Calves must have adequate rumen development to have a smooth transition at weaning time. Weaning means we switch calves from a liquid-based diet to a solid feed diet.
But the form of the feed is only part of the story. Milk is digested in the abomasum; grain and forage enter the rumen first. If the rumen environment is not prepared, calves will not be able to digest grain fully. Such calves experience a growth slump, and the nutritional stress can make them more susceptible to disease.
The conventional rule is that once calves eat 2 pounds of starter for three consecutive days they are ready for weaning. However, that “rule” is part of a system in which calves are offered grain by about 3 days of age, and they start eating noticeable amounts of grain by about 2 weeks of age. In this scenario, calves eat grain for three to four weeks before weaning at 5 to 6 weeks of age.
Compare this feeding program to one where calves receive 2 gallons or more of liquid feed per day. These calves do not begin eating starter at 2 weeks, and often they eat very little grain until milk is reduced the week before weaning, when their grain intake climbs dramatically. If we try to apply the same rule of eating 2 pounds of grain for three days in a row, calves are likely to struggle after weaning.
Research tells us rumen development takes time.
Calves pick up bacteria that populate the rumen from their environment and their diet, but diet determines the species that dominate. From the time calves begin eating grain, it takes two to three weeks for the bacterial population to adjust and multiply to a number that can efficiently convert the starch to butyrate and propionate. Rumen wall tissue uses butyrate to fuel the growth of papillae that increase the surface area available for absorbing nutrients.
The combination of physical development and the establishment of the bacterial population must be in place before calves can effectively convert grain to growth. Ease weaning stress by ensuring calves eat at least half a pound of grain per day for four weeks or a pound per day for two weeks and that they reach 2 pounds per day for three consecutive days before weaning.