The following answer was provided by Al Kertz, Dairy Field Technical Service with Milk Specialties Global Animal Nutrition.
Q: What about feeding hay with calf starters?
A: Recently, there seems to be conflicting results when hay is also fed with calf starters. How can this be interpreted and applied?
Let’s first look at the biology, and then what may be confounding factors. Studies done primarily in the 1950s and 1960s found that the volatile fatty acids (VFA) produced in the rumen in the order of first butyric, followed by propionic, and then by acetic led to development of the rumen papillae and functionality of the rumen. Yet, that is the opposite of the proportions of these VFAs produced in the rumen by normal fermentation, especially forage/fiber fermentation. Forage also ferments more slowly, and has an overall lower digestibility which results in more gut fill. If forage is not fed to young calves, then the key is to avoid marginal ruminal acidosis.
Adequate particle size in the calf starters must be present to stimulate chewing, which then results in saliva production for buffering and more nearly normalizing rumen fermentation. This avoids marginal ruminal acidosis and also favors fermentation resulting in enhanced butyric and propionic fatty acid production. These VFAs are then absorbed through the rumen wall (because they are short chain, which makes them volatile), where butyric is metabolized and plays the leading role in rumen papillae development.
When calf starters do not have adequate particle size or “texture,” then marginal ruminal acidosis will more likely occur. Unless some hay is also provided. But that is a “crutch” or band aid to not providing the best solution: an adequately texturized calf starter. There are particle size parameters for calf starters provided in journal articles published by Porter et al. (Prof. Anim. Scientist 23:395-400, 2007) and Hill et al.(J. Dairy Sci. 91:2684-2693, 2008).
With the popularity of all pelleted starters, the calf’s best welfare has been compromised. Some feel that you should provide some hay and that will make the calf starter program work. But a little bit of hay can impede rumen papillae development. Here is an example.
Some studies where hay was also fed in addition to calf starter have not measured height increases or provided some measure of gut fill in addition to body weight and daily gain. Thus, true growth cannot be separated from daily gain confounded by increased gut fill. A study this year in the Journal of Dairy Science (94:3547-3553, 2011) purported to show that providing hay along with a texturized calf starter improved daily gain. But the calf starter used only processed grains, which resulted in a rumen pH at 10-week slaughter of 5.06. This indicated the calf starter was not well texturized. Providing hay along with the calf starter significantly increased rumen pH to 5.49, but it also significantly increased rumen/reticulum tissue by 20 percent and full rumen-reticulum weight by a whopping 59 percent!
The solution is to feed a good texturized calf starter. For those who think a pelleted calf starter alone is OK, I have pictures of just-weaned calves bedded on straw. They were dutifully chewing up a wooden feed bunk with plenty of the pelleted calf starter in it! A veterinarian also told me about observing calves shallow panting when on a pelleted calf starter because they evidently were trying to ventilate their way out of their marginal rumen acidosis.
The most practical way to determine how well calves are doing on their calf starter program is to observe for rumination just as we do for cows. They should be ruminating by around three to four weeks of age, and 20 percent should be observed ruminating at one time.