The choice of calving season may well be a rancher's most important management decision. Thus, all ranch resources should be carefully inventoried and potential outcomes explored before any changes are made.
Is it possible the targeted level of genetic inputs should differ for various calving seasons? The answers aren't clear-cut but working through the sometimes-conflicting factors can reveal opportunities to more efficiently use resources to produce beef.
Match Genetics And Environment
Table 1 depicts how production environment can dictate different levels of genetic inputs for several major traits. If the environment offers abundant feed and low environmental stress, the genetic inputs (through choice of breeds and individual sires) might be high for milk, mature size and lean meat yield. Meanwhile, the need for genetic fleshing ability might be low.
Contrast this to the opposite extreme of genetic targets for areas of sparse feed availability and high environmental stress. In this discussion, fertility and calving ease are not being considered because they must be maintained at a high level regardless of the production environment.
Although these two examples represent extremes, the point is that optimum genetic inputs do differ for various production environments. The calving season does interact with feed availability and environmental stress at key times such as calving, rebreeding and post-weaning recovery of body condition.
Calving Season And Environment
Situations where producers have mismatched their choice of calving season to the production environment abound for a variety of excuses. It may be just tradition or a producer's concentration on a single trait like actual weaning weight.
|Production Environment||Level of Genetic Input for Various Traits|
|Feed availability1||Envir. stress2||Mature milk||Fleshing ability3||Lean ability||Yield|
|Abundant Medium Sparse||Low Medium High||High Medium Low||High Medium Low||Low Medium High||High Medium Low|
|1Feed availability is the quantity of grazable forage available as a product of rainfall, soil type, growing season and plant species.|
|2Environmental stress results from sustained exposure to heat, cold, mud altitude or pests.|
|3Fleshing ability is the ability to store body fat and regulate energy requirements as seasonal changes in feed availability occur.|
|Adapted from Beef Improvement Federation Guidelines for uniform Beef Improvement Programs, 2002.|
It's evident that February-March calves will be heavier than April-May calves at a set, shared weaning date. But if the extra weight per calf comes with higher death loss, more calving labor and more harvested feed fed during lactation, then the April-May calving season could easily be a more profitable system.
Starting the calving season at or just prior to peak native forage production — both in quality and quantity — should result in: excellent calving conditions, thus less calf death loss; faster return to estrus in cows; less harvested feed fed in late gestation; and little or no supplemental feed fed during lactation.
Such a system is even more beneficial to young cows, especially wet two-year olds.
Though these comments take a Northern Great Plains perspective, location from north to south (colder to warmer) and west to east (drier to wetter) greatly dictates when peak forage production occurs and will affect the choice of calving season.
Genetic Inputs To Calving Season
High genetic milk level and large mature size in early spring-calving cows should be avoided. First, it's inefficient to feed a cow to produce milk to feed her calf. Secondly, early calving of larger cows puts them 60-90 days away from peak forage production, thus making them totally dependent on harvested feed to support lactation.
When lactation occurs on green, growing forage or high-quality cured forage, a bit higher level of genetic milk might be acceptable because it likely won't interfere with the cow's ability to breed back. Fertility and cow body condition should always be used as the “yardsticks” to measure fitness of genetic inputs to calving season and production environment.
An additional consideration for alternative calving seasons is that cows calving in hot weather will have more pressure on mammary tissue due to heat and edema. As a result, higher milking cows likely would have more udder problems. Summer- and early fall-calving herds should be prepared to cull a bit heavier on teat and udder function.
The targeted method of marketing calves can impact the choice of calving season and argues for moderating genetic milk level and mature size. Early spring calves are more likely to be finished in feedlots as calves and harvested at 13-15 months, whereas most summer- and fall-born calves may be weaned earlier, grown slower and summered on grass before being finished and harvested at 16-20 months. Unless calves are sold directly off the cow, there's little value from high genetic levels of milk or mature size.
A case can be made that genetic fleshing ability would be very important regardless of calving season. However, spring-calving cows would seem to benefit the most from a higher genetic ability to store fat since they would be lactating more days on harvested feed. Thus, their body fat would come at a higher cost than for summer or fall calving cows storing body fat from grazed forage.
Carcass Quality And Calving Seasons
Although marbling in finished steers and body condition in cows aren't perfectly correlated, the traits are related as evidenced by breed differences, i.e., British breed steers will generally marble higher and cows will have higher fleshing ability than most Continental breeds. Conversely, the Continental breeds would have a distinct advantage in muscle mass or lean yield.
The antagonism between lean yield and marbling (and perhaps fleshing ability in cows) is well documented. Given known breed differences, crossbreeding can be used to strike a balance between these traits.
Market Goals And Calving Season
If the market goal is to produce cattle for a higher marbling program, then the month those cattle are harvested is very important. The USDA Choice-Select spread for box beef price indicates that when fewer Choice cattle are in the market, the spread is large ($8-$12). Alternately, when many Choice cattle are available, the Choice-Select spread is smaller ($4).
USDA's 5-year average Choice-Select spread for box beef indicates the supply of Choice cattle is greatest from December to April and lowest in June-November. Finishing cattle in hot weather (last 60 days of feeding) may also reduce the percent Choice cattle and affect programs that target higher marbling markets. Thus, market goals can have a big impact on the choice of calving seasons.
Multiplying The Bull Battery
Having two calving seasons instead of identifying the one “best” calving season may appeal to some production systems. If cow numbers are similar, a producer could get double use of the same bull battery.
Some producers might also choose to relax heifer development by allowing heifers born in one herd to calve in the second herd at 30 months instead of the traditional 24 months, thus reducing calving difficulty.
Additionally, wet, two-year olds that failed to rebreed in one herd could be given a brief opportunity to rebreed in the second herd before culling. Depending on the marketing goal, there could be an advantage in slotting cattle for harvest that are the product of two calving seasons.
Double use of a bull battery has few drawbacks for mature bulls, but would pressure yearling bulls. Excellent nutrition and management would be required for yearlings during the “rest period” between each of the multiple breeding seasons.
Definite dates to remove bulls from the breeding pasture would need to be carefully adhered to in order to have adequate “rest periods” between multiple breeding seasons that may be as short as 45 days. Breeding soundness exams for all bulls would be critical prior to each of the multiple breeding seasons.
Jim Gosey, PhD, is a University of Nebraska-Lincoln beef cattle specialist.