ca (Table 3). Reducing dietary nPP decreased (P < 0.01 to 0.05) ADG, ADFI, G:F, Ca intake, nPP intake, BBS, BBS/Ca, BAP, ASH, and ASH/Ca, but it increased (P < 0.01 to 0.04) BBS/nPP and ASH/nPP. The addition of Vm increased (P < 0.02 to 0.07) BAP, ASH, ASH/Ca, and ASH/nPP, but there were no interactive effects of Vm and Ca or nPP. The lack of an interaction was because

Table 2. Growth performance and bone response variables of broilers fed varying levels of virginiamycin (Vm), Ca, and nonphytate P (nPP) (experiment 1)1 0 ppm of Vm 2

Growth performance

ADG, g ADFI, g G:F, g/g Ca intake, mg/d nPP intake, mg/d Bone response variable4 BBS, kg BBS/Ca, kg/g BBS/nPP, kg/g Ash, % ASH, mg ASH/Ca, mg/g ASH/nPP, mg/g

PC

0.80Ca

11 ppm of Vm

0.35nPP

PC

0.80Ca

0.35nPP

24.71 33.98 0.727 340 153

23.64 32.16 0.701 257 145

24.09 32.10 0.751 321 112

24.68 33.39 0.739 334 150

24.58 34.26 0.724 274 154

26.19 34.94 0.750 349 122

14.1 2.30 5.11 57.81 546 90 199

11.0 2.23 3.96 57.18 446 84 149

10.2 1.76 5.04 56.39 427 74 211

13.9 2.31 5.13 58.21 513 85 189

11.8 2.37 4.22 57.47 503 102 181

13.3 2.12 6.05 56.96 497 79 226

Pooled SEM 0.59 0.86 0.012 8 4 0.7 0.11 0.27 0.45 26 4 9

P=F Ca × Vm

nPP

nPP × Vm

0.05 0.06 NS 0.06 0.09

3

NS NS 0.07 0.01 NS

NS NS NS NS NS

NS NS NS NS 0.01

0.07 0.05 NS 0.03 0.09

0.04 0.07 0.07 NS NS 0.05 NS

0.01 NS 0.01 NS 0.04 NS 0.01

NS NS NS NS 0.09 0.01 0.03

0.01 0.01 NS 0.01 0.01 0.01 0.01

0.03 0.10 0.06 NS 0.05 NS NS

Vm

Ca

1 PC = corn-soybean meal diet (C-SBM) with 1.0% Ca and 0.45% nPP, 0.80Ca = C-SBM with 0.80% Ca and 0.45% nPP, 0.35nPP = C-SBM with 1.0% Ca and 0.35% nPP, ADG = average daily gain, ADFI = average daily feed intake, BBS = bone breaking strength, BBS/Ca = kilograms of BBS per gram of total Ca intake, BBS/nPP = kilograms of BBS per gram of total nPP intake, ASH = milligrams of left tibia ash per bird, ASH/Ca = milligrams of ash per tibia per gram of Ca intake, and ASH/nPP = milligrams of ash per tibia per gram of nPP intake. 2 Data are means of 6 replicates of 6 broilers per replicate. Average initial and final BW were 40 and 494 g, respectively, and the experiment lasted from 0 to 18 d post-hatching. 3 P > 0.10. 4 Data are means of 3 tibias per replicate.

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VIRGINIAMYCIN AFFECTS CALCIUM AND PHOSPHORUS AVAILABILITY

Table 3. Growth performance and bone response variables of broilers fed varying levels of virginiamycin (Vm), Ca, and nonphytate P (nPP) (experiment 2)1 0 ppm of Vm 2

Growth performance

ADG, g ADFI, g G:F, g/g Ca intake, mg/d nPP intake, mg/d Bone response variable4 BBS, kg BBS/Ca, kg/g BBS/nPP, kg/g Ash, % ASH, mg ASH/Ca, mg/g ASH/nPP, mg/g

PC

0.80Ca

22 ppm of Vm

0.35nPP

PC

0.80Ca

0.35nPP

Pooled SEM

P=F Ca

Ca × Vm

nPP

nPP × Vm

3

Vm

27.81 35.20 0.791 349 157

28.04 35.88 0.782 287 161

25.66 32.92 0.78 329 115

28.68 36.23 0.792 362 163

28.29 35.83 0.789 287 161

26.21 33.78 0.782 338 118

0.79 1.09 0.007 11 5

NS NS NS NS NS

NS NS NS 0.01 NS

NS NS NS NS NS

0.01 0.04 0.01 0.05 0.01

NS NS NS NS NS

18.2 2.91 6.46 55.49 539 86 192

18.5 3.59 6.38 55.3 515 100 177

14.6 2.47 7.05 53.9 426 72 205

19.8 3.02 6.72 55.71 605 93 206

18.8 3.62 6.43 55.2 546 106 188

16.5 2.75 7.86 54.97 492 80 227

1.0 0.14 0.30 0.26 27 4 8

NS NS NS 0.07 0.02 0.04 0.02

NS 0.01 NS NS NS 0.02 0.04

NS NS NS NS NS NS NS

0.01 0.01 0.01 0.01 0.01 0.01 0.04

NS NS NS NS NS NS NS

1 PC = corn-soybean meal diet (C-SBM) with 1.0% Ca and 0.45% nPP, 0.80Ca = C-SBM with 0.80% Ca and 0.45% nPP, 0.35nPP = C-SBM with 1.0% Ca and 0.35% nPP, ADG = average daily gain, ADFI = average daily feed intake, BBS = bone breaking strength, BBS/Ca = kilograms of BBS per gram of total Ca intake, BBS/nPP = kilograms of BBS per gram of total nPP intake, ASH = milligrams of left tibia ash per bird, ASH/Ca = milligrams of ash per tibia per gram of Ca intake, and ASH/nPP = milligrams of ash per tibia per gram of nPP intake. 2 Data are means of 6 replicates of 6 broilers per replicate. Average initial and final BW were 47 and 524 g, respectively, and the experiment lasted from 0 to 18 d post-hatching. 3 P > 0.10. 4 Data are means of 6 tibias per replicate.

Vm had equally positive effects in the PC diet and in the reduced Ca and nPP diets.

EXP 3 Reducing dietary Ca decreased (P < 0.03 to 0.06) G:F and BBS, while it increased (P < 0.10) ADFI (Table 4). Reducing dietary nPP decreased (P < 0.01) ADG, ADFI, and BBS. The addition of Vm increased (P < 0.02) BBS in birds fed the PC diet but decreased (nPP × Vm, P < 0.06) BBS in birds fed the 0.25nPP diet.

EXP 4 Increasing dietary nPP increased (nPP linear and/or quadratic, P < 0.01) ADG, ADFI, G:F, Ca and nPP intake, BBS, BBS/Ca, BAP, ASH, and ASH/Ca (Table 5). Increasing dietary nPP decreased (P < 0.01) BBS/nPP and ASH/ nPP. The addition of Vm increased (Vm linear, P < 0.03

to 0.09) BBS, ASH, ASH/Ca, and ASH/nPP. The addition of 11 ppm of Vm decreased (Vm quadratic, P < 0.07) BBS/ Ca and BBS/nPP, but the 22-ppm addition increased these response variables (Vm quadratic, P < 0.07). The addition of Vm increased (nPP × Vm, P < 0.05) ADG and BBS in broilers fed diets containing 0.35 and 0.45% nPP but not in diets containing 0.15 or 0.25% nPP (Figure 1).

DISCUSSION Increasing dietary Ca from 0.7 or 0.8% to 1.0% increased G:F and many bone response variables, but it did not affect ADG or ADFI. The lack of increase in ADG and ADFI as Ca levels were increased agrees with the findings of Applegate et al. (2003), who reported that increasing the level of Ca supplementation from 0.4 to 0.9% had no effect or decreased ADG from 7 to 21 d or 14 to 24 d of age, respectively, but these data disagree with findings of other researchers who reported that ADG, ADFI, and

Table 4. Growth performance and bone response variables of broilers fed varying levels of virginiamycin (Vm), Ca, and nonphytate P (nPP) (experiment 3)1 0 ppm of Vm Growth performance2 ADG, g ADFI, g G:F, g/g Bone response variable4 BBS, kg

9 ppm of Vm

P=F

PC

0.70Ca

0.25nPP

PC

0.70Ca

0.25nPP

Pooled SEM

24.16 34.30 0.704

24.67 35.37 0.698

21.02 29.83 0.706

24.34 33.49 0.727

24.96 35.50 0.703

20.41 28.93 0.708

0.62 0.93 0.008

NS3 NS NS

NS 0.10 0.06

NS NS NS

0.01 0.01 NS

NS NS NS

12.7

10.4

14.3

13.8

0.7

0.02

0.03

NS

0.01

0.06

9.0

8.1

Vm

Ca

Ca × Vm

nPP

nPP × Vm

1 PC = corn-soybean meal diet (C-SBM) with 1.0% Ca and 0.45% nPP, 0.70Ca = C-SBM with 0.70% Ca and 0.45% nPP, 0.25nPP = C-SBM with 1.0% Ca and 0.25% nPP, ADG = average daily gain, ADFI = average daily feed intake, and BBS = bone breaking strength. 2 Data are means of 6 replicates of 6 broilers per replicate. Average initial and final BW were 45 and 462 g, respectively, and the experiment lasted from 0 to 18 d post-hatching. 3 P > 0.10. 4 Data are means of 3 tibias per replicate.

22.95 29.9 0.768 299 75 8.9 1.66 6.64 49.70 311 58 231

5.6 1.45 9.66 42.76 241 64 425

0.25% nPP

14.55 21.45 0.678 215 32

0.15% nPP

14.4 2.39 6.82 53.81 401 66 190

25.92 33.48 0.775 335 117

0.35% nPP

0 ppm of Vm

18.7 2.99 6.64 55.38 549 88 195

28.16 34.75 0.813 347 156

0.45% nPP

3.9 1.16 7.76 41.70 224 69 457

13.49 18.4 0.729 184 28

0.15% nPP

8.0 1.58 6.31 48.37 284 56 224

21.79 28.11 0.775 281 70

0.25% nPP

14.8 2.31 6.59 53.15 431 67 192

26.87 35.95 0.755 359 126

0.35% nPP

11 ppm of Vm

19.9 3.11 6.91 57.86 665 105 233

28.81 35.6 0.810 356 160

0.45% nPP

5.2 1.61 10.73 43.26 259 80 536

10.75 19.29 0.615 193 29

0.15% nPP

8.9 1.67 6.67 48.46 323 61 242

23.09 29.64 0.779 296 74

0.25% nPP

16.3 2.47 7.09 53.67 463 71 203

27.49 36.51 0.762 365 128

0.35% nPP

22 ppm of Vm

21.2 3.25 7.23 56.54 620 95 211

30.11 36.32 0.831 363 163

0.45% nPP

0.8 0.13 0.61 0.91 25 6 32

0.76 1.61 0.025 16 5

Pooled SEM

1 ADG = average daily gain, ADFI = average daily feed intake, BBS = bone breaking strength, BBS/Ca = kilograms of BBS per gram of total Ca intake, BBS/nPP = kilograms of BBS per gram of total nPP intake, ASH = miiligrams of left tibia ash per bird, ASH/Ca = milligrams of ash per tibia per gram of Ca intake, and ASH/nPP = mg of ash per tibia per gram of nPP intake. 2 Data are means of 6 replicates of 6 broilers per replicate. Average initial and final BW were 36 and 432 g, respectively, and the experiment lasted for 18 d. The dietary Ca level was 1.0%. 3 nPP linear (P < 0.01). 4 nPP quadratic (P < 0.01). 5 nPP × Vm linear (P < 0.05). 6 Data are means of 6 tibias per replicate. 7 Vm linear (P < 0.09). 8 Vm quadratic (P < 0.07). 9 Vm linear (P < 0.03).

ADG,3,4,5 g ADFI,3,4 g G:F,3 g/g Ca intake,3,4 mg/d nPP intake,3 mg/d Bone response variable6 BBS,3,5,7 kg BBS/Ca,3,4,8 kg/g BBS/nPP,3,4,8 kg/g Ash,3,4 % ASH,3,4,9 mg ASH/Ca,3,4,7 mg/g ASH/nPP,3,4,7 mg/g

Growth performance

2

Table 5. Growth performance and bone response variables of broilers fed varying levels of virginiamycin (Vm) and nonphytate P (nPP) (experiment 4)1

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VIRGINIAMYCIN AFFECTS CALCIUM AND PHOSPHORUS AVAILABILITY

Figure 1. Bone breaking strength of broilers fed varying levels of virginiamycin (Vm) and nonphytate P (NPP) (experiment 4).

G:F were increased as dietary Ca levels were increased (Boling-Frankenbach et al., 2001; Onyango et al., 2003). Increasing dietary nPP increased all growth variables and many bone response variables. These results agree with the findings of other researchers. Onyango et al. (2003) reported that growth performance variables and tibia ash were increased linearly, and tibia bone mineral content and density were increased linearly and quadratically as dietary concentrations of P were increased. The purpose of this research was to determine whether Vm increased the availability of Ca and nPP beyond its effect as a growth promotant. In EXP 1, reducing nPP to 0.35% decreased BBS and ASH, and the addition of Vm increased these response variables. However, Vm also increased feed intake; thus, the increase in BBS and ASH could be due to an increase in nPP intake and not to increased nPP utilization. However, BBS/nPP was also increased, suggesting that Vm increases nPP utilization. The addition of Vm also increased ASH/Ca, but the effect was not significant. In EXP 2, reducing nPP to 0.35% decreased growth and all bone response variables, and the addition of Vm improved or tended to improve many of these response variables. However, Vm was just as effective in the PC diet as the diet deficient in nPP. In EXP 3, reducing nPP levels to 0.25% decreased ADG, ADFI, and BBS. The addition of Vm did not improve any of these response variables, and in fact, Vm decreased BBS in birds fed 0.25% nPP. In EXP 4, decreasing dietary nPP levels decreased ADG and BBS, and there were significant Vm × nPP interactions. Virginiamycin decreased or did not affect ADG or BBS in birds fed 0.15 or 0.25% nPP, respectively, but Vm increased ADG and BBS in birds fed 0.35 or 0.45% nPP. The results of this research suggest that Vm may not affect Ca utilization beyond its effects as a growth promotant. In EXP 1 (0.80Ca) and EXP 3 (0.70Ca), BBS was decreased in the low Ca diets. In EXP 1, the addition of Vm did not affect BBS in chicks fed the low Ca diet, and in EXP 3, BBS was increased by the addition of Vm in birds fed the low Ca diet and the PC diet.

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Buresh et al. (1985) reported that Vm decreased the amount of P needed to increase BW. Agudelo et al. (2003) reported a 28% increase in P digestibility, an 11% increase in Ca digestibility, and an increase in absolute retention of P, Ca, Zn, and Mg in limit-fed pigs given Vm. Henry et al. (1986) reported that the addition of Vm increased Mn utilization regardless of the level of Mn supplementation and reduced intestinal weight in broilers. The reduction of intestinal weight was attributed to a thinning of the intestinal wall. There are several possible reasons for the nutrient-sparing effects of Vm. One possibilibility is that Vm acts on the mircoflora’s biochemical processes in the cell (Parks et al., 2001). Virginiamycin inhibits bacterial protein synthesis by binding to the 50s ribosomal subunit and blocks normal peptide formation (Cocito et al., 1974). This inhibition of protein synthesis gives Vm a broad-spectrum action on bacteria such as Lactobacillus, Bifidobacterium, and Streptococcus, which may be responsible for retarded growth in broilers (Cummings, 2003). Thus, by eliminating these harmful small intestine microflora, Vm may cause more nutrients to be available for the animal and not diverted to microflora. The failure of Vm to increase growth and bone response variables at dietary nPP levels <0.35% was not an anticipated response. One possible explanation for the lack of response to Vm at nPP levels of ≤0.25% could be an imbalance of Ca:nPP. Hulan et al. (1985) reported that as Ca:nPP was increased from 2.53:1 to 3.38:1 in broiler diets, BW was decreased. Larger Ca:total P have been reported to decrease the effectiveness of phytase in broilers at nPP levels of 0.27% (Qian et al., 1997). The increase in Ca:nPP in EXP 3 and 4 from 2.22:1 in the PC diet to 6.67:1 in 0.15% nPP could have similar effects on the effectiveness of Vm. Buresh et al. (1985) reported that Vm did not affect BW below 0.47% P, but the addition of Vm to diets >0.47% P resulted in an increase in BW, feed intake, and P utilization, which is consistent with our findings. In summary, Vm seems to improve nPP utilization, but it is difficult to separate this effect from the effect of Vm as a growth promotant. In one EXP but not another, Vm seemed to improve nPP utilization when dietary nPP level was 0.35%. Virginiamycin had no or negative effects when the level of nPP was ≤0.25%. In another EXP, Vm improved many of the response variables in birds fed the 0.35% nPP diet, but it was equally effective at 0.45% nPP, which is at or above the requirement. The implications of this increased utilization are numerous, such as a potential reduction in the amount of Ca and nPP that needs to be supplemented to C-SBM diets and a reduced loss of these nutrients to the environment. Further research is needed to ascertain the mode of action of Vm and its potential to increase the utilization of Ca and nPP in CSBM diets and to investigate the relationship between Ca:nPP and Vm.

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