Based on a large series of epidemiological studies, it has been proposed that exposure to an increased nutrient supply before birth increases the risk of developing obesity in postnatal life. The physiological mechanisms underlying the association between increased nutrition before birth and later obesity are, however, poorly understood. This thesis has investigated the impact of an increased fetal nutrient supply on the programming of key systems within the appetite - regulating network and / or the adipocytes before and after birth. The studies in this thesis have demonstrated that plasma concentrations of the adipostatic hormone leptin are directly related to adiposity and the size of adipose cells in fetuses of ewes fed at or above maintenance energy requirements, which suggests that leptin may act as a peripheral signal of fat mass before birth. It has also been demonstrated that the components of the central network for appetite regulation are expressed in the hypothalamus of the fetal sheep from at least 110 d gestation ( term = 150 ± 3 d gestation ), and that the expression of the appetite - regulating neuropeptides is responsive to signals of increased nutrient supply before birth. This thesis has also demonstrated that an increase in maternal nutrition in late pregnancy results in increases in both food intake and glucose concentrations in the lamb in early postnatal life and in a significant increase in subcutaneous adiposity on postnatal day 30. Importantly, increased maternal nutrition resulted in an altered relationship between signals of increased fat mass and nutrition and expression of a central appetiteinhibitory neuropeptide, CART, in the lamb hypothalamus. It was also demonstrated that there was an interaction between the prenatal and postnatal nutritional environments in the determination of lipogenesis in the early postnatal period. The findings presented in this thesis provide evidence that programmed changes to the sensitivity of the appetite - regulating neuropeptides to signals of increased adiposity and nutritional status in early postnatal life are an important part of the physiological pathway through which exposure to an increased nutrient supply before birth may lead to an increased risk of obesity in later life. / Thesis (Ph.D.)--School of Molecular and Biomedical Science, 2006.

Callipyge (CLPG, n=16) and normal (N, n=11) lambs were produced from Polypay dams and Dorset sires heterozygous for the CLPG gene to study the effects of the gene on growth and carcass and meat quality parameters. CLPG lambs had higher average daily gain than N lambs (0.26 vs 0.23 kg/day, p<.05); however, the CLPG gene did not affect feed efficiency. Lambs were slaughtered in three groups to achieve moderate uniformity in slaughter weight. At the time of slaughter, weights of head, pelt, and internal organs were recorded. Two leg muscles, two shoulder muscles, the longissimus dorsi muscle, and two loin chops cut 2.5 cm thick, were dissected from each carcass. CLPG lambs had a higher dressing percent (p<.01) and lighter head, pelt, liver (all p<.01), and kidney/pelvic fat (p<.05). CLPG lambs had less fat over 12th rib (p<.05) and larger ribeye area (p<.01). CLPG lambs had greater weights of Biceps femoris (42%, p<.05), Semimembranosus (34%, p<.01), Triceps brachii (20%, p<.05), longissimus dorsi muscle (29%, p<.01) and whole leg (6%, p<.05) than N lambs. All the dissected muscles from all carcasses and one whole leg from each ewe lamb carcasses (n=11) were cooked to an internal temperature of 70��C. CLPG carcasses produced higher Warner-Bratzler shear values for loin chops (4.79 vs 2.93 kg, p<.01), Biceps femoris (3.94 vs 2.92 kg, p<.05), Semimembranosus (4.75 vs 3.46 kg, p<.05) and Longissimus dorsi muscle (5.29 vs 3.4 kg, p<.01) than N lambs. However, no significant differences were detected in shear values for Biceps femoris (3.10 vs 3.04 kg) or Semimembranosus (3.77 vs 3.29 kg) when the muscles were dissected after roasting the whole leg. The CLPG gene also had no effect on the shear values for two dissected shoulder muscles (Deltoid and Triceps brachii). The two genotypes did not differ in either cooking loss or percent moisture in any of the muscles compared. / Graduation date: 1998

A study was conducted to determine the effects of trenbolone acetate (TBA) and estradiol-17B (E2) implantation on the characteristics of the glucocorticoid and E2 receptor, skeletal muscle protein turnover and tissue growth. Twenty-four lambs were utilized. Trenbolone acetate did not ,affect (P>.10) degradation rates in the semitendinosus (ST) and triceps brachii (TB) muscles, the production of cortisol, adrenal weights and cytosolic glucocorticoid binding capacity (Bmax). Trenbolone acetate decreased synthesis rate of muscle protein (P<.Ol), the percent of [3H] dexamethasone binding in the nuclear fraction, Bmax and the disociation constant (Kd) of the cytosolic E2 receptor, only in the TB muscle. Deoxyribonucleic acid (DNA) of the TB was increased (P<.05) with TBA. Pituitary weights were decreased (P<.005) with TBA and increased (P<.Ol) with E2. Estradiol decreased (P<.05) Bmax of the cytosolic E2 receptor in the ST and decreased (P<.05) Bmax of the nuclear E2 receptor in the TB muscle. The TB muscle had greater (P<.05) synthesis rates than the ST and the protein:RNA ratio was decreased (P<.05) in the TB. The TB muscle had greater (P<.005) Bmax for the cytosolic glucocorticoid receptor. / Master of Science

Thesis (MScAgric)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The following study is to determine if a creep feed balanced for limiting essential amino acids (EAA) at a certain non structural carbohydrate (NSC) level will elicit greater responses than lambs reared on a commercial creep feed. Lysine, Threonine, Methionine, Isoleucine, Phenylalanine and Leucine were determined as the limiting amino acids for nursing lambs. These amino acids were incorporated into the creep feed treatments CF1 and CF2 representing 157 g CP/kg, 477 g NSC/kg and 179 g CP/kg, 508 g NSC/kg, respectively. A commercial creep feed with no optimisation for EAA is represented as CFC with 139 g CP/kg and 455 g NSC/kg. A negative control (CON) treatment represents lambs receiving no creep feed but with ad libitum access to suckle their dams while feeding on kikuyu pasture. A growth trial was conducted on Merino x Döhne-Merino cross twin lambs averaging a birth weight of 4.42 kg ± 0.11 for 60 days following with a digestibility trial towards the end of the trial. Half of the lamb crop was slaughtered at an average live weight of 23.6 kg ± 0.56. The M. longissimus dorsi was removed on both the left and right half of the carcass between the 2nd - 3rd last thoracic vertebrae and the 4th - 5th lumbar vertebrae. A sample from the rumen wall was taken at the rumino-reticular fold to determine development characteristics. Results indicate that the feed conversion ratio for the CFC lambs were better than CF1 (P = 0.052) but not more than CF2 (P = 0.307). The FCR was 0.88, 1.19 and 1.01 (kilogram feed required to gain 1 kg in bodyweight) for CFC, CF1 and CF2, respectively. Dressing percentage was higher for CF2 than for both CFC (P = 0.012) and CF1 (P = 0.077). Along with BUN data it was concluded that the high CP level of CF2 resulted in the higher fat deposition. The optimised creep feeds had higher nitrogen and energy balances than the commercial CFC, this implicates that the optimised creep feeds were more efficiently utilised. Optimised creep feed treatments had longer papillae than CON (P < 0.0001). Papillae of creep feed 2 was longer than CFC (P = 0.0537). Papillae width decreased as the NSC level increased thus it is surmised that higher NSC levels resulted in longer but thinner papillae. Rumen muscularization was equally developed between all the treatments and was ascribed to the lambs’ access to course roughage. Meat quality in terms of physical and chemical characteristics was found to be in range with that expected for lambs at higher slaughter weights (40 kg). In conclusion, the balancing of the limiting EAA increases the benefits of creep feeding while simultaneously being more efficiently utilised. Intensive sheep production systems may benefit from the feeding of such creep feeds provided it fits economically into their farming system. / AFRIKAANSE OPSOMMING: Die volgende studie is om te bepaal of 'n kruipvoer wat gebalanseerd is vir beperkende essensiële aminosure (EAA) by 'n vasgestelde nie-strukturele koolhidraat (NSK) vlak verbeterde groei sal ontlok teenoor lammers wat grootgemaak word op 'n kommersiële kruipvoer. Lisien, Treonien, Metionien, Isoleusien, Fenylalanien en Leusien is bepaal as die beperkende aminosure vir suipende lammers. Hierdie aminosure is opgeneem in die geoptimiseerde kruipvoer behandelings CF1 en CF2 wat 157 g RP/kg, 477 g NSK/kg en 179 g RP/kg, 508 g NSK/kg onderskeidelik verteenwoordig. 'n Kommersiële kruipvoer met geen optimalisering vir EAA is verteenwoordig as CFC met 139 g RP/kg en 455 g NSK/kg. 'n Negatiewe kontrole (CON) behandeling is verteenwoordig deur lammers wat geen kruipvoer ontvang het nie, maar wat ad libitum toegang tot hul ooi gehad het om te soog terwyl die ooi op ‘n kikoejoeveld wei. 'n Groei proef is uitgevoer met Merino x Döhne-Merino kruis tweelinglammers met ‘n gemiddelde geboorte gewig van 4,42 ± 0,11 kg vir 60 dae en 'n verteerbaarheids proef is na aan die einde van die studie uitgevoer. Helfte van die lam kudde is geslag by die lewende gewig van 23,6 ± 0, 56 kg. Die M. longissimus dorsi was op beide die linker-en regter helfte van die karkas tussen die 2de - 3de laaste torakale werwels en die 4de - 5de lumbale werwels verwyder. 'n Monster van die rumen wand is geneem langs die rumino retikulêre vou sodat die rumen ontwikkeling eienskappe daarmee bepaal kon word. Resultate dui daarop aan dat die voeromsetverhouding (VOV) vir CFC lammers beter was as vir CF1 (P = 0,052), maar nie meer as vir CF2 (P = 0,307) nie. Die VOV was 0,88 , 1,19 en 1,01 (kilogram voer wat nodig is om 1 kg liggaamsmassa aan te sit) vir CFC, CF1 en CF2 onderskeidelik. Uitslag persentasie vir CF2 was hoër as beide CFC (P = 0,012) en CF1 (P = 0,077). Saam met die bloed, urea en stikstofbalans data is daar tot die gevolgtrekking gekom dat die hoë RP inhoud van CF2 gelei het tot ‘n hoër vetneerlegging. Die geoptimaliseerde kruipvoere het ‘n hoër stikstof- en energiebalans gehad teenoor die kommersiële CFC behandeling wat dus impliseer dat die optimale kruipvoere doeltreffender benut was. Die geoptimaliseerde kruipvoer behandelings het langer papillae gehad as CON (P < 0,0001). Papillae lengte van die CF2 behandeling is langer as die van CFC (P = 0,0537). Papillae breedte het dunner geraak soos wat die NSK-vlak gestyg het dus word vermoed dat hoër NSK-vlakke langer maar dunner papillae tot gevolg het. Rumen bespiering is ewe ontwikkeld tussen al die behandelings en word toegeskryf aan die lammers se toegang tot growwe ruvoer. Vleis kwaliteit in terme van fisiese- en chemiese eienskappe was inlyn met wat verwag kan word vir lammers by hoër slaggewigte (40 kg). Ten slotte, die balansering van beperkende aminosure verhoog die voordele van kruipvoeding en word terselfdertyd doeltreffender benut. Intensiewe skaap produksie stelsels kan dus voordeel trek uit die voeding van sodanige kruipvoere mits dit ekonomies pas in die boerdery stelsel.