The aim of this study was to evaluate the Small Ruminant Nutrition System (SRNS) model’s performance predictions for lambs under South African conditions using growth and body composition data of early- (Dorper) and late-maturing (South African Mutton Merino), indigenous sheep breeds. The Cornell Net Carbohydrate and Protein System (CNCPS) biological model has consistently been modified to include recent information. This has led to the development of the SRNS model, but up to now the SRNS model has only been validated with European sheep breeds under European conditions. Thirty two Dorper, 16 male and 16 female lambs, and 36 South African Mutton Merino, 18 male and 18 female lambs, were fed a grower diet for the experimental period of 60 days. Three groups of lambs of each breed were slaughtered as the lambs reached pre-determined target weights. The first group of 24 animals (slaughter group 1) was slaughtered at the onset of the experiment at a live weight of 20 kg. With the second group (slaughter group 2) the South African Mutton Merinos were slaughtered at an average weight of 35 kg and the Dorpers at an average weight of 30 kg. The last group (slaughter group 3) had an average weight of 50 kg for the South African Mutton Merinos and 40 kg for the Dorpers at slaughter. Using the data from this trial, predictions of the average daily gain (ADG), feed intake (DMI), empty body gain and the composition of the empty body gain were used to evaluate the model. The animals were divided into three slaughter groups, based on growth stage, for the determination of body composition data. Energy value of gain (EVG), fat and protein content on a shrunk and empty body weight basis were compared with the corresponding values predicted by the SRNS. Growth composition of the lambs was determined by dividing them into two growth periods. Average daily gain and DMI were evaluated in the experiment, and results compared to the mean ADG and DMI predictions obtained from the SNRS model. Two different equations were compared to estimate EVG and two sets of coefficients were also compared for the EVG. Five different equations were compared to estimate the efficiency of conversion of metabolisable energy (ME) to net energy (NE) for gain, kg. The correction factor to adjust for the increase in the size of the visceral organs as nutrient intake increases and the coefficient for the effect of gender on maintenance requirements were tested for relevance of use in the SRNS. Overall, based on these evaluations it appears that the original SRNS model gave the best predictions when compared to any of the modifications tested. With regards to ADG the model over-predicts the requirements of the lambs in the early growth stage and under-predicts the requirements of the lambs in the later growth stage. The DMI predictions that were made using the original SRNS were accurate. The evaluation of the SNRS predictions in relation to the composition of gain indicated that this model over-predicted both the fat and the protein content of gain. The predictions were accurate, however the precision was low. The low precision was probably due to the lack of variation in the measured range of fat and protein content of gain. Before field application further studies and adjustments to the SRNS model is required, especially with regard to predictions on the fat and protein content of gain and over or under predictions of ADG during different growth stages of Dorper and South African Mutton Merino lambs. / Dissertation (MSc)--University of Pretoria, 2013. / gm2014 / Animal and Wildlife Sciences / unrestricted

Fontes protéicas em rações ricas em amido foram avaliadas para cordeiros em confinamento. O primeiro aspecto foi investigar a variação do consumo de matéria seca (MS) de 28 cordeiros da raça Santa Inês; o ganho de peso médio diário (GMD), as características de carcaça e da carne e o custo dos alimentos. O delineamento foi em blocos completos casualizados, sendo as dietas isonitrogenadas, com 90% de concentrado e 10% de feno de coastcross. As rações foram formuladas pelo Small Ruminant Nutrition System (SRNS) versão 1.8.1 e diferiam quanto à fonte suplementar de proteína: farelo de soja, farelo de amendoim, farelo de canola, farelo de algodão. O segundo aspecto avaliado foi o ensaio metabólico com quatro borregos fistulados no rúmen distribuídos em delineamento em quadrado latino 4x4 sendo analisadas as características físicas de capacidade de retenção de água (CRA), solubilidade, tamanho médio de partículas e densidade das fontes protéicas relacionados com a degradabilidade ruminal e a taxa de passagem. A contaminação de nitrogênio microbiano na degradabilidade da proteína das rações totais foi corrigida pelo nitrogênio insolúvel em detergente neutro (NIDN). Determinou-se a digestibilidade dos nutrientes no trato digestório total, o balanço de nitrogênio, as concentrações de nitrogênio amoniacal (N-NH3), ácidos graxos de cadeia curta (AGCC), o pH ruminal e a síntese de proteína microbiana. Adicionalmente, o teor de amido nas fezes foi avaliado como indicador para estimar a digestibilidade do amido das rações. Como último aspecto estudado, confrontou-se os dados metabólicos e de desempenho obtidos no ensaio experimental com as estimativas obtidas no SRNS. As fontes protéicas não alteraram (P>0,05) os parâmetros de desempenho e as características de carcaça e da carne. A solubilidade e a CRA influenciaram (P<0,05) a degradabilidade efetiva da MS. A ração com o farelo de algodão apresentou menor (P<0,05) degradabilidade efetiva da proteína bruta o que refletiu em maior (P<0,05) excreção de nitrogênio nas fezes. A contaminação microbiana subestimou a taxa de degradação da ração total em aproximadamente 13,5%. O farelo de canola apresentou menor taxa de passagem (P<0,05) e o principal parâmetro físico relacionado com essa variável foi a CRA. A ração com o farelo de amendoim promoveu menor custo de nitrogênio por kg de ganho, maiores concentrações de (N-NH3) e menores proporções de (AGCC) (P<0,05), porém, a síntese de nitrogênio microbiano e a excreção de nitrogênio na urina foram semelhantes (P>0,05) entre os tratamentos. O teor de amido fecal mostrou-se eficiente como indicador na estimativa da digestibilidade do amido com coeficiente de determinação de 93%. As estimativas de desempenho e metabólica do sistema SRNS foram satisfatórias com algumas diferenças (P<0,05) na ingestão de MS e na taxa de passagem. Os resultados apresentados poderão contribuir com o banco de dados de sistemas de formulação de rações para ovinos em crescimento. / Protein sources in starch rich diets for finishing lambs were evaluated in this study. Twenty-eight Santa Ines ram lambs were used to determine the effects of using different protein sources in dry matter intake, average daily gain and characteristics of carcass and meat. Lambs were assigned, by weight and age at the beginning of the trial, in a complete randomized block design. Experimental diets were isonitrogen with 90% concentrate and 10% coastcross hay. Rations were formulated using the Small Ruminant Nutrition system (SRNS) version 1.8.1 and had one of the following protein sources: soybean meal, peanut meal, canola meal or cottonseed meal. A metabolism assay using a Latin square 4 x 4 design also was performed. Four rumen cannulated wethers were used to determine protein sources physical characteristics: water holding capacity (WHC), solubility, mean particle size and density in relation with ruminal degradability and rate of passage. Microbial nitrogen contamination of TMR was corrected by in neutral detergent fiber insoluble nitrogen. Total tract diet digestibility, nitrogen balance, ammonia nitrogen concentration (N-NH3), short chain fatty acids, ruminal pH and microbial protein synthesis were determined. In addition, fecal starch concentration was evaluated as an indicator to estimate starch digestibility in the ration. Performance and metabolic data were compared to SRNS estimates. Protein sources did not affected performance or carcass and meat characteristics. Water holding capacity and solubility affected (P<0.05) DM effective degradability. Cottonseed diet resulted in lower (P<0.05) CP effective degradability showing higher (P<0.05) excretion of fecal N. Microbial contamination underestimated diet degradation in 13.5%. Canola meal diet had the lower rate of passage and the main physical parameter related with this variable was water holding capacity. Peanut meal diet had high concentration of NNH3 and the lowest short chain fatty acids concentration. However, microbial N synthesis and excretion of N in urine were similar among treatments. Fecal starch concentration was a good indicator to estimate starch digestibility showing a coefficient of determination of 93%. Estimates from SRNS for DM intake and rate of passage were different from observed data. There results may contribute to predict nutrient requirements and biological value of feeds for lambs.

Fontes protéicas em rações ricas em amido foram avaliadas para cordeiros em confinamento. O primeiro aspecto foi investigar a variação do consumo de matéria seca (MS) de 28 cordeiros da raça Santa Inês; o ganho de peso médio diário (GMD), as características de carcaça e da carne e o custo dos alimentos. O delineamento foi em blocos completos casualizados, sendo as dietas isonitrogenadas, com 90% de concentrado e 10% de feno de coastcross. As rações foram formuladas pelo Small Ruminant Nutrition System (SRNS) versão 1.8.1 e diferiam quanto à fonte suplementar de proteína: farelo de soja, farelo de amendoim, farelo de canola, farelo de algodão. O segundo aspecto avaliado foi o ensaio metabólico com quatro borregos fistulados no rúmen distribuídos em delineamento em quadrado latino 4x4 sendo analisadas as características físicas de capacidade de retenção de água (CRA), solubilidade, tamanho médio de partículas e densidade das fontes protéicas relacionados com a degradabilidade ruminal e a taxa de passagem. A contaminação de nitrogênio microbiano na degradabilidade da proteína das rações totais foi corrigida pelo nitrogênio insolúvel em detergente neutro (NIDN). Determinou-se a digestibilidade dos nutrientes no trato digestório total, o balanço de nitrogênio, as concentrações de nitrogênio amoniacal (N-NH3), ácidos graxos de cadeia curta (AGCC), o pH ruminal e a síntese de proteína microbiana. Adicionalmente, o teor de amido nas fezes foi avaliado como indicador para estimar a digestibilidade do amido das rações. Como último aspecto estudado, confrontou-se os dados metabólicos e de desempenho obtidos no ensaio experimental com as estimativas obtidas no SRNS. As fontes protéicas não alteraram (P>0,05) os parâmetros de desempenho e as características de carcaça e da carne. A solubilidade e a CRA influenciaram (P<0,05) a degradabilidade efetiva da MS. A ração com o farelo de algodão apresentou menor (P<0,05) degradabilidade efetiva da proteína bruta o que refletiu em maior (P<0,05) excreção de nitrogênio nas fezes. A contaminação microbiana subestimou a taxa de degradação da ração total em aproximadamente 13,5%. O farelo de canola apresentou menor taxa de passagem (P<0,05) e o principal parâmetro físico relacionado com essa variável foi a CRA. A ração com o farelo de amendoim promoveu menor custo de nitrogênio por kg de ganho, maiores concentrações de (N-NH3) e menores proporções de (AGCC) (P<0,05), porém, a síntese de nitrogênio microbiano e a excreção de nitrogênio na urina foram semelhantes (P>0,05) entre os tratamentos. O teor de amido fecal mostrou-se eficiente como indicador na estimativa da digestibilidade do amido com coeficiente de determinação de 93%. As estimativas de desempenho e metabólica do sistema SRNS foram satisfatórias com algumas diferenças (P<0,05) na ingestão de MS e na taxa de passagem. Os resultados apresentados poderão contribuir com o banco de dados de sistemas de formulação de rações para ovinos em crescimento. / Protein sources in starch rich diets for finishing lambs were evaluated in this study. Twenty-eight Santa Ines ram lambs were used to determine the effects of using different protein sources in dry matter intake, average daily gain and characteristics of carcass and meat. Lambs were assigned, by weight and age at the beginning of the trial, in a complete randomized block design. Experimental diets were isonitrogen with 90% concentrate and 10% coastcross hay. Rations were formulated using the Small Ruminant Nutrition system (SRNS) version 1.8.1 and had one of the following protein sources: soybean meal, peanut meal, canola meal or cottonseed meal. A metabolism assay using a Latin square 4 x 4 design also was performed. Four rumen cannulated wethers were used to determine protein sources physical characteristics: water holding capacity (WHC), solubility, mean particle size and density in relation with ruminal degradability and rate of passage. Microbial nitrogen contamination of TMR was corrected by in neutral detergent fiber insoluble nitrogen. Total tract diet digestibility, nitrogen balance, ammonia nitrogen concentration (N-NH3), short chain fatty acids, ruminal pH and microbial protein synthesis were determined. In addition, fecal starch concentration was evaluated as an indicator to estimate starch digestibility in the ration. Performance and metabolic data were compared to SRNS estimates. Protein sources did not affected performance or carcass and meat characteristics. Water holding capacity and solubility affected (P<0.05) DM effective degradability. Cottonseed diet resulted in lower (P<0.05) CP effective degradability showing higher (P<0.05) excretion of fecal N. Microbial contamination underestimated diet degradation in 13.5%. Canola meal diet had the lower rate of passage and the main physical parameter related with this variable was water holding capacity. Peanut meal diet had high concentration of NNH3 and the lowest short chain fatty acids concentration. However, microbial N synthesis and excretion of N in urine were similar among treatments. Fecal starch concentration was a good indicator to estimate starch digestibility showing a coefficient of determination of 93%. Estimates from SRNS for DM intake and rate of passage were different from observed data. There results may contribute to predict nutrient requirements and biological value of feeds for lambs.