DESCRIPTION OF PROBLEM
Wet litter (>25%) has been and will continue to be a challenging issue for the broiler industry (Dunlop et al., 2016). Wet litter has been attributed to poor bird performance and footpad health (Martland, 1985; Bilgili et al., 2009; Shepherd and Fairchild, 2010; De Jong et al., 2012; Kazuyo et al., 2013). Wet litter in a 37 d broiler flock reduced BW gain by up to 160 g, increased feed conversion by 7 points, lowered carcass yield by 9%, and increased the rate of severe footpad lesions (De Jong et al., 2014). Wet litter has also been associated with higher ammonia production. It has been thoroughly documented that high levels of ammonia can impair a bird’s respiratory system and leave them more susceptible to disease (Al-Mashhadani and Beck, 1985; Miles et al., 2004).
Dunlop et al. (2016) published a comprehensive review covering the multifactorial causes of wet litter. Within the review, a survey was conducted on various individuals in the poultry industry, such as poultry veterinarians, practical nutritionists, academic nutritionists, and experienced poultry workers. The survey asked their opinion on the major environmental factors that contribute to or cause wet litter. The survey responses indicated poor drinker management and inadequate ventilation were the leading reasons for wet litter.
Producers may use several management practices to alleviate wet litter issues related to drinker management. These include following manufacturer guidelines in managing their drinker system, adjusting drinker line height, managing drinker line pressure, timely maintenance and repair of their drinker system, and drinker line sanitation (American Association of Avian Pathologists AAAP 2017). However, even with proper drinker management, wet litter can still occur under drinker lines (American Association of Avian Pathologists AAAP 2017).
Ventilation is one of the primary methods a producer may use to help control litter moisture. Ventilation aids in the removal of excess moisture from poultry houses (Czarick and Fairchild, 2012). How effectively a producer utilizes this moisture control method is determined mainly by their ability to monitor house RH and make daily adjustments to minimum ventilation rates to keep it within target levels (40–60%) (Czarick et al., 2019). A study by Weaver and Meijerhof (1991) indicated that maintaining an average RH of 50% (40–80%) resulted in significantly lower litter moisture versus a RH of 75%. With an RH of 50%, the average litter moisture ranged between 13% and 40% versus an RH of 75%, with an average litter moisture of 20 to 50%. However, on most farms today, during the coldest parts of the year, it is not uncommon for house RH levels to be between 70% and 80%, primarily caused by decreased minimum ventilation rates due to concerns over heating costs (Fairchild, 2019). To lower RH from 70% to 50%, a producer typically needs to increase their ventilation rates by approximately 60%, which could mean a 45% increase in heating costs (Czarick and Fairchild, 2014). Nonetheless, the research shows that maintaining drier litter is critical for bird health and welfare. The challenge is determining a more cost-effective approach for producers.
A possible partial solution to the problem would be to increase air movement over the litter. The study by Weaver and Meijerhof (1991), which looked at the effect of different RH levels on litter moisture, also evaluated the impact of air movement on litter moisture. The study assessed 15-20 ft/min (low) vs. 35 to 50 ft/min (high) but found no differences in litter moisture between the 2 air movement rates. Eriksson de Rezende et al. (2001) evaluated the effect of air movement on litter moisture, comparing 27 ft/min to a much higher degree of air movement of 155 ft/min. The data from that study showed that supplying air movement at 155 ft/min resulted in lower litter moisture versus 27 ft/min (28% vs. 41%) (Eriksson de Rezende et al., 2001). The data from these 2 studies suggest that higher levels of air movement (155 ft/min) may be more effective in litter-drying than lower levels of air movement (<50 ft/min).
A circulation fan system can increase air movement at floor level. However, these systems have primarily been used to decrease temperature stratification and reduce heating costs (Czarick and Lacy, 2000; Czarick, 2001; Czarick and Fairchild, 2003). To do so, the US broiler industry typically utilizes low-volume circulation fans. The low-volume fans have been purposefully used to produce minimum air movement (<30 ft/min) at floor level out of an abundance of concern over chilling chicks during the first 10 to 14 d (Aviagen, 2018). However, previous research by Weaver and Meijerhof (1991) and Eriksson de Rezende et al. (2001) has shown that air movement at low levels (<30–50 ft/min) is not as effective in litter-drying compared to higher levels of air movement (155 ft/min). In addition, recent work has shown that moving air over chicks at a speed of 200 ft/min does not chill birds if the air temperature is high enough (90°F or higher) (Lu, 2019). Therefore, air movement could be increased using high-volume circulation fans to obtain drier litter with less concern over chilling chicks.
Therefore, the objective of this field study was to evaluate the effects of combining a slightly higher than prescribed house RH (50–60%) and increased air movement (150 ft/min) over the litter on litter moisture and footpad health throughout the flock.
MATERIALS AND METHODS
The study took place November 2017 to February 2019 on 2 commercial broiler farms in Northeast Georgia. It was completed during the colder portions of the year (November through May), as litter moisture control is typically a greater issue due to lower ventilation rates. In addition, the study focused on the brood area, as litter moisture tends to be more challenging to manage in this portion of the house.
Two side-by-side 40′ × 500′ modern environmentally controlled broiler houses were used on each farm. Approximately 25,000-26,000 as-hatched chicks (final stocking density of 0.80 ft2/ bird) were placed in each house per flock and raised to 38 to 40 d of age to an average market weight of 4.40 lbs. Four flocks were studied, with each flock serving as a replicate (Farm 1: 3 flocks, Farm 2: 1 flock).
On both farms, birds were brooded in half of the house and turned out on d 12. On Farm 1, birds were brooded on the tunnel inlet end, while on Farm 2, they were brooded in the center of the house. Both farms utilized radiant tube heaters that were located along the center line of the house (Farm 1: twelve Space Ray ETS80 Infrared Tube Heaters, 80,000 BTUs/hr per heater; Farm 2: twelve Cumberland AV Radiant Tube Heaters, 80,000 BTUs/hr per heater). Houses were equipped with 2 automated feedlines running the length of the house, with nipple drinker lines on either side of the feedlines. Both farms utilized built-up litter originally comprised of pine shavings and sawdust. The approximate age of litter for Farm 1 was 5+ years, and 2.5 years for Farm 2. Litter depth was approximately 6 to 8” in depth on both farms. Litter was routinely decaked between flocks, and 2 d before chick placement, a chemical litter amendment (A7, Al2(SO4)3·14H2O·Al+Clear) was applied to the brooding area in both houses. Occasionally, a top dressing composed of fresh pine shavings and sawdust was applied before flock placement (Farm 1, Flocks 2 and 3). Downtime between flocks ranged between 14 and 21 d.
House/Treatment Assignment
On each farm, 1 house served as the control with no supplemental air movement (CTL), and the second was the treatment (TRT) with continuous air movement provided by 24”, 1/3 HP circulation fans. Farm 1 had 8 Multifan circulation fans (V6E63A3M10100, 7,240 cfm at 0.0” SP), and Farm 2 had 8 Aerotech circulation fans (AT24G, 6,280 cfm at 0.0” SP). The circulation fans were installed 1 foot to the side of radiant tube heaters and 6” from the ceiling and operated continuously from preheating up until the flock sold (Figures 1 and 2). The circulation fan system was designed to mix at least 20 to 25% of house air volume and generated an average air speed of approximately 150 ft/min at floor level.
Figure 1. Circulation fan placement on Farm 1. Black arrows represent direction of air flow from circulation fan. Black dotted line represents brood curtain. Farm 1 partial house brooded in the tunnel-inlet end
Figure 2. Circulation fan placement on Farm 2. Black arrows represent direction of air flow from circulation fan. Black dotted lines represent brood curtain. Farm 2 partial house brooded in the center 250’ area of the house.
Temperature and Humidity Control
Both farms produced birds for the same integrator; therefore, similar target temperatures were maintained throughout the flock. Ventilation rates were adjusted regularly by the farm manager in both houses to maintain a target house RH between 50% and 60% when possible.
Air Velocity Measurements
The air velocity was measured using an omnidirectional hot wire anemometer (Kanomax Climomaster Anemometer 6501, Andover, New Jersey). The data created an air velocity contour map (Surfer 15.5.382: Contouring, Gridding and 3D Surface Mapping Software; Golden, Colorado). Measurements were taken 8-10” above the litter every 12’ down the length of the brooding area and at 5 locations across the width of the brooding area before chick placement in the TRT and CTL house on both farms (5′, 10′, 15′, 25′, 35′).
Litter Moisture Evaluation
Litter samples were taken from the brooding area and were collected on d -2 (before preheating), 7, 14, 21, 28, and the end of the flock (1 d after birds were caught). The sample was collected from the top inch, and enough was collected to fill half of a 1-quart plastic bag to analyze for moisture content. Litter samples were taken across the width of the brooding area at 4 locations on both farms (1 foot off the inside drinker line towards the center and 1 foot off the outside drinker towards the sidewall) and down the length of the brooding area at 4 locations on Farm 1 (50′, 90′, 165′, and 210′) and 6 locations on Farm 2 (130′, 225′, 275′, 285′, 325′, and 365′). The sampling locations on both farms were chosen based on areas more likely prone to litter moisture issues. Samples were immediately transferred to a lab where a 200 g homogenized sample was oven-dried over 24 h at 160-170°F. The following day, samples were reweighed to calculate moisture content using the following equation:
Footpad Lesion Scoring
Birds in the brooding area had footpads scored on d 14, 21, 28, and at the end of the flock. The farm manager subdivided the brooding area into 2 sections using a migration pipe to help evenly distribute birds within the 250′ brooding area. During scoring in each subsection, birds were cordoned off by walking from the center area towards the sidewall area and gathered into a catch pen (3′ × 5′). One hundred birds from the pen had both feet scored for the presence of lesions using a 3-point scoring system scaled from 0 to 2 (Bilgili et al., 2009). A “0” represented a foot with no lesions. A score of “1” was minor, where less than 30% of the foot displayed lesions. A score of “2” was severe, with more than 30-40% of the foot showing lesions. All bird handling procedures used in this study were approved by the Institution Animal Care and Use Committee of the University of Georgia.
House Temperature and House Relative Humidity Measurements
On Farm 1, 6 Bluetooth temperature data loggers (Onset Comp HOBO MX100; Bourne, Massachusetts) were placed evenly in each house on the outside drinker line (80′, 160′, 240′, 320′, 400′, 480′) and Farm 2, 5 wireless temperature/RH data loggers (HOBOnet Temp/RH Sensor-RXW-THC-900 MHz; Bourne, Massachusetts) were placed in each house on the outside drinker line (45′, 140′, 250′, 365′, 460). A wireless temperature/RH data logger (Onset HOBO External Temperature/RH sensor data logger- MX2302A; Bourne, Massachusetts) was placed outside on both farms with a solar radiation shield to monitor and record outside conditions. On Farm 1, data from the Bluetooth temperature data loggers were downloaded during each farm visit, while on Farm 2, data from the wireless data loggers were recorded by a remote data logging system (Onset HOBO RX3000 Remote Monitoring Station Data Logger; Bourne, Massachusetts). On both farms, all data loggers were programmed to continuously record conditions every 5 minutes throughout each flock.
Infrared Thermal Imaging
Thermal images using Infrared Thermography technology (FLIR T640, Boston, Massachusetts) were occasionally taken throughout the brooding period to visually compare floor temperature and bird distribution between houses. Thermal images were analyzed using the thermal camera’s software (ThermaCAM Researcher Pro 2.8).
Data/Statistical Analysis
House/outside temperature and relative humidity were analyzed in Microsoft Excel (Version 2019) to obtain daily mean and SEM. Values were graphed to assess for differences between treatments and flocks. Microsoft Excel was also used to analyze litter moisture to evaluate differences in trends and patterns between CTL and TRT. Litter moisture samples were evaluated individually within each house, as all litter moisture samples were averaged together to obtain a house litter moisture value.
Each flock served as a replicate, totaling 3 flocks on Farm 1. The single flock on Farm 2 was analyzed individually. House litter moisture was analyzed in JMP Pro 14.1.0 using 1-way ANOVA to determine if there were differences between CTL and TRT. Means were separated using Tukey’s HSD test, where means were considered different if P ≤ 0.05. The variation in litter moisture values in the CTL and TRT houses was determined by calculating the coefficient of variance (%) within each sampling area. Values were analyzed using 1-way ANOVA to assess whether the variation in litter moisture between CTL and TRT differed. Means were separated using Tukey’s HSD test, where means were considered different if P ≤ 0.05.
Footpad lesion scores were analyzed by assessing the total occurrence of lesions (minor + severe) and the relative frequency of each lesion score (zero, minor, severe). The frequency of each lesion score was then converted to a percent basis by dividing the total occurrence of each lesion score by the total number of feet (400) scored in the house. Flocks from Farm 1 were averaged to obtain a mean occurrence of lesions and each lesion score. Similar to litter moisture data, the single flock of Farm 2 was analyzed separately.
In addition, footpad scores were analyzed using a nonparametric analysis (Wilcoxon test) in JMP Pro 14.1.0. Each bird served as an observation, and the average score of the 2 footpad scores of each bird was used in the analysis. Means were separated using Tukey’s HSD test, where means were considered different if P ≤ 0.05.
RESULTS AND DISCUSSION
Temperature and Relative Humidity
Average outside temperature for Flocks 1 to 4 was 46°F ± 9°F, 57°F ± 8°F, 61°F ± 6°F, and 47°F ± 9°F, respectively. Similar house target temperatures were maintained on both farms.
Managers on both farms made daily adjustments to the minimum ventilation rates of the CTL and TRT house to maintain an average RH between 50-60% for as much of the flock as possible. On Farm 1, the average house RH in the CTL house for Flocks 1-3 was 54% ± 7%, 57% ± 7%, and 53% ± 6%, respectively. The average house RH in the TRT house was 53% ± 7%, 58% ± 9%, and 53% ± 8%, respectively. On Farm 2, the average house RH in the CTL house was 55% ± 8%, while the average house RH in the TRT house was 56% ± 9%.
House RH tended to be more manageable in cooler weather especially with younger birds. During these periods, houses mainly operated in minimum ventilation mode, meaning the farm manager predominantly determined air exchange rates. When houses started to transition towards cooling mode, the environmental controller determined air exchange rates more, which would increase ventilation rates to maintain the desired set temperature. During cooling mode, the higher air exchange rates tended to cause house RH to mimic outside RH conditions, which may be higher or lower than the target RH range. Cooling mode tends to occur during the last few weeks of a flock when birds are bigger and produce a large amount of surplus heat which can cause the house temperature to increase and trigger the environmental controller to go into cooling mode. For example, during the first 21 d in the single flock on Farm 2, house RH stayed between 55% and 60%, which was well within the target range. From d 22 to the end of the flock, the house RH was, on average, 70%, 10% over the target range. The higher house RH was likely a result of the house operating primarily in cooling versus heating mode, which caused the house RH to more closely mimic actual outside RH, which, on average, was 80%.
During Flocks 1 and 2 on Farm 1, the house RH exceeded the target range from d 22 to d 26 and d 20 to the end of the flock, respectively, and in the single flock on Farm 2, the house RH exceeded the target range from d 26 to the end of the flock. These situations were due to times when daily adjustments to minimum ventilation rates were insufficient to keep RH within the target range (50–60%).
Floor temperature and Bird Distribution
Thermal images were taken to assess potential differences between the CTL and TRT houses indirectly. The CTL and TRT houses used radiant tube heaters on both farms to provide supplemental heat. The tube heaters tended to warm the floor above ambient air temperature when operating. The degree to which the floor was heated was a function of distance from the tube heater and runtime.
Figures 3 and 4 were taken on Farm 2 of the CTL and TRT house 12 h before bird placement and are typical of what was typically observed when the tube heaters were operating during brooding. Data from these representative thermal images created a floor temperature profile chart for the CTL and TRT houses. The average air temperature in the CTL and TRT houses was 92°F and 91°F, respectively. The largest differences in floor temperature were primarily in the center of the house in the area underneath the heaters. In contrast, the sidewall area tended to be similar between the 2 houses. From the sidewall to approximately 8′ off the sidewall, differences in floor temperature between the 2 houses were negligible (<2°F). About 9′ to 10′ from the sidewall, the floor in the CTL house was 4°F to 5°F warmer than the TRT house. This difference between CTL and TRT houses continued to increase to the center of the house (directly below the tube heater). Floor temperatures in the center of the CTL house were above 110°F versus the TRT house, below 100°F. Differences in floor temperature in the center area of the CTL and TRT house decreased as birds got older, and less supplemental heat was required.
Figure 3. Farm 2, CTL house. Typical floor temperature profile during the preheating phase.
Figure 4. Farm 2, TRT house. Typical floor temperature profile during the preheating phase.
Floor temperature patterns appeared to influence bird distribution, particularly during the first 7 to 14 d when heaters generally operated the most. A high percentage of birds in the CTL house were observed concentrating themselves within 10′ to 15′ off either sidewall and avoiding the center area of the house. In contrast, in the TRT house, observations found birds being more evenly distributed across the width of the house. In some instances, the pattern formed by birds appeared to form a circle rim in the floor area under heaters in the CTL houses, while in the TRT house, no distinctive pattern was noticed, and birds were dispersed evenly across the floor. In the CTL house, the distribution pattern was due to birds attempting to avoid the intense hot spots that can form in the center area of the CTL house. At times, the floor temperature in the center area was found to be upwards of 110°F which is likely too warm for young birds, considering research has shown broiler chicks can experience heat stress at air temperatures of 100°F to 115°F (Ernst et al., 1984; Han and Baker, 1993). In contrast to the CTL house, during the brooding period in the TRT house, floor temperatures in the center area were typically observed to be less than 100°F, which may have encouraged birds to occupy that area along with the sidewall area, resulting in more uniformly distributed birds.
The floor temperature pattern in the CTL houses is frequently seen with radiant tube heaters, which are widely used in many broiler houses today (Czarick and Fairchild, 2011). A primary reason for their widespread use may be that radiant tube heaters can deliver approximately 50% of the heat energy directly to the floor versus traditional hot air heating systems that are typically less efficient. Furthermore, as discussed, radiant tube heaters generate a gradient floor temperature profile, which allows young birds to choose what floor temperature they feel is most comfortable. However, in this study, the data indicated that radiant tube heaters may sometimes produce floor temperatures that can be too warm for birds.
The more uniform bird distribution observed in the TRT house is a result of the use of circulation fans. Circulation fans transfer the warm air generated by heating systems that collect near the ceiling back towards the floor. This heat transfer helps raise air temperature near the environmental control sensors more quickly in the TRT house, resulting in shorter heat cycle frequencies and less intense hot spots underneath the tube heaters. As a result, it encouraged birds in the TRT house to occupy the house’s center area, unlike the birds in the CTL house.
Average House Litter Moisture
Litter moisture samples for each house were averaged together to obtain a house litter moisture value per sample day. On Farm 1, litter moisture was significantly higher in the TRT versus the CTL house before preheating (25% vs. 17%) (Figure 5). The higher moisture content in the TRT house was due to possible differences in litter conditions in those houses from the previous flock. However, by the end of the first week, the average house litter moisture in the TRT house decreased and was significantly lower than CTL, as shown by the data on d 7 (16% vs. 20%). This data was of particular interest since it demonstrated that from before preheating to d 7, air movement over the litter surface had a litter-drying effect. On d 14, litter moisture exceeded the target level (25%) in the CTL house (30%), while in the TRT house, moisture levels were well below the target (19%). From d 21 to the last sampling day, litter moisture was consistently higher in the CTL house (>25%) vs. the TRT house, and moisture levels did not exceed 25% until d 28 in the TRT house.
Figure 5. House average litter moisture. Farm 1, Flock 1 (*P ≤ 0.05). Black dotted line represents target litter moisture.
During Flock 2 on Farm 1, CTL and TRT had no significant differences in average litter moisture before preheating. From before preheating to d 7 in the TRT house, litter moisture levels decreased (20–17%), while in the CTL house, litter moisture levels increased from 21% to 22% (Figure 6). This data and the evidence from Flock 1 provide additional support that air movement over the litter surface during this period aids in litter drying. From d 7 to d 14, average litter moisture increased 6% (22–28%) in the CTL house vs. the TRT house, which had a 2% increase in average litter moisture (17–19%). Like Flock 1, litter moisture surpassed the ideal target (25%) at d 14 in the CTL house, while litter was significantly lower in moisture (16–22%) and below the target level in the TRT house. From d 21 to the last sampling day, the average litter moisture was higher in the CTL vs. the TRT house. In addition, the average litter moisture did not surpass the target level of 25% on any sampling day in the TRT house.
Figure 6. House average litter moisture levels. Farm 1, Flock 2 (*P ≤ 0.05). Black dotted line represents target litter moisture.
In Flock 3, litter moisture was significantly higher in the CTL house before preheating. However, it was 7% below the target level of 25% (CTL: 18%, TRT: 15%). On d 7, 14, and 21, the average litter moisture in the CTL house was 24%, 20%, and 21%, respectively, which was significantly higher than the litter moisture in the TRT house, which was 16%, 16%, and 18%, respectively (Figure 7). On d 28, the CTL and TRT houses had similar moisture levels (22% vs. 21%). On the last sampling day, the CTL house had higher litter moisture than the TRT house (23% vs. 19%). Interestingly, for the entirety of Flock 3, litter moisture in both the CTL and TRT houses was below the target (25%). The likely cause is that Flock 3 occurred during warmer months (Late March through May) vs. the previous 2 flocks that occurred during colder months (November through early March). Litter moisture tends to be more manageable during warmer weather as producers increase ventilation rates to help keep birds cool (Hermans et al., 2006). With higher ventilation rates, there is potentially a greater amount of moisture being removed (Czarick and Fairchild, 2012).
Figure 7. House average litter moisture levels. Farm 1, Flock 3 (*P ≤ 0.05). Black dotted line represents target litter moisture.
During the single flock on Farm 2, the average litter moisture before preheating was above 25% in both the CTL and TRT houses (31% and 29%). From before preheating to d 7, litter moisture levels in both houses decreased; the CTL house went from 31% to 25%, and the TRT house went from 29% to 18% (Figure 8). This data shows that increasing house temperature can reduce litter moisture levels since there was an 8% drop in litter moisture in the CTL house. However, the data proved that heat plus air movement over the litter surface can be an even more effective method for litter-drying. From d 14 to the end of the flock, litter moisture was significantly higher in the CTL versus the TRT house. In the TRT house, the average litter moisture remained under the target of 25% from d 7 to d 28 versus the CTL house, which had an average litter moisture of 25% or higher from preheat to the last sampling day of the flock.
Figure 8. House average litter moisture levels. Farm 2, Flock 1 (*P ≤ 0.05). Black dotted line represents target litter moisture.
Throughout each flock at each sample day, except the before-preheat sample, the difference in litter moisture between CTL and TRT ranged between 4% and 13%. Though a difference as low as 4% may appear small, the average litter moisture in the TRT houses remained below the target level (25%) for the first 21 d for Flocks 1 and 2 on Farm 1 and up to d 28 for both Flock 3 on Farm 1 and the single flock on Farm 2. While in the CTL house, litter moisture exceeded 25% on d 14 for Flocks 1 and 2 on Farm 1 and the single flock on Farm 2. As described earlier, many suggest that once litter moisture exceeds 25%, litter begins to lose its ability to maintain functional properties such as insulation, absorption, and evaporation (Collett, 2007; Collett, 2012; Dunlop et al., 2016). Without these properties, litter becomes less beneficial and more detrimental to bird performance, health, and welfare. High litter moisture (> 25%) has been widely attributed to increased microbial activity, ammonia production, footpad lesion development, reduced performance, and decreased carcass yield (Carr et al., 1995; Miles et al., 2006; Shepherd and Fairchild, 2010; Cengiz et al., 2011; de Jong et al., 2014).
Litter Moisture Uniformity
Before placement, CTL and TRT had minimal differences in moisture uniformity (Figure 9). Differences in uniformity occurred once birds were placed and were most apparent during the single flock on Farm 2 (Figure 10). On d 7, the CTL house had a wider spread in moisture values and higher litter moisture values. As shown in Figure 10, the spread in litter moisture values was between the sidewall and center area, where the sidewall had higher litter moisture than the center area. The sidewall area was between 22% and 29%, while the center area ranged between 14% and 19%. In contrast, the spread in litter moisture values in the TRT house was smaller, ranging from 14% to 23%. The center and sidewall areas had relatively similar litter moisture levels, 14% to 18% and 15% to 23%, respectively. In addition, observations made during litter sampling found that in the CTL house, litter in the center area tended to be dustier and more friable versus the litter along the sidewall that was more likely to adhere together. In contrast, litter between the center and sidewall area in the TRT house had a similar consistency in which the litter was loose and dry. On d 14, the sidewall area in the CTL house continued to have higher litter moisture than the CTL house’s center area, 26% to 36% vs. 14% to 23%, respectively (Figure 11). Compared to the CTL house, in the TRT house, the range in litter moisture values between the center and sidewall areas were relatively similar, 14% to 21% versus 16% to 30%. On d 21, the trend continued where the CTL house had significantly higher moisture variation than the TRT house, and the sidewall continued to have higher moisture than the center area (Figure 12). By d 28, differences between CTL and TRT were less apparent (Figure 13). The range in litter moisture levels in the CTL and TRT house were similar, 26% to 39% versus 20% to 42%, respectively.
Figure 9. Litter moisture profile during the single flock on Farm 2, before preheat. One column bar represents 1 litter sample.
Figure 10. Litter moisture profile during the single flock on Farm 2, d 7. One column bar represents 1 litter sample.
Figure 11. Litter moisture profile during the single flock on Farm 2, d 14. One column bar represents 1 litter sample.
Figure 12. Litter moisture profile during the single flock on Farm 2, d 21. One column bar represents 1 litter sample.
Figure 13. Litter moisture profile during the single flock on Farm 2, d 28. One column bar represents 1 litter sample.
Differences in litter moisture uniformity between the 2 houses was due in large part to better air circulation which improved heat distribution thereby better, more uniform bird distribution. As previously discussed, during the first 7 to 14 d in the CTL house, when tube heaters were operating, there tended to be hot spots underneath the heaters where temperatures could be up to 120°F. Previous research suggested that temperatures above 100°F to 115°F can cause heat stress in young birds (Ernst et al., 1984; Han and Baker, 1993), which may be a likely reason why a high percentage of birds migrated away from hot areas and concentrated along the sidewall area where it was cooler. It is expected that with fewer birds in the center area and more along the sidewall, litter moisture would be lower in the center area and higher along the sidewall, as seen in the litter moisture data depicted in Figure 10, Figure 11, Figure 12, Figure 13. In the TRT house, however, observations found that floor temperatures tended to be more uniform across the house, which may be why birds were more evenly spread across the entire house floor. Having more even bird distribution led to uniform litter moisture conditions in the TRT house. The difference in variation between CTL and TRT lasted longer during the single flock on Farm 2 versus Flock 1 on Farm 1. One possible theory is that Flock 1 on Farm 1 had slightly warmer outside conditions versus the single flock on Farm 2, which may influence heater operation. From d 0 to 7, the average outside temperature for Flock 1 on Farm 1 and the single flock on Farm 2 was 58°F and 43°F, respectively. From d 7 to 14, the average outside temperature for Flock 1 on Farm 1 and the single flock on Farm 2 was 46°F and 44°F, and from d 14 to 21, the average was 46°F and 40°F. Overall, during the first 21 d, the outside temperature was, on average, 7°F warmer during Flock 1, Farm 1, versus the single flock on Farm 2. The average daily heat runtime was calculated for each house on both farms, and the data showed that from d 0 to 21, the heaters on Farm 2 ran, on average, 30% longer than Farm 1 (9.5 h vs. 6.5 h). It may be possible that with heaters running longer, the hot spots may have been more frequent on Farm 2 vs. Farm 1. The greater the occurrence of hot spots, the more likely birds in the CTL house would congregate near the sidewalls, thereby depositing more moisture in that area vs. the center area, which increased the variation in litter moisture. This data shows how influential floor temperature gradients and bird distribution can be on litter moisture uniformity in broiler houses.
The treatment effect appeared to dissipate as the flock got older. How effective the treatment is in litter-drying is primarily influenced by factors such as air movement and bird distribution. As birds grew larger, they covered more of the litter surface which prevented air from moving across the litter and wicking away moisture. This could explain why the litter moisture profile between the CTL and TRT house at the end of the flock were similar since in both houses, birds were occupying virtually the same amount of floor space. In addition, air movement alone cannot overcome all the factors that influence litter moisture control, particularly litter near the drinker lines. Litter moisture control in this area is one of the most challenging places in the house. The reason for it being such a challenge can be attributed to improper drinker management and bird activity. Improper management of drinkers can cause excess water to be deposited onto the floor. The excess water could be from running the pressure too high and water that doesn’t get ingested by the bird falls to the floor. Broken parts like leaky connections and/or drinker nipples often create havoc around the drinker line. Inadequate drinker height adjustment can also contribute to litter moisture issues. Drinkers that are too low can cause birds to have to angle their head to the side to obtain water which many times leads to water falling to the floor. Birds can also run into drinker lines that are too low and cause excess water to leak from nipples. As for bird activity, in addition to birds bumping into drinker lines, anytime birds obtain water from drinker nipples, there is the chance that not all the water is ingested by the bird and falls onto the floor. Compared to other areas of the house, litter underneath the drinker lines is extremely difficult to keep below 25%, even with additional air movement.
Footpad Lesions
Footpads were scored to determine the total frequency of lesions (minor + severe) and frequency of each type of lesion (minor or severe), and those values for each are summarized in Table 1, Table 2, Table 3 to 4. Additionally, on each sample day, the average footpad score of each bird was taken and used to conduct a nonparametric analysis for CTL and TRT. The analysis showed that the treatment had a significantly lower occurrence of footpad lesions on all sampling days in all 4 flocks. The treatment had the greatest effect during the single flock on Farm 2. On d 14, the CTL house had 47% more birds showing lesions (minor or severe) than the TRT house (56% versus 8%). On d 21, the rate of total lesions increased in the CTL house, where 70% of birds had lesions, versus 20% of birds in the TRT house. This trend continued into d 28, where 77% of birds showed lesions in the CTL house, while there was only a 6% increase in the frequency of total lesions in the TRT house (26%). At the end of the flock, 80% of sampled birds in the CTL house had lesions vs. 35% in the TRT house.
Table 1. Total occurrence of minor + severe footpad lesions (%) combined per flock on Farms 1 and 2 (d 14 and d 21).
| Empty Cell | Empty Cell | Empty Cell | d 14 | d 21 | ||
|---|---|---|---|---|---|---|
| Farm # | Flock # | Sample size1 | CTL | TRT | CTL | TRT |
| Farm 1 | 1 | 200 | 25 | 3 | 29 | 5 |
| 2 | 400 | 11 | 2 | 23 | 1 | |
| 3 | 400 | 2 | 4 | 15 | 8 | |
| Avg2 | 13 ± 7 | 3 ± 1 | 22 ± 4 | 4 ± 2 | ||
| Farm 2 | 1 | 400 | 56 | 8 | 70 | 20 |
- 1
-
Number of feet sampled per house on each sample day.
- 2
-
Mean value of Flocks 1-3 ± SEM.
Table 2. Total occurrence of minor + severe footpad lesions (%) combined per flock on Farms 1 and 2 (d 28 and d 39–41).
| Empty Cell | Empty Cell | d 28 | d 39–41 | Empty Cell | ||
|---|---|---|---|---|---|---|
| Farm # | Flock # | CTL | TRT | CTL | TRT | Flock period |
| Farm 1 | 1 | – | – | 82 | 61 | Nov–Jan |
| Empty Cell | 2 | 50 | 17 | 65 | 52 | Jan–Mar |
| Empty Cell | 3 | 34 | 10 | 53 | 30 | Mar–May |
| Empty Cell | Avg1 | 42 ± 8 | 13 ± 4 | 66 ± 9 | 48 ± 9 | |
| Farm 2 | 1 | 77 | 26 | 80 | 35 | Jan–Feb |
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Mean value of Flocks 1-3 ± SEM.
Table 3. Occurrence of minor and severe footpad lesions (%) per flock on Farms 1 and 2 (d 14 and d 21).
| Empty Cell | Empty Cell | d 14 | d 21 | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Empty Cell | Empty Cell | Minor | Severe | Minor | Severe | ||||
| Farm # | Flock # | CTL | TRT | CTL | TRT | CTL | TRT | CTL | TRT |
| Farm 1 | 1 | 19 | 3 | 7 | 0 | 14 | 3 | 14 | 3 |
| Empty Cell | 2 | 9 | 2 | 2 | 0 | 7 | 0 | 16 | 1 |
| Empty Cell | 3 | 1 | 3 | 1 | 1 | 10 | 7 | 5 | 1 |
| Empty Cell | Avg1 | 9 ± 5 | 2 ± 0.4 | 3 ± 2 | 0 ± 0.2 | 10 ± 2 | 3 ± 2 | 12 ± 4 | 1 ± 1 |
| Farm 2 | 1 | 12 | 4 | 45 | 4 | 15 | 8 | 55 | 11 |
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Mean value of Flocks 1-3 ± SEM.
Table 4. Occurrence of minor and severe footpad lesions (%) per flock on Farms 1 and 2 (d 28 and d 39-41).
| Empty Cell | Empty Cell | d 28 | d 39-41 | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Empty Cell | Empty Cell | Minor | Severe | Minor | Severe | ||||
| Farm # | Flock # | CTL | TRT | CTL | TRT | CTL | TRT | CTL | TRT |
| Farm 1 | 1 | – | – | – | – | 11 | 31 | 72 | 30 |
| Empty Cell | 2 | 13 | 10 | 37 | 7 | 11 | 32 | 54 | 20 |
| Empty Cell | 3 | 20 | 6 | 14 | 4 | 19 | 19 | 34 | 11 |
| Empty Cell | Avg1 | 17 ± 3 | 8 ± 2 | 26 ± 11 | 6 ± 2 | 13 ± 3 | 27 ± 4 | 53 ± 11 | 20 ± 5 |
| Farm 2 | 1 | 10 | 12 | 67 | 14 | 16 | 10 | 64 | 25 |
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Mean value of Flocks 1-3 ± SEM.
At each sampling day, most lesions in the CTL house were severe, while in the TRT house, most lesions were minor. On d 14, 45% out of the 56% of lesions were severe in the CTL house; in the TRT house, 4% out of the 8% were severe. On d 21, 55% out of the 70% of lesions were severe in the CTL house; in the TRT house, only 11% out of the 20% were severe. The trend continued at d 28 and the end of the flock, with the CTL house having more severe versus minor lesions (67% severe, 10% minor, 64% severe, and 16% minor, respectively). In comparison, in the TRT house, there was a relatively equal occurrence of either lesion (14% severe, 12% minor, 25% severe, and 10% minor, respectively). Overall, during the single flock on Farm 2, the CTL house had, on average, 48% more lesions versus the TRT house, with a majority of those lesions being severe.
A similar trend was seen during the 3 flocks on Farm 1. During Flock 1 on Farm 1, the CTL house had 22% more lesions than the TRT house. On d 21, the frequency of lesions increased from 22% to 29% in the CTL house vs. the TRT house, which had only a 2% increase (3–5%). At the end of the flock, 82% of birds had lesions in the CTL house vs. 61% in the TRT house. During Flock 2 on d 14 and d 21, the frequency of lesions in the CTL and TRT house was 11% vs. 2% and 23% versus 17%, respectively. On d 28, the occurrence was 50% vs. 17% in the CTL and TRT houses, respectively. At the end of the flock, 65% of birds had lesions in the CTL house versus 52% in the TRT house. During Flock 3 on d 14, the rate of lesions was minimal in both the CTL and TRT houses (2% versus 4%, respectively). On d 21, the TRT appeared to have an effect since the CTL house had 15% of birds showing lesions versus 8% in the TRT house. This difference between CTL and TRT continued onto d 28 and the last day of the flock, where the CTL house had more birds showing lesions vs. the TRT house, 34% versus 10% and 53% versus 30%, respectively.
For all 3 flocks from d 14 to 28, there was no consistent trend in the type of lesion in the CTL and TRT houses. In contrast, in the single flock on Farm 2, severe lesions were consistently more frequent than minor lesions in the CTL house, and in the TRT house, the frequency of both minor and severe lesions was similar. For example, on Farm 1 during Flock 1 on d 14, there were more minor versus severe lesions in the CTL and TRT house (19% minor, 7% severe, and 3% minor, 0% severe, respectively). Still, on d 21, there was an equal rate of minor and severe in CTL and TRT (14% minor, 14% severe, and 3% minor, 3% severe, respectively). At the end of Flocks 1,2 and 3 on Farm 1, however, there were more severe lesions than minor lesions in the CTL house (72% versus 11%, 54% versus 11%, and 34% versus 19%, respectively) and in the TRT house there were more minor lesions versus severe lesions (31% vs. 30%, 32% vs. 20%, and 19% vs. 11%, respectively).
The treatment of higher air movement on both farms appeared to be the most effective during the first 21 d of the flock, where lesions in the TRT house were between 1% and 20% vs. 2% and 70% in the CTL house. By d 28, the treatment effect seemed to lessen as lesions in the TRT house ranged between 10% and 26% but remained lower than in the CTL house, which ran between 34% and 77%. By the end of each flock, lesions in the TRT house increased to an average rate of 48%, though they remained less than the CTL house with an average lesion occurrence of 66%.
The frequency and severity of footpad health have been associated with multiple factors such as litter moisture, bedding material, litter depth, and nutrition (Shepherd and Fairchild, 2010; Opengart et al., 2018). In this study, litter moisture was the primary factor that caused the difference in footpad health between CTL and TRT. As previously discussed, overall, the CTL house had higher litter moisture and more variation throughout the house vs. the TRT house. High litter moisture negatively impacted footpad development leading to higher footpad lesions in the CTL house. Meanwhile, in the TRT house, litter was drier and more uniform for a longer period in each flock versus the CTL. These findings agree with a previous study that exposed birds to wet litter early on leading to higher rates of footpad lesion development (Kazuyo et al., 2013).
The study also documented the potential impact seasonality may have on the occurrence of footpad lesions. In Figure 14, the data shows a steady decrease in lesions from Flock 1 to Flock 3 on Farm 1. During the Nov-Jan flock, the average occurrence of lesions of the CTL and TRT house was 34%; from Jan-Mar, the average was 27%; and from Mar-May, the average was 19%, and for the single flock on Farm 2, which occurred between Jan-Feb the average occurrence was 46%. The data shows that there may be a correlation between footpad lesion development and season, where flocks that are raised during the colder months (November to February) may have a higher chance of developing footpad lesions versus flocks that occur during warmer months (March to May). This correlation has been seen by other groups who documented outside temperature conditions influencing footpad health (Da Costa et al., 2014). They generally noted that footpad lesions are in better condition during warmer and colder seasons.
Figure 14. Total occurrence of footpad lesions (minor + severe) per flock for Farms 1 and 2.
CONCLUSIONS AND APPLICATIONS
- 1.
Providing continuous air movement over the litter surface (150 ft/min) resulted in drier litter conditions from d 7 to the end of the flock.
- 2.
Continuous air movement provided by a circulation fan system helped improve heat distribution leading to more uniform floor temperatures. Uniform floor temperatures caused birds to distribute themselves more evenly resulting in less variation in litter moisture throughout the house.
- 3.
On both farms, from d 14 to 28, less than 26% of birds in the TRT house had signs of lesions vs. up to 77% in the CTL house. At the end of the flock, 48% of birds on average had lesions in the TRT house versus 66% in the CTL house on Farm 1, and on Farm 2 TRT house had 35% of the birds with lesions while CTL had 80% birds with lesions.
- 4.
At the end of each flock, flock, CTL house lesion incidence was primarily severe, whereas the TRT house had equal severe and minor lesion incidences.
Source: Science Direct
