In our research herd, submission rates were markedly different between the POS and NEG cows. The 3-week submission rates during lactations one and two were 87% and 88% in POS cows, compared with only 49% and 63% in NEG cows, respectively6.
Calving pattern in the first lactation was not the cause of the poor submission rates for NEG cows. Instead, the poor submission rates were due to 46% of the NEG cows not cycling (anoestrus) in the first six weeks of mating, compared with only 5% of the POS cows.
Furthermore, among the NEG cows that did cycle, their interval from calving to first oestrus was nine days longer than the POS cows that cycled. This delay in ovulation was seen in both lactations one and two.
The key finding here is that the ability of cows to resume cycling within a reasonable timeframe after calving (e.g., within six weeks) is likely to share a genetic link with the 6-week calving rate. So, measuring the time between a cow’s calving and first heat may help improve the accuracy of the Fertility BV. We’re currently investigating this possibility.
Conception and pregnancy rates
As we followed our research herd over the two seasons, we saw marked differences in the timing of conception and pregnancy rates between the POS and NEG animals. On average, the POS cows conceived 12 days earlier than the NEG cows. In lactations one and two, significantly more POS cows were pregnant by six weeks of artificial breeding6:
- Lactation 1: POS 67% vs NEG 34%.
- Lactation 2: POS 74% vs NEG 44%.
By the end of breeding in lactations one and two, there was a 10% to 14% difference in final in-calf rates between POS and NEG cows6. The high not-in-calf rates of the NEG cows resulted in a sizable percentage of this group being culled as nonpregnant each year (Figure 2).
These data support an argument for basing the Fertility BV on conception success as a more direct and earlier measure of fertility than re-calving data. Foetal-aged pregnancy testing is a routine practice on more than 4000 farms1, so there are enough industry records to use this trait in genetic evaluation.