Results (cont.). Results (cont.). Introduction. Table 3. Correlations of AFC and the traits included in the lifetime net merit index*.
Table 3. Correlations of AFC and the traits included in the lifetime net merit index*
Heifer rearing costs account for 15 to 20% of the total expense of milk production, and the decline in cow fertility over the last 40 years is well-documented. Genetic selection for younger age at first calving (AFC) may improve profitability and fertility.
Table 2. Summary statistics of PTA AFC for active bulls
Animal model used to predict variances and PTA:
y = hys + a + e
y = age at first calving
hys = fixed effect of herd-year-season of birth
a = random additive genetic effect
e = random residual error
*Correlations among PTA for bulls with reliabilities of AFC ≥ 0.90 (BS n=15, HO n=1,557 and JE n=126).
Figure 1. Sire genetic trend for AFC
Table 1. Summary of phenotypic AFC for cows