IRISHTACKLE FALLING COWFERTILITY
FALLING cow fertility means Irish dairy producers biggest concern is cow genotype and how this will affect herd performance.
Farm data on fertility performance clearly shows a decline over the last few years, says Teagasc senior researcher Pat Dillon. "More and more producers have moved to using Holstein genetics and this influence is becoming evident."
Previously cow fertility in commercial spring calving Irish herds has been consistent. "Over 60% would be pregnant to first service and less than 10% would end up not in-calf."
But since 1985 the rate of genetic increase has increased markedly with average Relative Breeding Index (RBI) of cows born increasing from 94 to 109 by 1995, and average genetic improvement a year is running at 1.3% in 1996.
Studies at Moorepark dairy research centre, comparing performance of high genetic merit cows and medium genetic merit cows, reveal that infertility rates for high genetic index cows (HGI) in 1996 and 1997, were 21% and 25% respectively (see table).
"If high index cows calved once a year and had similar fertility rates they would be more efficient, but with higher culling rates and associated costs of infertility they cost more."
Longer calving index
There is 10 days difference in calving index between the HGI cows and medium genetic index (MGI) cows, meaning HGI cows need 10 days longer to get back in-calf. "When you have a seasonal calving pattern, you do not have this time to get them back in-calf," adds Dr Dillon.
Producers selecting sires can increase the herds RBI to 120, equivalent to 50-60% Holstein, and produce 6850 kg of milk a cow, with less than 10% of cows left not in-calf at the end of a 13 week breeding season, he says.
However, where a herds RBI increases to 130, which means 100% Holstein genetics, then 20% of cows will not be in-calf at the end of the breeding season.
"Producers with HGI herds must be careful with their future breeding policy. Their best option is to opt for sires that maintain milk production, but increase milk composition, especially protein," says Dr Dillon.
But those herds with RBIs of 95-110 can look to increase genetic indexes, by using sires with figures that are +250 to 500kg of milk, positive for milk protein and have been tested on a grass based feeding system.
Irish improvements in cattle genetic indexes coincides with a move from British Friesian cows to Holstein Friesian types, says Dr Dillon.
"Breeding has increased milk production but without concern for other functional traits. We need an index that includes breeding and female traits, such as fertility."
Total merit index
Currently Dr Dillon is involved in a project to devise a total merit index suitable for Irish dairy systems. "We are looking for a type of cow that has high milk yields, 5600 – 7022 kg/cow, of good composition, therefore high in fat and protein. She must last three to four lactations and fit into a 365 day seasonal calving pattern."
Research will test daughters from sires in 54 commercial dairy herds to obtain information on traits like female fertility, mastitis resistance and calving difficulty.