The volume of calf starter grain being consumed by a calf has often been suggested as a workable guide to when we could stop feeding milk.
Some years ago we often used the threshold of 2 pounds per day. More recently the threshold has been moved up to between 4 and 5 pounds. This upper value has some good science behind it - and, it agrees with the threshold I used with my calves as well.
A recently published review of work on how calves utilize the nutrients in calf starter grains suggests that it could make sense to use an additional threshold. That is, "What is the total volume of calf starter grain consumed by the calf?"
This is not entirely new. We have been recommending that before taking calves completely off milk they should have been regularly eating calf starter grain for three weeks. That length of time implies a significant volume of grain consumed.
Quigley's work suggests that a minimum volume of starter should be consumed before rumen development will have progressed to the point where calves can be expected to be able to replace energy from milk with energy from grain.
Because calf starter grains vary widely in their composition I was not able to come up with a volume that fits all starters. However, this idea should make us think about the need to track starter intake on our "ready-to-wean calves." It's not just how much grain did she eat today - over time, has the total volume been enough to support the development of a functional rumen?
My current recommendation is calf starter grain consumption of at least one large handful daily for a minimum of three weeks and current grain intake of at least 4.5 - 5 pounds daily at full weaning.
Quigley, J.D., "Symposium Review: Re-evaluation of National Research Council energy estimates in calf starters" Journal of Dairy Science 102:3674-3683 December 2019
Sarah Morrison (W.H.Miner Agricultural Research Institute) recently reported on a study she completed while at the University of Illinois.
The key point that caught my attention was that even while scouring calves were receiving milk replacer and oral electrolytes they also drank free-choice water.
The free-water intake of these calves was recorded during the first 21 days at the research facility. Probably arriving at 3 to 5 days of age at arrival so the observation period was probably from 4 to 25 days old.
All the calves drank water. Overall, for the 21-day period it came to 12 gallons per calf. She noted that the calves with scours averaged an extra gallon of water compared to non-scouring calves.
Bottom Line? Make sure ALL the calves have water 24/7 if possible. Especially scouring calves, give them a chance to re-hydrate naturally on their own by sipping free-choice water in addition to their milk and electrolyte feedings.
Reference: Sarah Morrision "Calves with diarrhea have different intake, growth and efficiency" November Farm Report, William H. Miner Agricultural Research Institute, p3.
In a well-designed research project dairy calves were weaned either abruptly (7 days at half milk ration) or gradually (7 days at 60% followed by 7 more days at 30%).
Using several measures they estimated rumen development and ability to digest solid feeds.
The calves with the longer weaning period had superior rumen development at the end of the weaning period.
No surprise. The calves need to be eating a measurable amount of solid feed for at least three weeks before the end of milk feeding in order to have a level of rumen function that allows for replacing the energy from milk with that from solid feed. No short-cuts available. Biology always wins, no cheating.
Another research group suggests that a calf starter grain intake of at least 4.5 pounds per day is desirable for moving from a milk+grain ration to a 100% grain ration if consistent gain is desired (assumes moderate environmental temperature).
Reference: Klopp, R. N. and Others, "Effects of feeding different amounts of milk replacer on growth performance and nutrient digestibility in Holstein calves to 2 months of age using different weaning strategies." Journal of Dairy Science 102:11040-11050 December 2019.
In a presentation to a dairy audience in Minnesota Dr. Trevor DeVries (as reported in Progressive Dairy November 7, 2019, p 49) suggested these guidelines for 2-4 month-old heifers when we have a growth goal of about 2.5 pounds a day gain:
85 percent of dry matter intake (DMI) should come from concentrated feed.
Do not use fermented feeds in the ration for this age heifers because "they are too high in moisture and calves are not able to eat enough to achieve an appropriate level of dry matter."
Use a "dry" TMR that contains concentrate and chopped dry forage such as straw or hay. Dry TMR can be made in large batches, stored and fed out daily without concerns of "heating" common for high moisture TMR's.
Forage particle size in dry TMR should be limited to 1" in length to discourage sorting and should be well mixed in the TMR.
Remember to keep TMR in front of the calves (do not feed to a clean bunk) in order to discourage calves from developing the bad habit of "slug feeding."