Feed efficiency of Nellore cattle selected for postweaning weight

Abstract

-Two Nellore herds were compared, one selected for greater postweaning weight and the other, control, selected for average postweaning weight, to evaluate the effects of 29 years of selection on feed efficiency. Sixty Nellore males (41 selected and 19 control) averaging 205 kg and 267 days of age were evaluated in individual pens during performance test.Performance and dry matter intake were used to determine the following feed efficiency traits: feed conversion; residual feed intake; residual gain; partial growth efficiency; relative growth rate and Kleiber ratio. After the 112-day experimental period, control animals showed lower body weight when compared to selected animals, however, they did not differ for dry matter intake (% of body weight), rib-eye area and fat thickness at the 12 th rib subcutaneous region and on the rump region. Dry matter intake (kg/day) and average daily weight gain from selected animals were, respectively, 19.4% and 26.4% higher than the control ones. The highest average daily weight gain by selected animals promoted significant improvement, around 6%, on feed conversion; 70 g/day on residual gain; and 17% on Kleiber rate. The other feed efficiency traits (residual feed intake, partial growth efficiency and relative growth rate) did not differ between herds. The 29-year selection for post-weaning weight did not affect feed efficiency of Nellore cattle.Key Words: beef cattle, feed conversion, residual feed intake, selection Eficiência alimentar em bovinos Nelore selecionados para peso pós-desmame RESUMO -Foram comparados dois rebanhos Nelore, um selecionado para maior peso pós-desmame e outro controle, selecionado para a média de peso pós-desmame, para avaliar os efeitos de 29 anos de seleção sobre a eficiência alimentar.Sessenta machos Nelore com 205 kg e 267 dias de idade (41 selecionados e 19 controle), foram avaliados em baias individuais durante a prova de ganho de peso. O desempenho e o consumo de matéria seca foram utilizados para determinar as seguintes medidas de eficiência: conversão alimentar; consumo alimentar residual; ganho residual; eficiência parcial de crescimento; taxa de crescimento relativo; e taxa de Kleiber. Após o período experimental de 112 dias, os animais controle apresentaram menor peso vivo final em comparação aos selecionados, contudo, não diferiram quanto ao consumo de matéria seca (% do peso vivo), à área de olho-de-lombo e às espessuras de gordura subcutânea na altura da 12 a costela e na região da picanha. O consumo de matéria seca (kg/dia) e o ganho médio diário dos animais selecionados foram, respectivamente, 19,4 e 26,4% superiores aos dos controle. O maior ganho médio diário dos animais selecionados promoveu melhora significativa, em torno de 6%, na conversão alimentar; 70 g/dia no ganho residual; e de 17% na taxa de Kleiber. As demais medidas de eficiência (consumo alimentar residual, eficiência parcial de crescimento e taxa de crescimento relativo) não diferiram entre os rebanhos. Os 29 anos de seleção para peso pós-desmame não afetaram ...

Potentiality of Growth Traits for Selection to Improve Productivity in Nilotic Cattle

“…Another undesirable outcome from selection for growth traits is the increased cost of maintaining animals, due to increased feed intake. For instance, a study in Nellore cattle reported that animals selected for higher post-weaning BW, despite gaining more weight and better AGR and KR, consumed more metabolizable energy than animals selected based on null selection differential [38]. Moreover, there is a compelling body of evidence that selection for growth traits to improve growth, feed conversion efficiency or both could also increase appetite and feed intake, causing excessive deposition of body fat, with adverse consequences, including decreased milk production [4], [7], [8], [22] and [39].…”