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Management

Reproductive strategies conference looks at considerations for heifers

Written by Melissa Burke
Reproduction is the foundation upon which all other factors concerning living things are built.
    The cattle industry is no different, as evidenced by the number of people in attendance at the Applied Reproductive Strategies in Beef Cattle conference held Dec. 3-4 in Sioux Falls, S.D. Three hundred and fifty commercial cattlemen, seedstock producers, veterinarians, and others were present at the convention, along with an additional 30 to 40 listening to each presentation live via the internet.
    The event has been held yearly between rotating states as far east as Kentucky and as far west as Idaho. With these numbers, this one proved to be the second largest so far.
    Topics covered during the event included heifer maintenance, control of estrus, timing of A.I., managing bull development, DNA testing, handling of frozen semen, nutrition, cattle temperament, vaccination, embryo transfer and sexed semen.
Heifer effects
    One of the first speakers was Eric Mousel of the Department of Agricultural Sciences at Northwest Missouri State University. His presentation was “Effect of Heifer Calving Date on Longevity and Lifetime Productivity.”
    Mousel began by stating that fertility is a key component of longevity in the cowherd. Early calving increases both longevity and productivity. Females with longer reproductive lives wean more calves and thus have the potential for a higher lifetime weaning weight average.
    He cited a survey that indicated that 33 percent of cows are culled because they don’t become pregnant; it also reported that 15.6 percent of all culled cows leave the herd before age five, and still another 31.8 percent leave between ages five and nine.
    It takes five calves to pay for the development costs and annual maintenance of a replacement heifer. It makes sense to manage the herd to reduce the number of cows culled at a young age.
    One such management practice is to ensure that heifers conceive in their first breeding season. If they breed early, that is even more desirable as they will calve early. This helps ensure that they will have time to recover for rebreeding.
    “Get early calvers in the herd and keep them in the herd,” emphasized Mousel. “Increased profitability will result.”
Physiology
    “Physiological Factors that Affect Pregnancy Rate to Artificial Insemination” was covered by Michael Smith, professor of the Division of Animal Sciences at the University of Missouri. He explained that heifers should meet several criteria before beginning a successful estrus synchronization and A.I. breeding program.
    First, the determination should be made as to what the pregnancy rate has been in heifers over the past few years. Also, he encouraged producers to consider if growth promoting implants have been used. Previous studies show that implanting heifer calves within 30 days of birth impairs uterine function.
    Third, producers should ask if the target weight, or 65 percent of the heifer’s mature body weight, been attained, and fourth, is their reproductive tract score (RTS) greater than or equal to four?
    The RTS is a subjective measurement of the sexual maturity of a heifer, as performed by a veterinarian four to six weeks prior to the breeding season. Each heifer is assigned a score from one to five, with one being prepubertal and four or five referring to a pubertal or cycling heifer.
     Postpartum mature cows should have the ability to calve unassisted, be in good body condition, with body condition score at calving greater than or equal to five, be disease free and also be allowed an adequate period of recovery between calving and rebreeding.
    Once females have met the appropriate criteria, A.I. can be performed using either an estrus-based program where animals are visually monitored for estrus and subsequently inseminated, or by fixed-time insemination, in which precise synchronization culminates in a fertile ovulation at a predetermined time.
Hands on learning
    At the conference, attendees were able to rotate through several hands-on workstations. These included ultrasound of a pregnant uterus, semen handling, an A.I. simulation box, an embryo development display, synchronization injections, a carcass quality display and taste testing of different quality grades of beef.
    There was also an exhibit of six Angus heifers that had been DNA tested for marbling and rate of gain, with printouts of their individual scores available.
The conference was hosted by the Beef Reproduction Task Force, the Beef Reproduction Leadership Team and South Dakota State University in cooperation with the University of Missouri Conference Office.
    Melissa Burke writes for the Wyoming Livestock Roundup. Send comments on this article to This email address is being protected from spambots. You need JavaScript enabled to view it..

Temperament implications
    Reinaldo Cooke, assistant professor and beef cattle specialist at Oregon State University, discussed “Effects of Temperament and Handling on Fertility.”
    Cooke began by asking the audience, “What is temperament?”
    Temperament is a behavioral response of cattle when exposed to human handling. An inability to cope with this type of situation affects their well being, causing a stress response in the animal. This manifests itself as excitable and/or aggressive behavior.
    One of the main hormones produced during a stress response is cortisol. Elevated cortisol levels negatively influence reproduction, either by decreasing nutritional status or by altering the physiological mechanism required for ovulation and conception.
    Cattle temperament can be evaluated by many methods. One example is by chute exit velocity, in which the speed of an animal leaving a chute is actually measured in feet per second, using a predetermined distance. Another method is the chute score, where cattle are individually restrained in a chute and given a score from one to five based on their behavior. Using this procedure, one equals calm with no movement, and five equals violent and continuous struggling. Producers can utilize both techniques and average both scores to obtain an overall temperament score.
    “One means to improving temperament is to acclimate cattle to human handling,” concluded Cooke.
    This is best accomplished early in their lives in order to not only improve temperament but also to hasten reproductive development.