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Group newborn calves by age to lower disease risk

The health and well-being of the nursing calf starts before birth with the health and nutritional status of its mother. Nutrient needs of the cow increase during the last trimester of gestation and, by the last month prior to calving, the fetus is gaining approximately 1 pound per day.

In addition to this late-term fetal growth, the cow is preparing for lactation. Research has shown cows that are thin (less than 4 body condition score) have a decreased concentration of immunoglobulins in colostrum compared to cows in a body condition score of 5 to 6. Calves born to very thin cows may be weak and slow to nurse, reduc­ing the colostrum they consume and making them more susceptible to disease.

The newborn calf needs a healthy mother and a clean environment. Manure and mud provide an ideal environment for disease-causing bacteria and viruses. Early in the calving season, calves are exposed to these pathogens and often devel­op minor, undetectable infections. These young calves amplify the pathogen load in the environment faster than adult cattle do.

As the calving season progresses, newborn calves are challenged with increasingly higher levels of patho­gens. Infection with high doses of bacteria or viruses combined with other risk factors such as over­crowding, temperature extremes and precipitation can quickly overwhelm calves’ defenses. Scours may develop. Long calving seasons further exacerbate the situation by providing a steady supply of new calves susceptible to infection over a long period of time.

Segregating cow-calf pairs by age of the calf has helped reduce the incidence of scours outbreaks. Older calves tend to infect younger calves. The Sandhills Calving Sys­tem, developed by the University of Nebraska-Lincoln, is a system that utilizes a series of calving pastures to minimize newborn calves’ contact with disease agents. Named after the Sandhills area of north-central Ne­braska where it was tested, the sys­tem prevents direct contact between younger calves and older calves and keeps later-born calves from being exposed to an accumulation of pathogens in the environment. The idea is to minimize both the disease load and newborns’ exposure to the disease agents until their immune systems have sufficiently matured to better withstand them.

Key components of the system are age-segregation of calves and the frequent movement—every seven to 10 days—of pregnant cows to clean calving pastures. Every 10 days, or whenever 100 calves are born, the herd is divided by sorting cows that had not calved from the cow-calf pairs of the preceding group. In this manner, fewer cattle groups are required, although 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. After the youngest calves are 4 weeks old, all calves can be commingled.

The timing and the amount of colostrum consumption is also critical for the health of newborns. Ideally, calves need to stand and nurse within the first few hours to maximize antibody absorption and immunity. The best-case scenario occurs when a cow in good body condition gives birth to a vigor­ous calf in a clean environment, promptly stimulates the calf by licking it clean and the calf quickly nurses a large colostrum meal.

That first meal triggers a se­quence of gut changes. To protect the calf from pathogens, the gut begins to “close” (loses its ability to take contents directly into the blood) as soon as food is introduced to the intestinal tract. As a result, fewer and fewer antibodies can be absorbed from each subsequent meal until gut closure is complete.

If a calf has nothing to eat, it can still absorb some antibodies at 24 hours, but if the calf consumes anything, gut closure begins imme­diately. “Anything” can be a dose of colostrum that is too small, milk replacer or debris nursed from a dirty udder or environment. Bacte­ria nursed from a dirty environment can be directly absorbed into the blood and cause disease.

Disease transmission is less likely if colostrum from within the herd is used. Commercial colostrum replacers are also effective and come from carefully tested herds. These products must be mixed carefully according directions. Feeding co­lostrum banked from neighboring herds can be effective but could increase the risk of introducing diseases. Colostrum supplements are relatively safe in terms of disease transmission but typically do not contain a high enough concen­tration of antibodies to guarantee adequate passive transfer. Visit with your local veterinarian when con­sidering these options.

More from this March Today's Farmer Magazine Issue HERE .

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