In recent years, interest in the welfare of hens has been increasing. The public and activist groups than by scientific evidence have influenced much of current European legislation on the welfare of laying hens more. These groups proposed that the European Union abolish the cage housing system by the enriched cage system (750 cm2 of surface per bird); where the hens also have perches and nesting material (Bulmer y Gil, 2008). In this regard, in the United States of America, it is expected that by the year 2025 more than 90 % of the production of egg for plate will be carried out in cage-free systems (Regmi et al., 2018). However, conventional cages are still the main housing system for laying hens in the world, although this system has been for limiting the hens' ability criticized. to express certain behaviors (Khumput et al., 2018). On the other hand, poultry farmers believe that the productivity of hens housed on the floor has a higher productive performance (ItzaOtiz et al., 2016). In this regard, Camphell et al., 2017, reported that hens housed on the floor have a higher expression of behavior.
In Mexico, the world's first consumer per capita and fourth largest producer of egg for dishes (UNA, 2019), the main housing production system is conventional cages, but due to social and cultural situations, other systems also coexist, making it particularly interest to carry out studies in this regard.
Therefore, the objective of this study was to evaluate the variables of egg production, behavior, health status and physical quality; as indicators to determine animal welfare in Bovans White laying hens housed on the floor.
MATERIAL AND METHODS
The study was carried out at the Experimental Center for Poultry Research and Extension (CEIEPAv), of the Faculty of Veterinary Medicine of the National Autonomous University of Mexico, located in Mexico City, at an altitude of 2,250 meters above the level of the sea, and with an annual average temperature of 18 ºC (FMVZ, 2019). A batch of 50, 22- week-old Bovans White laying hens were housed on the floor; one hen for each 1,200 cm2, and as an additional accessory in its housing nest boxes were placed; they had no hangers. They were provided with a diet that covered recommendations for laying hens of the National Research Council,1994. During the 40 weeks of the study, they were provided with food and water ad libitum, and they had a photoperiod program of 16: 8 hours (light: dark). The temperature and humidity of the house remained at 20 ± 3 ºC and 65 to 70 % relative humidity, respectively. The hens were evaluated at 22, 30 and 62 weeks of age. The Ethics Committee (number DC-2017/1-5) of the Faculty of Veterinary Medicine and Animal Husbandry of the National Autonomous University of Mexico (UNAM) approved this study protocol.
The equation described by Dell et al., 2002, was used to compare groups of continuous variables: 𝑛 = 1 + 2𝐶 (𝑠/𝑑)2. Here C is a constant that depends on the value of selected α and β, where α = 0.05 and 1- β = 0.9; where s is the standard deviation of the variable to study, and d is the magnitude of the difference, which depend on the response variable; in our research, they were the behaviors to be evaluated. To determine the sample size with significant results, the number of subjects at the end of the study must be considered. For this purpose, the following calculation was performed: n (1/1-R), where: n represents the number of subjects without losses and R is the proportion of expected losses (García et al., 2013).
The averages of the productive data of the flock of the following variables were obtained: feed per bird/day, conversion rate, percentage of laying or egg production, mortality, percentage of dirty egg and percentage of broken egg.
Video cameras (Samsung HMX-F800 and Cannon VIXIA HF R70) were placed in front of the hens to accustom them to their presence and record their behavior (Martin y Bateson, 1993). A final focal observation range of 400 seconds per hen was selected between 10:00 a.m. and 11:00 a.m. as the designated time interval (Mishra et al., 2005). An ethogram was to assign the percentage, frequency and total time of observed behaviors developed, using the CowLog computer program (Haninnen y Pastell, 2009) with the Ubuntu Linux 8.04 operating system to create databases for the behaviors to be observed.
To know the health status of the hens, their feathers, legs and combs were evaluated with a modified rating system (Welfare Quality, 2009).
Physical quality of the egg
Weighing of all the eggs obtained from a single day, at 22, 30 and 62 weeks of age of the hens (Ohaus Navigator Digital Scale Model N1D110, (capacity 4,100 g and precision of 0.1 g) was performed; the length and Egg width (digital Vernier), shell thickness, diameter and yolk height. Albumin height (Haugh units) and yolk color were measured (Eggware VI.06, Technical Services and Supplies Inc).
The physical quality of the egg was analyzed with the Student's t-test and the behavioral data with the Wilcoxon test (IBM. SPSS Versión 21, 2012). The P value < 0.05 indicated the statistical significance. On the other hand, the accumulated percentage was used to assess the state of health and the averages (tabulated data) of the productive variables of the flock were obtained.
The following productive variables (table 1) in the flock were evaluated to detect any deficiency or sanitary problem during the study period. A greater increase in the conversion rate, feed consumption, and percentage of dirty egg was observed at week 62.
The most relevant differences between the behaviors were in the first instance in Frequency (Table 2). Differences (P < 0.05) were observed in the behaviors as Lie, Explore, Forage and Ground bath; the week with the most differences is 62 versus 22 and 30. On the other hand, Ground bath, lie down and stand is greater in week 62, with fewer frequencies in grooming, exploring and foraging behaviors. Likewise, in Time, in the Grooming behavior, differences were observed (P < 0.05), between week 30 versus 62. In addition, in the behaviors Feeding, ground bath, Lying, Exploring, Foraging, Standing and pecking the housing, the week that the most differences presented are 62 versus 22 and 30. Feeding and pecking the housing was greater in week 30. Ground bath, lying down and standing occupied a longer time in week 62, with less time in the grooming, exploring and Forage.
With respect to the correlations evaluated, only in the behavior Feeding was a positive correlation (0.91) of interest was observed between week 30 and 62.
Health condition. In the housing system, the rating of 1 was maintained for both indicators in legs and feathers. On the other hand, in week 62 the comb indicator was with a rating of 2 in 100 % of the hens observed (Table 3)
Physical quality of the egg. The differences between comparisons of the weeks (Table 4) show that only in Shell weight and Yolk height there are no differences between weeks. Week 22 was the one in which the most differences were found with the other weeks, having lower average values in Egg weight, Yolk color and Yolk diameter; this same week it has the highest values in the other variables.
Productive variables. The results generally complied with the provisions of the Bovans White line product guide by parent company Hendrix Isa, 2019; however, at week 62 feed consumption, conversion rate, and percentage of dirty eggs increased, which coincides with that reported by other authors (Ahammed et al., 2014; Golden y Anderson, 2012; Holt et al., 2011). It is important to highlight the concept of food safety, since the percentage of dirty eggs is a much-punished characteristic for the commercialization of eggs, added to the possible alteration in food safety (FAO, 2007).
Hens’ behavior. Defining, prioritizing, and measuring the needs for behavioral expression are crucial in a study with hens. Animals have behavioral needs that are evident for individual maintenance, such as feeding and drinking behaviors (Downing, 2012). During the present work, a large repertoire of behaviors was observed, where they highlighted Searching for Food, which is suggested to be a redirected behavior of Foraging, such as Pecking feather described by Johannson et al., 2015; both behaviors and foraging decreased in time towards the end of the study. On the other hand, at the end of the study, the frequency and duration of the ground bath behavior increased significantly in hens; this behavior is very important to keep the hen's plumage in good condition (Campbell et al., 2017).
In relation to the behavior Lying down, this increased remarkably until week 30, which is in accordance with what was reported (Singh et al., 2009), since in this week the hens required more food and rest, due to their high egg production rate. Furthermore, it was observed that the behaviors apparently linked at the time, such as Walking and Exploring, declined during the study from week 30. In this regard, the hens probably walk a short distance to reach another space inside the accommodation they change sides to another to escape other hens, or they have a longer walk for comfort as described by Mishra et al., 2005. In the present study, the hens did not have perches in the facilities; however, the motivation to fly did exist.
Health condition. The hens remained in very good physical condition until the end of the study, with a relative deterioration in the comb, and which is in accordance with what was reported by other authors (Weitzenbuger et al., 2006). On the other hand, the good health condition of the legs in the chickens was evident, which is confirmed by what has been described by some authors in relation to the low levels of hyperkeratosis in chickens that do not have access to perches (Navarra y Pinson, 2010).
Physical quality of the egg. The Haugh units that are indicators of the freshness of the egg varied during the study; however, they were found within the established parameters (NMX-FF-127-SCFI-2016), which also agrees with what was described by Farhad y Fariba, 2011 for hens on the floor. On the other hand, the color of the yolk was different between the weeks, which was undoubtedly influenced by the variation of the inclusion levels of pigment, carotenoids or xanthophylls in the diet. In general, the differences observed in the other variables are in accordance with that reported by Roberts et al., 2013, which attributes this to the age of the hen. In addition to the discussion, undoubtedly one of the most important factors in the production of egg for plate are the changes in population density, which can affect the patterns of various behaviors in the hen (Botreau et al., 2007).
The population density described in this work was similar to that reported for the barn or shed system (AVMA, 2012), with nest boxes and no hangers.
The evaluation of the animal welfare of hens on the floor showed a good physical quality of the egg, an expression of a wide repertoire of behaviors and a good state of health. However, it must be considered that at the end of the study, feed consumption, conversion rate and percentage of dirty eggs increased. The results found provide a benchmark for animal welfare in the Bovans White hen housed on the floor.