It is important to keep in mind that not all growth is the same on different milk replacers. Energy requirement is highest for maintenance but is greatly reduced once maintenance has been met. Alternatively, the protein requirement for maintenance is very low but increases for any additional growth. Consideration of feeding level is important when choosing a milk replacer. A typical 20:20 milk replacer for conventional feeding rates is not necessarily going to promote the same type of growth and composition at an accelerated feeding rate.
Fat deposition is different with different milk replacers and different feeding levels. As protein levels increase in the milk replacer, fat deposition decreases. This is true until about 28% crude protein (CP) which is similar to whole milk. Above this level, protein is wasted. At lower conventional levels (i.e. 8-10% of birth weight) where the goal is to get the calves off of milk and onto starter in the shortest amount of time, it is possible to overfeed protein because the limiting factor for growth becomes energy. Typically, accelerated feeding programs (i.e. 16-20% of body weight) will usually contain 24 to 26% CP as opposed to the 20% CP in the conventional feeding regimens because of the higher growth potential.
Overall, it is really beneficial to sit down and figure out how much protein and energy is being provided in the milk replacer that is fed to calves. Energy requirements are affected by thermoneutral conditions, immune status, and stress but also vary depending on size of the calf and body weight gain. Rethinking calf feeding in terms of energy density and total amount of energy provided in terms of Mcal and kg of dry matter of milk replacer provided as opposed to liters or quarts will help to target higher gains in calves. With these higher gains we should expect to see more productive animals in the future.
— Sarah Morrison, firstname.lastname@example.org
*References available upon request.
Source: Miner Institute Farm Report