Beef calves with diarrhea typically become ill or die within one to two weeks of age and are most likely to become infective and shed the agents in their feces in that time frame. Exposure to pathogens may occur through direct contact with other cattle, especially in crowded conditions, or via contact with contaminated environmental surfaces. Excessive heat, cold, rain, mud and/or snow are important stressors that may also influence pathogen numbers.
The average dose-load of pathogen exposure to calves is likely to increase over time within a calving season because calves infected earlier serve as pathogen-multipliers and become the primary source of exposure to younger susceptible calves, says David Smith, DVM, PhD, Dipl. ACVPM, University of Nebraska. “This can result in high calf-infectivity and widespread environmental contamination with pathogens, setting up the conditions for a scours outbreak among calves born later in the calving season.”
Disease-causing exposure to pathogens can be prevented by physically separating animals, reducing the level of exposure (e.g. through the use of sanitation or dilution over space), or minimizing contact time. These principles have been successfully applied in calf hutch systems on dairies, but beef producers are challenged to find ways to adopt the same principles.
Segregation is the key
The Sandhills Calving System institutes management to prevent effective contacts among beef calves by segregating them by age to prevent transmission of pathogens, and scheduled movement of pregnant cows to clean calving pastures to minimize pathogen dose-load in the environment and contact time between calves and the cow herd. Cows calve on ground that has been previously unoccupied by cattle (for at least some months), and older, infective calves are not present.
This system, in use since 2000, uses larger, contiguous pastures for calving, rather than high-density calving lots. Cows are turned into the first calving pasture (Pasture 1) as soon as the first calves are born and calving continues for two weeks. After two weeks the cows that have not yet calved are moved to Pasture 2. Existing cow-calf pairs remain in Pasture 1. After a week of calving in Pasture 2, cows that have not calved are moved to Pasture 3 and cow-calf pairs born in Pasture 2 remain in Pasture 2. Each subsequent week cows that have not calved are moved to a new pasture and pairs remain in their pasture of birth. Cow-calf pairs are distributed over multiple pastures, each containing calves within one week of age of each other. Cow-calf pairs from different pastures may be commingled after the youngest calf is four weeks of age and all calves are considered low-risk for neonatal diarrhea.
Smith notes that some ranchers have extended the time between pasture moves and found that calves born in pastures with two weeks or more between a move are more likely to scour. “This tells us that the pathogens are still present in these herds and that age segregation of calves is an important part of the system,” Smith says.
For intensive grass-management systems, cattle are moved to different pastures throughout the calving season as appropriate for forage utilization. Every 10 days, or whenever 100 calves are born, cows that have not calved are sorted off. The number of calves within any pasture group never exceeds 100, and all calves within a group are within 10 days of age of each other.
Veterinary involvement is important for the ranch have success with this system or others like it. “Veterinarians bring awareness and an understanding of the principles on which the system is based,” Smith says. “They can assure that the details are thought out and that an appropriate plan is in place prior to the calving season.” Because the system is improved with a short and well-defined calving season, veterinarians can help improve reproductive efficiency. “Fetal aging during pregnancy exams can help producers sort cows by due date so that they can put cows into the system as they near calving which can minimize the number of cows that start in the first pastures.”
Sandhills Calving System data
Data was captured from two ranches that were early adopters of the Sandhills Calving System. One ranch with 900 cows in a March-April calving season was losing 50-120 calves per year to scours (approximately 10% death loss to scours). “Since beginning the Sandhills Calving System, that ranch has not had a calf die from scours in the last eight years and has treated only four calves for scours in the first year,” explains David Smith, DVM, PhD. “For this ranch, the average annual cost for veterinary medications for the three years after implementing the Sandhills Calving System was 24-fold less than expenditures for the three years prior to implementing the system.”
On another ranch, Smith says, the death rate for all reasons from birth to weaning was significantly reduced for the four years after starting the system.