About one-third (36.6%) of U.S. cow/calf operations have established breeding and calving “seasons.” According to USDA data, these tend to be medium- and large-sized operations since they account for 51.1% of all beef cows. Among these operations, more than half start calving in February or March.
However, only 44.2% of single-season operations complete their calving season within a 60-day period. Nearly one-third have calving seasons that last longer than 90 days.
An Opportunity with a Shorter Season?
It appears that many cow/calf operations have an opportunity to shorten their calving season and possibly increase overall profitability through increased revenue and/or decreased costs.
Several potential benefits of a shortened calving season have been identified:
- Increased calf crop uniformity and value due to less variation in age and weight at weaning,
- Improved cowherd reproductive performance due to more emphasis (and genetic selection) on reproduction via removal of less fertile females,
- Fewer late born, light weight, and dink calves,
- Reduced need and cost for calving season labor,
- More effective nutritional management of the cowherd by meeting requirements of more cows (since most cows will be at a similar stage of pregnancy),
- More effective cowherd and calf crop management, including proper timing of vaccinations, branding, health management, weaning, shipping, etc. for more animals.
A long calving season results from a long breeding season. Yet, the breeding season lasts less than 64 days on only 31.1% of all operations (Figure 1). Since these operations only have 21.1% of the beef cows, it appears that many are smaller operators.
Options for Shortening the Calving Season
The two primary methods to shorten a calving season include: 1) shorten the breeding season by removing bulls earlier, and 2) identify and remove late-bred cows. Since most western cow/calf operations lack facilities and/or labor to easily remove bulls earlier, efforts to shorten the calving season should emphasize the identification and removal of late-bred cows.
Data that illustrate the distribution of calves born during an operation’s calving season are valuable. For instance, the distribution of calves born during a 67-day calving season for a 200-head commercial cowherd is included in Figure 2.
In this cowherd (typical of many U.S. herds), over 72% of calves were born in the first 30 days of the season (Table 1). Only about 6% of the cows calved during the last 23 days of the calving season (which constituted over one-third of the entire season).
If the 12 late-calving cows in the cowherd (6% x 200 cows = 12 cows) had been removed during the previous fall, calf age at weaning would only vary by 45 days (rather than 67 days). Additionally, the average calving date among these 12 cows was 33 days later than cows that calved during the first 45 days. This equates to an average postpartum interval that is 33 days shorter than the rest of the herd – giving these females much less time to recuperate and “prepare” to re-breed.
The average beef cow should re-breed approximately 82 days after calving in order to maintain an average calving interval of 365 days (365 days/year – 283 days of gestation = 82 day post-partum interval). In the above scenario, the 12 late-calving cows have an inadequate “rest” period during their post-partum period. Compared to early-calving cows, these cows are slower to start cycling, and therefore have fewer estrus periods while exposed to bulls.
Few management options exist to help late cows re-breed except for lengthening the breeding season, which lengthens the subsequent calving season. Unfortunately, extending the breeding season for late-breeding cows will perpetuate sub-fertility.
Among western cow/calf operations, 54.6% palpate their cows for pregnancy (USDA NAHMS, 1997). Of the operations that don’t pregnancy check cows, the most common reasons identified included the requirement for labor and time (34%), cost (19%), generally difficulty (14%), and lack of facilities (11%).
Currently, there are 3 methods available to pregnancy test cows, including physical examination (rectal palpation), ultrasonography, and chemical tests.
During rectal palpation, a veterinarian looks for 4 possible signs including palpation of:
- the amniotic vesicle (beginning about 28-35 days after conception),
- the fetal membrane as early as 30 days post-conception,
- placentomes (cotyledons and caruncles) by day 75-80 of pregnancy,
- actual fetus around day 65.
Ultrasonography has become more popular in recent years through the use of a rectal probe. Evaluation for pregnancy via ultrasound can be accomplished slightly earlier than rectal palpation, but still requires about 26-28 days post-conception.
New technologies that evaluate a body fluid (e.g. milk or blood) for the presence of absence of specific compounds are starting to become available to help producers determine the pregnancy status of cattle.
Progesterone tests are based on the concentration of progesterone (produced by the corpus luteum) in blood or milk which are associated with pregnancy. The test requires blood or milk from a cow bred 21 to 24 days before, and is very accurate (nearing 100%) for diagnosing a cow as not pregnant.
Early Pregnancy Factor Tests use milk or serum to determine if the Early Pregnancy Factor compound is present as a result of a signal from a fertilized egg shortly after conception. One such test can only be done 7-20 days after insemination.
Pregnancy-Associated Protein Tests are based on the presence of proteins that serve as signals and are exchanged between the dam and embryo in order to maintain pregnancy. These tests can be done beginning around 18-30 days post-breeding.
Some of these chemical tests focus on the identification of non-pregnant cows earlier than can be done via palpation or ultrasonography, so that cows can be “re-synchronized” and inseminated earlier than would occur normally. However, for many range-based cow/calf operations, early detection of pregnancy may not be as valuable as in confined beef or dairy cattle operations.
The Bottom Line
Many cow/calf operations either don’t have established breeding and calving “seasons,” or they have seasons that extend far beyond the industry ideal of 60 days. Condensing the breeding season by identification of late-bred females would help to decrease cost by enabling more effective management of the cowherd’s nutritional needs and increase revenue by enabling the marketing of a more uniform calf crop.
Pregnancy checking via rectal palpation, ultrasound, or a newly available chemical test could identify cows bred late in the season. By removing late-bred cows, which typically constitute a small percentage (often 5-10%) of a cowherd, a calving season can be shortened by three weeks or more.