Location: Range and Livestock Research2013 Annual Report
1a. Objectives (from AD-416):
1: Determine the impact of the level of harvested feed input on the sustainability of beef production systems, including annual reproductive success, lifetime productivity, and progeny performance. 2: Evaluate use of dormant, animal-harvested forages as a substitute for mechanically harvested feeds in developing replacement heifers. 3: Develop new and better genetic and physiological indicators of fertility in yearling bulls and beef cows to enhance annual and life-cycle reproductive success. 4: Assess locus-specific genetic effects attributable to heterozygosity on reproductive success and productivity in production systems making differential use of native range forages.
1b. Approach (from AD-416):
Feed consumption and replacement of cows, culled for reproductive failure, are two primary determinants of beef production efficiency. Our overarching goal is to develop strategies and technologies to alleviate these limitations. Sufficient nutrient intake resulting in adequate body energy stores are believed essential for reproduction. Thus, producers are challenged to match nutritional environment, which is subject to seasonal and annual variation, and various genotypes to obtain sustainable reproduction and retention rates. Our approach is, of necessity, long-term and multi-disciplinary, involving both basic and applied aspects of genetics, nutrition, and physiology in a semi-arid grazing production system. This proposal brings to fruition ongoing research and establishes investigations of genetic by environmental interactions and physiological mechanisms limiting reproductive success. Four distinct cattle populations (an intercross of Charolais (25%), Red Angus (50%) and Tarentaise (25%), Line 1 Hereford, purebred Angus, and Hereford-Angus herd) will be used to facilitate assessment of genetic factors affecting fitness (hybrid vigor). Distinct nutritional environments that utilize different contributions of harvested and grazed forage will be imposed to challenge the nutrition-reproduction interface to elucidate genetic, physiological, and management factors influencing feed utilization and lifetime productivity. Identification of genetic, nutritional, and physiological mechanisms that limit or contribute to beef production efficiency will facilitate early in life selection and management of replacement animals most fit for particular production environments. This research will result in the establishment of heifer development protocols that provide producers options for dealing with annual variations in availability and quality of forage.
3. Progress Report:
Phenotypic and genotypic data continue to be collected to assess the impact of the level of harvested feed input on the sustainability of beef production systems, including annual reproductive success, lifetime productivity, and progeny performance. Data have been analyzed to determine the effects that level of harvested feed and pubertal status have on pregnancy rate from the first and subsequent year of production. Heifer calves born in 2012 were subjected to experimental treatments (fenceline weaned and pasture developed vs. feedlot weaning and development). Methodology was established to measure consumption of mineral/supplement mix by individual animals in pasture setting. Natural service and AI fertility phenotypes were established for sires used over the last 10 years to provide data for genetic and physiological association studies. Heretability estimates demonstrate that fertility could be improved in bulls through selection pressure on scrotal circumference, % normal sperm and % abnormal sperm (especially, dag defect, bowed midpiece, proximal droplet, and bent principle piece). Purchase and rearing of Angus females was implemented. Initiated collection of data on feed intake and postweaning development traits.
1. Beta-hydroxybutyrate is an objective indicator of the nutritional status of cows. A major challenge for beef producers is providing sufficient nutritional inputs to cows to ensure timely rebreeding while minimizing feed expenses. Efforts by ARS researchers at Miles City, MT, to develop and validate appropriate phenotypes of reproductive capacity in cattle resulted in the identification that levels of beta-hydroxybutyrate (ketone) in the circulation are an objective indicator of the nutritional status of cows. Cows with greater levels of ketones in their blood took longer to become pregnant than cows with lower level. Research validated the use of an inexpensive hand held meter and commercially available test strips as a method for on farm or ranch measurement of beta-hydroxybutyrate, thereby providing producers with an objective method to access cow nutritional status.
2. Physiological and follicular determinants of pregnancy. Successful reproduction is the major output affecting efficiency of beef cattle production. However, much of the biology underlying establishment and maintenance of pregnancy remains to be elucidated. ARS researchers in Miles City, MT, recently completed very extensive analyses of data pertaining to factors controlling establishment and maintenance of pregnancy in beef cattle. Relationships among factors affecting fertilization and the subsequent maintenance of pregnancy were numerous. While no single variable controlled a preponderance of the variation in fertilization or maintenance of pregnancy, simultaneous consideration of several variables provided greater insight into the overall complexity and understanding of process contributing to reproductive success. The measurements that had the greatest effects on pregnancy establishment and maintenance included elevated serum estradiol concentrations (> 8.4 pg/ml) at time of breeding, elevated serum progesterone concentrations on day 7 after breeding, and ovulatory follicle diameter. Neither age of the ovulatory follicle nor serum progesterone concentrations during growth of this ovulatory follicle appear to affect pregnancy establishment to any significant effect.
3. Cost of feed is one of the greatest input expenses encountered by cattle producers. Research by ARS scientists at Miles City, MT, determined that development of heifers at rates of growth that are less than traditionally recommended reduced feed inputs, improved efficiency, and decreased cost of production without a reduction in reproductive performance. Reducing feed inputs during the heifer development period was shown to improve efficiency and decreases cost of production without reduction in reproductive performance. These findings have led to changes in current industry recommendations for heifer development that will be accompanied by decreases in cost and increased efficiency of production.
4. The microbial population in the rumen of a cow is expected to be intimately associated with production efficiency. A survey of the rumen microbial community by ARS researchers at Miles City, MT and scientist at the J. Craig Venter Institute revealed that the extent of microbial diversity in the bovine rumen is far greater than previously appreciated. Next generation sequencing technologies promise to reveal novel species, interactions, and pathways that will provide a better understanding of how the rumen microbial community structure and function affects ruminant feed efficiency, biofuel production, and environmental impact. Researchers identified two new rumen archaeal species and demonstrated that bacterial community profiles differ between liquid and solid (fiber) rumen fractions while the archaeal and fungal communities appear indifferent between these fractions. The research established the need to further explore the rumen ecosystem using metagenomics and functional analysis.
Cronin, M.A., MacNeil, M.D., Vu, N., Leesburg, V.L., Blackburn, H.D., Derr, J. 2013. Genetic variation in bison (bison bison) subspecies and cattle (Bos taurus) breeds and subspecies. Journal of Heredity. 104(4):500-509.