Feed restriction on performance and blood parameters of broilers fed diets with different sodium levels

Feed restriction on performance and blood parameters of broilers fed diets with different sodium levels

Junqueira OM^I; Fonseca LEC^II; Araújo LF^III; Duarte KF^IV; Araújo CS da S^IV; Rodrigues EAp^IV

^IDepartamento de Zootecnia – FCAV – UNESP/Jaboticabal – SP

^IIFaculdade de Medicina Veterinária – UNESP/Araçatuba – SP

^IIIFaculdade de Zootecnia e Eng. de Alimentos – USP – Pirassununga- SP

^IVGraduate student - Animal Science – FCAV – UNESP/ Jaboticabal – SP

^{Correspondence}

ABSTRACT

The experiment was conducted to evaluate the effect of feed restriction and different sodium levels in the diet on the performance and hematological values (erythrocyte, hemoglobin, hematocrit, mean cell volume, mean cell hemoglobin, mean cell hemoglobin concentration and white blood cell) of broilers from 22 to 42 days of age. A completely randomized design was used in a 4 x 2 x 2 factorial (levels of sodium: 0.16%, 0.19%, 0.22% and 0.25%; with or without feed restriction; male and female), and two replicates of thirty broilers each. Sodium levels did not affect performance (p>0.05). Feed restriction resulted in increased feed intake and affected weight gain and feed conversion negatively (p<0.05). Better weight gain and feed conversion (p<0.05) were seen in male broilers. Hematological values were not affected by sodium levels, feed restriction or sex (p>0.05).

Keywords: blood, broilers, feed restriction, nutrition, sodium, sodium bicarbonate.

INTRODUCTION

Environmental temperature in broiler houses must be within thermoneutrality so that the genetic potential of birds can be expressed. Thus, it is important to take measures in order to reduce detrimental effects caused by heat stress and maintain a high level of production, as well as bird welfare.

The concept of thermal comfort is vast and directly related to the microenvironment created inside the poultry house, which is naturally influenced by external environment conditions. An inadequate environment affects poultry production considerably. Temperatures lower than the ideal decrease bird growth and reduce feed conversion. On the other hand, high temperatures also reduce productive performance. Economical losses caused by heat stress might be minimized by using fogging devices and fans, changing nutrient levels, adding salts to diets or submitting birds to feed restriction.

Smith & Teeter (1988) reported that 28 day-old broilers submitted to a 12-hour fast showed significantly lower feed intake and higher surviving rate, with no effect on weight gain. Feed restriction for periods between 6 and 72 hours decreased mortality in birds exposed to high temperatures (Garcia, 1992).

Sodium bicarbonate (NaHCO₃) has been used in diet formulation as sodium source to reduce mortality rate and increase performance of birds during heat stress episodes (Balnave & Gorman, 1993). Silva et al. (1994) reported no significant effect on weight gain, feed intake and feed conversion when birds were given 0.5% and 1.0% NaHCO₃ in the diet from 1 to 49 days. Broiler diet supplementation with 0.60%, 1.20% and 1.80% NaHCO₃ resulted in a linear increase of weight gain (Rostagno, 1995).

Blood parameters have been increasingly used in poultry industry as a tool to detect physiological alterations and to help disease diagnosis. Wilson (1971) reported that hematology may be used to diagnose both quantitative and morphologic physiological alterations that might be associated to heat stress, such as changes in hematocrit, leukocyte counts and hemoglobin. According to Maxwell et al. (1990), hemoglobin was reduced when broilers were submitted to the stress caused by feed restriction, whereas the number of erythrocytes increased significantly. The increase in red cells may be due to higher release by the bone marrow, in order to compensate for the reduction in hemoglobin levels. Male broilers have higher erythrocyte counts, hemoglobin and hematocrit, but lower leukocyte counts than females, suggesting that males are more affected when submitted to a stress episode (Garcia, 1992).

The objective of the present study was to evaluate the effects of sodium levels and feed restriction on the performance and hematological values of broiler chickens from 22 to 42 days of age.

MATERIAL AND METHODS

Hubbard birds were sexed and a total of 1,440 birds were housed in 32 pens. During the initial phase (1-21 days), birds were managed according to Gomes et al. (1996). The experimental period corresponded to the growth phase (22-42 days), during which birds were submitted to feed restriction and different dietary calcium levels.

A completely randomized design was used in a 4x2x2 factorial arrangement with two repetitions of 30 birds each: 4 sodium levels resulting from the addition of NaHCO₃ to the basal diet (0.16%; 0.19%; 0.22% and 0.25%); feed restriction (with - w or without - w/o) and two sexes (male and female).

The experiment was conducted in a curtain-sided poultry house of 3 m height, 27 m length and 8.3 m width with asbestos-tiled roof and without air inlet. The poultry house was divided into 61 pens (1.5 m x 3.15 m), and wood shavings were used as litter material. Birds were given water and food ad libitum during the pre-experimental period (1 to 21 days). Initial feeders and drinkers were used until the tenth day and the environment was heated with infrared lamps. Gradually, according to the need and bird behavior, initial equipment was replaced by hanging tube feeders and bell-type drinkers. Light was provided continually (24 h) and a maximum-minimum thermometer was used to record the temperature inside the poultry house. During the experimental period, maximum temperature was 33ºC and minimum was 17ºC, so that mean temperature was 25.4ºC. Birds were given starter diet from 1 to 21 days and a grower diet from 22 to 42 days, as shown in Table 1.

Performance was evaluated by weight gain, feed intake, feed conversion and livability at 42 days of age. Blood samples were taken from two birds per parcel in the end of the experiment. The ulnar vein was punctured with disposable syringes containing heparin, and the blood was transferred to sterilized tubes. The samples were kept on ice and the following analyses were performed on the same day: erythrocyte count (He), hemoglobin (Hb), hematocrit (Ht), mean cell volume (MCV), mean cell hemoglobin (MCH), mean cell hemoglobin concentration (MCHC) and leukocyte count (LEU).

Total erythrocyte counts were obtained from blood diluted 0.02 mL in an automatic diluter CELM DA 500. The diluted sample was then analyzed in an automatic counter and the result was expressed in cell number/mm³.

Hemoglobin was determined by the cianometahemoglobin method. Cells were lysed and centrifuged for 5 min at 3,000 rpm. Color was read with a spectrophotometer at 540 nm and values were expressed in g/100 mL.

Hematocrit evaluation was done the microhematocrit method. Values were obtained by using appropriate tables and expressed in percentage.

Mean cell volume was obtained by multiplying the hematocrit result by 10 and dividing the result by erythrocyte count. The values were expressed in mm³.

Mean cell hemoglobin was calculated by multiplying the value of hemoglobin concentration by 10 and dividing the result by the number of erythrocytes. Values were expressed in picogram/cells (pg/cell).

Hemoglobin concentration in the erythocyte was calculated by multiplying hemoglobin by 100 and dividing the result by the hematocrit. Results were expressed in percentage.

White blood cell counts were determined using a Newbauer chamber and results were expressed in cell number/mm³.

Hematological analysis techniques used in the present study are in accordance to Jain (1986).

Birds were feed-restricted for 12 hours (7:00 to 19:00) daily throughout the experimental period (22-42 days), but had free access to water.

Data were statistically analyzed using the software ESTAT 2.0 (1992). Means were compared by Tukey's test at 5% probability level.

RESULTS AND DISCUSSION

Performance results are shown in Table 2. Different sodium levels in the diet had no effect on weight gain (p> 0.05). However, there was a significant effect of feed restriction and sex (p<0.05); males showed higher weight gain when compared to females and restricted birds had lower body weight gain. These results are similar to those obtained by Silva & Flemming (1990) and Borges (1997), who reported no effect of the different sodium levels given by bicarbonate on the weight gain of broilers.

Feed intake was not affected by different sodium levels (p>0.05), but it was influenced by feed restriction and sex (p<0.05). Restricted birds and males showed higher feed intake. These results corroborate results from Silva et al. (1994) and Branton et al. (1996), who reported that feed intake was not affect in broilers fed diets with 0.5% and 1.0% and 0.63% of sodium bicarbonate, respectively.

Sodium levels did not affect feed conversion (p>0.05), but full-fed birds showed better feed conversion (p<0.05). Silva & Fleming (1990) and Ali & Latshaw (1994) reported similar results showing no effect of dietary sodium levels on feed conversion when sodium bicarbonate was used.

Results reported herein are different from those reported by Teeter & Smith (1987), who showed that broilers submitted to a six-hour fast or to a twelve-hour restriction daily (Smith & Teeter, 1988) had no effect on weight gain. Lower feed intake and better feed conversion was also reported for restricted birds (Teeter & Smith, 1987; Smith & Teeter, 1988).

Livability was not affected by treatments (p>0.05), corroborating findings reported by Silva & Flemming (1990) and Borges (1997), who showed that sodium bicarbonate addition to the diet had no influence on the livability rate of broilers. Nevertheless, McCormick et al. (1979), Teeter (1989) and Garcia (1992) reported significantly better livability of birds submitted to feed restriction.

No hematological parameter was affected by treatments (Table 3). Such results are similar to those reported by Garcia (1992), in which no variation was seen on the blood patterns of birds housed under thermal stress. Junqueira et al. (1999) evaluated sodium bicarbonate supplementation together with ammonium chloride on the drinking water and found no effect of treatments on the hematological parameters.

Maxwell et al. (1990) studied the effects of feed restriction on erythrocyte characteristics and reported significant changes in Ht, He, Hb, MCV, MCH and LEU. Borges (1997) also reported similar values of He and Hb when different levels of sodium bicarbonate supplementation were used.

CONCLUSIONS

The findings of this study suggest that sodium bicarbonate given as sodium source in the diet, at the levels of 0.16%; 0.19%; 0.22% and 0.25%, do not affect broiler performance, however, feed restriction decreases weight gain and impairs feed conversion.

Hematological values (He, Hb, Ht, MCV, MCH, MCHC, LEU) are not affected by different sodium levels or by feed restriction

Arrived: december 2001

Approved: april 2003

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Publication Dates

• Publication in this collection
  12 Nov 2003
• Date of issue
  May 2003

History

• Accepted
  Apr 2003
• Received
  Dec 2001