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United States Department of Agriculture

Agricultural Research Service


Location: Range and Livestock Research

2013 Annual Report

1a. Objectives (from AD-416):
1: Characterize rumen microbial populations, including cellulolytic microbes, and elucidate dynamics of these populations through the use of metagenomic approaches. 2: Determine rumen microbial and host genetic effects associated with differences in measures of efficiency of heifers developed under divergent planes of nutrition or different diets. 3: Determine phenotypic and genetic relationships of early-in-life measures of feed consumption, growth and body composition, with subsequent reproduction and lifetime productivity. 4: Determine if the level of nutrition in utero and prior to puberty results in epigenetic effects on traits associated with production efficiency at later stages in life. 5: Develop and validate appropriate phenotypes for measuring fertility in cattle in order to determine interactions between variation in cow feed efficiency and reproductive performance. 6: Identify and fine map quantitative trait loci (QTL) affecting feed intake, growth and reproduction.

1b. Approach (from AD-416):
Line 1 Hereford, an intercross (CGC) of Charolais (25%), Red Angus (50%) and Tarentaise (25%), and two predominantly Hereford-Angus crossbred herds are used. Line 1 Hereford cattle are ~30% inbred, with consequently reduced fitness, and have close ties to the bovine genome sequence. Two distinct nutritional environments will be imposed on the CGC population to challenge the nutrition-reproduction axis. One Hereford-Angus cowherd provides donor and recipient females for studies using embryo transfer. The other Hereford-Angus cowherd calves in two seasons and thus has differential synchrony between nutritional value of range forage and nutrient requirements of the cows. 1: Identify new species of rumen microbes through whole genome shotgun sequencing of rumen microbial milieu. Compare rumen bacterial species diversity responses to different diets. 2: Evaluate rumen microbial diversity and host animal gene expression in samples of animals expressing extreme differences in feed efficiency. 3: Estimate genetic and phenotypic variances and covariances of longevity, stayability, number of calves produced, and cumulative production of beef cows with early-in-life measures of growth rate, feed consumption, and indicators of body composition. Determine effects of phenotypes measured early-in-life on subsequent fertility of bulls. 4: Determine effects of feed intake prior to puberty and level of supplementation during mid to late gestation on genetic (co)variance and gene expression of the treated animals and their progeny. Determine effects of nutrient intake during gestation on phenotypes of treated animals and their progeny. 5: Determine factors controlling establishment and maintenance of pregnancy in cows induced to ovulate different sized follicles. Establish relationships between previous nutrition, time post-partum, resumption of estrus, and energetic efficiency in young postpartum beef cows. 6: Identify QTL affecting growth and reproduction in an advanced intercross of Red Angus, Charolais, and Tarentaise. Identify QTL with over-dominance effects on fitness. Identify genes expressed in tissues of cattle.

3. Progress Report:
Final report (New project #5434-31000-017-00D). Progress was made on all objectives to advance basic and applied knowledge contributing to improved efficiency of production. Research assessing diversity of rumen microbial community established sample collection protocols for future investigations into metagenomics. Between 3181 to 7483 species-level Operational Taxonomic Units (OTU) were identified, the greatest number ever observed for a ruminant species. Considerable difference in microbial diversity existed between cows, which is expected to contribute to individual variation in efficiency and productivity. Level of feed input provided during postweaning development of heifers was shown to affect magnitude of association of feed intake with several output responses, illustrating importance of feed level when assessing relationships between economically critical inputs and outputs. Heifers subjected to feed restriction during postweaning exhibited greater efficiency with no reduction in pregnancy rate. In addition to potential savings occurring through improved efficiency, this strategy is estimated to reduce costs of developing each replacement female by more than $31. Results provide evidence that industry recommended rates of growth of heifer heifers during postweaning development need to be reconsidered because development at lower rates provides opportunity for improve efficiency and decreased cost. Research results provide evidence that several economically important traits are influenced by nutritional environment imposed on the mother of an animal during pregnancy. Interactions of nutritional treatments imposed in utero and during postweaning development were also observed. Results demonstrate that production characteristics and ability of an animal to cope with nutritional restrictions that may occur throughout life can be altered by levels of nutrition experienced during in utero and postweaning development. Novel phenotypes contributing to fertility in cattle have been identified, including size of the ovulatory follicle. Negative effects of ovulatory follicle size on pregnancy success were determined to be mediated by oocyte competence and positive effects through improved maternal uterine environment. Specific traits identified in this research provide targets for ongoing investigations into genetic and management factors contributing to variation in fertility.

4. Accomplishments

Last Modified: 10/20/2017
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