BeefTalk: Calving distribution is a key evaluator of reproductive success
November 24, 2011
Right now, cows are calving 88.8 percent of the time within the first 42 days of the calving season. That is good, so hats off to progressive cattle managers.
Cattle reproduction is a very talked-about number. As noted for years, if not decades, success in the cow-calf business is directly related to a producer’s ability to get the cows pregnant. The standard numbers referred to are relatively easy to calculate. These numbers are common numbers printed by cattle performance programs or simply calculated by hand.
The North Dakota Beef Cattle Improvement Association publishes annual numbers that serve as benchmarks for those who utilize the Cow Herd Appraisal Performance Software (CHAPS) program through the association. These benchmarks serve as achievable targets for producers as they set their managerial objectives.
The typical values for percent of cows pregnant are 93.6 and 92.9 percent of the cows calve. This means that of all the cows exposed to the bull, a little more than 7 percent of the cows never calve. In terms of overall evaluation of the cowherd, these numbers are good comparative numbers to see how one herd ranks with another.
Most producers cull the open cows, make managerial adjustments and anticipate a better calf crop the next year. These good managerial efforts help keep some positive reproductive pressure on the herd.
Reproduction is considered by many to be a lowly-heritable trait. In other words, genetic selection has less impact than environmental effects or general management. Many feel reproduction is fairly stable in most herds, pending any detrimental health effects.
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Another method to look at reproduction is to develop a calving distribution table. Calving distribution may seem harder to calculate, but the neat feature of these numbers is that a producer doesn’t need to know the number of cows exposed. Producers simply are dealing with the number of cows calving and recorded in the calving book.
The calving distribution table allows a producer to follow how cows are calving within the calving season, as well as the percentage that are calving within 21 days, 42 days, 63 days or later within the herd. These percentages can be compared with the benchmarks for overall herd evaluation or utilized to follow how individual cows calve within the herd.
The CHAPS benchmark for the percentage of cows calving within the first 21-day period of the calving season is 63.4 percent. The calving season is said to start when the third mature cow calves or is calculated based on a known bull turnout date utilizing a 283-day average gestation length.
The percentage of cows calving within the first 42 days of the calving season is 88.8 percent and within the first 63 days of the calving season is 95.3 percent. If a producer doesn’t have the CHAPS program, the calculations still are easy to figure from the calving book. Simply count the total number of mature cows that calved and note that number on a separate sheet of paper. Then go down the calving book and highlight or circle the third mature cow that calved. Disregard the first-calving heifers. Then count down 21 days from when the third mature cow calved and draw a line there, as well as at 42 days and 63 days after the third mature cow calved.
By counting the number of cows within each segment of the calving book and dividing by the total number of mature cows in the calving book, the percentage of cows calving at 21, 42 and 63 days is calculated. The first-calf heifers are not included in these calculations because oftentimes the bull turnout or artificial insemination dates are quite different from those of the mature cows.
Cow culling is upon us as the cows are brought home and sorted for winter. The logical approach would be to take a serious look at the calf book and simply draw a line on those late-calving cows and allow another producer with cows that calve later to bring them into his or her program.
No excuses need to be made for having a concise calving season.
May you find all your ear tags.