Table 3.
Comparison of the estimated association of hyperketonemia (HYK) status with pregnancy to first insemination, pregnancy by 150 DIM, and calving-to-conception interval, between each level of milk yield in the first week of lactation in 2,024 Holstein dairy cows
| Variable | HYK positive1 |
HYK negative |
||
|---|---|---|---|---|
| Days to pregnancy2 | Estimate (95% CI) | Days to pregnancy | Estimate (95% CI) | |
| Pregnancy to first AI3 | ||||
| Milk = high4 | — | 0.93 (0.57, 1.51) | — | Referent |
| Milk = mid | — | 0.96 (0.65, 1.42) | — | 0.99 (0.80, 1.23) |
| Milk = low | — | 0.55 (0.30, 1.00) | — | 0.89 (0.68, 1.16) |
| Pregnancy by 150 DIM5 | ||||
| Milk = high | — | 0.86 (0.59, 1.27) | — | Referent |
| Milk = mid | — | 0.90 (0.66, 1.24) | — | 1.00 (0.84, 1.19) |
| Milk = low | — | 0.56 (0.37, 0.83) | — | 0.79 (0.64, 0.99) |
| Calving-to-conception interval (d)6 | ||||
| Milk = high | 106 | 4.68 (−6.67, 16.04) | 101 | Referent |
| Milk = mid | 105 | 3.63 (−5.67, 12.85) | 102 | 0.27 (−4.97, 5.51) |
| Milk = low | 123 | 21.66 (11.46, 31.86) | 110 | 8.63 (2.36, 14.90) |
Cows were classified as HYK positive if they had at least one test above the cut-point (BHB ≥1.2 mmol/L) and were otherwise considered HYK negative.
Days to pregnancy as estimated marginal means.
Estimates of pregnancy to first insemination are reported as risk ratios and adjusted by disease in the first week.
Categories were calculated separately for primiparous and multiparous cows within each herd. Cows were considered low-yielding when their first-week postpartum milk yield average was under the 25th percentile; cows between the 25th and 75th percentiles were considered mid-yielding; cows over the 75th percentile were considered high-yielding.
Estimates of pregnancy by 150 DIM are reported as hazard ratios.
Calving-to-conception interval is reported as the mean difference in days.