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.
“Developing or purchasing replacement heifers is a huge investment and potential financial returns depend on future calf production,” explained Julie Walker, professor and South Dakota State University (SDSU) Extension beef specialist.
Walker points to research which indicates it takes net revenue from approximately six calves to cover the development and production cost of each replacement heifer.
Regarding calving timing, research conducted at USDA-Meat Animal Research Center (USDA MARC) and with South Dakota herds showed 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 South Dakota study looked at 2,195 heifers who calved in the first 21-day period. These heifers had increased longevity (5.1 years compared to 3.9 years).
The USDA MARC longevity data resulted in 8.2 years for heifers calving in the first calving period; 7.6 years for those calving in the second calving period and 7.2 years for heifers that calved in the last portion of the calving season.
In addition, the study reported improved weaning weights through the sixth calf born for the heifers that calved in the first calving period.
Nutritional development plays a big role in this too. Heifers developed in a drylot and turned out to grass immediately following breeding have fewer pregnancies in the first 21 days, for example.
“A possible reason is a negative plane of nutrition due to relearning grazing skills,” Walker said.
Walker points to research conducted at the Antelope Research Station, which reported that when heifers were moved from drylot to range, they lost weight (3.5 pounds per day) during the first week; whereas, range-developed heifers gained weight (2 pounds per day).
However, after 27 days of grazing, there was no difference in average daily gain 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,” Walker said.
A second possible reason in decreased pregnancy rates may be increased activity level.
Walker discusses an experiment conducted by SDSU researchers on 69 drylot-developed heifers allotted to one of two treatments: Heifers remained in the drylot or heifers that were moved to graze spring forage for 42 days prior to breeding.
Daily activity was measured by pedometers tracking 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,” Walker said.
Other considerations
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,” Walker said.
However, if a livestock producer wants to see an improvement in early-season heifer conception rates, there are a few management strategies to review:
- Body condition score—Heifers should be in a body condition score of 5 or 6 and range between 55 to 65 percent of their mature weight. Conception rates are impacted by heifers that are over- or under-conditioned.
- Reduce 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—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. — SDSU Extension
