Three balance experiments were conducted to determine the effects of dietary fiber on mineral balance and intestinal.morphology of growing pigs. Fiber sources were added to corn-soybean meal diets at levels which increased neutral-detergent fiber levels by 6 to 8%. In experiment 1, 10% oat hulls (OH) decreased Ca (P<.06) and Zn (P<.01) balances of pigs after a 7 d feeding period. Wheat bran (20%) increased Mg intake and balance (P<.02), but did not affect Ca and Zn balances. In experiment 2, pigs were fed diets (with or without supplements of Zn, Fe and Mg) containing 15% OH or soybean hulls (SH) for 5 d or 26 d. SH increased Fe intake and balance (P<.01) and ( Mg absorption (P<.01). Compared with balances at 5 d, Zn balance was similar, while Fe and Mg balances were higher at 26 d for pigs fed the basal (P<.05) or SH (P<.01) diets. However, Zn balance was lower (P<.05) at 26 d 1 but Fe balance did not change over time for pigs fed the OH diets. At each time period, Zn balance was not different between pigs fed the basal or high-fiber diets. In experiment 3, Ca, Zn and Mg absorption were not affected by 15% OH or SH or 20% alfalfa meal (AM) after 67 d or 39 d, although SH and AM increased Fe balance (P<.01). Intestinal surface morphology of 12 pigs fed in experiment 3 was examined by scanning electron microscopy. Villus morphology was variable in jejunum, ileum and colon, although evidence of villus blunting and folding accompanied by erosion of microvilli and loss of epithelial cells was observed in small intestine of some pigs fed the SH and AM diets. Damage was not consistent in all sites examined in individual pigs, and did not occur in all pigs fed any specific diets. Although Ca and Zn balances were decreased by OH in two of the balance trials, the inability of OH to consistently decrease mineral balance suggests that the ability of the pig to adapt to different diets may be sufficient to overcome the mild inhibitory effect on mineral absorption of some fiber sources. When viewed together, the results of the balance trials indicate that moderate amounts of dietary fiber have a minimal negative impact on mineral balance of pigs fed practical corn-soybean meal diets. However, the results also indicate that fiber sources such as SH and AM, are rich sources of some minerals for the pig, particularly Fe. Evidence of intestinal damage was evident in pigs fed the high-fiber diets. However, not all animals fed a particular diet were affected, which suggests that some pigs within a given population may be susceptible to detrimental effects of dietary fiber on intestinal structure or function. / Ph. D.

Determining the energy values of feed ingredients for poultry is of great concern, especially since production efficiency is associated with profit margins. Therefore, accurate, precise, and reproducible energy values for feed ingredients are of the utmost importance in formulating an economical diet. An important aspect in determining the apparent metabolizable energy (AME) of a feed ingredient is the procedure employed in the drying of excreta samples. During sample preparation, substantial grinding losses were incurred amounting to 3.5 to 5.2% of the dried sample weight. Also moisture uptake during sample grinding accounted for a 1.9 to 3.9% increase in sample weight. To properly account for such losses, freshly collected excreta samples should be weighed, oven-dried at 40 C, reweighed, allowed to equilibrate with atmospheric moisture, weighed, ground, reweighed, and stored in air-tight containers for subsequent analyses. From the oven-drying of feed and excreta samples at various temperatures, a linear decrease in sample weight occurred with increasing drying temperatures. When dried at 100 C or less, the energy content of feed and excreta samples remained unchanged, but increased significantly at higher temperatures. The nitrogen composition of feed and excreta samples exhibited a similar trend, but a significant loss of excreta nitrogen (2%) occurred at 100 C. The loss of excreta nitrogen at a temperature of 100 C is of relatively minor consequence in the determination of metabolizable dry matter, but is of major concern in nitrogen balance studies. Extraction of feed and excreta samples with N,N-dimethylformamide and titration with Karl Fischer reagent indicated that significant amounts of water were retained by samples dried at 40, 60, and 80 C. However, at temperatures of 100 C or greater, little water was retained but sample decomposition occurred. A drying temperature of 90 C or the Karl Fischer method may yield a more accurate value for the dry matter of feed or excreta. When seven roosters were subjected to a total collection method for five consecutive days, individual birds were better metabolizers of dry matter and energy than others. By either a voluntary intake method or by a total collection method, values for the nitrogen-corrected metabolizable energy of corn were similar. The total collection method proved to be more reliable since it provided the least amount of variation when <u>ad libitum</u> feed intake and total excreta output were measured over a period of several days. In past experiments, adding fats to a test diet at the expense of cerelose in amounts no greater than 20% of the diet to determine the metabolizable energy of the fat has been associated with a high degree of variability. From the force-feeding of fats at levels to 100%, the variation associated with the metabolizable energy value of a fat was greatly reduced. The methodology presented here provided reliable estimates and detected differences between the metabolizable energy of two feed-grade fats in comparison to previous methods. / Ph. D. / incomplete_metadata

Experiments were conducted to investigate the effects of E. coli and rotavirus as causative agents in producing infectious stunting syndrome of poults. The syndrome, as it occurs commercially, was characterized in two experiments to produce decreased digestible dry matter and nitrogen as well as increased excreta nitrogen and gross energy content of affected poults. The effects of E. coli and rotavirus on the nutritional performance of poults were compared to the commercial syndrome by digestibility trials and assay of intestinal mucosaI enzyme activities. The strain of E. coli used in these experiments was isolated from the yolk sac of stunted poults. Inoculation of day-old poults was done orally in one experiment and via the yolk sac in another series of experiments. Experiments were designed in a factorial arrangement of E. coli inoculation and dietary protein level (28 vs. 22%). Oral administration of the pathogenic E. coli at a low dose (.1 ml of a 10⁻² dilution of a 24-hr culture) to day-old poults produced a significant increase in feed efficiency by 21 days of age for birds fed either 28 or 22°0 protein diets. In this case, E. coli apparently was established as part of the normal intestinal microflora of the turkey without producing a toxic response. Similar concentrations of E. coli (10⁻³ and 10⁻² dilutions) inoculated into the yolk sac of day-old poults resulted in significant mortality and morbidity. The lower dilution (10⁻³) produced the desired response of stunted poults without substantial mortality. Body weight gain and feed consumption were severely decreased by E. coli inoculation at both levels of protein (28 or 22%). The 28% protein diet alleviated the reduction in feed consumption for birds infected with the lower concentration of E. coli. The 10⁻² dilution caused substantial mortality and similar responses on body weight at both levels of protein. A malabsorption of nutrients accompanied E. coli infection in spite of reduced feed consumption as indicated by increased excreta nitrogen and gross energy content for all infected poults. In three experiments, rotavirus was orally inoculated into poults over 21 days of age previously fed either 28 or 22% protein diets. The response of rotavirus was variable in the three experiments, however, the low protein diet (22%) increased the poults susceptibility to rotavirus infection. Serum antibodies to rotavirus were detected in all poults tested prior to inoculation. Ubiquitous in nature, rotavirus appears to produce clinical signs of infection in combination with stress on the poults. Effects of rotavirus on digestibility parameters were inconclusive. In experiments with either rotavirus or E. coli, activities of intestinal mucosal enzymes were found to vary more between poults within a treatment than by any effect of the various treatments. / Ph. D.

Two feeding trials were conducted involving diets supplemented with soybean meal, dried brewers, and wet brewers grains. The first trial involved 24 first-calf heifers averaging 82 d postpartum. After a 20 d protein depletion period in which a 9.4% CP diet was fed, cows were randomly assigned to a 2 x 3 factorial where pelleted (P) or unpelleted (UP) soybean meal supplemented corn diets to 12.2% (L), 15.4% (M), and 18.1% (H) crude protein. During depletion, milk production, dry matter intake, and yields of milk protein, fat, and solids decreased in the range of 15 to 25%. However, these all increased to pre-depletion levels after 26 d of repletion. Considering repletion response separately resulted in no significant differences between P and UP for milk production and constituents, feed intake, and plasma urea. However, using depletion to covariably adjust means resulted in P diets favoring greater milk production (P < .01) than UP as well as protein, fat, and solid yields. This response may be caused by a significant increase in feed intake for P diets. Use of a depletion period did increase precision of results but its use in practical feeding trials is controversial. Results in milk, milk protein, fat, and solid yields, and plasma urea were linear with protein level (L vs H). The second trial involved 44 multiparous cows averaging 114 d postpartum. Eight cows remained on a control (CON) diet of 11.7% CP while all others were randomly assigned in a 3 x 3 factorial in which dried (DBG) and wet brewers grains (WBG), and soybean meal (SBM) supplemented the CON to 14.8 (L), 16.3 (M), and 18.0% (H) CP. Diet composition varied in corn silage and ensiled ground-corn but alfalfa silage was constant on a dry matter basis. All diets were superior to CON in milk production and constituent yield. Brewers diets were superior to SBM for milk yield, protein, and solid yields. Part of this response may be related to superior intake for diets containing brewers and lower rumen ammonia and plasma urea. Cows receiving brewers diets have higher intakes than SBM and brewers appear to be utilized more efficiently. For mid-lactating cows an increase in milk at 18.0% CP resulted from brewers diets but not SBM. The H level resulted in a significant increase in milk yield and protein (kg) but also had the highest plasma urea and rumen ammonia level. / M.S.

Thesis (MScAgric) -- Stellenbosch University, 2004. / ENGLISH ABSTRACT: The ruminant has the ability to utilize forages more efficiently than any other production animal. The utilization of forage fibre is an important aspect of ruminant production systems, as this is the main source of energy available to the animal. The availability of high-fibre forage nutrients is, however, restricted by cell wall degradability, and since low quality forages contribute a great deal to ruminant production systems worldwide, the improvement of this degradation process is of major economic importance. The use of exogenous fibre degrading enzymes has been proposed as a means of enhancing this process, with positive results being obtained from in vitro studies incorporating exogenous enzyme preparations. Positive in vivo results with regard to forage digestibility and other animal production parameters have consequently also been obtained following the addition of exogenous fibre-degrading enzyme preparations to the ruminant diet. Two initial screening experiments were undertaken in order to identify fungal enzyme preparations that may have a positive effect on in vitro fibre degradability. The initial screening employed an in vitro organic matter digestibility technique, and was successful in identifying at least six enzyme preparations displaying enhanced digestibility results that were statistically significant. A second in vitro gas production procedure was used to confirm results obtained from organic matter digestibility assays, as well as to increase screening capacity in order to evaluate new enzyme preparations more time-efficiently. Statistical analysis of results obtained from the secondary screening identified various enzyme candidates producing promising results. Only one of these, Abo 374, proved to be statistically superior to the control and other enzyme preparations. A growth trial was subsequently conducted to assess the performance of this enzyme in vivo. The trial involved individual feeding of 32 Dohne Merino ram lambs grouped according to weights into four groups consisting of 8 lambs each. Each group represented a specific application level of enzyme to the wheat straw component of a high fibre diet, amounting to 10, 5, or 1 ml enzyme supematant/kg straw. The enzyme was diluted with water at appropriate rates to obtain an application rate of 300ml/kg straw. The fourth (control) group was treated with water at the same application rate. The trial was conducted over a period of six weeks, during which feed intakes, weekly weight gains, as well as feed conversion efficiencies were recorded. Results suggested significant weight gains in the high (10ml/kg) and medium (5ml/kg) treatment groups, indicated by a P-value of 0.04. Similarly, feed conversion efficiencies were improved for above-mentioned groups (P=0.05), while feed intakes did not differ significantly between the four experimental groups. / AFRIKAANSE OPSOMMING: Die herkouer besit die vermoee om ruvoere beter as enige ander produksiedier te kan benut. Die gebruik van ruvoervesel is 'n belangrike aspek van herkouer produksiesisteme, aangesien ruvoere die hoof bron van energie aan die herkouer verskaf. Die beskikbaarheid van hoe-vesel ruvoer nutriente word egter beperk deur die degradeerbaarheid van die selwand, en aangesien lae kwaliteit ruvoere 'n groot bydrae tot wereldwye herkouer-produksiesisteme maak, is die moontlike verbetering van hierdie degraderingsproses van groot ekonomiese belang. In 'n poging om hierdie verteringsproses te help bevoordeel, is die gebruik van eksogene veselverterende ensieme ondersoek, en positiewe resultate is verkry wanneer hierdie ensieme in in vitro studies gebruik is. Goeie verbeterings ten opsigte van ruvoer verteerbaarheid en ander diereproduksie parameters is ook verkry deur middel van in vivo studies waar eksogene ensieme by die ruvoer van herkouers gevoeg IS. Twee eksperimente is ondemeem in 'n poging om ensiempreparate wat 'n moontlike positiewe effek op in vitro veselvertering mag he, te identifiseer. Die eerste, 'n in vitro organiese materiaal verteerbaarheid tegniek, was suksesvol in die identifisering van minstens ses ensiem preparate wat statisties betekenisvolle verbeterings ten opsigte van verteringsresultate geproduseer het. 'n Tweede in vitro gasproduksie prosedure is vervolgens gebruik om resultate verkry vanaf die eerste tegniek, te bevestig, asook om evalueringskapasiteit te vergroot en sodoende, nuwe ensiempreparate meer tydseffektief te evalueer. Statistiese evaluering van resultate verkry uit die tweede in vitro tegniek het 'n reeks ensieme met positiewe resultate opgelewer. Een van hierdie, Ab0374, het statisties betekenisvolle resultate ten opsigte van die kontrole, sowel as ander ensieme getoon. In 'n volgende eksperiment is 'n groeiproef gedoen om die effektiwiteit van hierdie ensiem in vivo te toets. In die proef is 32 Dohne Merino ramlammers op grond van hul gewig in vier groepe van agt skape elk verdeel, en individueel gevoer. Die groepe het verskillende toedieningsvlakke van die toetsensiem, toegedien tot die koringstrooi komponent van 'n hoe-vesel dieet, ontvang. Toedieningsvlakke was 10, 5, of lml ensiemkonsentraat/kg strooi. Elke groep se ensiemkonsentraat is verdun met die toepaslike hoeveelheid water om 'n toedieningsvlak van 300ml ensiemoplossing/kg koringstrooi te verkry. 'n Vierde groep is behandel slegs met water teen dieselfde toedieningsvlak, en het gedien as 'n kontrole. Die eksperiment is oor 'n periode van 6 weke uitgevoer. Tydens die proeftydperk is voerinnames, weeklikse gewigstoenames, sowel as voeromsetverhoudings, gedokumenteer. Resultate het betekenisvolle gewigstoenames in die hoe (lOml/kg) en medium (5ml/kg) groepe opgelewer, aangedui deur 'n P-waarde van 0.04. Voeromsetverhoudinge het ook verbeteringe getoon vir bogenoemde twee groepe (P=0.05), terwyl voerinnames nie merkbaar tussen die vier groepe verskil het nie.

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.

Nitrogen use efficient (NUE) wheat varieties have potential to reduce input costs for growers, limit N runoff into water ways, and increase wheat adaptability to warmer environments. Previous studies have done little to explain the genetic basis for NUE and components, nitrogen uptake efficiency (NUpE) and nitrogen utilization efficiency (NUtE). Four studies were conducted to 1) determine genotypic stability of NUE under high and low N regimes and under warming 2) determine effect of warming on NUE 3) indentify QTL associated with NUE components 4) assess the utility of canopy spectral reflectance (CSR) as a high-throughput phenotyping device for NUE. Genotypic response to N stress or warming varied. Uptake efficiency was found to be more important than utilization efficiency to genotypic performance under high and low N environments and under warming. Selection under low N for NUpE and under high N for NUtE most efficiently identified NUE varieties. Uptake and utilization were lower under warming due to quickened development. No strong correlations between the CSR indices and NUE existed. No QTL were found to be significantly associated with NUE components. Further research into the mechanisms controlling NUE and to reveal plant response to N stress and under warming is necessary.

No description available.

Copies of the author's previously published articles inserted. Bibliography: leaves 142-159. Provides information on the significance of pea straw as a ruminant feed and the potential of two biological techniques for improving its feeding value.

A total of 114,351 Holstein first lactation records collected by the Quebec Dairy Herd Analysis Service (DHAS-PATLQ) between September, 1979 and January, 1994 were used to study the effects of adjusting records for linear and quadratic effects of 90- and 305-d feed intake measures (total energy, total protein and total dry matter) on estimation of heritabilities of and genetic correlations among yield and composition traits. Genetic parameters of feed intake measures, relationships between feed intake and age and weight at calving, and feed conversion efficiency traits were also examined in a series of studies. A sire model fitted by REML estimated heritabilities of 305-d milk, fat and protein yields, fat and protein percents as .45 +/- .04, .48 +/- .04, .44 +/- .03, .92 +/- .06, and .88 +/- .05, respectively. Correction of 305-d records for differences among cows in feed intake levels reduced heritabilities of milk, fat and protein yields to .35 +/- .03, .52 +/- .04, and .38 +/- .03, respectively. Heritabilities of composition traits (fat and protein percents) remained unchanged. Genetic and phenotypic correlations for yield traits were also reduced (48--170%, and 16--51%, respectively) which may indicate that genetic associations between yield traits are less than what we believed them to be. Heritabilities of 305-d total energy, total protein, total DM intake, grain energy, grain protein, grain DM, base energy, base protein, and base DM were .30 +/- .03, .24 +/- .02, .35 +/- .03, .23 +/- .02, .23 +/- .02, .23 +/- .02, .31 +/- .03, .26 +/- .02, and .40 +/- .03, respectively. Genetic correlations between feed intake measures were very high; they were approaching unity in some cases. Therefore, any one of these feed intake measures can represent the others. A multi-trait REML analysis estimated heritabilities of age and weight at first calving as .11 +/- .01 and .37 +/- .03, respectively. Age at calving was negatively associated with yield traits and with total e