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| Author(s): |
Tiago Zanett Albertini
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Piracicaba. |
| Institution: | Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC) |
| Defense date: | 2010-12-15 |
| Examining board members: |
Dante Pazzanese Duarte Lanna;
Eduardo Francisquine Delgado;
Roberto Daniel Sainz Gonzales;
Roberto Augusto de Almeida Torres Junior;
Silvio Sandoval Zocchi
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| Advisor: | Dante Pazzanese Duarte Lanna |
| Abstract | |
Our objective was to evaluate the effects of milk production, net energy requirements for lactation and mature live weigh of beef cows on energetic, economic and environmental efficiency of the cow-calf system. Several genotypes were used in a model that simulates the Brazilian cow-calf system in which data from three large experiments were analyzed by metaanalyses. The genotypes were Nellore (NL), Angus x Nellore (AN), Canchim x Nellore (CN), Caracu x Nellore (CR) and Simental Nellore (SN). An initial experiment defined the best approach to measure milk production as well as the parameters of the lactating curve. Two methodologies were tested: weigh-suckle-weigh (WSW) and machine milking (MM). Our results support the following: i) MM methodology is superior than WSW to predict genetic and environmental differences in milk production among beef cows and; ii) MM data analyzed by non-linear mixed (NLMM) models allow the evaluation of how different characteristics (e.g. genotype) affect the shape of the lactation curve and the net energy and protein requirements of the cows. With the data from the experiments, a cow-calf biologic, environmental and economic model was developed. The objective was to evaluate the effect of different parameters and productive characteristics of animals on efficiencies. Several statistical methods were used: lactation curve modeling by non-linear mixed-effects models (NLME), meta-analysis and structural equation modeling to establish the model. The complete cow-calf cycle simulation demonstrated the impact of mature body weight (BW) and milk production . Due to the lack of experimental reproductive data, the model assumed no genotype or requirements effects on the reproductive rates which were maintained constant. Results show that increasing mature BW reduces the system efficiency and reduces profitability by kilogram of weaned calf. The increase in milk production increases the efficiency and profitability of the cow-calf system (P < 0.05). Nellore cows presented lower energetic requirements than Nellore x Bos taurus cows (8 to 20% lower, P = 0.036). Cows having greater milk production potential and lower mature body weight are more profitable and at the same time have lower environmental impacts (less greenhouse gases emission per unit of beef). (AU) | |