Effect of bedding application and air change rates on environmental ammonia concentrations for intensively housed beef cattle

Abstract

<p><b>Context.</b> Manure deposition during livestock export voyages contributes to air ammonia levels, potentially affecting human and animal health if not managed. Mitigation strategies may include increased air change rates and application of bedding. <b>Aim.</b> This study examined the effect of bedding application rate (BAR) and air change rate (ACH) on air ammonia (NH₃) concentrations and pad properties, including pad surface condition, pH, moisture, and pad ammonium (NH₄⁺) concentrations, for intensively housed beef cattle. <b>Methods.</b> Six 7-day runs were conducted with 72 <i>Bos indicus</i> cross steers (mean liveweight ± s.d. = 338 ± 32 kg) housed in respiration chambers by using a 3 × 3 factorial design. The BARs were set to 0%, 50%, and 100% of the Australian Standards for the Export of Livestock (ASEL), and ACH were varied at 20, 35, and 52. Air NH₃ was measured twice daily at three heights. Pad surface condition was collected with the first air NH₃ measurement. Video footage captured standing and lying behaviours for each steer. Pad samples were collected on the final day for pad chemical analysis. <b>Key results.</b> The ACH of 20 changes per hour resulted in higher air NH₃ concentration than ACH of 35 and 52. Higher BAR led to lower pad pH and moisture, with slightly lower pad NH₄⁺ concentration in 100% and 50% BAR than 0% BAR. Although air NH₃ concentration on Day 7 was positively correlated with pad NH₄⁺ concentration, BAR had no marked effect on air NH<sun>3</sub> concentration (within the temperature range of this experiment). Drier and firmer pad surfaces were associated with each high BAR and high ACH. Moreover, high BAR increased the frequency of lying behaviour in steers. <b>Conclusions.</b> These findings indicated that NH₃ can be mitigated by optimising air changes to minimise air NH₃ concentration and utilising bedding to minimise pad NH₄⁺. This offers practical solutions for intensively housed beef cattle, such as livestock export voyages to improve human and animal welfare onboard. <b>Implications.</b> The study results emphasised the importance of optimising ACH to maintain low air NH₃ concentrations in livestock export conditions. Although there was no evidence that BAR affects air NH₃ directly, it reduced pad NH₄⁺ and improved pad conditions for overall animal comfort and environmental quality in confined housing with sufficient air changes.</p>