Veterinarians tell us there are two primary factors that determine whether an animal gets sick: susceptibility and exposure.

Nowhere is this principle more evident than in the case of calf scours, where exposure tends to build as the calving season progresses, and growing numbers of calves get sick as they reach a susceptible age.

Calfhood diarrhea, or scours, is one of the most economically devastating diseases a cow-calf producer faces. Medical expenses, lost performance and death loss frequently account for significant reductions in ranch income and profitability. University of Nebraska veterinarian David Smith says some beef-cattle herds lose 10 percent or more of their calves to scours, sometimes with sickness and treatment rates approaching 100 percent of calves.

How it happens
Several different pathogens that are common in beef herds can cause calf scours. These include viruses such as rotaviral enteritis, coronaviral enteritis and bacteria such as E. coli and Salmonella. In a typical calving environment, exposure to these pathogens increases dramatically as the calving season progresses through what Dr. Smith calls the “multiplier effect.” Pathogen levels are low when the season’s first calves are born, and scouring incidence is low. But as cows shed pathogens onto the pasture, a few calves develop scours and then begin shedding large numbers of pathogens. Subsequently, calves born a week or two later enter an environment with much higher pathogen populations.

The other issue is susceptibility. Calves that are born healthy and receive adequate colostrum from their dams acquire a level of passive immunity that temporarily protects them from most pathogens. At the same time, calves begin developing their own active immune systems for long-term protection. Unfortunately, acquired or passive immunity tends to decline before a calf’s active immune system is fully developed (see graph). This explains why most cases of scours occur during the second and third weeks of calves’ lives, Dr. Smith says. Environmental conditions also contribute to susceptibility.

A system to break the cycle
Applying their understanding of scours outbreaks, veterinarians in Nebraska developed the Sandhills calving system, a strategy intended to minimize the calf’s exposure to pathogens, particularly during the period of greatest susceptibility.

The Sandhills calving system interrupts the cycle of infection by segregating calves by age and by moving pregnant cows to new calving pastures to minimize exposure for the youngest calves. The basic idea is to use multiple calving pastures for a single cow herd. All of the cows start out in pasture 1 as calving begins. After a week to 10 days, cows that have not yet calved move to pasture 2. This process repeats through the calving season, with cows moving to fresh pasture for calving and groups of pairs remaining on the pastures where the calves were born (see diagram). Pairs can be commingled once.

Gail Nason of Rothwell/Nason Ranch of Tryon, Neb., says she has nothing but praise for the Sandhills system. Prior to implementing the system in 2001, Ms. Nason says the ranch typically lost up to 12 percent of each calf crop to scours. Over the past two years, the ranch has not lost any calves to scours. Ms. Nason says they have had a few cases of minor diarrhea, but far less than before. She also notes that calves have been more healthy overall, with a significant reduction in sickness and treatment costs at weaning.

Based on her experience, Ms. Nason offers several suggestions to other producers who want to try the Sandhills system. First, she says, take the time to talk with a veterinarian, extension specialist or other producers who have used the system. When she started, she had the opportunity to work closely with the Nebraska veterinarians who developed and tested the system. Still, she says, it has been a slow process to learn how to best make the strategy work. Every operation is different, with its own challenges in terms of forage resources, fencing, water sources, etc. She has, for example, gradually made changes in the pastures selected for calving and in handling practices for moving heavy cows to new pastures.

Her next piece of advice is to resist the temptation to cheat on the timing. “Wait until the youngest calf in a later group is at least 30 days old before putting it in with older ones,” she says. “And, do not go past that 10-day window to move cows that haven’t calved to the next pasture,” she adds. Seven days is best, according to Dr. Smith and other veterinarians who developed the system, but 10 days seems to be the limit. “It’s tempting,” Ms. Nason says, “but producers who have cheated have ended up with sick calves.” She also adds that a seven-day rotation offers the opportunity to move cows each weekend — a convenient schedule for family operations where school-age kids can help out.

Dr. Smith offers another piece of advice — plan ahead. He suggests drawing up a calving and cattle-movement plan ahead of the calving season. Map out the calving pastures and other features such as fences and water sources. Also, write up a schedule for when to move cows and when to commingle pairs. Ultimately, the goal is to make every week of calving just as easy as the first, Dr. Smith says.

Dale Grotelueschen, a technical-services veterinarian with Pfizer Animal Health, says that while the Sandhills system might sound like extra work, it really amounts to a re-allocation of management. In a conventional system, producers spend considerable time pulling pairs, treating sick calves and otherwise dealing with the effects of scours. With the Sandhills system, their efforts shift to moving cows and preventing scours from occurring.