Developing or purchasing replacement heifers is a huge investment and potential financial returns depends on future calf production. Research has indicated that it takes net revenue from approximately 6 calves to cover the development and production cost of each replacement heifer. Management strategies to develop the best possible conception rate for replacement heifers are critical to improve longevity in the herd. Hence the ultimate goal is the same, “getting the heifers bred” and preferably early in the breeding season.
Things to Consider
Time of Calving
Research conducted at USDA-Meat Animal Research Center and with SD herd showed that heifers that calved in the first 21 days had greater longevity and increased weaning weight compared to heifers that calved in the second 21 day period or later. The SD heifers (n = 2,195) that calved in the first 21 day period had increased longevity (5.1 compared to 3.9 years). The USDA MARC longevity data resulted in 8.2, 7.6 and 7.2 years for heifers that calved in the 1st, 2nd or later calving period, respectively. In addition, improved weaning weights were reported through the 6th calf born for the heifers that calved in the 1st calving period.
It has been reported numerous times that heifers developed in a drylot and immediately following breeding turned out to grass have lower pregnancies in the first 21 days. A possible reason is a negative plane of nutrition due to re-learning grazing skills. Research conducted at the Antelope Research Station reported that when heifers were moved from drylot to range, they lost weight (3.5 lbs/d) during the first week whereas range-developed heifers gained weight (2.0 lbs/d; Perry et al., 2013). However, after 27 d of grazing there was no difference in ADG between heifers developed in a drylot and heifers developed on forage. So, when observing heifers we may not notice this short period of negative energy; however, it can impact conception rates especially the early conceptions.
A second possible reason is increased activity level. We conducted an experiment on sixty-nine drylot developed heifers allotted to one of two treatments: 1) heifers remained in the drylot, or 2) heifers were moved to graze spring forage for 42 days prior to breeding. Daily activity was measured by pedometers (steps per day). Heifers that were grazing spring forage took more steps per day compared to heifers in the drylot. However, following being moved to spring pasture, heifers that remained in the drylot increased activity compared to those with previous experience grazing spring forage. This is significant because energy requirements increase with activity.
The question becomes what management strategies can help improve conception rates and promote heifers conceiving earlier in the breeding season. First if your heifer system is working, there is no reason to change.
- Heifers in proper body condition score. Heifers should be in a body condition score of 5 or 6 and range between 55 to 65% of their mature weight. Conception rates are impacted by heifers that are over or under-conditioned.
- Reduced changes in diet immediately following breeding. Heifers can be kept in the drylot and fed a similar diet or heifers can be adapted to pasture prior to the breeding season. The specific number of days that heifers should be on pasture prior to the breeding season is unknown. However, heifers should be on a positive plane of nutrition at the start of the breeding season.
- Estrous synchronization will group heifers to express estrus within a similar window of time as well as allow some heifers to express estrus earlier. Estrous synchronization can be completed with artificial insemination or natural service. More detail on specific estrous synchronization program can be found on the Applied Reproductive Strategies in Beef Cattle.
Source: Julie Walker, Professor & SDSU Extension Beef Specialist, iGrow