Thesis (M.Sc. (Agriculture)) --University of Limpopo, 2010 / Ten experiments were conducted to determine the effect of dietary energy to protein ratio level on growth and productivity of indigenous Venda chickens raised in closed confinement from day-old up to thirteen weeks of age. The ten experiments were based on five different energy levels of 12.2, 13, 13.2, 13.4 and 14 MJ ME/kg DM. Each dietary energy level had five different levels of protein concentrations of 220, 190, 180, 170 and 160 g/kg DM, thus ending up with twenty five different dietary energy to protein ratio levels. Experiments 1 to 5 examined the effect of dietary energy to protein ratio on productivity of unsexed Venda chickens aged one to six weeks. Experiments 1 to 5 each commenced with 160 unsexed day-old indigenous Venda chicks with an initial weight of 25 ± 2 g per bird and each lasted for a period of six weeks. In each experiment, the chicks were randomly assigned to five treatments with four replications, each having eight birds. Thus, 20 floor pens (1.5 m2 /pen) were used in total for each experiment. All the five experiments were carried out around the same time. A complete randomized design was used for each experiment. A quadratic regression model was used to determine the ratios for optimum feed intake, growth rate, feed conversion ratio, live weight, metabolisable energy and nitrogen retention in each experiment while a linear model was used to determine the relationship between optimal responses in the above variables and dietary energy to protein ratio levels. Dietary energy to protein ratio level for optimal response for any variable was relative and depended on the energy to protein ratio values of the diet. Energy to protein ratios of 63, 67, 70, 74 and 78 MJ ME/kg protein promoted optimal live weights of 415, 408, 370, 365 and 344 g at six weeks of age for diet energy levels of 12.2, 13, 13.2, 13.4 and 14 MJ ME/kg DM, respectively. However, optimal response trends for different variables were also influenced by the dietary energy to crude protein ratio. Optimal feed intake increased linearly with increasing dietary energy to protein ratio levels. Similarly, optimal metabolisable energy level increased linearly with increasing dietary energy to protein ratio levels without any increase in live weight. On the other hand, increasing dietary energy to protein ratio level decreased growth rate with a linear deteriorating feed conversion ratio,thus, negatively affecting live weight of the chickens at six weeks of age. However, increasing dietary energy to protein ratio levels improved efficiency of protein utilization with a linear deteriorating metabolisable energy utilization. In experiments 1 to 5, correlation analysis indicated that optimal feed intake, feed conversion ratio and metabolisable energy level were positively and strongly correlated with dietary energy to protein ratio levels while optimal live weight, growth rate and nitrogen retention were negatively and strongly correlated with dietary energy to protein ratio levels. The study indicated that a diet containing a crude protein content level of 178 g/kg DM and an energy level of 14 MJ ME/kg DM allowed for optimal utilization of absorbed protein and energy for growth in unsexed indigenous Venda chickens aged between one and six weeks. Experiments 6 to 10 examined the effect of dietary energy to protein ratio level on productivity of male Indigenous Venda chickens raised in closed confinement from seven up to 13 weeks of age. Each experiment commenced with 100 seven-week old male Venda chickens with an initial weight of 320 ± 2 g per bird. In each experiment, the chickens were randomly assigned to five treatments with four replications, each having five birds. Thus, 20 floor pens (1.5 m2/pen) were used in total for each experiment. All the five experiments were carried out around the same time and for a period of seven weeks. A complete randomized design wasused for each experiment. A quadratic regression model was used to determine energy to protein ratios for optimum feed intake, growth rate, feed conversion ratio,live weight, metabolisable energy, nitrogen retention, carcass yield, breast meatyield and fat pad deposition in each experiment while a linear model was used to determine the relationship between optimal responses of the above variables and dietary energy to protein ratio levels. Energy to protein ratios of 60, 71, 66, 72 and 71 MJ ME/kg protein promoted optimal live weights of 1167, 950, 983, 1235 and 1172 g at thirteen weeks of age for diet energy levels of 12.2, 13, 13.2, 13.4 and 14 MJ ME/kg DM, respectively. Optimal response trends in feed intake, growth rate, feed conversion ratio, nitrogen retention, and metabolisable energy intakes in male Venda chickens tended to increase with increase in dietary energy to protein ratio level. In contrast, optimal carcass and breast meat yield tended to decrease with increasing dietary energy to protein ratio level. However, optimal live weight and fat pad remained unchanged with increase in dietary energy to protein ratio value. Additionally, increasing dietary energy to protein ratio level improved efficiency of protein utilization with deteriorating metabolisable energy utilization.On the other hand, experiments 6 to 10 showed that optimal feed intake, growth rate, feed conversion ratio, live weight, metabolisable energy level, nitrogen retention and fat pad were positively and poorly correlated with dietary energy to protein ratio levels while optimal carcass weight and breast meat yield were negatively and poorly correlated with dietary energy to protein ratio levels This study indicated that a diet containing 193 g CP/kg DM and an energy level of 14 MJ ME/kg DM allowed for optimal utilization of absorbed protein and energy for growth in male indigenous Venda chickens aged between seven and thirteen weeks.It is, therefore, concluded that optimal response trends for different variables in growing unsexed Venda chickens offered diets differing in optimal dietary energy to protein ratio levels are influenced by the diet crude protein content rather than the feed energy level per se. Diets containing decreased dietary energy to protein ratio levels may promote improved growth rate and efficient feed conversion ratio while naturally restricting feed intake. Diets containing increased dietary energy to protein ratio levels favoured efficient utilization of consumed dietary protein. However, with such diets, protein became limiting and birds increased their feed intake attempting thereby to obtain more of the limiting protein in order to meet their protein requirement regardless of the energy value of the diet.It is, also, concluded that growing male Venda chickens increased their feed intake with increase in dietary energy to protein ratio. This is contrary to what has been observed in broiler chickens which decrease their intake with increase in diet energy value. It is suggested that this might reflect the differences between indigenous and broiler chickens in terms of their genetic and physiological abilities to regulate their feed intakes according to dietary energy levels. / National Research Foundation (NRF)

<p>Cilj istraživanja bio je da se ustanovi povezanost energetskog statusa krava u postpartalnom periodu, iskazanog<br />kroz vrijednost odnosa mliječna mast: proteini, i parametara reproduktivne efikasnosti. Istraživanje je sprovedeno<br />na ukupno 350 oteljenih krava hol&scaron;tajn rase (121 prvotelka, 115 drugotelki i 114 krava koje su se telile tri i vi&scaron;e<br />puta), smje&scaron;tenih na farmi mliječnih krava industrijskog tipa, u slobodnom sistemu držanja i hranjenih uobičajenim<br />obrocima za datu rasu goveda, proizvodnu kategoriju, stadijum laktacije i period godine. Sve ispitane krave, bez<br />obzira na paritet, podijeljene su u odnosu na stadijum laktacije (15-45 dana, 46-75 dana, 76-105 dana i 106-135<br />dana), a u okviru svakog njih formirane su podgrupe u odnosu na vrijednost odnosa mliječna mast : proteini (OMP<br />&lt; 1,0 , OMP 1,0-1,3 i OMP &gt; 1,3). Podjela krava unutar svakog pariteta (prvotelke, drugotelke, krave sa tri i vi&scaron;e<br />teljenja), izvr&scaron;ena je na osnovu trajanja servis perioda (SP do 60 dana, SP 61-90 dana, SP 91-135 dana). Praćeni su<br />sljedeći reproduktivni parametri: period do prvog vje&scaron;tačkog osjemenjavanja (dani), trajanje servis perioda (dani),<br />trajanje perioda od prvog vje&scaron;tačkog osjemenjavanja do uspostavljanja steonosti (dani), indeks osjemenjavanja,<br />trajanje graviditeta (dani) i trajanje međutelidbenog intervala (dani). Uzorci mlijeka uzimani su u okviru<br />uzorkovanja za potrebe selekcijske službe. U uzorcima mlijeka su određene koncentracije mliječne masti i proteina,<br />te je izračunat njihov međusobni odnos (OMP). Podaci su statistički obrađeni metodama deskriptivne statistike, a<br />značajnost razlika između grupa testirana je t-testom. Pored numeričkih vrijednosti za ispitane parametre, za sve<br />ispitane grupe krava u radu je dat i grafički prikaz odnosa mliječne masti i proteina. U prilogu je dat pregled<br />vrijednosti parametara deskriptivne statistike za ispitane parametre za sve ispitane grupe krava. U svakoj od<br />ispitanih grupa krava, bez obzira na način podjele, ustanovljen je veliki procenat krava sa vrijednostima OMP izvan<br />fiziolo&scaron;kih okvira, bilo da se radi o povi&scaron;enim ili sniženim vrijednostima. Zbirni podaci za svaku od ispitanih grupa<br />krava, prikazani na grafikonima, ukazuju na generalno nepovoljan metabolički status krava na ispitanoj farmi i<br />visok procenat subkliničkih poremećaja zdravlja, prije svega subkliničke forme ketoze, udružene sa različitim<br />stepenom zama&scaron;ćenja jetre, &scaron;to se odražava i na vrijednosti reproduktivnih parametara. Podaci o trajanju perioda do<br />prvog vje&scaron;tačkog osjemenjavanja u svim ispitanim grupama krava, bez obzira na način grupisanja, ukazuju na visok<br />stepen varijacija, kao rezultat različite sposobnosti krava prilagode nepovoljnom bilansu energije,. Energetski status<br />grla je, preko različitih mehanizama opisanih u radu, uticao i na trajanje perioda od prvog do uspje&scaron;nog vje&scaron;tačkog<br />osjemenjavanja i servis perioda, kao i na vrijednost indeksa osjemenjavanja u svim ispitanim grupama krava, pri<br />čemu su grla sa povoljnijim energetskim statusom generalno imala povoljnije vrijednosti ovih parametara. Pored<br />energetskog statusa, podaci prikazani u radu govore i o neadekvatnoj organizaciji otkrivanja estrusa, kao<br />značajnom ograničavajućem faktoru za postizanje optimalnih reproduktivnih rezultata na ispitanoj farmi. Prosječno<br />trajanje graviditeta u svim ispitanim grupama krava kretalo se u okvirima za datu vrstu i rasu, te je stoga trajanje<br />međutelidbenog intervala bilo primarno uslovljeno trajanjem servis perioda.<br />Rezultati ovog istraživanja ukazuju da postoji pozitivna veza između energetskog statusa krava, iskazanog kroz<br />vrijednosti odnosa mliječna mast : proteini, i reproduktivnih parametara, pri čemu prilikom tumačenja dobijenih<br />rezultata treba imati u vidu i niz dodatnih faktora, kao &scaron;to su rasa, visina dnevne proizvodnje mlijeka, sastav i<br />konzumacija obroka, ambijentalni uslovi i slično. Odabir grla na kojima je istraživanje sprovedeno uslovio je da se reproduktivni rezultati svih ispitanih grupa krava kreću u okvirima koji se u literaturi navode kao zadovoljavajući,<br />iako su njihove vrijednosti na nivou cijele farme značajno nepovoljnije. Rezultati ovog istraživanja ukazuju na<br />značajan potencijal primijenjene metode za rano otkrivanje grla sa predispozicijom za nastanak poremećaja<br />zdravlja i reprodukcije, te pravovremeno preduzimanje dijagnostičkih i terapijskih procedura sa ciljem da se<br />posljedice negativnog bilansa energije tokom perioda rane laktacije ublaže, i time omogući postizanje adekvatnih<br />reproduktivnih rezultata.</p>

The membrane proteins signal peptide peptidase, signal peptide peptidase like and presenilin are intramembrane aspartyl proteases located in the endoplasmic reticulum, plasma membrane and organelle. These membrane proteins are able to catalyze a hydrolytic reaction in a hydrophobic space. The downstream consequences of these reactions impact a variety of cellular functions such as cytokine production, inflammatory responses, embryogenesis, and immune system regulation. Additionally, the aspartyl proteases such as signal peptide peptidase and presenilin, a part of the γ-secretase complex, hydrolyze peptides leading to pathogen maturation and Alzheimer’s disease, respectively. Electron crystallography offers the unique aspect of studying membrane proteins in a near native state. Determining the structures of Haloarcula morismortui and Methanoculleus marisnigri JR1 signal peptide peptidases by electron crystallography may provide insight into how a hydrolysis reaction occurs in a hydrophobic environment and how the protein determines which transmembrane signal peptides to cleave. Additionally, structure determination may help answer questions regarding why human presenilin, part of the γ-secretase complex, incorrectly processes amyloid precursor protein into amyloid-beta peptides leading to Alzheimer’s disease. Such structural data may not only shed light on how amyloid precursor protein is processed but how other proteins are processed by signal peptide peptidase leading to immune responses, cell signaling, and pathogen maturation. In addition, structure-function data may have an impact on pharmaceutical drug designs that targets signal peptide peptidase, signal peptide peptidase like, and/or presenilin. To determine the structure of aspartyl proteases, two archaeal signal peptide peptidases were used for two-dimensional crystallization trials to be able to study their structure by electron crystallography. Haloarcula morismortui and Methanoculleus marisnigri JR1 signal peptide peptidases, both human signal peptide peptidase homologues, were recombinantly over-expressed and purified. During dialysis trials, various lipid-to-protein ratios, sodium chloride concentrations, temperatures, detergents and a variety of other variables were tested. Methanoculleus marisnigri JR1 signal peptide peptidase showed the most promising results in terms of crystallinity. Optimizing dialysis conditions, specifically narrowing the lipid to protein ratio, resulted in two-dimensional crystals. Ordered arrays measuring up to 200 nm x 200 nm were observed. These ordered arrays have been shown to be reproducible amongst multiple batches of purified Methanoculleus marisnigri JR1 signal peptide peptidase. Preliminary projection maps of negatively stained ordered arrays show unit cell dimensions of a = 178 Å, b = 160 Å, γ = 92.0 Å and a = 175 Å, b = 167 Å, γ = 92.0 Å. The monomer measurements are approximately 70 Å by 80 Å. This is the first time a signal peptide peptidase homologue has been crystallized by two-dimensional crystallization.

L’objectif de ce travail est de comprendre les effets d’un changement de composition des modèles fromagers sur la mobilité, la libération et la perception de molécules de la flaveur (sel, composés d’arôme). Six modèles fromagers aromatisés ont été formulés (3 ratios lipides/protéines (L/P) et 2 teneurs en sel). La microstructure et les propriétés rhéologiques des modèles fromagers ont été caractérisées respectivement par microscopie confocale et par compression uniaxiale. La mobilité des ions sodium a été analysée par RMN 23Na. La cinétique de libération des ions sodium a été suivie dans l’eau, puis dans la salive, en situation de consommation. La libération rétronasale des composés d’arôme a été suivie par nose-space APCI-MS, simultanément au suivi des déglutitions, et de la mastication par électromyographie. Enfin, les propriétés sensorielles des modèles fromagers (intensité salée, arôme, texture) ont été étudiées.Une diminution du ratio L/P et une diminution de la teneur en sel diminuent la taille des gouttelettes lipidiques et augmentent la fermeté. Cela conduit à une diminution de la mobilité des ions sodium, qui se traduit par une diminution de la quantité de sodium libéré dans la salive et une diminution de la perception salée. De plus, le maximum de libération d’arôme est atteint plus tard et la perception aromatique est diminuée. Ces effets peuvent être expliqués par la répartition lipides/protéines observée en microscopie, par une déglutition plus tardive et une plus grande activité masticatoire / The aim of this work is to understand the effects of changes in the composition of model cheeses on mobility, release and perception of flavor molecules (salt, aroma compounds). Six flavoured model cheeses were formulated (3 lipid/protein (L/P) ratios and 2 salt contents). The microstructure and the rheological properties of the model cheeses were characterized respectively by confocal microscopy and by uniaxial compression test. The mobility of sodium ions was analyzed by 23Na NMR. The kinetics of sodium release was followed in water and then in saliva during consumption of the model cheeses. The retronasal release of aroma compounds was followed by nose-space APCI-MS, simultaneously with the study of swallowing and chewing by electromyography. Then, the sensory properties of the model cheeses (saltiness, aroma, texture) were studied.A decrease in the L/P ratio and a decrease in salt content reduce the fat droplet size and increase the hardness. This leads to a decrease in sodium ion mobility, which results in a decrease in sodium release in saliva and a decrease in salty perception. Moreover, the maximum intensity of aroma release is reached later and the aroma perception is decreased. These effects can be explained by the observed lipid/protein distribution in microscopy, by the later swallowing and by the higher chewing activity