Background and Objective: Alternative production systems have been welcomed and supported by consumers and egg producers. However, the classic free-range layer farming is a profitable business and suitable to produce egg and meat. The production performance of a layer is determined during the rearing phase. Thus, proper management is essential in order to achieve adequate weight and body composition at the beginning of the production phase so that the birds may reach the fullness of their genetic potential. In this sense, this study was conducted to evaluate the effect of the management on maintaining the weight uniformity of birds during rearing phase and on the production performance of laying hens. Materials and Methods: This study used the database of the Laboratory of Poultry Science, referring to Hy Line Brown® chickens of the AVIUFSC Lot 018, raised during the period from March 28, 2019 to January 22, 2021. The obtained data were used to determine the growth curves until the end of the rearing phase. The data were also used for exploratory principal component analysis (PCA). Mean and variance of body weight per week per group in the rearing phase before and after the relocation was calculated. Results: Raising semi-heavy chickens without controlling weight uniformity during rearing phase produced lighter and more heterogeneous pullets. During rearing, grouping of pullets according to their weight produced more uniform and heavier pullets at transfer age. Heavier pullets become hens with higher egg production per week up to 49 weeks of age. Conclusion: Grouping of pullets according to weight during rearing phase produced more uniform and heavier pullets at transfer age.
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Layer farming has greatly developed in Brazil due to increased technological investment in genetic improvement, nutrition, health and management of commercial strains. In addition, the growing demand for high quality and low-cost animal protein has increased the per capita egg consumption (255 eggs per capita in 2021) that is almost 4 eggs more than the previous year1.
Commercial layer farming depends on the production of a quality chicken. Therefore, Therefore, it is essential to acquire healthy chicks from suppliers. Proper poultry management is an important component from arrival of chicks at the farm to the growth and transfer of the birds to the production house. Thus, with adequate weight and body composition at the beginning of the production phase, the birds will tend to reach the fullness of their genetic potential. If the flock has problems during rearing phase, the deficiencies are unlikely to be corrected in the production phase2.
Chicken weight is the most practical and common way to evaluate flock quality, at rearing. However, at the time of transfer to the production house, the weight should not be considered as the only evaluation tool, it should be accompanied by a history of bird development3.
The development of laying birds follows a multiphase pattern. The first growth wave occurs from the first to fifth week of age, a period when the digestive system and vital organs develop rapidly. The second growth wave occurs from the sixth to the twelfth week of age, a period when the bones, muscles and feathers develop most rapidly. Finally, the third growth wave occurs from the 12th week until the end of the rearing phase, when the development of the reproductive system occurs4,5. Thus, the maintenance of optimal growth, in each of the phases, will be reflected in the productivity of the future chicken. It is also desirable to end the rearing phase with a good fat reserve in order to provide body reserve for the pre-peak phase that can lead to sudden increase in egg production when birds are still growing and have low feed intake6.
This project was developed to evaluate the effect of body weight of laying hens during rearing, laying and production phase. The present study aimed to evaluate the effect of homogenization management of laying hens on pullet development and its implications on the productive characteristics during the productive phase.
MATERIALS AND METHODS
Bird management and facilities: The heating, lighting, vaccination and feeding program for Hy-Line Brown chicken was managed according to the manual. The birds were reared up to 17 weeks of age (rearing phase) and they were transferred to the production house at 8 weeks of age and grouped according to the weight. The rearing house was divided into three stalls, equipped with a tubular feeder and pendular (bell type) drinking trough, providing food and water at will.
The production house was also divided into 3 units, for Light weight (16 m2), Medium weight (30 m2) and Heavy weight (16 m2) birds. Each unit was equipped with tubular feeders, pendular drinkers, nests for egg collection and perches. The birds had access to external enclosures for foraging and performing other natural behavioral practices. The pasture was composed of grass (Cynodon dactylon) and Cynodon spp.. Population density in the outdoor environment was two birds per m2.
Experimental birds were handled as recommended by the manual of the strain. Birds were vaccinated according to the standard protocol of the Aviculture-UFSC Laboratory. The birds were weighed weekly, until culling of birds, at 92 weeks of age. Eggs were collected four times a day, three in the morning and one in the evening.
Experimental design and variables analyzed: To conduct this study, the database of the Laboratory of poultry science was used, referring to Hy Line Brown® chickens of the AVIUFSC Lot 018, raised during the period from March 28, 2019 to January 22, 2021, making up 92 weeks of age. Upon housing, the birds were weighed individually to obtain the average weight and standard deviation (33.5 g±3.36 g), Birds were divided into 3 groups according to their weight: Light weight group (23-29 g, n = 75), Middle weight group (30-36 g = 150) and Heavy weight group (37-44 g, n = 75). The birds were weighed weekly and at eight weeks of age, they were regrouped, according to the new weight. The new categories established were: Lightweight (<600 g = 75), Middle weight (651-690 g = 150) and Heavyweight (>690 g, n = 75).
The growth profile of the pullets during the entire rearing phase (up to 17 weeks of age) was performed to verify the effect of grouping on the productive performance of the hens. The growth curve for different weight categories was obtained by weighing the pullets weekly from day 0-8 weeks of age. Using these data, the prediction equations for the growth curve up to 17 weeks of age were determined, when the birds were transferred to the production phase.
After regrouping, weight of the birds was maintained until transfer to the production phase. These weighing data were used to determine the growth curves until the end of the rearing phase. The data obtained were also used for exploratory principal component analysis (PCA), to verify if the regrouping of the birds at 8 weeks of age improved the production performance of the hens.
Average egg production per bird per week was recorded from start of laying to 49 weeks of age to measure the production performance of hens. That is, in each week it was found that which group of birds (heavy, medium, or light) showed the highest egg production per bird. The hens with the highest egg production per week were placed in class 1 and those with the lowest production were placed in class 2.
Mean and variance of body weight per week per group in the rearing phase before the relocation (from housing to 8 weeks of age) and after the relocation (from 7-17 weeks of age) was calculated. The influence of regrouping according to the weight of birds in classes 1 and 2 was also studied.
RESULTS AND DISCUSSION
The predicted growth curves up to 17 weeks of age in pullets of different weight categories are shown in Fig. 1. It is possible to observe that during the rearing phase, body weights fit a simple linear regression model.
The analysis indicated that during the rearing phase, birds were classified as “heavy birds” at housing (weight = 0.098753/week). The probability value (p = 2.2*1016) showed a linear relationship between the data. Coefficient of determination (R2 = 0.9697) indicated 96.97% of the variance for a dependent variable and best fit of the model to the data. The regression analysis for the average weight of birds from 0-8 weeks of age is presented in Table 2.
The analysis indicated that during the rearing phase the average weight of bird was 0.0890086/week. The p-value (2.2*1016) and coefficient of determination (R2 = 0.9668) indicated that there was a linear relationship between the weight and age of birds (weeks) and the linear model explained 96.68% of the variance in weight and age (weeks) and model was best fit for the given data set. The regression analysis for the light weight birds from 0-8 weeks of age is presented in Table 3.
Figure 2 shows the predicted growth curve for birds during the rearing phase. Table 3 indicates that the weight of “light weight birds” is 0.0813154/week. The probability value (p = 2.2*1016), showed that there was a linear relationship between the data and a coefficient of determination (R2 = 0.958) indicated 95.8% of the variance in weight and model was best fit for the given data set.
For each weight class the good fit models for the given data set were obtained. These models made it possible to obtain the predicted mean values for each weight class from housing to 17 weeks of age. It means that it is possible to find out the average weight that each group of birds would attain in each week until their transfer to the production house.
Using these equations, the predicted values for the weights of the animals for the entire rearing period (week 0-17) was calculated. Figure 2 shows the predicted growth curve for the rearing phase.
During the rearing phase, growth of birds is natural in a heterogeneous manner and it may be possible to have larger pullets and lighter birds in the same flock7. This weight variation present since hatching, tends to increase as the birds grow, making the flock increasingly non uniform in Fig. 2. However, weight uniformity at the time of transfer is considered profitable because homogeneous flocks reach sexual maturity at the correct age with higher peak of laying and more uniform egg production. It also leads to higher number of eggs per bird and decreased occurrence of prolapse8,9. There was a correlation between the body weight of the birds at rearing and egg production. Ray et al.9 and Los et al.10 have already indicated this hypothesis that focused on the need of establishing reference periods regarding control and uniformity of body weight. Therefore, inadequate management at the time of training of the birds, in its different structures, can negatively impact the performance of birds in the production phase.
For this reason, at 8 weeks of age, the birds were regrouped, according to the new weight standards achieved. The new categories established were: Lightweight (<600 g, n = 75), Middleweight (651-690 g, n = 150) and Heavyweight (>690 g, n = 75). Pullets remained in their respective categories until transfer to the production phase at the end of the 17th week. With the individual weighing data, obtained weekly from this regrouping, it was possible to construct new growth curves until 17 weeks of age (Table 4).
Table 4 shows the growth profile and weight (0.1100256/week) of the pullets. This model had a significant p-value (2.2*1016), indicating a linear relationship between the data and coefficient of determination (R2 = 0.9852) indicated 98.52% of the variance in weight and the model is best fit to the data studied.
Table 5 presents the results of the regression analysis for the middle weight group of birds during rearing, considering regrouping by weight at 8 weeks. Table 5 shows the growth curve for the average weight of birds (Weight = 0.100432/week). This model had a significant p-value (p = 2.2*1016), indicating a linear relationship between the data and a coefficient of determination (R2 = 0.9864) indicated 98.64% of the variance in weight and best fit of the model to the data. Regression analysis of light weight birds at 8 weeks of age is presented in Table 6.
Growth of lightweight pullets with weight = 0.0962586/week is presented in Table 6. This model had a significant p-value (2.2*1016), indicating a linear relationship between the data and coefficient of determination (R2 = 0.9756) showed 97.56% of the variance in weight indicating a good fit of the model to the data.
All the obtained models for each weight category showed best fit to the data, it was possible to obtain the average growth values of the birds until the transfer to the production house (Fig. 3). It is important to note that this model considers relocation at 8 weeks of age.
Figure 4 shows the importance of the grouping according to weight at rearing and at 8 weeks of age and its impact on the characteristics of the birds at transfer. Regrouping of pullets at rearing increased the weight of birds of all categories (p<0.01-comparison by t-test of angular coefficients), indicating the importance of this management practice. -In Middleweight and Lightweight category reduction in body weight was observed due to the fact that the birds in these groups were more homogeneous (Fig. 4).