Current Issues in Calf-Feeding

By Jane Fyksen Crops Editor
Thursday, July 31, 2008 8:51 AM CDT

There’s a “new paradigm” in preweaned calf management n one that recognizes that “this is a newborn calf with nutrient requirements for growth that are not satisfied by (traditional) limit-feeding programs,” says Virginia Tech dairy scientist Bob James.

That’s just one of several current issues in feeding preweaned heifers that, he announces, are “receiving noteworthy attention from both academia and industry.” Others include: Pasteurizing colostrum, specialized feeding of smaller calves, and alternative proteins to trim costs of milk replacer diets.

For the last 30 years, James says the “accepted paradigm” for wet-calf management has been limit-feeding milk or replacer to encourage early weaning and accelerate rumen development and consumption of less-expensive dry feeds. Such strategies encouraged limited gains during the calf’s first month.

Recently, he reports, “academics and industry” have questioned this strategy, especially considering no other facet of livestock agriculture limit-feeds newborns to encourage early weaning.

A “new paradigm” recognizes that newborn calves have nutrient requirements for growth not satisfied by limit-feeding regimens, reports James.

“Logic argues that some deposition of fat may be desirable” in young calves, as body reserves to better endure colder temperatures or as energy stores when intake is depressed during illness, he mentions. New goals for growth encourage doubling a calf’s birth weight by 56 days.

In other words, practices should be adopted “which first address the biological needs of the calf” and “then seek to achieve reasonable feed cost and labor efficiency,” he reports of the industry also countering a growing concern within the general public on animal well-being issues.

“It’s important to remember some facts about the neonatal calf,” states James. “This is a newborn animal that is immuno-incompetent and dependent upon timely absorption of colostrum. It requires a nutrient-dense diet and is highly susceptible to heat loss… Consequences of mismanagement include diarrhea, respiratory disease and death.”

“Sometimes it seems as if we lose sight of the forest for the trees,” he admits of slipping into habits or traditions “with little consideration to what our original goals were for the subject at hand” (i.e. a baby calf).

Calves have long been viewed as a “cost center,” when in fact, they represent “an investment in the future,” says James. While cost-control has been one of the primary factors determining calf-rearing practices, calves have risen in value considerably over the past five years. “Consideration needs to shift towards practices which reduce the risk of calf mortality,” he contends, leading off with the relatively new practice of pasteurizing colostrum to improve biosecurity and reduce “early microbial loads on the gut of the calf.”

Failure of passive transfer continues to be a problem with nearly 30 percent of U.S. dairy calves. Research way back in the late ‘70s demonstrated that early microbial contamination of the intestine could impair absorption of colostrum antibodies. The second concern with colostrum is that it represents the earliest potential exposure to infectious bacteria like Mycoplasma, Mycobacterium, Salmonella and coliforms.

While early research using pasteurizers yielded disappointing results (i.e. reduced immunoglobins or Ig concentration) and/or unacceptable thickening of the colostrum, last year, Minnesota researchers reported that heat-treating colostrum for 60 minutes at 140 degrees in a commercial batch pasteurizer results in destruction of pathogens while minimizing destruction of colostrum Ig.

A field study showed that calves fed colostrum using that protocol more efficiently absorbed colostrum Ig and had higher levels of serum Ig at 24 hours old, compared to calves fed untreated colostrum.

James recommends the following protocol to pasteurize colostrum:

- Routinely monitor times and temperature to make sure the temperature doesn’t exceed 141 degrees for 60 minutes

- Culture colostrum to assure that post-pasteurized standard plate counts (SPCs) are less than 20,000 cfu per ml

- Routinely monitor health records and passive transfer rates in calves; use a refractometer to monitor serum proteins in calves from 24 hours to seven days of age. The goal should be to have 90 percent of the calves with a serum protein value of over 5.0 g/dl.

Advice on smaller calves

James says a common misconception is that producers must guard against overfeeding calves, lest they succumb to diarrhea - especially the smaller Jerseys. However, recent research at Virginia Tech compared growth and body composition of Jersey bull calves fed either a 20 percent protein: 20 percent fat milk replacer, a 29 percent protein:16 percent fat replacer, a 27 percent protein:33 percent fat replacer, or whole milk. The whole milk and higher protein replacer diets were fed to provide sufficient protein (180 grams) for 1.43 pounds of average daily gain. At the end of five weeks, calf body composition was measured.

Calves didn’t differ in their average weekly scour score or medication days. Feed efficiency and ADG was highest for calves fed whole milk and lowest for calves limit fed the 20:20 milk replacer. Calves fed whole milk or 27:33 milk replacer had the highest body fat content and gained more grams of fat than calves on the other diets. Calves fed the 29:16 and 20:20 replacers had similar body fat composition.

“It’s interesting that although diets were formulated for an average daily gain of 650 g (1.43 pounds), all calves gained less than predicted by the NRC, in spite of the study being conducted during relatively thermoneutral environmental conditions,” he notes.

This demonstrated that the practice of feeding limited quantities of 20:20 replacer provides sufficient nutrients for very limited body weight gains. Nutrient requirements for maintenance are probably higher than originally proposed by the NRC (in 2001), notes James.

Based on estimated efficiencies of nutrient utilization for gain, it’s been proposed that nutrient requirements for maintenance are 21 to 39 percent higher than estimated by NRC. “This is logical when one considers that smaller animals possess more surface area relative to their body size and therefore would likely lose body heat more readily than larger calves,” says James.

By extrapolating from these data, a milk replacer containing 28 percent protein and 25 percent fat has been developed for feeding Jersey calves, which he says should provide sufficient energy to account for their increased needs due to disease and environmental stresses.

Alternative proteins eyed

During the past year, ingredient costs for replacers have fluctuated widely. Whey protein concentrate (used more for human food) and dried whey have climbed in price; calf feeders have sought more cost-effective milk replacer formulations.

At present, soy, wheat and egg proteins have been evaluated as possible substitutes for a portion of the milk protein. The most popular substitutes at present, according to James, are those manufactured utilizing soy-based proteins.

A study of 120 bull calves looked at replacing up to 50 percent of milk proteins with wheat gluten in replacers containing either 18 or 20 percent crude protein. The feeding rate was 1.19 pounds of replacer powder reconstituted with warm water to 12 percent DM. A commercial calf starter containing 16 percent CP was also provided. Within a given protein percentage, body weight gains weren’t affected by protein composition. James notes these calves were limit-fed; results would likely be different at higher feeding rates.

The use of egg as a substitute for milk proteins shows less promise, he says, “in spite of the long-held belief that a raw egg was the best thing for a sick calf.” Another set of 120 bull calves were fed diets for 42 days in which spray-dried whole egg comprised 0, 10 or 20 percent of the milk replacer formulation. Increasing spray-dried whole egg resulted in linear reductions in body weight gain at 28 and 56 days, calf starter intake and feed efficiency.

Other research found no difference in calf performance when liquid egg was limited to 10 percent of the diet as a substitute for milk protein.

James shares data from Land O’Lakes Animal Health on alternative proteins, compared to all-milk. The alternatives in this study were: Glymaxene (50 percent of protein source), soy protein concentrate (50 percent), soy isolate (50 percent), egg albumin (25 percent), wheat gluten (25 percent) and 2 percent protein substitution with lysine. Glymaxene represents a treated soy flour product that’s been proven as an acceptable partial substitute for whey proteins in replacers fed for more limited gains.

He highlights the reduced rate of daily gain in all cases where vegetable or egg proteins substituted for milk proteins. He warns that the prices of milk replacer ingredients are very dynamic and must be considered in relation to the milk price. During the last half of last year, when replacer prices surged, so did the price of milk. “More recently, the increased value of soybeans and wheat has likely altered the relative producer price of milk replacers containing alternative proteins,” he mentions.

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