As the bulls are being removed from the replacement heifers, this would be an ideal time to call and make arrangements with your local veterinarian to have those heifers evaluated for pregnancy in about 60 days.  In two months, experienced palpaters should have no difficulty identifying which heifers are pregnant and which heifers are not pregnant (open).  Those heifers that are determined to be "open" after this breeding season, should be strong candidates for culling.  Culling these heifers immediately after pregnancy checking serves three very useful purposes. 

1) Identifying and culling open heifers early will remove sub-fertile females from the herd.   Lifetime cow studies from Montana indicated that properly developed heifers that were exposed to fertile bulls, but DID NOT become pregnant were often sub-fertile compared to the heifers that did conceive.  In fact, when the heifers that failed to breed in the first breeding season were followed throughout their lifetimes, they averaged a 55% yearly calf crop.  Despite the fact that reproduction is not a highly heritable trait, it also makes sense to remove this genetic material from the herd so as to not proliferate females that are difficult to get bred. 

2) Culling open heifers early will reduce winter costs.  If the rancher waits until next spring to find out which heifers do not calve, the winter feed expense will still be lost and there will be no calf to help eventually help pay the bills.  This is money that can better be spent in properly feeding cows that are pregnant and will be producing a salable product the following fall. 

3) Identifying the open heifers shortly after (60 days) the breeding season is over will allow for marketing the heifers while still young enough to go to a feedlot and be fed for the choice beef market. The grading change of two years ago has a great impact on the merchandising of culled replacement heifers.   "B" maturity carcasses (those estimated to be 30 months of age or older) are no longer allowed to be graded choice.  Therefore, it is imperative to send heifers to the feedlot while they are young enough to be fed for 4 to 5 months and not be near the "B" maturity age group. Auction barn order buyers will be especially leery of heifers that may be near 18 to 20 months of age, because of the risk of "B" maturity beef that receives a considerable discount when harvested at the packing plant. 

Certainly the percentage of open heifers will vary from ranch to ranch.  Do not be concerned, if after a good heifer development program and adequate breeding season, that you find that 10% of the heifers still are not bred.  These are the very heifers that you want to identify early and remove from the herd.  It just makes good economic business sense to identify and cull non-pregnant replacement heifers as soon as possible.