This dissertation research contained three studies. The first two studies were conducted to investigate the ability of ewes to rebreed while lactating during seasonal anestrus. Breeds studied included the Virginia Tech Out-of-season (OOS) Line, which is a wool line genetically selected to lamb in the fall, and the St. Croix, a hair breed of tropical origin thought to be lowly seasonal. When January-lambing ewes were exposed to rams while lactating in April, significantly more OOS than St. Croix ewes were marked by rams in the first 21 d and total 39 d of ram exposure (58.3 vs. 8.7%, P = 0.0003 and 95.8 vs. 43.5%, P < 0.0001). Percentages of ewes diagnosed pregnant (53.2%) and percentages of ewes lambing (41.3%) were not different between breeds. When March-lambing OOS ewes were exposed to rams while lactating in May, 52.9% of ewes were marked though only 20% of ewes exposed to rams gave birth to viable lambs. Both OOS and St. Croix ewes appear to be well suited to accelerated production systems involving 7 to 8 mo lambing intervals. However, reduction of lambing intervals to 6 to 7 mo appeared to have detrimental effects on fetal survival in OOS ewes. In a third study, alterations in endocrine profiles associated with differing degrees of hypothalamic sensitivity to estradiol-negative feedback and changing daylength in OOS, St. Croix, and Suffolk ewes in the absence of rams were investigated for 1 yr. The results show for the first time that based on progesterone profiles from intact ewes, St. Croix ewes do not have shorter anestrous periods than ewes of wool breeds, as previously thought. Based on luteinizing hormone profiles from ovariectomized ewes treated with estradiol implants, the duration of luteinizing hormone inhibition was shorter in OOS than Suffolk ewes (68 vs. 170.2 d, P = 0.02), but was not different from that found in St. Croix ewes (124.8 d). Specific roles for thyroxine and prolactin in timing the breeding season could not be assigned. This study was the first known use of the ovariectomized, estradiol-implanted ewe model to compare degree of reproductive seasonality in different breeds. / Ph. D.

LD2668 .T4 1947 M6 / Master of Science

During peak lactation female mammals reach a limit in their maximal sustained energy intake (SusEI). The causes of such limits is disputed. In this thesis, I examined the causes of the limits on SusEI at peak lactation, and then explored the consequences of such limits for reproductive performance. Finally I tested a possible physiological mechanism that may underpin the trade-off between reproduction and somatic protection (the oxidative stress theory). To answer these questions, I studied reproductive performance and oxidative stress in two lines of mice previously selected for high and low food intake (MH and ML, respectively). I found that these mice reached a plateau in their food intake around day 13 of lactation. In support of the heat dissipation limits theory, reproductive performance in the MH mice was significantly higher than that of the ML mice. Oxidative damage is expected to be higher among lactating individuals. Moreover, lactating mice with greater reproductive performance are also predicted to experience more oxidative damage. By measuring multiple-markers of oxidative damage and protection in different tissues, I found that lactation resulted in reduced oxidative damage in both brain and serum. Additionally, it did not increase oxidative damage to proteins and DNA in liver. Moreover, multiple measures of oxidative stress in the mammary gland were not significantly different between mice with different reproductive effort. Furthermore, I found that lactating mice with greater reproductive performance (litter size and litter mass) had reduced protein damage in their livers and upregulated protection (HSP70) in their brains. These results were inconsistent with the oxidative stress theory. Finally, I employed a novel approach to assess oxidative stress differences with metabolomics analysis. I found that lactation resulted in significant differences in the metabolome. By focusing on the metabolites that are related to vi oxidative stress, I found that most of these metabolites measured in livers and brains were not affected by lactation which provides more evidence against the oxidative stress theory. My results provide support for the heat dissipation theory as a mechanism explaining the limits on reproductive performance. Moreover it provides comprehensive information against oxidative stress as a mediator of life history trade-offs.

This quasi-experimental study, using Orem's Nursing Systems Construct as a theoretical base, was conducted to determine the effects of education and support given by a lactation consultant on early breastfeeding problem incidence and resolution. Mothers were recruited in the hospital and interviewed by telephone two to three weeks postpartum to determine problem incidence, rate of resolution, perception of the problems' interference, self-care measures, and support network characteristics. The study sample consisted of 16 first-time breastfeeding mothers placed in naturally occurring experimental (n = 7) and control (n = 9) groups. The groups did not differ significantly in age, education, ethnicity, mode of birth, or presence of a support person in the home. The groups did not differ significantly in number of problems, problem resolution length, or perceptions regarding problems' severity. A significant difference was found in the use of formula supplements, with the control group using supplementation more than the experimental group.

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Mammals usually develop immunity to gastrointestinal nematode parasites. However, during late pregnancy and lactation, this immunity often breaks down, resulting in elevated levels of parasitism. This periparturient relaxation of immunity (PPRI) renders lactating hosts main sources of infection for their parasite-naïve offspring, and may have a nutritional basis. Results of studies on parasitized hosts suggest that both crude protein (CP) and metabolizable energy (ME) supply may be important in regulating the degree of PPRI by affecting the immune response towards parasites. However there is a scarcity of data supporting such a role for ME in periparturient hosts, while there is sufficient evidence to support the view that CP in general, and amino acids are potent immunonutrients in various disease states (Chapter 1). In the first experiment (Chapter 2) I seperated effects of CP and ME on PPRI by feeding parasitized lactating rats at two levels of ME supply and one of three levels of CP supply. The results show that PPRI is sensitive to CP scarcity, and not to moderate ME scarcity. Increasing CP supply improved lactational performance and reduced PPRI, as observed by reduced worm burdens. In the second experiment (Chapter 3) I examined the rate at which improved nutrition can restore immunity by feeding low protein diets to rats nursing high number of pups, and then reduced litter size in a sub-group so that host nutritional status would change from scarce to adequate. The egg production of the parasite population of the latter group reduced within days to similarly low levels as rats that had always reared low number of pups and this was associated with an increased number of musosal mast cells and increased dam weight gain. Since host responses to dietary CP are almost by ii definition responses to essential amino acids, the third experiment assessed the sensitivity of PPRI to methionine and leucine deficiency (Chapter 4). The latter resulted in increased worm burdens and egg production to similar levels when low protein diets are fed and imposed penalties in lactational performance. Finally, in the fourth experiment it was investigated whether similar outcomes can be expected in periparturient ruminant hosts by supplementing sheep with field beans, which are deficient in methionine, instead of soybean meal (Chapter 5). Indeed, feeding high protein diets based on field beans was less effective in reducing the worm egg excretion and improving lactational performance. The data from this thesis (Chapter 6) provide novel information on the nutritional basis of PPRI, showing that the latter can be rapidly reduced through improved protein nutrition. This may be seen as a response to the protein quality of the diet and the supply of amino acids in optimum quantities. These results have implications for parasite control strategies in farm animals.

In this investigation energy demands from offspring were varied for the MF1 mouse after litter sizes were manipulated and set to 5 pups/litter or 16 pups/litter by cross-fostering to examine the effects on immediate lactation and subsequent reproductive performance. Pups reared in manipulated large litters grew slower and were weaned lighter (half the size of pups reared in small litters) than pups reared in manipulated small litters.  Mortality of pups was high in the large litters but pups did not die in small litters. The results of a subsequent reproduction that followed the first lactation suggested an apparent cost for the female group that previously reared pups in large litters.  This is because in the subsequent reproduction, the group raised litters that were significantly (P&lt;0.05) 12.7g less in mass than litters raised by females that previously reared pups in small litters.  This apparent cost, however, did not appear to have severe negative impact on the general reproductive performance because data showed comparable litter sizes and masses at birth, growth rates of pups, and the number and masses of pups weaned between this group and females that previously reared pups in small litters. At reproductive age, female offspring previously weaned from large litters weighted significantly (P&lt;0.05) 5.8g less than female offspring previously weaned from small litters.  During their first breeding attempt or episode, female offspring previously weaned from large litters did not catch-up in body mass with those previously weaned from small litters.  In spite of this, the two groups ingested similar quantities of food prior to mating and during lactation.  The groups did not differ significantly (P&gt;0.05) in efficiencies of energy utilization, milk energy output and daily energy expenditure.  Consequently, they showed comparable breeding success. Different age groups of male and female offspring previously weaned from manipulated small (5 pups/litter) or large litters (16 pups/litter) and unmanipulated normal litters (10 pups/litter) varied significantly in body mass and did not show compensatory growth at the time they were examined for susceptibility to obesity and glucose intolerance.  A batch of six months old male offspring previously weaned from litters whose mothers were fed a particular macronutrient diet during lactation did not differ significantly in body mass when they were also examined for susceptibility to obesity.  All groups and sexes showed a tendency to develop obesity when they were challenged with a diet that contained up to 45% fat by calories.  Development of obesity did not appear to depend on  a particular litter size in which the mice were previously reared and weaned or whether the mice were previously suckled by mothers that were fed a particular macronutrient diet.  However, the development of obesity exhibited sexual dimorphism with the male offspring showing a higher tendency to develop obesity than female offspring.