Conception setbacks in high-merit cows
HIGH genetic merit animals are less fertile and need more services a conception than those of low merit.
Thats the result of studies comparing the performance of second lactation animals on three grazing-based feeding systems at Teagascs Moorepark Dairy Research Centre, Cork, Ireland.
But the poor fertility was not due to poor nutrition, claims Mooreparks Dr Pat Dillon.
Of the high merit, 10 cows averaging £80 PIN failed to get in calf, but only three average merit animals (£35 PIN) were infertile.
However, six of the 13 cows failing to conceive were in a high concentrate fed group offered a minimum of 5kg/day during early lactation.
The cows on the Moorepark – standard Irish practice – system were under more pressure, with high and average merit cows fed only 650kg/year of concentrate, yet only one cow in these two groups failed to get in calf in the 13-week breeding season. In the high grass system, where adequate grass was always available, six cows in the two groups failed to get in calf.
"From 11 weeks into lactation when the breeding season started, high and low merit cows were gaining body weight at 0.35kg/day," says Dr Dillon.
Submission rates – cows put forward for service – were 88% for both high and average merit cows in the first three weeks of the service period, he adds. The calving to service intervals and calving to conception intervals were also the same.
"But the high merit cows did have a higher infertility rate and required more services a conception for cows that conceived."
• Second lactation yields in the Moorepark study confirm that high merit cows show massive potential to milk off grazed grass, says Pat Dillon.
High merit cows on the Moorepark system fed 650kg of concentrates a year produced 6582kg in the first 33 weeks of lactation compared with 5680kg for the medium merit cows.
The differences on the high grass and high concentrate systems were about 700kg in this 33-week period.
Both high and medium merit cows responded well to concentrates giving an extra 0.86kg of milk for each extra 1kg of concentrate fed, claims Dr Dillon.
This was higher than in the first year of the study when the response rate was 0.67kg milk/kg of concentrate.
"This response was higher than we would see normally, and in some periods the response was better than others," he says. "At an average milk price the return is 16.8p for each 1kg of concentrate fed."
Pat Dillon…poor fertility in high-merit cows is not due to poor nutrition.