Cattlemen for years have noted that first calf heifers tend to
have lower pregnancy rates and breed back later in the breeding season
following their first calf. Much of this problem (not all) can be
tied to those heifers that were younger and smaller or thinner in body
condition going into their first breeding season. Heifers that were
small at the start of the breeding season often are found to be open or
non-pregnant upon palpation after the breeding season is over. However,
some of the small, light, poorly developed heifers still get bred.
At first this may see to be blessing, but research data indicates that
their potential for problems are not over. Heifers that were bred
when weighing only about 50% of their mature weight (instead of the target
of 65% of mature weight) will be poor gambles to stay in the herd in years
to come. Data from a number of years of ago with Hereford heifers
illustrates this point.
Table 1. The effects of weight at first breeding on reproductive
performance
Weight at start of first breeding season
Less than 550 lbs
550 - 600 lbs
More than 600 lbs
| Number of heifers |
40 |
166 |
45 |
| Pregnant 1st year |
56% |
77% |
90% |
| Pregnant 2nd year of heifers calving |
18% |
57% |
69% |
| Pregnant 2nd year of original heifers |
8% |
40% |
60% |
Source: Sprott and Troxel. Management of Replacement Heifers
for a High Reproductive and Calving Rate. B-1213. Texas Agricultural Extension
Service.
The data in table 1 above indicates two problems with heifers that are
too light at first breeding. Not many get pregnant as virgin heifers
and they have a MUCH lower chance of getting pregnany while nursing their
first calves. Only 56 percent of the heifers weighing less than 550
pounds were pregnant. In the subsequent breeding season, only 18
percent of those calving from this group were pregnant. Only 8 percent
of the lightweight heifers exposed the first year did not skip a calf.
Although some heifers will cycle and breed at very young ages and light
weights, they may not have the capability to produce a calf and re breed.
Certainly heifers must attain proper growth to avoid serious calving problems.
If they do get bred, have a calf, their chances of being rebred are quite
low.
Keeping or culling light weight pregnant heifers is a tough decision.
The data above would suggest that those that are very light are a poor
risk to keep around. If the light weight heifer is kept until calving
time, the producer must make every effort to allow the heifer optimum growth
without exceeding the body condition score of 6 by the time that she calves.
This should give the best opportunity to deliver a calf (probably with
assistance) and to rebreed if she kept in the herd. But remember
she is still a bad bet. Avoiding this condition while she was a young
developing heifer is the best remedy!
