Abstract

In the Dutch poultry meat production chain, first week mortality (FWM) of the chicks is an important measure to quality and is therefore highly related to the price of the chicks that the broiler farm has to pay to the hatchery. Therefore, next to the total number of broiler eggs produced per hen and hatchability, this figure is often used as a measure of efficiency in the breeder-hatchery-broiler production chain. In this study, factors that are related to chick mortality in the first week at broiler farms were investigated. Field data obtained from 2 commercial Dutch hatcheries, for which 482 broiler farms voluntarily recorded FWM of 16,365 flocks of broiler chicks over the years 2004, 2005, and 2006, were analyzed. These represented 79% of the total number of day-old chicks delivered to separate broiler farms. First week mortality was significantly related to breeder age, egg storage length at the hatchery, season, strain, feed company of the breeder farm, year, and hatchery. Furthermore, FWM differed significantly between chicks originating from eggs of different breeder flocks and which were kept for grow-out at different broiler farms.

INTRODUCTION

In the broiler production chain, the production of high-quality day-old chicks that are healthy and vigorous is crucial and is the hinge that determines the economic efficiency of the chain process. Poultry production in general and broiler production in particular are very important in the Dutch economy. In 2006, a total of 590 million broilers were produced for slaughter, 19.2% of which were exported, with a value of approximately 84 million euros (PVE, 2007). Mortality in broilers means a loss in income to broiler farms as well as to the hatcheries.

In addition to the above-mentioned economic importance, there are 2 main reasons to focus on first week mortality (FWM) in the Dutch broiler chain. The first reason is that FWM is an important measure for quality and is related with the price of the chicks that the broiler farm has to pay to the hatchery. The second reason is the new European Union directive, which aims to increase the welfare of broilers. Chick mortality is used as one of the indicators of the occurrence of welfare problems (European Union, 2007). The members of the European Commission agreed that high welfare standards at the broiler farm are conditional on the achievement of low mortality rates and guides to good management practice. Accordingly, to justify increased stocking density at the broiler farm, the daily cumulative mortality rate in at least 7 consecutive flocks should be below 1% + 0.6% × slaughter age of the flocks per day. When mortality rates are often too high, the broiler farmer should reduce the number of chicks in the next round.

At the broiler farm, the weekly mortality rate changes through time. According to Heier et al. (2002), the average weekly cumulative mortality during the first week was 1.54 and 0.48% a week during the remainder of the grow-out period.

The first week life of broiler chicks is important because modern broiler chicks grow faster than ever in their early days, resulting in a short lifetime at the broiler farm. In addition, the first few days of the chick’s life are a transitional period from a very conditioned life at the hatchery to a more independent life at the broiler farm. A major change occurs in the morphophysiology of the digestive, immune, and the thermoregulatory systems of the posthatch chicks. Furthermore, in the posthatch chick, the source of nutrients is replaced with an exogenous diet and the hatchlings switch from utilizing a yolk nutrient-based diet to a solid external feed diet. These changes require an adaptation period for the entire physiological system of the chick (Vieira and Moran, 1999). This means that there is more stress on management during the first week, which has to be able to establish a healthy appetite with good feeding and drinking behavior quickly to maximize their opportunity for growth. Therefore, the mortality rate during the first week can be an indicator of the performance of the flock during the rearing period.

Different factors affect the survivability and performance of broiler chicks at the broiler farm. The performance of a chick at the broiler farm depends on quality of the chick that is delivered, the daily management, and the housing environment at the broiler farm. Vigorous and healthy day-old chicks are the basis for a broiler flock to perform efficiently. Sick, underweight, dehydrated, stressed, or weak chicks will not perform to their genetic potential (Wilson, 1991, 1997; Joseph and Moran, 2005; Tona et al., 2005; Decuypere and Bruggeman, 2007). Breeder age affects the performance of a broiler flock differently throughout the grow-out period (Peebles et al., 1999). Furthermore, incubation condition, which is mostly related to breeder age (Joseph and Moran, 2005), and egg storage length (Tona et al., 2004) affect the performance of the chicks at the broiler farm. Lourens et al. (2005) mentioned the importance of controlling the eggshell temperature during the incubation period because it affects the rectal temperature (body temperature) of the chick during the first week.

Additionally, the potential of a chick to survive the first week is directly related to the quality of the day-old broiler (Goodhope, 1991). The day-old chick quality depends on the genetic line of the breeders, breeder age, egg weight, egg storage conditions and duration, and incubation conditions such as temperature, humidity, gas levels, and altitude (Wilson, 1991; Peebles et al., 1999; Vieira and Moran, 1999; Decuypere et al., 2001; Tona et al., 2004, 2005; Decuypere and Bruggeman, 2007). Moreover, according to the result from a field study using data of commercial Dutch hatcheries (Yassin et al., 2008), a good hatch result depends on flock, breeder age, the age at first delivery of hatching egg, strain, feed-providing companies of the breeder farms, storage length at hatcheries, season, and the hatchery.

Factors such as rearing season (Imaeda, 2000), shipping distance and delivery route (Chou et al., 2004), stocking density, flock size, feeding management, drinking system, ventilation, and floor insulation at the broiler farm (Heier et al., 2002) are related to FWM. According to Heier et al. (2002), for example, the mortality of large flocks and flocks with a high stocking density was significantly lower than in small flocks and flocks with small density. In addition Chou et al. (2004) found the lowest cumulative FWM in broiler chicks raised in rooms with open-curtain ventilation (1.30%) than those raised in rooms with negative-pressure ventilation (1.42%) and water-cooled ventilation (1.37%).

In contrast to previous studies, which were based on predesigned experimental protocols, the aim of this research was to study the relationship between several factors and FWM at the broiler farm, using field data from Dutch hatcheries. The effects of management factors that are related to breeders and hatcheries were addressed in this study.

MATERIALS AND METHODS

Description of the Data

First week mortality data, which were collected by 2 commercial Dutch hatcheries (Table 1), were analyzed. The data included 482 broiler farms, who voluntarily recorded FWM of 16,365 flocks of broiler chicks over the years 2004, 2005, and 2006. This covered 79% of the total number of day-old chicks delivered to separate broiler farms.

The statistical unit used is a broiler flock (i.e., a flock housed in 1 barn and that originates from 1 breeder flock or from a mixture of breeder flocks at a specific date and time). Note that it is possible that chicks from 1 breeder flock can be housed in different barns (at 1 or different broiler farms). Additionally, chicks originating from different breeder flocks can be housed in 1 barn (31% of the data set). In this case, more records (multiple origins breeder flocks per barn) were included but, in the model, a variable percentage of chicks delivered per breeder flock per barn was calculated for correction.

The data set included the following: flock code, breeder age (wk), length of storage at the hatcheries (d), number of eggs set, date of set, the age of the hens at first delivery, strain, feed company of the breeder farm, year, hatcheries, number of chicks sold to the broiler farm, broiler farm code, date of chick delivery, barn number, percentage of chicks delivered per breeder flock per barn, feed company of the broiler farm, and number of dead chicks in the first week.

First week mortality is calculated as the total number of chicks that died in the first week after housing (Dead chicks) as the numerator and the number of chicks housed (Housed chicks) at the start as the denominator:

graphic

Statistical Analyses

Data were analyzed using Genstat version 8 for Windows (VSN International, Hemel Hempstead, UK). The data structure was interdependent. Each breeder farm usually delivers all eggs to 1 hatchery and most of the time, a broiler farmer asks for chicks that are originating from a specific breeder farm. However, because a broiler farm uses the all-in-all-out system and a breeder farm delivers eggs to the hatchery on average twice a week, a hatchery might be forced to deliver a flock to another broiler farm that it does not usually deliver to. Therefore, FWM was tested using a generalized mixed model with the method of restricted maximum likelihood (Harville, 1977), where the logistic (logit) transformation was used. Effects of breeder flock and broiler flock per barn were included in the random part of the model.

Some restrictions were made in the data set. The breeder age was restricted between 25 and 65 wk to avoid molted flocks and the egg storage length between 2 and 14 d. In the data set, 12 strains were recorded, 8 of which were defined (Ross 308, Ross 508, Ross 708, Cobb, Cobb 500, Cobb 600, Hubbard, and Hybro) and 4 were not. Additionally, 16 feed companies of the breeder farm and 8 feed companies of the broiler farm were recorded, and 1 from both was undefined. If no strain of the breeder flock or no feed company of the breeder farm was known, a variable “unknown” was included in the data set.

The independent variables in the random part of the model were breeder farms and broiler farms, whereas age at start delivery to the hatchery (wk), breeder age (wk), egg storage length at hatchery (d), strain, feed company of the breeders, feed company of the broilers, hatcheries, and season were taken as explanatory variables in the fixed part of the model.

Statistical Model

Initially, all of the variables and interaction terms until the 4-way interactions were included in the so-called full model. A stepwise selection procedure was applied, starting to exclude nonsignificant 4-way interaction terms (P < 0.05, Wald’s test), then excluding the 3-way interactions, 2-way interactions, and single factors to come to the final model. Therefore, the final model included only significant single factors and interactions.

The final model is described as follows:

graphic

where C is the intercept, εbf is the random effect of a breeder flock [εbf ~N (0,σbf2,)], εbrf is the random effect of a broiler flock [εbrf ~N (0, σbf2,)], εbrf.s is the random effect of a broiler flock in a barn [εbrf.s ~N (0, σbrf.s2,)], H is the hatchery, A is the breeder age (number of weeks – 24), ES is the egg storage length at the hatcheries (d), B is the strain, YR is the year, FC is the feed company of the breeder farm, and d the dth day of the year in the seasonality function:graphic + graphic.

The following model choices were made. To allow for a (nonlinear) curve of FWM with breeder age, A + ln(A + 1) was included where A is the breeder age minus 24 wk. Furthermore, to allow for smooth seasonality effects, the function graphic + graphic was included and tested, using the date of chick delivery to calculate the dth day of the year (Grossman et al., 1986).

RESULTS

The FWM in broiler chick flocks ranged from 0.0% (5th percentile) to 3.3% (95th percentile) with an average of 1.5%. Furthermore, the results of the random model showed that there was a significant difference in FWM between flocks originating from different breeder farms and between flocks kept at different broiler farms (Table 2). The model explains 66% of the variation that occurred in FWM.

In the fixed part of the model, a lot of variables and interactions were tested to be significantly related with FWM [εbrf.s ~N (0, sbrf.s2,) and Table 2].

First, breeder age was related to FWM of the chicks at the broiler farm (P < 0.002; Table 2). On average, 1.82% of the broiler chicks died, if the breeder age was 25 wk. In breeder flocks aged between 38 and 44 wk, mortality was 1.02% and mortality increased to 1.20%, if the breeder flock was 60 wk. This hyperbolic curve is called the mortality curve (Figure 1; panels B to E).

Second, the egg storage length at the hatcheries was negatively related with FWM of broiler chicks at the broiler farms (P < 0.005) and its effect depended on breeder age (Figure 1; panel A). However, the difference between the different storage lengths was not large. The average increase in FWM per extra day storage at hatchery was 0.0018% (Figure 1; panel A). The effect of storage on FWM was related to the hatcheries; the increase in FWM for hatchery A was 0.0015% and for hatchery B 0.0022%.

Third, there was a significant difference in FWM among the broiler chick flocks, which originated from the 2 hatcheries. For breeder flocks that were 25 wk of age, the average difference in FWM between the 2 hatcheries was 1.13%. For breeder flocks that were between the ages of 37 and 44 wk, the average difference was 0.64%, and for 60-wk-old breeder flocks, the average difference was 0.75%.

Fourth, there was a significant difference in FWM in the different years. The average SD in FWM among the years was 0.21%, in which the lowest mortality was found in 2004 and the highest in 2006. Furthermore, the interaction hatchery × year (Figure 1; panel B) was also significant (P < 0.002), indicating that the difference in SD among the years was much smaller for hatchery A, which was on average 0.16%, than 0.29% for hatchery B.

Fifth, FWM in broiler chick flocks was related to the dth day of the year or in other words to the season (P < 0.001). The highest mortality (on average 1.18%) was found from mid-March until mid-April, whereas the lowest mortality (on average 1.08%) was found from mid-September to mid-October (Figure 1; panel F).

Sixth, a difference in FWM was found among the strains (P < 0.001; Figure 1; panel C). The difference in SD in FWM among the strains was 0.40% if the strains were 25 wk of age. If the strains were between 37 and 44 wk, the difference was 0.23%, and if the strains were 60 wk, the difference was 0.26%. Furthermore, there was a difference in FWM within the strains in different years (P < 0.001; Figure 1; panel D). The difference among the strains and within the strains was breeder age-dependent.

Finally, the feed company of the breeder farms was significantly related to FWM (P < 0.029; Figure 1; panel E). The effect of the feed company of the breeder farm on FWM of the broiler flocks was also breeder age-dependent. If the breeder age was 25 wk, the difference in SD in FWM was 0.46%, and if the breeder flock had an age between 37 and 44 wk, the difference decreased to 0.26%, whereas it increased to 0.31% if breeder age was 60 wk.

DISCUSSION

In this study, FWM was analyzed from data collected by commercial Dutch hatcheries. The data were collected based on voluntary reports on FWM at the broiler farms. Generally, the price of the day-old chicks is corrected for FWM, when mortality is higher than an agreed level, which is written down in the contract between the hatchery and the broiler farm. This economic incentive might have affected the motivation of the broiler farmer to report FWM and thus the reported level of mortality. However, the relations found between FWM and the different variables cannot be influenced by the reporting bias.

Furthermore, this study has the advantage of utilizing an extremely large field-based data set, with conclusions being based on significant relationships discussed in the light of experimental literature to suggest causality and to indicate where knowledge is lacking.

First week mortality is, in addition to other production criteria, an important performance measurement of the broiler farm. The potential of the chicks to survive the first week is directly related to the quality of the day-old broilers (Goodhope, 1991). Therefore, in this study, it was tested whether factors that have been shown to be related to hatchability and day-old chick quality such as breeder age, egg storage length, incubation condition, strain, and feed (Decuypere et al., 2001; Yassin et al., 2008) are also related to FWM.

Confirming the results of Heier et al. (2002), there was difference in FWM among flocks originating from different breeder farms. The difference in FWM may indicate the different management protocols followed at the breeder farms, which influence the performance of the chicks at the broiler farms. These management protocols concern nutrition and growth profiles related to photo stimulation (Renema et al., 2008). The significant influence of breeder management suggests that the broiler farmer needs information about the origin of the chicks to optimize management at the farm.

In addition, a significant difference in FWM was found among broiler farmers. This can be due to the difference in chick management upon arrival (especially floor temperature) and during the first week, which is mostly related to feed and water provision, housing environment (i.e., insulation and ventilation systems), stocking density, as well as health management.

First week mortality was highly related to breeder age following a negative hyperbolic shape. Increased FWM in broiler chicks was found more often for young breeders (Wilson, 1991; Peebles et al., 2004; Pedroso et al., 2005). Younger breeders produce smaller eggs with a larger proportion of albumen DM, a smaller proportion of yolk DM, and a thick shell, due to which the weight of the live chicks and the yolk sac content is smaller (Vieira and Moran, 1998a). There is a direct relationship between the nutrients provided by yolk sac and the subsequent performance of the chicks (Vieira and Moran, 1999). Generally, yolk sac content is high in fat and protein and low in carbohydrate, which is a direct source of energy. However, chicks of young breeders have a reduced yolk lipid mobilization and a reduced lipoprotein transfer to mobilize the energy for their development. This is usually associated with reduced viability of the chicks during the first week (Latour et al., 1998). Moreover, chicks from young broiler breeders have lower feed intake and BW during the first week compared with chicks from older breeders (Maiorka et al., 2004). Therefore, special management of chicks of young breeders is required during the first week. Adjustments of the temperature (house and floor) and height of drinking nipples; provision of required feed nutrients, especially energy source; as well as good health control are important measures.

The increased FWM for chicks from older breeders could result from bad navel and navel-yolk sac infections more often found in chicks from older flocks. Another reason for an increased mortality of chicks of older breeders is that eggs from older breeders hatch earlier (Suarez et al., 1997) and therefore the risk of dehydration of chicks increases with breeder age if management in the hatchery with respect to the time of collecting chicks is not adjusted. Because breeder age affects broiler performance throughout brooding to maturity phase (Peebles et al., 1999), breeder age should always be taken into consideration during any production management decision.

Storage length of eggs at the hatchery increased FWM at the broiler farms significantly. Merritt (1963) also found increased FWM with increased length of storage time, which was 2.2 and 2.9% for storage length of 1 to 7 and 8 to 14 d, respectively. It is also known that storage of eggs affects egg quality (Decuypere and Bruggeman, 2007; Fasenko, 2007), which subsequently affects the quality of the chick and depresses the relative growth during the first week at the farm (Tona et al., 2004).

First week mortality differed between broiler flocks that originated from the 2 hatcheries. Heier et al. (2002) also found a significant difference in mortality between flocks originating from various hatcheries in Norway. It was interesting to notice that the hatchery that had higher hatchability during the first study (Yassin et al., 2008) also showed higher FWM. The difference between hatcheries might be explained but needs further investigation, by a difference in egg sanitation practice, climate conditions during incubation and chick handling, transportation conditions, and the transport time to the broiler farms.

First week mortality was significantly different among the 3 yr: 2004, 2005, and 2006. Similarly, Heier et al. (2002) found difference in FWM in different years.

Seasonality of FWM in this study could be related to weather because of the temperate climate in the Netherlands. In addition, fluctuation in the market might have played a role. For example, in case of high market demand, the hatcheries mostly buy eggs from the free market to fulfill the extra need. These eggs, however, are mostly of varied quality and therefore might result in low-quality day-old chicks. Additionally, weather conditions, especially the temperature of the barn (floor and house), and ventilation are very critical and vary between seasons. From this result, it is concluded that breeder farms, hatcheries, and broiler farms should make adjustments of management practices on the season to maximize profit.

From the large-scale data analysis, difference of FWM was observed among the different broiler strains. This observation is in accordance with results from small-scale experiments. Some of the strain-related factors that influence chicks’ quality are the difference in egg weight (Vieira and Moran, 1998b) and embryo metabolic activity during incubation (Hamidu et al., 2007). A significant difference in mortality between strains after brooding stage through maturity was also found before (Awobajo et al., 2007).

The different feed-providing companies of the breeder farms caused a significant difference in FWM of the broiler chicks. It is well known that the nutrition of the parent is transferred to the chick embryo through the egg content (Wilson, 1997) and that the nutrition of the breeder hens affects the progeny viability and early growth (Kidd, 2003; Enting et al., 2007). Therefore, any aspect that reduces the quality and quantity of the required diet and results in undernourishment of the breeder could affect the chick’s viability at the farm.

In summary, there is interrelation between FWM at the broiler farms and management factors at the breeder farms (like the breeder age, strain, and feed company of the breeder farms) and at the hatcheries (like egg storage management, hatching management, and season). On-time information exchange and analysis of the production result and feedback from each chain participant to the partners is very crucial. Therefore, a good information exchange system is recommended for the chain to take timely measures and avoid probable management mistakes to result in a maximal chain profit. For this to be realized, good quality production data should be kept, analyzed, and interpreted to support a better management decision at each level of the chain.

Table 1

Description of the data set on first week mortality (FWM)

Independent variable Unit Range Average Total number Missing 
1Codes of the hatcheries. 
2Codes of the strains. 
3Codes of the feed companies. 
4Percentage of voluntarily reported FWM from the total number of flocks delivered by the hatcheries, which was 100% from hatchery A and 43% from hatchery B. 
Hatcheries involved code A and B1 — — 
Breeder flock code — — 511 — 
Broiler farms code   482 — 
Strain code R1 to R112 — 11 
Date of delivery at the broiler farm date Jan. 22, 2004 to Jan. 12, 2006 —  
Feed company of breeder farms code V1 to V163 — 16 
Feed company of broiler farms code MV1 to MV83 — 
Age of hens (breeder age) wk 24 to 65 41 — 34 
Egg storage length days 2 to 14  
Number of broiler flocks in 3 yr number — — 16,365 — 
Total number of chicken delivered per year  — — 99,430,748 — 
Response rate on FWM percent 79%4 — — — 
Mortality rate 5th, 50th, and 95th percentile percent 0.0%, 0.9%, 3.3% — — — 
Independent variable Unit Range Average Total number Missing 
1Codes of the hatcheries. 
2Codes of the strains. 
3Codes of the feed companies. 
4Percentage of voluntarily reported FWM from the total number of flocks delivered by the hatcheries, which was 100% from hatchery A and 43% from hatchery B. 
Hatcheries involved code A and B1 — — 
Breeder flock code — — 511 — 
Broiler farms code   482 — 
Strain code R1 to R112 — 11 
Date of delivery at the broiler farm date Jan. 22, 2004 to Jan. 12, 2006 —  
Feed company of breeder farms code V1 to V163 — 16 
Feed company of broiler farms code MV1 to MV83 — 
Age of hens (breeder age) wk 24 to 65 41 — 34 
Egg storage length days 2 to 14  
Number of broiler flocks in 3 yr number — — 16,365 — 
Total number of chicken delivered per year  — — 99,430,748 — 
Response rate on FWM percent 79%4 — — — 
Mortality rate 5th, 50th, and 95th percentile percent 0.0%, 0.9%, 3.3% — — — 
Table 2

Estimates, SE, and χ2 probability of the fixed model

Variables  Descriptions  Estimates  SE  χ2 probability 
1εbf, εbrf, and εbrf.s are the variation components of the model. 
2Ref = the reference used in calculating the estimates. 
εbf1  Breeder flock  0.0304  0.0068  0.001 
εbrf1  Broiler flock  0.5452  0.0408  0.001 
εbrf.s1  Broiler flock × barn  0.0000  Bound  — 
C  Intercept  −4.38  0.2   
β 1* H  Hatchery    0.12  0.001 
A  Ref2     
B  0.62     
β 2* Age  Breeder age  0.03  0.003  0.002 
β 3* ln(Age+1)  ln(Breeder age + 1)  −0.46  0.04  0.001 
β 4* ES  Egg storage length  0.002  0.004  0.005 
β 5* B  Strain  0.22  0.43  <0.001 
β 6* YR  Year    0.21  <0.001 
2004    Ref     
2005    0.29     
2006    0.34     
β 7* B*YR  Strain ×·year    0.45  <0.001 
2004    Ref     
2005    0.13     
2006    −0.18     
β 8* FC  Feed company  0.05  0.2  0.029 
graphic  Sine of the dth day of the year  0.04  0.02  <0.001 
graphic  Cosine of the dth day of the year  0.11  0.01  <0.001 
β 11* H*YR  Hatchery × year    0.11  0.002 
A-2004    Ref     
A-2005    Ref     
A-2006    Ref     
B-2004    0.00     
B-2005    −0.36     
B-2006    −0.31     
Variables  Descriptions  Estimates  SE  χ2 probability 
1εbf, εbrf, and εbrf.s are the variation components of the model. 
2Ref = the reference used in calculating the estimates. 
εbf1  Breeder flock  0.0304  0.0068  0.001 
εbrf1  Broiler flock  0.5452  0.0408  0.001 
εbrf.s1  Broiler flock × barn  0.0000  Bound  — 
C  Intercept  −4.38  0.2   
β 1* H  Hatchery    0.12  0.001 
A  Ref2     
B  0.62     
β 2* Age  Breeder age  0.03  0.003  0.002 
β 3* ln(Age+1)  ln(Breeder age + 1)  −0.46  0.04  0.001 
β 4* ES  Egg storage length  0.002  0.004  0.005 
β 5* B  Strain  0.22  0.43  <0.001 
β 6* YR  Year    0.21  <0.001 
2004    Ref     
2005    0.29     
2006    0.34     
β 7* B*YR  Strain ×·year    0.45  <0.001 
2004    Ref     
2005    0.13     
2006    −0.18     
β 8* FC  Feed company  0.05  0.2  0.029 
graphic  Sine of the dth day of the year  0.04  0.02  <0.001 
graphic  Cosine of the dth day of the year  0.11  0.01  <0.001 
β 11* H*YR  Hatchery × year    0.11  0.002 
A-2004    Ref     
A-2005    Ref     
A-2006    Ref     
B-2004    0.00     
B-2005    −0.36     
B-2006    −0.31     
Figure 1

A) Increase in first week mortality (FWM) in relation to egg storage length at the hatchery. B) Difference in FWM between chicks originating from 2 hatcheries in years. C) The difference in FWM among strains. D) The difference in FWM within strains in years. E) The difference in FWM in relation to different feed-providing companies of the breeder flock. F) The seasonality of FWM.

Figure 1

A) Increase in first week mortality (FWM) in relation to egg storage length at the hatchery. B) Difference in FWM between chicks originating from 2 hatcheries in years. C) The difference in FWM among strains. D) The difference in FWM within strains in years. E) The difference in FWM in relation to different feed-providing companies of the breeder flock. F) The seasonality of FWM.

We thank hatcheries Probroed & Sloot in Groenlo and Meppel, the Netherlands, and Munsterhuis in Saasveld, the Netherlands, for providing the data and “Stichting Fonds voor Pluimveebelangen” in the Netherlands for funding the project.

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