The effect of stocking density on the production of ammonia and faecal pad formation under thermoneutral climatic conditions

Context. Ammonia (NH₃) production and manure pad characteristics are important animal welfare considerations for intensively housed livestock, such as those on-board livestock export vessels.

Aim. This study investigated the effects of five allometric stocking densities (k = 0.030, 0.033, 0.037, 0.042 and 0.047) on manure pad formation, air NH₃ concentrations, lying behaviour and liveweight of Merino wethers under thermoneutral conditions.

Methods. Wethers were group housed in 10 respiration chambers for 21 days, across two runs. Air NH₃ was measured at eight heights twice daily. Daily visual assessments of faecal pad condition, depth and moisture were conducted. Pad samples were collected from each chamber on Days 7, 14 and 21 for analysis of pH, electrical conductivity, ammonium and bulk density. Pad depth was measured at 25 locations per chamber on Day 21. Sheep standing and lying behaviours were recorded every second day at 15-min intervals, and liveweights were measured at the start and end of the voyage.>

Key results. Lower stocking densities resulted in fewer sheep standing and reduced mean NH₃ concentrations compared with the highest density. Stocking density had minimal effect on liveweight. The air NH₃ concentrations measured at 5 and 215 cm from the surface of the manure pad were slightly lower than at the other heights. Pad depth increased with higher densities, whereas pads were drier at the lowest density. Pad ammonium concentration and pH were higher at the lowest stocking density, with little variation across pad depths or locations

Conclusions. Reducing stocking density improved manure pad conditions and reduced air NH₃ concentrations under thermoneutral conditions.

Implications. These findings suggest that manipulating stocking density could complement ventilation strategies to manage air quality and pad conditions in intensive sheep housing systems, including livestock export vessels and feedlots.