A high stocking rate has no negative impact on the fertility of pasture-based dairy cows provided they get the correct nutrition and are the right breed for the system.
Researchers from Teagasc in Ireland have compared the effect of three different stocking rates on herd fertility.
Three groups of high economic breeding index (EBI) Holstein Friesians and three of Jersey cross-breeds were stocked at 2.5, 2.9 and 3.3 cows a hectare.
Each group was managed identically except for the post-grazing sward heights, which were set at 4.5-5cm for the two low stocking rate groups, 4-4.5cm for the medium and 3.5-4cm for the high.
Pasture productivity was high during the study, with average annual growth rates of 15.5t DM/ha.
The fertility performance of each group was monitored for two years, over the 12-week breeding seasons.
Results from the study show:
- The interval from calving to first ovulation was the same regardless of stocking rate
- There was a shorter interval to first ovulation for the Holstein Friesians compared with the Jersey cross-breeds.
- The cross-breeds had a higher six-week in-calf rate – 63.1% compared with 56.3% for the Holstein Friesians.
The study concluded there is minimal variation in fertility performance among the three stocking rates as long as nutrition is adequate.
One of the researchers involved in the study, Brendan Horan, says the results clearly show there is no direct relationship between stocking rate and fertility performance.
The results also suggest increased stocking rates can be achieved without any adverse effects on overall pregnancy rate when animals appropriate to the system are selected.
“Stocking rate is widely accepted as the main driver of productivity within grazing systems, and recent research studies have further highlighted the beneficial effects of optimum stocking rates on animal productivity, grazed grass utilisation and overall farm system efficiency,’’ says Mr Horan.