Calves

Disease Variables

True Breeding Values and Ratios

Disease traits were simulated as normally distributed traits per animal, with genetic covariances among the traits and with milk production and growth traits. Each trait had a phenotypic variance of 100.

To convert the normally distributed trait to a probability, 100 was added to the phenotypic trait value (genetic plus residual effects), and then that was divided by 100 to give a value from 0.5 to 1.5 range. Suppose p=0.1 is the probability of a disease occurrence in that parity, season, DIM, then p is multiplied by the cow ratio. Values greater than 1 increase the probability of occurrence, and less than 1 reduce the probability of occurrence. The range of the cow ratios varies with the disease and the heritability of that disease.

Factors Affecting Disease Incidences

A set of tables were made for the probabilities of each disease occurring, by parity number and by days in milk. The table below contains the odds ratios for the increase in probability of a disease given that the cow has had another disease.

Cow HasMFLDAKetMast.Ret.Pl.Cyst.Ov.Metritis
Milk Fever12.612.511111
Ret. Pl. 1112.13113.53
Mastitis 11112.392.041
Metritis 112.201.9512.771
Ketosis 17.9811111
LDA 116.881111

Below is a table of the days in milk when a disease most likely occurs during a lactation, and the incidences of the disease by lactation number.

TraitEarliest DIMLatest DIMParity 1Parity 23rd +
Mastitis03050.0560.0840.087
Lameness03050.0210.0250.025
Cyst. Ov.311500.0320.0520.065
LDA 0150 0.0050.0050.011
Ketosis 030 0.0030.005 0.011
Metritis0150 0.0960.089 0.101
Milk Fever0300.0030.005 0.026
Ret. Pl.0300.0130.0190.022

The following table contains odds ratios for the 4 seasons of the year, increases or decreases in probabilities.

TraitWinterSpringSummerFall
Mastitis11.001.110.96
Lameness11.040.500.18
Cyst. Ov.10.640.620.19
LDA11.180.791.00
Ketosis11.912.041.88
Metritis10.851.190.68
Milk Fever11.010.800.98
Ret. Pl.11.971.701.10

Diseases have different effects on production, weights, and reproduction, and for different durations during the lactation. The reductions in performance were in percentages of usual production.

TraitMilkDaysWeightDaysFeedDaysCRDays
Mastitis0.95305101010
Lameness10101010
Cyst. Ov.10101010
LDA100.77280.702810
Ketosis0.85210.82210.902110
Metritis0.871410100.62119
Milk Fever0.94210.90210.902110
Ret. Pl.0.87141.000100.62119

Diseases require labour hours and drug costs, as shown in the following table. Some cases result in death or culling, the percentages are shown below.

TraitLabour HoursDrug CostDeath %Cull %
Dystocia1440.0100.022
Mastitis1150.0110.070
Lameness.5260.0100.120
Cyst. Ov.1500.0010.050
LDA1860.0200.080
Ketosis.67190.0050.050
Metritis.67200.0150.060
Milk Fever.5250.0400.050
Ret. Pl..67200.0150.060