Feeding the Newborn Calf

Introduction

Feeding high-quality colostrum to the calf as soon as possible after birth is the most important thing you can do for calf health, including for dairy bull calves and beef x dairy calves. Calves are born with an immature immune system, which means they have little defense or immunity against disease. Unlike key nutrients, the placenta does not allow the transfer of the dam’s immune cells to the unborn calf¹. However, the dam transfers immune cells to colostrum, which she begins to make five weeks prior to calving². The timely ingestion of adequate amounts of high-quality colostrum allows the calf to acquire passive immunity from the dam. Passive immunity helps the calf to fight disease during the first four months of life as its immature immune system is developing³.

Factors Affecting Passive Transfer

Passive transfer occurs when immunoglobulin G (IgG), immune cells (white blood cells), and hormones are absorbed through the lining of the calf’s gut from the mother’s colostrum⁴. After a calf is born, oral stimulation starts the passive transfer clock. To maximize passive transfer, the calf should be fed colostrum within the first 2 hours of life². After four hours, there is a progressive decline in the efficiency of absorption (Figure 1)⁵. The passive transfer process ends 24 hours after birth³.

Absorption efficiency also influences passive transfer. Conneely et al.⁷ reported that calves absorb IgG most efficiently when fed colostrum at approximately 8.5% of body weight, with absorption rates declining as feeding volume increases. For example, absorption decreased from 38% at 8.5% of body weight to 29% at 10% of body weight. Frederick et al. (2025)⁸ evaluated colostrum feeding rates of 6%, 8%, 10%, and 12% of body weight. Serum IgG concentrations at 24 hours were lowest in calves fed 6% of body weight (28.8 g/L) and highest in calves fed 10% (41.1 g/L) and 12% (43.4 g/L)⁸. However, IgG absorption efficiency declined as feeding volume increased, from 47.8% and 46.2% in the 6% and 8% groups, respectively, to 41.0% and 36.3% in the 10% and 12% groups⁸. Signs of colic-like behavior, indicative of discomfort, were observed only in calves fed 10% or 12% of body weight⁸.

It is important that newborn calves are born in clean, dry environments so they do not ingest manure or other materials from the calving process while learning to stand. Remember, whatever is ingested first starts the passive transfer clock. It is not desirable to have fecal bacteria absorbed first. The passive transfer process allows large molecules to pass from the gut into the bloodstream of the calf. Bacteria may also bind IgG in the gut, preventing transfer into the bloodstream^{9, 10}.

It is also important to minimize bacterial contamination in colostrum. Contaminated colostrum is one of the earliest potential exposures to infectious agents, such as Salmonella, Mycoplasma, fecal coliforms, and the organism that causes Johne’s disease^{11, 12, 13}. These infectious agents are known to cause diarrhea and septicemia.

Factors Affecting Colostrum Quality

It is recommended that fresh colostrum contain less than 100,000 colony-forming units per milliliter (cfu/mL) total bacteria count and fewer than 10,000 cfu/mL total coliform count¹⁴. Ideally, herds should meet the Dairy Calf and Heifer Association recommendations of less than 50,000 cfu/mL total bacteria count and fewer than 5,000 cfu/mL total coliform count¹⁵. There are three main sources of bacterial contamination of colostrum: infection or fecal contamination on the udder; contamination during collection, storage, or while feeding from dirty equipment; and bacterial proliferation in stored colostrum². Collect colostrum from udders that have been prepared the same as if milk were going into the bulk tank for human consumption; use clean, sanitized equipment. Feed fresh colostrum immediately, refrigerate, or freeze in individual serving sizes.

Colostrum quality varies dramatically among cows. Several factors, including dam vaccination¹⁶, length of the dry period¹⁷, and the time of colostrum collection, can be managed by producers.^2. Colostrum should be collected within three hours of giving birth to minimize dilution of IgG by milk production¹⁸. It is not recommended to feed colostrum that is of low quality, bloody, from cows with mastitis, or positive with Johne’s disease¹⁹.

A tool to help reduce colostrum bacterial counts is pasteurization. In this process, colostrum is heated to 140⁰F for 60 minutes²⁰. Pasteurization is recommended even though the process destroys 80 – 90 percent of the colostrum’s white blood cells. Heating at this low temperature for an hour maintains immunoglobulin activity and colostrum fluid characteristics, while reducing important pathogens including E.coli, Salmonella, Mycoplasma, and the Johne’s disease pathogen^{20, 21}.

Measuring Colostrum Quality

Good quality colostrum should have an IgG concentration above 75 grams/Liter (g/L)²². Although colostrum’s IgG measurement does not indicate the white blood cells and hormones that are also included, it is an excellent indicator of colostrum quality. Fair quality colostrum has an IgG concentration between 50  and 74.9 g/L, and poor quality colostrum has an IgG concentration between 25 and 49.9 g/L (Table 1)²². Producers should measure the quality of the colostrum prior to feeding by measuring it on-farm using a refractometer or a cow-side immunoassay kit.

Tools for Measuring Colostrum Quality

A refractometer is designed to measure the amount of soluble solids in a sample, meaning it measures all the solids dissolved in the water, beginning with sugar, salts, protein, and acids. It is not dependent on the temperature of the colostrum. A Brix value of 25% corresponds to 75 g/L of IgG²². Therefore, a colostrum sample with a value greater than 25% on a Brix refractometer represents a good-quality sample; scores of 30% represent an excellent-quality sample²².

To use a portable refractometer (Image 1), place a few drops of colostrum on the prism and cover the sample. The refractometer is then held up to a light source. Read the Brix value at the line between the light and dark areas on the scale. The prism and sample cover must be thoroughly cleaned after each use. To use an electronic refractometer (Image 2), place the manufacturer-specified amount into the designated spot on the refractometer. Select the BRIX scale to display the colostrum quality. The manufacturer should provide instructions on checking and adjusting the calibration. Distilled water should have a reading of zero if the instrument is calibrated correctly²³.

Colostrum quality may also be measured using an immunoassay test such as the DVM Rapid Test II™ system by MAI Animal Health. This is a cow-side immunoassay kit that differentiates high- from low- quality colostrum²⁴. The test yields only a positive or negative result, and does not provide an estimate of the actual IgG concentration. Each sample takes about 20 minutes to complete.

The Colostrometer™ (Image 3) is a low-cost method of differentiating colostrum quality that was developed in the 1980s by Dr. D.S. Fleenor and G.H. Stott²⁵. The Colostrometer™ measures specific gravity and uses a color-coded scale to indicate quality. Unfortunately, colostrum components other than IgG can affect specific gravity, which can give inaccurate readings. Colostrum measured in the green area of the Colostrometer™ contains > 50 g/L of Ig, yellow contains 20 – 50 g/L, and red contains <20 g/L.

To use the Colostrometer™, the colostrum must first be at room temperature (72⁰F). At lower temperatures, the Colostrometer™ overestimates the IgG concentration, while IgG is underestimated at higher temperatures²³. To read the measurement, float the Colostrometer™ in the cylinder filled with room-temperature colostrum, wait approximately one minute, and determine the color reading. Please note that a green value from the Colostrometer™ suggests a value of > 50 g/L of IgG, which is considered fair with the new colostrum quality standards²².

How Much Colostrum Does the Calf Need?

To achieve passive transfer, a calf should be fed a minimum of 200 g of IgG in the first feeding of colostrum, and 100 g of IgG in the second feeding of colostrum²². However, because producers frequently do not know the concentration of IgG in the colostrum being fed, it is currently recommended that calves be fed 8%-10% of their body weight in colostrum at first feeding². This means the calf should be fed three to four liters of colostrum at birth and an additional two liters by 12 hours after birth. Research has shown calves fed four liters of colostrum at birth and two liters 12 hours later have higher blood serum IgG levels at 24 hours of life²⁶. The calf should be hand-fed a known volume of colostrum using either a bottle or an esophageal feeder to guarantee enough colostrum is consumed¹⁴.

Comparing Maternal Colostrum with Colostrum Supplements and Replacers

Feeding high-quality maternal colostrum is the best, and should be the first option. If the colostrum from the dam is not of adequate quality, then either feed acceptable colostrum collected or stored from another animal, or add a colostrum supplement. A colostrum supplement is designed to be fed with the maternal colostrum because it does not provide the desired 50 g/L IgG when fed alone²⁶.

Colostrum replacer may be fed when good quality colostrum is not available. A good quality colostrum replacer contains at least 50 g/L IgG extracted from cow’s milk and provides fat, protein, vitamins, and minerals like colostrum would²⁷. Serum-based colostrum replacers are also available that contain IgG harvested from bovine blood, but they do not contain intact white blood cells or hormones. When feeding a colostrum replacer product, it is still important to feed 200g of IgG in the first feeding, and 100g of IgG in the second feeding to achieve passive transfer²². If feeding a replacer product that has 50 g/L of IgG, then you will need to feed 4 L or 4 packets of replacer product for the first feeding, and 2L or 2 packets of the replacer product for the second feeding.  

 It is important to keep in mind that colostrum replacers are designed to be fed in place of colostrum, while colostrum supplements are to be fed in addition to maternal colostrum. Although colostrum replacers are designed to replace colostrum, there have been mixed results, with many products failing to routinely provide the necessary 10 milligram/milliliter (mg/mL) IgG in the blood serum of calves ^{27, 28, 29, 30}.

How to Store Colostrum

If you have extra good-quality colostrum (> 75g/L), it can be saved for use when you do not have good-quality colostrum readily available. To store colostrum, immediately divide it into portions less than two quarts in size to enhance cooling and reduce bacterial growth. Immediately refrigerate these portions if they will be used within five days. Adding potassium ascorbate as a preservative enhances refrigerator shelf life³¹. Colostrum can also be frozen for future needs. Frozen colostrum can last up to six months when frozen in a chest or deep freezer³². Freezing in a refrigerator freezer is not advised due to the freeze/thaw cycles. Slowly thaw only the amount of frozen colostrum that you need. Colostrum should be thawed in a water bath with a temperature between 104 and 140⁰F³³. A 3-quart bag of colostrum will take about 30 minutes to completely thaw at a temperature of 125⁰F³³. Do not microwave or rapidly thaw. Rapidly thawing can destroy some of the IgG content. Freezing kills all white blood cells found in colostrum². Therefore, always feed some fresh or refrigerated colostrum along with the colostrum that was frozen. Do not refrigerate any unused thawed colostrum.

Measure Calves for Rate of Passive Transfer

It is important to routinely check all of your pre-weaned calves for failure of passive transfer. Calves that experience failure of passive transfer are more likely to become sick or die in the first two months of life as compared to calves with adequate immunity³⁴. Failure of passive transfer occurs when the calf does not absorb an adequate amount of antibodies from the colostrum. In the United States, mortality rates in pre-weaned dairy heifers are estimated to range from 8% to 11%³⁵. This can happen for many reasons, including not feeding high-quality colostrum (IgG > 75 g/L), not feeding an adequate amount of colostrum (8%-10% of body weight), and not feeding colostrum in a timely fashion( <2 hours).

The major factor affecting the absorption of IgG molecules is how quickly after birth the calf was fed colostrum. A calf is considered to have failure of passive transfer if its blood serum IgG levels are less than 10 mg/mL.  An indirect measurement of serum IgG is performed by measuring serum total protein (TP) in calves that have been fed fresh or frozen colostrum and are 24 hours to seven days old. Unfortunately, serum total protein and IgG concentrations for calves fed a colostrum replacer product are poorly correlated³⁶.  This means that you cannot use serum total protein as an indicator of passive transfer success or failure if the calf has been fed a colostrum replacer.  Producers should work with their veterinarian to develop a plan for measuring TP. This plan should include drawing blood weekly from healthy calves 1-7 days of age and testing the serum with a refractometer. Interpret the results at the group level. The goal is for 80% of those calves tested to have a TP greater than or equal to 5.5 grams/deciliter (g/dL). Researchers are finding that higher TP levels (>6 g/dL) are better³³. However, TP > 7.5 g/dL in calves less than one week of age indicates an inflammatory immune response; >8 g/dL indicates dehydration.

The Importance of Colostrum for Calves Leaving the Farm

Feeding sufficient amounts of high-quality colostrum to calves at a young age is the most important management factor in determining health and survival of the neonatal calf³⁷. It is vitally important for calves leaving the farm, such as market dairy bulls, heifers, and beef x dairy calves. These market calves will encounter increased pathogen levels during transport, at the market, and when grouped in their next feeding facility. Share your farm’s passive transfer protocol and TP history with the next buyer of your calves. Doing so will build buyer trust in your market calves.