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METABOLISM AND NUTRITION |


* Department of Poultry Science, Mississippi State University, Mississippi State 39759-9665;
The Ohio State University, Columbus 43210; and
Degussa Corporation, Kennesaw, GA 30144
3 Corresponding author: mkidd{at}poultry.msstate.edu
| ABSTRACT |
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Key Words: stress corticosterone digestibility amino acid broiler
| INTRODUCTION |
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One possible means of learning how to better combat stress is to conduct research delineating the effects of stress on nutrient digestibility. This knowledge could aid in the nutritionists ability to establish nutrient requirements for stressed broilers. Unfortunately, very little research of this type has been conducted. One such study by Puvadolpirod and Thaxton (2000d) examined the nutrient digestibility of broilers given ACTH-dispensing implants. These researchers concluded that broilers treated with ACTH had significantly lower protein and carbohydrate digestibility than nonstressed broilers (Puvadolpirod and Thaxton, 2000d).
More recently, much attention has been given to estimating amino acid (AA) digestibility using the apparent ileal digestibility assay (Ravindran et al., 1999). The ileal digestibility assay entails the removal of the ileum from the bird, followed by the removal of its contents (Ravindran et al., 1999). The ileal contents can then be dried, digested, and analyzed for nutrient content using HPLC (Ravindran et al., 1999). This assay has several advantages. For example, it is easy to obtain ileal contents (i.e., sacrifice bird and remove ileal contents), it can be performed on chicks, and it is very precise with low variability (Lemme et al., 2004). Furthermore, it is not necessary to monitor feed intake or force feed birds because this assay is able to utilize the inclusion of an indigestible marker (i.e., chromic oxide, titanium dioxide, or ash insoluble ash) in the treatment diet (Kadim et al., 2002). One of the most important advantages of this assay is that because the digesta is obtained from the ileum, variation is reduced because contamination from hindgut fermentation and urinary waste does not occur (Lemme et al., 2004).
If more research were conducted to contribute to the understanding of the effects of stress on AA digestibility, perhaps nutritionists could better estimate AA requirements for periods when known stressors are present. Thus, the purpose of this research was to examine the effects of CS-induced stress on AA digestibility in Ross broilers using the apparent ileal digestibility assay.
| MATERIALS AND METHODS |
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This research consisted of 2 experiments (Exp.). Experiments 1 and 2 differed very little. In Exp. 1, 192 Ross x Ross 708 male broilers were placed into 16 pens of a floor pen facility (12 birds/pen). In Exp. 2, 120 Ross x Ross 308 male broilers were placed into 10 pens of a floor pen facility (12 birds/pen). Other than the former noted differences, both experiments were identical. Each pen contained 1 Chore-Time tube feeder (Chore-Time Poultry Production Systems, Milford, IN), a nipple drinker line (4 nipples/pen), and built-up softwood shavings. From d 1 to 20, chicks were fed a common starter diet (Table 1
), which exceeded the AA requirements established by the NRC (1994). On d 21, broilers and feed were weighed by pen, and treatment feed was administered from d 21 to 30. Treatments consisted of 1) control diet; 2) control diet plus 15 mg CS/kg of diet. Addition of CS to the feed was accomplished by dissolving CS into soybean oil. Previous experimentation to validate this stress model led to the usage of the CS inclusion level herein (Virden et al., 2005). Experiments 1 and 2 had 8 replications/treatment and 5 replications/treatment, respectively. At 30 d of age, broilers and feed were weighed by pen to calculate BW gain, feed intake, and feed conversion. Furthermore, 3 birds per pen were selected at random and killed by cervical dislocation. The liver was removed from each bird, pooled by pen, and weighed to obtain a wet liver weight. The livers were dried in a drying oven for approximately 7 d and then weighed to obtain a dry liver weight. Also, ileal contents from these same 3 birds were obtained from each bird, pooled by pen, then analyzed for AA digestibility.
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This research utilized the apparent ileal digestibility assay for AA digestibility determinations (Lemme et al., 2004). Briefly, chromic oxide was added to the test diets in both experiments at a level of 0.3% as an indigestible marker. Broilers were given ad libitum access to food and water at all times. As previously mentioned 3 birds per pen were killed in both experiments, and ileums (i.e., the section of the small intestine beginning at a point directly below the Meckels diverticulum and ending at a point approximately 4 cm anterior to the ileo-cecal junction) were removed. The digesta were removed from each ileum and pooled by pen. The digesta samples were dried for approximately 3 d in a forced air drying oven at 65°C. The ileal contents were then ground into a fine powder using a mortar and pestal. After the necessary chemical analyses were performed to determine the AA and Cr levels in the test diet and the digesta samples, apparent digestibility coefficients (DC) were calculated using the following equation: DC = 100 (Cr diet x AA contents/Cr digesta x AA diet) x 100.
Chemical Analysis
Amino acid levels in the dietary treatments and ileal samples were determined by following the procedures described by Llames and Fontaine (1994). Briefly, compos ite samples of the test diets and digesta were analyzed by HPLC after acid hydrolysis. The TSAA degradation of the test diet and digesta samples was circumvented by treating samples with performic acid prior to hydrolysis. This step facilitates the conversion of Met and Cys to Met sulfone and cysteic acid (Llames and Fontaine, 1994). These compounds can be analyzed using HPLC, allowing for the calculation of the Met and Cys contents of the samples in accordance with AOAC 994.12 (Llames and Fontaine, 1994).
Statistical Analysis
Both experiments were completely randomized designs using pen as the experimental unit. All data were analyzed using the GLM procedure of SAS Institute (1998). Means differing significantly were separated using the LSMEANS procedure of SAS Institute (1998).
| RESULTS |
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| DISCUSSION |
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Based on these findings, the AA digestibility of Ross x Ross 308 and 708 broilers should not be affected by CS-induced stress at the dosage level utilized herein. Thus environmental stressors, other than temperature, should not affect AA digestibility. Future research should focus on nutrient (e.g., AA) utilization during and after periods of physiological stress or AA digestibility in the presence of specific stressors.
| FOOTNOTES |
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2 Use of trade names in this publication does not imply endorsement by the Mississippi Agricultural and Forestry Experiment Station of the products, nor similar ones not mentioned. ![]()
Received for publication June 27, 2006. Accepted for publication October 28, 2006.
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