The height and leafiness of plants in pasture should give ranchers clues as to how long they can leave cattle grazing – and how large to make pastures.
That’s according to Stacey Gunter, research leader at the Agricultural Research Service (ARS) Southern Plains Range Research Station in Woodward, OK. He worked with former doctoral student Pablo Gregorini and Woodward colleagues to demonstrate this approach using beef steers grazing in fenced-off corridors in wheat pastures.
The pastures, chosen to represent a range of natural variations in plant heights and upper plant leafiness, were grazed freely by steers. The animals were removed when they reached the end of a corridor, regardless of how much time they took. Each steer was videotaped with two trained observers who counted bites and walking steps.
Most grazing behavior studies are done on "artificial seedings,” specially planted pastures or small plots that are fairly uniform. Gunter and Gregorini integrated standard study methods with much less uniform, in-field pasture conditions.
Cattle like their food to be accessible, with leaves high on plants and a minimum of stem interference with cow tongues. Cattle use their tongues to wrap around and pull off leaves. Those with canopies of luscious leaves took larger bites and were able to get their daily rations with lower calorie expenditure.
That resulted in greater eating efficiency, which was measured by dividing the total amount of pasture plants eaten per steer by the total eating time. This is known as herbage intake rate, a key determinant of weight gain for grazing cattle.
The research was published in the Journal of Animal Science.