Connecting the dots—Calving difficulty, age at first calving, and enhanced cow production

Purpose: We aimed to explore the relationships among calving difficulty (CD), production traits, age at first calving (AFC), and culling in dairy cattle. Sources: Data from 687 US dairy farms, encompassing 1,048,574 CD observations scored from 1 to 5, were analyzed. Scores of CD 5 were adjusted to 4 due to limited interactions with other variables. The focus was on Holstein, Jersey, and dairy cross breeds, and parity was categorized as primiparous or multiparous.
Synthesis: The study comprised 4 steps. Step 1 assessed the effect of CD on milk yield, fat, protein, ECM, and peak milk production with fixed effects of CD, parity, calf sex (CS), and breed and random effects of calving year, calving season, and herd. Step 2 analyzed AFC, using linear and quadratic covariates, on the same parameters. Step 3 examined CD as the response variable in the step 2 database. Step 4 used logistic regression to assess risk factors associated with CD and culling reasons. Our results showed the following. Step 1: CD significantly affected milk yield, ECM, fat, protein, and peak milk production, with declines in production traits for CD >2, the least values at CD 4. Step 2: Significant linear and quadratic AFC covariates showed optimal milk performance at 27 to 28 mo. Step 3: CD was influenced by breed, CS, AFC, and interactions, with minimal CD observed at AFC of 23 to 26 mo. Step 4: Greater CD was linked to culling for nondairy purposes.
Conclusions and Applications: Calving difficulty affects production traits and is influenced by parity, breed, and CS, but its effect is less significant than expected. The AFC, particularly over 26 mo, has a more pronounced effect on CD. Greater CD levels are associated with increased involuntary culling.