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As annual temperatures continue to increase, winter and spring precipitation in the Midwest U.S. are also expected to increase 20 – 30% by the end of the century (Hayhoe et al., 2010). As a result, producers in this area of the country are dealing with muddy conditions in pastures and lots, making it especially difficult to manage their gestating heifers and cows in these conditions. While it is currently accepted that mud and precipitation increase cattle’s net energy requirements, it is uncertain by how much in gestating females and the long-term impacts on fetal and postnatal growth of the offspring. This dissertation aimed to estimate the energetic cost of mud to the mature beef cow and the pregnant beef heifer, and to determine the effects of dam energy restriction during gestation on the subsequent growth of their calves. In the first experimental chapter, presented in Chapter Two, I aimed to estimate the net energy requirement for mature cows housed in muddy environmental conditions during late gestation. I hypothesized that the NASEM (2016) net energy requirements for maintenance and gestation would not be sufficient to maintain cow body weight and body condition during late gestation when cows were housed in muddy conditions. I further hypothesized that calves born from cows housed in mud during late gestation would have a lesser birth weight compared with calves born from cows that were housed in bedding but exposed to the same weather patterns. This study demonstrated that though cows were pair fed and consumed the same amount of dry matter throughout the treatment period, cows housed in muddy environmental conditions decreased their body weight, conceptus free live weight, and body condition scores. We estimated that the energetic cost of mud to the mature beef cow was approximately 3.9 Mcal/day, which is greater than the 1.1 Mcal/day when calculated using the NASEM (2016). Despite differences in cow body weight at the end of the treatment period, calf birth weight was not different between the two treatments. The second study, presented in Chapter Three, aimed to investigate the developmental programming effects after birth and into the growing phase with beef steers born from cows that were housed in a muddy environment during late gestation compared with steers born from cows that were housed in wood chip bedding during late gestation. Though there was a significant difference in dam body weight throughout late gestation, there did not seem to be an effect on calf birth weight, growth up to weaning, weaning weight, or growth during the growing phase in the feedlot. Additionally, we did not observe any effects of dam treatment on measures of efficiency, dry matter intake, or metabolic parameters during the growing phase. These results indicate that mature cows in sufficient body condition during late gestation are able to mobilize their own body stores in response to being energy restricted in a muddy environment to provide for adequate fetal growth and development. The third study, presented in Chapter Four, aimed to validate the use of a chute-side hand-held glucometer (Precision Xtra; Abbott Diabetes Care Inc., Mississauga, ON, Canada) during a glucose tolerance test compared with the traditional colorimetric assay laboratory method (Stanbio Glucose LiquiColor; Stanbio Laboratory, Boerne, TX, USA). The validation of a hand-held glucometer for glucose tolerance tests would make performing these tests much easier and cost-effective for research purposes. I hypothesized that the two methods would agree with each other when quantifying plasma glucose concentrations during a glucose tolerance test. The glucose tolerance test data comparing the glucometer and laboratory method provided acceptable agreement in the Bland-Altman plots and moderate agreement according to the Lin’s concordance correlation coefficient. Therefore, we concluded that the hand-held glucometer is acceptable to use for rapid, chute-side testing of blood glucose concentration in beef cattle.The next study, presented in Chapter Five, aimed to evaluate the effects of energy restriction and energy restriction combined with muddy environmental conditions on the body weight and net energy requirements of pregnant heifers. I hypothesized that the increase in net energy requirements because of the muddy conditions would be greater in pregnant heifers compared with the mature cows, as they were still growing to achieve the recommended 80% of mature wight by their first calving. Therefore, I hypothesized that energy restricted heifers housed in muddy conditions during late gestation would have increased net energy requirements compared with heifers that were energy restricted but housed in wood chip bedding. We further hypothesized that energy restricted heifers housed in muddy conditions would mobilize body tissues, decrease body weight and body condition, and produce calves with a decreased birth weight compared with heifers that were housed in wood chip bedding but exposed to the same weather patterns. Results of this study indicated that the energetic cost of mud to the pregnant heifer is 4.3 Mcal/day. This is numerically greater than the 3.9 Mcal/day estimate that we reported for mature cows. However, while heifers housed in mud during late gestation decreased their body weight, conceptus free live weight, and body condition scores, we did not observe an accompanying decrease in calf birth weight. The last experimental chapter of this dissertation, presented in Chapter Six, aimed to model conceptus free live weight and body condition scores of mature cows over time if the additional 3.9 Mcal/day of net energy estimated in Chapter Two of this dissertation is not provided. I further aimed to evaluate various supplementation costs if producers were to supplement the additional 3.9 Mcal of net energy per day. I found that if a mature cow was not supplemented the additional 3.9 Mcal/day during late gestation, she would decrease her body condition score approximately 1 score each year, having great impacts on herd reproduction and productivity. I then evaluated several supplementation options that are available to producers in the Midwest U.S. and determined that corn gluten feed was the cheapest supplement option at $0.24 per head per day, whereas alfalfa meal was the most expensive option at $1.03 per head per day. Overall, the present work demonstrates that mud greatly increases net energy requirements during late gestation in both mature cows and pregnant heifers. We estimate that this energetic cost is 3.9 Mcal/day for the mature cow and 4.3 Mcal/day for the pregnant heifer, which are both greater estimates than what is calculated using the NASEM (2016) equations. It is noteworthy; however, that though cows and heifers were energy restricted when housed in mud during late gestation, they seemed to be able to mobilize their own body stores to provide for adequate fetal growth and development.

Weaning is considered the most stressful period in a beef calf's life, as well as the most difficult for a producer to manage. The most common weaning strategy in the American beef industry is abrupt removal of calves from their dams. This abrupt separation results in decreased calf growth and efficiency, and often morbidity manifested as bovine respiratory disease. Ultimately, this results in compromised calf welfare and increased production costs for beef producers. To evaluate alternative weaning strategies, both a pharmacological and a behavioral method to reduce stress were investigated. In the first experiment, 80 heifer calves were randomly allocated to one of two treatments: Social Facilitator (SF): calves placed on pasture at weaning with a social facilitator or Control (CON): calves placed on pasture at weaning without a social facilitator. With four replications total, the social facilitator in each replication was a confirmed bred heifer. All calves were tracked using a Garmin® Astro 430/T5 GPS/GLONASS Dog Tracking System. Body weight, chute score, and exit velocity were recorded for two weeks post-weaning, and blood samples were taken to quantify nonesterified fatty acid and β-hydroxybutyrate concentrations. Calf behavior was also recorded using instantaneous scan sampling for two weeks post-weaning. Calves placed with a social facilitator at weaning walked fewer kilometers and devoted less time towalking on day 0. Body weight, average daily gain, chute score, exit velocity, and βhydroxybutyrate concentrations were not affected by the weaning treatment. Nonesterified fatty acid concentrations were, however, greater in the SF treatment group on day 7 and 14 post-weaning. The results from this experiment indicate that the addition of a social facilitator at weaning does decrease the distance and amount of time calves spend walking. Therefore, this weaning method may be beneficial to behavioral responses at weaning and calf production. The second experiment evaluated the use of intranasal oxytocin, at weaning. Twenty heifer calves were randomly allocated to one of two treatment groups: Intranasal Oxytocin (OXT) or Intranasal Saline (SAL) administered at weaning. Once calves received their intranasal treatment on the day of weaning, they were all housed together on pasture for the duration of the experiment. All calves were again fitted with their own Garmin® Astro 430/T5 GPS/GLONASS Dog Tracking System. Body weight, chute score, exit velocity, and behavior was also recorded for two weeks post-weaning. Blood samples were taken and used to quantify non-esterified fatty acid, β-hydroxybutyrate, and cortisol concentrations. There were no differences among the treatment groups in regard to GPS data, body weight, average daily gain, chute score, exit velocity, βhydroxybutyrate, or cortisol concentrations, however, calves in the SAL treatment group had greater non-esterified fatty acid concentrations on day 1 post-weaning. Therefore, oxytocin may have had a short-term effect on plasma metabolites related to energy balance.