“First hollow stem” will be arriving at wheat field near you very soon.  The Mesonet predictor of first hollow stem indicates that Southern Oklahoma may have already reached that stage.  Wheat producers that are using wheat pasture to grow yearling replacement heifers must decide if they are going to leave the heifers on the wheat pasture until April just before the breeding season, or remove them soon to maximize wheat grain production.  Science has shown us that the cattle must be removed from the wheat at or near the time of the first hollow stem to achieve the highest possible grain yields.  Replacement heifers that are scheduled to be bred artificially often must be moved to a pasture close to working chutes for synchronization and insemination.  Whether the move from wheat pasture occurs now, or in April (just before breeding), the heifers need to consume a diet that will allow them to continue to grow at a rate of 1 to 1.5 pounds per head per day.  Heifers placed on low quality dormant native range or dormant bermudagrass will need supplementation to continue this rate of gain.  Without supplementation the heifers may be slower to reach puberty and maintain cycling activity. 

Replacement heifers that have just reached puberty and started cycling may be vulnerable to any drastic change in feed intake. A small trial conducted at Oklahoma State University (White, et al., 2001) illustrates the impact that sudden severe reduction in energy intake can have on cycling activity in replacement heifers. Nineteen heifers were divided into two groups. Both groups were fed at 120% of the maintenance requirements needed for yearling heifers. By the use of hormone assay and ultrasonography, it was determined that all heifers were cycling when the treatments began. Nine of the heifers were continued on the 120% of maintenance diet. The other ten heifers were placed on a diet that was 40% of the requirement for maintenance. They remained on this diet for 14 days. At the conclusion of the 14 day treatment period, only 3 of the feed restricted heifers were still cycling, whereas all of the heifers receiving the 120% of maintenance were still cycling.

Table 1. Imact of sudden, severe reduction in feed intake on cycling activity of yearling heifers

 

Treatments

 

120% of Maintenance

40% of Maintenance

Day of treatment

Day 0

Day 14

Day 0

Day 14

# of Heifers

9

9

10

10

Weight

704

711

691

658

# cycling

9

9

10

3

 

This very small, but impressive, data set illustrates that we must be cautious about any disruption in the feed intake of replacement heifers at the start of their breeding season.  Movement from high quality cool season grass (in the spring) to dormant winter native range may cause such a weight loss in a short period of time. Making changes in supplement programs at the start of the breeding season should be done carefully and gradually to avoid any chance of digestive disorder and the possibility of the heifers going "off-feed".