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Effect of dietary supplementation of medium-chain fatty acids on growth performance and prevalence of carcass defects in broiler chickens raised in different stocking densities
C 2015 Poultry Science Association, Inc.
Effect of dietary supplementation of medium-chain fatty acids on growth performance and prevalence of carcass defects in broiler chickens raised in different stocking densities H. Khosravinia1
Primary Audience: Poultry Nutritionists, Researchers SUMMARY A 3 × 3 factorial experiment was conducted to examine the effect of medium-chain fatty acids (MCFA) on performance and occurrence of carcass defects in broiler chickens raised in stocking densities of 14, 16, and 18 birds/m2 . A total number of 720 Ross 308 broiler chicks that were 1 d old were reared up to 49 d of age. Corn- and soybean meal (SBM)–based starter and grower diets were supplemented with 0, 1.5, and 2 g/kg Aromabiotic and provided to the birds ad libitum. Inclusion of 2 g/kg Aromabiotic in the diet significantly improved weight gain of the birds during 1 to 21 d of age compared with control birds (P < 0.001). A significant reduction in mortality (P = 0.004) and a significant increase in European performance efficiency index (EPEI; P = 0.036) were noted in the birds that received diets containing 2 g/kg Aromabiotic compared with control birds at 49 d of age. The birds grown in a placement density of 18 birds/m2 had significantly improved FCR along with reduced feed intake (FI) during 1 to 49 d of age compared with those reared in a density of 14 birds/m2 . The mean EPEI was significantly greater in the birds raised in a density of 16 birds/m2 (P < 0.001). At 48 d of age, litter caking was significantly increased in the birds raised in a density of 18 birds/m2 and decreased in the birds that received dietary supplementation of Aromabiotic (P < 0.05). The influence of dietary Aromabiotic was significant related to reduced incidence and severity of footpad lesions and hock burns (P < 0.01). Frequency of lesions with a score of 2 to 5 on footpad and hock significantly increased for the birds raised in densities higher than 14 birds/m2 . It was concluded that dietary supplementation of 2 g/kg Aromabiotic improved early productive performance of broiler chickens and enhanced the PEI mainly due to decreased mortality. Dietary Aromabiotic improved broiler welfare as indicated by reduced foot defects in the birds raised in placement densities of 16 and 18 birds/m2 . Key words: medium-chain fatty acids, performance, heat stress, broiler chicken, carcass defects 2015 J. Appl. Poult. Res. 00:1–9 http://dx.doi.org/10.3382/japr/pfu001
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Corresponding author: [email protected]
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Department of Animal Sciences, Faculty of Agriculture, Lorestan University, Khoramabad 68137-17133, Lorestan, Iran
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DESCRIPTION OF PROBLEM
MATERIALS AND METHODS Experimental Flock and Treatments A local hatchery provided 720 chicks that were 1 d of age. [18]. They were housed in a concrete floor cross-ventilated shed up to 49 d of age. The floor was covered in a 5 cm deep layer of fresh wood shavings. Intermediately, room temperature was maintained 3 to 5◦ C higher than the recommended standard (except in the first week). The birds were distributed in 45 pens to examine the effect of 9 experimental treatments comprising 3 feeding regimens: basal diet without Aromabiotic supplement (control group) and basal diet (Table 1) supplemented with either 1.5 or 2 g/kg Aromabiotic (Vitamex, Drongen, Belgium), which was fed to the birds raised in a stocking density of 14, 16, or 18 birds/m2 in 5 replicates. Feed and water were available ad libitum during the experiment. All procedures used in this experiment complied with the Animal Care Guidelines of the Animal Ethics Committee at Shiraz University, Iran. Data Collection Live BW and feed intake were recorded weekly up to 49 d of age, and the data were used to calculate ADG, ADFI, and FCR. Mortality was recorded upon occurrence. All dead birds were weighed, and the data were used to adjust FCR. At d 48 of the experiment, litter moisture, pH, and temperature (at 3 cm depth) were measured, and litter caking percentage was evaluated by giving a score of 0 to 100 proportional to the caked area observed in each pan’s litter. Cleanliness of plumage for all birds was evaluated by assigning a score of 0 to 100 considering the proportion of the feathers discolored by litter contamination. At d 49 of the study, 8 birds per replicate were chosen randomly, weighed, euthanized, and processed manually. Carcass yield and abdominal fat percentage were recorded. The European performance efficiency factor (EPEF)
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Fatty acids with a chain length between 6 and 12 carbon atoms are regarded as mediumchain fatty acids (MCFA). Many experiments in vitro have confirmed the antimicrobial properties of MCFA against enteric pathogens Escherichia coli [1], Salmonella typhymurium [2, 3], Campylobacter jejuni [4, 5], and Clostridium perfringens [6]. Considering such antibacterial properties, MCFA are among the candidates for new nonantibiotic feed additives helpful in providing healthy gastrointestinal conditions in broilers. Based on research with poultry, MCFA can be an alternative to antibiotic growth promoters. Aromabiotic is a commercial product containing a mixture of MCFA that demonstrates antimicrobial, physiological, and immunological properties [7]. It was reported that Aromabiotic decreased the invasion of Salmonella and mortality, and also had positive effects on weight gain and FCR in broiler chickens [8] and piglets [9]. Stocking density is important in broiler production [10]. Poultry producers generally prefer higher stocking density because increasing space allowances in production systems can have a major depressive economic impact, as revenue per unit of space increases linearly with density [11–13]. In broiler flocks, high densities can be stressful, with an associated decline in BW, feed intake and utilization, flock uniformity, and leg health, and increased frequencies of tibial dischondroplasia, carcass bruising, and scratching [14, 15]. Moreover, high stocking density has been reported to increase ammonia production, foot pad lesions, litter moisture, bird locomotion, and preening, especially under heat stress conditions [16]. Beloor et al. [17] reported that limited space allowance influences the disturbances or exacerbated mortality related to heat stress in broiler flocks. Supplementation of diet with ideal additives may support a healthy gastrointestinal tract in broilers affected by environmental and social stressors. The objective of this study was to evaluate how MCFA dietary supplementation using Aromabiotic affects productive performance, litter characteristics, and carcass defects in broiler chickens raised in higher stocking densities under heat stress conditions. It was hypothesized
that inclusion of MCFA in broiler diets improves performance and enhances the welfare of broiler chickens reared in flocks with lower space allowance and high ambient temperature.
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Table 1. Percentage inclusion of ingredients and calculated composition of basal diets. Starter (1 to 21 d)
Grower (22 to 49 d)
Corn Soybean meal Fish meal Soybean oil Wheat Calcium carbonate Wheat bran Dicalcium phosphate DL-Methoinine L-Lysine Common salt Mineral premix1 Vitamin permix2 Coccidiostat
52.00 25.00 7.00 4.00 3.50 2.00 2.50 2.00 0.20 0.10 0.25 0.50 0.85 0.10
56.00 22.5 5.00 4.00 3.50 2.00 3.00 2.00 0.20 0.10 0.25 0.50 0.85 0.10
3,000 22.24 1.10 0.45 0.52 1.15
3,150 20.02 1.00 0.40 0.40 1.10
Calculated composition ME (kcal/kg) Crude protein (%) Calcium (%) Available phosphorus (%) Methionine (%) Lysine (%) 1
Mineral mix supplied/kg diet: Mn, 55 mg; Zn, 50 mg; Fe, 80 mg; Cu, 5 mg; Se, 0.1 mg; I, 0.18 mg 2 Vitamin mix supplied/kg diet: vitamin A, 18,000 IU; vitamin D3 , 4,000 IU; vitamin E, 36 mg; vitamin K3 , 4 mg; vitamin B12 , 0.03 mg; thiamine, 1.8 mg; riboflavin, 13.2 mg; pyridoxine, 6 mg; niacin, 60 mg; calcium pantothenate, 20 mg; folic acid, 2 mg; biotin, 0.2 mg; choline chloride, 500 mg
was calculated according to the following equation [19]: EPEF = [(LW×S)/(FCR×AS)] × 100, where LW is live weight (kg), S is survival rate (%), FCR is feed conversion ratio, and AS is age of slaughter (d). Lesion Score All the birds were scored for severity of breast blisters, footpad dermatitis, and hock burns at 48 d of age. In brief, visual appraisal was made on each live bird, and tissue degeneration on the breast, footpad, and hock joint was scored on a 6-point scale as follows: 0 = no lesions; 1 = mild lesion affecting a very small area of skin (less than 15% of surface); 2 = mild to moderate lesion (about 15 to 40% of surface); 3 = moderate lesion (about 40 to 60% of surface); 4 = moderate to severe lesion (about 40 to 60% of surface); and 5 = grossly affected region with
lesion covering most of the surface. All lesion evaluations were performed by one experienced evaluator. Statistical Analysis The present study was conducted using a completely randomized design (CRD) with factorial arrangement. The data were subjected to ANOVA using the general linear models (GLM) procedures of SAS-9.3 software [20], and the corresponding means were compared by Duncan multiple range test at P < 0.05. Mortality data were subjected to arcsine transformation. The statistical model was as follows: Yijk = μ + ALi + SDj + (AL × SD)ij + eijk Where: Yijkl = Individual observation
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Ingredient (%)
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4 μ = Experimental mean ALi = Aromabiotic level effect SDj = Stocking density level effect (AL × SD)ij = Aromabiotic by stocking density interaction eijkl = Error term with mean 0 and variance σe2
RESULTS Inclusion of Aromabiotic into the diet at 2 g/kg significantly increased daily weight gain (DWG) of the birds during 1 to 21 d of age compared with the control birds (P < 0.001; Table 2). The mean FI and FCR during 1 to 21 and 1 to 49 d of age did not differ by supplementation of diet with Aromabiotic (P > 0.05). A significant reduction in mortality (P = 0.004) and a significant increase in European performance efficiency index (EPEI) (P =
Table 2. Effect of dietary levels of medium-chain fatty acids (MCFA) and stocking density (SD) on daily weight gain (DWG), feed intake (FI), feed conversion ratio (FCR), mortality (%), and European performance efficiency index (EPEI) on broiler chickens1 . DWG (g/day)
FI (g/day)
FCR (g:g)
Mort.
EPEI
d 1 to 21
d 1 to 49
d 1 to 21
d 1 to 49
d 1 to 21
d 1 to 49
35.58b 36.81ab 36.95a 1.35
46.02 43.10 46.36 20.96
52.23 53.34 53.21 1.82
83.11 82.06 83.09 1.17
1.47 1.45 1.44 0.11
1.81 1.90 1.79 0.18
2.70a 2.40ab 2.10b 0.54
234b 232b 247a 9.11
35.76 35.91 36.14 0.87
45.10 45.85 45.69 1.15
53.15a 52.48a 48.72c 1.43
83.16 81.34 78.73 2.39
1.48a 1.45ab 1.35b 0.11
1.84 1.78 1.72 0.23
3.00 1.50 2.00 1.34
234b 244a 236ab 7.43
∗∗∗ NS ∗∗∗
NS NS NS
NS ∗ NS
NS NS NS
NS ∗ NS
NS NS NS
∗∗ NS ∗∗∗
∗ ∗∗∗ ∗∗∗
MCFA (g/kg) 0 1.5 2.0 SEM SD (bird/m2 ) 14 16 18 SEM Significance MCFA SD MCFA × SD
Means within a column with no common superscript differ significantly (P < 0.05). Each value represents the mean of 5 replicates (16 birds/replicate). ∗ P < 0.05; ∗∗ P < 0.01; ∗∗∗ P < 0.001; NS = P ≥ 0.05. a-b 1
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For analysis of qualitative variables, the chisquare test was used. Frequency analysis was applied for the data on carcass defects using the PROC FREQ and the relevant contingency tables in SAS-9.3 [20].
0.036) were observed in the birds that received diets containing 20 g/kg Aromabiotic compared with control birds at 49 d of age. Calculation of a fitted line for dietary Aromabiotic against mortality showed that there was a strong linear relationship (R2 = 0.96). Increased stocking density from 14 to 16 and 18 birds/m2 significantly improved FCR, and there was a slight decrease in FI and a minor improvement in weight gain from 1 to 21 d of age, while there was no change in DWG (P = 0.133), FI (P = 0.874), and FCR from 1 to 49 d of age (P = 0.808). Cumulative mortality up to 49 d of age did not differ among the birds raised in various stocking densities. The mean EPEI was significantly greater in the birds raised in a density of 16 birds/m2 (P < 0.001). At 49 d of age, carcass weight (CW), carcass yield (CY), and abdominal fat weight (AFW) and percentage (AFP) were not affected by inclusion of Aromabiotic in the diet and increased stocking densities (Table 3). The effects of Aromabiotic and stocking density on litter properties are shown in Table 4. Dietary levels of Aromabiotic significantly reduced litter caking at 48 d of age, while the cleanliness score of the birds improved at the same age (P > 0.05). Raising the broiler
KHOSRAVINIA: MEDIUM-CHAIN FATTY ACIDS IN BROILER NUTRITION Table 3. Effect of dietary levels of medium-chain fatty acids (MCFA) and stocking density (SD) on carcass weight (CW), carcass yield (CY), and abdominal fat weight (AFW) and percentage (AFP) in broiler chicken at 49 d of age1 . Factor
CY (%)
AFW (g)
AFP (%)
1597 1562 1519 25.68
71.36 71.34 71.82 0.56
56.15 71.34 53.73 2.01
2.57 3.54 3.60 0.12
1599 1557 1598 40.56
72.07 70.61 72.40 1.07
56.62 56.89 57.54 2.24
3.60 3.68 3.60 0.11
NS NS NS
NS NS NS
NS NS NS
NS NS NS
MCFA (g/kg) 0 1.5 2.0 SEM SD (bird/m2 ) 14 16 18 SEM Significance MCFA SD MCFA × SD a-b
Means within a column with no common superscript differ significantly (P < 0.05). 1 Each value represents the mean of 40 observations (5 replicates × 8 birds/replicate). NS = P ≥ 0.05.
chickens in a density of 18 birds/m2 resulted in a significant increase in caking percentage of litter and improved the cleanliness score of the birds compared with those grown at a density of 14
or 16 birds/m2 (P < 0.05). Litter pH, moisture percentage, and temperature were not affected by dietary Aromabiotic and incremental levels of stocking density (P > 0.05). Inclusion of Aromabiotic in the diet had no significant effect on incidence of breast blisters defected by severe scores (Table 5). The frequency of breast blisters with low severity was not affected by stocking density, but the incidence of breast blisters with greater severities (scores 4 and 5) increased with higher stocking densities. The birds fed Aromabiotic-containing diets had a lower frequency of severe lesions on the footpads (score 4 and 5) at 48 d of age (P < 0.01). Dietary supplementation with Aromabiotic resulted in a significant decrease in the incidence and severity of hock burns (Table 5). Based on an analysis of footpad dermatitis and hock burn frequency data, both variables were affected by stocking density. The frequency of lesions on the footpad as well as hock with a score of 2 to 5 increased significantly for the birds raised in densities higher than 14 birds/m2 .
DISCUSSION Aromabiotic is a balanced mixture of 60% MCFA (C6, C8, C10, and C12) derived from
Table 4. Effect of dietary levels of medium-chain fatty acids (MCFA) and stocking density (SD) on litter pH value, moisture, temperature, caking percentage, and cleanliness score of broiler chickens at 48 d of age1 . Factor
pH
Moisture (%)
Temperature (◦ C)
Caking percentage
Cleanliness score
7.74 7.50 7.57 0.10
57.31 53.50 53.95 1.48
24.48 25.13 24.78 0.12
75.00a 70.00ab 66.67b 2.01
71.67 76.67 80.00 3.33
7.46 7.62 7.68 0.05
56.17 55.63 55.71 0.73
24.68 24.73 25.24 0.20
65.00b 65.00b 75.00a 1.62
82.50a 82.50a 75.00b 2.41
NS NS NS
NS NS NS
NS NS NS
∗∗ ∗ NS
NS ∗ NS
MCFA (g/kg) 0 1.5 2.0 SEM SD (bird/m2 ) 14 16 18 SEM Significance MCFA SD MCFA × SD
Means within a column with no common superscript differ significantly (P < 0.05). Each value represents the mean of 5 observations (5 replicates). ∗ P < 0.05; ∗∗ P < 0.01; NS = P ≥ 0.05. a-b 1
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CW (g)
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Table 5. Effect of dietary levels of medium-chain fatty acids (MCFA) and stocking density (SD) on severity score of breast blisters, footpad lesions, and hock burns at 48 d of age χ 2 (significance)2
Defect severity score1 (%)
Factor 0
1
2
3
4
5
Breast blisters MCFA (g/kg) 0 1.5 2.0
1.66 1.66 2.33
4.97 9.28 11.61
8.95 8.62 10.61
8.29 7.95 6.96
4.98 3.32 1.99
3.99 1.00 1.66
20.82 (0.14)
9.44 10.69 5.66
11.32 10.69 9.44
8.17 10.69 8.81
2.50 2.50 3.78
0.63 0.63 2.51
39.02 (0.04)
SD (bird/m2 ) 0.63 0.63 1.25
Foot pad lesions MCFA (g/kg) 0 1.5 2.0
2.62 6.13 11.40
7.45 12.71 10.28
5.70 6.57 3.07
2.62 4.81 4.38
8.32 3.94 3.07
4.81 0.43 1.32
64.71 (P > 0.01)
14.97 13.68 10.42
9.11 5.86 5.21
1.29 7.15 3.90
0.64 3.25 4.37
0.64 0.64 1.96
101.88 (P > 0.01)
SD (bird/m2 ) 14 16 18
7.15 5.86 3.90
Hock burns MCFA (g/kg) 0 1.5 2.0
3.18 4.54 8.62
12.25 18.15 13.15
7.26 7.71 4.08
4.98 4.53 4.08
3.17 0.45 0.90
1.80 0.45 0.45
42.52 (P > 0.01)
21.12 15.11 14.56
5.10 4.16 3.56
2.17 5.10 7.28
0.72 1.45 2.91
0.00 0.73 1.47
71.58 (P > 0.01)
SD (bird/m2 ) 14 16 18
6.73 5.01 3.65
Score: 0 = no defect, 1 = mild, 2 = mild to medium, 3 = medium, 4 = medium to severe, 5 = severe 2 Effective sample size = 338 and DF = 24 1
tropical plant sources on a support of silicium dioxide [7]. The product can be provided to pigs and poultry through feed and acts by controlling the balance of microflora in the intestine. In the current study, Aromabiotic significantly promoted early growth and slightly improved FI and FCR. These effects may be attributed to a healthier and more stable gut environment created by the MCFA. The improved early weight gain confirmed that the antimicrobial activity of MCFA [21–23] helped diminished intestinal infection pressure and improved intestinal morphology, resulting in better digestive and absorptive capacities [24]. Moreover, dietary MCFA
possibly helped to promote immune function, as mortality was significantly reduced in the birds that received Aromabiotic-containing diets. The findings of this study are similar to the results of Chaveerach et al. [25] and Van Immerseel et al. [3], who reported reduced mortality rates in broiler chickens fed Aromabiotic-supplemented diets. Previously, Aromabiotic was shown to be effective against a wide range of opportunistic microorganisms, including E. coli [1], Salmonella [3], Campylobacter, and Clostridia [5], which are more harmful to broiler performance in stressful conditions. Commercial broiler
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BW of 1.8 to 3.5 kg [13, 28, 15]. By studying the performance and well-being of broilers grown to a final BW of 1.8 kg, Dozier et al. [29] indicated that increasing stocking density from 30 to 45 kg/m2 of floor space decreased the cumulative growth rate by approx. 6%. The results of this study are inconsistent with many reports that have demonstrated that stocking density did not adversely affect broiler performance. These results confirm that unless specific measures are taken, stocking density, on its own, may have less effect on performance in broiler chickens than the consequences of stocking density such as deterioration in air and litter quality [30, 31]. Footpad lesions and hock burns are considered indicitive of broiler welfare [32, 30]. Increasing levels of stocking density from 14 to 18 birds/m2 caused a greater occurrence of severe tissue degenerations on both footpad and hock, while these adverse outcomes were reduced by dietry supplentation of Aromabiotic. These results are inconsisitent with previous reports claiming stocking density may have no effect on broiler welfare in commercial conditions [30]. These results also do not confirm the findings of Thaxtone et al. [33], who reported stocking densities from 20 to 55 kg/m2 of floor space did not cause physiological adaptive changes indicative of stress in broiler chickens. Based on the results of the current study, dietary supplementation with MCFA could result in improvements in broiler welfare and further help shift the emphasis to dietary factors that influence broiler welfare.
CONCLUSIONS AND APPLICATIONS Dietary supplementation of 2 g/kg Aromabiotic improved the productive performance of broiler chickens at early ages and enhanced the final performance efficiency index mainly due to decreased mortality. 1. Increased stocking density from 14 to 18 birds/m2 of floor space adversely affected broiler welfare with no adverse effect on their performance. 2. Dietary Aromabiotic supplementation improved broiler welfare, as demonstrated by
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producers are often tempted to increase the number of birds/m2 per house to reduce housing, equipment, and labor costs per bird. However, based on reported literature, a high stocking density can have detrimental effects on the economics and welfare of broiler production and may be considered stressful by the broilers [26]. It was expected that inclusion of Aromabiotic in broiler diets would have a positive effect on performance of birds raised in stocking densities of 16 and 18 birds/m2 compared with those with greater space allowance. However, increasing stocking density had no effect on production performance or mortality rate [27]. Based on these data, stocking densities may not have been high enough to affect growth and mortality. Furthermore, these experimental flocks may not provide a perfect understanding of the effects of stocking density on bird performance and welfare because in these experimental conditions, in which there were far fewer birds than are usually found in commercial conditions, the birds confined in pens were constantly allowed space, and the space of the shed, the lighting, and ventilation were not identical to those found in commercial situations. Therefore, it seems that the stocking density is not equivalent to space necessary to walk and exhibit natural behaviors. Stocking density is a multifaceted issue related to ammonia volatilization, heat production, and aerosols, among many other factors inside the house. In this study, the incidence of either footpad lesions or hock burns with higher severities (scores 4 and 5) was significantly reduced in the birds that received Aromabiotic-supplemented diets and was increased in the birds raised in higher densities. The apparent effect of dietary Aromabiotic on the incidence of foot defects may be due to factors independent from the litter characteristics measured in this study. Considering that Aromabiotic supplementation and increased density did not seem to affect litter pH, moisture percentage, or temperature, it was speculated that the lower microbial load of the litter could have occurred because decreased expulsion of bacteria through fecal matter provided a less irritating litter environment. High stocking densities have been shown to adversely affect growth, external carcass quality, and processing yields in broilers grown to final
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8 reduced foot defects in the birds raised in high placement densities of 16 and 18 birds/m2 of floor space.
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1. Kabara, J. J., and D. L. Marshal. 2005. Medium-chain fatty acids and esters. Pages 327–360 in Antimicrobials in Food. CRC Press, Boca Raton, FL. 2. Bruggeman, G. 2002. Evaluation of the effect of alternatives for growth promoters against Salmonella infection in pigs. PhD Thesis. Univ. Ghent, Belgium. 3. Van Immerseel, F., J. De Buck, F. Boyen, L. Bohez, F. Pasmans, J. Volf, M. Sevcik, I. Rychlik, F. Haesebrouck, and R. Ducatelle. 2004. Medium-chain fatty acids decrease colonization and invasion through hilA suppression shortly after infection of chickens with Salmonella enterica serovar Enteritidis. Appl. Environ. Microbiol. 70:3582–3587. 4. Newell, D. G., and J. A. Wagenaar. 2000. Poultry infections and their control at farm level. Pages 497–509 in Campylobacter, Nachamkin, I., and M. J. Blaser eds. 2nd ed. ASM Press, Washington, DC. 5. Hermans, D., K. Van Deun, W. Messens, and A. Martel. 2011. Campylobacter control in poultry by current intervention measures ineffective: Urgent need for intensified fundamental research. Vet. Microbiol. 52: 219–228. 6. Skrivanova, E., M. Marounek, G. Dlouha, and J. Kanha. 2005. Susceptibility of Clostridium perfringens to C2-C18 fatty acids. Letters Appl. Microbiol. 41: 77–81. 7. Isaac, D., K. Deschepper, E. Vanmeenen, and L. Maertens. 2013. The effect of a balanced mixture of medium chain fatty acids on zootechnical performance in broilers. Pages 196–199 in Proc. 24th Ann. Aust. Poult. Sci. Sym., Sydney. 8. Gutierrez Del Alamo, A., J. De Los Mozos, J. T. P. Aan Dam, and P. Perez De Ayala. 2006. The use of short and medium chain fatty acids as an alternative to antibiotic promotersin broilers infected with malabsorption syndrome. Pages 317–320 in Proc. 16th European Sym. Poult. Nutr., Stasbourg, France. 9. Dierick, N. A., J. A. Decuypere, K. Molly, E. Van Beek, and E. Vanderbeke. 2002. The combined use of triacylglycerols (TAGs) containing medium-chain fatty acids (MCFAs) and exogenous lipolytic enzymes as an alternative to nutritional antibiotics in piglet nutrition. II. In vivo release of MCFAs in gastric cannulated and slaughtered piglets by endogenous and exogenous lipases; effects on the luminal gut flora and growth performance. Livestock Product. Sci. 76:1–16. 10. Ekstrand, C. 1993. Effects of stocking density on the health, behaviour and productivity of broilers: A literature review. PhD Thesis. Swedish Univ., Skara. 11. Proudfoot, F. G., H. W. Hulan, and D. R. Ramey. 1979. Effect of 4 stocking densities on broiler carcass grade, the incidence of breast blisters, and other performance traits. Poult. Sci. 58:791–793. 12. Shanawany, M. M. 1988. Broiler performance under high stocking densities. Br. Poult. Sci. 29:43–52. 13. Feddes, J. J. R., E. J. Emmanuel, and M. J. Zuidhof. 2002. Broiler performance, BW variance, feed and water
intake, and carcass quality at different stocking densities. Poult. Sci. 81:774–779. 14. Sanotra, G. S., L. G. Lawson, and K. S. Vestergaard. 2001. Influence of stocking density on tonic immobility, lameness, and tibial dyschondroplasia in broilers. J. Appl. Anim. Welf. Sci. 4:71–87. 15. Estevez, I. 2007. Density allowances for broilers: Where to set the limits? Poult. Sci. 86:1265–1272. 16. Skrbic, Z., Z. Pavlovski, and M. Lukic. 2010. Stocking density: Factor of production performance, quality and broiler welfare. Biotechnol. Anim. Husbandry 25: 359–372. 17. Beloor, J., H. K. Kang, Y. J. Kim, V. K. Subramani, I. S. Jang, S. H. Soha, and Y. S. Moon. 2010. The effect of stocking density on stress related genes and telomeric length in broiler chicken. Asian-Australas. J. Anim. Sci. 23:437– 443. 18. Ross 308, Dorbar Broiler Breeders Co., Borujerd, Iran. 19. Samarakoon, S. M. R., and K. Samarasinghe. 2012. Strategies to improve the cost effectiveness of broiler production. Trop. Agric. Res. 23:338–346. 20. . 2003. Version 9.3 ed. SAS Inst. Inc., Cary, NC. 21. Kabara, J. J. 1978. Fatty acids and derivatives as antimicrobial agents, p. 1–14. In Kabara, J. J. (ed.), The Pharmacological Effect of Lipids. American Oil Chemists Society, St. Louis, Mo. 22. Skrivanova, E., M. Marounek, V. Benda, and P. Brezina. 2006. Susceptibility of Escherichia coli, Salmonella sp. and Clostridium perfringens to organic acids and monolaurin. Vet. Med. 51:81–88. 23. Batovska, D. I., I. T. Todorova, I. V. Tsvetkova, and H. M. Najdenski. 2009. Antibacterial study of the medium chain fatty acids and their 1- monoglycerides: Individual effects and synergistic relationships. Polish J. Micrbiol. 58: 43–47. 24. Deschepper, K., M. Lippens, G. Huyghebaert, and K. Molly. 2003. The effect of Aromabiotic and GALI D’OR on technical performances and intestinal morphology of broilers. Pages 189–192 in Proc. 14th European Symp. Poult. Nutr., Lillehammer, Norway. 25. Chaveerach, P., D. A. Keuzemkamp, H. A. P. Urlings, L. J. A Limpman, and F. Van Knapen. 2002. In vitro study on the effect of organic acids on Campylobacter jejuni/coli populations in mixtures of water and feed. Poult. Sci. 81:621– 628. 26. Hall, A. L. 2001. The effect of stocking density on the welfare and behaviour of broiler chickens reared commercially. Anim. Welf. 10:23–40. 27. North, M. O. 1982. Commercial Chicken Production Manual. 2nd ed. El Manual Moderno, Mexico, D.F. 28. Dozier, W. A., J. P. Thaxton, J. L. Purswell, H. A. Olanrewaju, S. L. Branton, and W. B. Roush. 2006. Stocking density effects on male broilers grown to 1.8 kilograms of BW. Poult. Sci. 85:344–351. 29. Dozier, W. A., J. P. Thaxton, S. L. Branton, G. W. Morgan, D. M. Miles, W. B. Roush, B. D. Lott, and Y. VizzierThaxton. 2005. Stocking density effects on growth performance and processing yields of heavy broilers. Poult. Sci. 84:1332–1338. 30. Dawkins, M. S., C. A. Donnelly, and T. A. Jones. 2004. Chicken welfare is influenced more by housing conditions than by stocking density. Nature 427: 342–344.
KHOSRAVINIA: MEDIUM-CHAIN FATTY ACIDS IN BROILER NUTRITION 31. Jones, T. A., C. A. Donnelly, and M. S. Dawkins. 2005. Environmental and management factors affecting the welfare of chickens on commercial farms in the United Kingdom and Denmark stocked at five densities. Poult. Sci. 84:1155–1165. 32. Berg, C. C. 1998. Foot-pad dermatitis in broilers and turkeys prevalence, risk factors and prevention. PhD Thesis. Swedish Univ., Skara. 33. Thaxton, J. P., W. A. Dozier, S. L. Branton, G. W. Morgan, D. W. Miles, W. B. Roush, B. D. Lott, and
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Y. Vizzier-Thaxton. 2006. Stocking density and physiological adaptive responses of broilers. Poult. Sci. 85: 819–824.
Acknowledgments The fruitful collaboration of S. Ghaem-maghami, Pouyesh Olkeh Cooperative, Tehran, in providing Aromabiotic is gratefully acknowledged.
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Effect of dietary supplementation of medium-chain fatty acids on growth performance and prevalence of carcass defects in broiler chickens raised in different stocking densities H. Khosravinia1
Primary Audience: Poultry Nutritionists, Researchers SUMMARY A 3 × 3 factorial experiment was conducted to examine the effect of medium-chain fatty acids (MCFA) on performance and occurrence of carcass defects in broiler chickens raised in stocking densities of 14, 16, and 18 birds/m2 . A total number of 720 Ross 308 broiler chicks that were 1 d old were reared up to 49 d of age. Corn- and soybean meal (SBM)–based starter and grower diets were supplemented with 0, 1.5, and 2 g/kg Aromabiotic and provided to the birds ad libitum. Inclusion of 2 g/kg Aromabiotic in the diet significantly improved weight gain of the birds during 1 to 21 d of age compared with control birds (P < 0.001). A significant reduction in mortality (P = 0.004) and a significant increase in European performance efficiency index (EPEI; P = 0.036) were noted in the birds that received diets containing 2 g/kg Aromabiotic compared with control birds at 49 d of age. The birds grown in a placement density of 18 birds/m2 had significantly improved FCR along with reduced feed intake (FI) during 1 to 49 d of age compared with those reared in a density of 14 birds/m2 . The mean EPEI was significantly greater in the birds raised in a density of 16 birds/m2 (P < 0.001). At 48 d of age, litter caking was significantly increased in the birds raised in a density of 18 birds/m2 and decreased in the birds that received dietary supplementation of Aromabiotic (P < 0.05). The influence of dietary Aromabiotic was significant related to reduced incidence and severity of footpad lesions and hock burns (P < 0.01). Frequency of lesions with a score of 2 to 5 on footpad and hock significantly increased for the birds raised in densities higher than 14 birds/m2 . It was concluded that dietary supplementation of 2 g/kg Aromabiotic improved early productive performance of broiler chickens and enhanced the PEI mainly due to decreased mortality. Dietary Aromabiotic improved broiler welfare as indicated by reduced foot defects in the birds raised in placement densities of 16 and 18 birds/m2 . Key words: medium-chain fatty acids, performance, heat stress, broiler chicken, carcass defects 2015 J. Appl. Poult. Res. 00:1–9 http://dx.doi.org/10.3382/japr/pfu001
1
Corresponding author: [email protected]
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Department of Animal Sciences, Faculty of Agriculture, Lorestan University, Khoramabad 68137-17133, Lorestan, Iran
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DESCRIPTION OF PROBLEM
MATERIALS AND METHODS Experimental Flock and Treatments A local hatchery provided 720 chicks that were 1 d of age. [18]. They were housed in a concrete floor cross-ventilated shed up to 49 d of age. The floor was covered in a 5 cm deep layer of fresh wood shavings. Intermediately, room temperature was maintained 3 to 5◦ C higher than the recommended standard (except in the first week). The birds were distributed in 45 pens to examine the effect of 9 experimental treatments comprising 3 feeding regimens: basal diet without Aromabiotic supplement (control group) and basal diet (Table 1) supplemented with either 1.5 or 2 g/kg Aromabiotic (Vitamex, Drongen, Belgium), which was fed to the birds raised in a stocking density of 14, 16, or 18 birds/m2 in 5 replicates. Feed and water were available ad libitum during the experiment. All procedures used in this experiment complied with the Animal Care Guidelines of the Animal Ethics Committee at Shiraz University, Iran. Data Collection Live BW and feed intake were recorded weekly up to 49 d of age, and the data were used to calculate ADG, ADFI, and FCR. Mortality was recorded upon occurrence. All dead birds were weighed, and the data were used to adjust FCR. At d 48 of the experiment, litter moisture, pH, and temperature (at 3 cm depth) were measured, and litter caking percentage was evaluated by giving a score of 0 to 100 proportional to the caked area observed in each pan’s litter. Cleanliness of plumage for all birds was evaluated by assigning a score of 0 to 100 considering the proportion of the feathers discolored by litter contamination. At d 49 of the study, 8 birds per replicate were chosen randomly, weighed, euthanized, and processed manually. Carcass yield and abdominal fat percentage were recorded. The European performance efficiency factor (EPEF)
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Fatty acids with a chain length between 6 and 12 carbon atoms are regarded as mediumchain fatty acids (MCFA). Many experiments in vitro have confirmed the antimicrobial properties of MCFA against enteric pathogens Escherichia coli [1], Salmonella typhymurium [2, 3], Campylobacter jejuni [4, 5], and Clostridium perfringens [6]. Considering such antibacterial properties, MCFA are among the candidates for new nonantibiotic feed additives helpful in providing healthy gastrointestinal conditions in broilers. Based on research with poultry, MCFA can be an alternative to antibiotic growth promoters. Aromabiotic is a commercial product containing a mixture of MCFA that demonstrates antimicrobial, physiological, and immunological properties [7]. It was reported that Aromabiotic decreased the invasion of Salmonella and mortality, and also had positive effects on weight gain and FCR in broiler chickens [8] and piglets [9]. Stocking density is important in broiler production [10]. Poultry producers generally prefer higher stocking density because increasing space allowances in production systems can have a major depressive economic impact, as revenue per unit of space increases linearly with density [11–13]. In broiler flocks, high densities can be stressful, with an associated decline in BW, feed intake and utilization, flock uniformity, and leg health, and increased frequencies of tibial dischondroplasia, carcass bruising, and scratching [14, 15]. Moreover, high stocking density has been reported to increase ammonia production, foot pad lesions, litter moisture, bird locomotion, and preening, especially under heat stress conditions [16]. Beloor et al. [17] reported that limited space allowance influences the disturbances or exacerbated mortality related to heat stress in broiler flocks. Supplementation of diet with ideal additives may support a healthy gastrointestinal tract in broilers affected by environmental and social stressors. The objective of this study was to evaluate how MCFA dietary supplementation using Aromabiotic affects productive performance, litter characteristics, and carcass defects in broiler chickens raised in higher stocking densities under heat stress conditions. It was hypothesized
that inclusion of MCFA in broiler diets improves performance and enhances the welfare of broiler chickens reared in flocks with lower space allowance and high ambient temperature.
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Table 1. Percentage inclusion of ingredients and calculated composition of basal diets. Starter (1 to 21 d)
Grower (22 to 49 d)
Corn Soybean meal Fish meal Soybean oil Wheat Calcium carbonate Wheat bran Dicalcium phosphate DL-Methoinine L-Lysine Common salt Mineral premix1 Vitamin permix2 Coccidiostat
52.00 25.00 7.00 4.00 3.50 2.00 2.50 2.00 0.20 0.10 0.25 0.50 0.85 0.10
56.00 22.5 5.00 4.00 3.50 2.00 3.00 2.00 0.20 0.10 0.25 0.50 0.85 0.10
3,000 22.24 1.10 0.45 0.52 1.15
3,150 20.02 1.00 0.40 0.40 1.10
Calculated composition ME (kcal/kg) Crude protein (%) Calcium (%) Available phosphorus (%) Methionine (%) Lysine (%) 1
Mineral mix supplied/kg diet: Mn, 55 mg; Zn, 50 mg; Fe, 80 mg; Cu, 5 mg; Se, 0.1 mg; I, 0.18 mg 2 Vitamin mix supplied/kg diet: vitamin A, 18,000 IU; vitamin D3 , 4,000 IU; vitamin E, 36 mg; vitamin K3 , 4 mg; vitamin B12 , 0.03 mg; thiamine, 1.8 mg; riboflavin, 13.2 mg; pyridoxine, 6 mg; niacin, 60 mg; calcium pantothenate, 20 mg; folic acid, 2 mg; biotin, 0.2 mg; choline chloride, 500 mg
was calculated according to the following equation [19]: EPEF = [(LW×S)/(FCR×AS)] × 100, where LW is live weight (kg), S is survival rate (%), FCR is feed conversion ratio, and AS is age of slaughter (d). Lesion Score All the birds were scored for severity of breast blisters, footpad dermatitis, and hock burns at 48 d of age. In brief, visual appraisal was made on each live bird, and tissue degeneration on the breast, footpad, and hock joint was scored on a 6-point scale as follows: 0 = no lesions; 1 = mild lesion affecting a very small area of skin (less than 15% of surface); 2 = mild to moderate lesion (about 15 to 40% of surface); 3 = moderate lesion (about 40 to 60% of surface); 4 = moderate to severe lesion (about 40 to 60% of surface); and 5 = grossly affected region with
lesion covering most of the surface. All lesion evaluations were performed by one experienced evaluator. Statistical Analysis The present study was conducted using a completely randomized design (CRD) with factorial arrangement. The data were subjected to ANOVA using the general linear models (GLM) procedures of SAS-9.3 software [20], and the corresponding means were compared by Duncan multiple range test at P < 0.05. Mortality data were subjected to arcsine transformation. The statistical model was as follows: Yijk = μ + ALi + SDj + (AL × SD)ij + eijk Where: Yijkl = Individual observation
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Ingredient (%)
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4 μ = Experimental mean ALi = Aromabiotic level effect SDj = Stocking density level effect (AL × SD)ij = Aromabiotic by stocking density interaction eijkl = Error term with mean 0 and variance σe2
RESULTS Inclusion of Aromabiotic into the diet at 2 g/kg significantly increased daily weight gain (DWG) of the birds during 1 to 21 d of age compared with the control birds (P < 0.001; Table 2). The mean FI and FCR during 1 to 21 and 1 to 49 d of age did not differ by supplementation of diet with Aromabiotic (P > 0.05). A significant reduction in mortality (P = 0.004) and a significant increase in European performance efficiency index (EPEI) (P =
Table 2. Effect of dietary levels of medium-chain fatty acids (MCFA) and stocking density (SD) on daily weight gain (DWG), feed intake (FI), feed conversion ratio (FCR), mortality (%), and European performance efficiency index (EPEI) on broiler chickens1 . DWG (g/day)
FI (g/day)
FCR (g:g)
Mort.
EPEI
d 1 to 21
d 1 to 49
d 1 to 21
d 1 to 49
d 1 to 21
d 1 to 49
35.58b 36.81ab 36.95a 1.35
46.02 43.10 46.36 20.96
52.23 53.34 53.21 1.82
83.11 82.06 83.09 1.17
1.47 1.45 1.44 0.11
1.81 1.90 1.79 0.18
2.70a 2.40ab 2.10b 0.54
234b 232b 247a 9.11
35.76 35.91 36.14 0.87
45.10 45.85 45.69 1.15
53.15a 52.48a 48.72c 1.43
83.16 81.34 78.73 2.39
1.48a 1.45ab 1.35b 0.11
1.84 1.78 1.72 0.23
3.00 1.50 2.00 1.34
234b 244a 236ab 7.43
∗∗∗ NS ∗∗∗
NS NS NS
NS ∗ NS
NS NS NS
NS ∗ NS
NS NS NS
∗∗ NS ∗∗∗
∗ ∗∗∗ ∗∗∗
MCFA (g/kg) 0 1.5 2.0 SEM SD (bird/m2 ) 14 16 18 SEM Significance MCFA SD MCFA × SD
Means within a column with no common superscript differ significantly (P < 0.05). Each value represents the mean of 5 replicates (16 birds/replicate). ∗ P < 0.05; ∗∗ P < 0.01; ∗∗∗ P < 0.001; NS = P ≥ 0.05. a-b 1
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For analysis of qualitative variables, the chisquare test was used. Frequency analysis was applied for the data on carcass defects using the PROC FREQ and the relevant contingency tables in SAS-9.3 [20].
0.036) were observed in the birds that received diets containing 20 g/kg Aromabiotic compared with control birds at 49 d of age. Calculation of a fitted line for dietary Aromabiotic against mortality showed that there was a strong linear relationship (R2 = 0.96). Increased stocking density from 14 to 16 and 18 birds/m2 significantly improved FCR, and there was a slight decrease in FI and a minor improvement in weight gain from 1 to 21 d of age, while there was no change in DWG (P = 0.133), FI (P = 0.874), and FCR from 1 to 49 d of age (P = 0.808). Cumulative mortality up to 49 d of age did not differ among the birds raised in various stocking densities. The mean EPEI was significantly greater in the birds raised in a density of 16 birds/m2 (P < 0.001). At 49 d of age, carcass weight (CW), carcass yield (CY), and abdominal fat weight (AFW) and percentage (AFP) were not affected by inclusion of Aromabiotic in the diet and increased stocking densities (Table 3). The effects of Aromabiotic and stocking density on litter properties are shown in Table 4. Dietary levels of Aromabiotic significantly reduced litter caking at 48 d of age, while the cleanliness score of the birds improved at the same age (P > 0.05). Raising the broiler
KHOSRAVINIA: MEDIUM-CHAIN FATTY ACIDS IN BROILER NUTRITION Table 3. Effect of dietary levels of medium-chain fatty acids (MCFA) and stocking density (SD) on carcass weight (CW), carcass yield (CY), and abdominal fat weight (AFW) and percentage (AFP) in broiler chicken at 49 d of age1 . Factor
CY (%)
AFW (g)
AFP (%)
1597 1562 1519 25.68
71.36 71.34 71.82 0.56
56.15 71.34 53.73 2.01
2.57 3.54 3.60 0.12
1599 1557 1598 40.56
72.07 70.61 72.40 1.07
56.62 56.89 57.54 2.24
3.60 3.68 3.60 0.11
NS NS NS
NS NS NS
NS NS NS
NS NS NS
MCFA (g/kg) 0 1.5 2.0 SEM SD (bird/m2 ) 14 16 18 SEM Significance MCFA SD MCFA × SD a-b
Means within a column with no common superscript differ significantly (P < 0.05). 1 Each value represents the mean of 40 observations (5 replicates × 8 birds/replicate). NS = P ≥ 0.05.
chickens in a density of 18 birds/m2 resulted in a significant increase in caking percentage of litter and improved the cleanliness score of the birds compared with those grown at a density of 14
or 16 birds/m2 (P < 0.05). Litter pH, moisture percentage, and temperature were not affected by dietary Aromabiotic and incremental levels of stocking density (P > 0.05). Inclusion of Aromabiotic in the diet had no significant effect on incidence of breast blisters defected by severe scores (Table 5). The frequency of breast blisters with low severity was not affected by stocking density, but the incidence of breast blisters with greater severities (scores 4 and 5) increased with higher stocking densities. The birds fed Aromabiotic-containing diets had a lower frequency of severe lesions on the footpads (score 4 and 5) at 48 d of age (P < 0.01). Dietary supplementation with Aromabiotic resulted in a significant decrease in the incidence and severity of hock burns (Table 5). Based on an analysis of footpad dermatitis and hock burn frequency data, both variables were affected by stocking density. The frequency of lesions on the footpad as well as hock with a score of 2 to 5 increased significantly for the birds raised in densities higher than 14 birds/m2 .
DISCUSSION Aromabiotic is a balanced mixture of 60% MCFA (C6, C8, C10, and C12) derived from
Table 4. Effect of dietary levels of medium-chain fatty acids (MCFA) and stocking density (SD) on litter pH value, moisture, temperature, caking percentage, and cleanliness score of broiler chickens at 48 d of age1 . Factor
pH
Moisture (%)
Temperature (◦ C)
Caking percentage
Cleanliness score
7.74 7.50 7.57 0.10
57.31 53.50 53.95 1.48
24.48 25.13 24.78 0.12
75.00a 70.00ab 66.67b 2.01
71.67 76.67 80.00 3.33
7.46 7.62 7.68 0.05
56.17 55.63 55.71 0.73
24.68 24.73 25.24 0.20
65.00b 65.00b 75.00a 1.62
82.50a 82.50a 75.00b 2.41
NS NS NS
NS NS NS
NS NS NS
∗∗ ∗ NS
NS ∗ NS
MCFA (g/kg) 0 1.5 2.0 SEM SD (bird/m2 ) 14 16 18 SEM Significance MCFA SD MCFA × SD
Means within a column with no common superscript differ significantly (P < 0.05). Each value represents the mean of 5 observations (5 replicates). ∗ P < 0.05; ∗∗ P < 0.01; NS = P ≥ 0.05. a-b 1
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CW (g)
5
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Table 5. Effect of dietary levels of medium-chain fatty acids (MCFA) and stocking density (SD) on severity score of breast blisters, footpad lesions, and hock burns at 48 d of age χ 2 (significance)2
Defect severity score1 (%)
Factor 0
1
2
3
4
5
Breast blisters MCFA (g/kg) 0 1.5 2.0
1.66 1.66 2.33
4.97 9.28 11.61
8.95 8.62 10.61
8.29 7.95 6.96
4.98 3.32 1.99
3.99 1.00 1.66
20.82 (0.14)
9.44 10.69 5.66
11.32 10.69 9.44
8.17 10.69 8.81
2.50 2.50 3.78
0.63 0.63 2.51
39.02 (0.04)
SD (bird/m2 ) 0.63 0.63 1.25
Foot pad lesions MCFA (g/kg) 0 1.5 2.0
2.62 6.13 11.40
7.45 12.71 10.28
5.70 6.57 3.07
2.62 4.81 4.38
8.32 3.94 3.07
4.81 0.43 1.32
64.71 (P > 0.01)
14.97 13.68 10.42
9.11 5.86 5.21
1.29 7.15 3.90
0.64 3.25 4.37
0.64 0.64 1.96
101.88 (P > 0.01)
SD (bird/m2 ) 14 16 18
7.15 5.86 3.90
Hock burns MCFA (g/kg) 0 1.5 2.0
3.18 4.54 8.62
12.25 18.15 13.15
7.26 7.71 4.08
4.98 4.53 4.08
3.17 0.45 0.90
1.80 0.45 0.45
42.52 (P > 0.01)
21.12 15.11 14.56
5.10 4.16 3.56
2.17 5.10 7.28
0.72 1.45 2.91
0.00 0.73 1.47
71.58 (P > 0.01)
SD (bird/m2 ) 14 16 18
6.73 5.01 3.65
Score: 0 = no defect, 1 = mild, 2 = mild to medium, 3 = medium, 4 = medium to severe, 5 = severe 2 Effective sample size = 338 and DF = 24 1
tropical plant sources on a support of silicium dioxide [7]. The product can be provided to pigs and poultry through feed and acts by controlling the balance of microflora in the intestine. In the current study, Aromabiotic significantly promoted early growth and slightly improved FI and FCR. These effects may be attributed to a healthier and more stable gut environment created by the MCFA. The improved early weight gain confirmed that the antimicrobial activity of MCFA [21–23] helped diminished intestinal infection pressure and improved intestinal morphology, resulting in better digestive and absorptive capacities [24]. Moreover, dietary MCFA
possibly helped to promote immune function, as mortality was significantly reduced in the birds that received Aromabiotic-containing diets. The findings of this study are similar to the results of Chaveerach et al. [25] and Van Immerseel et al. [3], who reported reduced mortality rates in broiler chickens fed Aromabiotic-supplemented diets. Previously, Aromabiotic was shown to be effective against a wide range of opportunistic microorganisms, including E. coli [1], Salmonella [3], Campylobacter, and Clostridia [5], which are more harmful to broiler performance in stressful conditions. Commercial broiler
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14 16 18
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BW of 1.8 to 3.5 kg [13, 28, 15]. By studying the performance and well-being of broilers grown to a final BW of 1.8 kg, Dozier et al. [29] indicated that increasing stocking density from 30 to 45 kg/m2 of floor space decreased the cumulative growth rate by approx. 6%. The results of this study are inconsistent with many reports that have demonstrated that stocking density did not adversely affect broiler performance. These results confirm that unless specific measures are taken, stocking density, on its own, may have less effect on performance in broiler chickens than the consequences of stocking density such as deterioration in air and litter quality [30, 31]. Footpad lesions and hock burns are considered indicitive of broiler welfare [32, 30]. Increasing levels of stocking density from 14 to 18 birds/m2 caused a greater occurrence of severe tissue degenerations on both footpad and hock, while these adverse outcomes were reduced by dietry supplentation of Aromabiotic. These results are inconsisitent with previous reports claiming stocking density may have no effect on broiler welfare in commercial conditions [30]. These results also do not confirm the findings of Thaxtone et al. [33], who reported stocking densities from 20 to 55 kg/m2 of floor space did not cause physiological adaptive changes indicative of stress in broiler chickens. Based on the results of the current study, dietary supplementation with MCFA could result in improvements in broiler welfare and further help shift the emphasis to dietary factors that influence broiler welfare.
CONCLUSIONS AND APPLICATIONS Dietary supplementation of 2 g/kg Aromabiotic improved the productive performance of broiler chickens at early ages and enhanced the final performance efficiency index mainly due to decreased mortality. 1. Increased stocking density from 14 to 18 birds/m2 of floor space adversely affected broiler welfare with no adverse effect on their performance. 2. Dietary Aromabiotic supplementation improved broiler welfare, as demonstrated by
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producers are often tempted to increase the number of birds/m2 per house to reduce housing, equipment, and labor costs per bird. However, based on reported literature, a high stocking density can have detrimental effects on the economics and welfare of broiler production and may be considered stressful by the broilers [26]. It was expected that inclusion of Aromabiotic in broiler diets would have a positive effect on performance of birds raised in stocking densities of 16 and 18 birds/m2 compared with those with greater space allowance. However, increasing stocking density had no effect on production performance or mortality rate [27]. Based on these data, stocking densities may not have been high enough to affect growth and mortality. Furthermore, these experimental flocks may not provide a perfect understanding of the effects of stocking density on bird performance and welfare because in these experimental conditions, in which there were far fewer birds than are usually found in commercial conditions, the birds confined in pens were constantly allowed space, and the space of the shed, the lighting, and ventilation were not identical to those found in commercial situations. Therefore, it seems that the stocking density is not equivalent to space necessary to walk and exhibit natural behaviors. Stocking density is a multifaceted issue related to ammonia volatilization, heat production, and aerosols, among many other factors inside the house. In this study, the incidence of either footpad lesions or hock burns with higher severities (scores 4 and 5) was significantly reduced in the birds that received Aromabiotic-supplemented diets and was increased in the birds raised in higher densities. The apparent effect of dietary Aromabiotic on the incidence of foot defects may be due to factors independent from the litter characteristics measured in this study. Considering that Aromabiotic supplementation and increased density did not seem to affect litter pH, moisture percentage, or temperature, it was speculated that the lower microbial load of the litter could have occurred because decreased expulsion of bacteria through fecal matter provided a less irritating litter environment. High stocking densities have been shown to adversely affect growth, external carcass quality, and processing yields in broilers grown to final
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8 reduced foot defects in the birds raised in high placement densities of 16 and 18 birds/m2 of floor space.
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Acknowledgments The fruitful collaboration of S. Ghaem-maghami, Pouyesh Olkeh Cooperative, Tehran, in providing Aromabiotic is gratefully acknowledged.
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