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Item The influence of dam age and heifer post-weaning voluntary feed intake on subsequent production, reproduction and lifetime productivity of Angus beef females(Montana State University - Bozeman, College of Agriculture, 2022) Wellnitz, Krista Rose; Chairperson, Graduate Committee: Megan Van Emon and Timothy DelCurto (co-chair); This is a manuscript style paper that includes co-authored chapters.Limited research has been done to evaluate the impacts of dam age or post-weaning voluntary feed intake and its impact on subsequent performance and longevity in the beef herds, specifically female offspring. Therefore, the objectives of this research were to investigate how dam age and post-weaning voluntary feed intake influences lifetime productivity of commercial Angus females. First-calf heifers and mature cows were used to conduct three studies. Results indicate that classification of replacement heifers based on intake as a heifer had little to no impact on subsequent productivity as a mature female, while dam age had a greater influence overall. Productivity as a measure of total pounds of calf weaned through 5 yrs indicated that cows from dams that were 8-yr old or older weaned more total pounds of calf than cows from 3- yr old dams. Results indicated that heifers classified as low intake heifers, had greater mature BW at breeding and greater BCS than cows that were classified as average or high intake as heifers. However, DMI expressed as g/kg of BW displayed no differences with respect to cow age. Milk production was influenced by post-weaning intake for 2 and 5-yr old cows. The dam age study, indicated that dam age will affect future outcomes of replacement heifers. Cow BW at weaning displayed significance for dam age with cows born from 5- and 8-yr old and older dams having greater BW than cows born from 2-yr old. Cow yearling weight was significant for dam age with cows from 5-, 6/7-, and 8-years and older dams having greater yearling weights than cows from 2- and 3-yr old dams. The probability of remaining in the herd at 5-yr old varied across dam age groups with cows from 2-yr old and 5-yr old dams having greater probability to remain in the herd than the other age groups. Therefore, our research suggests that selection of replacement heifers based on post-weaning voluntary feed intake at 45 d post-weaning is not a strong indicator of lifetime productivity. Instead, cow age has a greater impact on lifetime productivity than heifer post-weaning voluntary feed intake.Item Spatial and temporal dynamics of conifer expansion in southwest Montana(Montana State University - Bozeman, College of Agriculture, 2022) Haygood, Nathaniel Paul; Chairperson, Graduate Committee: Craig Carr; This is a manuscript style paper that includes co-authored chapters.Since the mid-19th century, pinyon-juniper woodlands in western North America have experienced an expansion in range and density and a corresponding degradation in the provision of ecological goods and services including forage production, watershed function, biological diversity, and habitat values. While this is well-documented in other systems, there is little information characterizing shifts in tree range and abundance within the northern extent of these juniper and pine woodlands. The purpose of this research project was twofold: 1) identify and improve understanding of Rocky Mountain juniper and limber pine age distribution and compare these data to other systems, and 2) evaluate understory dynamics along the gradient of woodland development to assess impacts to understory species composition and abundance, as tree densities and range increase. We aged 278 trees across 38 plots in southwest Montana. We recorded soil moisture throughout the growing season (May-July), aspect, elevation, soil texture, herbaceous production and diversity, and tree density and canopy cover from 2019-2021. Greater than 95% of all trees were under 100 years old and the oldest tree (juniper) was 247 years old. Across the study site, limber pine was younger than Rocky Mountain juniper and appeared to prefer different sites. Maximum and mean juniper age was higher on dry sites with high sand content and lower on moist sites with low sand content in the top 15cm of the soil profile. Understory shrub and cool-season perennial grass cover was negatively influenced by heavy tree canopy cover on southwest to southeast aspects. The results from this study indicate 1) limber pine and Rocky Mountain juniper generally occupy different sites, 2) juniper and pine stand age is lower on north facing aspects with coarse soils and higher soil moisture content in late spring and early summer. Currently, increasing conifer dominance on north facing aspects appears to minimally impact cool-season perennial grass cover and production. Comparatively, increasing conifer dominance on south facing slopes may reduce cool-season perennial grass and shrub cover and production. We recommend the inclusion of these findings, as land managers seek to sustain delivery of necessary ecological goods and services.Item Evaluation of sustained release mineral boluses as a long-term nutrient delivery method for beef cattle(Montana State University - Bozeman, College of Agriculture, 2021) Carlisle, Tanner Jay; Chairperson, Graduate Committee: Timothy DelCurto; Samuel A. Wyffels, Steve D. Stafford, Anna R. Taylor, Megan L. Van Emon and Timothy DelCurto were co-authors of the article, 'Evaluation of sustained release mineral boluses as a long-term nutrient delivery method for beef cattle' in the journal 'Animal feed science and technology' which is contained within this thesis.Two studies were conducted to evaluate the efficacy of sustained release mineral boluses as an alternative nutrient delivery method for beef cattle. For both studies 16 ruminally-cannulated cows were used in a completely randomized design. In study 1, we evaluated degradation rates of two bolus prototypes and cow age (2-yr-old versus 3-yr-old cows) over an 87-d study period. In study 2, we evaluated two bolus types (90-d degradation target versus 180-d degradation target), as well as two diet qualities contrasting low-quality high-fiber forage (> 65% NDF and < 8% CP) and high-quality low-fiber forage (< 55% NDF and > 15% CP). For both Studies intake and digestion periods were conducted to evaluate cow age (study 1) or diet quality (study 2) effects on intake and rumen/reticulum function. In study 1, models containing an asymptotic effect of day and an interaction between day and bolus type received virtually all support of candidate models for bolus degradation rate. Cow age did not affect bolus degradation rates (Beta = -0.81 + or - 1.13; P= 0.48) and degradation rates were greater for bolus prototype B compared to bolus A (Beta prototype B = -20.39 + or - 1.13; Beta prototype A = -9.64 + or - 0.81; P < 0.01). In study 2, models containing a linear effect of day and an interaction between day and diet received virtually all support of candidate models for the degradation rate of the 90-d and 180-d prototype. In addition, both bolus protoypes displayed a diet quality + or - time interaction (P < 0.01) for bolus degradation rate. Cattle treated with the 90-d bolus and fed a high-quality diet had greater degradation rates (Beta High-quality = -2.64 + or - 0.08; Beta Low-quality = -1.97 + or - 0.10; P < 0.01) than the cows that were fed a low-quality diet. In contrast, cattle treated with the 180-d bolus expressed greater degradation rates (Beta Low-quality = -0.09 + or - 0.007; Beta High-quality = -0.04 + or - 0.005; P < 0.01) with cows on the low-quality diet versus the high-quality diet. Across both studies, two of four bolus prototypes met target release rates at 90 days. However, bolus degradation characteristics varied and were influenced by diet quality.