Prevalent diseases and mortality in egg type layers  under subtropical environment

M Farooq, M A Mian, F R Durrani and M Syed

Faculty of Animal Husbandry and Veterinary Sciences,
NWFP, Agricultural University, Peshawar, Pakistan.
geanes@psh.paknet.com.pk   ,  durraniff@yahoo.com

Abstract

This study was carried out during the years 2000-2001 in 109 flocks to investigate prevalent diseases and mortality in egg type layers in Chakwal district. Mortality was defined as the sum of culled and dead birds during a 52 week period prior to disposal of the flock.

Overall mortality due to various anomalies was 6.67% and there was no known etiology for around 2% of the losses. 2.74% of birds were culled over the whole period. Diseases caused higher mortality during brooding (50.4%) and laying (31.3%) than during growing (18.3%). Coccidiosis was the major problem causing 19.1% mortality with higher incidence during brooding and in birds kept on the floor.  Egg prolapse and enteritis resulted in 12.1% and 8.4% mortality, respectively. About 7% of loss was due to disease outbreaks including E. coli, Infectious Coryza and Chronic Respiratory disease (CRD). Losses due to Infectious Bronchitis (IB), Omphalitis, yolk sac infection, ascities and feed toxicity in each case were around 6%, while Hydro-pericardium syndrome and cannibalism caused below 5% losses. Overall mortality was 11.4±1.14% with a coefficient of variation of 108%, representing a relative percent mortality rate of 31.4±0.46, 25.5±0.53 and 43.2±0.49 during brooding, growing and laying periods, respectively. Hygienic condition, housing system, cage vs. floor rearing, strain of the chicken and flock size affected mortality in egg type layers. Mortality was found negatively correlated with peak lay (r= -0.43; p<0.001), percent lay (r= -0.29; p<0.002), hen-day egg production (r= -0.25; p<0.017) and net profit per bird (r= -0.68; p<0.001) but positively correlated with age at first lay (r= 0.19 p<0.04). Higher mortality at any stage was observed in small sized flocks, overcrowded houses and birds maintained under poor hygienic conditions. Mortality during lay was also higher in birds kept on the floor than those in cages.

Avoiding overcrowding, effective use of  brood-grow house under better hygiene, appropriate light schedule and use of cages instead of floor houses for egg type layers will reduce mortality.

Key words: Stocking density, cage vs floor rearing, Coccidiosis, culling, mortality, housing, hygiene 

Introduction

Mortality plays a major role in determining profit from egg type layers and is a function of dead and culled birds over the growth and production period.  A negative association of mortality with net profit in chicken production has been reported by Farooq et al (2001), Zaheer-ud-Din et al (2001) and Asghar et al (2000). Kitsopanidis and Manos (1991) also reported a reduction in net profit when mortality was more than 2-5%,  whereas North (1984) reported poor economic performance of egg type layers at mortality level of more than 10%. Chew (1983) reported a mortality in layers ranging from 3.1 to 18%. Mortality in egg type chicken at any stage of life will affect performance of egg type layers; however, higher mortality during the laying period will badly affect productivity. Ghodasara et al (1992) reported relatively higher mortality rate during laying (49%) than during the brooding (26%) and growing period (24%), resulting in poor performance.

Possible causes of higher mortality in egg type layers could be severe out breaks of infectious and non-infectious diseases, accidental deaths, substandard hygiene/management conditions, poor quality chicks/feed and egg prolapses. A higher incidence of Salmonellosis was found in flocks maintained under poor management conditions (Majid et al 1991). The most prevalent diseases resulting in higher mortality in egg type layers were Infectious Bronchitis (90% mortality; Rikula et al 1993), Infectious Bursal disease (40.4%, Anjum et al 1993), Newcastle disease (51.5%, Amin et al 1995), Coccidiosis and yolk sac infection (35.2 and 31.4%, respectively; Ghodasara et al 1992). According to North (1984), coccidiosis was more detrimental beyond the age of 20 weeks as it adversely affected egg production performance of egg type layers. The author stated that layers should develop full immunity against coccidiosis before the egg production process is initiated as coccidiosats are not added in the layer ration and an incidence of coccidiosis during the laying period would therefore result in poor egg production. Egg prolapse was one of the serious problems reported to cause 9.4% mortality in egg type layers (Tablante et al 1994). Besides its direct contribution to mortality, it usually leads to cannibalism in the flock causing additional loss.

Age of the chicken and onset of seasonal and climatic conditions could also play a major role in prevalence of the diseases. Birds vaccinated against IBD before the 10th day-age were more affected than others (Anjum et al 1993). Singh et al (1994) reported higher prevalence of IBD, Coccidiosis, E. coli and other bacterial infections in between the age of 6 and11 weeks, than at the age of 18 to 22 weeks. Assurance of a healthy environment (Khurshid et al 1995), effective vaccination against diseases, antibiotic therapy, maintenance of healthy environment and protection of birds from extreme climatic conditions could reduce incidence of mortality many folds according to Mukherjee and Khamapurkar (1994).

The present study was an effort to investigate prevalent diseases and mortality in egg type layers at various stages of life and suggest effective strategies to minimize mortality.

Materials and methods

Data source and prediction of sample size

The present study was carried out during the years 2000-2001 to investigate mortality and prevalent diseases in egg type layers in Chakwal, Punjab, Pakistan.  Sample size for the study was predicted by calculating the coefficient of variation from the data generated in the same area by Tariq et al (2000). Maximum coefficient of variation was found for total number of eggs produced/flock and was selected as an index for predicting sample size to accommodate both maximum and minimum values of variations in other production and economic traits. The following model, developed by Casely and Kumar (1989), was adopted for determining sample

                          K² * V²  

                       N =   -----------

                                     D²

Where “N” was sample size, “K” the normal deviation at 95% confidence interval, “V” the coefficient of variation of the selected variable and  “D” the margin of error assumed to be 0.1.

Data collection

After predicting the required sample size, data from 109 flocks regarding shed capacity, flock size, strain of the chicken, mortality, culling, causes of mortality, system of housing, rearing facility (cage vs. floor), hygienic measures adopted, vaccination practice, egg production traits, cost of production and returns were collected. The hygienic status of the farm was categorized as good, average and poor on the basis of floor and house construction, vicinity of the farm, distance between sheds or other dwellings, house conditions, “all in… all out” system, cleanliness and sanitation of equipments/houses and disinfecting procedures adopted. All the farmers were following a standard vaccination/debeaking program advised by the chick suppliers.  Density of layers in a shed was assessed on the basis of number of chicks or birds/m². Deviation above or below the recommended level was grouped as over or under utilization of the available space.

Data analysis

The data were analyzed, using relevant statistical techniques, namely, univariate, weighted mean procedures, Pearson’s correlation, general linear model (GLM) procedures and production functions.

Weighted means or averages

To account for the wide variability in flock size, weighted means were calculated instead of simple averages, using the following equation;

                                               S WiXi                          

                               X =   ----------------------                 

                                                  SWi   

Where  “X “ was the weighted mean, “Xi “ the variable, “Wi” the weight factor / number for a particular variable. The effect of density of birds/m² area in the shed, hygienic condition on the farm, strain of chicken, flock size, cage vs. floor rearing and system of housing on overall mortality in egg type layers maintained was studied adopting the procedure of Steel and Torrie  (1981). The following statistical model was constructed to ascertain the effect of aforementioned model on overall mortality;

       Y_ijklmno = µ + a_i + b_j + c_k + d_l  +  e_m  + f_n  + (axb)_ij  +  g_ijklmno  

Where “Y_ijklmno“ was the response variable (overall mortality in egg type layers),  “µ” the population constant common to all observations, “a_i“ the effect of i-th hygienic condition of the farm (i= poor, average and good), “b_j“ the effect of j-th fdensity of birds/m² (j= over utilized, optimally utilized and under utilized),  “c_k“ the effect of k-th housing system (k = brood-grow-lay house, brood-grow house and grow -lay house), “d_l” the effect of l-th housing facility (l= cage vs. floor rearing), “e_m” the effect of m-th flock size (m= small; <1000, medium; >10000<20000 and large; >20000), “f_n” the effect of n-th strain of the chicken (n= Babcock, Nick-chick, Hyline and Hisex), “(axb)_ij“ the interaction between i-th hygienic condition and j-th density of birds/m² and “g_ijklmno” the residual term associated with each Y_ijklmno, normally, independently and identically distributed with mean zero and unit variance.

Pearson's correlations between mortality, age at first lay, peak lay, percent lay,  hen-day egg production, egg laying period, cost of production, therapeutic cost and net profit per bird were worked out using the following formula,

                        r_X,Y       =          Cov (X,Y)

                                                   ó_xó_y

Results and discussion

Prevalent diseases in egg type layers

Necropsy  records maintained on the farms were scrutinized to investigate prevalent diseases. Overall mortality due to various anomalies was 6.67%. No necropsies’ records were available for around 2% losses. Total mortality due to various anomalies revealed higher prevalence of diseases during brooding (50.4%) and laying (31.3%) than during growing (18.3%). Coccidiosis was found as a major problem. Ghodasara et al (1992) reported higher incidence of coccidiosis (35.3%) than the present findings (23.4%). Relative rate of coccidiosis among layers in Chakwal revealed higher mortality during brooding than during laying. The higher incidence of coccidiosis than any other disease in the present findings may be attributed to poor hygienic conditions on the farms coupled with poor management

Egg prolapse was the second most prevalent problem. Tablante et al (1994) reported lower mortality (9.4%) due to egg prolapse than the present findings. Enteritis was another major problem in the present study.  Farooq et al (2001) reported an almost similar incidence of CRD, Coryza and E. coli but higher incidence of IBD in egg type layers among the cases submitted to the Poultry Research Institute in Chakwal. Higher losses due to IBD have also been reported by Rikula et al (1993) and Amin et al (1995) compared with the present findings. In the current study, the  data on the prevalent diseases which revealed lower incidence of infectious diseases like ND and IBD indicate the effective role of vaccination for infectious diseases and the need for good hygiene and management conditions.

Mortality and management

Overall mortality was higher in Hyline and Hisex strains thanin Babcock and Nick-chick (Table 2).  Petek (1999) and Tolimir and Masic (2000) also reported differences in mortality among various strains of egg type birds.       

Mortality was higher in small than in large sized flocks (Table 3). Verma and Singh (1997) and Farooq et al (2000) also reported higher mortality in small than in large sized flocks. The findings of the present study suggest that flock owners maintaining a larger flock size would have ensured better utilization of inputs and available resources to avoid undue risks of mortality.

Mortality was higher in flocks produced in brood-grow-lay houses than in those produced in brood-grow and lay houses (Table 4). 

Mortality rate was highest in over-crowded houses and lowest in house with the optimum bird density (Table 5).

Mortality decreased as hygiene improved (Table 6). Asghar et al (2000) and Zahir-ud-Din et al (2001) reported higher mortality in chickens under poor hygienic conditions in densely populated houses. Adams and Craig (1985) and Carey et al  (1995) also reported higher mortality in overcrowded houses. Exposure of birds to more adverse and stressful conditions in crowded houses is likely to result in lowered immune response of chicken to resist diseases.

Lower mortality was found among flocks reared in cages than in those kept on the floor (Table 7).  Horne-Van and Van-Horne (1994) and North (1984) also reported higher mortality in flocks kept on the floor than those kept in cages. This can be attributed to poor litter management and greater disease risk. Coccidiosis during the laying period was higher in birds kept on the floor than in cages. 

Mortality was negatively correlated with peak lay (r = -0.43), percent lay (r = -0.29), hen-day egg production (r = -0.24) and net profit per bird (r = -0.68) but tended to be positively correlated with age at first lay (r= 0.19). The findings suggested that increased rate of mortality delayed age at first lay and resulted in a decrease in egg production performance and profit.

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Received 4 February 2002

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