16 April 2007

6 minute read

Various studies have suggested that scours are the cause of 15-20% of all calf deaths prior to weaning. Scours are caused by bacteria (E. coli, Salmonella spp., Clostridium perfringens), viruses (coronavirus, rotavirus) and protozoa (Cryptosporidium parvum, or "crypto", and in older calves - coccidia of the Eimeria spp.). Most of these infections are actually carried and spread in manure and on body surfaces by healthy-appearing adult cows. Disease results when management and environmental conditions favor their transmission and the calf's resistance is reduced. In fact many of these organisms are present on many, if not MOST, farms (dairy and beef) but may not cause enough loss to be recognized until conditions are favorable for an outbreak of scours. As an example, in an Ohio State study of Cryptosporidium on dairy farms, all four farms studied were infected, and over 85% of all calves on each farm became infected during the first 3 weeks of life. Calf scours were not identified as a significant problem except on one farm on which Salmonella in scouring calves was also identified. Other studies have revealed similar data. Reports of studies by the National Animal Health Monitoring System suggest that at least 40% of cow/calf operations have Cryptosporidia infections. Cold and wet weather, mud, overcrowding, poor sanitation, poor nutrition of the cows, and dystocia (or calving difficulty) are all factors that favor the development of scours.

When a scours outbreak occurs, producers often focus a great deal of labor and money on treatment of calves with fluids and antibiotics, but the environment may not be recognized as an important part of the problem. Once the first case of scours develops, even a clean environment often becomes extremely contaminated very quickly. Calves with E. coli scours may be shedding billions of bacteria in a single stool. A similar situation occurs with the viruses where it has been estimated that within three days of infection, a calf may be shedding 500,000,000,000 virus particles in a teaspoon of stool material. In our work with crypto, we measured the shedding of Cryptosporidium parvum as high as 17 million oocysts per cc of stool in some calves. With this organism, infection may occur with ingestion of as few as 10 oocysts. Cows carry scour-causing organisms on their udder, hair coat, and feet and legs and spread them around the environment ensuring that other susceptible calves are exposed unless something is done to reduce the potential for calf exposure.

Over the years, several strategies to limit environmental contamination and calf exposure to scours pathogens have been described. Because calves born to heifers are often more at risk, it is a good idea to feed and calve heifers in separate areas from the cowherd. Various strategies have suggested moving pregnant cows from the wintering area to a clean calving area one to two weeks before calving begins. If the herd is large and approximate breeding dates are known, dividing it into smaller, more manageable groups may be helpful. In one of these systems, producers are advised to move cow-calf pairs to different nursery areas within a day of calving and manage them as small groups. If scours breaks out in one of these groups, no new calves are added to the group and care is taken not to spread the contamination from that group by equipment or people. (People can be efficient spreaders of disease-causing organisms.) The idea is to try to limit the infection and pathogen load, as well as the labor of treatment, to one area. When the calves in these groups are three to four weeks old, they may then be moved to spring/summer grazing areas.

Over the last four to five years, Dr. David Smith and his colleagues at the University of Nebraska-Lincoln have developed and demonstrated the Sandhills Calving System (sometimes called the "Sandhills Shuffle") as a tool for preventing or reducing calf scours. The objective of this system is to prevent "effective contact" of calves with calf scours pathogens(germs). An effective contact is defined as an exposure of the calf to pathogens in a dose, or for a duration of time, sufficient to cause disease. In the Sandhills system, effective contacts are minimized by 1) segregating calves by age to prevent transmission of pathogens from older to younger calves; and 2) scheduled movement of pregnant cows to clean calving pastures. The overall idea is to re-create the more ideal conditions that are usually present at the start of calving season at each subsequent week of the calving season.

The system uses several clean pastures for calving rather than a high animal density lot or pasture. In practice, the cows are turned into the first pasture as soon as the first cow calves, and calving continues for two weeks. At the end of two weeks, the cows that have not calved are moved to a second pasture and the existing cow/calf pairs stay in the first pasture. After a week of calving in the second pasture, pregnant cows are again moved to a third pasture and the cows that calved remain in pasture two. Each subsequent week, cows that have not yet calved are moved to a new pasture thus distributing cows with calves within one week-of-age of each other in separate groups. Cattle from different pastures may be commingled after the youngest calf in a group is four weeks old. Generally, calves of this age are at low risk for scours.

The success of this system relies on two key principles. Age segregation of calves helps prevent the transmission of pathogens from older calves to younger calves and assists in management of scours outbreaks within groups if this does happen. The routine movement of pregnant cows to fresh calving pastures helps prevent the buildup of scours-causing germs in the calving environment that often leads to exposure of the youngest calves to overwhelming doses in more conventional systems where cow/calf pairs are not segregated.

Moving pregnant cows can be easier and less disruptive than moving cow/calf pairs, and each week the number of cows in the group that has to be watched for calving is reduced. If pregnancy examination information is available, cows that are expected to calve later in the calving season can be maintained as a separate group and added to the system as appropriate.

This system should be planned well ahead of the calving season to maximize its potential. It may be somewhat difficult for some farms to adopt it because of pasture, water, or shelter limitations. In addition, the planning has to take into account potential weather conditions likely to occur during the calving season and the potential for damage to pastures if it turns wet and muddy. However, with some "tweaking" of the system, many Ohio herd owners could develop a farm-specific plan that utilizes the basic principles of the Sandhills system. Combined with a sound nutrition program; an effective reproductive management program, including breeding soundness exams in bulls; a vaccination program; and a biosecurity program, the negative impact of calf scours can be minimized.

April 2007