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Developed by Rob Costello, Merrick's Technical Specialist Intensive feeding of milk replacer to baby calves has generated much interest, resulting in a variety of feeding programs that are now available. Each program has its specific formulation, mixing ratio, feeding rate and its own growth rate. Some programs are well designed, providing good economical growth while others are proving to be costly and challenging to manage. Deciding on the right program, or even if you should consider an intensive growth program, can certainly be perplexing. Why change your calf feeding strategy? The general philosophy of raising dairy replacements has been to convert them to ruminants as soon as possible after birth. Once calves are on dry feed, health problems, labor cost and feed cost all tend to decrease. These are good incentives. To achieve this, we limit the amount of milk replacer a calf receives each day to about 8 oz. of milk replacer powder in 2 quarts of water at each feeding. Restricting milk replacer intake forces the calf to begin eating starter feed to satisfy its nutrient requirements. A calf will usually begin to consume a significant amount of a good quality starter beginning in its third week of life. From that point, it usually takes a couple of weeks to achieve adequate rumen function for weaning. During a calf's first 2 weeks, milk replacer intake supports a growth rate of about 0.25 lb per day. Figure 1 shows typical growth and starter intake patterns for a Holstein calf weighing about 95 lb at birth. Data were collected at Merrick's Calf Research Facility in Union Center, Wisconsin. Weaning age is 42 days. Figure 1 
Calf growth is primarily due to increasing starter intake. The slow growth in the first two weeks with conventional feeding is not due to an inability of the calf to grow. Figure 2 shows that when calves receive an intensive growth milk replacer formula mixed and fed at higher rates, growth is markedly improved during the first two weeks and continues even beyond weaning. Starter intake is similar between the two milk replacer feeding programs. Figure 2 
Conventional feeding of milk replacer provides adequate nutrients to maintain the calf during the first two weeks of life at which time starter intake and calf growth begin. When weather and disease challenges are combined with limited feed intake and an immature immune system, it's easy to see why calves are sometimes quick to succumb to the different stressors on the farm. Dairy calves remain unique among the different livestock groups in that they are the only group where we seriously and deliberately limit feed intake in early life to encourage adaptation and growth. Although this approach can work quite well, it's little wonder that dairy calf mortality rates are among the highest of all animal enterprises. A second reason to alter calf and heifer feeding strategies is to reduce the age at first calving. A realistic goal is for heifers to calve between 22 and 24 months of age. Lowering age at first calving reduces a heifer's rearing cost and quickens her payback on investment. This will likely require changes to both the feeding and breeding program so that heifers are the right size and weight at calving. Adjustments to heifer growth rates can begin when they are baby calves. Intensive Milk Replacer Formulas. With intensive feeding programs, calves consume a higher volume of milk replacer than they do with a conventional program. Milk replacer formulation needs to reflect this higher feeding rate. A calf's energy intake drives the protein requirement, and both need to be properly balanced with the feeding rate. With intensive milk replacer feeding, a calf's energy intake increases. If too little protein is provided relative to fat, the calf consumes excess energy. Without the necessary protein to convert this energy into lean tissue, the calf simply converts the excess energy to body fat. This is what happens when a 20% protein, 20% fat milk replacer is used in an intensive feeding situation. Intensive milk replacer formulas are generally in the range of 25 to 28% protein and 15 to 17% fat. As the feeding level and desired growth rate go up, the protein and fat level required in the milk replacer must also go up. For example, if we assume that programs are put together correctly, we would expect a 28-17 milk replacer to be fed at a higher level and support a higher growth rate than a 25-15 formula. Figure 3 shows how the Crude Protein (CP) level of milk replacer must change as the calf intake of milk replacer powder, or dry matter, increases. As Dry Matter Intake (DMI) increases, so does growth rate. Very aggressive milk replacer feeding programs can achieve growth rates over 2.25 lb per day. Keep in mind that energy intake is the driving force behind higher weight gains. Protein intake must be correctly balanced with energy to assure lean growth without overfeeding protein, and to avoid fat deposition due to underfeeding protein. Figure 3 
Should you aim for a high average daily rate of gain? Although aggressive growth rates over 2.25 lb per day are achievable, the majority of research evidence suggests this might not be wise. Heifers grown at these high rates will reach 1400 lb, which is about the ideal body weight for calving, when they are between 18 to 21 months of age. This is well below the target range of 22-24 months of age. Heifers calving at less than 21 months of age produce significantly less milk than heifers calving within the target range. However, if breeding is delayed with these large heifers, they will be heavier than desired at calving, and there is little evidence of any benefit to milk production from calving at heavier body weights. It costs more to feed them, and if they deposit additional fat, they are more likely to have calving related problems. One of the most important effects of heifer growth rate is on mammary gland development. Rapid growth of heifers prior to puberty has been shown to impair mammary development and future milk production. Recent research at Michigan State University showed that feeding heifers for prepuberty growth of 2.5 lb per day reduced milk production by 12% when compared to a growth rate of 1.7 lb per day. Most scientific evidence points to a maximum target growth rate between 1.7 to 1.9 lb per day prior to puberty. With conventional feeding, calves grow slower during the first 3 months of life than they do after that point. Feeding these heifers to calve between 22 to 24 months of age at a body weight of 1400 lb requires a rate of gain near 1.9 lb per day after 3 months of age. This leaves little room for error. However, if growth rate were improved during the first three months there would be less pressure to push growth rates later on. Choose the right intensive milk replacer feeding program. An intensive feeding milk replacer must be properly formulated and fed at the right level if calf growth rate is to stay within the prescribed growth rate range of 1.7 to 1.9 lb per day. A milk replacer formulated at 25% protein and 15% fat and fed at 1.5 lb per day provides the basis for a nutritionally sound program to achieve this growth objective. Research conducted at Merrick's Research Facility in Union Center, Wisconsin compared Merrick's Super Star 25-15 milk replacer feeding program to a conventional feeding program using Merrick's Gold Star 20-20. One group of calves was fed 1.5 lb of the 25-15 formula mixed in 4 qt of water each day, while the other group received 1.0 lb of the 20-20 formula in 4 qt of water each day. So the total volume of milk replacer fed each day was the same for both groups. Calves received free-choice water and an 18% crude protein starter feed from Day 1. The trial was 8 weeks long with calves being weaned at 6 weeks. Table 1 shows the total amount of milk replacer and starter consumed by weaning time and by the end of weeks 7 and 8. For example, calves receiving the 25-15 formula ate 64 lb of milk replacer by weaning time compared to 42 lb for calves receiving the 20-20 formula. Starter intake was the same for both groups.
The total amount of feed consumed by the 25-15 calves by weaning was 112 lb compared to 91 lb for the 20-20 calves. Since no additional milk replacer was fed after week 6, milk replacer amounts remain the same for weeks 7 and 8. Although the amount of starter feed consumed is the same for both groups at weaning, the 25-15 calves are eating over 1.0 lb per day more by week 8. Table 2 compares the weight gain for each group. At weaning, the 25-15 calves weighed about 19 lb more than the conventionally raised calves. Two weeks after weaning, this weight difference increased to 22 lb. This corresponds to the increasing starter intake of 25-15 calves seen in Table 1.
Table 3 shows the average daily gain for each group of calves. By the end of week 8, calves receiving the 25-15 formula reached the target growth rate range of 1.7 to 1.9 lb per day. Calves raised on the conventional milk replacer feeding program will take at least 3 weeks longer to reach the target range.
Intensive programs that feed more milk replacer than the 25-15 program can generate somewhat higher average daily gains during much of the milk feeding stage. These programs usually require a step-down feature where milk replacer is reduced by one half for the week prior to weaning. This is necessary for calves that are not eating sufficient starter and do not have adequate rumen function for weaning. In other words, the more aggressive programs still rely on reducing or limiting nutrient intake to transition calves much like the traditional 20-20 program. As a result, average daily gain usually declines before weaning, diminishing any growth advantage achieved earlier. The more moderate approach of the 25-15 program promotes a better blend of growth rate with the need to transition calves to ruminants. Faster growth programs that overshoot their mark tend to be more costly as well as inefficient. Summary. A well-designed intensive milk replacer feeding program improves the nutrient intake level and growth rate of the calf. In addition it reduces the pressure to push growth rate during that critical mammary development period prior to puberty. The other major benefit of this program is that it is a simple way to provide a better nutritional base for the calf so it can better weather the challenges of becoming a ruminant.  
A Subsidiary of Merrick Animal Nutrition, Inc. 2415 Parview Road * P.O. Box 620307 * Middleton, WI 53562-0307 USA 1-608-831-3440 * 1-800-MER-RICK (637-7425) FAX: 1-608-836-8943 Email us at: mersales@merricks.com | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||