The breeding and reproductive biology of the vlei rat Otomys irroratus representing three allopatric populations (Committee's Drift, Hogsback and Karkloof) have been studied in the laboratory. The study attempted to establish whether the three populations differed in respect of selected reproductive parameters, and whether the populations are reproductively isolated from one another. The breeding biology of the Hogsback and Karkloof populations was similar while the Committee's Drift population differed from the other two in respect of its smaller litter size and increased interval between pairing and the production of the first litter. Pre-copulatory behaviour differed among populations, with a gradation of increasing intersexual aggression from Hogsback to Karkloof to Committee's Drift pairs. Postnatal growth and development patterns, as well as male reproductive morphology, were indistinguishable among the populations. Attempts at interpopulation breeding were successful. However, some hybrids died before weaning, while those that survived beyond weaning were sterile, particularly those resulting from cross-matings of Hogsback animals with individuals representing the other populations. Interpopulation pairs displayed higher levels of agonistic interaction than did the pure pairings. Growth and development and the reproductive morphology of male hybrids were indistinguishable from those of the parental populations. Interpopulation reproductive variation in o. irroratus appears to be due to a combination of environmental and phylogenetic constraints. 80th pre- and post-zygotic isolating mechanisms would impede gene flow between the populations should they meet in nature. All populations appear to be undergoing active speciation. / Thesis (M.Sc.)-University of Natal, Durban, 1990.

The distributional range of the Tete veld rat, Aethomys ineptus, extends from the Limpopo Province in the north through to the south of KwaZulu Natal. The Tete veld rat is a seasonal breeder, with the breeding period confmed to the wet summer months of the year in the Gauteng Province of South Africa. The seasonality of reproduction in the Tete veld rat is confirmed by reproductive tract morphometrics, ovarian histology, plasma progesterone, and oestradiol-17β in females, and testicular histology and plasma testosterone concentrations in males. The presence of some spermatogenic activity and spermatozoa in the epididymides, as well as some follicular activity and raised circulating progesterone, and oestradiol-17β concentrations in some females during winter intimates that the Tete veld rat is possibly an opportunistic breeder. Reproduction during winter is presumably restricted by food availability and adverse winter conditions. The Namaqua rock mouse, Aethomys Namaquensis, on the other hand is widely distributed in the southern African subregion. Reproductive tract morphometrics, ovarian histology, plasma progesterone and oestradiol-17β in females, and testicular histology, seminiferous tubule diameters and plasma testosterone concentrations in males confirm that the Namaqua rock mouse is a strictly seasonal breeder. The breeding period starts in October and extends to the end of February. The absence of Graafian follicles, corpora lutea, corpora albicans, corpus hemorrhagicum, lower plasma progesterone and oestradiol concentrations in females, and small seminiferous tubule diameters, and lower testosterone concentrations during winter months suggest that reproduction is completely inhibited during this period of the year. Photoperiodic responsiveness was determined in both the Tete veld rat and the Namaqua rock mouse by exposing the animals to long day (LD) and short day (SD) lengths. Testicular mass expressed against body mass, testicular volume, and seminiferous tubule diameters were significantly larger and plasma testosterone concentrations were significantly higher in males subjected to a long day photoperiod than in males exposed to a short day. These fmdings suggest that both species are photoperiodically responsive and that photoperiod could potentially play a role in reproduction in both the Tete veld rat and the Namaqua rock mouse. In conclusion, the results in this study suggest that the Tete veld rat is a seasonal breeder with the breeding period confined to the rainy summer months in South Africa. The breeding season starts in October and extends to April. Reproduction in the Tete veld rat appears to involve photoperiod. The Namaqua rock mouse is a strictly seasonal breeder with a breeding period occurring between October and the end of February. Breeding during the winter months is completely inhibited. The Namaqua rock mouse may also utilize photoperiod to initiate reproductive events. / Dissertation (MSc)--University of Pretoria, 2006. / Zoology and Entomology / Unrestricted

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Since glucose is the principal substrate used during exercise and is also the main metabolic fuel for the developing embryo and fetus, exercising during pregnancy could induce a competition for fuel between fetus and exercising muscles, perturbing glucose homeostasis. To determine if exercise during pregnancy would predispose the fetus to increased risk, pregnant rats were randomly assigned to a low (4%), moderate (12%) or high (60%) carbohydrate diet, and either rested or exercised on a rodent treadmill at a moderate (15.5 m/min) or high (24.3 m/min) intensity from day 16-21 of gestation. When food intake was controlled for in the statistical model as a covariate, the level of maternal dietary carbohydrate significantly influenced maternal liver weight, heart glycogen, insulin, amniotic fluid glucose and lactate, but not maternal plasma glucose, liver or skeletal muscle glycogens. In contrast, a restricted level of maternal dietary carbohydrate, lowered fetal weight as well as fetal plasma glucose, insulin and liver glycogen. Exercise intensity significantly altered only maternal lactate levels. The results indicate that acute exercise during pregnancy can have detrimental effects on fetal development only if carbohydrate energy is restricted. Otherwise, adequate carbohydrate in the maternal diet appears to protect the fetus.

Exercise and dietary carbohydrate restriction during pregnancy independently reduce maternal weight gain and offspring survival. It was hypothesized that the combined stress of exercise and dietary carbohydrate restriction would decrease offspring survival more than the independent effects. Within the exercise and sedentary groups pregnant rats were randomly assigned to be fed either 60%, 40%, or 20% dietary carbohydrate ad libitum. No statistical interactions were found between exercise and diet. Main effects were found for litter weight, maternal feed intake and weight gain, but not for litter size, pup birthweight, or pup survival in the first two days postpartum. Exercised rats gained less weight and ate more on a per gram body weight basis than sedentary rats. Rats fed carbohydrate restricted diets ate less and gained less weight than the rats fed 60% carbohydrate. These results demonstrate that the neonatal rat is not vulnerable to the effects of moderate maternal exercise and carbohydrate restriction during pregnancy.

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Experiments were conducted with littermate gilts maintained in stainless steel metabolism cages within environmentally controlled rooms and consuming a corn-soybean meal based diet. The objectives of these studies were to investigate the impact of different dietary levels of manganese (Mn) and/or stage of the reproductive cycle on mineral metabolism and more specifically Mn metabolism in primigravid gilts and rats. Nutritional status was assessed using conventional balance studies, the analyses of physiological fluids (urine, plasma, colostrum, milk), tissues of the dam and offspring, and by a radioisotope dilution-balance technique. Trace element retention in the first-litter gilt was not significantly altered by dietary Mn restriction (11 $ mu$g/g DM) or by different stages of the reproductive cycle. In contrast, among the macro elements, phosphorus and perhaps calcium retention were improved in late gestation, whereas magnesium and nitrogen retention were unchanged. The weight of the litter at birth from dams consuming the low Mn (LMn) diet was significantly less than high Mn (HMn) gilts (96 $ mu$g/g DM). The Mn concentration in the liver and kidney of HMn gilts were significantly higher than in LMn gilts at the end of lactation. Likewise, the bones from HMn piglets contained higher concentrations of Mn at birth, and the liver and kidney concentrations were greater at weaning. Dietary Mn intake did not influence the rate of $ sp{54}$Mn excretion by the gilt during late gestation. The endogenous fecal Mn component was of similar magnitude, averaging 0.26 and 0.21 mg/d for the HMn and LMn gilts, respectively. However, the endogenous contribution to total fecal Mn was almost 8 fold different, representing 0.12% and 0.82% of total fecal Mn for the HMn and LMn gilts, respectively. The biological half-life of Mn in the body of the gilt was not influenced by dietary Mn within the intake range of 26 to 210 mg/d and averaged 54 days. The turnover rate (TR) of Mn was es

Glucose is a principle precursor for milk lactose and de novo synthesis of milk fat; therefore exercising during lactation could create competition for glucose between exercising muscle and lactating mammary gland. This study investigated the combined effects of maternal dietary glucose (20%, 40%, 60%), exercise (chronically exercised, sedentary) and litter size (8, 12 pups) on rat mammary gland composition, milk composition, milk yield and pup growth. Chronic exercise increased milk fat concentrations and an interaction between chronic exercise and 20% dietary glucose decreased milk lactose concentrations compared to 40% or 60% glucose diets. Restricting maternal dietary glucose also decreased milk fat concentrations and exercise decreased mammary fat. In addition, pups of dams fed the 40% glucose diet were heavier on lactation day 15 than pups of dams fed the 60% diet. These results suggest that competition for glucose occurs and that a 40% glucose maternal diet may be more appropriate for pup growth.