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.
Experimental Animals. Sixty two Bonsmara bulls obtained from the Chapman Ranch were used in this experiment. The bulls originated from a ranch in New Mexico and were vaccinated with Bovashield 4 at weaning and again 3 wk later with Cattlemaster 4 and 7-way with Somnus. Average 205-d adjusted weaning weights of the bulls were 183 ± 20 kg. Upon arrival at the McGregor Research Center, bulls were weighed, dehorned and given Cydectin pour-on. Bulls were stratified by body weight and randomly assigned to one of 17 pens (four bulls per pen) equipped with Calan gate feeders. During a 35-d adaptation period, bulls were adapted to the experimental diet and trained to eat from Calan gate feeders. The experimental diet included: 50% cottonseed hulls, 13.5% dry rolled corn, 13.5% ground milo, 14.5% cottonseed meal, 6% molasses, and 2.5% vitamin/trace mineral premix.
Performance Study. Individual feed intakes and body weights were measured weekly for 70 d. Feed offerings were recorded and provided once daily at approximately 07:30. Feed refusals were collected and weighed weekly to determine individual feed intakes. Samples of the experimental diet were obtained weekly and a composite sample was sent to the Dairy One Forage Laboratory for chemical analysis. On d 0 and 70 of the study, ultrasound measurements of 12th rib and rump fat thicknesses, longissimus muscle area and percentage intramuscular fat were obtained using a Scanner 200 real-time ultrasound unit. Body condition scores (1 to 5) and hip heights were recorded on d 0 and 70 of the performance study. Temperament of bulls was evaluated using two subjective scores on d 0 of the study. Chute temperament scores (1 being docile to 5 being very aggressive) were evaluated while bulls were restrained in a squeeze chute. Pen temperament scores (using similar 1 to 5 scale) were evaluated as bulls returned from the processing facility to their assigned pen. Temperament of bulls was also evaluated by measuring exit velocity on d 0 and 70 of the experiment. Exit velocity was measured as the speed (m/sec) the bulls traversed a fixed distance of 1.83 m upon exiting a squeeze chute as described by Burrow et al. (1988).
Breeding Soundness Examinations. Scrotal circumference was measured on d 0 and 70 of the experiment and on d 61 following the end of the 70-d performance study. Breeding soundness examinations were performed on d 5 and 61 following the 70-d performance study. For each breeding soundness examination, bulls were classified as unsatisfactory, questionable, or satisfactory for breeding. Penile extension (full, partial or none), semen consistency (milky, moderate or thin), sperm abnormality (> 30 % abnormal or < 30 % abnormal) and breeding soundness (satisfactory, questionable or unsatisfactory) were recorded as discrete variables. Statistical Analysis. The Proc REG procedure of SAS (1999) was used to regress 14-d body weight data on days on test to more accurately measure ADG. This regression model was also used to determine initial (d 0) and final (d 70) body weights. Feed conversion ratio was calculated as daily dry matter intake divided by daily gain. NFI was calculated using one of three statistical models. NFI-1 was calculated as the difference between actual and expected feed intake from the following linear regression model: DM intake = b0 + b1 mid-test BW^0.75 + b2 ADG + error Where DM intake is dry matter intake (kg/day), mid-test BW^0.75 is average body weight raised to the 0.75 power and ADG is average daily gain (kg/day). NFI-2 and NFI-3 were calculated in a similar manner, but also included d-70 12th rib fat thickness (NFI-2) and gain in 12th rib fat thickness over the 70-d performance study (NFI-3) as independent effects. Partial correlations were performed using the Proc CORR procedure of SAS (1999) to determine significant relationships between feed efficiency traits and performance, body composition, temperament and breeding soundness examination traits. Using NFI-1 measurements, bulls were ranked by NFI and assigned to low, medium and high NFI groups that were < -0.5 SD, ± 0.5 SD, and > 0.5 SD from the mean NFI of 0.0 ± 1.09 SD kg/d, respectively. The least-squares means option of the GLM procedure of SAS (1999) was used to evaluate differences in body composition traits, temperament, and performance traits among NFI groups. The chi-square option of Proc FREQ (SAS, 1999) was used to determine differences in extension of penis, semen consistency, sperm abnormality, or breeding soundness classification between NFI groups of bulls.
Performance and Feed Efficiency. Overall ADG, dry matter intake, and NFI-1 for the 70-d performance study were 1.77 (SD = 0.20), 11.1 (SD = 1.67), and 0.00 (SD = 1.09) kg/d, respectively. Dry matter intakes were phenotypically correlated (P < 0.001) with ADG (r = 0.66), initial BW (r = 0.56), final BW (r = 0.71) and mid-test BW^0.75 (r = 0.48). As expected, NFI-1 were not phenotypically correlated with initial BW, final BW, or ADG, as these traits are included as independent variables to calculate NFI-1. These observations are in agreement with previous studies that have found NFI to be genetically independent of BW and ADG. Including d-70 12th rib fat thickness (NFI-2) and gain in 12th rib fat thickness over the 70-d study (NFI-3) as an independent variables did not substantially affect correlated responses between NFI and performance traits. In addition, including these carcass fatness measurements as independent variables did not substantially improve the R2 values of the linear regression models. The R2 values for the regression models to calculate NFI-1, NFI-2 and NFI-3 were 0.58, 0.60 and 0.61, respectively. These results suggest that NFI can be calculated without using ultrasound measurements of carcass fatness as independent variables. In the current study, NFI-1 was phenotypically correlated (P < 0.001) with FCR (r = 0.85). There was a tendency (P = 0.15) for FCR to be negatively correlated with ADG. Most studies have demonstrated that FCR is highly correlated in a negative manner with ADG. As a consequence, cattle with low FCR (more efficient) will typically be the fastest gaining cattle. Feed conversion ratio and NFI-1 were both positively correlated (P < 0.001) with DMI (r = 0.62 and r = 0.65, respectively), suggesting that more efficient animals consume less feed on a daily basis. Average NFI for bulls identified as having low (< 0.5 SD below the mean NFI), medium (± 0.5 SD from the mean), and high (> 0.5 SD above the mean) NFI were -1.32, -0.03, and 1.11 ± 0.13 kg/d, respectively. Growth rate, initial BW, and final BW were not statistically different between low, medium, and high NFI bulls. However, high NFI bulls (less efficient) consumed 25% more DMI than low NFI (more efficient) bulls, resulting in the high NFI bulls having 26% higher FCR than the low NFI bulls. These results are consistent with Carstens et al. (2002) who reported that high NFI steers had 21% greater dry matter intake and 23% higher FCR compared to low NFI steers.
Body Composition and Temperament Traits. Body condition scores were not correlated with NFI-1 on d 0 or 70. Body condition scores tended (P < 0.10) to be positively correlated with FCR (r = 0.23) on d 0, but not on d 70 of the performance study. NFI-1 was not correlated with hip height on d 0 or 70 of the performance study. Ultrasound estimates of longissimus muscle area (REA) on d 0 and 70 were not correlated with either of the feed efficiency measurements, which is consistent with results from other studies. Percent intramuscular fat of the longissimus muscle (IM) on d 0 was not correlated with NFI-1 or FCR. However, final IM was phenotypically correlated (P < 0.05) with FCR (r = 0.25), and tended (P < 0.10) to be phenotypically correlated with NFI-1 (r = 0.23). Backfat thickness measured on d 0 and 70 was not correlated with FCR. Initial, but not final backfat thickness tended (P < 0.10) to be phenotypically correlated with NFI-1. These results are similar to Basarab et al. (2003) who reported a tendency (P = 0.07) for NFI to be correlated with initial, but not final backfat thickness. These results suggest that bulls with low NFI (improved efficiency) are slightly leaner than bulls with high NFI, but the magnitude of differences in ultrasound estimates of body composition between low and high NFI bulls is small. Exit velocity on d 0 was phenotypically correlated in a negative manner (P < 0.05) with ADG (r = -0.25) and dry matter intake (r = 0.34). However, exit velocity was not significantly correlated with any of the feed efficiency measurements. Breeding Soundness Examinations. Scrotal circumference on d 0 was not correlated with NFI-1, but was phenotypically correlated (P < 0.01) with FCR (r = 0.29). Likewise, final scrotal circumference was not correlated with NFI, but was correlated with FCR (r = 0.25). Scrotal circumference measured 61 d post-trial was not correlated with NFI-1, but tended (P = 0.11) to be correlated with FCR (r = 0.21). Arthur et al. (2001a) did not observe significant genetic correlations between scrotal circumference and NFI, or between scrotal circumference and FCR. Sperm motility measurements at 5 and 61 d post-trial were not correlated with any of the feed efficiency traits. Chi-square analysis revealed no significant differences between NFI groups in penile extension, semen consistency, sperm abnormality, or overall breeding soundness. Net feed intake was phenotypically correlated with FCR while remaining independent of body weight and ADG in Bonsmara bulls. Bulls with low net feed intakes consumed 20% less feed than bulls with high net feed intakes. Net feed intake was not correlated with longissimus muscle area, but tended to be correlated with subcutaneous fat at the 12th rib and percent intramuscular fat of the longissimus muscle. Exit velocity, an estimate of temperament was correlated with feed intake and ADG, but was not correlated with either of the feed efficiency measurements. NFI was not related to any of the bull fertility traits, but FCR was correlated with scrotal circumference. In previous studies, feed efficiency traits have been shown to be moderately heritable. Results from this study suggest that applying selection pressure against net feed intake would improve feed efficiency without comprising growth, muscling, temperament, or bull fertility traits.
Educational & Outreach Activities
Fox, J.T. Characterization of residual feed intake and relationships with performance, carcass and temperament traits in growing calves. Summer, 2004. Master’s thesis. Texas A&M University.
Fox, J.T., G.E. Carstens, E.G. Brown, M.B. White, III, S.A. Woods, T.H. Welsh, Jr., J.W. Holloway, B.G. Warrington, R.D. Randel, D.W. Forrest and D.K. Lunt. 2004. Residual feed intake in growing bulls and relationships with temperament, fertility and performance traits. J. Anim. Sci. 82(Suppl. 2):6.
Brown, E.G., G.E. Carstens, J.T. Fox, K.O. Curley, T.M. Bryan, L.J. Slay, T.H. Welsh, Jr., R.D. Randel, J.W. Holloway and D.H. Keisler. 2004. Physiological indicators of performance and feed efficiency traits in growing steers and bulls. J. Anim. Sci. 82(Suppl. 2):13.
Fox, J.T., G.E. Carstens, F.M. Rouquette, Jr., and D.P. Hutcheson. 2004. Effects of stocker supplementation on feedlot performance, feed efficiency and carcass traits in Simmental crossbred calves. Plains Nutrition Council: AREC 04-14:97.
White, M.B., G.E. Carstens, J.T. Fox, R.C. Vann, R.D. Randel and J.W. Holloway. 2004. Exit velocity as a measure of temperament to predict performance of growing cattle. Plains Nutrition Council: AREC 04-14:113.
Popular Press Article:
A New Measure of Efficiency. The Cattleman. May, 2003.
- In this study, bulls with high net feed intake (less efficient) consumed 25% more feed than bulls with low NFI (more efficient) even though both sets of bulls were similar in body weight and growth. As a result, bulls with high net feed intakes had 26% higher FCR than bulls with low net feed intakes.
Results demonstrate that substantial phenotypic variation exists in net feed intake in growing bulls.
Results suggest that NFI can be calculated without using ultrasound measurements of carcass fatness as independent variables.
Results suggest that bulls with low NFI (improved efficiency) are slightly leaner than bulls with high NFI, but the magnitude of differences in ultrasound estimates of body composition between low and high NFI bulls is small.
Exit velocity, an estimate of temperament was correlated with feed intake and ADG, but was not correlated with either of the feed efficiency measurements.
NFI was not related to any of the bull fertility traits, but FCR was correlated with scrotal circumference.
Competition from major beef exporting countries (e.g., Australia, Brazil) will continue to increase as they improve their infrastructure, develop feed grain industries, and incorporate use of U.S. technologies and genetics to improve production efficiencies. Improving genetic merit for NFI will reduce costs of production and improve competitive position of U.S. beef industry. Australian research has recently 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. If selection pressure were applied to improve genetic merit of cattle by 7.5%, the feedlot sector of the US beef industry would potentially save about $480 million per year. Likewise, a 7.5% improvement in NFI would also potentially save the cow/calf sector $640 million per year.
New federal goals to reduce the environmental impact of beef production will increase cost of producing U.S. beef. In response to societal concerns about global warming, there is a need to reduce greenhouse gas emissions (methane, nitrous oxide) from cattle. Improving genetic merit for NFI will reduce nitrogen and phosphorus excretions, and reduce greenhouse gases, thereby, reducing the cost to the US beef industry to comply with environmental regulations. The ability to cost-effectively select cattle for improved NFI will improve profitability of small- as well as large-sized beef operations and enhance the environmental sustainability of the beef industry.
The long-term goal of this project is to validate the use of new technology to measure feed intake and growth rate of individual bulls and develop test protocols to accurately measure net feed intake in commercial bull-test facilities. The study described in this report was conducted in cooperation with a Texas beef producer. Results from this study will be presented to other beef producers who have previously tested bulls at commercial bull-test facilities. We are in the final stages of installing a computerized feed intake measurement system in a commercial bull-test facility that will provide opportunities for producers to evaluate net feed intake as well as growth and carcass traits in their bulls. The results from the study described in this report will help demonstrate the value of measuring net feed intake in bulls, and will facilitate early adoption of this technology.
Areas needing additional study
The primary limit to implementing selection programs that focus on net feed intake is the inability to accurately measure individual feed intakes of bulls in a cost-effective manner. Emerging commercialization of new technologies will soon provide opportunities for beef producers to accurately measure feed intake in cattle. However, additional research is needed to further develop this technology in order to reduce the cost of measuring net feed intake in growing bulls in commercial facilities. In addition, more research is warranted to examine the long-term effects of selection for improved net feed intake on reproductive performance of bulls, meat quality of slaughter progeny and the efficiency of mature cows sired by bulls with superior net feed intakes. Recent studies suggest that cattle with improved net feed intakes will excrete less manure nitrogen and phosphorus, and generate less greenhouse gases (nitrous oxide, methane). More research is warranted to quantify the impact of selection for improved net feed intake on mitigating the environmental impact of beef production systems.