Data for this study was collected over a six-year period (1970 through 1975) on 217 bulls and 211 steers at the Bland Correctional Center, Bland, Virginia. Animals of this study were primarily cross-breds of Angus, Charolais, Hereford, Holstein and Simmental breeds. The objective of this study was to compare bulls and steers for growth and carcass traits. Bulls (220, 310, 449 kg) weighed more than did steers (204, 273, 381 kg) at weaning, 12 and 18 months of age, respectively, (P < .05), and scored higher on condition at weaning and 18 months of age (P< .05). Bulls (501, 281, 0.48 kg) were also heavier than steers (414, 219, 0.39 kg) for live slaughter weight, carcass weight, and carcass weight per day of age, respectively, (P< .05). Bulls and steers did not differ in ribeye area per 100 kg of carcass weight, backfat thickness, and marbling scores. Percent kidney and kidney fat per carcass weight was less in bulls (1.59%) than steers (2.58%) (P < .05). Bull carcasses graded low good whereas steer carcasses graded low to middle good. Armour tenderometer measurements were 8.25 kg and 7.09 kg for bulls and steers, respectively, (P < .05) , with any reading below 8.2 kg being of acceptable tenderness. Carcass yield grades were 1.29 and 1.90 for bulls and steers, respectively, (P < .05). The superior growth rate of bulls and the minimal sex differences in carcass quality renders the present market bias against bull beef questionable. / Master of Science

Beef cattle follow a daily, cyclical pattern of grazing, rumination, and digestion that coincides with their environment and season. Traditionally backgrounding operations hand feed any supplement in the morning. However, this practice may interrupt typical grazing patterns during early morning and subsequent rumination during the heat of the day. Self-fed concentrate feeds containing intake limiters are used to minimize the labor associated with hand feeding and allow cattle to eat throughout the day. The objectives of this experiment were to investigate the effect of supplement feeding time on performance and grazing behavior of backgrounded beef steers. Crossbred beef steers (n = 54; 7 ± 1 m of age; body weight, BW = 243 ± 2 kg) were sourced from a regional cattleman's association and grazed on tall fescue pasture (Festuca arundinacea) at the Southwest Virginia Agricultural Research and Extension Center in Glade Spring, VA from October 1 to November 7, 2019. Cattle were stratified by BW and source and allotted to 9 pasture groups (6 steers per pasture) in a randomized design. Pasture groups were randomly assigned to 1 of 3 treatments (3 pastures per treatment): 1) steers hand-fed supplement at 0930 h (AM), 2) steers hand-fed supplement at 1330 h (PM), or 3) steers fed a self-feeder supplement with an intake limiter (SELF). Hand-fed groups were fed a commercial commodity blend (38% corn gluten feed pellets, 30% cracked corn, 22% soy hull pellets, and 10% dried distillers grains) daily at 1.5% BW on an as fed basis. The SELF supplement was a blend of 70% cracked corn and 30% of an intake limiter-containing pellet that was formulated to maintain voluntary supplement intake at 1.5% BW on an as fed basis. Cattle were weighed on 2 consecutive days at the start and end of the experiment, and feed adjustments were made following three interim weigh-ins. Motion-sensing cameras were used to monitor cattle visits to the feeder and waterer portions of the pasture. Treatment did not impact (P = 0.13) BW, flesh condition score (FCS), dry matter intake (DMI), average daily gain (ADG), and backfat thickness. SELF steers were significantly more feed efficient than the AM supplemented groups (P = 0.03) and tended to be a greater G:F ratio (P = 0.08) for the PM supplemented groups vs. AM supplemented steers. Steers with access to a self-feeder showed behavioral differences to hand supplemented cattle, with more feeder visits in a 24 h period (P = 0.01) compared to AM and PM steers. Despite these behavioral observations, any disruption in natural grazing behavior was not dramatic enough to negatively influence backgrounded cattle growth performance. / Master of Science / Grazing beef cattle tend to follow a general pattern of grazing, rumination, and digestion that coincides with their environment and the time of year. Backgrounded cattle managed in pasture-based systems are traditionally offered supplemental feedings in the morning. However, this practice could be decreasing how efficiently cattle utilize forage resources. Natural grazing behaviors are more intense preceding the heat of the day and interruption of morning grazing bouts could decrease forage intake by causing cattle to come to the feeder to consume supplement feedings. To examine how feeding time potentially influences performance and grazing behavior of backgrounded beef cattle, 52 crossbred beef steers 7 to 8 months of age and weighing 243 kg were grazed on tall fescue pastures at the Southwest Virginia Agricultural Research and Extension Center from October 1 to November 8, 2019. Cattle were supplemented with either a commodity blend or cracked corn mixed with an intake limiter. Cattle were sourced from 4 local producers and allotted to 9 pastures by body weight (BW) and source. Pasture groups were randomly assigned to 1 of 3 treatments (3 pastures per treatment): 1) steers hand-fed supplement at 0930 h (AM), 2) steers hand-fed supplement at 1330 h (PM), or 3) steers fed a self-feeder supplement with an intake limiter (SELF). Hand-fed groups were fed a commercial commodity blend (38% corn gluten feed pellets, 30% cracked corn, 22% soy hull pellets, and 10% dried distillers grains) daily at 1.5% BW on an as fed basis. The SELF supplement was a blend of 70% cracked corn and 30% of an intake limiter-containing pellet that was formulated to maintain voluntary supplement intake at 1.5% BW on an as fed basis. Adjustments were made to the average BW of pasture groups, following three interim weigh dates at d 11, d 21, and d 30, to keep intake levels accurately at 1.5% BW. Flesh condition scores (FCS) were assigned on a scal of 1 to 9, with 1 considered emaciated and 9 excessively fat. 12th rib fat thickness (FT) was measured using an Aloka 500SC ultrasound. Both measurements were taken on the first and final day of the experiment. Motion-sensing cameras were installed in each pasture to capture pictures every one-minute following motion detection. Subsequent pictures were used to analysis the number of feed and water visits, along with time of day, in an attempt to characterize intake behavior. There were no major differences seen by treatment groups for BW, flesh condition score, DMI, ADG, and backfat thickness. Cattle on the SELF treatment had greater G:F than AM, with PM cattle being intermediate and not different than either. Steers with access to a self-feeder visited the feeder more than double the number of times in a 24 h period than either of the hand supplemented group. Despite differences in observed cattle behavior, any disruption in natural grazing behavior did not negatively influence performance of backgrounded steers.

Estimating feed efficiency in grazing environments is challenging due to difficulties in quantifying food intakes and diet choices in free-grazing animals. The plant-wax marker technique may be a useful tool to redress this problem. However, its reliability needs to be validated before its wider application. This study was designed to assess the reliability of plant-wax markers for estimating botanical composition of test diets, and diet choices in beef cattle, and provided opportunities to evaluate efficiency in growing heifers. To test estimation of botanical composition, samples of red clover and fescue hay were mixed to form test diets containing 0-100% of either forage. To test estimation of diet choices, 24 heifers from large and moderate frame size lines were evaluated at two instances. Cubed red clover and fescue hays were offered ad libitum. After an acclimation period, feed intakes and body weights were collected for 10 days; fecal samples were collected for the final 5 days. Hydrocarbons and alcohols were quantified with gas chromatography. Estimates were based on least squares. Operator expertise affected measured concentrations of shorter-chained n-alkanes (P<0.041) and long-chain alcohols (P<0.02). Still, overall reliability of the technique was unaffected. Large and moderate framed animals did not differ in efficiency (P>0.05), although large framed animals had increased red clover intakes (P<0.01). Once corrected for fecal losses of n-alkanes, diet choices were estimated accurately. Plant-wax markers provided reliable estimates of botanical composition of diets, and diet choices of animals, suggesting it is a valuable tool to assess efficiencies of grazing cattle. / Master of Science

Thesis (MScAgric) -- Stellenbosch University, 2009. / ENGLISH ABSTRACT: The two main determinants of post-slaughter processing outcomes are rates of pH and temperature decline. Muscle pH and temperature interact continuously during rigor development to affect both the muscle contracture and proteolytic enzyme activity. The pH, however, can be manipulated independently of temperature by electrical inputs applied to the carcass. Electrical inputs that should be considered range from electrical stunning to the various forms of electrical immobilisation (EI) and stimulation (ES) that occur during and after the dressing procedures. EI is used to suppress convulsions that occur after electrical stunning to ensure operator safety to maintain high throughputs speeds while ES is used to induce rapid tenderisation, although having other biochemical and biophysical effects on meat. The objective of the study was to supply information on the effect of different EI and ES treatments, frequencies and pulse widths on the meat quality of beef. There are very little data on the effect of EI when it is combined with ES on meat quality. This study used two different EI frequencies (high – 800 Hz; HFI and low – 15 Hz; LFI) combined with either high (1040 V; HVS) or medium (300 V; MVS) voltage ES to study the effect of these treatments on meat quality. In the following experiment the EI waveform and ES was standardised using HFI with MVS with the frequency being changed to either 5, 15 or 50 Hz. Then the pulse width of the waveform was changed to 0.1, 0.5, 1 and 10 ms to optimise the ES system. Meat quality measurements were made from the Longisimmus dorsi (LD) and Semimembranosus (SM) after 1, 5 and 9 days of chilled storage at 0 C. The LD (shear force = 94.3±2.2; cooking loss = 26.85±0.29; retail drip = 0.996±0.037; storage drip = 2.78±0.155; WBC (water binding capacity) = 45.4±0.36) had significantly lower shear force and higher water binding capacity than the SM (shear force = 103.7±2.5; cooking loss = 34.63±0.25; retail drip = 2.12±0.103; storage drip = 3.63±0.245; WBC = 59.3±0.57). Day of assessment (Day 1 = 122.7±2.9; Day 5 = 87.7±2.2; Day 9 = 81.0±2.4) had a significant effect on tenderness of the LD as shear force declined with an increase of day of assessment. The LFI HVS (storage drip = 3.30±0.223; shear force = 102.9±4.5) produced significantly greater drip during storage and shear force values when compared to the HFI followed by either HVS (storage drip = 2.45±0.261; shear force = 85.2±4.0) or MVS (storage drip = 2.60±0.178; shear force = 94.2±4.2) in the LD, probably attributable to different rates of pH decline post mortem. LFI HVS (a* = 20.79±0.31; chroma = 22.92) and LFI MVS (a* = 20.24±0.27; chroma = 22.23±0.30) had a redder and more vivid bloomed colour than HFI HVS (a* = 19.71±0.33; chroma = 21.49±0.37) and HFI MVS (a* = 20.00±0.27; chroma = 21.98±0.31), while LFI HVS (a* = 15.27±0.40) and HFI MVS (a* = 14.64±0.29) had a redder colour compared to HFI HVS (13.85±0.35) at day 9 for the LD. The oxygen consumption rate (MTT assay) correlated inversely linear (r = -0.63 and -0.73) with the a* values 24 hrs post mortem allowing for 3 hrs of bloom. Stimulation with 15 Hz (0.47±0.040) and 5 Hz (0.41±0.045) had a higher pH decline (ΔpH) during stimulation than 50 Hz (0.29±0.027). Shear force measurements and cooking loss percentage were obtained from the LD after 24 hrs of chilled storage at 0 C. There were no difference between the stimulation treatments for shear force (15 Hz = 121.3±3.3; 5 Hz = 123.8±7.6; 50 Hz =114.8±7.94), while cooking loss was higher in 15 Hz (28.8±0.47) than 50 Hz (25.9±0.71) which correlated (r = 0.43; p = 0.01) with ΔpH. There were no differences between 10 ms (0.46±0.020), 1 ms (0.43±0.020) and 0.5 ms (0.44±0.019) pulse widths on the ΔpH while 0.1 ms (0.33±0.020) had a lower decline. Stimulation with a 1 ms (94.6±5.6) pulse width had the lowest shear force that varied from 10 (111.3±3.8) and 0.1 ms (111.3±5.8). While cooking loss (0.1 = 25.3±0.48; 0.5 = 26.9±0.67; 1 = 25.9±0.63; 10 = 25.5±0.66) and water-holding capacity (0.1 = 36.1±1.60; 0.5 = 37.3±1.42; 1 = 37.5±1.15; 10 = 36.9±1.45) was not affected in the LD after 24 hrs of chilled storage at 0 C. Colour measurements on the SM indicated that a 0.1(a* = 19.38±0.50; chroma = 22.70±0.51), 0.5 (a* = 20.89±0.49; chroma = 24.34±0.56) and 10 ms (a* = 19.69±0.46; chroma = 22.98±0.58) pulse width had a deeper red and a more vivid colour than 1 ms (a* = 16.66±0.37; chroma = 19.99±0.32) at day nine of retail display. In conclusion, HFI improves meat quality when combined with either HVS or MVS and that MVS either improves (colour stability) or has no adverse effects on meat quality (tenderness and WBC) in relation to HVS when combined HFI. In addition, it shows that there are alternative electrical parameters to voltage that can be used to change the pH decline and by changing frequency and pulse width, subtle changes can be made to an ES system. Since every abattoir is different due to layout, chiller space and cooling regime these electrical parameters can be modulated to optimise an electrical stimulation system without expensive modification to the whole system. / AFRIKAANSE OPSOMMING: Die tempo van pH en temperatuur daling is die twee hoof bepalings van na-slag prosseserings uitkomste. Spier pH en temperatuur het ’n gedurige interaksie tydens rigor ontwikkeling en beïvloed die spier sametrekking en proteolitiese ensiem aktiwiteit. Die spier pH kan onafhanklik van temperatuur gemanipuleer word, deur elektriese golfvorms deur die karkas te stuur. Die elektriese golfvorms wat in ag geneem moet word varieer van elektriese impulse tydens bedwelming tot die verskeie golfvorms van elektriese immobilisasie (EI) en stimulasie (ES) wat gebruik kan word gedurende en na die slagproses. EI word gebruik om konvulsies te beheer wat onstaan na elektriese bedwelming om werker veiligheid en hoë deurvloei tempos te verseker, terwyl ES die verouderings proses versnel, alhoewel dit ander biochemiese en biofisiese uitwerkings het op vleis. Die studie het verneem om inligting te verskaf oor die effek van verskillende EI en ES kombinasies, frekwensie en puls wydtes op die kwaliteit van beesvleis. Daar is baie min inligting van EI in kombinasie met ES se effek op vleis kwaliteit. Die studie het gebruik gemaak van twee verskillende (EI) frekwensies (hoog – 800 Hz; HFI and laag – 15 Hz; LFI) wat gekombineer is met of hoë (1040 V; HVS) of medium (300 V; MVS) spanning ES se effek op vleis kwaliteit. In die volgende eksperiment was die EI golfvorm en die ES gestandardiseer en HFI met MVS was gebruik met die frekwensie wat verander is tussen 5, 15 en 50 Hz. Daarna was die pulse wydte van die golfvorm verander tussen 0.1, 0.5, 1en 10 ms om die ES sisteem te optimiseer. Vleis kwaliteit van die Longisimmus dorsi (LD) en Semimembranosus (SM) spiere was bepaal na 1, 5 en 9 dae van verkoelde storing teen 0°C. Die LD (skeurkrag = 94.3±2.2; kookverlies = 26.85±0.29; kleinhandel drup verlies = 0.996±0.037; storing drip verlies = 2.78±0.155; WBV (water bindings vermoë) = 45.4±0.36) het ‘n betekenisvolle laer skeurkrag waardes en hoër water bindings vermoë gehad in vergelyking met die SM (skeurkrag = 103.7±2.5; kookverlies = 34.63±0.25; kleinhandel drupverlies = 2.12±0.103; bergings drupverlies = 3.63±0.245; WBV = 59.3±0.57). Die dag van assesering (Dag 1 = 122.7±2.9; Dag 5 = 87.7±2.2; Dag 9 = 81.0±2.4) het ’n betekenisvolle effek gehad op die skeur krag waardes en het afgeneem met ’n toename in die dag van assesering. LFI HVS (storing drupverlies = 3.30±0.223; skeurkrag = 102.9±4.5) het betekenisvolle hoër vog verliese gehad tydens verkoelde storing en skeur krag wanneer dit vergelyk word met HFI gevolg deur of HVS (storing drupverlies = 2.45±0.261; skeurkrag = 85.2±4.0) of MVS (storing drupverlies = 2.60±0.178; skeurkrag = 94.2±4.2). LFI HVS (a* = 20.79±0.31; chroma = 22.92) en LFI MVS (a* = 20.24±0.27; chroma = 22.23±0.30) het ‘n helder en dieper rooi kleur gehad in vergelyking met HFI HVS (a* = 19.71±0.33; chroma = 21.49±0.37) en HFI MVS (a* = 20.00±0.27; chroma = 21.98±0.31), terwyl LFI HVS (a* = 15.27±0.40) en HFI MVS (a* = 14.64±0.29) ’n rooier en helderer kleur as HFI HVS (13.85±0.35) gehad het in die LD. Die suurstof verbruik tempo (MTT analise) korreleer omgekeerd (r = -0.63 en -0.73) met die a* waardes 24 hr post mortem na 3 hr van blootstelling van lug. Stimulasie met 15 (0.47±0.040) en 5 Hz (0.41±0.045) het ’n hoër pH daling (ΔpH) tydens stimulasie as 50 Hz (0.29±0.027). Skeurkrag waardes en kookverliese is verkry vanaf die LD na 1 dag van verkoelde storing teen 0 C. Daar was geen verskil tussen stimulasie frekwensie se effek of skeurkrag (15 Hz = 121.3±3.3; 5 Hz = 123.8±7.6; 50 Hz =114.8±7.94) nie, terwyl die kookverliese hoër was in die 15 Hz (28.8±0.47) as 50 Hz (25.9±0.71) behandeling wat gekorreleer (r = 0.43; p = 0.01) het met ΔpH. Daar was geen verskill tussen 10 (0.46±0.020), 1 (0.43±0.020) en 0.5 ms (0.44±0.019) puls wydtes se effek op ΔpH nie, terwyl 0.1 (0.33±0.020) ms ‘n kleiner afname tot gevolg gehad het. Stimulasie met ‘n 1 ms (94.6±5.6) puls wydte het die laagste skeurkrag gehad wat verskil het van die 10 (111.3±3.8) and 0.1 ms (111.3±5.8) puls wydtes, terwyl kookverliese (0.1 = 25.3±0.48; 0.5 = 26.9±0.67; 1 = 25.9±0.63; 10 = 25.5±0.66) en waterbindingsvermoë (0.1 = 36.1±1.60; 0.5 = 37.3±1.42; 1 = 37.5±1.15; 10 = 36.9±1.45) nie beïvloed was nie. Kleur metings van die SM het getoon dat ‘n 0.1 (a* = 19.38±0.50; chroma = 22.70±0.51), 0.5 (a* = 20.89±0.49; chroma = 24.34±0.56) en 10 ms (a* = 19.69±0.46; chroma = 22.98±0.58 puls wydtes die helder en dieper rooi kleur gehad het as 1 ms (a* = 16.66±0.37; chroma = 19.99±0.32) teen dag 9 van kleinhandel vertoning. Ter opsomming, lei HFI tot beter vleis kwaliteit wanneer dit gekombineer word met of HVS of MVS. Verder lei MVS tot of ’n verbetering (kleur stabiliteit) of geen nadelige effek op vleis kwaliteit (sagtheid en WBV) in vergelyking met HVS wanneer dit gekombineer word met HFI. Die studie bewys ook dat daar ander elektriese parameters bestaan as spanning, wat verander kan word om die pH daling te beïvloed. Deur die frekwensie en pulswydte te verander, kan klein veranderinge aangebring word aan ’n ES sisteem. Elke abattoir is verskillend as gevolg van uitleg, koelkamer spasie en verkoelings tempo en hierdie elektriese parameters kan verander word om ’n ES sisteem te optimiseer sonder enige duur veranderinge aan die hele sisteem.

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

Linseed meal (LSM) was fed to ovariectomized ewes exposed to estradiol 17-ß (E2) implants over time, and LSM was supplemented to beef cows during late gestation and early lactation to evaluate the estrogenic potential of the phytoestrogen secoisolariciresinol diglycoside (SDG) found in LSM. Forty-eight ovariectomized ewes were fed a diet containing 12.5% LSM for 0, 1, 7, or 14 d and implanted with estradiol-17ß (E2) for 0, 6, or 24 h before tissue collection. Uterine cellular proliferation, vascularity, and the expression of the angiogenic factors and their receptors were recorded. There was an interaction of LSM and E2 on uterine mass (P = 0.05). At 24 h of E2 exposure, proliferation was reduced (P < 0.001) when ewes were fed for 14 d compared to being fed 0 or 1 days. There was a LSM x E2 interaction (P ≤ 0.03) on VEGF receptor-2 (KDR) and hasicfihrohlast growth factor receptor (FGFR2) decreasing by 24 h E2 exposure. Exposure of LSM and E2 may impact the estrogenic response of sensitive tissue. Two studies were conducted to examine the effects of supplementing beef cows with LSM during late gestation or early lactation on calf growth and development. In Experiment 1, multiparous cows received either LSM or a control (CON) supplement (approximately 10% diet dry matter) for the last 60 d of gestation. Offspring weights, ADG, heifer age at puberty, conception percentage and steer carcass characteristics were recorded. In Experiment 2, multiparous cows received LSM or CON supplements (approximately 10% diet dry matter) during the first 60 d of lactation, and only heifer calf development performance was observed and recorded. Heifer calf weight, average daily gain, and attainment of puberty were assessed. For both experiments, birth weight, weaning weight and ADG were not affected (P > 0.31) by LSM supplementation. While final body weights were heavier (P = 0.04) for steer calves in Experiment 1, there was no effect (P = 0.09) of supplementation on carcass characteristics. In Experiment 1 and 2, attainment of puberty in heifer calves was not influenced (P > 0.58) by supplement type. Linseed meal supplementation during late gestation or early lactation does not appear to have a negative impact on calf growth, onset of puberty in heifer calves, or steer carcass quality, implicating that it may make a good supplement choice in cattle.

Excessive dietary protein may affect MP use because of energetic costs of excreting excess N. Amino acids also may influence post-ruminal digestion. Therefore, two experiments were designed to evaluate the effects of MP intake and post-ruminal flow of AA on growth performance and pancreatic digestive enzymes. In experiment 1, treatments supplied different amounts of MP intake to cattle and the effects on growth performance and feeding behavior were evaluated. In experiment 2, duodenal infusion of glutamate or casein was examined and the effects on pancreatic enzymes were measured. Experiment 1 suggests that feeding steers 906 g MP/d in finishing diets supplied enough MP for the greatest growth performance and carcass characteristics. Interestingly, MP intake caused different responses on feeding behavior with greater effects on steers fed 626 and 1444 g MP/d. In experiment 2, casein infusion increased α-amylase activity but not trypsin activity. Glutamate did not influence pancreatic digestive enzymes.

The aim of the study was to determine the effects of different dietary fibre levels on methane production and growth performance of Bonsmara and Nguni steers. Nine Bonsmara and nine Nguni male weaners aged 8 – 9 months were used for the study. On arrival, animals were fed Eragrostis curvula hay on ad libitum basis for the first 14 days as part of adaptation to the feedlot environment. Animals were gradually adapted to treatments to prevent metabolic disorders. The study was conducted as a 3 x 3 x 2 factorial experiment. Treatments were allocated in a completely randomised design. Data were submitted to analysis of variance (ANOVA). Student's t-LSD was calculated at the 5 % level (P < 0.05) to compare treatment means for significant effects. Feeding a diet that is low in crude fibre content had significantly increased (P < 0.05) growth performance in both breeds. Bonsmara steers had significantly higher growth performance (P < 0.0001) across all treatment diets compared to Nguni steers. High rumen total microbial count was observed in animals that received diets with low crude fibre. Reducing dietary crude fibre resulted in reduced methane production. Low dietary fibre showed low rumen archaea counts. There was a positive correlation between rumen pH and methane emission for both Bonsmara (R2 = 0.9105) and Nguni (R2 = 0.9517) steers. However, a negative correlation was observed between rumen total microbial count and feed conversion ratio for both Bonsmara (R2 = 0.8286) and Nguni (R2 = 0.7208) steers. The low rumen archaea counts were detected from the Bonsmara. Feeding diets with low fibre levels is recommended for improving growth performance and reducing methane production for Bonsmara and Nguni steers. / Agriculture and  Animal Health / M. Sc. (Agriculture)

Total weaning weight records of 29,832 Angus and 15,765 Hereford calves born during 1953 through 1983 in Virginia were used to evaluate phenotypic and genetic trends for adjusted weaning weight (AWWT), weaning weight ratio (WWR) and deviation of AWWT from the mean AWWT of the contemporaries (DEVN). Two approaches, namely the regression techniques and maximum likelihood (ML) procedure were taken to estimate the above trends. The estimates of annual phenotypic trend for AWWT in the Angus and Hereford breeds were .96 and .82 kg/yr, respectively. The sire and dam genetic trends obtained from both approaches for the traits of interest were positive and significant; however, the estimates from the regression analyses were slightly higher than those- from the ML procedure. The estimates of one-half of the sire genetic trends obtained from ML procedure for WWR and DEVN were .40 ± .04 ratio units/yr and .72 ± .07 kg/yr in the Angus breed and the corresponding values for the Hereford breed were .25 ± .06 ratio units/yr and .45 ± .12 kg/yr. The estimates of one-half of the darn trends for the corresponding traits were .32 ± .02 ratio units/yr and .55 ± .04 kg/yr for Angus and .21 ± .03 ratio units/yr and .30 ± .07 kg/yr for Herefords. The application of adjustment factors (to eliminate the bias due to non-random mating and culling levels) to estimates of sire genetic trends in the regression analyses produced estimates more similar to the estimates obtained from the ML procedure. The average annual genetic trends over the study period from the ML procedure for AWWT were 1.27 kg/yr for Angus and .75 kg/yr for Herefords. / Ph. D.