Investigation of Ventilation Efficacy on Live Sheep Vessels

Summary

The scope of project LIVE.212 was truncated from three voyages to two voyages as the principal objectives had been met and the work had been overtaken by the heat stress risk management project LIVE.116.The literature review and the two voyages undertaken provided data on the response of sheep and goats to heat stress. These data have assisted in the estimation of the base heat stress threshold and mortality limit figures required for LIVE.116 and the HS software. The data were also used to assess the factors through which acclimatisation, weight and coat are taken to adjust the assessed heat stress threshold and mortality limit.Voyage 1 sailed to the Middle East in June/July 2002, having loaded sheep in both Portland and Fremantle. All decks were closed at the ship sides and were single tier, giving high headroom.Voyage 2 sailed to the Middle East in September 2002, carrying a range of sheep, all in low headroom decks. Closed deck ventilation rates (pen air turnover) varied significantly between sample pens. Several open deck pens were also studied on Voyage 2.Ambient wet bulb temperature peaked at 27.9oC on day 13 of Voyage 2. The highest corresponding wet bulb peak in the closed observation decks was 33.2oC, a rise below decks of 5.3oC.The heat stress threshold (HST) for sheep was estimated from Voyage 1 to be 28 to 30oC wet bulb. The Voyage 2 data confirmed that the majority of animals have a HST below 30oC wet bulb, but also indicated elevated rectal temperatures at wet bulb temperatures as low as 26oC wet bulb.Although Voyage 2 was generally cooler than Voyage 1, an increase in mortality was seen coincident with the hottest conditions. Wet bulb temperatures around 32oC appeared to trigger a rise in mortality rate among Merino sheep. The peak daily mortality rates were still relatively low. The rise is considered to be the result of heat stress compounding the problems for sheep already weakened by other effects. A heat event causing healthy sheep to die would be expected to affect very large numbers.The overall wet bulb temperature difference between ambient and exhaust air was consistent with an estimate made using methods developed previously, applying a metabolic heat production rate of 3.2W per kg of liveweight for sheep. The deck wet bulb temperature rises were also consistent with earlier work.A number of Voyage 2 experiments did not give useful results because the conditions were too mild or, in the case of open decks, too breezy. It is recommended that understanding of open decks is best advanced by computational studies, possibly followed by unattended data logging on ships. Such computational studies have now been done as part of LIVE.116 and the authors are assisting the industry to set up the data logging.Weight change data from the voyages varied widely and were not self-consistent. We consider that the weight change data are not informative.