Location: Range and Livestock Research2012 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:
Results from research assessing diversity of rumen microbial community have been submitted for publication. Analyses of changes in rumen microbial community associated with dietary changes in diet are proceeding. Gene expression data in tissues from animals differing in measures of efficiency are currently being analyzed. Collection of phenotypic data from CGC and Line 1 Hereford populations has occurred as planned. Analysis of data collected from CGC cattle to date indicates interactions among year, dam treatment and progeny treatment resulting in the decision to continue collection of phenotypes measured later in life (more time needed to obtain data of progeny produced in the last few years). DNA samples from >2000 animals from the CGC composite herd of cattle have been genotyped. Genome wide association studies (GWAS) identified genomic regions that account for variation in birth weight, preweaning gain, scrotal circumference and several semen characteristics. Preparation of report delayed by the retirement of Dr. MacNeil. Efforts to develop and validate appropriate phenotypes of reproductive capacity in cattle have identified beta-hydroxybutyrate (BHB) as an objective indicator of the nutritional status of cows. Cows with greater levels of BHB in their blood took longer to become pregnant than cows with lower levels of BHB. The use of an inexpensive hand held meter and commercially available test strips provides opportunity for on farm or ranch measurement of BHB.
1. Management opportunities for range livestock producers during drought. Dealing with drought is a major challenge for livestock producers. To provide producers with options to help deal with drought situations, ARS researchers at Miles City, MT evaluated the impact of early weaning calves at 80 days of age on all segments of range livestock production. Early weaning was shown to improve body weight and condition of cows through the subsequent winter, (especially in young cows, which are generally more adversely affected by drought), had no effect on heifers calves that were retained for replacements, and could be managed to improve performance of steers calves entering the food chain. Early weaning of calves provides producers with a method to conserve available forages as well as minimize the negative impact that herd reduction can have on the genetic composition of the livestock producers may spend years developing.
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.
3. Supplementing methionine to heifers in late gestation improves amino acid utilization. Heifers raised in rangeland environments depend not only on the quality and quantity of the available forage but also the quality of any supplemental feed they may consume. When essential nutrient(s) are limited, efficiency of nutrient use can be compromised. Recent work by ARS researchers in Miles City, MT, found that providing additional methionine during winter, when forage quality was low, resulted in improved forage digestion and utilization of other plasma amino acids. Identification and supplementation of limiting nutrients improves the nutrient use by the cows and reduces the excretion of usable nutrients back to the environment.
4. Effectiveness of radio frequency identification (RFID) ear tags as a method for long-term identification and tracking of individual animals. Long-term identification of individual animals is a prerequisite for any national animal identification program developed to facilitate monitoring of animal movement and provide trace back in case of a disease outbreak. ARS researchers in Miles City, MT, recently evaluated retention of RFID ear tags in adult cattle over a five year period. Loss of RFID tags increased with time after application, and may exceed 5% after 3 years and up to 20% after 5 years, depending on tag type and location of placement in the ear. Retention of RFID tags over prolonged periods of time may not be sufficient to function as a sole method of individual animal identification.Endecott, R.L., Cox, S.H., Rubio, C.M., Loest, C.A., Hawkins, D.E., Petersen, M.K. 2012. Effects of supplements with increasing glucogenic precursor content on reproduction and nutrient partitioning in young postpartum range cows. Livestock Science 145:109–118.