Call number: LD2668 .T4 1954 W57 / Master of Science

Call number: LD2668 .T4 1955 B68 / Master of Science

Call number: LD2668 .T4 1964 U57 / Master of Science

Call number: LD2668 .T4 1965 B91 / Master of Science

Thesis (MScAgric)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The purpose of this study was to determine the essential amino acid requirements of beef cattle under feedlot conditions through evaluation of the duodenal and whole empty body essential amino acid compositions. To define the ideal protein required for growth, the whole empty body essential amino acid compositions of 8 beef steers (Simmental and Hereford crosses) was investigated. The amino acid composition of the components (carcass, metabolic organs and residual fraction), was pooled relative to their respective mass and protein contribution, resulting in the calculated whole empty body amino acid composition: arginine 6.81; histidine 2.69; isoleucine 4.02; leucine 6.96; lysine 7.43; methionine 2.01; phenylalanine 4.03; threonine 4.01; valine 5.30; tryptophan 0.82. Variations in profiles were found between scientific reports, either indicating that ratios change with growth and implants or possibly through genotype. The present study's body amino acid ratios were used to estimate dietary amino acid requirements through evaluation of the duodenal essential amino acid compositions from three different maize based feedlot diets. Although there was a general increase in the biological value of protein after rumen fermentation, the duodenal essential amino acids in comparison with the whole empty body recorded deficient/unbalanced profiles of essential amino acids for growth. The chemical scores suggested that the first-to-thirdlimiting amino acids in the duodenal digesta of beef cattle, that received three different commercially available feedlot diets, were: histidine, lysine, methionine/arginine (Diet 1), histidine, arginine, lysine (Diet 2) and arginine, methionine, histidine (Diet 3). Thedisproportionate duodenal amino acid concentrations obtained from the three diets, emphasise the necessity to enhance the intestinal delivery of amino acid profiles through different undegradable protein sources, with the objective to maximise protein utilisation and obtain the genetic potential for optimal growth in feedlot cattle. When amino acid requirements and flows to the duodenum were simulated using the Cornell Net Carbohydrate and Protein system (CNCPS), predictions indicated that lysine amino acid flow was limiting the metabolizable allowable average daily gain in Diet 1 and 3. Predicted profiles indicated that the order of limitation was: lysine, arginine, histidine (Diet 1), lysine, arginine, histidine, methionine (Diet 2) and lysine, arginine, histidine (Diet 3). The predicted profiles were in accordance with observed duodenal values, except for methionine that was observed limiting in Diet 1 and 3; however, the sequence and extent of limitation varied. Results indicate that prediction models have potential in predicting requirements; however there are still limitations for use to accurately define requirements for particular EAA's. From the present study, it is clear that the protein accretion was constrained by quantity and/or disproportionality of amino acids available for absorption. Further research should therefore be directed towards obtaining a more desirable array of amino acids to the lower digestive tract that is digestible, absorbable and an economically viable option for the feedlot operator. / AFRIKAANSE OPSOMMING: Aminosuurbehoeftes van Voerkraalbeeste Volgens die Duodenale en Totale Lee Liggaam Essensiele Aminosuur Profiel: Die doel van hierdie studie was om die essensiele aminosuur vereistes van vleisbeeste onder voerkraal toestande te bepaal deur die evaluering van die duodenale en totale lee liggaam essensiele aminosuursamesteilings. Om die idea Ie proteiene wat vir groei benodig word te definieer, is 'n ondersoek ingestel na die totale lee liggaam essensiele aminosuursamesteilings van 8 vleisbees osse (Simmetailer en Hereford kruise). Die aminosuursamesteiling van die komponente (karkas, metaboliese organe en residuele fraksie), se massa en proteien bydrae is gebruik om die totale lee liggaam aminosuursamestelling 5005 volg te bereken: arginien 6.81; histidien 2.69; isoleusien 4.02; leusien 6.96; lisien 7.43; metionien 2.01; fenielalanien 4.03; treonien 4.01; valien 5.3; triptofaan 0.82. Variasies in profiele tussen wetenskaplike verslae is gevind. Dit dui daarop dat groei en inplantings of moontlik genotipe 'n invloed op profiele kan he. Die huidige studie se liggaam aminosuurverhoudings is gebruik om die dieet aminosuurbehoeftes te skat deur evaluering van die duodenale essensiele aminosuursamesteilings van drie verskiilende mielie-gebaseerde voerkraal diete. Alhoewel daar 'n algemene toe name in die biologiese waarde van die proteien na rumen fermentasie was, het die duodenale essensiele aminosure in vergelyking met die totale lee liggaam, ongebalanseerde profiele van essensiele aminosure vir groei getoon. Die chemiese teilings toon aan dat die eerste-tot-derde-beperkende aminosure in die duodenale inhoud van vleisbeeste wat drie verskillende kommersieel beskikbare voerkraal diete ontvang het, soos volg is: histidien, lisien, metionieniarginien (Dieet 1), histidien, arginien, lisien (Dieet 2) en arginien, metionien, histidien (Dieet 3). Die ongebalanseerde aminosuur konsentrasies wat in die duodenum van die drie dlete verkry is, beklemtoon die noodsaaklikheid om die intestinale lewering van aminosuurprofiele te verbeter deur verskillende nie-degradeerbare proteien bronne te voer. Die doelwit moet wees om proteien verbruik te optimaliseer en daardeur die genetiese potensiaal vir optimale groei in voerkraalbeeste te bereik. Met die simulering van aminosuurbehoeftes en vloei na die duodenum van die drie standaard voerkraal diete met behulp van die "Cornell Net Carbohydrate and Protein System" (CNCPS), het voorspellings gewys dat lisien aminosuurvloei die metaboliseerbare toelaatbare gemiddelde daaglikse toename in Dieet 1 en 3 beperk het. Voorspelde profiele wys dat die volgorde van beperking soos volg sou wees: lisien, arginien, histidien (Dieet 1), lisien, arginien, histidien, metionien (Dieet 2)' en lisien arginien, histidien (Dieet 3). Die voorspelde profiele was in ooreenstemming met die waargeneemde duodenale waardes, behalwe vir metionien wat beperkend was in Dieet 1 en 3; die volgorde en mate van beperking was egter verskillend. Resultate wys dat voorspellingsmodelle die potensiaal het om behoeftes te voorspel. Vir die akkurate definisie van behoeftes vir spesifieke essensiele aminosuure is daar egter nog beperkinge. Uit die huidige studie, is dit duidelik dat protetenneerleqqinq deur die hoeveelheid en/of oneweredigheid van geabsorbeerde aminosure beperk is. Verdere navorsing moet dus fokus op die verkryging van In meer geskikte profiel van aminosure wat verteerbaar, opneembaar en 'n ekonomiese lewensvatbare opsie vir die voerkraalbestuurder is.

Diets were based on steam-flaked milo and contained chopped alfalfa hay in the control diet. At the 65% concentrate level, cottonseed hulls or chopped wheat straw replaced half the alfalfa hay. At the 90% concentrate level, roughage sources were chopped alfalfa hay, cottonseed hulls, or wheat straw. Six growing steers and three mature, rumen-cannulated steers per concentrate level were used in separate Latin square experiments. Total tract digestion coefficients, particulate passage rates, liquid turnover rates, and rumination time were measured in the intact steers. In situ digestion, rumen pH, and rumen dry matter distribution were evaluated in the cannulated steers. Competition between rates of passage and digestion were used to calculate apparent extent of ruminal digestion (AED). At the 65% concentrate level, total tract digestion coefficients for the wheat straw vs alfalfa hay diet were not different, apparently due to increased milo and alfalfa hay neutral detergent fiber (NDF) digestion in the wheat straw diet. Milo and alfalfa hay AED for NDF were higher (P<.10). Dietary AED for DM, NDF, and cell solubles were highest (P<.05) for the alfalfa hay diet. Differences between diets were minimal, indicating roughage source in 90% concentrate diets does not substantially influence milo digestion or passage as it does in 65% concentrate diets.

Total tract digestion coefficients for dry matter (DM) and neutral detergent fiber (NDF), passage rates for grain and roughage components of diets and liquid turnover were measured for 65 and 90% concentrate diets in separate 4 x 4 Latin square experiments using intact growing steers. Kinetics of in situ digestion for DM and NDF in diet ingredients, rumen pH, volume and DM distribution were determined in mature, rumen cannulated steers. Rates of passage and digestion were combined to calculate apparent extent of ruminal digestion (AERD) for diet ingredients. Diets were based on steam flaked milo. The control roughage was chopped alfalfa hay (AH). In 65% concentrate diets, chopped wheat straw (WS), bermudagrass straw (BS) or cottonseed hulls (CSH) replaced 50% of the AH. In 90% concentrate diets, all of the AH was replaced by WS, BS or CSH. Total tract starch digestion was not influenced by source of roughage at either concentrate level. In 65% concentrate diets, total tract digestion of DM and NDF was not adversely affected by substitution of WS for 50% of the AH. Digestion of these fractions was lower (P<.05) for BS and CSH diets, but the severity of depression was greatest (P<.05) for the CSH diet. Reduced digestibility of the CSH diet was attributed to lower digestibility of CSH in comparison with AH. Although WS and BS were also less digestible than AH, their inclusion in the diet improved (P<.05) AERD of DM and NDF from milo and AH. Improved AERD for NDF appeared to be related to the raft-forming properties of WS and BS, and their ability to maintain rumen pH in a more desirable range for NDF digestion. In 90% concentrate diets, effects of roughage source on utilization of milo were minimal. Total tract digestion of DM and NDF was lower (P<.05) for WS, BS and CSH diets than for the AH diet, because of dilution of the more digestible AH by these roughages. Wheat straw had a tendency to moderate ruminal pH and consequently might be more useful in high concentrate diets than roughages such as CSH and BS.

Cattle grazing patterns on Lehmann lovegrass rangelands often create heavily-grazed (HG) areas surrounded by lightly-grazed (LG) or ungrazed patches. The purpose of this study was to characterize the forage resource and ingestive behavior of cattle grazing Lehmann lovegrass plants in both LG and HG patches on the Santa Rita Experimental Range. The general hypothesis was that residual bunchgrass vegetation resulted in sward characteristics which physically inhibited the efficiency of cattle grazing by increasing the manipulative activity per harvested bite. The overall heights of residual stems and green tillers averaged 70 and 49 cm for LG, 8 and 9 cm for HG patches. Biomass of total standing crop (SC), residual vegetation (RV) and green herbage (GH) averaged 4159, 3395 and 764 kg/ha for LG, 345, 185 and 160 kg/ha for HG patches, respectively. Bulk density of SC, RV and GH of LG and HG patches averaged 58, 48, and 19 [(gm/cm³) X 10⁻⁵] for LG, 38, 23 and 20 [(gm/cm³) X 10⁻⁵] for HG patches, respectively. The ratio of green herbage to residual vegetation averaged 0.22 for LG and 0.86 for HG patches. The different sward structure of LG and HG patches affected the ingestive behavior of the grazing cows. Overall handling time for each grazing bite averaged 1.5 and 1.2 sec/bite in LG and HG patches, respectively. Cows employed different foraging tactics in response to the dynamic changes of the sward conditions. Cows employed top biting extensively to harvest the seed-head and other green herbage at the top of the sward surface. As the height of residual stems increased and dominated the upper strata of the sward, side and low biting were mainly used by the cows as grazing methods to bite the plants to reduce the manipulative activity. Avoidance of LG patches or preference for HG patches was related to the sward structure and largely shaped by the build-up of residual vegetation. Removal of residual vegetation through fire, mowing or heavy utilization for short periods late in the growing season to allow for more accessible green herbage could improve both animal and pasture utilization of the range resource.

The abundance of Lehmann lovegrass (Eragrostis lehmanniana, Nees.) on Arizona ranges prompted this research to evaluate the animal production and winter palatability of this species. Sulfurcoated urea (SCU) was applied to desert grassland range to minimize the risks of fertilization that are brought about by drought and unseasonable rainfall. Tebuthiuron (TEB) was also applied to pasture to document any beneficial effects on forage production and palatability. During the 2 years of this project, two experiments were conducted. A preference study examined forage and animal responses to one-time applications of fertilizer or herbicide treatments and combinations. The second experiment compared the potentials for improved animal production from SCU and SCU + TEB with untreated range. Results indicated that the fertilizer and combination treatments produced more forage than the untreated plots. Tebuthiuron improved forage production by 200 percent in the first year but reduced yields in the second year. The high rate of TEB was detrimental in both years. Forage utilization was improved by all treatments. Nitrogen increased the crude protein content of the grasses proportional to the rate applied. Tebuthiuron also enhanced the protein content of the forage. Total available carbohydrates were lowest in TEB treated forages, but digestibility was increased. Only the 31 lb SCU appeared to be economically profitable. However, excellent carry-over by the 60 SCU treatment suggested profitability after 3 years. Results from the grazing study indicated that production was significantly improved by both treatments. Although forage production was similar for the treatments, the SCU-only pasture provided superior animal gains and greater carrying capacity than the SCU + TEB pasture, even though forage digestibility and apparent disappearance were greater on the combination pasture. The difference in animal performance was attributed to low levels of carbohydrates available from the combination pasture. Treatment of Lehmann lovegrass/blue grama range with 40 SCU/acre appeared profitable for raising growing beef animals, but not for maintenance of a breeding cow herd.

Two lactation studies with accompanying digestion trials were conducted to compare the feeding value of Pima cottonseed, with differing degrees of processing, to short staple cottonseed for lactating dairy cows. Additional tests were conducted to examine physical and chemical characteristics of both Pima and short staple cottonseed and the effect of processing on storage characteristics of cottonseeds. Pima cottonseed is higher in CP and ether extract and lower in NDF and ADF than short staple seed. Pima seed has a greater bulk density, a greater proportion of the (-)-gossypol isomer and a lower proportion of the (+)-gossypol compared to short staple cottonseed. In the first lactation study, milk yield was similar across all treatments. Milk fat was higher (P < .05) for finely cracked Pima (x 3.0 mm) and whole Pima diets. Feed efficiency was greatest (P < .05) for the cracked Pima diet. Percentage whole seed passing into the feces of that consumed, was 11% for the whole Pima and 5.2% for the short staple. Total tract digestibility of ADF decreased and that of ether extract increased in cows fed cracked Pima compared to whole Pima or short staple. In the second lactation study, milk yield was higher (P < .05) for cows fed ground Pima (x 2.5 mm), than either whole Pima or coarsely cracked Pima (x 3.5 mm), with short staple intermediate. Feed efficiency (SCM/DMI) was greater for cows fed ground Pima and short staple diets (1.14) than for those fed cracked Pima or whole Pima. Stearic acid was lower, and linoleic and linolenic acids were higher in milk of cows fed ground Pima compared to short staple. Passage of whole seed was two-times greater for cows fed whole Pima compared to whole short staple (12.3% vs. 6.2%), and processing of Pima seed eliminated whole seeds passing in the feces. Ether extract digestibility was lower for the whole Pima compared to the other treatments. Storage of whole, cracked or ground seeds at 32°C and 30% relative humidity for up to 30 d did not cause rancidity or aflatoxin contamination. Storage of processed seeds in covered containers for nine months caused only slight increases in free fatty acid content, and no change in the whole seeds.