Many of the common management practices that are used to raise dairy calves while on milk and during weaning actually result in the calf developing rumen acidosis. It is important to understand how these management practices cause acidosis, so that these paradigms that have existed for many years can be changed and new management procedures implemented that will result in a healthier calf. Avoiding acidosis in young calves will result in reduced stress, lower morbidity and mortality rates, improved average daily gains, reduced age at first calving and more milk production when the animal enters the lactating herd.
When the calf is born, the rumen only makes up approximately 25% of the volume of the stomachs, and the volume of the abomasum is about 65% to 70%. For the first two weeks of life, the gastrointestinal tract of the calf functions basically the same as a monogastric animal. When milk is provided to the calf, either in a bucket or in a bottle, the esophageal groove closes, and the milk goes directly into the abomasum. In order to develop the rumen, there has to be a liquid environment in the rumen so that anaerobic bacteria are able to grow. Freechoice access to water is important in early life. This water passes into the rumen and provides the liquid environment necessary for the growth of anaerobic bacteria.
There also has to be a rapidly available form of starch in the rumen, which is fermented into butyric acid. Butyric acid is the primary substance responsible for developing the rumen and rumen papillae. It is common to see whole-kernel corn used in calf starters. The starch in whole-kernel corn is not very available to the calf, and rumen development is slower when compared to rolled corn. This is especially true if the whole corn has a "flinty" endosperm. The starch is tightly bound with prolamine bonds in this type of corn. There are newer strains of corn available that contain a "floury-type" endosperm," in which the starch is much more available for fermentation in the rumen.
There are two things that can occur early in the life of the calf that will predispose it to rumen acidosis. One is "rumen drinkers" and the other is not providing enough milk to the calf.
Some calves may be born with a congenital defect of the esophageal groove, allowing milk to enter directly into the rumen. There is obviously nothing that can be done to rectify this problem. There are two main ways that calves can develop rumen acidosis. One is by abomasal reflux, and the other is by fermentation of milk or milk replacer in the rumen. The most common cause is when milk or milk replacer enters the rumen. In the past, there has been controversy around whether or not calves that drink from buckets are more prone to milk entering the rumen than calves that are bottle fed. However, there is well-documented research that proves that the closure of the esophageal groove is equally efficient regardless of whether the calf is bucket or bottle fed.
When milk enters the rumen it is fermented into volatile fatty acids and lactic acid. These acids are normally absorbed by the rumen papillae, but since the rumen papillae are not developed yet, these acids accumulate in the rumen and result in lowering the rumen pH from a normal level of around 6.5 to 7.0, to a level often of less than 5.0, resulting in rumen acidosis. Lactic acid may eventually be absorbed across the rumen wall and result in systemic acidosis. Signs of systemic acidosis may include depression and loss of appetite, and sometimes death.
Some of the things that are thought to predispose calves to being rumen drinkers are:
- Neonatal diarrhea
- Low-quality milk or milk replacer
- Changing the feeding times
- Milk or milk replacer fed at too cold a temperature
- Environmental stressors such as changing housing
- Hauling calves long distances
Calves that have ruminal acidosis as a result of rumen drinking will often go off feed and have a poor appetite. If the acidosis is severe, the calf may show signs of pain such as vocalization, kicking at its abdomen, shifting its weight from one foot to another, arched back, etc. If it has developed diarrhea, dehydration may also result. There also may be accumulation of gas in the rumen resulting in bloat. Poor growth rates and depression are also commonly observed. It has also been reported that the feces from these calves may be sticky and clay-like, with a white putty-like appearance.
INSUFFICIENT AMOUNTS OF MILK
Traditionally, newborn calves are routinely fed 2 qt. of milk two times per day for a total of 4 qt. per day. Research has shown that this volume of milk is not sufficient for the calf to maintain its body temperature and gain weight, especially in colder temperatures. As a result, the calf starts consuming calf starter at a very early age in an effort to increase its nutrient intake and meet its nutrient requirements. However, since the rumen is not developed yet, the fermentation of the larger volumes of starch consumed in the calf starter results in the accumulation of acids in the rumen and, consequently, rumen acidosis. Whenever a significant amount of starter is consumed by calves that are only 2 to 4 weeks old, it should be considered to be a sign of malnutrition. Calves this age should get the majority of their nutrient intake from milk and not calf starter, since the rumen does not have the ability to efficiently absorb the acids due to the starch fermentation.
Following colostrum feeding, the newborn calf should receive 15% of its birth weight in milk for the first seven days of life. This would be approximately 6 qt. per day for the first seven days for the average Holstein calf. It would also improve the gain on these calves if the solids level of the milk or milk replacer were increased to around 15%. This can be safely done without creating a problem with nutritional diarrhea.
If the calf was left on its mother, it would nurse an average of 10 times per day and consume an average of 20% of its birth weight per day in milk. The ability of the calf to drink larger volumes of milk increases rapidly. At 8 days of age, the amount of milk should be increased to 8 qt. per day or approximately 20% of the birth weight of the calf. Again, it would be preferable to increase the solids content to 15% to improve daily nutrient intake. This amount of milk should be maintained until the calf has consumed enough calf starter to start the weaning process. This would be about 2 lb. per day of a high-protein calf starter (23%-25% crude protein), or around 4 lb. of a typical calf starter that is only 18% crude protein. Calves that do not receive this amount of milk will increase their starter consumption too rapidly, greatly increasing the chances for rumen acidosis.
Part 2 of this series will further explore the roles of insufficient amounts of milk, sudden reductions in milk and weaning management systems on acidosis in calves.