Beef Cattle Reproduction Research at Fort Keogh:
R.A. Bellows (Retired ARS Scientist)
"We see further and our vision is clearer only because we stand upon the accomplishments of our predecessors"
The formal beginning of reproduction research at this location was in April 1960. A cooperative study was approved involving the U.S. Range Livestock Experiment Station, the Montana Agricultural Experiment Station, and the American Breeders Service, Chicago, IL. The objective was to study problems related to artificial breeding of beef cattle under range conditions. But since the establishing of the research program at the Fort Keogh Laboratory in 1924, various reproduction studies and observations have been completed.
Early studies involved horses, mules, swine, sheep, and turkeys in addition to beef cattle. These early works were primarily breeding and nutrition studies, but reproduction information such as pregnancy rates, numbers of offspring produced, and birth weights were collected on all the species, plus fertility and hatchability data on turkey eggs. The beef cattle, horse, mule, swine, and sheep studies were initiated in 1925 with turkey research being added in 1929.
A cooperative project was initiated with the University of Missouri in 1937 to study estrus and ovulation in the mare. This work was expanded in 1938 to include methods of equine semen collection and artificial insemination. This work was not only pioneering equine research but also set the stage for scientific reproduction studies in all species of farm animals at many locations. These classical studies were conducted and published by F.N. Andrews and F.F. McKenzie.
During the period from 1935 through 1939, studies were conducted on infectious abortion (brucellosis) in cattle and equine encephalomyelitis in horses. The Laboratory was the first location to investigate methods to control brucellosis applicable to cattle under range and semi-range conditions. This work was under the direction of veterinarians from both Montana State University and the USDA. Recommendations were published in 1940 by H.H. Marsh and H. Welch. The encephalomyelitis study was the first to suggest a difference in genetic susceptibility in some breeds of horses and was published by W.V. Lambert and coworkers in 1939.
Studies on bloat were conducted in 1940-41. Results indicated that the incidence of bloat was markedly reduced when 50% of the barley in the ration was replaced by an equal amount of molasses dried beet pulp. The studies, which were published in 1943 by B. Knapp, Jr. and his coworkers, also identified that progeny of certain bulls had a greater incidence of bloat, and this could be identified by progeny testing.
The first formal paper on fertility of cattle from the Research Laboratory herds was published in 1944 by A.L. Baker and J.R. Quesenberry. Some of the recommendations made from this work are still applicable today: 1) individually identify cattle so effective culling can be made; 2) cull cows that fail to produce calves; and 3) test bulls for semen quality before the breeding season. This work was followed by papers on vaginal and uterine prolapse (1956) and on causes of stillbirths (1959). The latter two papers were authored by R.R. Woodward and coworkers.
F.J. Rice, a geneticist, was the first staff scientist to obtain project approval to conduct specific reproduction studies with cattle at this Laboratory. The project was initiated in 1960 with objectives to determine: 1) time of occurrence of the first estrus after parturition; 2) various methods of heat detection; and 3) calving percentages in herds bred artificially or by natural service.
The formal program in reproductive physiology started in 1962 under R.A. Bellows. Work was initiated to include studies on essentially all phases of reproduction in the female plus puberty studies in the male. Staff expansion occurred in 1967 with the addition of R.E. Short, whose research emphasis was in postpartum physiology. R.D. Randel and R.B. Staigmiller were added to the staff in 1971 and 1974, respectively. In 1970, construction of a new office-laboratory complex was completed allowing expansion of the research program into laboratory analyses for hormones controlling reproduction. This laboratory expansion was under the direction of Drs. Randel and Staigmiller.
Reproduction is the largest factor affecting efficiency of production in range beef cattle. The objective of reproduction research at this Laboratory has been to increase the efficiency of reproductive processes at all phases of the production cycle. The largest single reason that cows do not wean calves is because they fail to become pregnant during the breeding season. The second largest loss is due to calf deaths at or shortly after birth. These areas have received major emphasis in reproduction studies since 1962 involving both basic and applied approaches.
Increasing Reproductive Efficiency
Puberty. Replacement heifers make up approximately one in five females in the breeding herds of most ranches. Production of suitable replacements is an expensive process, and developing methods to reduce this cost and yet assure a high pregnancy rate are the objectives of the puberty research at this Laboratory. This work has shown that adequate nutrition from weaning to one year of age can increase conception rates up to 27%. By separating heifers into heavy or light groups based on their weaning weight and feeding to meet their nutrient needs, pregnancy rate was increased 19% in the first breeding season with no increase in total feed costs. Adding monensin to the ration during the first wintering period following weaning hastened puberty, and feeding heifers for maximum skeletal growth resulted in larger pelvic openings and a reduction in calving problems. Use of zeranol (Ralgro?) implants increased rates of gain in both heifers and bulls but reduced pregnancy rates in heifers and testicle size and semen production in bulls. This compound must be used with caution in animals that are potential breeding animals.
Up to 22% of all replacement heifers exhibit a nonpuberal estrus at some time prior to reaching puberty. This estrus is not fertile since the heifer does not ovulate. The condition is not abnormal since the subsequent pregnancy rates following its occurrence are the same as in heifers in which it was not observed.
Recent work at this Laboratory has shown that heifers bred at their third postpuberal estrus had a 21% higher conception rate than did heifers that were bred at their puberal estrus. Embryo transfer has been used to determine the mechanisms controlling this effect and has revealed the pregnancy maintenance capabilities of the uterus in the puberal heifer are inferior to those of the older animal. This work clearly shows that the replacement heifer should be cycling prior to the beginning of the breeding season if we are to obtain maximum conception rates.
Basic research studies have been conducted at this Laboratory to determine hormone changes prior to and at puberty. Puberty was successfully induced by mimicking the changes through hormone administration. Detailed chemical analyses of heifers slaughtered at puberty revealed that puberty did not occur at a constant body composition. The roles of melatonin and thymosin in attainment of puberty are also being studied. Research in these areas will result in a more in-depth understanding of the basic mechanisms controlling puberty and will play a key role in developing management systems to assure early conception.
Research on puberty in bulls has also been conducted at this Laboratory. Age at attainment of production of 100 million sperm and age when the bull was capable of successful mating were determined in straightbred and crossbred animals. Angus bulls were the youngest at puberty, and crossbred bulls reached puberty and attained successful mating ability at younger ages than did straightbreds.
Calving difficulty. Calf losses at birth result in a major reduction in the net calf crop. Data from this Laboratory show that 60% of these losses are due to dystocia (defined as delayed and difficult birth) and at least 50% of these calf deaths could be prevented by giving timely obstetrical assistance. Laboratory studies have shown dams that experience rapid completion of calving (labor) had pregnancy rates 13% higher than did dams in which labor was prolonged. Additionally, calves that experienced rapid birth gained 7 to 12% faster from birth to weaning than calves experiencing prolonged labor. Research from this Laboratory was the first to conclusively establish that calf birth weight is the most important factor affecting dystocia. Calf birth weight is the result of fetal growth while in the uterus and is affected by the genetic growth potential and the maternal uterine environment. The fetal growth potential can be modified by crude protein or energy content of the gestation diet which alters the blood metabolite levels of the dam, but the effect on dystocia is neither predictable nor large. Exercise during the last trimester of gestation did not affect incidence or severity of dystocia but markedly increased feed requirements of the dam. Exercise resulted in a 14.8% increase in pregnancy rate in the subsequent breeding season. Laboratory scientists were the first to demonstrate the effects of fetal genotype x maternal environment interaction on fetus weight. Some maternal environments seem to complement fetal growth while others suppress it.
Research from this Laboratory has found that precalving hormone changes in heifers that experience dystocia differ from those that calve without difficulty. This adds a new dimension to dystocia causes and indicates that high birth weights and hormone abnormalities acting separately or together can affect the incidence and severity of dystocia. Testosterone (the male sex hormone) concentrations at 231 days of gestation in the peripheral circulation of the dam gestating a male fetus are higher than in dams gestating a female fetus. Treatment of the pregnant heifer with porcine relaxin had no effect on precalving changes in the birth canal of the dam or incidence or severity of dystocia. An electronic calving monitor is being developed to determine maternal and fetal stress during calving and relate this to calf survival and length of the postpartum interval to estrus and rebreeding in the dam. These studies are important since they are leading the way for developing methods to reduce the $800 million calf and cow loss that occurs each year at calving in the nation's beef herds.
Postpartum reproduction. Timely rebreeding of the cow herd is a necessary prerequisite to profitability, and this is highly dependent on the length of the interval elapsing from calving to first estrus. Suckling by the calf has a major prolonging effect on this interval. The interval can be shortened by high levels of feeding, weaning the calf, or by surgical removal of the mammary gland. Additional research from this Laboratory revealed that suckling prolonged the postpartum interval by inhibiting the pulsatile release of luteinizing hormone from the pituitary gland of the cow. The effect of weaning was mimicked by giving low-dose injections of gonadotropin releasing hormone (GnRh) every 2 hours, but the effectiveness of the GnRh injections was dependent on whether the cow was fat or thin. These findings provided new information on the mechanisms controlling the postpartum interval and emphasized the role of adequate nutrition for successful postpartum reproduction in the cow. Basic studies have attempted to further determine how such effects as feed level, suckling, and steroid-hormone feedback control the release of pituitary hormones. The nervous system may be a part of this control through production of endogenous opioid peptides(EOP). Results from this Laboratory indicate that EOP do have a limited role during the estrous cycle but little effect during the postpartum period.
Reproduction-nutrition. Cows failing to rebreed or rebreeding late in the breeding season result in a 15 to 25% reduction in the potential pounds of calf weaned per cow exposed to the bull. Research from this Laboratory has shown the major cause of this reduction to be inadequate nutrition during one or both of two critical nutritional periods. The first critical period is during the last 3 months of pregnancy, and the second is during the time from calving until adequate forage is available to meet the nutrient demands of the lactating dam. Research results from this Laboratory show that having cows attain a minimum body condition score of 5 at calving is an excellent method to assure that nutrient requirements have been met during gestation and that some body reserves are available in the dam that can be utilized during the time period from calving until adequate forage nutrients are available to meet her needs.
Artificial insemination. Laboratory research has been conducted on estrous synchronization. Results to date show a combination of a progestogen, either implanted or fed, with injected prostaglandin is the most promising. Research from this Laboratory has also shown that conception rates from artificial insemination (A.I.) can be increased over 6% in cows by manual massage of the clitoris for 3 seconds following completion of routine A.I.
Studies on synchronization of estrus and artificial insemination in swine have been conducted at this Laboratory. Estrus was successfully synchronized with a synthetic progestogen, and litter size was greater in females bred by natural service than in those bred artificially with frozen-thawed semen. Conception rates were not improved by mating the female to a vasectomized boar immediately following A.I. This work was under the direction of V.G. Pursel, USDA-ARS, Beltsville, MD.
Multiple births. Successful production of twin and triplet calves from beef cows or heifers has been accomplished at this Laboratory. This research was the first to successfully combine synchronization of estrus and gonadotropin superovulation treatments. Calf crops up to 119% were produced following a single breeding-treatment sequence compared to 70% in untreated controls. The calves were artificially reared on cold whole milk or cold milk replacer plus grain and hay. Unrelated twins have also been produced by transferring an embryo into a cow that had been bred naturally 8 days prior to the transfer. Genetic markers were used so the natural and transferred calves could be identified. In another study, an embryo was collected from a Holstein donor cow in Beltsville, Maryland, placed in the uterus of a live rabbit and shipped to this Laboratory. The embryo was flushed from the rabbit uterus on day 7 and the embryo transferred to the uterus of a recipient Brahman-cross cow resulting in the birth of a normal Holstein calf 281 days later.
Ovarian response to superovulation treatments has been studied in cows given pituitary extracts from swine, sheep, or horses or given a dimeric follicle stimulating hormone produced from bovine anterior pituitary cells through recombinant DNA technology. Results uniformly indicated variability in ovarian response was a typical characteristic regardless of gonadotropin used or treatment sequence.
Follicle-oocyte. Laboratory research on superovulation has led to basic studies of the ovarian follicle and the oocyte. This work has helped define the difference in follicular function associated with a viable oocyte (nonatretic follicle) compared to a nonviable oocyte (atretic follicle). These findings showed that visual appraisal of the nuclear configuration of the cells was not an accurate means of determining oocyte quality or maturation. Additionally, this work showed the total dependence of the oocyte on intercellular exchange with other cells to achieve developmental competence. Portions of this work involved aspiration of oocytes from ovarian follicles both in vivo and in vitro and in vitro fertilization and maturation. These studies can potentially result in an unlimited supply of embryos for transfer, storage, or genetic manipulation. As secrets of the follicle are unlocked, results can assist in determining why approximately 35% of the matings in a cattle population do not result in a viable pregnancy.
Pine needle-induced abortion. Abortions in cattle are commonly the result of disease conditions. Abortion can be induced in cattle and buffalo, but not sheep or goats, by feeding needles from Ponderosa pine. These findings, based on research from this Laboratory, show that the abortion response is dependent on stage of pregnancy when fed, amount of needles fed, and duration of feeding. Three to four pounds of dried needles fed daily for 7 days during late pregnancy resulted in essentially a 100% abortion rate. Nutritional variables such as feed level, ration protein content, or various supplements, including vitamin A or bentonite, did not affect the response. Cooperative work with scientists at Iowa State University has identified the mechanism of action to be that of the abortifacient compound reducing the blood flow to the placental caruncles by 80%, thus creating fetal stress and initiating a normal parturition sequence. Incidence of retained placenta and calf mortality are high due to the calf being premature at birth. Recent results indicate major progress is being made on identification of the abortifacient compound.
Since successful reproduction will remain a critical component of profitable and sustainable beef production, research on mechanisms controlling reproductive processes will continue at this Laboratory. Puberty research will emphasize maximizing conception rates in the young female. Additional research will be directed toward determining the reasons for the marked increase in pregnancy rate that occurs in heifers bred at their third vs first estrus. Dystocia research will determine the effects of sire, dam, and nutrition on prepartum hormone changes and how these are related to labor patterns, heart rate of the dam and fetus, and body temperature changes in the dam. Results will be related to calf survival and gains and subsequent reproductive performance of the dam. Research on pine-needle induced abortion will identify the abortifacient compound. Once the compound is identified, methods of counteracting or neutralizing its effects will be determined. Management systems based on controlling all phases of the reproduction cycle will be developed. These systems will be designed to increase production efficiency and make major contributions toward assuring sustainability of beef production from the range resource well into the 21st century.
Individuals Associated with Reproductive Research at Fort Keogh
This was published as part of the 1995 Field Day.
USDA, ARS Fort Keogh Livestock and Range Research Laboratory