Thesis (MScAgric )--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The main object of this study was to estimate heritabilities and possible genetic correlations for and between reproductive traits in a composite multi breed beef cattle herd. Reproduction is a complex process with many components. Due to the nature of the data, obtained from the two farms of the Johannesburg Metropolitan Council from 1974 to 1993, only calving date (CD), calving date with a penalty score (CDP), calving success (CS), calving interval (CI), age at first calving (AFC), longevity and stayability at 36, 48, 60, 72 and 84 months were investigated. A GFCAT set of programmes was used and fitted on a sire model to analyse all the categorical traits. Heritabilities and product moment correlations between predicted breeding values for stayability at 36, 48, 60, 72, 84 months, calving success (CS) and longevity, were estimated. The estimated heritabilities on the underlying scale for these traits were 0.06, 0.10, 0.06, 0.03, 0.11, 0.03 and 0.08, respectively. Product moment correlations between breeding values for stayability traits were very low. The highest correlation of 0.22 was obtained between 36 and 48 months. Heritability estimates and correlations between traits appear to be of such a low magnitude that selection for these characteristics would result in limited improvement and indicate that the sire had little influence on his daughter's stayability, longevity and CS. For the analyses oflinear traits (CI, CD, CDP and AFC), a REML procedure fitting a multitrait animal model (using REML VCE 4.2.5 package of Groeneveld, 1998) was used. Heritabilities and geneticcorrelations for and between calving interval (CI), calving date (CD), calving date with a penalty score (CDP) and age at first calving (AFC) were estimated as traits of the dam. The estimated heritabilities for CI, CD, CDP and AFC obtained in this study were 0.01, 0.04, 0.06 and 0.40, respectively with a repeatability of 0.07, 0.12 and 0.13 for CI, CD and CDP, respectively. Genetic correlations between traits obtained varied from low to moderate, except for the high correlations between CD and CDP (0.98), CI and CD (0.75) and CI and CDP (0.79). Heritabilities, genetic correlations and repeatabilities of CD and CDP obtained in this study suggest that CD and CDP are the same traits and that selection for CDP rather than for CD does not have any additional advantage. Due to the additional advantages of CD over CI and the fact that CD is a less biased measurement of the female reproductive complex, CD appears to be of genetic value and should.be considered-as a possible selection criterion to ensure genetic improvement for reproduction in a beef cattle herd. / AFRIKAANSE OPSOMMING: Die doeI met hierdie studie was om oorerflikhede vir en moontlike genetiese korrelasies tussen verskillende reproduksiekenmerke in 'n meerras vleisbeeskudde te bepaal. Reproduksie is 'n komplekse proses en bestaan uit veelvuldige komponente. Weens die aard van die data, verkry vanaf die Johannesburg Metropolitaanse Raad se twee plase (vanaf 1974 tot 1993), is slegs kalfdatum (CD), kalf datum met 'n verswaringswaarde (CDP), kalwingsukses (CS), kalfinterval (CI), ouderdom met eerste kalwing (AFC), langlewendheid en volhoubaarheid van die moeders om reproduktief in die kudde tot op onderskeidelik 36, 48, 60, 72 en 84 maande te bly, bestudeer. Kategoriese kenmerke is deur middel van 'n GFCAT stel programme, wat op 'n vadermodel gepas is, geanaliseer. Oorerflikhede vir en die produkmoment korrelasies tussen die voorspelde teelwaardes vir CS, langlewendheid en volhoubaarheid op onderskeidelik 36, 48, 60, 72 en 84 maande, is bereken. Die oorerflikhede vir bogenoemde kenmerke was onderskeidelik 0.03, 0.08, 0.06, 0.10, 0.06, 0.03 en 0.11. Die korrelasie tussen die voorspelde teelwaardes vir die verskillende volhoubaarheidskenmerke was laag. Die hoogste korrelasie, n1. 0.22, is tussen 36 en 84 maande verkry. Die oorerflikhede en korrelasies tussen die kenmerke blyk van so 'n lae omvang te wees dat direkte seleksie vir die kenmerke slegs tot 'n beperkte genetiese verbetering sal lei en dui daarop dat die vader slegs 'n beperkte invloed op CS, volhoubaarheid en die langlewendheid van sy dogters het. Vir die analise van die lineere kenmerke (CI, CD, CDP en AFC), is 'n REML-prosedure gebruik wat op 'n multikenmerk dieremodel gepas is (deur die gebruik van die REML VCE 4.2.5 pakket van Groeneveld, 1998). Oorerflikhede vir en genetiese korrelasies tussen CI, CD, CDP en AFC is bereken as kenmerke van die moeder. In hierdie studie is die beraamde oorerflikhede vir CI, CD, CDP en AFC as onderskeidelik 0.01, 0.04, 0.06 en 0.40 bepaal, met herhaalbaarhede van onderskeidelik 0.07, 0.l2 en 0.13 vir CI, CD en CDP. Genetiese korrelasies tussen die kenmerke het van laag tot matig gevarieer, behalwe vir die hoe korrelasies tussen CD en CDP (0.98), CI en CD (0.75) en CI en CDP (0.79). Die oorerflikhede en herhaalbaarhede vir en genetiese korrelasie tussen CI en CDP verkry in hierdie studie, veronderstel dat CD en CDP in wese dieselfde kenmerk is en dat seleksie vir CDP in plaas van CD geen addisionele voordele inhou nie. Weens die addisionele voordele wat CD inhou, bo die van CI, en die feit dat CD 'n minder sydige bepaling van die vroulike reproduksiekompleks is, blyk CD van genetiese waarde te wees en moet dit as 'n moontlike seleksie kriterium, om genetiese verbetering in 'n vleisbeeskudde te verseker, oorweeg word.

An experiment was conducted to study the effect of prolonged nutritional stress on the reproductive performance of twelve Holstein dairy heifers. Energy intake was reduced to 60% NE(m). The animals lost 20% of their body weight during energy restriction (97 days) and gained 29% during the high energy feeding (44 days). Estrous cycles were irregular, delayed, or ceased completely. The conception rate was only 25% during energy reduction. Cycles were reestablished and conception rate improved (67%) during the high energy feeding. Heifers were designated as fertile or infertile according to their success or failure to conceive during the energy reduction period. Serum thyroxine (T₄) levels were slightly decreased (P > .05) while triiodothyronine (T₃) levels were significantly depressed (P < .01) during energy restriction in both fertile and infertile heifers. Serum thyroxine levels were slightly increased (P > .05) in the fertile heifers, but significantly increased (P < .01) in the infertile heifers during high energy feeding. Serum triiodothyronine levels were significantly increased during high energy feeding in both fertile (P < .05) and infertile (P < .01) heifers. Concentrations of blood cortisol were relatively higher in the fertile than in the infertile heifers during the ad libitum and energy restriction periods. This suggests that the fertile heifers possessed elevated adrenal activity that the infertile heifers did not have. Concentrations of blood progesterone of the infertile heifers were severely depressed (P < .01) during the submaintenance feeding while those of the fertile group were not affected (P > .05). Blood glucose levels were significantly reduced during energy reduction and significantly increased during high energy feeding in both groups of heifers (P < .01 for infertile heifers). Blood glucose levels of the infertile heifers at time of insemination (period of energy restriction) were as low as their average levels of the period. Glucose levels of the fertile heifers at time of breeding (period of energy restriction) were greater than their mean concentration during that period and were similar to the mean levels of glucose during the ad libitum period. Low progesterone levels are indicative of ovarian inactivity under such stressful conditions. Adrenal inactivity, (as reflected by low cortisol secretion) and low blood glucose levels at time of insemination of the infertile heifers are probably associated with infertility during submaintenance feeding in dairy heifers.

Orientador: Roberto Carvalheiro / Banca: Renata Helena Branco Arnandes / Banca: Henrique Nunes de Oliveira / Banca: Aníbal Eugênio Vercesi Filho / Banca: Fernando Sebastian Baldi Rey / Resumo: Biotécnicas reprodutivas e cruzamento constituem importantes ferramentas para o aumento da eficiência econômica e produtiva em bovinos de corte. A determinação da intensidade do uso dessas biotécnicas e o cruzamento, nas diferentes condições ambientais, de manejo e mercado, são fundamentais para otimizar a relação custo-benefício de sua adoção, visando aumentar a rentabilidade do sistema produtivo. Objetivou-se com este estudo estimar o ganho genético e econômico da utilização de diferentes biotécnicas reprodutivas e cruzamento, em um sistema produtivo de bovinos de corte, usando simulações determinísticas. O estudo foi baseado em um sistema de produção com capacidade para 1000 UA (UA = 450kg de peso vivo), adotando pastejo contínuo e taxa de lotação variável. O primeiro cenário foi caracterizado pela inseminação artificial (IA) (sêmen Nelore) e repasse com monta natural (MN) com touros Nelore. Os outros cenários envolveram o uso de ao menos uma dessas técnicas: inseminação artificial em tempo fixo (IATF), fertilização "in vitro" (FIV) e cruzamento de vacas Nelore com touros Angus (sêmen). Os parâmetros econômicos foram extraídos de instituições da região central do Brasil. Foi estimada a porcentagem de produção de animais superiores e o ganho genético, e calculado para o curto (5 anos), médio (10 anos) e longo (15 anos) prazos. Indicadores econômicos como quantidade de progênie produzida, custo total estimado a desmama e ao abate, lucro estimado a desmama e ao abate e taxa d... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: - Reproductive biotechniques and crossbreeding are important tools for increasing economic and productive efficiency in beef cattle. The determination of the intensity of use of these biotechniques and the crossbreeding, in the different environmental, management and market conditions, are fundamental to certify a better cost-benefit relation of its adoption, in order to increase the profitability of the production system. The objective of this study was to estimate the genetic and economic gain using different reproductive biotechniques and crossbreeding for a production system of beef cattle by means of deterministic simulations. The study was based on a production system with capacity for 1000 AU (AU = 992,08 pounds of body weight), adopting the continuous grazing and variable stocking rate. The first scenario was characterized by artificial insemination (AI) (Nellore) and natural mating (NM) with Nellore bulls. The other scenarios involved the use of at least one of these techniques: fixed-time artificial insemination (FTAI), in vitro fertilization (IVF), and crossbreeding of Nellore cows with Angus bulls. The economic values were extracted from institutions of the central region of Brazil. The percentage of production of superior animals and genetic gain were calculated in the short (5 years), medium (10 years) and long (15 years) time. Economic indicators such as amount of progeny produced, estimated total cost of weaning and slaughter, estimated profit of weaning and s... (Complete abstract click electronic access below) / Doutor

Orientador: Euice Oba / Banca: Fabiana Ferreira Souza / Banca: Thales Ricardo Rigo Barreiros / Resumo: Após o parto, alguns eventos fisiológicos ocorrem no útero de vacas para reparar as modificações ocorridas durante a prenhez e o parto. O uso do cloprostenol sódico no período puerperal visa reduzir o período de involução uterina, atuando na contração uterina, auxiliando na redução do tamanho do útero, na limpeza do útero e no retorno da atividade ovariana. Portanto, o objetivo deste trabalho foi avaliar o efeito da aplicação de cloprostenol sódio no pós-parto sobre a involução uterina, dosagem hormonal de progesterona (P4) e 13,14 -di-hidro-15-ceto prostaglandina F2a (PGMF), sobre as variáveis histológicas, de expressão do mRNA do receptor de PGF2 (FP), caspase - 3 (CASP - 3) e ciclo-oxigenase 2 (COX - 2), e também sobre a expressão proteica de FP e da COX - 2. Para isso, vacas Nelore multíparas (n=24) foram tratadas ou não com cloprostenol sódio nos dias 1 e 4 pós-parto (D0 = parto) e foram feitos exames ultrassonográficos, de palpação transretal, vaginoscopia e coleta de sangue em D1, D7, D14, D21, D28, D35 e D42 pós-parto (D0 = parto). Adicionalmente, biópsias endometriais foram colhidas com uma pinça de biópsia Yomann em D1, D7 , D14 , D28 e D42 para análise histológica, de expressão do mRNA por RT-PCR em tempo real e imunolocalização por imunohistoquímica. De acordo com os resultados, o cloprostenol sódio exerceu influência (P< 0,05) sobre a descarga cervical e expressão de mRNA da CASP-3. Para as variáveis relacionadas à dosagem hormonal, involução uterina, variáveis histológicas (glândulas endometriais e grau de inflamação), foi observado efeito apenas nos momento e para as demais, nenhum tipo de influência foi notada. Com base nos resultados, conclui-se que o uso deste protocolo em vacas Nelore multíparas selecionadas geneticamente, com manejo adequado e saúde pode ser desnecessário para reduzir período pós-parto e pode promover despesa ... / Abstract: After calving, some physiological events occur in the uterus of cows to repair the modifications occurred during pregnancy and delivery. The use of cloprostenol sodium at postpartum period aims to reduce the period of uterine involution by acting at uterine contraction, helping in reducing uterine size, at uterine cleaning, and at the resumption of ovary activity. For this, the aim of this work was to evaluate the effect of the application of cloprostenol sodium on postpartum on uterine involution, hormonal dosage of progesterone (P4) and 13,14-dihydro-15-keto prostaglandin F2 (PGMF), histological variables, mRNA expression of PGF2 receptor (FP), caspase- 3 (CASP-3) and cyclooxygenase 2 (COX-2), and also protein expression of FP and COX-2. For this, multiparous Nelore cows (n=24) were treated or not with cloprostenol sodium on days 1 and 4 postpartum (D0 = birth) and it was done ultrasound, transretal palpation, vaginoscopy exams and blood collection on D1, D7, D14, D21, D28, D35 and 42 postpartum (D0 = birth). Also, endometrial biopsies were collected with a Yomann biopsy instrument at D1, D7, D14, D28 and D42 for histological analysis, mRNA expression by qRT-PCR and immunolocalization by imunohistochemistry. According to the results, cloprostenol sodium had influence (P< 0,05) on cervical discharge and integrity and mRNA expression of CASP-3. For the variables related to hormonal dosage, uterine involution, histological variables (endometrial glands and degree of inflammation) there was observed effect only on moment and for the others, any kind of influence was noted. Based on the results, it can be conclude that the use of this protocol in multiparous Nelore cows with good genetic selection, adequate management and health can be unnecessary to reduce postpartum period and can promote additional spending. However, further studies should be conducted using cloprostenol or other analogs of PGF2 at different doses and moments of ... / Mestre

Orientador: Fabíola Freitas de Paula Lopes / Banca: José Antônio Visintin / Banca: Marcelo Fábio Gouvia Nogueira / Resumo: As alterações no microambiente do trato reprodutivo comprometem a competência oocitária e o desenvolvimento embrionário pré-implantacional em bovinos. Vacas Bos indicus apresentam adaptações fenotípicas e genotípicas conferindo maior resistência e tolerância à temperatura elevada quando comparadas as vacas Bos taurus, que sofrem redução nos índices de prenhez durante os meses quentes do ano. Esta infertilidade causada pelo estresse térmico é um problema de ordem multifatorial, entretanto já foi demonstrado que o oócito e embrião são extremamente susceptíveis aos efeitos deletérios da temperatura elevada. Os danos celulares desencadeados pela temperatura elevada podem ser manipulados pelo fator de crescimento semelhante à insulina-I (IGF-I), que além de minimizar a morte celular espontânea, resgata células que já iniciaram apoptose induzida por diferentes agentes ou estresses. A primeira etapa deste projeto visou avaliar o efeito dose resposta do IGF-I durante a maturação in vitro (MIV) em meio quimicamente não definido (pré-experimento 1: meio MIV - 10% de soro fetal bovino) e semidefinido (pré-experimento 2: meio MIV - 6 mg/mL de albumina sérica bovina) na competência de desenvolvimento de oócitos bovinos. Para tanto, complexos cumulus-oócito (CCOs) de vacas (mestiças Bos indicus) oriundas de abatedouro foram maturados in vitro em meio MIV não definido ou semidefinido suplementado com 0 (controle veículo), 6,25; 12,5; 25; 50; 100 ou 200 ng/mL de IGF-I por 22-24 h. Em seguida os oócitos foram fecundados (FIV) e cultivados in vitro (CIV). A adição de 25 ng/mL de IGF-I no meio MIV semidefinido ou não definido aumentou a porcentagem de oócitos clivados no dia 3 e a taxa de blastocisto no dia 8 após a fecundação. Dessa forma, a dose de 25 ng/mL de IGF-I foi utilizada na segunda etapa deste projeto, cujo objetivo foi avaliar o papel do IGF-I na competência de desenvolvimento de ... / Abstract: Microenvironmental alterations on reproductive tract compromise oocyte competence and pre-implicational embryo development in bovine. This fact is well characterized in animals exposed to heat stress. Bos indicus have fenotypic and genotypic adaptations which confers a higher tolerance to high temperatures compared with Bos taurus, suffering a reduction in the pregnancy rates during the hot months. This infertility caused by heat stress is a multifactorial problem, however it has been shown that oocyte and embryo are very susceptible to deleterious effects of high temperature. The cellular damage induced by high temperature could be manipulated by insulin-like growth factor I (IGF-I), which besides minimizing the spontaneous cell death, IGF-I rescue cells which have already initiated the apoptosis induced by different agents or stresses. The first step of this project aimed to evaluate dose-response effect of IGF-I during the maturation in vitro (MIV) in a non-defined medium (pre-experiment 1: MIV - 10% of bovine fetal serum) and semi-defined (preexperiment 2: MIV - 6 mg/mL of bovine albumin serum) in competence of bovine oocytes. Therefore, cumulus-oocyte complexes (CCOs) obtained of cows (Bos indicus crossbreed) from a slaughterhouse were matured in vitro in non-defined and semidefined MIV medium supplemented with 0 (vehicle control), 6,25; 12,5; 25; 50; 100 or 200 ng/mL of IGF-I for 22-24 h. After, oocytes were fertilized (FIV) and cultured in vitro (CIV). The adition of 25 ng/ml of IGF-I on non-defined and semi-defined MIV medium increased porcentage of cleavage on day 3 and blastocysts rate in day 8 after fertilization. In this way, 25 ng/ml IGF-I was used on second step of this experiment, which objective was to evaluate the role of IGF-I on oocyte competence of oocytes collected from Bos indicus - Nelore (NEL; n= 6) and Bos taurus-Holstein (HPB; n= 6) exposed to heat stress. Therefore, cows adapted ... / Mestre

Experiments were conducted to determine whether endogenous progesterone regulates synthesis and/or secretion of luteal oxytocin (OT). In experiment 1, mature ewes (n=5 per group) were assigned randomly to control or mifepristone (RU 486) treatment groups. Ewes were injected twice daily s.c. with vehicle or 10 mg RU 486 from days 5-7 of the estrous cycle (estrus=day 0). On day 8, following an i.v. prostaglandin F₂α (250 μg cloprostenol) challenge, venous samples were collected at frequent intervals to determine plasma OT concentrations. Plasma OT in RU 486-treated animals did not differ significantly from those of the control animals (P>0.05). In Experiment 2, ewes were injected s.c. daily with vehicle or 175 mg RU 486 from days 2-5 of the estrous cycle followed by a prostaglandin F₂α (250 μg cloprostenol) challenge on day 6. Four of five RU 486-treated ewes exhibited "split-estrus" (estrous behavior through 36 hours and again 84 to 108 hours after the onset of initial estrus). There was no significant difference in mean plasma OT or progesterone levels between treatment groups (P>0.05). Mean mature corpus luteum (CL) weights of control and RU 486-treated ewes on day 6 did not differ (394.8 ± 28.8 vs. 319.5 ± 48.3 mg; P>0.05). Mifepristone-treated ewes contained mature CL, new CL (2 of 4 ewes), and/or preovulatory follicles (≥ 10 mm, 2 of 4 ewes). Average interestrous interval for RU 486-treated ewes was 9 days longer than that of control animals (26.2 ± 2.9 vs. 17 ± 0.5 days; P<0.025). A subsequent study was conducted to determine the effects of gonadotropin-releasing hormone (GnRH)-stimulated release of luteinizing hormone (LH) on luteal OT and progesterone production in beef heifers. Ten heifers with normal estrous cycles were assigned randomly in equal numbers to a control and treatment group. On day 2 of the estrous cycle (estrus=day 0) heifers were injected with either physiological saline or 100 pg GnRH every 4 hours for 56 hours. Samples were collected 0 min pre- and 180 min post-GnRH challenge for progesterone analysis. Sixty hours after the initial injection of GnRH or saline, heifers were challenged with an i.v. injection of 500 pg prostagland in F₂α (cloprostenol) and blood was collected at frequent intervals for OT analysis. Luteal OT synthesis was suppressed (P<0.01) in heifers receiving repeated injections of GnRH compared to saline-treated control animals. Progesterone secretion was significantly greater in saline-treated animals compared to GnRH-treated animals pre- and post-challenge (1.0 ± 0.06 vs. 0.93 ± 0.11 ng/ml and 1.16 ± 0.05 vs. 0.96 ± 0.13 ng/ml, respectively; P<0.05). / Graduation date: 2003

Graduation date: 1998

To determine whether membrane-related events may be involved in attenuated luteal function after gonadotropin-releasing hormone (GnRH) administration, corpora lutea (CL) were removed from 10 beef heifers on day 7 of the estrous cycle after i.v. injection of GnRH or saline on day 2 of the cycle. Luteal slices were incubated with saline (control), luteinizing hormone (LH) or 8-bromo-cAMP for 2 h. In vivo administration of GnRH reduced LH and cAMP-stimulated progesterone production by tissue (p<0.01), but basal progesterone production was not affected (p>0.05). Luteal adenylyl cyclase activity did not differ between saline and GnRH-treated animals (p>0.05). Results of this experiment suggested that GnRH-induced alteration of bovine luteal function may be due to an effect distal to the point of cAMP accumulation. To explore further the effect of GnRH on luteal cell function, 10 heifers were injected with saline or GnRH and CL removed as above. Dissociated (mixed) and small luteal cells (SC) were cultured overnight, then incubated for 2 h with medium alone (control), LH or cAMP. In vitro treatment with LH and cAMP increased progesterone in the medium relative to controls (p<0.01), however, there was no effect of GnRH injection on progesterone production (p>0.05) nor in the percentage of large cells (LC) present in the mixed cell cultures (p=0.95). It has been previously found that the ratio of LC to SC increases in GnRH-treated animals. Many LC can be ruptured during dissociation of the CL, and it is possible that this procedure altered the number of LC, such that any differences that may have existed between the saline and GnRH-exposed CL were minimized. These data suggest that differences in the LC to SC ratio may indeed account for attenuated luteal function after exposure to GnRH. To examine if early administration of GnRH alters response of the CL to prostaglandin (PG) Fav beef heifers were injected with saline or GnRH on day 2 of the cycle (n=4/group), then injected with PGF[subscript 2��], on day 8 and the CL removed 60 min later. Blood samples were collected for oxytocin (OT) analysis at frequent intervals after PGF[subscript 2��], injection and for progesterone at 0 and 60 min. Induction of the early response gene c-jun or release of OT by PGF[subscript 2��], was not altered by GnRH injection (p>0.05). Injection of PGF[subscript 2��], decreased serum progesterone by 60 min post-injection (p<0.05), but was also unaffected by GnRH (p>0.05). These data support the hypotheses that c-jun expression and OT release are involved in PGF[subscript 2��]-induced luteolysis, but early administration of GnRH did not affect these processes. / Graduation date: 1996

Graduation date: 1994

Bos indicus influenced primiparous heifers (n = 300) and yearling Beefmaster heifers (n = 172) were evaluated to determine relationships between serial carcass ultrasound traits and ability to breed in short (45 to 90 d) breeding seasons. Data collected included carcass ultrasound traits: ribeye area (REA), intramuscular fat (IMF), rump fat (UFAT), ribfat, weight, and body condition score taken at yearling age, pregnancy determination, before breeding, and after the breeding season when pregnancy status was recorded. A logistic regression analysis was used to determine the influence of ultrasound traits and body condition on pregnancy status. Odds ratios suggested the likelihood of primiparous cattle rebreeding would have been increased by 93% if IMF would have averaged 3.5% instead of 2.5% as yearlings, or an increase in the average ribfat as yearlings from 0.287 to 0.387 cm would have increased the odds of rebreeding by 88%. Increased average body condition score of 6.5 rather than 5.5 at 30 days postpartum in primiparous cows was estimated to have increased rebreeding 367%. The odds of yearling Beefmaster heifers successfully breeding during a 45-day season would have been increased by 73% (year 1) or 274% (year 2) by increasing REA 6.4 to 6.5 cm^2 at a year of age. Steers were serially scanned beginning at approximately 265 kg of body weight through harvest in 56 day +/- 6 intervals. Data collected included ultrasound measurements (ribeye area (REA), 12th rib fat thickness (RibFat), percent intramuscular fat (IMF), and rump fat (UFAT)), weight, and carcass data. Days to choice was calculated for each steer based on a linear regression. The IMF deposition was quantified as quadratic from scans 1-6 and linear when cattle were on full feed. Prediction models at scans 1, 2, 3, 4, 5, and 6 yielded R-square values of 0.20, 0.25, 0.41, 0.48, 0.59, and 0.49, respectively for days to choice. Odds ratios suggested that if steers in this study had averaged 3.78% at day 0 rather than 2.78, the odds of cattle grading premium choice or greater would have been increased by 300%.