- Animals: bovine
- Animal Production: feed rations
- Education and Training: demonstration, extension, participatory research
- Farm Business Management: budgets/cost and returns
Net feed intake (NFI) is a moderately heritable feed efficiency trait that is independent of changes in ADG and body weight in cattle. Objectives of this study were to measure NFI in growing bulls and examine phenotypic correlations between NFI and performance, body composition, escape velocity (indicator of temperament) and fertility traits. Sixty-two Bonsmara bulls were individually fed a roughage-based diet using Calan-gate feeders. Following a 35-d adaptation period, weekly body weights and feed intakes were measured for 70 d, and NFI calculated as the residual value from linear regression of dry matter feed intake (DMI) on mid-test BW^0.75 and ADG. Ultrasound measures of 12th rib fat thickness (BF), longissimus muscle area (REA), percent intramuscular fat (IM), escape velocity, and scrotal circumference were measured on d 0 and 70. Breeding soundness exams were performed at 5 d post-trial. As expected, NFI was not correlated with final body weight or ADG, but was correlated (P < .001) with DMI (r = 0.65), and feed conversion ratio (FCR; r = 0.85). FCR was correlated with final body weight (r = 0.26; P < .05), ADG (r = -0.18; P = .15), and DMI (r = 0.62; P < .001). NFI of low (< 0.5 SD below the mean; n = 17) and high (> 0.5 SD above the mean; n = 21) bulls were -1.32 and 1.11 ± .13 kg/d, respectively. Low NFI bulls had 21% lower (P < .001) FCR than high NFI bulls even though overall ADG (1.77 ± .05 kg/d) and final body weight (382 ± 9.0 kg) were not different. NFI was not correlated with REA, but there was a tendency (P < .10) for NFI to be correlated with final BF (r = 0.20), and final IM (r = 0.23). FCR was correlated with IM (r = 0.25; P < .05), but not with BF or REA. Escape velocity on d 0 was correlated (P < .05) with DMI (r = -0.34) and ADG (r = -0.25), but not with NFI or FCR. Scrotal circumference was not correlated with NFI on d 0 or 70, but was correlated (P < .05) with FCR on d 0 (r = 0.39) and d 70 (r = 0.25). Sperm motility was not correlated with NFI or FCR. These results suggest that selection for NFI to improve feed efficiency independent of growth traits will not alter bull fertility. Results from this study will help demonstrate to beef producers the value of measuring net feed intake in bulls, in order to facilitate early adoption of this technology.
Rising input costs, global competition and societal concerns about food safety and the environment are challenging the long-term economic viability of small forage-based beef enterprises. Innovative cost-effective technologies are needed to improve the profit margins of these beef operations while enhancing the ecological and environmental sustainability of pastures and rangelands. Considerable genetic variation is known to exist in the efficiency with which cattle utilize forages, thus providing opportunities to improve the efficiency of forage-base beef systems through selection. However, the expense of measuring feed intake in cattle has been a major obstacle to implementation of breeding programs to improve genetic merit for feed efficiency. Moreover, the traditional measure of feed efficiency, feed conversion ratio (FCR), is known to be inversely related to growth and mature size, such that selection for low FCR will increase cow size. Two recent developments provide opportunities to select for more efficient cattle: (1) emerging commercialization of new technologies to cost-effectively measure feed intake in cattle, and (2) discovery of an alternative measure of efficiency for beef cattle (net feed intake; NFI), that facilitates selection for improved feed efficiency without impacting genetic merit for growth or mature size.
Net feed intake measures the variation in feed intake that remains after the requirements for maintenance and growth are accounted for, and is calculated as the difference between an animal's actual feed intake and the feed an animal is expected to consume based on its weight and growth rate. Australian research has demonstrated that calves born to parents selected for improved NFI after almost two generations consumed 15% less feed, but weighed the same and grew at the same rate as calves born to parents selected for inferior NFI. Net feed intake has been shown to be moderately heritable and genetically independent of body weight and growth in growing cattle. Moreover, recent studies suggest that cattle with improved NFI will excrete less manure nitrogen and phosphorus, and generate less greenhouse gases (nitrous oxide, methane). Implementation of selection programs to improve NFI offers the potential to reduce grazing and feed costs, and minimize environmental impact of forage-based beef systems without compromising animal performance.
- Examine relationships between net feed intake in bulls and performance, temperament, body composition and fertility traits in growing bulls.
Evaluate alternative statistical equations to calculate net feed intake in bulls to facilitate optimal selection of bulls with improved genetic merit for feed efficiency.
Begin development of test protocols to accurately measure the parameters (e.g., feed intake, feeding behavior, body weight) needed to accurately measure net feed intake in commercial bull-test facilities.