Review of Nutrient Requirements of Dairy Cattle: Requirements for Young Calves

The National Academies of Sciences, Engineering, and Medicine: Nutrient Requirements of Dairy Cattle, Eighth Edition incorporates and summarizes new information and research on various topics related to dairy cattle nutrition. This document serves as a tool for the dairy industry, students, and educators to improve the efficiency of milk production with consideration for animal health. The following information is summarized from the recently published Eighth Revised Edition of the Nutrient Requirements of Dairy Cattle. (2021)

Introduction

Dairy calves go through multiple changes in nutrition programs, typically from predominantly liquid diets to post-weaning where calves consume solid feeds. This difference in feed physical form is mainly driven by changes in the physical structure of the rumen as it begins to develop. Offering calves grain at an early age is encouraged and widely practiced throughout Pennsylvania. Grain supplementation in a starter feed provides a source of rapidly fermentable carbohydrates that stimulates butyrate production and drives rumen papillae development. Absorption of volatile fatty acids from the rumen increases as papillae develop, raising the pH to suitable levels for fiber fermentation. While young calves cannot utilize forages efficiently, adequate particle size of starter feeds is important. Very fine particle size can create abnormal papillae development, keratinization, or compaction of fine particles between papillae.

Dry Matter Intake

Dry matter intake for calves determines the amount of nutrients an animal receives, even during the liquid feeding phase. Dairy calves are rarely fed unlimited amounts of liquid feeds (i.e., milk or milk replacer) and maximal dry matter intake of liquid feeds for calves is typically around 2.25 percent of body weight and drops to 2 percent of body weight during the first week of life. However, calves are offered liquid feeds and starter during the early phases of life. Total dry matter intake will increase as animals grow and for calves under 8 weeks of age ranges from 1.17 to 3.06 percent of body weight with an average of 1.93±0.33 percent of body weight. Post-weaning dry matter intake of solid feeds for calves increases rapidly to 3.06±0.31 percent of body weight.

Energy Requirements

Energy requirements are calculated as metabolizable energy, which can come from fats, carbohydrates, and proteins. It is critical to note that while a variety of feeds can contribute to metabolizable energy, the source may alter the nutrients available and further alter the growth and health of the calf.

Fats

Twenty to sometimes over 40 percent of energy in milk replacer is supplied by fats. Historically, milk fat was replaced with tallow, lard, or coconut oil. However, restrictions on animal fats being fed have caused a shift towards palm oil, rapeseed oil, and other hydrogenated vegetable oils to be used in milk replacer. Digestibility of various fatty acids in young calves has not been studied in detail. However, it has been shown that milk replacer fortified with butyrate, medium-chain fatty acids, essential polyunsaturated fatty acids (C18:3, linoleic), and flax oil have shown promise in improving immune function. Dairy cattle require feeds to supplement linoleic (C18:2) and linoleic (C18:3) as these cannot be synthesized by the animal. Based on a comparison of fatty acid profiles in common milk replacer ingredients and standard milk fat, there is potential for supplemental C18:3 milk replacer.

Carbohydrates

Young dairy calves have a large capacity to digest lactose and are not typically limited by enzymatic activity. Alternatives such as glucose, galactose, fructose, glycerol, and dextrin are frequently used and have little difference in energy and nitrogen retention in calves, besides higher fecal loss for fructose may also be used with calves.

While sugar sources in milk replacer are variable, it is important for dairy producers to remember that starch sources need to be available to young animals for rumen development and to ease weaning stress.

Determining whether to feed more fat or increased carbohydrate from milk will depend on the goal for the calf. Body fat is not synthesized from milk-based carbohydrates and in feed programs where protein is not limited, milk-based carbohydrates will contribute to body protein deposition. In contrast, higher levels of dietary fat may increase body fat deposition.

Proteins

It is important to note the difference between dietary crude protein (CP) and metabolizable protein (MP). Dietary CP accounts for the total amount of nitrogen present in the feed, while MP is representative of the amount of protein reaching the small intestine that can be absorbed into the bloodstream. The MP can consist of protein not degraded in the rumen and from microbes that pass from the rumen. Therefore, it is important to discuss conversions of CP to MP in the young calf. A conversion factor of CP to MP of 0.95 is used for milk or milk-derived ingredients, while 0.75 can be assumed for young calves without a developed rumen and 0.70 for calves with a functioning rumen. It is equally important to keep in mind that milk replacers using non-milk protein sources might have lower conversion efficiencies. For milk replacers that use non-milk protein, adequate amounts of lysine, methionine, and threonine need to be supplemented.

Rates of Feeding Milk Replacer

While it is common to feed low amounts of milk or milk replacers to encourage starter intakes in young animals, it is important to remember that animals must obtain enough nutrients for maintenance, growth, and to drive immune system function. It is traditional in the dairy industry to feed milk or milk replacer at 8 to 10 percent of the calf’s body weight. However, feeding 8 to 10 percent body weight might be insufficient as animals fed free-choice whole milk will consume up to 20 percent of their body weight. Calves offered less than 8 L/d of whole milk showed obvious signs of hunger. It is important to keep in mind that typical milk replacers contain 10 to 20 percent less energy than whole milk due to lower fat content, and higher volumes of milk replacer may need to be fed to meet nutrient requirements. If animals are housed in challenging environments or are in areas where their immune system might be activated, additional nutrients will be needed to supplement this draw.

Starter

It is widely known that dairy calves should be offered fermentable carbohydrates within the first week of life, typically found in starch for animals fed starter and as sugars and fructosans for animals raised in pasture systems. This practice is known to help develop the rumen of young animals and support rumen microbial growth through butyrate production. Given this, the two most important factors of starter are palatability and fermentable carbohydrate content. Starters typically range between 20 to 40 percent starch, supplied by cereal grains.

High starch concentrations benefit the production of butyrate and development of the rumen, but, like cows, high starch can cause very low ruminal pH. This low ruminal pH results in slower VFA absorption and a low rate of saliva production. Having a starter formula with some slowly fermentable starch and more digestible fiber might help maintain rumen pH at levels hospitable to microbial communities responsible for fiber fermentation. Rapidly fermentable fiber sources include beet pulp, brewer’s grains, soy hulls, and citrus pulp.

Protein sources in starters typically include soybean, canola, cottonseed, sunflower seed, linseed, or corn gluten meals with soybean meal being the most common. Dried distiller’s grains are also commonly used as a protein source. The required protein content of calf starter is widely generalized and should instead be determined in accordance with protein supply from milk or milk replacer. Feeding lower rates of milk or milk replacer might result in a need for a higher crude protein starter. For large breed calves, recommended crude protein percentage ranges from 18 to 24%, depending on the ratio of milk replacer to starter intake and average daily gain goal.

The physical form of calf starter is another consideration for animal health and efficiency of gain. While there is wide debate on starter form, few studies show agreement for the best physical form of the starter or ingredient composition. However, the available body of research typically agrees that calves should not be fed a ground or pelleted starter without either offering some forage or housing animals on straw bedding.

Forage

It is a common practice to not offer young calves any forage supplementation. This recommendation was founded under the interaction between forage consumption and lower concentrate consumption. Additionally, forage is not well utilized by the calf due to limited establishment of fiber-fermenting microbial populations, and feeding forage has been viewed as potentially wasteful. However, addition of a forage source to the diet of a young calf is based on factors including particle size of the starter, type and amount of forage, whether forage is offered separately or as part of a total mixed ration, and the type of bedding material provided to the calf (i.e., straw or other organic bedding material).

To highlight this, a few studies and their associated results were provided as examples. One study referenced found that calves housed on straw bedding and fed a textured starter with adequate particle size had lower average daily gain and decreased starter intake when offered grass hay or cottonseed hulls. Contrastingly, another study found that when housed on sawdust, calves fed large amounts of milk (8 kg/d) and offered a textured starter had a higher rumen pH without impact on growth measurements or empty body weight when offered free-choice grass hay. In contrast, a similar study with calves housed on sawdust and fed a pelleted starter and free choice access to forages (except alfalfa) demonstrated increased starter intake and average daily gain. Interestingly, alfalfa hay was consumed at 14 percent of total dry matter intake and reduced starter intake. Contrarily, when calves consumed oat hay at 8 percent of dry matter intake starter intake improved. Similarly, other forages offered, including barely straw, ryegrass straw, triticale silage, and corn silage at 4 to 5 percent of dry matter intake, resulted in starter intake being stimulated. When addressing concerns with gut fill and feeding forages, gut fill is more likely to have an impact at greater than 15 percent of total intake or has been found when alfalfa was fed instead of grasses.

In summary, there is evidence that offering forages when animals are fed pelleted starters and not bedded on chopped straw could be beneficial to the rumen environment and to starter intake. However, when animals are fed a textured starter of average particle size and housed on chopped straw, there might be little benefit to offering forages. In general, alfalfa hay should be limited to less than 10 percent of total dry matter intake for calves and other chopped forages should be offered in small amounts or less than 5 percent of total dry matter in a starter or total mixed ration.

Summary

Calves should be offered water from birth and grain starting at 3 days of age. Fresh grain and water should be offered daily and should be kept clean and away from the elements. Grain intake should be monitored through prior to weaning to ensure a smooth weaning process. Calves are the future of the herd and should be fed and managed appropriately to ensure their health and well-being.

Reference

National Academies of Sciences, Engineering, and Medicine. 2021. Nutrient Requirements of Dairy Cattle: Eighth Revised Edition. Washington, DC: The National Academies Press.