The Transition from Hay to Fermented Feeds
I had the opportunity to visit two dairies the same day. In each case I walked the transition heifer pens. I must admit that I did not have any scale data in order calculate growth rates for these heifers - I just walked by slowing making visual assessments of the animals.
On dairy #1 heifers are moved from individual to group pens of 10 calves, the ration for these heifers age 9 to 13 weeks was free-choice grower pelleted concentrate, free-choice medium-quality hay and water. Before coming into these transition pens their ration was the same pellet and water free-choice.
Around 13 weeks old their ration changes from the pellets and hay to a heifer TMR formulated specifically for heifers 3-12 months of age.
On dairy #2 heifers are moved from individual to group pens of 10 calves, the ration for these heifers 9 to 10 weeks was free-choice grower pelleted concentrate, the amount of good-quality hay they can clean up in an hour and free-choice water. Before coming into these transition pens their ration was the same pellet and water free-choice.
At 11 weeks these heifer are moved to another barn, pens of 10 heifers, ration changes to free-choice hay, pellets and water.
At 13 weeks the ration changes by adding the amount of heifer TMR they will clean up in about an hour - several large shovels-full it look like to me.
At 15 weeks the rations changes entirely to the heifer TMR formulated specifically for heifers 4-12 months of age.
What is the difference between the two feeding protocols?
Dairy #2 - the heifers had close to two weeks of eating the fermented feed before they moved to entirely TMR.
Dairy #1 - there was an abrupt change from dry forage to fermented forage in one day.
What are the plus and minus factors involved at these two dairies?
On dairy #1 it is likely to be nearly a full week before these heifers are able to achieve a new balance of fiber-digesting microbes that work on fermented feeds. Thus, these heifers will be short on energy and protein. As long as there are no stress factors (abrupt change in weather, over-crowding, vaccinations, introduction of new animals into the pen) these shortages are not likely to have any negative effects other than some compromised growth.
On dairy #2 the switch to fermented feeds is likely to have little effect on the availability of energy and protein for these heifers - they have received rumen pre-conditioning to smooth the change in forage from dry hay to the TMR.
I am sure you can see my preference for pre-conditioning the rumen when making a ration change. I believe this management choice is better than buying a feed-grade antibiotic (for example, AS700, Aureomycin) to top dress the ration while the heifers adapt to the ration change.