Dairy cattle

Genetic parameters for productive life and daughter pregnancy rate related to fly prevalence in grazing dairy cattle.

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Abstract

The objective of this study was to evaluate the association between fly prevalence and economic traits in grazing dairy cows and heifers during the summer grazing season. Holstein, Jersey, and crossbred dairy cows and heifers (n = 584) were from 3 grazing farms in Minnesota and Wisconsin. Cattle were born between 2017 to 2025. Fly prevalence was determined with a 0 to 4 scale based on fly coverage on one side of the body where 0 indicated few to no flies and 4 indicated high number of flies. Animals were scored once a month during the 2025 grazing season (June to September). All cattle were genotyped with the 65K SNP chip from Neogen Dairy Genomics (Lincoln, NE, USA). Genetic correlations were estimated utilizing gPTA's for productive life (PL) and daughter pregnancy rate (DPR) across breed groups, with additional analyses incorporating percent Holstein genetics, feed saved, and health trait index (HT). Results indicated that PL and DPR were negatively correlated (-0.116), suggesting that improvements in fertility may be lowly associated with reduced longevity in the herd. Within-breed analysis found that the genetic correlation between PL and DPR was negative for Holsteins (-0.327, n = 411) and the genetic correlation for Jerseys was positive (0.206, n = 78). Health trait index was positively correlated (0.435) with PL, which would explain that healthier cattle tend to stay longer in the herd. Simple linear regression models were fit with the fixed effect of average fly score and response variables of PL, lifetime net merit (NM$), and DPR. Lifetime net merit declined by $63.77 for each unit increase in fly score (SE = 39.70; P

Keywords: 2026

How to Cite:

Fredin, S., Dechow, C., Haagen, I. & Heins, B., (2026) “Genetic parameters for productive life and daughter pregnancy rate related to fly prevalence in grazing dairy cattle.”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2287376. doi: https://doi.org/10.31274/wcgalp.24280

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