Congenital Defects May Be Linked to Silage Consumption During Pregnancy
How to avoid deformed calves when feeding silage to pregnant cows.
Dan Buskirk, beef Extension specialist at Michigan State University, says corn silage is an excellent feed in terms of energy content for most classes of livestock. Occasionally, however, producers have seen congenital defects in calves after feeding silage to their cows during pregnancy.
“Affected calves, called ‘acorn calves’ or ‘bulldog calves,’ are the result of a condition referred to as congenital joint laxity and dwarfism (CJLD), congenital spinal stenosis or congenital chondrodystrophy of unknown origin (CCUO),” he says. There seems to be association of CCUO with grazing drought-affected pastures, feeding silage-only diets or supplementing pregnant cows with apple pulp.
Reports of a skeletal system deformity in calves were first noted in 1932 in California’s Sierra Nevada region. Ranchers referred to these deformed calves as acorn calves because they thought ingestion of acorns by pregnant cows during gestation led to the condition.
“This theory was dismissed after observation of the deformity in calves from dams with no access to acorns. Frequent reported cases of the condition, now called CCUO, occur in the northern U.S. and Canada. The condition may afflict only a few calves or many calves in a herd,” he says.
Calves affected with CCUO are born with bowed or sickle-shaped legs with weak joints (joint laxity), shortened legs (disproportionate dwarfism), and in some cases a notable underbite with the lower jaw much shorter than the upper jaw. Joint laxity may contribute to calving difficulty, early calf mortality and a staggering or wobbly gait. Within a few weeks after birth, the joints of surviving calves may begin to stabilize, allowing them to walk more normally. However, affected calves typically remain much smaller and are slower growing than herdmates, says Buskirk.
Although the definitive cause of CCUO has not been determined, this condition is usually associated with feeding fermented forages (as the only feed) to spring-calving cows during mid- to late gestation.
Calf affected with congenital joint laxity and dwarfism. |
“Researchers think it might be due to interference with manganese absorption, but it’s been a hard thing to pinpoint,” Buskirk explains. “There may be some other factors, unique to specific geographical areas, that cause CCUO; but most investigators think the underlying cause relates to a maternal nutritional deficiency of manganese. Affected calves have low concentrations of manganese in the liver. It is possible that bioavailability of manganese is reduced in ensiled forages, although other minerals or factors may contribute to the necessary conditions to trigger CCUO.”
The apparent good health and generally good mineral status of dams giving birth to CCUO calves suggests that any nutritional deficiency arising during gestation may be either short term, resolving before symptoms are shown in dams, or not severe enough to affect dam health. He recommends adding a little dry feed to the diet to prevent the problem overall.
In recorded outbreaks of CCUO, spring-born calves seem most susceptible. This corresponds with mid-gestation supplemental feeding or grazing of drought pastures during the last two trimesters. A few anecdotal accounts point to clover, especially sweet clover, or grass silages posing the greatest risk, especially to young cows, but it’s hard to nail down, he says.
Experimentally, supplementation of silage diets with dry forages or dried grains reduces or eliminates the risk of CCUO. “In one study, as little as 5 pounds of dry hay and 1.5 pounds of dry rolled barley daily per animal eliminated the condition in cows fed silage diets. The critical feeding period is likely within the last 180 days of gestation. Feeding a balanced, loose mineral-vitamin supplement is recommended, but there is not sufficient evidence to suggest that mineral supplementation alone can prevent occurrence of CCUO when cows are fed only fermented forages,” he says.
Editor’s note: Heather Smith Thomas is a freelance writer from Salmon, Idaho. [Photos courtesy of Heather Smith Thomas.]
