Estimação do valor energético da pastagem e simulação de parâmetros do desempenho produtivo de novilhas em pasto Estimation of pasture energy value and simulation of productive performance of heifers under grazing

Estimaram-se o valor energético das forrageiras e o consumo de matéria seca por novilhas, em função do ganho de peso, criadas em pastagens de capim-elefante (Pennisetum purpureum Schum. cv. Napier) e capim-mombaça (Panicum maximum, cv. Mombaça), manejadas sob sistema rotacionado, mediante amostras tomadas via extrusa esofágica. As amostras relativas ao terceiro, segundo e primeiro dias de ocupação foram utilizadas para determinar os teores matéria seca, proteína bruta, extrato etéreo, fibra em detergente neutro, fibra em detergente ácido, lignina e cinzas para calcular os nutrientes digestíveis totais (NDT). Os valores do NDT preditos pelo sistema americano (NRC) e os estimados a partir do ganho de peso foram comparados com ajustamento de modelo de regressão linear simples. Os ganhos médios de peso diário foram de 0,649kg e de 0,590kg, respectivamente, para o capim-elefante e para o capim-mombaça, o que resultou na rejeição da hipótese de nulidade, ou seja, resultou em ausência de equivalência entre os valores preditos pelo sistema e os observados. A incorporação do fator empírico de correção (0,85) em substituição ao valor (0,667) proposto pelo NRC minimizou a ocorrência deste comportamento viesado.<br>Elephantgrass (Pennisetum purpureum, Schum. cv. Napier) and mombaçagrass (Panicum maximum, cv. Mombaça) pastures were evaluated under rotational grazing with samplings taken by esophageal extrusa. The energy value of grasses and the dry matter intake of heifers as a function of the weight gains were estimated. Samples relating to the third, second, and first days of the occupation period were used to determine the dry matter (DM), crude protein (CP), ether extract (EE), organic matter (OM), neutral detergent fiber (NDF), and acid detergent fiber (ADF) to calculate the total digestible nutrients (TDN). The TDN values predicted by the American System (NRC) and those estimated from heifers weight gains were compared with adjustment of simple linear regression. The average weight gains were 0.649 and 0.590kg, respectively, for elephantgrass and mombaçagrass, that resulted in the rejection of nullity hypothesis, which means, it resulted in absence of similarity among values predicted by the system and those observed. The incorporation of the empirical factor (0.85) replacing the value (0.667) proposed by NRC resulted in better estimation

Significance of diet type and diet quality for ecological diversity of African ungulates

1.We test two nutritional hypotheses for the ecological diversity of ungulates, the browser/grazer (diet type) and diet quality models, among free-ranging herbivores in a South African savanna, the Kruger National Park. Tests are based on assessment of relationships between diet type and diet quality with body mass and hypsodonty, two morphological features that have been associated with both elements. 2.We use stable carbon isotope ratios of faeces to reconstruct diet in terms of proportions of C3 plants (browse) and C4 plants (grass) consumed by different species in different seasons. These data are combined with proxies for diet quality (per cent nitrogen, neutral detergent fibre, acid detergent fibre, and acid detergent lignin) from faeces to track changes in diet quality. 3.Two statistical approaches are used in model selection, i.e. tests of significant correlations based on linear regression analyses, and an information-theory approach (Akaike’s Information Criterion) providing insight into strength of evidence for models. 4.Results of both methods show that, contrary to many predictions, body mass and diet type are not related, but these data confirm predictions that diet quality decreases with increasing body size, especially during the dry season. Hypsodonty, as expected, varies with diet type, increasing with increased grass intake. 5.These findings support both a diet type and diet quality model, implying some degree of exclusivity. We propose that congruence between models may be achieved through addition of diet quality proxies not included here, because hypsodonty is more likely a reflection of the abrasive properties of consumed foods, i.e. related to food quality, rather than food type. This implies that adaptation to diets of varying quality, through changes in body size and dental features, has been the primary mechanism for diversification in ungulates. 6. Our interpretation contrasts with several recent studies advocating diet type as the primary factor, exemplifying that further reconciliation between the two models is needed. We discuss the implications of this study for future approaches to achieve a more cohesive understanding of the evolutionary outcomes of herbivore nutrition