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Influences of Feeding Conventional and Semisynthetic Diets and Transport of Broilers on Weight Gain, Digestive Tract Mass, and Plasma Hormone and Metabolite Concentrations

E. Nijdam^*,1, E. Lambooij, M. J. A. Nabuurs, E. Decuypere and J. A. Stegeman^*

^* Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, PO Box 80151, 3508 TD Utrecht, The Netherlands; Animal Science Group of Wageningen University and Research Centre, PO Box 65, 8200 AB Lelystad, The Netherlands; and Laboratory of Physiology and Immunology of Domestic Animals, Faculty of Applied Bioscience and Engineering, K.U. Leuven, Kardinaal Mercierlaan 92, 3001 Heverlee, Belgium

¹ Corresponding author: edwinnijdam{at}hotmail.com

	ABSTRACT

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Two replicate experiments were done to investigate if special diets provided to broilers in their last phase of life could reduce the negative effects of feed withdrawal and transport without an increased content of the digestive tract. In each experiment, 240 broilers were used. The experiments consisted of 2 interventions: the feed intervention and the transport intervention. The feed intervention took 72 h, in which broilers had full access to a conventional grower diet, a conventional grower diet with an increased carbohydrate level, a conventional grower diet with an increased fat level, a semi-synthetic diet, or a semisynthetic diet with an increased carbohydrate level. The diets differed remarkably in carbohydrate content; carbohydrate content was approximately 67% in the semisynthetic diets and 42%, on average, in the conventional diets. Moreover, all of the carbohydrates in semisynthetic diets were highly soluble and digestible. The diets were compared with a feed withdrawal period of 24 h before transport. The transport intervention took 3 h; broilers were caught, crated, loaded, transported for 1.5 h, and had to wait in the crates for 1 h thereafter; or remained in the pens. After the transport intervention, blood samples were taken to determine plasma corticosterone, triiodothyronine, glucose, lactate, uric acid, nonesterified fatty acid, and triglyceride concentrations. Also, changes in live weight (LW) and digestive tract mass were assessed. The LW losses of broilers fed with semisynthetic diets after transport were 0.24% per hour less than of feed-withdrawn broilers. Moreover, intake of semisynthetic diets was approximately 200 g, whereas the intake of conventional diets was approximately 300 g. Therefore, the digestive tract mass as a percentage of LW was lower for semisynthetic-fed broilers in comparison with conventional-fed broilers, which can lead to a lesser degree of contamination during evisceration. No increase of corticosterone was found due to transport in semisynthetic-fed broilers. Semisynthetic feed with high carbohydrate concentration could be a good alternative for the feed withdrawal period held before transportation to the processing plant.

Key Words: broiler • diet • weight gain • digestive tract mass • plasma hormone and metabolite concentration

	INTRODUCTION

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Withdrawal of feed from broilers before slaughter is common practice. An important reason to do so is to reduce fecal contamination of carcasses during evisceration (Wabeck, 1972). For that purpose, feed withdrawal times varying from 4 to 12 h have been recommended (Wabeck, 1972; Warriss et al., 1988, 2004). However, longer total withdrawal times can occur due to extended catching, transport, or lairage times. For example, in the Netherlands total feed withdrawal time lasts, on average, 12 h and 45 min; however, in a worst-case scenario, feed withdrawal time can be as much as 33 h and 30 min (Nijdam et al., 2004).

Feed withdrawal leads to changes in shear strengths of the intestines (Bilgili, 1988; Northcutt et al., 1997), viscera weight (Buhr et al., 1998; Warriss et al., 2004), and reduction of live weight (LW) ranging from 0.22 to 0.56% per hour (Chen et al., 1983; Veerkamp, 1986; Lyon et al., 1991; Knowles et al., 1995; Buhr et al., 1998; Warriss et al., 2004; Nijdam et al., 2005). This loss of LW is highest during the first 6 h, due to evacuation of the gastrointestinal tract (Veerkamp, 1986; Buhr et al., 1998). Live weight is also significantly affected by transport. Nijdam et al. (2005) showed that losses of LW in broilers that were feed withdrawn and transported exceeded those of broilers that were only withdrawn of feed for the same period of time. Other studies about the relation between feed withdrawal and LW losses did not include a transport intervention (Veerkamp, 1986; Knowles et al., 1995; Buhr et al., 1998; Warriss et al., 2004).

Feed withdrawal and long transport times cause exhaustion, shown by depletion of glycogen stores in the liver (Warriss et al., 1988). Moreover, feed withdrawal, followed by transport, influences metabolic processes. Triiodothyronine (T₃) values decrease after feed withdrawal (Buyse et al., 2000; Nijdam et al., 2005). Corticosterone (CORT) values are increased by feed deprivation (Scott et al., 1983; Knowles et al., 1995) and transport (Freeman et al., 1984; Nijdam et al., 2005). Uric acid values are also increased due to transport (Nijdam et al., 2005). Both transport and feed withdrawal decrease triglyceride (TG) and increase nonesterified fatty acid (NEFA) values (Langslow et al., 1970; Van der Wal et al., 1999; Nijdam et al., 2005). Moreover, lactate and glucose values decrease following feed withdrawal. These findings show that the last day of the broiler’s life is associated with a negative energy balance and stress (Nijdam et al., 2005).

A limited number of studies were done to investigate the effects of feed withdrawal supplements as an alternative to a feed withdrawal period. Young et al. (2004) supplemented broilers with glucose combined with either pyruvate or creatine via the drinking water to examine the effect on meat quality; metabolic changes and LW losses were not investigated. However, LW losses were investigated by Farhat et al. (2002) and Northcutt et al. (2003). They used diets, based upon a commercial carbohydrate source, which was highly soluble and digestible. Broilers fed these diets had reduced LW losses compared with broilers that had no access to feed (Farhat et al., 2002) and with broilers that received normal feed (Northcutt et al., 2003).

In this study, we investigated a number of diets with high energy content, different macronutrient composition, and low crude fiber content, which can be provided during the last phase of life to reduce the negative effects of feed withdrawal and transport, such as stress and LW losses, without an increased content of the digestive tract.

Therefore, we compared 5 different diets that were provided to broilers in their last phase of life with feed withdrawal during the last day. To mimic practical procedures, a transport intervention (including catching, crating, transport of 1.5 h, and lairage of 1 h) was included in the study. We used weight gain, digestive tract mass (DTM), and plasma concentrations of CORT, T₃, glucose, lactate, uric acid, NEFA, and TG to assess the effect of the interventions.

	MATERIALS AND METHODS

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Broilers and Housing
Two similar experiments were performed with commercial Ross 308 (Aviagen, Newbridge, Scotland) broilers. For each experiment, 240 broilers of 3 wk of age were obtained from a commercial broiler farm. At the Farm Animal Health Research Farm of Utrecht University, The Netherlands, these broilers were kept in 24 floor pens (10 birds/pen) of approximately 1 m² on wood shavings. The broilers were maintained on a commercial grower diet (20% CP, 2,975 kcal of ME/kg) and fresh water ad libitum and exposed to a light cycle of 24L. Broilers were slaughtered at 49 d of age in the first experiment and at 46 d in the second experiment.

Approval for carrying out both experiments was obtained from the Animal Experimental Committee of the Veterinary Faculty of Utrecht University, The Netherlands.

Experimental Design
In the experiments, a 6 x 2 factorial design was used. The factors were feed and transport regimens. In the feed regimen, 5 different types of pelleted diets were given or broilers were feed withdrawn. During the transport regimen, broilers were crated, transported, and kept in lairage, or broilers had to remain in the pens before slaughter.

The following 6 feed regimens were included:

1. A commercial grower diet composed of conventional ingredients (Con);
   
2. The Con diet with an increased carbohydrate level (Con-starch);
   
3. The Con diet with increased fat level (Con-fat);
   
4. A diet composed of semisynthetic ingredients (SS);
   
5. The SS diet with an increased carbohydrate level (SS-starch; Table 1);
   
6. Broilers, which had no access to any of the diets, had a feed withdrawal (FW) period of 24 h before transport. This extended FW period was chosen to establish a more accurate calculation of weight gain as a percentage per hour.
   

The following 2 transport regimens were included:

1. A transport intervention (half of the groups). To mimic field circumstances, the transport intervention of 3 h began with grasping the bird by the leg and inverting the animal. After catching 4 to 6 birds in this manner, the catcher carried them for a distance of 10 m to a crate with a surface of 0.53 m². Birds of 1 pen were placed together into 1 crate. The crates were then loaded into a ventilated van (0.5 h). Subsequently, the birds were transported for 1.5 h. After transport, the birds remained in the crates for 1 h. During these activities, the broilers did not have access to feed and water.
   
2. Birds that were not subjected to the transport intervention of 3 h remained in the pens where they had no access to feed and water.
   

Due to a mistake during the transport regimen of Experiment 2, an extra group with Con broilers was subjected to the transport intervention, although they should have remained in the pen. For the Con-fat group, the opposite occurred. The transport regimen had a duration of 3 h, after which it took 4 h on average until slaughter. Therefore, the total time that the diets were withdrawn before slaughter was 7 h.

Measurements and Variables
Broilers were weighed 24 h before transport (LW1), and also just before euthanasia (LW2). The period between LW1 and LW2 was 31 h (24-h feed regimen, 3-h transport intervention, 4-h average waiting time until slaughter). Weight gain (g) as a percentage per hour was calculated by [(LW2 –LW1)/LW2] x 100/31. During slaughter, the crop and the proventriculus, together with the gizzard, and the intestines were removed from the carcass and weighed. The sum of these parts was defined as DTM. The DTM as a percentage of LW was calculated by (DTM/LW2) x 100.

Blood sampling started immediately after the end of the transport intervention. Broilers were taken carefully out of the pens or crates, depending on the treatment, and blood was collected by puncturing the vena ulnaris. This procedure did not exceed 45 s per broiler. Approximately 4 mL of blood per broiler was taken and stored on ice in tubes containing sodium fluoride. In plasma, concentrations of CORT, T₃, glucose, lactate, uric acid, TG, and NEFA were determined. Due to errors at storage immediately after blood sampling in Experiment 1, only 133 samples were suitable for analysis.

Analysis of Plasma Samples
Blood samples were kept on ice until plasma was separated by centrifugation at 503 x g for 10 min. Plasma samples were stored at –20°C until assayed. Plasma CORT, and T₃ concentrations were measured using a sensitive and highly specific radioimmunoassay kit (IDS Inc., Boldon, UK) with a sensitivity of 0.39 ng/mL and cross-reactions with aldosterone (0.20%), cortisol (0.40%), and deoxycorticosterone (3.30%). Samples were added in duplicate to check intraassay variability. Plasma CORT and T₃ concentrations had intraassay variability of 3.9 and 4.5%, respectively. Plasma metabolite concentrations of glucose, lactate, uric acid, TG, and NEFA were determined using a commercial kit validated for chicken plasma (procedure no. 826-UV, Sigma Diagnostics, Steinheim, Germany) modified for use in the Monarch Chemistry System (Instrumentation. Laboratory, Zaventem, Belgium). All measurements for each variable were run in the same assay to avoid interassay variability.

Statistical Analyses
The statistical analyses were performed in the SAS-PC System (SAS Institute, 2000). Additionally, PROC FREQ and PROC MEANS were used for the descriptive analyses. The assumption of normality of the outcomes was assessed applying stem-and-leaf plots and normal probability plots. The distribution of the plasma CORT, lactate, uric acid, and TG concentrations was skewed, and, therefore, a logarithmic transformation was applied.

Broiler was taken as a statistical unit, but pen was included as a random effect in the model to account for dependency among birds in the same pen (SAS Institute, 2000). Therefore, SE and probabilities were calculated using the type III MS for pen as an error term. Experiment, feed regimen, transport intervention, and interaction term feed regimen x transport intervention were analyzed using a GLM performed by PROC GLM on the plasma concentration variables and growth yield. An experiment effect was found for NEFA, lactate, TG, and DTM as a percentage of LW. Significant differences among treatments were separated using least squares means procedures of SAS. All statements of significance are based on the probability level of 0.05.

	RESULTS

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LW and Feed Intake
Feed intake during LW1 is shown in Table 2. At the start of the experiments, mean LW was 2,819 g, and no significant differences were observed among groups. Feed intake of SS and SS-starch diets was significantly lower compared with the other diets. Broilers that had no access to feed from 31 h before slaughter showed a negative weight change of 219 g, which differed significantly from that of broilers that were fed until 7 h before slaughter.

Plasma NEFA was increased in all transported groups. Nontransported SS-starch groups showed the lowest value (0.38 mmol/L). The NEFA values in conventional ingredient-fed groups and in FW groups were higher than in semisynthetic ingredient-fed groups. Plasma TG concentrations showed a tendency for lower values for feed withdrawn broilers. However, significant effects for transport of feed regimen were not observed.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

 
In this study, we investigated the influences of a number of diets, which were provided before transport to the processing plant, on stress, energy balance, and LW of broilers. We also investigated whether these diets could be used as a possible alternative for feed withdrawal before catching and transport. Broilers on semisynthetic diets had lower LW loss than FW broilers, and feed intake of semisynthetic feed was lower compared with conventional feed. Therefore, the DTM as a percentage of LW was lower for semisynthetic-fed broilers in comparison with conventional-fed broilers, which could lead to a lesser degree of contamination during evisceration. Moreover, no increase of CORT was found due to transport in semisynthetic-fed broilers. However, there was an experiment effect found for NEFA, lactate, TG, and DTM as a percentage of LW. This experiment effect is probably caused by the fact that the broilers in the 2 experiments were of different ages. In addition, a time effect could have contributed to the experiment effect, because Experiment 2 was done 2 mo after Experiment 1.

Transport is an essential factor in studies on the effects of FW before slaughter. In this study, a transport effect was found for DTM as a percentage of LW in FW broilers. Apparently, catching, crating, and transport stimulate clearance of the digestive tract. Nijdam et al. (2005) showed that losses of LW in broilers that were feed withdrawn and transported exceeded those of broilers that were withdrawn from feed, but not transported, for the same period of time. This could be caused partly by clearance of the digestive tract during transport. Furthermore, transport influenced plasma NEFA and lactate values and CORT values of broilers fed conventional diets. At least 1 of these transport effects was shown in earlier studies of Freeman et al. (1984), Kannan and Mench (1996), and Nijdam et al. (2005).

Even though it was concluded that stress or transport influences plasma glucose, uric acid, and TG values in other studies (Puvadolpirod and Thaxton, 2000; Nijdam et al., 2005), the current study found that this influence was not present. An important reason for this could be the percentage of missing values in Experiment 1 (45%) due to errors during storage of blood samples. Moreover, Lin et al. (2004) showed that changes in uric acid and glucose values occur within 3 h after CORT supplementation due to enhanced gluconeogenesis and protein catabolism. In this investigation, no significant increase of CORT occurred after transport; therefore, it is likely that no significant changes in uric acid and glucose values were found. Nevertheless, the plasma uric acid values tended to be higher after transport.

No feed withdrawal effects on plasma concentrations were found, whereas other studies showed a feed withdrawal effect on T₃ (Buyse et al., 2000; Nijdam et al., 2005), glucose (Langslow et al., 1970; Knowles et al., 1995; Van der Wal et al., 1999; Nijdam et al., 2005), NEFA (Langslow et al., 1970; Van der Wal et al., 1999), and TG (Nijdam et al., 2005). Nevertheless, average values of T₃, glucose, lactate, uric acid, and TG were lowest for FW groups.

CORT values for FW groups did not increase. Studies about the relation between feed withdrawal and CORT concentration are contradictory. This study clearly showed that a feed withdrawal period of 27 h did not increase CORT. Nijdam et al. (2005) found the same results for a feed withdrawal period of 13 h. The results are similar to studies of Freeman (1983), who reported 2 studies in which CORT was not increased after feed withdrawal. However, Scott et al. (1983) and Knowles et al. (1995) showed an increase in CORT after a feed withdrawal period of 10 and 24 h, respectively. Because CORT is one of the most reliable indicators of stress in chickens (Thaxton and Puvadolpirod, 2000), one can conclude that standard feed withdrawal times before catching are not likely to lead to excessive stress.

Differences in diet composition with regard to macro-nutrients might lead to metabolic changes (Collin et al., 2003; Machin et al., 2004). In this study, metabolic changes already were present after a supplementation period of only 3 d. Semisynthetic ingredients led to changes in CORT, lactate, and NEFA values. On average, the semi-synthetic diets consisted of approximately 67% carbohydrates, whereas the conventional diets consisted of 42% carbohydrates. Moreover, all carbohydrates in semisynthetic feed were highly soluble and digestible. The other macronutrients and ME did not differ substantially among the diets.

The decreased NEFA values that were found in semi-synthetic-fed broilers were not due to a decreased feed intake or to a possible dependency on CORT. The high NEFA values in conventional-fed groups and FW groups indicated an increased lipolysis (Nijdam et al., 2005). However, in broilers fed with high carbohydrate concentrated feed, glucose is probably preferable to fulfill the energy needs instead of lipids. A tendency for higher glucose values after transport was shown for semisynthetic-fed groups, possibly due to the high carbohydrate intake. In contrast, the conventional and FW groups showed a slight decrease of glucose concentration after transport. This might be the reason for significantly higher lactate values for semisynthetic groups compared with FW groups.

In conclusion, semisynthetic feed with a high carbohydrate concentration can be a good alternative for the feed withdrawal period before catching and transport. Semi-synthetic feed reduces LW losses and does not result in an increase in CORT levels after transport. Nevertheless, investigations must be done to find out whether semisynthetic diets are cost-effective, and more research is necessary to investigate the consequences of feeding semisynthetic feed on shear strength of the intestines. This parameter can be used to predict the risk of condemnation during evisceration. Also, changes in metabolism as a consequence of diet composition were shown. The effects of these changes in plasma metabolites on meat quality must be investigated, as well as other stress indicators. Finally, the ideal duration of the supplementation period before catching and slaughter must be investigated.

	ACKNOWLEDGMENTS

 
We thank Nabuurs Groep for financial support. We thank Lutien Groeneveld of Ab Diets (Woerden, The Netherlands) for composing and producing the experimental diets. Furthermore, we are very grateful to Jo van Eck (Utrecht University, The Netherlands) and Evelyne Delezie (Katholieke Universiteit Leuven, Belgium) for critically reading the manuscript and for giving advice.

Received for publication September 9, 2005. Accepted for publication March 24, 2006.

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This Article Abstract Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Nijdam, E. Articles by Stegeman, J. A. Search for Related Content PubMed PubMed Citation Articles by Nijdam, E. Articles by Stegeman, J. A.