The most difficult step in executing an artificial insemination (AI) program successfully is heat detection. A cow will conceive only when she is in heat, or estrus, which occurs every 18 to 24 days. Estrus is the period of time when a cow or heifer is sexually receptive and an egg is ready to be released for fertilization.

Terry Goehring of South Dakota State University wrote that heat detection is simply the observation of changes in behavior due to a cow or heifer being in standing heat. Standing heat is the period when a female will stand firmly when mounted or ridden by another animal. Detection of cows in standing heat requires close observation of the cow herd at least twice a day, preferably in early morning and at sunset. In research studies at Cornell University, 43 percent of a cow herd exhibited heat signs between midnight and 6 a.m.; 25 percent between 6 p.m. and midnight; 22 percent between 6 a.m. and noon and only 10 percent between noon and 6 p.m. These data indicate that the best times to identify animals in heat are not during working hours. Fortunately there are other ways to detect estrus.

Goehring said, “Other physical changes are created that may be associated with standing heat. If enough of these changes are noted, a confident decision can be made on whether a cow is in heat without actually seeing her stand. Certain cow behavior occurs 4 to 48 hours before the onset of standing heat and will last until an animal goes out of heat. One of these early indications is a cow excessively and nervously walking and bawling while other cattle are relatively stationary. She periodically grazes while walking or makes frequent trips to the feed bunk. Cows during this period may be more observant and give the appearance of studying her surroundings or looking for something.

“Cows riding animals in heat may be in estrus themselves,” stated Goehring. “A cow that mounts a few times, drifts off and shows no further interest probably isn’t in heat. The cow that constantly rides others and doesn’t drift away, or perhaps goes away and comes back, should be observed closely. Look for a thick clear mucus discharge and signs of being ridden. A string of mucus may be expelled from a cow in heat as she rides other cows.

“Cattle in heat naturally seek each other, forming little clusters of activity. Watch for small numbers of cattle on the move and for fenceline attraction between two groups of cattle in bordering pastures. Some cows will have a small amount of mucus that may be observed when she is lying down or standing up and stretching. When cows show the above symptoms, they should be checked closely for the next one to two days for signs of progressing estrus.”

A second group of observations indicate standing heat or less than 12 hours from coming into heat,” said Goehring. One of these latter symptoms is thick clear mucus on the tail or hip of a cow. Cattle in heat stand head to tail and circle each other butting heads in mock fighting. They also rest their chins on the backs of other cows and rub on other animals’ hips. Cows in heat form attachments to each other and may try to  prevent other cows from riding their partner. A physical characteristic is a somewhat reddened and swollen loose vulva. Normally hair on the tail-head is lying down and pointed toward the tail. A cow that has been ridden hard will sometimes have the hair rubbed off her tail-head down to the hide. Both sides of the cow must be rubbed to be a true indication of heat.”

“Two to three days after standing heat, a bloody discharge from the vulva may be observed,” continued Goehring. “The bloody discharge is normal and only means the cow was in heat, If not inseminated already, it is too late. A bloody discharge has no relationship to whether or not conception occurred.”

EPDs (Expected Progeny Differences) are commonly used by cow/calf operators to select herd sires either to buy semen for artificial insemination or bulls to breed cows naturally. Even though EPDs are an accepted herd sire purchasing tool, their definitions, correct use and significance are not always clearly understood. To be reliable, EPDs should be compared between animals of the same breed. In other words, EPDs do not provide accurate comparisons between an Angus and Hereford bull. To use EPDs successfully, a producer needs a herd breeding plan and a clear understanding of the desired characteristics of his cattle.

Scott Greiner, Virginia Tech University explained, “EPDs estimate an animal’s genetic values and are calculated with performance data from the individual, its ancestors and relatives. Breed associations collect performance data, calculate EPDs using complex statistical equations and models and publish the results in annual sire summaries.”

“Most breed associations report birth weight, weaning weight, yearling weight and milk EPDs,” wrote Stephen Hammack and Joe Paschal of Texas AgriLife Extension. “Other reported traits might include direct calving ease, gestation length and scrotal circumference.”

Birth weight is an important EPD because most calving difficulty is caused by delivery of heavy calves. Considerable interest should be placed on birth weight EPDs when selecting bulls for use on heifers.

Greiner gives an example of birth weight EPD interpretation. Assume that Bull A has a birth weight EPD of +5 and that Bull B has +1. According to this data, Bull A is expected to sire calves that average four pounds heavier at birth than calves sired by Bull B.

“Weaning and yearling weight EPDs are indicators of growth genes that will be passed from an animal to its progeny,” wrote Greiner. “Weaning weight EPDs are a prediction of calf weights for a standard weaning age of 205 days. Rapid early growth is an important selection criterion for cow-calf producers since feeder cattle are sold by the pound. Yearling weight EPDs predict calf weights at a year of age or 365 days and is the most useful growth rate indicator for feedyards. This EPD indicates how long it will take an animal to reach a good harvest weight.”

“Milk EPDs reflect milking ability of an animal’s daughters,” Greiner further stated. This difference in milking ability is expressed as additional pounds of weaned calf. Milk EPDs are important in bull selection when replacements are retained in the herd. Bull selection should be based on milk EPDs that match feed resources and operation environment. More milk is not necessarily better since heavier milking cows may require more nutritional inputs to maintain body condition and reproductive efficiency.”

“Direct calving ease is the percentage or ratio of unassisted births in relation to total births,” stated Hammack and Paschal. “This EPD depends primarily on the size of the calf. If it is available, the direct calving ease EPD should be emphasized instead of birth weight. Birth weight only indirectly estimates calving ease.”

Gestation length EPD is reported by some breed associations and is defined by Greiner as a prediction of difference in gestation length in days for a bull’s progeny. “Bulls with lower gestation length EPDs are expected to sire calves that are born earlier. Shorter gestation lengths have been associated with slight decreases in birth weights and improved calving ease.”

“Scrotal circumference EPD is expressed in centimeters and predicts differences that will be passed on to progeny,” stated Greiner. “Bulls with larger scrotal circumference EPDs are expected to sire daughters that reach puberty at an earlier age and have earlier calving dates. Scrotal circumference is also an indicator of semen quantity produced by bulls.”

Only a few of the common EPDs are discussed here. Others will be highlighted at a later date.

Which EPDs do you find helpful in your bull selection? Let us know by typing your comment into the “Share your thoughts” area below.

“Genetic percentage contributed by a bull to the calf crop depends upon the breeding plan,” explained Joe Paschal, Livestock Specialist with Texas AgriLife Extension Service. “A bull and cow each contribute 50 percent of the genetics to their calf. If the first heifer is bred back to the bull, each of them will contribute 50 percent of the genetic traits to the heifer’s offspring. However, half of the genes in the heifer’s DNA came from the bull. So 75 percent of the genetic composition of the heifer’s calf will be from the bull and only 25 percent from the dam. If the bull is bred back to the heifer’s calf, then 87.5 percent of the new calf’s heredity will be from the bull and only 12.5 percent from the dam.”

Significance of bull power increases when bulls are bred to their daughters and granddaughters. Bull selection is also important because a bull will breed 15 to 35 cows. If you make a bad choice on the bull, you usually affect the performance of more than one cow.

“The reason that I believe in bull power is that you can see a difference in the calf crop the first year you add a good bull to the herd,” said Ronald Lastovica, who owns and operates Milano Livestock Exchange at Milano, Texas with his brother, Steven. “For this to happen, however, you must purchase a bull that matches your cows.”

“Buying a bull is the most important investment a rancher can make,” added Steven Lastovica. “The right bull can make a cattleman a lot of money. Before you decide what type of bull you want, it is important to make sure you know your objectives for that animal. Is it to increase weaning weights, to raise good replacement heifers or some other goal? After you have determined your objective for the bull, select a reputable breeder from which to buy your new herd sire.”

“Make sure that the bull, you select, merits the cost,” continued Steven Lastovica. “The bull should look like a bull. He should have good muscle, good bone, an adequate frame and testicular development. Determine if the bull is structurally sound and then look at his genetics.

“We find if you put a really good bull with fertile cows that produce an adequate milk supply, you can top the market with the calf crop. The cow has to give the calf the ability to live up to its genetic potential.”

Ronald Lastovica gave an example of investment returns that can occur when a well-bred bull is matched with the right cows. He assumed that the newly purchased bull breeds 25 cows resulting in a 90 percent calf crop which is 22 calves. The bull produces calves with an additional 50 pounds weaning weight than produced by the previous herd sire for a total additional weight for the 22 calves of 1100 pounds. If the calves sell at a dollar per pound, the new bull has provided an additional $1100 income to the ranch. With this amount of return, it won’t take long for the bull to pay for himself.

“It continually becomes more difficult to make money in the cow/calf business,” said Steven Lastovica. “Most cattlemen have reduced their variable costs as much as possible without affecting income. The remaining avenue available for increasing income and profit is through improved efficiency and genetics of the cow herd. A key area on which to focus is buying the right bull. Some of our customers spend as much on their bulls as seedstock producers and it is making them money.”

Lee Manske of the Dickinson North Dakota Research Extension Center said that nutritional values for grass from early May to the end of the grazing season in October have a defined pattern. Crude protein percentage starts high at more than 17 percent in May and slowly decreases during the grazing season to less than five percent by fall.

“Peak lactation requirements are one month after calving, so it makes sense to have cows with month-old calves on a high-protein pasture in May,” reported Kris Ringwall at North Dakota State University. “Decrease in pasture protein production will coincide with the gradual decline in cow and calf protein requirements. Dates of high protein production in forage are location dependent, so every producer needs to get access to the numbers for his or her geographical area and environment.”

If you have good winter pasture, then calving to coincide with peak market values is a good option. The seasonal price index for 500 to 600 pound Texas feeder steers from 1989 through 1998 show the highest prices occurring in March, April and May. The lowest prices occurred in September through December. Ernest Davis, et al. explained that this pattern is logical because approximately 76 percent of the annual calf crop is born in the first six months of the year. There are short supplies of 500- to 600-pound calves during that period, but larger supplies are available after August when fall weaning and marketing begin.

Whether the goal is to breed cows to take advantage of peak forage protein production or seasonally high market prices, calving has to occur during a relatively short period of time to be successful. Bruce Carpenter, Extension Livestock Specialist at Fort Stockton, Texas said that when the calving season is too long, management is more difficult and many cows will not calve every year. Shorter calving seasons make the bottom line better because both herd management expenses and marketing income are controlled more easily.

“Cows are pregnant for about 285 days of a 365-day year,” Carpenter continued. “There is not much time left for reproductive tract recovery and subsequent rebreeding. If cows are to calve every 12 months, the calving season can be no longer than 80 days per year (365-285=80). Thus, a calving season of 80 days would be followed by an 80-day breeding season.”

Once a calving period has been selected, the next step is to determine what percentage of the herd is calving outside of the desired months. This can be done by recording calving dates for individual cows or by rectal palpation. Most cattle naturally breed at the time of the year when forage nutrition is best. So if this is your target, getting the herd on a controlled schedule is often just a matter of culling a few animals. The culls would be those females calving at the wrong time and those that do not calve consistently. The key is to replace culls with heifers or cows that are bred to calve slightly before, or near the start of, the desired calving period.

“If a large percentage of the herd is calving in undesirable months, there may be two options,” said Carpenter. “One option is to slowly tighten the breeding season over a period of three to four years, replacing culls with heifers or cows bred to calve before or near the start of the desired period. The second option is to split the herd into two herds (typically spring and fall calving cows) and add replacement animals to only one herd. Attrition will eventually take care of the herd that is calving at the undesired time.”

Glenn Selk, Oklahoma State University Extension cattle reproduction specialist says:

“When the heifers that failed to breed in the first breeding season were followed throughout their lifetimes, they averaged a 55% yearly calf crop. Despite the fact that reproduction isn’t a highly heritable trait, it also makes sense to remove this genetic material from the herd so as to not proliferate females that are difficult to get bred. ”

Read the complete article Preg Check and Cull Replacement Heifers Early

Looking for additional articles about culling? Check out last month’s post about the influence that open cows have on your bottom line.

A cattle software program such as CattleMax can help you keep track of palpation results, breeding records and more, which will help you more easily identify poor-producing females.

Just how much influence does an open cow have on your operation? Ted G. Dyer, UGA Extension Animal Scientist, explains the impact:

“Open cows are the greatest contributor to a low weaning percentage (# calves weaned/ # cows exposed at breeding). On the average, a cow that does not breed one time will lose 15-20 percent of her lifetime production potential. Furthermore, it will take the net return from two or three productive cows to pay for the maintenance of the open cow.”

Read the complete article “Producers Must Make Obvious Culling Decisions in the Spring”

Speaking of culling, have you checked out Nathan’s article about options for selling cull cows and bulls?

How are your culling plans going? What factors are you using to determine which cows to keep and which to sell? Post a comment – we want to hear!

Glenn Selk with Oklahoma State University says a few include average age of the herd, predicting the number of females that will become pregnant and understanding typical heifer growing patterns can all be helpful in answering this question.

Even in the very best scenarios, some heifers will be difficult or impossible to breed.  Most extension specialists and researchers write about the need to always expose at least 10% more heifers than you need even when they are grown properly and all weigh at least 65% of the expected mature weight.

Read the article “How Many Heifers to Keep”

The CattleMax software includes several graphs and reports that can help you with making these kinds of decisions – see the Reports & Graphs options in action.

How do you determine how many heifers to keep? Click on the Comments link below and share your experience!

Some producers hesitate to implement such a system because they envision the resulting calf crop being born on a single day and creating a problem if the heifers require calving assistance. Fortunately, biological variability takes care of this potential problem.

Click to read the article at the Noble Foundation

Did you know CattleMax software can help tremendously in keeping up with synchronization (through medical records herd update) and also AI bulls, semen inventory, and AI breeding?

Check it out at http://www.cattle.com/

Advantages of the blood test method:

• Simple, quick, clean sampling. The tail bleeding was very easy to do. We only had trouble with one cow, and the process was much cleaner that palpating.
• You can test earlier. You only have to wait 30 days after breeding.
• Quick results. We received the results of our test the same day the samples were delivered to the lab. Obviously, this isn’t as quick as the immediate response you get with palpation, but you can also sample cattle on your own time, instead of working with your veterinarian’s schedule (if you don’t palpate yourself).
• It seems to be highly accurate. Of course, we won’t find out for ourselves until calving season, but the results we read about seem promising. We were trying to sell a bred cow (assuming she was bred) the same week, and wanted to be accurate with the preg check to avoid an unhappy customer.

Disadvantages of the blood test method:

• Only gives the result of open or bred. The blood tests cannot reveal how far along each cow is. For our purposes, this wasn’t necessarily a big issue. Since all the cows we checked were AI bred, we had an exact breeding date anyway.
• Waiting for samples to travel through the mail. There are only a handful of facilities that can do the testing. Unless you live close to a BioPRYN affiliate that can run the test, you have to mail in your samples. It took ours two days to travel from Arizona to Kansas, even though it was sent “overnight”.

If you  are thinking about using the blood testing method to preg check your own cows, CattleMax does have the proper record fields to enter the results in your Pregnancy Check History or Pregnancy and Breeding History screen.

Have you already tried the blood test method to preg check in your herd? If so, what did you think? What are some of the advantages and disadvantages you found?