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The purpose of the study was to develop a realistic method of determining the optimum replacement time of steers in a feedlot in which there are sequential feeding cycles. There are two models for steers developed and discussed in this paper. The first model optimizes the length of stay in the feedlot assuming that feedlot capacity is the limiting constraint. The second model optimizes the length of stay in the feedlot when working capital is the limiting constraint. A third model is developed to determine the optimum length of feeding time for market hogs in a feeding barn. An evaluation of each model is made. It is concluded that the cattle models have a limited use because of the high variability in performance. The hog replacement model is quite valid and can be used in a modern hog feeding enterprise. / Land and Food Systems, Faculty of / Graduate

Methane (CH₄) production from enteric fermentation in ruminant animals is a contributor to global greenhouse gas emissions. Because CH₄ has an impact on increasing global temperatures, there is a push for government regulations to reduce CH₄ from livestock animals. At 1.9% of U.S. CH₄ emissions beef cattle are a large contributor to agricultural CH₄ emissions or (EPA, 2020). Enteric CH₄ emissions are also a loss of energy for the animal, accounting for 2-12% of energy loss from the ruminant animal (Johnson & Johnson, 1995). This energy loss from the diet is contingent upon forage content, where increasing forages in the diet increases CH₄ yield (g/kg of gross energy intake; van Gastelen et al., 2019). Mootral is a feed supplement that contains garlic (<i>Allium sativum</i>) and bitter orange (<i>Citrus aurantium</i>) extracts. The organosulfur compounds in garlic the flavonoids found in bitter orange extracts are known to decrease CH₄ production, (Busquet et al., 2005a; Balcells et al., 2012; Seradj et al., 2014). However, it is unclear how the forage content and Mootral inclusion will interact to effect CH₄production and animal performance. Because feedlot cattle are fed a range of forage:concentrate ratios while in the feedlot, it is important to know how effective mitigation strategies are in different forage:concentrate diets. Therefore, the objective of the current study was to quantify CH₄ production and determine growth, intake, and carcass characteristics of feedlot steers fed Mootral in diets with a low, medium, and high forage content. Knowing the effect of garlic and flavonoids on methanogenesis, we hypothesized that Mootral would decrease CH₄ emissions without impacting growth, intake, and carcass characteristics of feedlot steers. We expect that the CH₄ mitigating ability of Mootral will be greatest in the diet with the most forage. For the experiment, 144 Angus x Simmental steers were allotted by body weight (BW; 363 kg, breed composition, and farm origin to a 3 x 2 factorial arrangement of 6 treatments (4 pens per treatment) to determine the effect of Mootral (garlic + citrus extract; 0.25% of the diet DM vs. 0.0%) on methane emissions, growth and carcass characteristics of feedlot cattle. During the first 84 days, cattle were fed three different forage concentrations in the diet (15, 41.5, or 68% corn silage) with or without Mootral. From day 85 to slaughter, corn silage was included at 15% of the diet DM with or without Mootral. Methane emissions were measured on day 42-46 and day 203-207. Data were analyzed using the GLIMMIX procedure of SAS. There was an interaction (<i>P </i>= 0.03) between forage content and Mootral for DMI from d 0 to 84, where Mootral decreased DMI of steers fed 15% corn silage but did not affect DMI of steers fed 41.5 or 68% corn silage. There were no effects (<i>P </i>≥ 0.22) of forage content or Mootral on BW or average daily gain at any time, or on DMI from d 84 to slaughter and overall. Intake from d 0-84 was lower and gain:feed from d 0-84 and overall was greater (<i>P </i>= 0.04) for steers fed 68% compared to 15 or 41.5% corn silage. On d 42-46, steers fed 41.5 and 68% corn silage had increased (<i>P </i>≤ 0.02) methane emissions compared to steers fed 15% corn silage. Mootral did not affect methane emissions on day 42-46 (<i>P</i> ≥ 0.47), but there was a forage effect, where steers fed the 41.5 and 68% corn silage diets emitted more methane on a g/d (<i>P</i> = 0.05) and a g/kg of DMI (<i>P</i> = 0.007) basis and tended (<i>P</i> = 0.07) to produce more methane on g/kg BW basis compared to steers fed the 15% corn silage diet. Steers fed Mootral emitted less (<i>P </i>≤ 0.03) methane on a g/d, g/kg DMI, and g/kg BW basis on d 203-207 compared to steers not fed Mootral. Mootral tended to decrease (<i>P </i>≤ 0.09) fat thickness and yield grade. In conclusion, increasing forage content increased methane emissions and Mootral decreased methane production in 15% corn silage diets and improved carcass leanness.

The objective of this study was to evaluate digestibility of cubed hay as a feedstuff for ruminants. Angus (n=6), Hereford (n=3), and Charolais (n=3; total n=12; 226 ± 21.8kg) steers, stratified by breed, were randomly assigned to 3 treatment groups: 1) hay; 2) chopped; 3) cubed. There was no difference (P > 0.05) of DMI or digestibility of DM, OM, NDF, ADF, hemicellulose, and energy among treatments. Steers consuming hay digested more CP than those consuming chopped. Steers consuming cubed digested less CP than those consuming hay or chopped. More fat was digested by steers consuming hay or chopped than by those consuming cubed. Steers consuming cubed retained more nitrogen than those consuming chopped. Those consuming hay were intermediate. Nitrogen metabolized was greater for steers consuming hay than for steers consuming chopped. Those consuming cubed were intermediate. Steers consuming hay and cubed had greater metabolizable protein than those consuming chopped.

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Overfeeding of phosphorus (P) is a contributing factor to P levels in surface waters. The objective of this study was to determine the impact of increasing levels of corn gluten feed (CGF) as a supplemental source of P on fecal P excretions. Eight Hereford steers (427±79 kg) were randomly assigned to one of four dietary treatments in a 4 x 4 replicated Latin square design. Steers were fed chopped grass hay ad libitum (0.13% P) and 0, 0.5, 1.0 or 1.5 kg/d of dried CGF pellets. All steers were supplemented with 0.91 kg/d beet pulp, 0.34 kg/d rumen-inert fat supplement and 18.14 g/d trace mineral salt. Urea was added to the respective diets at levels of 95.25, 72.57, 49.90, and 31.75 g/d to ensure equal dietary protein across treatments. Steers were housed individually and fitted with total fecal collection bags. Steers were adjusted to each diet for 9-d followed by a 5-d collection period. Following the final collection of each period, a 10 ml jugular blood sample was collected and analyzed to determine serum inorganic P. Dietary total P increased (P < 0.05) as CGF level increased: 8.72, 12.59, 16.75 and 20.88 g/d. Dry matter digestibility increased linearly (P < 0.05) as dietary P increased: 50.35, 53.66, 54.25 and 55.42%. Total P excretion increased linearly (P < 0.05) with increasing CGF level: 9.66, 11.71, 14.29, 16.96 g/day. Inorganic P excretion increased linearly (P < 0.05) with increasing CGF level: 4.11, 5.93, 8.36 and 9.92 g/day. Total P excretion was highly related (P < 0.05; r2 = 0.79) to inorganic P excretion. Serum inorganic P increased linearly (P < 0.05) with increasing dietary P content: 5.61, 5.87, 6.64 and 6.80 mg/dL. Fecal P increased as CGF level increased in steers fed varying dietary levels of P from plant sources. Management of P intake can be a strategic practice to reduce P fecal excretions in beef cattle. / Master of Science

Two experiments were conducted to determine the efficacy of supplemented feedstuffs to improve the performance of cattle consuming fescue-based rations. The objective of the first experiment was to evaluate growth and reproductive characteristics of heifers consuming endophyte-infected (EI) fescue seed with or without sodium bicarbonate supplementation. Forty-eight heifers (8 mo; BW = 268 ± 24 kg) were utilized in a 2 x 2 factorial design. Treatments were either high-EI fescue seed without sodium bicarbonate (E+B-), high-EI fescue seed with sodium bicarbonate supplementation (E+B+), low-EI fescue seed without sodium bicarbonate (E-B-), or low-EI fescue seed with sodium bicarbonate supplementation (E-B+). At d 56, G:F (P= 0.084) and ADG (P = 0.071) tended to be improved for heifers fed E+B+. By d 84 bicarbonate supplementation tended to decrease ADG (P = 0.087). Bicarbonate supplementation ameliorated the negative effects of E+ at 28 d, but by d 84 negatively impacted animal performance. The objective of the second experiment was to determine the energy content of corn gluten feed (CGF) relative to corn in forage-based beef rations. Forty-two steers (13.8 ± 0.4 mo; BW = 382 ± 8 kg) were supplemented with either corn or CGF at 0.15% (L), 0.54% (M) or 0.96% (H) BW for 63 d. Steer ADG was greater for steers supplemented with CGF relative to steers supplemented with corn (P = 0.034). Energy value of CGF relative to corn was calculated by adjusting supplement TDN in the 2016 Nutrient Requirements of Beef Cattle Model. The energy values of CGF relative to corn were 106%, 107%, and 112% for L, M, and H. / Master of Science / Tall fescue is the predominant forage in the southeast United States, and has a symbiotic relationship with an endophytic fungus, providing drought and pest resistance to the plant. However, the fungal endophytes produce toxic ergot alkaloids which can result in decreased performance when cattle consume tall fescue. Performance losses, resulting from the consumption of these ergot alkaloids, are costly and economical strategies to reduce the negative impact of endophyte-infected fescue consumption on animal performance are needed. Previous research indicates that ruminal buffering capacity and nutrient uptake may be impaired in cattle consuming endophyte-infected fescue seed. Providing a dietary buffer is a low-cost strategy that my help to improve nutrient utilization in cattle, resulting in improved animal performance. Aside from reduced performance resulting from the consumption of ergot alkaloids, forage nutrient content can vary throughout the year, resulting in situations where the animals’ nutrient requirements are not met by the forage alone. Historically, corn has been the major energy supplement used, but recent data suggest that co-products of the corn sweetener and ethanol industries have greater energy compared to corn in both feedlot and forage-based beef rations. Supplementing corn gluten feed at low levels may improve performance of cattle consuming forage-based rations without driving up the cost of production. The objective of this thesis is to evaluate two strategies to mitigate the negative effects of endophyte-infected fescue consumption on animal performance. The first experiment was conducted to evaluate the efficacy of sodium bicarbonate to mitigate the negative effects of endophyte-infected fescue on replacement heifers. Heifers were fed a basal corn silage diet. Fescue seed and bicarbonate were supplemented at 1.5 kg/day and 0.25 kg/day, respectively. After a 56 d treatment period, bicarbonate supplementation tended to improve performance of heifers fed endophyte-infected seed with bicarbonate relative to those fed un-infected seed without bicarbonate supplementation. However, by d 84 of the experiment, the benefits of bicarbonate supplementation were no longer observed. More research is needed to understand why the benefits of sodium bicarbonate supplementation were not sustained over the full experimental period. The second experiment was conducted to evaluate the feeding value of corn gluten feed relative to corn when fed to steers consuming a forage-based ration. Steers had free-choice access to fescue hay, and individual hay and supplement intake were recorded daily. Steers supplemented with corn gluten feed had greater average daily gain than steers supplemented corn. This translated to a greater energy value relative to corn for all inclusion levels, exceeding model predictions. These experiments help to shed light on low-cost solutions to improve performance and profitability for fescue forage-based beef production systems.

Genetic parameters were estimated using 8086 weaning weight records of Mashona cattle from commercial herds in Zimbabwe, through Derivative-free Restricted Maximum Likelihood (DFREML) procedure fitting an individual animal model. All known additive relationships among animals were incorporated and all sires were assumed to have been bred by unknown parents. A simulation study was carried out to estimate the amount of bias in the estimated genetic parameters caused by the failure to account for the true relationships among the breeding animals. / Genetic differences between the weaning weights of Mashona cattle in commercial herds and in small holder herds were estimated using performance records of progeny from 2 reference bulls, 3 bulls from commercial herds, 14 bulls from Makoholi Research Station and 20 bulls from small holder farms. The findings from this study were used as a basis for simulating different strategies of improving the weaning weights of Mashona cattle through the creation of nucleus herds. Estimates ($ pm$s.e) of direct heritability (h$ sb{ rm A} sp2$), maternal heritability (h$ sb{ rm M} sp2$) and the correlation between direct and maternal genetic effects (r$ sb{ rm AM}$) were 0.243 $ pm$ 0.046, 0.392 $ pm$ 0.031 and $-$0.282 $ pm$ 0.081, respectively. When a permanent environmental effect of the dam (c$ sp2$) was fitted, the estimates of h$ sb{ rm A} sp2$, h$ sb{ rm M} sp2$, r$ sb{ rm AM}$ and c$ sp2$ were 0.281 $ pm$ 0.026, 0.113 $ pm$ 0.022, $-$0.269 $ pm$ 0.106 and 0.228 $ pm$ 0.023, respectively. No significant trends were observed in direct breeding values but there was a decline in maternal breeding values. The simulation study indicated that the bias in h$ sb{ rm A} sp2$ and h$ sb{ rm M} sp2$ resulting from the lack of sire pedigrees was trivial if the correlation between direct and maternal genetic effects was high and a large proportion of dams had known pedigrees. / The progeny test showed that both the mean breeding values of the reference sires and the bulls from commercial farms were significantly higher than the mean breeding values of small holder bulls for birth weight (by 1.6 and 1.7 kg, respectively) and weaning weight (by 10.4 and 11.0 kg, respectively). The strategies that selected breeding animals on their maternal genetic values resulted in the highest responses for weaning weight. / It was concluded that maternal genetic values of Mashona cattle should be improved to allow this breed to compete favourably as a maternal breed in commercial agriculture.