Managing rumen development on a high fat milk replacer

The benefits of feeding a high-fat milk replacer:

1. Additional energy, for every 5% increase in oil the energy density of the powder is increased by 6%.
2. Reduced scours, energy in milk replacers comes from either fat or carbohydrate (oil or lactose), high fat milk replacers have lower lactose, naturally lowering their osmolality and reducing the incidence of scour. 
3. Improved resilience, during periods of stress, disease challenge or low temperatures the calf’s energy requirement increases. Calves have very little body fat stored and rely on a constant supply of energy meaning increased requirements are more easily met with a high-fat milk replacer. 

A study conducted in 2021 looked at the behaviour and performance differences seen in calves offered either a high-fat milk replacer (23% Protein, 23% Oil) or a high lactose milk replacer (23% Protein, 17% Oil) ad-lib for the first 35 days. During this ad-lib phase, the high-lactose group consumed more milk than the high-fat group but energy intake and performance remained the same. This study shows that a calf will manage their own intake to meet their energy requirements.

The benefits of using a high-energy milk replacer are numerous but do provide extra energy in the liquid feed prevent high intakes of starter feed from driving rumen development?

As the calf grows its maintenance energy requirement increases. During the first 3 weeks of life, this requirement must be met by liquid feed because the rumen is not yet capable of fermentation. With the calf’s size restricting its daily intakes the only way to increase both growth and resilience is to increase the amount of energy fed per litre of milk.

After 3 weeks starter feed comes into play albeit in small amounts, where the calf is meeting its energy requirements with its milk feeds starter feed intake will be reduced. Although as you can see in the table below as the calf’s body weight dictates a greater energy requirement and milk feeds are reduced to initiate weaning starter feed consumption comes into line.

Table A, below, compares the starter feed requirements of a calf on a 17% oil powder vs. a calf on a 25% oil powder, both containing 23% protein. The starter feed is a 12.4MJ/kg DM nut and the following amounts are set to achieve 0.8kg/day growth.

To conclude, providing more energy via milk feeding facilitates growth and resilience in early life where challenges tend to be at their highest. The digestibility of milk replacer also outweighs that of starter feed in the first 4 – 6 weeks. Where milk replacer feeding is elevated above 6L on high-energy powders weaning needs to be considered more carefully as starter feed intake will be delayed, but as with all feed plans stepping down the milk and achieving starter intakes of 2kg/day on a 12MJ/kg DM or above starter feed before milk feeding is withdrawn completely will maintain growth rates.