What, how, and how much do herbivores eat? The Continuous Bite Monitoring method for assessing forage intake of grazing animals

Abstract Determining herbage intake is pivotal for studies on grazing ecology. Direct observation of animals allows describing the interactions of animals with the pastoral environment along the complex grazing process. The objectives of the study were to evaluate the reliability of the continuous bite monitoring (CBM) method in determining herbage intake in grazing sheep compared to the standard double‐weighing technique method during 45‐min feeding bouts; evaluate the degree of agreement between the two techniques; and to test the effect of different potential sources of variation on the reliability of the CBM. The CBM method has been used to describe the intake behavior of grazing herbivores. In this study, we evaluated a new approach to this method, that is, whether it is a good proxy for determining the intake of grazing animals. Three experiments with grazing sheep were carried out in which we tested for different sources of variations, such as the number of observers, level of detail of bite coding grid, forage species, forage allowance, sward surface height heterogeneity, experiment site, and animal weight, to determine the short‐term intake rate (45 min). Observer (Pexp1 = 0.018, Pexp2 = 0.078, and Pexp3 = 0.006), sward surface height (Pexp2 < 0.001), total number of bites observed per grazing session (Pexp2 < 0.001 and Pexp3 < 0.001), and sward depletion (Pexp3 < 0.001) were found to affect the absolute error of intake estimation. The results showed a high correlation and agreement between the two methods in the three experiments, although intake was overestimation by CBM on experiments 2 and 3 (181.38 and 214.24 units, respectively). This outcome indicates the potential of CBM to determining forage intake with the benefit of a greater level of detail on foraging patterns and components of the diet. Furthermore, direct observation is not invasive nor disrupts natural animal behavior.

Fes 1 * Bite with greater mass compared to the others. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at the sward surface height of 14 cm.

Fes 2
Bite with greater mass compared to the others. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at the sward surface height of 17 cm.

Fes 3
Bite with greater mass compared to the others. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at the sward surface height of 20 cm.

Fes 4
Bite with greater mass compared to the others. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at the sward surface height of 23 cm.

Fes 5
Bite with greater mass compared to the others. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at the sward surface height of 26 cm.

Tu 1
Bite similar to FES but with less mass. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at the sward surface height of 14 cm.

Tu 2
Bite similar to FES but with less mass. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at the sward surface height of 17 cm.

Tu 3
Bite similar to FES but with less mass. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at the sward surface height of 20 cm.

Tu 4
Bite similar to FES but with less mass. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at the sward surface height of 23 cm.

Tu 5
Bite similar to FES but with less mass. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at the sward surface height of 26 cm.

Den 1
Bite of exploration of tall fescue leaves from lower strata or close to the ground at the sward surface height of 14 cm.

Den 2
Bite of exploration of tall fescue leaves from lower strata or close to the ground at the sward surface height of 17 cm.

Den 3
Bite of exploration of tall fescue leaves from lower strata or close to the ground at the sward surface height of 20 cm.

Den 4
Bite of exploration of tall fescue leaves from lower strata or close to the ground at the sward surface height of 23 cm.

Den 5
Bite of exploration of tall fescue leaves from lower strata or close to the ground at the sward surface height of 26 cm.

Po 1
Exploration bite of 4 to 2 leaf tips at the sward surface height of 14 cm. Bite with low mass.

Po 2
Exploration bite of 4 to 2 leaf tips at the sward surface height of 17 cm. Bite with low mass.

Po 3
Exploration bite of 4 to 2 leaf tips at the sward surface height of 20 cm. Bite with low mass.

Po 4
Exploration bite of 4 to 2 leaf tips at the sward surface height of 23 cm. Bite with low mass.

Po 5
Exploration bite of 4 to 2 leaf tips at the sward surface height of 26 cm. Bite with low mass.

Co 1
Exploration bite of 1 leaf tip at the sward surface height of 14 cm. Bites with less mass compared to the others.

Co 2
Exploration bite of 1 leaf tip at the sward surface height of 17 cm. Bites with less mass compared to the others.

Co 3
Exploration bite of 1 leaf tip at the sward surface height of 20 cm. Bites with less mass compared to the others.

Co 4
Exploration bite of 1 leaf tip at the sward surface height of 23 cm. Bites with less mass compared to the others.

Co 5
Exploration bite of 1 leaf tip at the sward surface height of 26 cm. Bites with less mass compared to the others.

Re 1
Bite in places where they have already been grazed (second grazing horizon) within the same feeding station at the sward surface height of 14 cm. Bite made by the animal itself after intake the first grazing horizon.

Re 2
Bite in places where they have already been grazed (second grazing horizon) within the same feeding station at the sward surface height of 17 cm. Bite made by the animal itself after intake the first grazing horizon.

Re 3
Bite in places where they have already been grazed (second grazing horizon) within the same feeding station at the sward surface height of 20 cm. Bite made by the animal itself after intake the first grazing horizon.

Re 4
Bite in places where they have already been grazed (second grazing horizon) within the same feeding station at the sward surface height of 23 cm. Bite made by the animal itself after intake the first grazing horizon.

Re 5
Bite in places where they have already been grazed (second grazing horizon) within the same feeding station at the sward surface height of 26 cm. Bite made by the animal itself after intake the first grazing horizon.

Rede 1
Bite in places where they have already been grazed (second grazing horizon) outside of feeding station at the sward surface height of 14 cm. Bite performed in places grazed by another animal.

Rede 2
Bite in places where they have already been grazed (second grazing horizon) outside of feeding station at the sward surface height of 17 cm. Bite performed in places grazed by another animal.

Rede 3
Bite in places where they have already been grazed (second grazing horizon) outside of feeding station at the sward surface height of 20 cm. Bite performed in places grazed by another animal.

Rede 4
Bite in places where they have already been grazed (second grazing horizon) outside of feeding station at the sward surface height of 23 cm. Bite performed in places grazed by another animal.

Rede 5
Bite in places where they have already been grazed (second grazing horizon) outside of feeding station at the sward surface height of 26 cm. Bite performed in places grazed by another animal.
In 1 Bite in other species at the sward surface height of 14 cm.
In 2 Bite in other species at the sward surface height of 17 cm.
In 3 Bite in other species at the sward surface height of 20 cm.
In 4 Bite in other species at the sward surface height of 23 cm.
In 5 Bite in other species at the sward surface height of 26 cm.

Experiment 3
Fes A Bite with greater mass compared to the others. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at 0% depletion of pasture sward.

Fes B
Bite with greater mass compared to the others. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at 20% depletion of pasture sward.

Fes C
Bite with greater mass compared to the others. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at 40% depletion of pasture sward.

Fes D
Bite with greater mass compared to the others. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at 60% depletion of pasture sward.

Fes E
Bite with greater mass compared to the others. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at 70% depletion of pasture sward.
Tu A Bite similar to FES but with less mass. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at 0% depletion of pasture sward.

Tu B
Bite similar to FES but with less mass. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at 20% depletion of pasture sward.
Tu C Bite similar to FES but with less mass. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at 40% depletion of pasture sward.
Tu D Bite similar to FES but with less mass. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at 60% depletion of pasture sward.
Tu E Bite similar to FES but with less mass. Bites depth corresponding to 40 to 50% of the sward surface height of the tall fescue (first grazing horizon) at 70% depletion of pasture sward.

Den A
Bite of exploration of tall fescue leaves from lower strata or close to the ground at 0% depletion of pasture sward.

Den B
Bite of exploration of tall fescue leaves from lower strata or close to the ground at 20% depletion of pasture sward.

Den C
Bite of exploration of tall fescue leaves from lower strata or close to the at 40% depletion of pasture sward.

Den D
Bite of exploration of tall fescue leaves from lower strata or close to the ground at 60% depletion of pasture sward.

Den E
Bite of exploration of tall fescue leaves from lower strata or close to the ground at 70% depletion of pasture sward.
Po A Exploration bite of 4 to 2 leaf tips at 0% depletion of pasture sward. Bite with low mass.

Po B
Exploration bite of 4 to 2 leaf tips at 20% depletion of pasture sward. Bite with low mass.
Po C Exploration bite of 4 to 2 leaf tips at 40% depletion of pasture sward. Bite with low mass.
Po D Exploration bite of 4 to 2 leaf tips at 60% depletion of pasture sward. Bite with low mass.
Po E Exploration bite of 4 to 2 leaf tips at 70% depletion of pasture. Bite with low mass sward.
Co A Exploration bite of 1 leaf tip at 0% depletion of pasture sward. Bites with less mass compared to the others.

Co B
Exploration bite of 1 leaf tip at 20% depletion of pasture sward. Bites with less mass compared to the others.

Co C
Exploration bite of 1 leaf tip at 40% depletion of pasture sward. Bites with less mass compared to the others.
Co D Exploration bite of 1 leaf tip at 60% depletion of pasture sward. Bites with less mass compared to the others.