Estimation of the Economic Impact of a Unit Change in Predicted Transmitting Ability for Daughter Pregnancy Rate and Other Predicted Transmitting Ability in the Merit Indexes

These studies deal with lifetime profit analyses for individual cows, and using these estimates to determine the economic value of genetic changes in traits for which genetic evaluations (predicted transmitting ability, PTA) are currently available. Data were collected from six states processed by Dairy Records Management Systems (DRMS) from herds on continuous test for at least 10 yr.

The purpose of the first study was to determine how well estimators of lifetime net income based on 305-d lactation yields and a 10-yr opportunity (RNI305.10) and based on complete lactation data but a 5-yr opportunity (RNIc.5) predict the estimate based on complete lactations and a 10-yr opportunity (RNIc.10). Records for 22,854 cows in Virginia herds born in 1988, 1990, and 1992 from the DRMS in Raleigh, NC were used. Each RNI was calculated using fluid (skim/fat) pricing and milk-fat-protein pricing. Regression analyses including herd and birth year were used in the model to estimate the regression of RNIc.10 on RNIc.5, and RNIc.10 on RNI305.10. The resulting regression coefficients for fluid (skim/fat) pricing were $1.53 and $1.12 explaining 67 and 97% of the variation of RNIc.10, respectively. The corresponding results for milk-fat-protein pricing were $1.52 and $1.14 explaining 68 and 96% of the variation of RNIc.10, respectively. Using RNIc.10 as the measure to estimate lifetime profit is strongly recommended over the two alternatives tested.

In the second study, the economic impacts of a unit change in PTA of daughter pregnancy rate (DPR) and other PTA in the merit indexes on lifetime profit estimates of a bull's daughters were estimated to determine an economic weight for the PTADPR and other PTA in economic indexes. Records for 71,094 cows born in 1988, 1990, and 1992 from six states processed at DRMS were used: Florida [10,940 cows], Indiana [8,231 cows], North Carolina [12,280 cows], Texas [4,786 cows], Virginia [20,341 cows], and Vermont [14,516 cows]. The basic RNI function consisted of [total milk, fat, and protein income ?feed cost for production] (yield income, YI) + [net value of calves + net salvage value] (non yield income, NYI) ?rearing cost (RC) ?[(daily cost for labor, maintenance feed, supplies, and fixed expenses) x days in herd] (daily cost, DC). Some of the economic impacts of PTA described for the merit indexes were not included in the basic RNI. These were added to RNI by multiplying the respective sire PTA by the economic impact. These included -165PTASCS (M); 33udder composite + 15feet and legs composite -14.86body size composite (T); and 8.064PTA for daughter pregnancy rate -4.80PTA for daughter calving ease (PRCE). Each ARNI was calculated using all production records initiated prior to the cow's tenth birthday with three milk pricing systems comparable to the prices in USDA three merit indexes: fluid (skim/fat) pricing (FARNI), milk-fat-protein pricing (NMARNI), and cheese pricing (CARNI). Two levels of prices for rearing cost per day and daily cost were used for calculating FARNI, NMARNI, and CARNI. Regression analyses including herd and birth year in the model were used to estimate the simple and partial regressions of ARNI or partitioned ARNI on sire PTA. Partial regression included all PTA in Net Merit, except service sire calving ease. Ignoring other PTA, one unit increase in PTADPR increased 476.25kg of lifetime total milk or 18 days of total DIM. One unit decrease in PTASCS increased 4372.50kg of lifetime total milk. With low daily and rearing costs, each 1% change in PTADPR increased ARNI by $59.31 to $55.82 depending on the milk pricing systems. The corresponding results with high daily and rearing costs were $27.50 to $24.01. Standardized multiple regression enabled the comparison of the economic weights of this study with those of USDA. The PTA for productive life (PL) in all three USDA merit index was emphasized less than the results from this study; however, PTADPR in USDA indexes was emphasized more than this study. In this study, the economic weight of PTADPR was negative within the low daily and rearing costs, but it was positive in the high daily and rearing costs.