Cattle and Heat: a case for developing a cattle-specific heat stress forecast product

Cattle and Heat: a case for developing a cattle-specific heat stress forecast product

Northern Australia's tropical/semi-arid region covers an area of around 5.5 million km2 and supports ~15 million head of cattle. While grazing livestock are generally well acclimatized to the tropical heat, protracted extreme heat can significantly impact cattle (e.g., calves) that are better suited to temperate climates such as Bos taurus. During the northern wet season (Oct – Apr), maximum daily temperatures often exceed 35°C for extended periods, and heatwaves with daytime temperatures surpassing 40°C have been observed in the recent past, e.g., the northern tropics in late 2018 and early 2019. Feedback from the red-meat Industry Reference Groups, including survey data from northern beef producers, have pointed to the need for a forecast product related to cattle heat stress. Here, we evaluate three different cattle heat stress indices: the Temperature-Humidity Index (THI), the Heat Load Index (HLI) and Cattle Comfort Index (CCI). These indices are calculated using daily Australian Gridded Climate Data from 1990 with the aim of ground truthing past heat events where impacts on cattle were recorded. We will show that for some historic heat events, the HLI and CCI are better at capturing the heat stress conditions on cattle than the THI, because they both include the effects of solar exposure on temperatures that the cattle experience in open pastures. We will also discuss some initial developments in producing a prototype cattle heat stress forecast product for both the 7-day and multi-week outlook periods using NWP deterministic and ACCESS-S2 probabilistic forecasts, respectively.

There are no files associated with this item.