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Associations between predictions of Lifetime Net Merit and profitability of dairy cows.

G. L. Pezzella



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Associations between predictions of Lifetime Net Merit and profitability of dairy cows.
G. L. Pezzella*1, C. D. Dechow2, A. De Vries1. 1University of Florida Gainesville, FL, 2The Pennsylvania State University University Park, PA.

The objective of this study was to determine the associations between estimates of Lifetime Net Merit (NM$) that were derived independently of the cow's own performance, and observed profitability of dairy cows. The Pennsylvania State University provided daily BW and daily milk production data (yields, fat, and protein), birth dates, calving dates, dry-off dates, and disease treatment data for 2,305 cows in their herd from 1998 to 2017. Python and Microsoft Excel were used to calculate the total milk revenue, health and feed costs, and net profit per cow per lactation. The health events in the analysis include displaced abomasum, mastitis, ketosis, metritis, milk fever, and retained placenta with their costs taken from the literature. Replacement and other costs were not included. Profit was measured as total lifetime profit and standardized lifetime profit calculated as profit per day x 305 � 2.78. Genetic estimates of NM$ included Direct Genomic Values (DGV) from the April 2018 genetic evaluation for 725 cows and Predicted Transmitting Ability (PTA*) values calculated as sire + 1/2 maternal grandsire + 1/4 maternal great-grandsire PTA from the December 2019 genetic evaluation. Therefore cows' own performance data had little effect on genetic estimates. Simple linear regression was used to calculate slopes (b) and R2. Results showed a positive association between PTA*(y) and DGV(x) (n = 671, b = 1.544, R2 = 0.700) where the expected value was b = 1.75. The DGV predicted total lifetime profit (n = 532, b = 1.599, R2 = 0.062) and standardized lifetime profit (n = 532, b = 2.139, R2 = 0.124) where the expectation was b = 2. The PTA* predicted total lifetime profit (n = 1,109, b = 1.740, R2 = 0.059) and standardized lifetime profit (n = 1,109, b = 1.180, R2 = 0.128) where the expectation was b = 1.14. These findings confirm that predictions of genetic merit of profit can be observed in differences in real profitability of dairy cows. The association was strongest for standardized lifetime profit, which implies that the opportunity cost of delayed replacement must be considered.

Keywords: profitability, genetics, selection index.