No description available.

<p> There is a large literature discussing social influences on diet choices in rats. However, the ontogeny of social influences on diet choices is poorly understood. Early experiences have dramatic affects on the development and expression of future behaviors.</p> <p> The present research investigates whether early social experience altered the susceptibility to social influences on diet choices in juvenile Norway rats (R. norvegicus). Interactions with dam and siblings between parturition and weaning are prominent features of early rats development. It was hypothesized social behavior developed during this period and rearing pups in social isolation would disrupt the development of normal social behaviors.</p> <p> Conspecifics influence the diet preferences of others by socially interacting. The first experiment investigated whether demonstrators could influence diet choices of rats with no social experience. In terms of diet preferences, demonstrators influenced both normally reared rats and rats reared in social isolation.</p> <p> Interactions with conspecifics and exposure to diet odors without social contexts influenced the diet choices of 21 day old pups. Only interactions with conspecifics influenced diet choices of 28 day old rats. Rearing rats in social isolation may delay the onset of social specificity and the results of experiment 1 may have been the product of two different mechanisms. The second experiment investigated whether rats reared in social isolation attended to socially specific cues or to general olfactory cues. Exposure to flavored diets in a non-social context did not influence diet choices of rats reared in social isolation or normally-reared rats. Thus early social interactions do not appear to be necessary for demonstrator rats to influence the diet choices of other rats.</p> / Thesis / Master of Science (MSc)

Estimating feed efficiency in grazing environments is challenging due to difficulties in quantifying food intakes and diet choices in free-grazing animals. The plant-wax marker technique may be a useful tool to redress this problem. However, its reliability needs to be validated before its wider application. This study was designed to assess the reliability of plant-wax markers for estimating botanical composition of test diets, and diet choices in beef cattle, and provided opportunities to evaluate efficiency in growing heifers. To test estimation of botanical composition, samples of red clover and fescue hay were mixed to form test diets containing 0-100% of either forage. To test estimation of diet choices, 24 heifers from large and moderate frame size lines were evaluated at two instances. Cubed red clover and fescue hays were offered ad libitum. After an acclimation period, feed intakes and body weights were collected for 10 days; fecal samples were collected for the final 5 days. Hydrocarbons and alcohols were quantified with gas chromatography. Estimates were based on least squares. Operator expertise affected measured concentrations of shorter-chained n-alkanes (P<0.041) and long-chain alcohols (P<0.02). Still, overall reliability of the technique was unaffected. Large and moderate framed animals did not differ in efficiency (P>0.05), although large framed animals had increased red clover intakes (P<0.01). Once corrected for fecal losses of n-alkanes, diet choices were estimated accurately. Plant-wax markers provided reliable estimates of botanical composition of diets, and diet choices of animals, suggesting it is a valuable tool to assess efficiencies of grazing cattle. / Master of Science

Foi objetivo do presente estudo avaliar o efeito do estresse térmico sobre a seleção da dieta e digestibilidade dos nutrientes em bovinos através de um ensaio delineado inteiramente ao acaso, utilizando-se doze vacas secas, não gestantes e portadoras de cânulas ruminais. O ensaio foi conduzido no período de 20 dias e contou com dois tratamentos: conforto (galpão aberto, 21°C) e estresse (câmara climática, 38°C). Os alimentos oferecidos, separadamente e à vontade, foram cana-de-açúcar e uréia (14% PB) e concentrado a base de milho e farelo de soja (14% PB). A capacidade de seleção dos animais foi identificada através da comparação da dieta selecionada nos dois diferentes ambientes, dos parâmetros da fermentação ruminal e digestibilidade total obtida pelo marcador externo óxido de cromo. Os animais em estresse térmico reduziram em 22% o consumo de matéria seca (kgMS/dia) comparados aos mantidos em temperatura de conforto. A relação concentrado:volumoso escolhida não diferiu entre os tratamentos. Isto sugere que os animais reduziram a ingestão total de matéria seca sem alterar a concentração de energia e fibra das suas dietas, na tentativa de manter estável o ambiente ruminal. Quanto aos parâmetros ruminais, não houve diferença sobre a concentração total dos ácidos graxos voláteis, porcentagens molares dos ácidos acético, propiônico e butírico, relação acético/propiônico e pH ruminal. Foi observado aumento de 47% na concentração de N-amoniacal nos animais estressados. Esses achados sugerem que os animais, através da seleção de dietas, objetivam a manutenção de seu ambiente ótimo, corrigindo desbalanços e minimizando seu desconforto. Em contrapartida, houve redução na digestibilidade (49% para a matéria seca, 55% para a proteína bruta, 26% para extrativo não nitrogenado, 31% para extrato etéreo, 44% para o amido e 52% para energia bruta) nos animais em estresse térmico, reduzindo assim a disponibilidade dos nutrientes da dieta pelos bovinos. / The effect of heat stress on diet selection of ruminants was studied in a completely randomized design with 12 fistulated dry cows. The trial was conducted in 20 days with two treatments: thermal comfort (open barn, 21°C) and heat stress (climatic chamber, 38°C). Feeds were offered separately and ad libitum and composed by sugar cane + urea (14% CP) and concentrate, based on corn + soybean meal (14% CP). The ability of bovine to select their diets was identified comparing the composition of diet selected, ruminal fermentation parameters and total tract digestibility (chromic oxide as external marker) in different environments. A decrease of 22% in total dry matter intake was observed for animals in heat stress compared to the ones in comfort environment. Concentrate:roughage radio chosen was similar for both treatments. These data suggest that animals decreased dry matter intake without changing energy and fiber concentration in their diets, attempting maintain a stable ruminal environment. There was not difference on total volatile fatty acids production in the rumen, molar percentage of acetate, propionate and butirate, acetate/propionate ratio and ruminal pH. Ammoniacal-N concentration in the rumen was 47% higher for stressed than for comfort animals. This indicates that animals do make wise choices in order to maintain an ideal ruminal environment. However, there was a decrease in digestibility (49% for dry matter, 55% for crude protein, 26% for nitrogen-free extractive, 31% for ether extract, 44% for starch and 52% for gross energy) for animals in stress, reducing the availability of nutrients for bovine.

Foi objetivo do presente estudo avaliar o efeito do estresse térmico sobre a seleção da dieta e digestibilidade dos nutrientes em bovinos através de um ensaio delineado inteiramente ao acaso, utilizando-se doze vacas secas, não gestantes e portadoras de cânulas ruminais. O ensaio foi conduzido no período de 20 dias e contou com dois tratamentos: conforto (galpão aberto, 21°C) e estresse (câmara climática, 38°C). Os alimentos oferecidos, separadamente e à vontade, foram cana-de-açúcar e uréia (14% PB) e concentrado a base de milho e farelo de soja (14% PB). A capacidade de seleção dos animais foi identificada através da comparação da dieta selecionada nos dois diferentes ambientes, dos parâmetros da fermentação ruminal e digestibilidade total obtida pelo marcador externo óxido de cromo. Os animais em estresse térmico reduziram em 22% o consumo de matéria seca (kgMS/dia) comparados aos mantidos em temperatura de conforto. A relação concentrado:volumoso escolhida não diferiu entre os tratamentos. Isto sugere que os animais reduziram a ingestão total de matéria seca sem alterar a concentração de energia e fibra das suas dietas, na tentativa de manter estável o ambiente ruminal. Quanto aos parâmetros ruminais, não houve diferença sobre a concentração total dos ácidos graxos voláteis, porcentagens molares dos ácidos acético, propiônico e butírico, relação acético/propiônico e pH ruminal. Foi observado aumento de 47% na concentração de N-amoniacal nos animais estressados. Esses achados sugerem que os animais, através da seleção de dietas, objetivam a manutenção de seu ambiente ótimo, corrigindo desbalanços e minimizando seu desconforto. Em contrapartida, houve redução na digestibilidade (49% para a matéria seca, 55% para a proteína bruta, 26% para extrativo não nitrogenado, 31% para extrato etéreo, 44% para o amido e 52% para energia bruta) nos animais em estresse térmico, reduzindo assim a disponibilidade dos nutrientes da dieta pelos bovinos. / The effect of heat stress on diet selection of ruminants was studied in a completely randomized design with 12 fistulated dry cows. The trial was conducted in 20 days with two treatments: thermal comfort (open barn, 21°C) and heat stress (climatic chamber, 38°C). Feeds were offered separately and ad libitum and composed by sugar cane + urea (14% CP) and concentrate, based on corn + soybean meal (14% CP). The ability of bovine to select their diets was identified comparing the composition of diet selected, ruminal fermentation parameters and total tract digestibility (chromic oxide as external marker) in different environments. A decrease of 22% in total dry matter intake was observed for animals in heat stress compared to the ones in comfort environment. Concentrate:roughage radio chosen was similar for both treatments. These data suggest that animals decreased dry matter intake without changing energy and fiber concentration in their diets, attempting maintain a stable ruminal environment. There was not difference on total volatile fatty acids production in the rumen, molar percentage of acetate, propionate and butirate, acetate/propionate ratio and ruminal pH. Ammoniacal-N concentration in the rumen was 47% higher for stressed than for comfort animals. This indicates that animals do make wise choices in order to maintain an ideal ruminal environment. However, there was a decrease in digestibility (49% for dry matter, 55% for crude protein, 26% for nitrogen-free extractive, 31% for ether extract, 44% for starch and 52% for gross energy) for animals in stress, reducing the availability of nutrients for bovine.