Ra. Distel et al., PATCH SELECTION BY CATTLE - MAXIMIZATION OF INTAKE RATE IN HORIZONTALLY HETEROGENEOUS PASTURES, Applied animal behaviour science, 45(1-2), 1995, pp. 11-21
The role of various perceptual cues on selectivity patterns of cattle
grazing heterogeneous swards were studied in a controlled experiment.
Patches of different height and/or bulk density, representing similar
or dissimilar potential instantaneous intake rate (IR), were created i
n a ryegrass (Lolium perenne L.) pasture to study foraging responses o
f cattle (Bos taurus) to heterogeneity in patch structure. The experim
ent involved three heterogeneity treatments with two patch types each.
One patch type (short-dense) was present in all three treatments. In
all treatments, cattle encountered and entered both patch types availa
ble with the same frequency. In contrast, average residence time and t
otal number of bites removed were greater in the patch type that allow
ed greater instantaneous intake rate. Patch utilization and residence
time agreed with qualitative predictions of a rate-maximizing model. R
esidence time in short-dense patches was shortest in the treatment tha
t allowed the greatest intake rate, and longest in the one that allowe
d the lowest intake rate. Short-dense patches were relatively avoided
when the alternative patch was tall and dense, but they were preferred
when the alternative patch was short and sparse. The pattern of relat
ive preference for the different patches ruled out vegetation height,
density and herbage mass as cues for the allocation of residence time.
Steers consistently spent more time in the patches that allowed great
er bite weights and instantaneous intake rate while at the patch. Rela
tive preference of patches exhibited a pattern of overmatching, under
the assumption that herbage intake was the reward to grazing behavior.
Overmatching indicates that behavior was allocated to patches more th
an proportionally to the relative rewards. However, the degree of over
matching was less than predicted by maximization of intake rate, Grazi
ng behavior and residence time did not respond to repeated short-term
exposures to a treatment within the same day.