Master of Science / Department of Biological & Agricultural Engineering / Ronaldo G. Maghirang / Large cattle feedlots emit considerable amounts of particulate matter (PM), including TSP (total suspended particulates), PM[subscript]10 (PM with equivalent aerodynamic diameter of 10 μm or less), and PM[subscript]2.5 (PM with equivalent aerodynamic diameter of 2.5 μm or less). Particulate emissions result from pen surface disturbance by cattle hoof action, vehicle traffic on unpaved roads and alleyways, and wind erosion. Research is needed to determine concentrations of various size fractions, size distribution, and emission rates from various sources in feedlots. This research was conducted to measure particle size distribution using laser diffraction method and estimate emissions from unpaved roads and wind erosion. Particle size distribution and concentrations of PM[subscript]10 and PM[subscript]2.5 at a commercial cattle feedlot in Kansas (Feedlot 1) were measured over a 2-yr period. The feedlot had a capacity of 30,000 head and total pen area of 50 ha and was equipped with a sprinkler system for dust control. Collocated low-volume samplers for TSP, PM[subscript]10, and PM[subscript]2.5 were used to measure concentrations of TSP, PM[subscript]10, and PM[subscript]2.5 at the upwind and downwind edges of the feedlot. Dust samples that were collected by TSP samplers were analyzed with a laser diffraction analyzer to determine particle size distribution. Particle size distribution at the downwind edge of the feedlot was also measured with micro-orifice uniform deposit impactor (MOUDI). The laser diffraction method and MOUDI did not differ significantly in mean geometric mean diameter (13.7 vs. 13.0 μm) but differed in mean geometric standard deviation (2.9 vs. 2.3). From laser diffraction and TSP data, PM[subscript]10 and PM[subscript]2.5 concentrations were also calculated and were not significantly different from those measured by low-volume PM[subscript]10 and PM[subscript]2.5 samplers (122 vs. 131 μg/m[superscript]3 for PM[subscript]10; 26 vs. 35 μg/m[superscript]3 for PM[subscript]2.5). Both PM[subscript]10 and PM[subscript]2.5 fractions decreased as pen surface moisture contents increased, while the PM[subscript]2.5/PM[subscript]10 ratio did not change much with pen surface moisture content. Published emission models were used to estimate PM[subscript]10 emissions from unpaved roads and wind erosion at Feedlot 1 and another nearby feedlot (Feedlot 2). Feedlot 2 had a capacity of 30,000 head, total pen surface area of 59 ha, and used water trucks for dust control. Estimated PM[subscript]10 emissions from unpaved roads and wind erosion were less than 20% of total PM[subscript]10 emissions obtained from inverse dispersion modeling. Further research is needed to establish the applicability of published emission estimation models for cattle feedlots.

The stable fly, Stomoxys calcitrans (L.) is a haematophagous fly that feeds primarily on the forelegs of cattle stimulating a range of avoidance behaviours in confinement situations such as feedlots. From literature it is apparent that stable flies associated with feedlots have a significant impact on cattle especially with regard to economic parameters such as a decline in feed intake and thus a lower average daily gain resulting in less meat production due to irritation caused by painful bites. The abundance of the stable flies was studied in a large commercial feedlot near Heidelberg from October 2012 to September 2013. Two tsetse fly traps, namely the NZI and the Vavoua fly traps, were used and evaluated in determining the seasonal abundance of the stable flies. The tsetse traps proved to be most effective for sampling stable flies compared to other designs. The NZI and Vavoua tsetse type trap were compared and although there were no significant difference the NZI trap proved to be more reliable and user friendly for this study. Stable flies were more abundant from late December with a peak in numbers late in January through February and became less abundant from early March. Minimum to no fly abundance occurred in the winter months from May to June 2013. The data indicated a strong edge effect for the stable flies, the flies were more abundant in pens and corridors that were surrounded by vegetation, manure run off and holding ponds. The numbers collected in traps were correlated with stable fly counts on the cattle to be used in calculating a future threshold in chemical control. Preliminary observations on the influence of temperature, wind speed and rainfall were also made. This research will form part of a larger project to determine an integrated fly management program for the feedlot. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2014

The stable fly, Stomoxys calcitrans (L.) is a haematophagous fly that feeds primarily on the forelegs of cattle stimulating a range of avoidance behaviours in confinement situations such as feedlots. From literature it is apparent that stable flies associated with feedlots have a significant impact on cattle especially with regard to economic parameters such as a decline in feed intake and thus a lower average daily gain resulting in less meat production due to irritation caused by painful bites. The abundance of the stable flies was studied in a large commercial feedlot near Heidelberg from October 2012 to September 2013. Two tsetse fly traps, namely the NZI and the Vavoua fly traps, were used and evaluated in determining the seasonal abundance of the stable flies. The tsetse traps proved to be most effective for sampling stable flies compared to other designs. The NZI and Vavoua tsetse type trap were compared and although there were no significant difference the NZI trap proved to be more reliable and user friendly for this study. Stable flies were more abundant from late December with a peak in numbers late in January through February and became less abundant from early March. Minimum to no fly abundance occurred in the winter months from May to June 2013. The data indicated a strong edge effect for the stable flies, the flies were more abundant in pens and corridors that were surrounded by vegetation, manure run off and holding ponds. The numbers collected in traps were correlated with stable fly counts on the cattle to be used in calculating a future threshold in chemical control. Preliminary observations on the influence of temperature, wind speed and rainfall were also made. This research will form part of a larger project to determine an integrated fly management program for the feedlot. / MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2014

Thesis (PhD (Agric))--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: It is generally accepted that feed intake and growth (gain) are the most important economic components when calculating profitability in a growth test or feedlot. Feeding cost of animals is a major determinant of profitability in livestock production enterprises. Genetic selection to improve feed efficiency aims to reduce the cost of feeding in beef cattle production and thereby improve profitability. The objective of this study was to define a clear selection objective to enable South African beef breeders and especially the feedlot industry to select for post-weaning growth or feedlot performance and to identify factors influencing profitability in a feedlot environment. Because of the recording of individual feed intake and weight gain values in the South African Agricultural Research Councils' centralized growth tests, it was also possible to calculate a phenotypic value for feedlot profitability (R-value) for each bull tested in a centralized growth test. (Co)variances, using multitrait as well as random regression models, for and between feedlot profitability, weaning weight and other production, reproduction and efficiency traits were estimated. Residual feed intake (RFI) and feed conversion ratio (FCR) as efficiency traits were also compared to growth (average daily gain (ADG), weaning weight (WW) and shoulder height (SHD)), reproductive (scrotum circumference (SCR)) and profitability (feedlot profitability) traits measured in growth tests of young Bonsmara bulls. Consequently, a single post-weaning growth selection index value based on the economic and breeding values of different selection criteria related to feedlot profitability was composed. (Co)variance components, heritabilities and genetic correlations for and between initial weight (lW), final weight (FW), total feed intake (FI) and shoulder height (SHD) were estimated through the use of multitrait restricted maximum likelihood (REML) procedures. These breeding values (EBV s) were then used in a selection index to calculate a single economical value for each animal. This economical value is an indication of the gross profitability value or gross test value (GTV) of the animal in a post-weaning growth test. The heritability estimate of 0.36 for R-value, obtained from the multitrait analysis, shows that this trait is genetically inherited and that it can be selected for. The heritability for R-value obtained from the single trait random regression model varied between 0.57 and 0.62. The genetic correlations between the R-value and the other traits, obtained from the multitrait analysis, varied from negligible to high. The heritability estimated for FCR was 0.34 and for RFl 0.31 with a genetic correlation estimate of 0.75 between the traits. The estimated genetic correlation between profitability (R-value) and FCR and RFl were -0.92 and -0.59, respectively. The genetic correlation estimate of -0.92 between FCR and R-value is largely due to the part-whole relationship between these two traits. This is also shown in their genetic trends. The genetic correlations and expected correlated responses between RFl and FCR with R-value suggest that indirect selection for R-value through the direct selection for FCR and/or RFl will result in slower genetic progress in Rvalue than direct selection for R-value. However, where the R-value cannot be calculated and/or where direct selection for R-value is not possible, it would be better to select indirectly for R-value through the use of FCR rather than RF!. Consequently, a regression equation was developed (with an R2 of 0.82) to estimate a feed intake value for all performance-tested Bonsmara bulls which were group fed and whose feed intakes were unknown. These predicted feed intake values made it possible to calculate a feedlot or post-weaning growth profitability value (R-value) for all tested bulls even where individual feed intakes were unknown. Subsequently, an R-value for each bull was calculated in a favourable economic environment (FEE), an average economic environment (AEE) and in an unfavourable economic environment (VEE). The high Pearson and Spearman correlations between the EBV s based on AEE and the other two environments suggested that the average economic environment could be used to calculate EBVs for R-value or feedlot growth profitability. It is therefore not necessary to change the carcass, weaner or feed price on a regular basis to account for possible re-rankings based on R-value EBVs. Heritabilities for lW, FW, Fl and SHD were 0.41, 0.40, 0.33 and 0.51, respectively. The highest genetic correlations between these traits were the 0.78 (between lW and FW) and 0.70 (between Fl and FW). GTV values varied between -R192.l7 and R231.38, with an average of R9.31. The Pearson correlations between EBVs (for production and efficiency traits) and GTV range from -0.51 to 0.68. The lowest correlation (closest to zero) was 0.26 between the Kleiber ratio (KLB) and GTV. Correlations of 0.68 and -0.51 were estimated between average daily gain (ADG) and GTV and feed conversion ratio (FCR) and GTV, respectively. The heritabilities of the different traits included in the selection index suggest that it is possible to select for a GTV. The selection index can benefit feedlotting In selecting offspring of bulls with high GTV values to maximize profitability. The Pearson and Spearman correlations between the R-value EBVs and the index values (GTV) were very high (0.97). This high correlation of 97% indicates that it is not important which method is used to calculate a genetic post-weaning growth of feedlot profitability value. The selection index value is, however, more simplified than the feedlot profitability with less assumption. Therefore, it is recommended that the post-weaning selection index value be used as a selection objective in breeding programmes to improve post-weaning growth profitability rather than the more complex feedlot profitability value. / AFRIKAANSE OPSOMMING: 'N GENETIESE ANALIESE VAN DIE BIOLOGIESE EN EKONOMIESE DOELTREFFENTHEID VAN NASPEENSE GROEI IN VLEISBEESTE IN DIE VOERKRAAL: Dit word algemeen aanvaar dat voerinname en groei die twee ekonomies mees belangrike komponente in die berekening van 'n naspeense groei- of voerkraalwinsgewindheidswaarde is. Voerkostes is 'n bepalende faktor van winsgewindheid in enige lewendehawe boerderypraktyk. Seleksie om voerdoeltreffendheid te verbeter, verminder dus die voerkostes in vleisbeesproduksie en gevolglik 'n verhoging in die winsgewindheid. Die doelwit van die studie was om faktore te identifiseer wat 'n invloed op winsgewindheid in die voerkraaiomgewing het asook om 'n duidelike seleksiedoelwit te formuleer wat die Suid- Afrikaanse vleisbeesteiers en veral die voerkraalbedryf instaat sal kan stelom vir naspeense groeidoeltreffendheid ofvoerkraalwinsgewindheid te selekteer. As gevolg van die aantekening en rekordhouding van weeklikse individuele voennnames en gewigstoenames van alle prestasiegetoetsde bulle, in 'n gesentraliseerde groeitoets deur die Suid- Afrikaanse Landbou Navorsingsraad getoets, was dit moontlik om vir elk van hierdie bulle 'n fenotipiese voerkraalwinsgewindheidswaarde (R-waarde) te kon bereken. (Ko)variansies is vir en tussen voerkraalwinsgewindheid, speengewig en ander produksie-, reproduksie- en doeltreffendheidseienskappe bereken deur van meereienskap en ewekansige regressie modelle gebruik te maak. Twee doeltreffendheidseienskappe naamlik residuele voerinname (RFI) en voeromsetverhouding (FCR) is ook met groei (gemiddelde daaglikse toename (ADG), speengewig (WW) en skouerhoogte (SHD)), reproduksie (skrotumomvang (SCR)) en winsgewindheidseienskappe (voerkraalwinsgewindheid (R-waarde)) vergelyk, om sodoende te bepaal watter een die mees geskikte eienskap is om indirek vir voerkraalwinsgewindheid of groei, gebaseer op teeltwaardes en ekonomiese waardes vir die verskillende eienskappe, wat 'n invloed op naspeense groei winsgewindheid het, gestruktueer. (Ko)variansiekomponente, oorerflikhede en genetiese korrelasies vir en tussen begingewig (lW), eindgewig (FW), voerinname (FI) en skouerhoogte (SHD) is bereken deur van 'n meereienskap (REML) ontleding gebruik te maak. Hierdie teelwaardes (EBVs) is vervolgens in 'n seleksie-indeks gebruik om 'n enkele ekonomies of voerkraal-winsgewindheids seleksie-indekswaarde (GTV) vir elke dier te bereken. Hierdie ekonomiese waarde is 'n aanduiding van die bruto winsgewindheidswaarde ofbruto toetswaarde (GTV) van die dier in 'n naspeentoets. Die oorerflikheid, vanuit die meereienskapontleding vir R-waarde beraam, was 0.36. Hierdie oorerflikheid dui daarop dat die eienskap oorerflik is en dat dit wel moontlik is om daarvoor te selekteer. Die ooreflikhede van R-waarde, voorspel vanuit die enkeleienskap ewekansige regressieontleding varieer tussen 0.57 en 0.62. Die genetiese korrelasie tussen R-waarde en ander eienskappe, vanuit die meereienskap ontleding beraam, varieer tussen weglaatbaar klein tot hoog. Die oorerflikheid van FeR was 0.34 en van RFI 0.31 met 'n genetiese korrelasie van 0.75 tussen die twee eienskappe. Die genetiese korrelasie tussen R-waarde en FeR, en R-waarde en RFI was onderskeidelik -0.92 en -0.59. Die rede vir die hoë negatiewe genetiese korrelasie tussen R-waarde en FeR van -0.92 is omdat dieselfde komponente in die berekening van die twee eienskappe gebruik is. Dit word ook in die genetiese tendense weerspeël. Die genetiese korrelasies en verwagte gekorreleerde responsies tussen R-waarde en FeR, en tussen R-waarde en RFI dui daarop dat stadiger genetiese vordering verkry sal word in R-waarde deur direkte seleksie vir beide FeR en RFI as wat verkry sal word deur die direkte seleksie vir R-waarde. Wanneer 'n R-waarde egter nie bereken kan word nie of waar dit nie moontlik is om direk vir R-waarde te selekteer nie, sal vinniger genetiese vordering in R-waarde gemaak word deur die direkte seleksie vir FeR as vir RF!. 'n Regressievergelyking is geformuleer (met 'n R2 van 0.82) om vir alle prestasiegetoetsde bulle, waar bulle in 'n groep gevoer is en individuele voerinnames onbekend is, 'n voerinnamewaarde te voorspel. Hierdie voorspelde voerinnames maak dit moontlik om vir elke prestasiegetoetsde bul ,'n naspeengroei- of voerkraalwinswaarde (R-waarde) te bereken, al is hulle individuele voerinnames onbekend. Vervolgens is drie verskillende R-waarde vir vleisproduksie vir elke bul bereken naamlik, in 'n gunstige ekonomiese omgewing (FEE), 'n gemiddelde ekonomiese omgewing (AEE) en 'n ongunstige ekonomiese omgewing (VEE). Die hoë Pearson en Spearman korrelasies tussen die EBVs vir R-waarde, bereken in die AEE en die EBVs in die ander twee ekonomiese omgewings, dui daarop dat die AEE gebruik kan word om EBVs vir naspeense groeiof voerkraalwins te bereken. Dit is dus nie nodig om op 'n gereelde grondslag die karkasprys, lewendige speenkalfprys of die voerprys te verander nie. Oorerflikhede, vanuit die meereienskap ontledings VIr lW, FW, FI en SHD verkry, was onderskeidelik 0.41, 0.40, 0.33 en 0.51. Die hoogste genetiese korrelasies tussen die eienskappe was 0.78 tussen lW en FW en 0.70 tussen FI en FW. GTV indekswaardes varieer tussen -Rl92.17 en R231.38 met 'n gemiddelde waarde van R9.31. Die Pearson korrelasies tussen die EBVs van produksie- en doeltreffenheidseienskappe en GTV het tussen -0.51 en 0.68 gevarieer. Die korrelasie naaste aan zero, van 0.26, was die korrelasie tussen GTV en die Kleiber-verhouding. Die korrelasies tussen GTV en ADG, en GTV en FeR was onderskeidelik 0.68 en -0.51. Die oorerflikhede van die verskillende eienskappe wat in die seleksie-indeks ingesluit is, dui daarop dat die indekswaarde weloorerflik is en dat seleksie hiervoor wel moontlik is. Hierdie indekswaarde kan deur die voerkraaiindustrie gebruik word om nageslag van diere met hoë GTV waardes te selekteer om sodoende maksimum wins uit die voerkraai te genereer. Die Pearson en Spearman korrelasies tussen R-waarde EBVs en die indekswaardes (GTV) was besonder hoog (0.97). Hierdie hoë korrelasie dui daarop dat dit geen verskil sal maak watter een van die twee metodes gebruik word in die berekeninge van 'n naspeense groei- of voerkraalwinswaarde nie. Die seleksie-indeks metode is egter minder gekompliseerd met minder aannames as in die geval van die rekeningkundige fenotipiese benadering (R-waarde). As gevolg hiervan, word die naspeense seleksie-indeks waardes (GTV) aanbeveel om te gebruik as 'n teeldoelwit in telingsprogramme om naspeense groei- of voerkraaiwins geneties te verbeter, eerder as die meer gekompliseerde fenotipiese voerkraaiwins (R-waardes) metode.

Feedlot finishing of beef cattle in Southern Alberta involves income risk due to the variability of prices of feeders, feed and finished cattle. Several strategies are available to reduce this risk, including hedging of cattle on feed, participation in a Federal- Provincial government and producer established income stabilization program for finished cattle (National Tripartite Stabilization Plan) and diversification of production plans. This study evaluated the efficacy and interaction effects of these strategies in reducing net income variability in cattle feeding in Southern Alberta. Concerns that were addressed included: (1) whether participation in hedging or Stabilization would increase firm-level slaughter cattle output, (2) whether portfolio effects exist between production and marketing alternatives, (3) whether participation in Stabilization would reduce participation in hedging (4) whether hedging performance could be increased by hedging the Canadian dollar, and (5) whether privately supplied hedging versus publicly supplied Stabilization is better able to handle income risk in cattle feeding. The theory of decision making under uncertainty was reviewed to determine how to best incorporate the risk aspects of the feedlot , management problem. Expected Value-Variance (EV)and safety-first risk analyses were identified as frameworks for formulation of the feedlot management problem in a mathematical programming context. Using data from 1976-87, linear risk programming (MOTAD and Target MOTAD) models of the feedlot process were constructed to analyze the alternatives for reducing income risk. Results for the 1986-87 feeding year suggested that, at moderate levels of risk aversion, feedlot managers should maintain high levels of hedging of both live cattle and the Canadian dollar with moderate participation (25 percent of cattle on feed) in the Stabilization plan. Significant portfolio effects were present. Hedging, but not Stabilization, was found to increase firm-level output by increasing the average weight to which a group of cattle would be finished. Participation in Stabilization was found to reduce hedging participation by an average of 10 percent. Hedging of the Canadian dollar improved the performance of live cattle hedging. Whether hedging was better at reducing risk and maintaining income than Stabilization depended on the definition of risk. / Graduation date: 1989

Embora no passado a seleção para eficiência alimentar tenha sido relegada a um segundo plano pela indústria da carne bovina, hoje há um crescente interesse por estudos abordando eficiência alimentar de bovinos de corte e esta discussão norteou o primeiro capítulo desta tese. No segundo capítulo foram analisados dados de consumo de MS de 36 tourinhos do rebanho Nelore Seleção (NeS) e 36 do rebanho Nelore Controle (NeC) oriundos da Estação Experimental de Zootecnia de Sertãozinho. A média obtida para consumo alimentar residual (CAR) foi de 0,00±0,41 kg/dia, com valores mínimo e máximo de -0,73 e +0,95 kg/dia, confirmando que há uma satisfatória variabilidade para esta característica em animais Bos indicus. Tourinhos NeS apresentaram maiores pesos inicial e final e ganharam peso mais rapidamente que tourinhos NeC. Tourinhos NeS apresentaram consumos de MS superiores aos consumos de tourinhos NeC, quando expressos em kg/dia ou em g/kg PV0,75. Tourinhos NeC apresentaram índices de eficiência alimentar mais altos e estimativas de CAR mais baixas que tourinhos NeS. Enquanto que tourinhos NeS apresentaram valores de energia retida 11,7% superiores que tourinhos NeC, a produção de calor dos animais selecionados foi 17,9% maior. Tourinhos NeS apresentaram ainda maiores estimativas de exigência energética para mantença. As equações de predição de consumo de MS do NRC foram desenvolvidas com dados obtidos principalmente de bovinos europeus, implantados e alimentados com dietas de alta proporção de concentrado e com ionóforos. O terceiro capítulo estimou e validou uma equação de predição de consumo para zebuínos. Métodos de meta-análise foram aplicados em 17 experimentos com bovinos Nelore. Entre as 193 unidades experimentais, a concentração energética da dieta variou de 51,2 a 78,0% NDT. A equação sugerida para estimar o consumo alimentar de bovinos Bos indicus é: CMS (kg/d) = (PVj0,75 * (0,2039*ELm - 0,03844*ELm 2 - 0,07376))/ELm Bovinos Bos taurus apresentaram consumos de MS progressivamente mais altos que bovinos Bos indicus, quando a concentração da ELm foi superior a 1,4 Mcal/kg. Os resultados demonstraram que o comportamento ingestivo do Bos indicus em diferentes concentrações energéticas é incorretamente estimado pelas equações do NRC. No quarto capítulo foram desenvolvidas curvas de consumo de MS e eficiência alimentar no tempo para tourinhos em confinamento. O experimento foi realizado na Embrapa Pecuária Sudeste e utilizou 188 machos não-castrados da raça Nelore (NE) e cruzados ½Canchim + ½Nelore (CN), ½Angus + ½Nelore (AN) e ½Simental + ½Nelore (SN), distribuídos em três anos e 85 baias. Os animais foram distribuídos nas baias, de acordo com o grupo genético e tratamento experimental no período anterior ao confinamento. Machos NE apresentaram menor consumo de MS (kg/dia) do que machos cruzados AN, CN e SN. A presente análise não indicou menor eficiência dos machos NE em relação aos mestiços. Quanto ao efeito de tratamento anterior, o ganho de peso compensatório parcial e a melhor eficiência alimentar dos bovinos que não receberam concentrado no período anterior ao confinamento, reduziram as vantagens da suplementação em pastejo. Os efeitos de raça e sexo sobre características de desempenho em dois grandes confinamentos comerciais foram avaliados no quinto capítulo. Após impor restrições ao arquivo original, restaram 116.376 animais distribuídos em 608 lotes. Animais cruzados apresentaram taxas de ganho de peso e estimativas de consumo de MS mais altas que animais Nelore. Conseqüentemente, não foi observada diferença significativa na eficiência alimentar entre animais cruzados e zebuínos. O ganho de peso diário foi numericamente mais alto para os bovinos inteiros. Quando o consumo de MS foi expresso em kg/dia, lotes de animais inteiros apresentaram maiores consumos que lotes de animais castrados. Não foram observadas diferenças significativas entre bovinos inteiros e castrados para eficiência alimentar. As equações de predição de consumo de MS analisadas subestimaram os consumos reais observados, o que sugere uma grande heterogeneidade dos animais na entrada do confinamento e a ausência de fatores de ajuste para ganho compensatório. / Although selection for feed efficiency was withdrawn to a minor role by the beef industry in the past, nowadays there is a growing attention by studies dealing with feed efficiency traits in beef cattle and this subject was discussed in the first chapter. The second chapter analyzed dry matter (DM) intake data of 36 Nellore young bulls from the Selected Nellore (NeS) line and 36 from the Control Nellore (NeC), both from Experimental Station of Sertãozinho. Overall average for residual feed intake (RFI) was 0.00±0.41 kg/day, with minimum and maximum RFI estimates of -0.73 and +0.95 kg/day. These estimates confirm that there is enough variability for this new trait among Bos indicus animals. Selected Nellore young bulls were heavier at the beginning and at the end of the trial and they grown more rapidly than NeC young bulls. Selected Nellore young bulls showed larger DM intakes than NeC young bulls, when expressed on kg/day or g/kg mid-BW0.75. Control Nellore young bulls were more efficient and showed lower RFI estimates than NeS young bulls. While NeS young bulls showed retained energy estimates 11.7% greater than NeC cattle, NeS estimates for heat production were 17.9% larger. Lastly, NeS young bulls showed greater maintenance requirements than NeC young bulls. Current prediction equations for DM intake from NRC were mainly obtained from Bos taurus breeds, from cattle implanted with a growth-promoting implant and fed low forage diets, supplemented with ionophores. The third chapter developed and validated a DM intake prediction equation for Zebu cattle. Meta-analyses methods were applied to 17 experiments conducted with Nellore cattle. Among the 193 experimental units, dietary energy concentration ranged from 51.2 to 78.0% TDN. The suggested equation to predic feed intake by Bos indicus cattle is: DMI (kg/d) = (SBW0,75 * (0.2039*NEm - 0.03844*NEm 2 - 0.07376))/NEm Above 1.4 Mcal/kg the new equation predicted progressively lower intakes for Nellore than European genotypes. These results showed that the intake behaviour from Bos indicus cattle in a broad range of dietary NEm concentration is incorrectly predicted by the current NRC equations. The fourth chapter described the relationships of dry matter intake and feed efficiency to days on feed for young bulls in feedlots. The trial was conducted on Embrapa Pecuária Sudeste, and included records from 188 beef young bulls from four different genetic groups: purebred Nellore (NE), ½Canchim + ½Nellore (CN), ½Angus + ½Nellore (AN), and ½Simental + ½Nellore crossbreds (SN), distributed on three years and 85 pens. Animals were distributed on pens in a ramdomized block design by genetic group and previous experimental treatment. NE young bulls showed a lower DM intake (kg/day) than AN, CN and SN crossbreds bulls. The analysis did not show a lower feed efficiency for NE bulls compared with the feed efficiency estimated for the remaining genetic groups. Partial compensatory growth and better feed efficiency for the bulls that were not supplemented with a concentrate before being fully fed during the experimental period diminished the advantages of supplementation during the grazing period. The fifth chapter evaluated the effects of breed and gender on performance traits em two large commercial feedlots in the Brazilian Central Region. After editing the original data set, it remained 116,376 animals distributed on 608 pens. Crossbreds showed higher average daily gains and DM intakes than Nellore animals. Consequently, it was not observed significant differences on feed efficiency between crossbreds and Bos indicus cattle. Average daily gain was higher for the bulls. When DM intake was expressed as kg/day, bulls showed higher intakes than steers. There were not statistically differences between bulls and steers for the feed efficiency traits analyzed. The equations to predict DM feed intake clearly underestimated the observed intakes. This suggests a large heterogeneity among animals coming into a feedyard and the absence of adjusting factors for compensatory growth.

Embora no passado a seleção para eficiência alimentar tenha sido relegada a um segundo plano pela indústria da carne bovina, hoje há um crescente interesse por estudos abordando eficiência alimentar de bovinos de corte e esta discussão norteou o primeiro capítulo desta tese. No segundo capítulo foram analisados dados de consumo de MS de 36 tourinhos do rebanho Nelore Seleção (NeS) e 36 do rebanho Nelore Controle (NeC) oriundos da Estação Experimental de Zootecnia de Sertãozinho. A média obtida para consumo alimentar residual (CAR) foi de 0,00±0,41 kg/dia, com valores mínimo e máximo de –0,73 e +0,95 kg/dia, confirmando que há uma satisfatória variabilidade para esta característica em animais Bos indicus. Tourinhos NeS apresentaram maiores pesos inicial e final e ganharam peso mais rapidamente que tourinhos NeC. Tourinhos NeS apresentaram consumos de MS superiores aos consumos de tourinhos NeC, quando expressos em kg/dia ou em g/kg PV0,75. Tourinhos NeC apresentaram índices de eficiência alimentar mais altos e estimativas de CAR mais baixas que tourinhos NeS. Enquanto que tourinhos NeS apresentaram valores de energia retida 11,7% superiores que tourinhos NeC, a produção de calor dos animais selecionados foi 17,9% maior. Tourinhos NeS apresentaram ainda maiores estimativas de exigência energética para mantença. As equações de predição de consumo de MS do NRC foram desenvolvidas com dados obtidos principalmente de bovinos europeus, implantados e alimentados com dietas de alta proporção de concentrado e com ionóforos. O terceiro capítulo estimou e validou uma equação de predição de consumo para zebuínos. Métodos de meta-análise foram aplicados em 17 experimentos com bovinos Nelore. Entre as 193 unidades experimentais, a concentração energética da dieta variou de 51,2 a 78,0% NDT. A equação sugerida para estimar o consumo alimentar de bovinos Bos indicus é: CMS (kg/d) = (PVj0,75 * (0,2039*ELm – 0,03844*ELm 2 – 0,07376))/ELm Bovinos Bos taurus apresentaram consumos de MS progressivamente mais altos que bovinos Bos indicus, quando a concentração da ELm foi superior a 1,4 Mcal/kg. Os resultados demonstraram que o comportamento ingestivo do Bos indicus em diferentes concentrações energéticas é incorretamente estimado pelas equações do NRC. No quarto capítulo foram desenvolvidas curvas de consumo de MS e eficiência alimentar no tempo para tourinhos em confinamento. O experimento foi realizado na Embrapa Pecuária Sudeste e utilizou 188 machos não-castrados da raça Nelore (NE) e cruzados ½Canchim + ½Nelore (CN), ½Angus + ½Nelore (AN) e ½Simental + ½Nelore (SN), distribuídos em três anos e 85 baias. Os animais foram distribuídos nas baias, de acordo com o grupo genético e tratamento experimental no período anterior ao confinamento. Machos NE apresentaram menor consumo de MS (kg/dia) do que machos cruzados AN, CN e SN. A presente análise não indicou menor eficiência dos machos NE em relação aos mestiços. Quanto ao efeito de tratamento anterior, o ganho de peso compensatório parcial e a melhor eficiência alimentar dos bovinos que não receberam concentrado no período anterior ao confinamento, reduziram as vantagens da suplementação em pastejo. Os efeitos de raça e sexo sobre características de desempenho em dois grandes confinamentos comerciais foram avaliados no quinto capítulo. Após impor restrições ao arquivo original, restaram 116.376 animais distribuídos em 608 lotes. Animais cruzados apresentaram taxas de ganho de peso e estimativas de consumo de MS mais altas que animais Nelore. Conseqüentemente, não foi observada diferença significativa na eficiência alimentar entre animais cruzados e zebuínos. O ganho de peso diário foi numericamente mais alto para os bovinos inteiros. Quando o consumo de MS foi expresso em kg/dia, lotes de animais inteiros apresentaram maiores consumos que lotes de animais castrados. Não foram observadas diferenças significativas entre bovinos inteiros e castrados para eficiência alimentar. As equações de predição de consumo de MS analisadas subestimaram os consumos reais observados, o que sugere uma grande heterogeneidade dos animais na entrada do confinamento e a ausência de fatores de ajuste para ganho compensatório. / Although selection for feed efficiency was withdrawn to a minor role by the beef industry in the past, nowadays there is a growing attention by studies dealing with feed efficiency traits in beef cattle and this subject was discussed in the first chapter. The second chapter analyzed dry matter (DM) intake data of 36 Nellore young bulls from the Selected Nellore (NeS) line and 36 from the Control Nellore (NeC), both from Experimental Station of Sertãozinho. Overall average for residual feed intake (RFI) was 0.00±0.41 kg/day, with minimum and maximum RFI estimates of –0.73 and +0.95 kg/day. These estimates confirm that there is enough variability for this new trait among Bos indicus animals. Selected Nellore young bulls were heavier at the beginning and at the end of the trial and they grown more rapidly than NeC young bulls. Selected Nellore young bulls showed larger DM intakes than NeC young bulls, when expressed on kg/day or g/kg mid-BW0.75. Control Nellore young bulls were more efficient and showed lower RFI estimates than NeS young bulls. While NeS young bulls showed retained energy estimates 11.7% greater than NeC cattle, NeS estimates for heat production were 17.9% larger. Lastly, NeS young bulls showed greater maintenance requirements than NeC young bulls. Current prediction equations for DM intake from NRC were mainly obtained from Bos taurus breeds, from cattle implanted with a growth-promoting implant and fed low forage diets, supplemented with ionophores. The third chapter developed and validated a DM intake prediction equation for Zebu cattle. Meta-analyses methods were applied to 17 experiments conducted with Nellore cattle. Among the 193 experimental units, dietary energy concentration ranged from 51.2 to 78.0% TDN. The suggested equation to predic feed intake by Bos indicus cattle is: DMI (kg/d) = (SBW0,75 * (0.2039*NEm – 0.03844*NEm 2 – 0.07376))/NEm Above 1.4 Mcal/kg the new equation predicted progressively lower intakes for Nellore than European genotypes. These results showed that the intake behaviour from Bos indicus cattle in a broad range of dietary NEm concentration is incorrectly predicted by the current NRC equations. The fourth chapter described the relationships of dry matter intake and feed efficiency to days on feed for young bulls in feedlots. The trial was conducted on Embrapa Pecuária Sudeste, and included records from 188 beef young bulls from four different genetic groups: purebred Nellore (NE), ½Canchim + ½Nellore (CN), ½Angus + ½Nellore (AN), and ½Simental + ½Nellore crossbreds (SN), distributed on three years and 85 pens. Animals were distributed on pens in a ramdomized block design by genetic group and previous experimental treatment. NE young bulls showed a lower DM intake (kg/day) than AN, CN and SN crossbreds bulls. The analysis did not show a lower feed efficiency for NE bulls compared with the feed efficiency estimated for the remaining genetic groups. Partial compensatory growth and better feed efficiency for the bulls that were not supplemented with a concentrate before being fully fed during the experimental period diminished the advantages of supplementation during the grazing period. The fifth chapter evaluated the effects of breed and gender on performance traits em two large commercial feedlots in the Brazilian Central Region. After editing the original data set, it remained 116,376 animals distributed on 608 pens. Crossbreds showed higher average daily gains and DM intakes than Nellore animals. Consequently, it was not observed significant differences on feed efficiency between crossbreds and Bos indicus cattle. Average daily gain was higher for the bulls. When DM intake was expressed as kg/day, bulls showed higher intakes than steers. There were not statistically differences between bulls and steers for the feed efficiency traits analyzed. The equations to predict DM feed intake clearly underestimated the observed intakes. This suggests a large heterogeneity among animals coming into a feedyard and the absence of adjusting factors for compensatory growth.

No description available.

This thesis describes the detection, and characterization of putative extended-spectrum β-lactamases (ESBLs) producing Escherichia coli isolated from feedlot cattle in southern Alberta. Cattle either received no antimicrobials or were administered subtherapeutic antimicrobials in feed. In total, 7,184 E. coli isolates were collected, and screened for resistance to either ceftazidime (2μg mL-1 ) or cefpodoxime (2μg mL-1), and from these results 237 E. coli isolates were considered presumptive ESBL producers. Antimicrobial resistant bacteria were isolated throughout the experiment; however, ESBL-producing E. coli were not prevalent throughout the study. In total, only three isolates (B221B1, C152C1, C98A1) exhibited the ESBL phenotype. Molecular subtyping of these isolates revealed no clonality between these strains. Molecular characterization of the 237 isolates investigated in this study revealed blaTEM to be the most prevalent AMR determinant among the ampicillin-resistant isolates with resistance to ceftazidime (2μg mL-1 ) or cefpodoxime (2μg mL-1). These data suggest that ESBLs are not frequent among Canadian feedlot cattle and MDR resistance (55 of 237) was observed but is not prominent among both the subgroup and total isolates collected. It was determined that isolate B221B1 was ESBL-producing, and harboured the blaTEM-1 gene. The genes responsible for ESBL production in isolates C98A1 and C152C1 were not characterized. In order to characterize the antimicrobial resistance (AMR) genes coding for ESBL-production in these 2 isolates, cloning and conjugation experiments were attempted. However, I was unable to resolve the mechanism responsible for ESBL phenotype in these two isolates. The results of this study imply that the development of ESBL-producing E. coli is complex, and is probably affected by both the administration of antimicrobials and numerous other presently undefined environmental factors. / xii, 104 leaves : ill. ; 28 cm

Metabolic were used to evaluate Enterococcus as an indicator of faecal pollution. Enterococci were isolated using m-Enterococcus agar and speciated using conventional biochemical tests. Forty percent of the isolates were identified and metabolically characterized by the automated Biolog system. The biochemical test scheme recognized 16 enterococcal species, while Biolog recognized nine. Both methods identified E. faecalis at the greatest frequency. Overall species frequencies varied between the two methods. Biolog was unable to identify 31% of the isolates; 7% of the isolates were unidentified by the biochemical test scheme. Of the identified isolates, metabolic profiling with Biolog achieved speciation with 60 substrates. Unique profiles were obtained for 89% of the isolates. Isolates also demonstrated inter-trial differntial metabolism of substrates. This and the large number of unidentified isolates suggest great diversity among enterococci. Diversity and inter-trial metabolic inconsistencies will complicate use of enterococcal metabolic profiles as a source-tracking tool. / xxiii, 264 leaves ; 29 cm.