Location: Livestock and Range Research Laboratory
Project Number: 3030-31000-019-000-D
Project Type: In-House Appropriated
Start Date: Oct 1, 2022
End Date: Sep 30, 2027
Objective 1. Determine the limiting nutrients for efficient growth of beef calves and reproduction in beef females grazing native forages at different stages of maturity. Sub-objective 1A: Determine effects of autumn/winter utilization (i.e., dormant) rangeland forage utilization on heifer development, and subsequent reproductive performance. Sub-objective 1B: Develop management strategies to improve rangeland cattle production and ecological stability through effective use of rangeland forage and supplementation of young cows. Sub-objective 1C: Identify better strategies for extensive rangeland livestock operations to prepare for seasonal and/or extended droughts through strategic supplementation of mature cows that optimize milk constituents and improve calf gain. Sub-objective 1D: Evaluation of livestock nutrition models for predicting weight gains/losses and body condition for livestock under supplemental and precision feeding. Objective 2. Determine the limitations of efficient embryonic development involving successful placentation and implantation to mitigate embryonic losses that decrease reproductive efficiency in cattle. Sub-objective 2A: Determine the physiological role of estradiol in endometrial function, conceptus growth, and gene expression that contribute to increased pregnancy success in cattle. Sub-objective 2B: Determine specific nutritional impacts on ovum fertility and early embryonic development in beef heifers that contribute to pregnancy success. Sub-objective 2C: Determine the effect of fertilization by suboptimal sperm on embryonic mortality in beef cattle. Objective 3. Optimize selection and assign breeding to maintain genetic variation (limit inbreeding) in Line 1 Hereford population. Sub-objective 3A: Utilize recombination rate to increase genetic variation and mitigate the accumulation of inbreeding. Sub-objective 3B: Evaluate the effects of selection on runs of homozygosity on inbreeding depression and performance of Line 1 Hereford. Objective 4. Determine G x E (genetic/genomic x environmental/management) interactions and the effect of heterozygosity on the composite trait of lifetime production efficiency in order to enable management practices that favor desired outcomes. Sub-objective 4A: Determine effects of dry lot heifer development, and subsequent reproductive performance from dams developed on different nutritional planes and evaluate the genetic variation and the existence and extent of genotype by nutritional environment interaction in heifer development. Sub-objective 4B: Determine differences in respiration gas fluxes throughout a production year from weaning to 3 years of age by cattle from dams developed on different planes of nutrition. Sub-objective 4C: Determine effects of variation among adult cows that experienced in utero nutrient restriction on embryonic survival of genetically similar embryos and their performance as calves.
Feed consumption, genetic selection and reproductive efficiency, are primary determinants of beef production efficiency. Our overarching goal is to better define these variables and develop strategies and technologies to alleviate their limitations to beef production efficiency. 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 female retention rates. Our approach is, of necessity, multi-disciplinary, involving both basic and applied aspects of genetics, nutrition, and physiology in a semi-arid grazing production system. This plan brings to fruition ongoing research and establishes investigations of genetic by environmental interactions as well as nutritional and physiological mechanisms limiting reproductive success. Four distinct cattle populations (an intercross of Charolaise (25%), Red Angus (50%) and Tarentaise (25%) herd, Line 1 Hereford herd, Precision Livestock Hereford-Angus herd, and Physiology Hereford-Angus herd) will be used to facilitate assessment of genetic, strategic nutritional and physiological factors affecting productivity. Distinct nutritional environments differing in provision of strategic supplements to cattle grazing forage will be tested to challenge the nutrition-reproduction interface to reveal roles of genetic, physiological, and management factors influencing feed utilization and animal 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 that are most fit for rangeland environments. This research will result in the establishment of evidence-based selection, development and management protocols that provide producers options for addressing industry needs and dealing with climate and environmental variability.