| Literature DB >> 34306618 |
Anderson Michel Soares Bolzan1, Leonardo S Szymczak1,2, Laura Nadin3, Olivier Jean F Bonnet1,4, Marcelo O Wallau5, Anibal de Moraes2, Renata F Moraes2, Alda L G Monteiro6, Paulo C F Carvalho1.
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.Entities:
Keywords: Italian ryegrass; foraging; grasslands; grazing ecology; herbage intake; short‐term intake rate; tall fescue
Year: 2021 PMID: 34306618 PMCID: PMC8293712 DOI: 10.1002/ece3.7477
Source DB: PubMed Journal: Ecol Evol ISSN: 2045-7758 Impact factor: 2.912
FIGURE 1Representation of the types of sheep bites with their respective codes used in the Continuous Bite Monitoring method in experiment 1 (a) with Italian ryegrass, 2 and 3 (b) with Tall fescue. Drawing, in experiment 2 and 3 (b), represents the codes used in all tested heights, here demonstrated for the height of 20 cm. Note: The same codes were used for the other treatments. The arrows represent the depth of the bite in bite type. Description of bites is in Table 1 in Supporting Information
ANOVA table for the potential sources of variation of the error in the estimation of fresh matter intake through CBM. Day refers to the number of days with observation since the beginning of the experiment, Period to the period of the day evaluated (morning or afternoon) and Total bites to the total number of bites observed during one trial. Interactions were not significant and were removed from the final model
| Source of variation |
|
|
|
|---|---|---|---|
| Experiment 1 | |||
| Observer | 2 | 4.75 | .018 |
| Animal | 3 | 1.97 | .14 |
| Day | 1 | 0.06 | .81 |
| Total bites | 1 | 0.17 | .68 |
| Experiment 2 | |||
| Sward surface height | 4 | 12.478 | .0002 |
| Observer | 1 | 3.633 | .078 |
| Day | 4 | 1.091 | .314 |
| Period | 1 | 0.083 | .777 |
| Total bites | 1 | 27.927 | .0000 |
| Experiment 3 | |||
| Sward depletion | 4 | 91.46 | .0000 |
| Observer | 1 | 11.02 | .006 |
| Day | 4 | 7.724 | .101 |
| Period | 1 | 1.640 | .68 |
| Total bites | 1 | 15.392 | .0000 |
FIGURE 2Relationship between the total intake of fresh matter (g FM) of ewes during grazing sessions of 45 min estimated through continuous bite monitoring assessed by the double weight technique, in experiment 1 (a), 2 (a) and 3 (C). Solid line represents the linear model between the two methods (p <.001), dashed lines represents identity (Y = X), and gray area represent the confidence interval of the measurement through double weight with regard to scale precision
FIGURE 3Bland–Altman plots showing the paired differences against the average between CBM and DWM methods in experiments 1 (a, p =.1052 in one‐sample t test), 2 (b, p =.0002 in one‐sample t test), and 3 (c, p =.0001 in one‐sample t test). Mean bias is represented by black line and limits of agreement are shown by the dashed lines, while confidence intervals are shown by the gray areas