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One of the fundamental steps during the creation of the Code of Practice for the Care and Handling of Chickens, Turkeys and Breeders, was a review of all the relevant scientific literature. The literature review focused on poultry management practices and environmental conditions of poultry barns and their effects on bird welfare. The poultry report from 2013 provided an objective summary of the literature without providing recommendations. The current manuscript will follow the same format used in the previous report and update the information of the section ‘Air and Litter Quality’ (Section 4, pages 17-27).
The authors of the 2013 poultry report concluded that:
Dust particles are composed of organic material from the birds, as well feed, litter and other housing materials. Because of its composition, dust can be a vector for microorganisms and toxins, acting as a source of contagion among animals (David et al., 2015). Very little research has been conducted regarding the effect of dust on broiler welfare since 2013. Birds infected with infectious bursal disease virus were found to shed the virus mainly through their feces (Zhao et al., 2013). However, the virus was also detected in the dust present in the exhausted air. In another study, air samples from three cage- type broiler houses were collected at day 6, 21 and 37 of production (Zhang et al., 2019). The authors found that the concentration of breathable particulate matter increased with bird age, in accordance with previous studies. Similarly, the concentration of bacteria also increased with age, and the presence of pathogenic bacteria could be detected in dust samples through the entire growth cycle.
Some studies focused on dust mitigation approaches. When assessing the effect of oil application rate (8- or 16-mL m-2) and frequency (every 24 or 48 h), Winkel et al. (2014) found that the emission of particular matter was significantly reduced by 59-64% (large particles PM10) and 74-81% (small particles PM2.5) in the 8 and 16 mL m-2 d-1 treatments. No differences in the effect of frequency were found. On the other hand, a sprinkling cooling system were only numerically lower when comparing two broiler houses (Williams Ischer et al., 2017).
Finally, one study assessed the effect of litter thickness on dust buildup. When testing four different sawdust thicknesses (4, 8, 12 and 16 cm deep), Shao et al. (2015) found that, although there was an inverse relationship between litter thickness and litter moisture, the amount of dust increased in a direct fashion.
Relative humidity is a key environmental factor that has a significant role on air quality, temperature control and health (Xiong et al., 2017). However, research assessing the single direct effect of relative humidity on bird welfare is lacking.
A study conducted in Brazil, assessed the effect of crate microclimate and transportation distances (15 vs. 90 km). The authors found no differences between the average relative humidity of transportation crates between distances during the rainy (RH: 67%) or the dry season (RH 44%). However, mortality in the 90 km treatment during the dry season was double than that on the 15 km treatment (0.22 and 0.11%, respectively), which the authors attributed to the stress produced by the lower relative humidity level during long transport.
As stated in the previous report, the effect of litter on broiler welfare is mostly related to litter moisture. When the effect of two levels of litter moisture were assessed (wet: 31-57% vs. dry: 15-40%) weekly on the foot pad health of broilers from 7 to 49 days of age, those of the wet treatment had significantly higher (worse) food pad scores at 21, 28, 35 42 and 49 days of age (Taira et al., 2014). When birds were moved from the dry to the wet treatment at 21 and 28 days of age, foot pat scores worsened rapidly, while the opposite was true for the birds that were moved from the wet to the dry treatment. Another study tested the effect of stocking density of broilers (16, 18, 20 or 22 birds/m2) raised under conventional or environmentally controlled conditions (Farhadi et al., 2016). Litter moisture was higher and foot pad lesions more prevalent in the conventionally grew broiler treatment. No effect of stocking density on litter quality was found, but birds raised at 22 bids/m2 presented worse foot pad scores. In relation to litter moisture, one study induced a high incidence and severity of foot pad dermatitis at time of slaughter by maintaining high litter moisture (n=8; de Jong et al., 2014). The wet litter treatment had worse performance (body weight gain, feed intake, feed efficiency and water intake), but did not affect mortality. The wet litter treatment also had a negative impact on breast cleanliness and irritation, hock burns and gait score, while it had lower incidence of thigh scratches as compared to the dry treatment.
Since the last poultry report, only one study focused on the effect litter thickness (4, 8, 12 or 16 cm; n=20) on broiler performance and welfare (Shao et al., 2015). On one hand, sawdust thickness was found to be directly associated with body weight, body weight gain, feed intake and dust levels. On the other hand, an inverse relationship of sawdust thickness with liver weight, litter moisture, plumage cleanliness, the incidence of foot pad dermatitis, hock swelling, and breast blisters was found. No effect of treatment was found on feed efficiency, spleen, bursa or thymus weight, gait score, plumage damage and hock burn.
Some research has been conducted on the effects of litter amendments. Soliman and Hassan (2017) tested the effects of using superphosphate and meta-bisulfide (for the control of ammonia) on broiler performance and litter and air quality (n=40). Both treatments significantly reduced litter moisture and pH, and improved body weight and body weight gain as compared to the control treatment, with superphosphate reaching the best values. Superphosphate resulted in the highest bursa weight, while meta-bisulfide resulted in the highest spleen and thymus weights. In a later study Soliman et al. (2018) tested the effect of superphosphate, meta-bisulfide and charcoal on bacterial counts (n=48) under laboratory settings. All treatments significantly reduced litter moisture and pH, with superphosphate and meta-bisulfide reaching the best numbers. The total bacterial counts and Salmonella colony forming units were significantly different in all the treatments, with the highest values in the positive control, followed by charcoal, superphosphate and meta-bisulfide. A similar result was found regarding E. Coli, with the highest values in the positive control, followed by charcoal and superphosphate, and meta- bisulfide showing the lowest values. Eimeria oocyst sporulation was found in all the treatments, with the exception of superphosphate.
In a metanalysis of the literature, no effect of litter treatment was found on feed intake, feed efficiency or mortality (de Toledo et al., 2020). However, when litter was treated with acidifiers, a positive effect on body weight gain and mortality, and a trend to improve feed efficiency was observed. Litter treatment with acidifiers also significantly reduced the concentration and volatility of ammonia. Overall, the addition of amendments to the litter significantly reduced moisture and pathogenic microbiota load.
In a substrate choice test between wood shavings, sand, rice hulls and straw, broilers (n=32) preferred to spend time in sand, with no significant differences among the other substrates (Villagra et al., 2014). In terms of behaviour, while resting occurred mostly in wood shavings and straw, dustbathing occurred more in sand, and rice hulls were the preferred substrate for pecking and scratching. A study was conducted to assess the effect of stocking density (15, 19 or 23 birds/m2) and litter type (rice hulls or wheat straw; Petek et al., 2014). While increasing stocking density had a negative effect on body weight, foot pad health, litter pH and moisture, no effect of litter type was found. In another study the effect of litter material and platforms on the foot health and feather cleanliness of broiler breeders was determined (n= 16 farms; Kaukonen et al., 2017). Foot pad lesion scores were worse in birds kept on wood shaving and ground straw as compared to peat. No significant differences in litter condition or ammonia content were found between wood shavings and peat, but the pH and moisture of wood shavings increased with time. When peat and straw were compared, the straw-based litter presented a worse litter condition score than peat (1.0 vs. 0.7). The ground straw layer was thinner and had a lower final pH. No differences in litter moisture or ammonia content were found between peat and straw.
Vieria et al. (2015) studied the effect of using fresh coffee hulls or wood shavings and over several cycles of use (4). Treatments had not effect on performance, including mortality. While the bacteria E. coli was found in all the litter samples, the presence of salmonella was associate with litter humidity and wood shavings. In another study, comparing the effects of several litter materials (wheat straw, rice husk, mustard stalks and sand; n=16), Dhaliwal et al. (2018) found a negative effect of sand on bird performance, with lower body weight, feed intake and higher mortality. However, mustard resulted in higher feed:gain ratio. Litter moisture was highest in rice, followed by wheat and mustard, and finally sand, while the percentage of nitrogen, phosphorus and potassium, was highest in rice husks, followed by wheat and mustard and, lowest in sand.
A number of studies assessed the effect on platforms on bird welfare, with no clear results. The foot health of 100 broiler breeders in 18 flocks was assessed at 19, 24, 36, 48 weeks of age and at slaughter (Kaukonen et al., 2016). Foot pad score worsened with age, and the incidence of severe lesions reached 64% at slaughter. Although litter became drier with time, litter pH and ammonia increased from 24 to 48 weeks of age. In addition, an association between large, slatted areas and foot pad condition was found. No effect on hock burns or breast blisters was found. In a follow up study, the effect of litter material and platforms on the foot health and feather cleanliness of broiler breeders was determined (Kaukonen et al., 2017). In this study, no effect of platforms was found on foot pad lesions or feather cleanliness (n=18 farms). Li et al. (2017) also studied the effect of conventional litter or the use of engineer netting floors (n=8). They found no effect of treatment on performance, foot health, panting, huddling, fearfulness or the ability to walk. However, engineer netting floors increased feather cleanliness and reduced foot pad dermatitis at the end of the production cycle, and had a small effect by increasing the incidence of breast blisters.
In another study, the effect of 100% litter, 50% litter-50% slatted floors and 100% slatted floors was tested (n=15; Cavusoglu et al., 2018). The authors found that birds in litter had better feather cover and lower hock burn, but lower body weight. However, the incidence of foot pad lesions was highest in litter, followed by the 50/50 treatment, showing the lowest incidence in the slatted floors treatment. No effect on gait score was found. In a similar study, the effect of 100% wood shavings, 100% wood shavings and in-floor heating, 50% wood shavings and 50% slatted floors and slatted floors with a sand bath was assessed on broiler and turkey production (n=12; Chuppava et al., 2018). Treatments with floor slats produced the heavier broilers, but not other effect of treatment on performance or foot pad health were found. Turkeys in the slat treatment with sand bath had higher body weight and worse foot pads than the other treatments. Feed intake and feed conversion ratio were higher in the slatted floor treatment than in the wood shavings and wood shavings with floor heating treatments. When the effect of 50% slatted flooring vs. 100% wood shavings was assessed through 8 flocks, Heitmann et al. (2020) found no differences in body weight, litter moisture content or pH. No differences were found on the levels of coliform bacteria or E. coli either, but a trend for total bacterial count to be higher in the 100% wood shavings treatment was found.
There has been some interest in assessing the effect of litter re-use. The effect of litter type (Coffee hulls vs. wood shavings) and cycle of use (1-4) was assessed (Vieria et al., 2015). No effect of treatment was found on feed efficiency, body weight gain, or mortality. However, when coffee hulls were used, the incidence of foot pad lesions at 35-45 days of age increased from 60.0 to 90.3% between the first and the second cycle of use. In a similar study, where the effect of fresh vs. re-used pine shavings litter was assessed, no differences in mortality were found and Salmonella, Clostridium perfringens or Campylobacter were not detected in any of the samples (Wang et al., 2016). However, litter management affected the bacterial community present in the gut of broilers especially at young ages (10 day of age), and in particular litter management affected the amounts of some butyrate producing bacteria and lactobacillus which could affect performance and immunological status of the birds.
Ammonia is an alkaline and corrosive gas that can negatively affect the nasal cavity and the eyes of poultry (Naseem and King, 2018). It can also affect the immunity status of broilers. When two levels of ammonia (30 and 70 mg/kg) and three relative humidity levels (35, 60 and 85%; n=36), Wei et al. (2015) found an inverse relationship between ammonia level and serum lysozyme concentration in young broilers, and globulin serum concentration by the third week. Ammonia level also negatively impacted the lymphocyte stimulus index and increased the expression of IL-1β at all tested ages. In a similar experiment, broilers were exposed to 3 or 75 µL/L of ammonia (n=30) and performance and hepatic proteins were measured (Zhang et al., 2015). Ammonia treatment negatively impacted broiler performance (body weight gain, feed intake and efficiency). In addition, the levels of proteins associated with hepatic injury (alkaline aminotransferase, aspartate aminotransferase and creatine kinase) and stress were significantly elevated.
Housing floor can affect ammonia emissions and broiler welfare (Soliman and Hassan, 2020). When the use of wood shavings, rice husks, wheat straw, slats or battery cages were assessed (n=20), average ammonia levels over five weeks were highest in the wood shavings treatment (26.2 ppm), followed by rice husks (19.4 ppm), wheat straw (16.1 ppm), battery cages (4.9 ppm) and slats (4.1 ppm). Performance index was best in battery cages, followed by slats, wheat straw, wood shavings and finally rice husks. Corticosterone levels (stress) were highest in the wood shavings treatment, followed by rice husks, wheat straw and finally slats and battery cages, while IgG and IgM levels were highest in battery cages, followed by slats, wheat straw, rice husks and wood shavings. In another study the effect of conventional litter (fresh rice hulls) and perforated floors (accumulation of manure) was assessed on broiler performance, environmental measures and welfare (n=8; Li et al., 2017). Ammonia concentration was overall higher in the perforated floors environments. No effect of flooring on production parameters or mortality were found. Perforated floors promoted feather cleanliness and lower foot pad dermatitis, but no effect on gait score or behaviour was found. In addition to substrate, the thickness of the litter can affect ammonia levels and welfare. When the effect of using 4, 8, 12 and 16 cm of sawdust thickness was assessed, Shao et al. (2015) found and inverse relationship between air ammonia and litter thickness. This was also associated with higher body weight, body weight gain and feed intake and lower plumage cleanliness, foot pad score, hock swelling and breast blister.
The effect of sodium biosulfate, an acidifier to control ammonia volatilization, was assessed (n=6; Li et al., 2014). Mortality rate was significantly reduced in the sodium biosulfate treatment (3.92 vs. 3.67%), but no other differences in performance were found. The level of nitrogen present in litter samples was significantly higher in the sodium biosulfare treatment. The ammonia emissions were numerically lower in the treated litter, but no significant differences were found. In the same study, similar results were found under laboratory settings. When foot pad health was assessed under laboratory settings, a significant reduction of foot pad score was found (1.33 vs. 0.67). In a similar study, when the effect of superphosphate and meta-bisulfate was tested, aerial ammonia was significantly reduced and body weight and feed efficiency were improved by the use of both treatments (Soliman and Hassan, 2017); however, superphosphate was the most effective.
A metanalysis of the literature revealed that treating the litter has no effect on feed intake or feed efficiency (de Toledo et al., 2020). However, the use of acidifiers proved to have a positive effect on body weight gain, mortality and tended to improve feed efficiency, while significantly reducing ammonia concentrations and volatility.
Body weight, body weight gain and feed intake increase with sawdust thickness (n=2; Shao et al., 2015). This is associated with a reduction in carbon dioxide levels from 1,177.6 ppm when sawdust thickness was 4 cm depth to 742.2 ppm compared to 723.3 ppm when thickness was of 12 and 16 cm. When turkeys were exposed to three levels of CO2 (2,000, 4,000 or 6,000 ppm; n=9; Candido et al., 2018), turkey body weight was significantly lower in 4,000 ppm as compared to 2,000, but no differences in feed intake, feed efficiency or mortality were observed. Activity levels were highest at 4,000 ppm, followed by 6,000 ppm and lowest at 2,000 ppm.
The conclusions of the 2013 Poultry Report regarding Air and Litter quality were:
The information reported between 2013 and 2020 supports this statement. Increases in dust and ammonia and environmental conditions are associated with reductions in performance.
Very little research has focused on the effect of dust. Dust can be a vector of pathogenic bacteria and the use of management techniques can reduce dust levels (e.g. oil spraying).
A strong association of litter humidity (particularly over 30%) and foot health has been described. However, the physicochemical characteristics of floor bedding, as well as cycle of use, can affect the prevalence of foot pad dermatitis and the presence of pathogenic bacteria.
This was confirmed by the 2013-2020 information, but litter moisture was not the only factor.
Research published between 2013 and 2020 has confirmed a strong relationship between ammonia levels and immune function.
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