WHY cows retain their placenta remains something of a mystery. But boosting vitamin E levels and reducing stress around calving can help avoid it.
About 8% of cows retain foetal membranes beyond 12 hours after calving, according to ADAS Bridgets research vet Richard Laven. "Cows with retained placentas are likely to have poorer fertility and more disease, although the retained placenta may not be directly responsible for these."
Instead, reduced immunity around the time of calving may be to blame, suggests Dr Laven. "Cows are prone to infections, such as metritis, around calving because there is a downgrading of their immune system at this time."
Trying to remove the placenta can do more harm than good, says Dr Laven. "Although pulling out the placenta means it is no longer visible outside the cow, much still remains inside. It is best to let the cow expel it herself because interfering may introduce harmful bacteria, increasing chance of disease."
Unlike calving, expulsion of placenta cannot be induced. "Separation of the placenta from the uterus is not related to hormone changes. The placenta must mature – which can take 5-6 days – before it is ready for separation."
The condition is much more prevalent in cows than other species. "This is due to cows anatomy. Most cows adapt to having a retained placenta without any problems."
However, keeping a close eye on cows which have retained their placenta will help minimise future fertility problems, says Dr Laven. "These cows can be problem cows and oestrus detection may be more difficult. Look out for them bulling before 42 days after calving when the intention is to serve them at 63 days."
A high incidence of retained placentas can reflect mismanagement before calving, explains Dr Laven. "Cows with energy or protein deficiency in the dry period or excessively fat cows are more likely to retain their placentas."
There is also a close link between vitamin E or selenium deficiency and retained placentas. The most likely explanation for this is that vitamin E and selenium are necessary for the immune system to function adequately, he says.
"Around calving, cows eat less meaning they break down body fat. This increases vitamin E requirement. Cows at grass are unlikely to require vitamin E supplementation, however, for housed cows, high levels of vitamin E in the late dry period may be beneficial."
Recommended vitamin E levels are 15mg/kg DM, however, these were calculated to avoid white muscle disease in calves.
"But in the US, cows in the late dry period are fed 1000mg/day of vitamin E with no ill effects."n *
• 8% of cows.
• Dont interfere.
• Supplement with vitamin E.