by: Dr. George Perry
South Dakota State, University Extension
Research has indicated it takes the net revenue from approximately six calves to cover the development and production costs of each replacement heifer. In addition, any cow that misses a single calving is not likely to recover the lost revenue of that missed calf. Therefore, longevity of a beef female is very important to the sustainability and profitability of any beef operation.
Considering the importance of longevity, an important question is as follows: Why are females culled from a beef herd? According to the 2008 NAHMS survey the greatest percentage of cows culled from the herd were for pregnancy status (33.0 percent); other reasons for culling included age or bad teeth (32.1 percent), economic reasons (14.6 percent), other reproductive problems (3.9 percent), producing poor calves (3.6 percent), temperament (3.6 percent), injury (2.9 percent), udder problems (2.7 percent), bad eyes (1.8 percent), and other problems (1.8 percent).
"Furthermore, 15.6 percent of animals culled were less than five years of age and 31.8 percent were five to nine years of age. These females that are culled from a herd prior to producing six calves increase the developmental cost of other heifers and do not contribute to the profitability and sustainability of the farm.
To achieve maximum lifetime productivity, heifers need to calve by 24 months of age, and heifers that lose a pregnancy or conceive late in the breeding season are likely to not have enough time to rebreed during a defined breeding season. In addition, heifers that calve early with their first calf have a longer post-partum interval and are more likely to breed back as two year olds and continue to calve early in the calving season. This is important to overall profitability since age of calf at weaning is the single largest factor affecting weaning weight.
In a recent collaborative study between SDSU and the USDA Meat Animal Research Center (MARC), longevity data was collected on 2,195 heifers from producers in South Dakota, and longevity and weaning weight data was collected on 16,549 heifers at the USDA-MARC. Data was limited to heifers that conceived during their first breeding season. Heifers that calved with their first calf during the first 21-day period of the calving season had increased longevity compared to heifers that calved in the second 21-day period, or later.
Average longevity for South Dakota heifers that calved in the first or later period was 5.1 and 3.9 years, respectively. Average longevity for USDA-MARC heifers that calved in the first, second, and later period was 8.2, 7.6, and 7.2 years, respectively. Calving period also influenced weaning weight of the subsequent calves born from these heifers.
In addition, calving period influenced total pounds weaned and average weaning weight, with heifers that calved during the first period having increased weaning weights, total pounds weaned, and average weaning weight compared to heifers calving later, and heifers calving during the second period had increased weaning weight, total pounds weaned, and average weaning weight compared to heifers calving later.
Therefore, heifers that calved early in the calving season with their first calf had increased longevity and pounds weaned compared to heifers that calved later in the calving season.
So, when we think about increasing longevity in our beef cattle, we need to begin with management decisions that impact our replacement heifers. If we get them developed correctly and get them to calve early in the season they will continue to be productive for several years.
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