Location: Livestock and Range Research Laboratory2020 Annual Report
Objective 1: Evaluate effects of heifer development and winter supplementation protocols that differ in level and type of harvested feed inputs on the sustainability of beef production systems, including annual reproductive success, lifetime productivity, and progeny performance. Component 1: Problem Statement 1A, 1B Objective 2: Establish postweaning heifer development protocols that provide opportunities for improved fertility and differential forage utilization. Component 1: Problem Statement 1A, 1B Objective 3: Integration of phenomics and genomics data to dissect the genetic basis of reproductive and growth traits in beef cattle. Component 1: Problem Statement 1A, 1B Component 2: Problem Statement 2A, 2B, 2D Objective 4: Study the effect of environment, management and genetic interaction on range beef cattle production. Component 1: Problem Statement 1A, 1B Component 2: Problem Statement 2B, 2D We have proposed a series of experiments that will contribute to the alleviation of rate limiting factors that compromise beef production efficiency by: 1) Collectively increasing knowledge of the phenotypic and genetic interplay between nutrition and lifetime reproductive efficiency (Objectives 1, 2, 3 and 4) thus facilitating the economic optimization of feed level and identification of germplasm that is of less risk of reproductive failure when feed level is reduced; 2) Developing strategies that will provide producers management approaches to better utilize forage and better cope with yearly environmental variation (Objective 1, 2, and 4); 3) Further identifying phenotypic and genomic factors controlling fertility in bulls and establishment and maintenance of pregnancy in females thus leading to targets for managerial interventions that increase pregnancy rate, decrease replacement rate and reduce cost associated with producing replacement females (Objective 1, 3, and 4); 4) Prioritizing weighting of phenotypic and genotypic traits influencing production at the time selection decisions occur (typically at approximately one year of age) targeting lifetime performance (Objectives 1, 2, 3, and 4) thus facilitating selection of breeding stock for efficient low-cost production. Work needed to accomplish our objectives is multi-disciplinary and contributions from more than one scientist are expected in order to bring each objective to fruition.
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 Charolaise (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 differing in provision of harvested or grazed forage will be tested to challenge the nutrition-reproduction interface to reveal roles of 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 evidence based beef female development and management protocols that provide producers options for dealing with annual environmental variations.
Objective 1, Sub-objective 1A: Progress on our project included continuation of female retention (pregnancy success) within the Red Angus/Charolais/Tarentaise-composite cow herd and offspring performance to one year of age in heifer calves. Our state budget necessitated sale of bull calves before one year of age, which limited collection of some performance measures. Objective 2, Sub-objective 2A: Forage utilization of heifers during development was recorded for heifers developed in the feedlot and estimated for heifers developed on range. Objective 2, Sub-objective 2B: Post-weaning development of these heifers did not influence herd retention but did influence grazing behavior upon introduction to spring/summer pastures. Objective 2, Sub-objective 2C: Global position satellite data revealed that heifers developed in the feedlot traveled farther and covered larger areas of the pasture during the first few days of spring grazing than heifers developed on range and provided a protein supplement. Objective 2, Sub-objective 2D: The required sale of bull calves before one year of age prevented collection of planned data but performance data collection still proceeded on heifer calves. Objective 3, Sub-objective 3A: Feed intake, fertility and longevity measures were collected from females in the composite cowherd to allow comparisons of early in life measurements on reproductive longevity. Objective 3, sub-objective 3B: Bull fertility phenotypes and semen were collected in 2018 & 2019 from yearling bulls within the Line 1 Hereford-Angus heterosis project and evaluated using standard and 4 novel flow-cytometry measures of fertility. Samples were then frozen for further evaluations post-thaw. We have not yet completed the post-thaw evaluation of these semen samples. Furthermore, a study was conducted to examine in utero and/or postnatal melatonin supplementation on production and fertility traits in yearling bulls with similar genetics (full brothers). We are still in the process of evaluating these traits. Additional studies on bull fertility were conducted in which yearling bulls were fed a high distillers grain (feed high in sulfur) or sulfate supplementation. Bulls fed diets high in distillers grain produced sperm with decreased ability for prolonged motility/lifespan than control bulls and bulls fed a diet high in sulfur. This work was presented at the American Society of Animal Science. Finally, an additional fertility measure was validated on frozen/thawed semen that will allow more insight into effects of heterosis and developmental management on bull fertility. Objective 3, Sub-objective 3C: As part of the Grand Challenge collaboration with the Meat Animal Research Center, Grazinglands Research Laboratory, and Rangeland Resources & Systems Research Laboratory, growth and carcass data were collected for calves finished in 2019 and is ongoing for calves being finished in 2020. Objective 4, Sub-objective 4A: A study was conducted to develop a method to classify inbreeding into new and old inbreeding based on a grid search. The proposed method was tested using data from the Line 1 Hereford cattle population. Genomic data consisted of 50K single nucleotide polymorphism genotypes. Effects of recent and ancient inbreeding were assessed on four growth traits (birth, weaning and yearling weights and average daily gain). Thresholds to classify inbreeding into recent and ancient classes varied across traits and sources of information. Using pedigree information, inbreeding generated in the last 10 to 11 generations was considered as recent. When genomic information was used, thresholds ranged between 4 to 7 generations, indicating the ability of runs of heterozygosity segments to better characterize the harmful impact of inbreeding in shorter periods of time. Comparing several models, the proposed method was generally better than existing approaches, particularly compared to pedigree-based methods. Recent inbreeding seemed to be more harmful across all growth traits. However, both new and old inbreeding were found to be associated with decreased yearling weight and average daily gain, supporting the hypothesis that inbreeding depression is caused by the accumulation of deleterious mutations. Selection may have played a role in limiting overall impacts of inbreeding in some traits through purging of deleterious alleles over time. Potential biases in the estimation of inbreeding effects may occur when new and old inbreeding were discriminated based on arbitrary thresholds due to the reduced ability to accurately reflect the observed inbreeding. To manage inbreeding in a population, mating designs should take the different inbreeding origins into consideration. The proposed method provided a more objective quantitative approach for the classification of inbreeding. This work was presented at the American Society of Animal Science. Objective 4, Sub-objective 4B: Pregnancy success is greater and embryonic mortality is less among cows that are induced to ovulate a large (physiologically mature) follicle compared to a small (physiologically less mature) follicle. Oocytes from differentially mature follicles at the time of induced ovulation are more similar than the ovarian granulosa cells (cumulus cells) that contribute to essential transcriptome production required for oocyte growth and maturation in preparation for pregnancy establishment and maintenance. Sorting out the differentially expressed genes from these cell types within these populations and the physiologic pathways limiting fertility is ongoing. Objective 4, Sub-objective 4C: Furthermore, cows that ovulate a larger follicle also experience greater circulating concentrations of preovulatory estradiol and early pregnancy progesterone. Preovulatory estradiol and early pregnancy progesterone concentrations are positively correlated because the same cells are involved in production of both hormones. A study that characterizes the differential roles of preovulatory estradiol concentration and subsequent progesterone concentration on pregnancy establishment and embryonic mortality was conducted by ARS researchers in Miles City, Montana, in collaboration with South Dakota State University and University of Missouri scientists. Increased preovulatory estradiol concentration was more important for pregnancy success (and embryonic survival) than circulating concentration of progesterone during early pregnancy. Elevated postovulatory progesterone only improved pregnancy success when preovulatory estradiol was low.
1. Programing offspring for longevity. Epigenetics is the process by which environmental cues alter expression of genes, which in turn alters the characteristics of an animal. ARS researchers at Miles City, Montana, evaluated the epigenetic effects of different feeding strategies imposed over three generations. This research revealed generational impacts of nutritional treatments on weight at birth through maturity, loin muscle size and intramuscular fat measured in offspring at one year of age, and pregnancy success measured at specific ages in cows. Estimates of genetic potential for growth and carcass characteristics were also shown to be influenced by feeding strategy imposed on dam and granddam (genetic by environment interaction). Furthermore, a genomic association study demonstrated effects of dam treatment (in utero nutrition) on specific results (genomic by nutritional environment interaction). Results demonstrate that small differences in winter feeding strategies can impact lifetime production characteristics of future generations, and these changes are associated with altered genetic estimates and the predictive importance of genomic markers. Thus, genetic prediction of animal merits may be erroneous when livestock producers do not consider differences in production environments.
2. Uterine factors and signals of improved fertility in cattle. Identifying and changing the limitations to pregnancy success in cattle is obligatory for improving productivity. The role that the uterus has in pregnancy maintenance was evaluated in heifers by ARS researchers at Miles City, Montana, in collaboration with colleagues at the University of Missouri. Survival and growth of the bovine conceptus (embryo and associated extraembryonic membranes) are dependent on uterine secretions. Differences in glucose, prostaglandins and lipids within the uterus of day 17 pregnant and non-pregnant, fertility-classified heifers were measured. Concentrations of glucose in the uterine luminal fluid (ULF) were increased by pregnancy, and expression of genes involved with glucose uptake and utilization were different between high-fertility (HF) and sub-fertility (SF) heifers. Specific prostaglandins (PGE2 and PGF2a) were increased in ULF of HF heifers compared to SF heifers. Similarly, differences in gene expression of enzymes regulating prostaglandin signaling existed among conceptuses and endometrium from fertility-classified heifers. Expression of several lipid metabolism genes differed between HF and SF conceptuses and several fatty acids were differentially abundant in the ULF of pregnant HF and SF heifers. These results support the ideas that uterine secretions impact conceptus survival, programs its development, and are involved in embryonic loss in SF cattle during the implantation period of pregnancy establishment. Overcoming these deficiencies may lessen the 30 to 50% embryonic mortality that occurs in beef and dairy cows.
3. Stressors early in life affect calf productivity. Beef cattle are often exposed to varying weather conditions including extreme temperatures. A study was conducted by ARS researchers at Miles City, Montana, to assess the impact of cold stress on the performance of beef cattle. Data consisting of approximately 4000 animals from a composite beef cattle breed were used. Comprehensive climate index (CCI), a measure of cold stress was classified as mild (CCI < -5), moderate (CCI < -15), and severe (CCI < -25). The results showed that cold stress resulted in a significant decrease in weaning weight for mild (27.90 kg) and moderate (17.42 kg) cold stress. On the other hand, cold stress had a limited effect on birth weight. Overall, the impact of genotype by environment interaction due to cold stress on birth weight and weaning weight was minimal which could be due to the potential adaptation of this cattle population to cold weather conditions.
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