Evaluation of Dietary Glycerin Inclusion during Different Broiler Rearing Phases

The objective of this study was to evaluate the effect of the dietary addition of different levels of glycerin on the performance, litter moisture, pododermatitis incidence, and carcass and parts yield of broilers. In total, 1,610 broilers were reared in 35 pens with 46 birds each. A completely randomized experimental design, with five treatments with seven replicates was applied. The experimental treatments were: T1: control diet; T2: dietary inclusion of 5% glycerin from 1-42 days of age; T3: dietary inclusion of 10% glycerin from 1-42 days of age; T4: dietary inclusion of 5% glycerin from 7-42 days of age; T5: dietary inclusion of 10% glycerin from 7-42 days of age. The diets containing glycerin fed since the pre-starter period improved broiler weight gain and feed conversion ratio, but did not influence feed intake or livability. At the end of the experiment, the production efficiency index of the broilers fed 10% glycerin during the entire rearing period was significantly reduced compared with the other treatments. Litter moisture in the pens of broilers fed 10% glycerin during the entire rearing period was higher compared to the other treatments since day 21.Diets containing 10% glycerin, both for the entire rearing period (1-42 days) or only after the pre-starter phase (7-42 days), influenced broiler performance and incidence of severe pododermatitis, reducing the production efficiency indexes at 42 days. Glycerin may be added up to 5% in broiler ́s diets with no effect on performance, litter moisture and carcass yield, indicating that this co-product of the biodiesel industry can be used as an alternative feedstuff for broilers.


INtRODUCtION
Corn is the main energy source used in poultry feeds.Approximately 80% of Brazilian corn production is used in the formulation of feeds.Corn accounts for 65-70% of poultry feed composition.It is a valuable grain also used in human foods, and its replacement in feeds by other energy sources may reduce animal feeding costs.
The use of alternative feedstuffs, particularly in poultry production, may reduce production costs and increase the availability of traditional ingredients for human foods.Among alternative feedstuffs, glycerin is an energy-rich and low-cost ingredient.The glycerin obtained from biodiesel production contains 70-80% glycerol.Literature reports a wide range of chemical composition and energy values for glycerin.This variation may be due to the lack of purity of the samples because of the methods used for biodiesel production (Zavarize et al., 2014).
The objective of this study was to evaluate the effect of the dietary addition of different levels of glycerin on the performance, litter moisture, pododermatitis incidence, carcass and parts yield of broilers relative to glycerin feeding period.

MAteRIAl AND MethODS
In total, 1,610 Cobb 500 broilers were reared in 35 pens with 46 birds each.A completely randomized experimental design, with five treatments with seven replicates was applied.The experimental treatments were T1: control diet; T2: dietary inclusion of 5% glycerin from 1-42 days of age; T3: dietary inclusion of 10% glycerin from 1-42 days of age; T4: dietary inclusion of 5% glycerin from 7-42 days of age; T5: dietary inclusion of 10% glycerin from 7-42 days of age.
The glycerin product added to the diets contained 83% glycerol, 0.09% ether extract, 7% ashes, and 1.8% sodium.Glycerin gross energy value was determined in a bomb calorimeter as 3,620 kcal/kg, and the metabolizable energy value (3,258 kcal AMEn/ kg) used for feed formulation was calculated as 90% of the GE value.
Birds and feed residues were weekly weighed to calculate the live performance parameters (feed intake, weight gain, feed conversion ratio, live weight, livability, and production efficiency index).Production efficiency index was calculated according to the equation: PEI = [(daily weight gain x livability)/ feed conversion ratio] x 100.
On day 7, one bird per replicate, with the average body weight of the replicate, was selected, identified, sacrificed by neck dislocation, and immediately frozen at -18 o C. Carcass samples were freeze-dried for 170 days for subsequent determination of their dry matter content.
Litter moisture percentage was determined on days 21, 28, 35, and 42.Litter samples were collected from three different locations in each pen, distant from the feeder and drinker Litter samples were weighed and

Evaluation of Dietary Glycerin Inclusion during Different Broiler Rearing Phases
dried in a forced-ventilation oven (55°C for 72 hours), and weighed again.On day 42, four birds per replicate were scored for pododermatitis according to a 0-1 scale as: 0 (no lesions), 1 (lesion covering up to 50% of the footpad surface), and 2 (lesion covering more than 50% of the footpad surface).
On day 48, all birds were fasted for eight hours, weighed, and sacrificed to determine carcass, parts, and abdominal fat yields.Birds were sacrificed by electrical stunning and bled.After evisceration and removal of the abdominal fat, carcasses were not placed in the chiller.Carcasses with no feet, head, neck, and offal were weighed to calculate their yield as a percentage of live weight.Carcasses were then cut up according to industrial processing methods into breast, legs (thighs and drumsticks), back, and wings; and their yields were calculated as a percentage of carcass weight.Feet, head + neck, and abdominal fat (removed from the abdominal cavity and from the gizzard) yields were calculated as a percentage of live weight.
The results obtained for performance parameters, carcass dry matter content, and carcass traits were submitted to analysis of variance using the PROC GLM of SAS statistical package version 9.2.When significant effects (p<0.05) were detected, means were compared by the test of Tukey at 5% significance level.
Pododermatitis scores were analyzed by the PROC FREQ of SAS statistical package version 9.2, and treatment means were compared by the test of Kruskal-Wallis (p<0.05).When significant effects were determined, means were submitted to the Chi-square test (χ2 ).(2010).In addition, consistent with studies evaluating the addition of increasing glycerin levels (up to 10%) in broiler diets (Zavarize et al., 2012;Menten et al., 2008;Fernandes et al., 2010), no negative effect of the inclusion of up to 8% of glycerin was detected on broiler performance, suggesting that glycerin can be included in broiler diets, provided its chemical composition.Mandalawi et al. 2014 showed that raw glycerin from the biodiesel industry can be used efficiently, up to 10% of the diet, as a source of energy for broilers from 1 to 21 days of age and that the energy content of well-processed raw glycerin depends primarily on its glycerol content.However, when high glycerin levels were added to the diet (20 and 25%), Simon et al. (1997) performance impairment was observed.Guerra et al. (2011) obtained worse feed conversion ratios due to high feed intake when broilers were fed a diet with 10% glycerin relative to lower levels of glycerin inclusion.On the other hand, Cerrate et al. (2006) obtained lower feed intake in broilers fed diets of 10% of glycerin compared with 5%, and attributed this result to the reduced flow of the feed in the feeders, which consequently limited feed intake.Whole carcass dry matter content of the broilers sacrificed with seven days of age are shown in Table 3.There was no effect of dietary glycerin inclusion (p>0.05) on whole carcass dry matter content of broilers sacrificed with seven days of age.Previous studies indicated that the inclusion of high glycerin levels in starter broiler diets increased weight gain during the first days of rearing; however, when fed during the entire rearing period, performance losses were observed (Simon et al., 1997;Cerrate et al, 2006;Silva et al., 2012).This result suggests that the use of glycerin does not promote water retention in the carcass, but true weight gain.

ReSUltS AND DISCUSSION
Carcass trait results are shown in Table 4.The was no effect of the treatments (p>0.05) on carcass and parts yield.These results are consistent with the findings of Guerra et al. (2011), Silva et al. (2012), and Gianfelici (2009), using a maximum level of 10% of glycerin in broiler diets.This indicates that glycerin can be added up to this level in the diet with no adverse effects on carcass yield or commercial parts yields.However, Cerrate et al. (2006) observed that broilers fed diets containing 2.5 and 5% of glycerin, presented  12.061 Treatments: T1 -control diet (no glycerin inclusion); T2 -diet with 5% glycerin inclusion from 1-42 days; T3 -diet with 10% glycerin inclusion from 1-42 days; T4 -diet with 5% glycerin inclusion from 7-42 days; and T5 -diet with 10% glycerin inclusion from 7-42 days. 2 CV: coefficient of variation.a,b,c Means in the same column followed by different superscripts are different by the test of Tukey (p<0.05).carrying water during its excretion.Gianfelici (2009) and Romano et al. (2014) observed that levels higher than 7.5% of glycerin in broiler diets increased water consumption and excretion, which may have adverse effects on the field due to higher litter moisture.Glycerin is a low molecular weight hydrophilic compound, which is easily excreted by the kidneys.Silva et al. (2012) described a positive linear effect of dietary glycerin levels on litter moisture evaluated when broilers were 43 days old, and observed higher excreta moisture after the third week of rearing in broilers fed 10% of glycerin.The incidence of pododermatitis observed in the present study is shown in Table 6.The incidence of

LW, Menten JFM, Zavarize KC, Pereira R, Romano GG, Lima MB, Dias CTS
Table3presents the performance results obtained.The statistical analyses showed that the diet with the inclusion of 5% glycerin promoted significantly better

Table 3 -
Performance parameters measured in the periods of 1-7, 1-21, and 1-42 days of the rearing period of broilers fed with glycerin.
2 BW:body weight on day 42. 3 WG: weight gain. 4FI:feed intake. 5FCR:feed conversion rati o. 6 L:Livability. 7PEI:production efficiency index. 8CV:coefficient of variation. 9Carcass dry matter:Carcass dry matter after freeze-drying.a,b Means in the same row followed by different superscripts are different by the test of Tukey (p<0.05).

Table 6 -
Incidence and severity (score) of pododermatitis in the right footpad (RF) and left footpad (LF) of broilers fed with different glycerin levels at 42 days.