Rangeland cattle weight predicted from US govt satellites
© Adobe Stock US government scientists have predicted cattle weight gain at grass by using satellite imagery of rangelands to assess pasture quality and quantity.
The system estimated kg dry matter (DM)/ha, crude protein and digestible organic matter in rangeland grasses from satellite images above Colorado.
Other systems estimate growth and cover, but this system used a quality measurement to predict performance, explained US Department of Agriculture spatial ecologist Sean Kearney.
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This means that rangeland satellite monitoring packages – rather than pasture metres and grass sampling – could forecast cattle growth and inform when to graze, move and sell cattle.
Some springs see forage “green up” early, resulting in an early grazing season, but unless rains come, forage quality can deteriorate.
Tough climate
The 10-year study, published in research journal Ecological Applications, monitored weight gain in about 200 yearling steers each year for 10 summers on 40 paddocks.
Study facts
- Location was the Central Plains Experimental Range, Eastern Colorado
- 350mm of rain/year with summer temperatures up to 40C
- Pasture growth is very low – a good year might produce 2t DM/ha a year
- Average daily liveweight gain averaged 0.9kg/day (range 0.6-1.2kg/day)
- Cattle entered the grazing platform at 280kg (range 268-299kg)
- Cattle left the platform at 412kg (range 365-452kg)
- Grazing season mid-May to October
With about 0.5-2t DM/ha to graze, timing grazing to when pasture quality was high was important for maximising growth of the range. Weight gain across a grazing season could vary from as little as 80kg to 172kg.
Mr Kearney told Farmers Weekly that, working on a livestock unit of a 454kg suckler cow, the rangeland could support 0.1-0.3 animal units/ha. The ranch grazed cattle across a total of 6,000ha.
“The model performed better temporally (across repeated observations in the same paddock) than spatially (across all paddocks within a given year), highlighting the need for accurate vegetation maps and robust field data collection across both space and time,” he said.
Next steps
The system is still under development and will be studied alongside GPS collars to better understand foraging behaviour.
Mr Kearney stressed that 10 years of grassland data monitoring and more than 20 years of cattle weight gain data were key to being sure about the figures.
“We think that you need six to seven years of data before the error starts to plateau to an acceptable level,” he said.
“The satellite imagery is freely available to anyone that wants it, but there are a lot of steps to take the images through to digestibility and diet quality.
“And the current system we have is only applicable on the shorter-statured, warm season grasses in this corner of Colorado.”