Feed Efficiency in the West Virginia Bull Test Evaluation Program

Felton, E.E.D., Warren, J.E.Jr., Wagner, W.R. and J.W. Yates

The profitability of beef production systems is a function of both minimizing inputs and maximizing outputs. Genetic improvement of the beef herd has generally targeted traits that increased outputs such as weight gain, live-weight, carcass traits and meat quality. Feed costs account for an estimated 60-70% of total beef unit operating costs and are the most significant cost item in most production systems. Furthermore, in beef production systems the weight of the animal is the single most important component in determining value. It has long been known that efficiency of energy usage is different for maintenance and growth and is different for the type of tissue deposited during growth. Thus, the ability to accurately identify and propagate cattle that are efficient in converting feed into weight gain is an important component of a successful production program. Improvements in feed efficiency selection should be attainable since feed efficiency/feed conversion ratio is considered a moderately to highly heritable trait (heritability = 0.30 to 0.46).  Even so, feed efficiency is generally not measured in beef cattle performance testing programs because the amount of feed consumed is extremely difficult and labor intensive to measure on an individual basis.  Recent technological advances are making the collection of the necessary measurements attainable.

The “GrowSafe 4000E” system was installed and used to measure individual feed intake during the 2003-2004 West Virginia Bull Test Evaluation Program. This system of hardware and software consists of feed troughs mounted on load cells. An antenna grid is incorporated in the trough, and animals are fitted with electronic ear tags that are read by the antenna grid. An animal feeding at a trough is identified at five second intervals and feed available in each trough is weighed every second with an accuracy within 50g. The animal identification and feed consumed data are sent wireless via a communication panel to a computer with software to compile individual feed intake and individual feeding events. Bulls arrived at the test station in mid-October, 2003. Following a 3-week acclimation period, bulls were weighed on d 1 and 2 (averaged for on test body weight (BW), 42, 77, and 104 and 105 (averaged for off test BW). During the acclimation period and the 105-day test, bulls were fed ad-libitum a total-mixed-ration containing 13.6% crude protein and 73.6 and 45.0 Mcals of NEm and NEg per cwt, respectively.  Of 117 bulls completing the 105 d test, 113 were Angus, 2 were Hereford and 2 were Charolais.  Means (standard deviation) for age of bulls at the end of test, initial and final BW, total and average daily weight gain, and feed consumed as percent of body weight were 370 (24) days, 811 (108) and 1268 (115) lb, 454 (49) and 4.32 (0.46) lb, and 2.6 (0.27) percent, respectively.  Raw feed efficiency measured as units of feed per unit of gain (F:G) ranged from 4.49 to 8.93 (mean of 6.50) over the entire 105 d test and was correlated (P< 0.01) with age (0.42), birth weight   (-0.32), and average daily gain (-0.60).  During the middle 35 d period when most bulls should have been on the straight line proportion of their growth curve, F:G ranged from 4.14 to 12.75 (mean of 6.08).  Since raw F:G is not independent of rate of gain and birth weight it should not be used as a single selection criterion.  This could result in concomitant selection for increased mature body size of brood cows that is generally not desired by the industry.  Residual feed intake (RFI) is calculated as the difference in expected intake versus actual intake.  When based upon the 1996 NRC beef cattle model, which included adjustments for mature size, age, and degree of finish, RFI ranged from -35.25 to -1.03 suggesting that all bulls tested were above average in efficiency compared to animals used to develop the model.   However, this method does not eliminate the relationship of feed efficiency to animal gain and mature weight.  RFI was also calculated based upon linear regression of the experimental group body weights and gains over the test period.  By this method, animals of different physiological age, breed and mature size can be accurately compared in terms of metabolic efficiency of energy use.  Animals are compared based upon the average of the contemporary group (mean of 0).  RFI calculated by this method ranged from -8.39 to +7.22.  This method allows selection for feed efficiency independent of other important production variables, particularly rate of gain and mature body size.

In beef production systems the weight of the animal is the single most important component in determining value. Thus, the ability to identify and propagate cattle that are efficient in converting feed into weight gain becomes an important component of a successful production program. Because a one pound improvement in dry matter feed conversion of feeder calves reduces feed cost by as much as $50 per head, improved feed efficiency in cow-calf operations will reduce input cost and enhanced profit potential for beef producers. Furthermore, the production of offspring is the driving force behind most cow/calf operations. Thus, improving the efficiency of maintaining brood cows and of production of their offspring is of vital importance to the economic success of any cattle operation.  Appropriate means of analyzing feed efficiency must be employed to account for differences in stage of growth, maturity, and body type when growth and feed consumption are measured.