The following article outlines some guidelines we recommend for consulting with herd managers regarding evaluating calf diarrhea outbreaks.
Clinical syndrome
Careful monitoring of calves during their neonatal period (1-28 days) reveals that most of them–even in purportedly low morbidity farms–experience at least one bout of loose stools. Therefore, the severity of individual cases as well as the percentage of the population affected must be considered in deciding if the herd has a diarrhea problem. A diarrhea problem exists if, over any continuous one month period, > 20% of calves are observed to be clinically affected with a diarrheal syndrome that results in partial or complete anorexia, reluctance or inability to stand, and/or dehydration. Three major types of outbreaks are recognized.
- Very watery diarrhea beginning in the first 2 days of life. This syndrome is associated with enterotoxigenic E. coli (ETEC).
- Pasty to liquid diarrhea, often foul smelling and gaseous, with a peak during the 2nd and 3rd weeks of life (7-21 days of age). This syndrome is associated with several viral agents and Cryptosporidium.
- Pasty to liquid diarrhea, sometimes with blood, most commonly beginning in the second or third week of life and usually extending into post-weaning groups. Accompanied by signs of bacteremia in some of the cases. This syndrome is associated with Salmonella spp.
Epidemiology of agents
Most of the agents of calf diarrhea exist in every cattle herd, the major exception being Salmonella. For agents such as cryptosporidium, rotavirus, and coronavirus, infection is near-universal (all calves on all farms) at some time during the neonatal period (1-28 days of age). Thus, efforts to identify these agents provide little or no diagnostic utility in that one would expect to find one or more of these agents in over half of calves (healthy or sick) sampled between 7 and 21 days of age, even in a herd not experiencing a problem with calf diarrhea.
Goal of consultation
To determine the management factors which need to be adjusted in order to minimize exposure doses of ubiquitous agents, to minimize probability of exposure for epidemic agents (i.e., Salmonella), and to increase calf resistance. The main areas of concern are: passive transfer, nutrition, housing, and infection control. A brief synopsis follows which lists the details which should be examined in each of these major areas.
Passive Transfer
ASSESSMENT: The only reliable means of assessing passive transfer management is to take blood samples from calves and measure the passive immune levels of groups of calves. Questioning management about policies, though important, will not give an accurate picture of passive transfer.
TEST: The easiest test for passive transfer is total serum protein by refractometry. Calves should be at least 24 hours old and under 7 days old when sampled. All calves available in this age range should be sampled. In a herd with optimum management of passive transfer, >90% of calves should have TP of 5.0 g/dl or greater (corresponds roughly to 10 mg/ml IgG1). The occurrence of any calves with TP of < 4.5 g/dl is a clear indication of failure to properly feed colostrum.
FORCE FED: All dairy calves should be force fed colostrum. A stomach tube or esophageal feeder is the only practical way of feeding an adequate volume under most conditions.
AMOUNT: Holsteins should be force fed 1 gallon of colostrum; Jerseys 3 quarts.
TIME: Force feeding should occur within 8 hours of birth; within 4 hours is ideal but difficult to achieve on some dairies.
WHICH COLOSTRUM: Only first milking colostrum should be used. The traditional practice of saving only colostrum from older cows places unnecessary constraints on the program since colostrum from first parity animals does not differ notably in IgG concentration from that of older cows. Indeed, the colostrum from older cows which give high volumes in their first milking is the more predictably low in IgG than is colostrum from heifers.
COLOSTRUM TESTS: Tests based on specific gravity only modestly correlate with IgG concentration (r~.5). If an adequate colostrum feeding program is in place (1 gallon, 1st milking colostrum, tube fed to every calf within 8 hours), testing colostrum and discarding those with low test results will not significantly improve the passive transfer results achieved.
STORAGE: Colostrum should not be stored at room temperature as it will provide a medium for tremendous bacterial growth. Storage in a refrigerator is ideal; colostrum which is collected in a clean manner (in parlor under normal milking conditions) can be kept for a week in the refrigerator. Freezing is also acceptable, though the time required for thawing discourages proper feeding of calves.
COLOSTRUM SUPPLEMENTS: Powdered colostrum supplements are very expensive, particularly considered in terms of cost per gram of circulating IgG1 delivered to the calf. We are unaware of any product which is able to regularly achieve even a moderately high passive immune level (greater 10 mg/ml IgG1) at the amounts which are recommended and affordable. It is noteworthy that proper feeding of colostrum will almost always achieve this level.
Nutrition
LIQUID DIET CALORIES: Calves should receive a liquid diet that at least meets their maintenance energy requirement (see Tables 1 and 2). If waste milk is diluted (e.g., with hot water to warm it up), one must consider only the original (undiluted) volume fed to the calf in figuring caloric adequacy. Calves fed less than maintenance will lose weight for the first week or two of life and will be more readily put into an energy crisis by the anorexia and malabsorption of diarrheal disease. Calves in a negative energy balance are also more susceptible to the effects of rapid temperature changes (e.g., a cold front).
MILK REPLACER. Only all milk-protein milk replacers should be fed to calves < 2 weeks of age. Though, in theory proteins from whey byproducts may not be as digestible as those from skim milk or casein products, calves generally do well on milk replacers containing most of the protein from whey products.
GRAIN FEEDING: Calves should be offered grain at some point beginning in the first week of life. Calf grain should contain at least 16% protein and should consist of whole or rolled grain along with a protein pellet. Grain mixes made for cows should not be used for calf feeding. For new calves only a handful of grain per day should be offered, and the residue should be discarded at least as often as every third day. One common mistake in feeding calves is to continue to add new grain onto the top of old grain, gradually filling the bucket with stale, moist, mold-infested, bacteria-rich grain. Calves are reluctant to eat this mess and will thus have reduced gains. To the extent they do eat it, gastrointestinal disturbances can result.
WATER: Ideally calves will have clean water in front of them all the time. Calves can make up for some of their fluid losses from diarrhea by increasing voluntary water intake. Also, the lack of supplemental water will reduce grain intake. Provision for round-the-clock access to water is impossible in the winter months in cold housing (e.g., hutches). During freezing weather, a small amount of water (1 quart) can be placed in each calf’s bucket between feedings; remaining water is dumped 30 minutes to 1 hour later before it freezes solidly.
HAY: Calves pre-weaning and grouping need not be offered hay. Ruminal papillary development will proceed normally for calves fed only grain.
SELENIUM: In the dairy producing areas of the Pacific NW (and most of the US), calves should be given selenium injections within 3 days of birth unless testing of calves has demonstrated that they are not deficient.
Housing
ENCLOSED HOUSING: Where calves are confined in an enclosed space, agent-laden aerosols can settle out on calves haircoats and onto feed and utensils, and can thus be ingested. This provides an additional–difficult to control–means of transmission that is not experienced by calves in hutches and in properly managed naturally ventilated structures. The ventilation system of an enclosed barn influences aerosol transmission by direct removal of agents and by lowering humidity which in turn decreases survival time of (some) agents. Assessment of ventilation adequacy of enclosed barns consists broadly of measuring airflow per calf (e.g., summer requirement of 100 ft3/calf/min) and evaluating airflow patterns (drafts and dead spots). The subject is too extensive to cover in detail here, though it can be said that few enclosed barns in the Pacific NW have been found to be adequately ventilated and that this likely plays a major role in the perpetual diarrheal and respiratory disease suffered by the occupants of such buildings. For more details on evaluating ventilation of enclosed housing, call Dale Hancock (509-335-0711).
HUTCHES: Though hutches are an ideal method of housing calves, several important details must be examined.
Hutches should be tight to the ground–no slats or cracks through which wind can blow onto calf from underneath.
Open end of hutches should be south- or south-east facing during cold months, and the other three walls should be solid with no openings.
The portion of the hutch which is completely enclosed on three sides should be of sufficient depth to keep calves out of wind and drifting snow–6 feet is ideal.
Hutch design should provide for upward air drainage; body heat will make air rise in winter, and moisture will accumulate unless roof is single-sloped upward toward opening or unless a vent is located at the highest point of hutch ceiling.
Substrate should provide for adequate liquid (urine, etc) drainage from the hutch; 4 inches or more of crushed rock is an ideal substrate.
Bedding should provide for adequate thermal insulation–straw is preferred over shavings in winter. Additional bedding should be added weekly; old bedding should be removed only after calves are weaned and moved out.
NATURALLY VENTILATED BARNS: Naturally ventilated barns are those for which there is no mechanical ventilation system and in which no attempt is made to warm the air above outside temperature. Calves are kept in stalls or tethered, and are bedded during cold weather. The adequacy of naturally ventilated housing depends on the natural air purification produced by body heat- and wind-driven air flow and diffusion through openings. The adequacy can be assessed by comparing the design to specifications for opening size and positions found in a farm animal housing publication (e.g., Dairy Housing and Equipment Handbook, Midwest Plan Service, Iowa State University, Ames 50011, 1985). For example, one major design type requires a ridge vent; specific requirements for width of the ridge vent can be determined from building dimensions. One can also assess adequacy of air movement by measuring carbon dioxide concentration in the calf barn on a still day; if it is much above atmospheric levels, the natural air purification created by the structural design and operation is not adequate. For more details, contact Dale Hancock (509-335-0711).
POST-WEANING GROUPING OF CALVES: Calves should be weaned while they are still in individual housing and a least 5 days before they are moved into group housing. The group pen into which calves are first moved should have the following characteristics: no more than 10 calves, no more than 2 months in age difference among calves in group, and at least 1 foot of feed bunk space per calf. Putting newly weaned calves into large groups of mixed ages with inadequate bunk space will result in a period of high stress and reduced caloric intake of newly weaned calves.