Too Much Hay Too Quickly
Again I visited a dairy with self-reported "issues" with transition heifers. The calves were raised from birth to weaning in individual pens. With the intensive milk replacer feeding program calves were gaining well. At 42 days the milk replacer ration was cut in half with ad lib. water and calf starter grain. At 49 days all milk feeding was stopped and at 56 days the calves were moved into group pens.
The group pen ration was ad lib. calf grower grain, water and a palatable hay. Calves loved the hay and grain consumption dropped drastically. Within a week calves were starting to look rough and some of them had to be treated for pneumonia.
After coming back to the vet clinic I spent time using the NRC 2001 calf growth simulation software trying to dig into this nutritional puzzle. Based on my field experience over the past decade or so I made some assumptions about how calves respond to weaning and pen moves. And, I estimated intakes of both grain and hay from the period of 35 to 82 days of age.
If you click Here you can see the graph showing estimates of daily gain with two transition rations in the group pens:
(1) Limited-Hay ration with Week 1 = no change from individual pen, ad lib grower grain and water; Week 2 = add 1 pound hay per day per calf; Week 2 = add 2 pounds hay per day per calf; Week 3 = Ad Lib. grain, water and hay.
(2) Ad Lib. Hay ration with Week 1 = Ad Lib. hay, grower grain and water; Weeks 2 and 3 = same as week 2.
The data for the graph are NOT from a research project. They come from my personal field observations.
The "Ad Lib. Hay" line (should be red on your screen) reflects pretty much what I saw on this dairy - the calves stood still (that is, no growth) after the move into the group pen and ration change. After about three weeks (around day 76) the heifers seemed to turn around and were looking good again.
Too much hay to quickly. A more gradual introduction of hay combined with the ad lib. grower grain allowed calves to continue to grow while their rumen "bugs" adjusted to the new feed.