Identification of energetically efficient mature cows and characterization of biological differences between efficient and inefficient cows

• Ano de defesa: 2019
• Autor(a) principal: Reis, Bárbara Roqueto dos
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Beef cattle; Eficiência energética; Energy efficiency; Energy efficiency index; Índice de eficiência energética; Vacas de corte
• Link de acesso: http://www.teses.usp.br/teses/disponiveis/74/74131/tde-25042019-094418/

Beef cows classified as efficient utilize less resources to achieve the same output than inefficient animals in a sustainable environment. The objective of this study was to utilize a mathematical model to identify beef cows that use energy more efficiently to support maintenance requirements and calf growth based an energy efficiency index (EEI). The EEI was computed as the ratio of metabolizable energy requirements (MER) of the cow to weaning weight of the calf. Data were collected from one herd of 69 Angus crossbred cows over two consecutive years for a performance experiment. The EEI was used to rank the cows for efficiency, cows with low EEI are more efficient because they require less metabolizable energy for the same calf weaning weight. After the cows were ranked in year 1, low (n=8) and high (n=8) EEI cows were selected for an energy metabolism experiment during late lactation and late gestation in year 2. Relationships among performance and efficiency traits were computed with PROC CORR of SAS. Metabolism experiment data were analyzed as a randomized complete block design using PROC MIXED of SAS with side of barn as the random blocking factor. Correlation coefficients were considered different from zero and LSmeans were considered different at P < 0.05. The EEI was strongly negatively correlated (P < 0.05) with model predicted peak milk and calf weaning weight, and moderately, positively correlated (P < 0.05) with cow body weight in both years such that more efficient cows weaned heavier calves and had lesser body weight. Energy efficiency index was moderately, positively correlated (P < 0.05) among years indicating that those cows ranked as efficient in one year tend to be more efficient cows in subsequent years. Low EEI cows had lesser (P < 0.05) dry matter digestibility during late lactation, but not during late gestation than high EEI cows. There were no differences in energy metabolism between low and high EEI cows during late lactation or late gestation. In conclusion, more efficient cows based on EEI wean heavier calves and require less energy but the mechanism by which low EEI cows are more efficient does not appear to be differences in the energy partitioning.