In the last few days, there have been several reports of cows eating stones at grazing. This abnormal behaviour, which may also involve licking or chewing wood fences or other non-nutritive material, is called pica. While animals showing pica can look healthy, this behaviour can lead to undesirable consequences, such as ingestion of objects which could damage the gut.
The reasons behind the occurrence of pica are not completely clear: this abnormal appetite is generally associated with mineral deficiencies (sodium and phosphorus) and/or lack of structural fibre. Other possible causes are energy or protein imbalances, intestinal parasites or other mineral deficiencies. In some cases, the cause is unknown.
As the grass plant moves into the reproductive phase it is unlikely that lack of structural fibre is the cause for grazing herds on this occasion.
Talk to your vet regarding the possibility of running blood tests to check the mineral status of your cows. However, diagnosis of mineral deficiencies in cattle through a blood test is not always easy.