Table 4.
Model inputs and distributions used in the stochastic model
| Parameter | Symbol* | Value and distribution | Unit | Source |
|---|---|---|---|---|
| Global parameters (affecting more than one intervention cost) | ||||
| Average number of breeding cows in herd† | N | Gamma (2·84, 53·9) | Number | National Milk Records, 2011 |
| Proportion of cows calving per year† | CP | Gamma (2·64, 0·142) | Proportion | National Milk Records, 2011 |
| Perinatal mortality (birth to 24 h)† | PM | Pearson 5 (4·52, 0·295) | Proportion | [11] |
| Young stock mortality (age 24 h to 3 months)† | MTM | Exponential (0·0215) | Proportion | [11] |
| Young stock mortality rate (age 3–18 months)† | YM | Exponential (0·0402) | Proportion | [11] |
| Proportion served to dairy | SD | Varied in scenario modelling | n.a. | |
| Labour cost | L | Constant (13·08) | £/hour | [12] |
| Keeping bedding dry (BD) | ||||
| Time for keeping bedding dry (baseline) | BDB | Uniform (0·66, 1·0) equivalent to 2–3 min every 3 days | Minutes/animal/day | User defined estimate |
| Time for keeping bedding dry (intervention) | BDI | Uniform (1·0, 2·0) | Minutes/animal/day | User defined estimate |
| No direct contact with other cattle (DC) | ||||
| Stocking density (grazing)† | SDG | Gamma (12·0, 0·198) | Cows/ha | Promar, 2011 |
| Fencing cost (consumables and labour) | FC | Uniform (0·0098, 0·32) | £/metre | Primary data collection |
| Fencing construction cost | FCC | Constant (3·45) | £/metre | [12] |
| Grass keep | GK | Constant (110·0) | £/ha/year | [12] |
| Set aside variable cost | SAC | Constant (20·0) | £/ha/year | [13] |
| Proportion of perimeter double fenced | Varied in scenario modelling | n.a. | ||
| No new animals being brought into the herd (CH) | ||||
| Extra labour in quarantine | QT | Uniform (0·0, 1·52) | Hours/day | Primary data collection |
| Bedding use in quarantine | QB | Uniform (0·0, 58·0) | Kg/cow/day | Primary data collection |
| Culling rate† | CR | Gamma (4·12, 0·080) | Proportion/year | National milk records, 2011 |
| Proportion that calve after reaching age 18 months† | SDC | Exponential (0·045) | Proportion | [11] |
| Barley straw† | BS | Logistic (58·4, 1·90) | £/tonne | [20] |
| Sand cost | SN | Constant (15·0) | £/tonne | Cardigan Sand and Gravel Ltd, 2011 |
| Sawdust cost | SDU | Uniform (45·0, 90·0) | £/tonne | NW Resources Ltd, 2011 |
| Main herd bedding (straw yards) | SSY | Constant (5·48) | Kg/cow/day | [12] |
| Main herd bedding (deep sand cubicles) | DSC | Uniform (7·5, 10·0) | Kg/cow/day | [14] |
| Main herd bedding (sawdust on mattresses) | SDM | Uniform (0·75, 1·0) | Kg/cow/day | [14] |
| Main herd bedding (straw on cubicles) | SUC | Uniform (2·5, 4·0) | Kg/cow/day | [14] |
| Average group size purchased | AGS | Varied in scenario modelling | n.a. | |
n.a., Not applicable.
*
For explanation of symbols see Table 2.
†
Parameters fitted to original data using @Risk 5.5 (Palisade Corporation, USA).