Introduction
Recently, our research group published an article in the Journal of Dairy Science that presented a set of linear and non-linear equations to predict dry-feed intake in young calves (Quigley et al., 2021). I described the equations in Calf Note #224 and explained how the main factors affect dry feed prediction in Calf Note #225. The simplest non-linear was implemented into a simple Excel spreadsheet that demonstrates how to implement the prediction equations. The link is here.
The simplest equation accounts for effects of age and “MEgap” (the energy needed by the calf above that consumed in milk or milk replacer). Other equations also included ration effects such as NDF content as well as effect of ambient temperature.
In this Calf Note, I’d like to point out some important caveats to dry feed prediction, particularly when using on age of the calf and MEgap as the independent variables. The concept of “MEgap” is relatively straightforward. It’s the amount of energy the calf needs for maintenance and growth above that which the calf consumes from milk or milk replacer. The “gap” is basically the energy deficit the calf senses after it consumes it’s allocation of liquid feed. There are several caveats, however. Only IF calf’s desire to eat dry feed is driven by hunger, AND IF the calf knows that calf starter is food that can satiate that hunger AND IF the calf’s digestive mechanisms are sufficiently developed AND IF the calf can eat enough starter to meet ME demands, AND IF the starter is formulated so that it doesn’t cause digestive upsets when consumed in large amounts, THEN the calf will increase its starter intake to meet the “gap” in energy (i.e., the MEgap).
The caveats here are important! They indicate that simply limiting the CMR allocation so “calves are hungry” can result in catastrophic failure, as is often the case when calves are fed 400-500 grams of CMR per day and weaned at 30 days of age. It’s important to keep these considerations in mind when designing a feeding and weaning program for calves.
One approach to determining whether the calf is metabolically ready for weaning is to determine the age at which it consumes a total of 15 kg of NFC from calf starter. In Calf Note #209, I outlined the importance of cumulative intake of 15 kg of NFC as a target for “mature rumen development”. This is the point at which the calf’s ability to extract energy from dry feed is similar to that of an adult cow. That is, the rumen and the remainder of the digestive tract has matured sufficiently so that it can reasonably be weaned.
I made a few changes to the original Excel spreadsheet (in Calf Note #224) to allow the user to enter the NFC content of calf starter fed to the calf. Consult with your feed representative for more information on how to calculate NFC in a starter. This spreadsheet then calculates the age at which the calf reaches 15 kg of cumulative NFC intake – that is, when it can safely be weaned. You can change the milk replacer feeding program, the ME content of the milk and the NFC content of the starter affect the age at which weaning is reasonable. The link to the updated spreadsheet is here.
Best of luck!