Dynamics of animal growth and milk yield using animal and diet characteristics

• Ano de defesa: 2018
• Autor(a) principal: Amaral, Rafael Marzall do
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Ovelhas - Nutrição; Ovelhas - Crescimento; Leite - Produção; Dinâmica de Sistemas; Produção Animal
• Link de acesso: http://www.locus.ufv.br/handle/123456789/24816

This thesis is composed by two studies that aim to simulate biological process of animal production using System Dynamics (SD) approach. The first study aimed to use SD and mechanistic equations from current nutritional systems to describe and simulate the energy and protein requirements, the composition of gain, growth rate, and body mass of feedlot lambs. The developed model was evaluated with a dataset of 564 individual measures of final body mass and diet energy concentration. The simulation provides a graphical and numerical description of the nutrient requirements, composition of gain, and estimates animal performance over time. The simulation of final body mass presents a root-mean-squared error of 3.11 kilograms (kg), which corresponds to 7.79% of observed final body mass and a R2 of 0.89 indicating accuracy and precision, respectively. Based on empirical and conceptual equations proposed on scientific literature, the second study aimed to model the dry matter intake based on physiological energy demand and on physical limitation theory, the nutritional requirements, metabolizable energy intake, milk yield allowed, and methane production from enteric and manure fermentation as a function of fiber composition. By using the simulated information, the amount of each variable required per unit of fat corrected milk, the efficiency of feed and energy use, and the emission intensity were calculated. A simulation was conducted with chemical composition data of five maturity stages Pennisetum purpureum Schum. grass (61, 82, 103,124 and 145 days after planting) as exclusive diet to a 450 kg double purpose cow with 20 kgd-1 of potential milk yield with 3.5% of fat. The dry matter intake was limited by rumen fill capacity to all grasses maturities and decreases as neutral detergent fiber composition increases with forage maturity, reducing metabolizable energy intake, fermentative substrate intake, and milk yield. Milk yield allowed was ranged from 9.407 to 4.568 kg d-1 to younger and older forage, respectively. Methane production from enteric fermentation reduces with forage maturity, simulated values range from 103.8 and 74.5 gday-1, to younger and older forage, respectively. A reduction of feed efficiency of 9.25% was estimated from 61 to 82 days of growing grass, accounting the reduction of feed intake and the metabolizable energy concentration. Simulated methane production per unit of product presents a difference of 32.33% ranging between 11.0 and 16.3 grams per kilogram of product to 61 and 145 days of regrowth, respectively. The models can be used as a support decision and as learning tools to illustrate practical principles of animal nutrition, nutrient requirement relationships, body composition changes, understanding of standard body mass implications, feed intake regulation, tropical dairy cattle performance, feed and energy efficiencies, and methane emissions from enteric and manure fermentation as function of fiber composition.