Brian J. Rude, Darrell L. Rankins, Jr, S. Eddy Peacock, and John T. Eason

Feeding broiler litter to brood cows as a winter feedstuff has been practiced for several years because oi its economic advantages. However, some cows consuming broiler litter during pregnancy have exhibited signs of milk fever following calving. Milk fever is a calcium deficiency in the cow as a result of the increased demands of milk production. A recent AAES study showed that a small amount of hay each day was beneficial for partially alleviating the suppressed serum calcium observed in cows fed broiler litter.

The first trial was conducted at the Sand Mountain Substation in Crossville in 1993. In late October, 45 pregnant cows were divided into three equal groups and fed hay or a diet containing 80% broiler litter and 20% corn or the broiler litter and corn diet with 2% ammonium chloride. Ammonium chloride has been used in the dairy industry to prevent milk fever. Diets were fed through early April.

Two digestibility trials were conducted with the first being at the initiation of the study and the second immediately following calving. Although clinical milk fever was not observed in any of the cows fed broiler litter, blood calcium concentrations were suppressed. Cows fed broiler litter absorbed more calcium, without increasing urinary or milk output of calcium, yet serum calcium concentrations were decreased, thus predisposing the cows to milk fever. Cows fed hay exhibited normal concentrations of serum calcium.

In this study, cows consuming broiler litter were depositing calcium into the bone when they should have been resorbing calcium from the bone. Addition of ammonium chloride was not effective in minimizing the effect broiler litter had on calcium status in these cows.

A second trial was conducted at the Sand Mountain Substation in 1994 to determine if supplemental hay would offset the negative effect that broiler litter was having on calcium status in cows after calving. In late October, 48 pregnant cows were divided into three equal groups and fed hay, broiler litter and corn, or broiler litter and corn with five pounds of hay per cow per day.

As in the previous trial, broiler litter decreased serum calcium concentrations; however, addition of hay to the broiler litter diet tended to offset these changes. Measuring serum hydroxyproline, an indicator of bone breakdown, indicated that cows fed broiler litter were depositing calcium into the bone instead of using it for milk production. Addition of hay to the broiler litter diet allowed less calcium to be deposited, and apparently maintained serum calcium within acceptable limits.

A third trial was conducted on the AU campus in 1995 to further assess the effects of supplemental hay on calcium status in animals fed broiler litter. To accomplish this objective, pregnant goats were used as a model for brood cows. Beginning in October, these goats were fed three diets similar to those in the second trial. Goats were subjected to metabolism trials immediately before and after kidding.

As observed in cows, broiler litter consumption suppressed serum calcium, even though more calcium was retained in the body of goats fed broiler litter. Again, it was determined that bone deposition of calcium was occurring in goats that had been consuming broiler litter during pregnancy. Similar to the second trial, serum calcium was increased and bone deposition was decreased in goats consuming broiler litter and supplemented with hay.

Results of these studies indicate that the milk fever problems frequently observed in cows consuming broiler litter during pregnancy is a result of abnormal calcium metabolism. The decreased serum calcium is a result of calcium metabolism being directed towards bone deposition at calving. These cows need to maintain serum calcium at this time due to the demands of milk production. The primary mechanism to accomplish this is through bone resorption of calcium. It was also shown that the potential for this problem can be minimized with addition of hay to broiler litter diets.

Although serum calcium was suppressed in each of these trials, it should also be pointed out that clinical milk fever was only observed in two cows consuming broiler litter. In general, the cows that exhibit milk fever, and thus require treatment, are the older cows (greater than eight years of age) and the best milk producers (i.e., wean the heaviest calves).