Feeding Young Dairy Calves

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 casein clotting 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 whole milk, waste milk, transition milk, and milk replacers. Milk and transition milk can be high-quality feeds for suckling calves. When various cow milk resources (ie, whole, transition, or waste) are fed, adequate biosecurity precautions, such as pasteurization and screening of cows for chronic infectious diseases such as bovine leukosis and Johne’s disease (paratuberculosis), 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 old, 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 decrease 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. Emulsifying agents (lecithin, monoglycerides, or a combination) are usually added. Fat concentration substantially influences the energy concentration of a 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 decreases as replacer fat concentration increases.

Solid feed should be introduced early (by 3 days old) 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 and 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 (approximately 12–15% neutral detergent fiber [NDF]). Recent research suggests inclusion of a minimum of 5% coarse fiber (chopped straw) to decrease papillae hyperkeratosis and maintain rumen papillae health.

Amount and form of starch is of concern relative to the 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 fresh water readily available. 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, or to stimulate solid feed intake.

Compared to older cattle, calves have greater surface area per unit of body weight, resulting in a lower thermoneutral zone limit. Calves between birth and 3 weeks old have a lower thermoneutral zone limit of 20ºC, and calves > 3 weeks old have a lower thermoneutral zone limit of 10ºC. Maintenance energy requirement increases as ambient 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.

The diet of the preweaned calf is the single most expensive diet on the farm. The traditional nursing calf feeding program was based on limiting milk consumption to facilitate starter intake in attempting to achieve an appropriately developed rumen system to minimize stress through the weaning process. An alternative approach to nursing calf feeding is what is referred to as a natural growth or accelerated growth calf rearing program. In this approach, larger quantities of liquid feeds are fed during the preweaning period, allowing for a greater expression of the calf’s growth potential. Any nursing calf feeding program requires proper colostrum feeding management.

In feeding larger quantities of liquid feed, rumen development will be delayed because it depends on solid feed fermentation generating volatile fatty acids (ie, butyrate and propionate). In this system, weaning is often delayed, taking advantage of greater growth rate and improved health. The delay in sufficient solid feed consumption (relative to traditional programs) requires a gradual rather than abrupt weaning process to ensure sufficient rumen development to make a successful transition to solid feed.

An important aspect of this approach to calf feeding is to ensure sufficient feeding practices after weaning to ensure continued growth efficiency and minimize postweaning growth depression. After weaning, forage is not offered until heifers are > 3 months old. Dietary protein concentrations during the pre- and postweaning periods are increased (relative to traditional programs) to assure adequate lean gain and to avoid excessive fattening. Rates of gain can be as high as 1 kg/day, with heifers entering the milking herd at 22–23 months old. Close monitoring is necessary to ensure that heifers have adequate frame development and do not become excessively fat.

The accelerated growth program has been advocated based on calf health as well as increased milk production at first lactation, although not all studies support this contention. To realize a return on investment requires improved animal health, lower age at first calving, and increased milk production. Most financial studies generally do not show a positive return compared to traditional calf feeding programs that achieve a similar age at first calving.

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