To assure adequate passive transfer of antibodies, all calves should receive at least 3 L of high-quality colostrum (IgG concentration >50 mg/mL) within 6 hours after birth. A second feeding should occur between 8 and 12 hours after birth. An alternative approach is to provide 4.2 L (1 gal) of colostrum within 6 hours of birth. Colostrum feeding should continue until calves are 3 days old; however, the initial feeding of colostrum is critical for passive transfer of immunity.
Traditional System of Replacement Dairy Calf Feeding
After colostrum feeding, the traditional nutritional strategy for raising dairy replacement calves has been to minimize financial input in successfully growing the calf to weaning, because this period of feeding is the single most costly period in raising the replacement heifer. The approach is based on feeding a limited quantity of liquid feed to stimulate solid feed consumption, which stimulates early rumen development, thus allowing the calf to be weaned at a relatively young age (usually 4–8 weeks). Although growth rates are less than maximal, feed costs are minimal. In addition, the risk of enteric disease after weaning is less than during the liquid feeding period, making early weaning beneficial in the management of enteric disease.
In this feeding system, targeted mean daily gain for calves of large dairy breeds is between 400 and 600 g/day for the first 3–4 weeks of life. To achieve this rate of gain, expected dry-matter intake of 600–750 g/day is required, of which approximately 450 g is supplied from liquid feed. This equates to slightly more than 4 L of milk or reconstituted milk replacer/day for calves weighing 40–50 kg at birth. Typically, this amount is divided between 2 feedings/day. The ability to feed fewer meals per day is attributed to the presence of abomasal renin that induces clotting of casein in milk and slow release of digested material to the small intestine. The remaining contribution to dry-matter intake comes from a high-quality calf starter, which is a concentrate mixture specially prepared for young calves. As calves grow, the amount of liquid feed/day remains constant, and increases in growth rate are accounted for by increases in calf starter consumption.
Liquid feeds for preweaned calves include milk, waste milk, excess colostrum, and milk replacers. Milk and excess colostrum can be high-quality feeds for suckling calves; however, adequate biosecurity precautions, such as pasteurization and screening of cows for chronic infectious diseases such as bovine leukosis Bovine Leukosis Bovine leukosis is caused by an oncogenic retrovirus of cattle. Most animals remain asymptomatic despite becoming persistently infected by the virus, but a proportion of cattle will develop... read more and Johne’s disease (paratuberculosis Paratuberculosis in Ruminants Paratuberculosis, caused by Mycobacterium avium paratuberculosis , is a chronic, contagious granulomatous enteritis characterized in cattle and other ruminants by progressive weight loss... read more ), need to be implemented.
A wide range of commercial milk replacers are designed to mimic bovine milk and thus contain a source of protein, fat, and carbohydrate. Protein concentrations in milk replacers vary from 18% to as much as 30% on a dry-matter basis but typically are 20%–25%.
The protein source can substantially affect the quality of the replacer. Preferred protein sources in milk replacers, especially for calves < 3 weeks of age are those derived from milk protein sources. These sources include whey protein isolate, delactosed whey, dried skim milk, and casein, though quality can be influenced by processing methods. Other animal proteins, such as plasma proteins, also may be of good quality. Plant protein sources vary in their acceptability, particularly for calves <3 weeks old: appropriately processed plant proteins may be acceptable; however, they are generally less desirable than animal proteins. Plant proteins acceptable for use in milk replacers include soy protein isolate and soy protein concentrate; these proteins may be processed to reduce antigenicity and to remove antinutritional factors such as trypsin inhibitor. The extent of processing varies by manufacturer, and not all milk replacers containing these protein sources are of equal quality. Unprocessed soy flour and wheat flour are unacceptable protein sources for milk replacers.
Fat concentrations in milk replacers are typically 10%–30%; most are 15%–20%. Fat sources usually include coconut oil and, in larger amounts, tallow, choice white grease, or lard. Lecithin, monoglycerides, or a combination are usually added as emulsifying agents. Fat concentration substantially influences the energy concentration of milk replacer. In cold climates in which high energy consumption is critical for young calves, fat concentration should be ≥15%. The drawback of higher fat concentrations is that the rate of starter consumption is reduced as replacer fat concentrations increase.
Solid feed should be introduced early (by 3 days of age) in the traditional calf feeding program. Calf starter feed stimulates rumen development via the production of volatile fatty acids generated by microbial fermentation. Butyrate is considered the most important inducer of rumen papillae development, and some milk replacers include sodium butyrate as a rumen development stimulant.
Newborn calves have an underdeveloped, nonfunctional reticulorumen. Rapid rumen development is critical for successful early weaning with minimal adverse impacts on calf health or growth. High-quality calf starters are composed of moderately fermentable carbohydrates in a mixture that is coarse in texture, contains few fine or powdery particles, and has a relatively high fiber concentration (~12%–15% NDF). Recent research suggests inclusion of a minimum of 5% coarse fiber (chopped straw) to maintain rumen papillae health.
Amount and form of starch is of concern relative to induction of ruminal acidosis; however, defined amounts have not been established. The crude protein concentration should be 18%–20% on a dry-matter basis, though some products may contain up to 26% crude protein. Calf starters with more than 20% crude protein are often used in accelerated feeding programs to ensure sufficient protein in support of lean growth.
Historically, hay has been fed or offered to preweaned calves. Other than potentially providing the physical fiber to minimize papillae hyperkeratinization, hay will not induce papillae development in preparing the rumen for the weaning transition to solid feed.
A critical factor in stimulating starter consumption is the availability of fresh water. Calves should always have readily available fresh water. Water consumption will vary greatly by calf but may be >4 L/day in addition to milk or milk replacer. Water in milk or milk replacer is not sufficient to meet the calf’s water requirement, especially in hot weather, nor to stimulate solid feed intake.
Feeding Dairy Calves in Cold Weather
Compared to older cattle, calves have greater surface area per unit of body weight, resulting in a lower limit to their thermoneutral zone. Calves between birth and 3 weeks of age have a lower thermoneutral zone limit of 20ºC, and calves >3 weeks of age have a lower thermoneutral zone limit of 10ºC. Maintenance energy requirement increases as temperatures fall below these values. To compensate for these increased energy requirements, milk replacers with fat concentrations ≥15% should be fed in cold weather. Furthermore, the amount of dry powder should be increased by 50 g/day for each incremental decline of 5ºC below the thermoneutral zone.
For example, if calves <3 weeks old are receiving milk replacer powder at 450 g/day at ≥20ºC, the amount should be increased to 650 g/day at 0ºC and to 900 g/day at –25ºC. The dry powder should be reconstituted with the prescribed amount of water and a higher volume of liquid feed provided. Increasing feeding frequency to 3 times daily is preferable to feeding larger volumes twice daily. Additionally, calves should be well-bedded (legs completely covered by bedding when reclining) and protected from drafts. In addition to milk or milk replacer, fresh water should be made available at least twice daily. Relying on increased starter intake is not reasonable to accommodate cold weather stress.
Feeding Dairy Calves with Enteric Disease
Diarrhea (scours Diarrhea in Neonatal Ruminants Neonatal diarrhea in ruminants remains the most important cause of death in calves under one month of age. Various bacterial, viral, and protozoal agents are recognized as causative agents,... read more ) is a common medical condition in young calves and frequently results in life-threatening dehydration. Underlying causes of diarrhea include infectious agents such as bacteria, viruses, and parasites as well as nutritional factors. Electrolyte solutions administered orally can be beneficial in supporting hydration and successfully treating calves with diarrhea. Electrolyte solutions may be administered orally or parenterally, depending on severity, to help control and correct dehydration. Often milk or milk replacer feeding is withdrawn during this treatment; however, electrolyte solutions do not provide sufficient nutrients to support the calf or account for increased metabolism resultant of the disease process. Electrolyte solutions can be fed along with milk or milk replacer. Supporting the calf with adequate nutrition speeds restoration of the gut epithelium and generally improves calf health and immunity.