Abstract
The objective was to evaluate protein turnover, nitrogen balance, feed energy partitioning, behavior patterns and plasma cortisol in Nellore (B. indicus) cattle with high and low residual feed intake (RFI = actual minus expected dry matter intake). Seventy-two Nellore steers (16 to 21 months-old, 334±19 kg initial body weight) were fed a feedlot diet for 70 days ad libitum. Daily dry matter intake (DMI) and average daily gain (ADG) were recorded individually and RFI was calculated. The 12 steers of lowest (Low-RFI, most efficient) RFI and the 12 ones of highest RFI (High-RFI, least efficient) were evaluated with respect to their behavior patterns and plasma cortisol concentration. Urine was collected for determination of daily 3-methylhistidine excretion (3MH) and myofibrillar protein breakdown rates. Urinary, gaseous and fecal energy losses were determined as well as the N retention and excretion. High-RFI steers tended to have shorter lying and idle periods and greater feeding time and plasma cortisol levels than low-RFI cattle. No RFI effects were seen for urine 3MH excretion and for rates of protein degradation and synthesis. No effects of efficiency class were observed for N excretion or N retention. No RFI effects were observed for dry matter digestibility, digestible energy (DE) and metabolizable energy (ME) content and DE/ME ratio. Methane energy losses were lower for low- compared with high-RFI steers. Protein turnover seems not to affect feed efficiency in Nellore steers. Improved RFI in Nellore steers is probably associated with lower degrees of activity and responsiveness to stress and lower losses of dietary energy as methane.
Highlights
Improving feed efficiency (FE) in livestock has been recognized as an important tool to decrease production costs and negative environmental impacts
No residual feed intake (RFI) effects were observed for dry matter digestibility, digestible energy (DE) and metabolizable energy (ME) content and DE/ME ratio
The steers were fed in feedlots a diet composed of coastcross hay (25.4%), ground corn (35.8%), soybean hulls (35%), 45% crude protein (CP), soybean meal (2.2%), mineral premix (0.6%) and urea (1%), on a dry basis, with estimated CP and metabolizable energy (ME) content of 14.3% and 2.63 Mcal/kg DM (NRC, 1996)
Summary
Improving feed efficiency (FE) in livestock has been recognized as an important tool to decrease production costs and negative environmental impacts. Studies have shown that the lower energy losses as methane during digestion (Nkrumah et al, 2006) and greater energy retention as protein (Basarab et al, 2003) may contribute to the better efficiency of feed use in low-RFI cattle. Other factors such as physical activity (Barea et al, 2010; Luiting et al, 1994) and responsiveness to stress (Knott et al, 2008; 2010) can be linked to FE due to their impact on metabolic rate and, on the requirements of energy for maintenance. The same mechanisms affecting RFI in British breeds affect FE in B. indicus, the differences in aspects significantly associated with FE require that specific investigations be conducted
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
