PAPER: NFI of growing bulls and relationships with performance, fertility and ultrasound composition traits

PAPER: Relationships between NFI and ultrasound measures of carcass composition in growing beef steers

The following is from a slide show explaining the concept of Net Feed Intake and visually illustrating results of the Texas A&M bull tests. From Texas A&M Beef Cattle Nutritionist Gordon Carstens.

Click here to download the full presentation (1 MB)

One of the key limits to being able to select bulls for improved feed efficiency is the cost of measuring feed intake. Technology now is available to automatically record feeding events and feed intake of individual animals, such as the system being marketed by GrowSafe. Researchers at Texas A&M University have installed an 18-bunk GrowSafe feed intake system at The Beef Development Center of Texas, a commercial bull testing facility near Millican, Texas, owned by Matt Moore. Using this facility, Beef Cattle Nutritionist Gordon Carstens is in the process of measuring efficiency traits in producer-owned bulls. Currently, it takes about 100 days to accurately measure net feed intake (NFI) in bulls.  This includes a 28-day adaptation period followed by a 70-day feed-intake measurement period with each bull’s body weight measured at 14-day intervals.  Development of technology to more accurately measure average daily gain of bulls using in-pen scales may provide opportunities to obtain accurate measurements of net feed intake during a shorter test, thereby reducing the costs to the producer. Key to further adoption of this technology by the industry will be the establishment of standard methods to measure net feed intake and eventual development of EPD for this trait; or development of selection indexes that incorporate a measure of feed efficiency. Additionally, discovery of genetic markers for net feed intake will certainly help to facilitate more accurate prediction of bulls with superior genetic merit for NFI.  The use of genetic or phenotypic markers of NFI will likely be used as part of a two-stage selection process, whereby one or more genetic or phenotypic markers of NFI are used to prescreen bulls for actual measurement of NFI.

The GrowSafe System at the Beef Development Center of Texas uses radio frequency (RFID) ear tags, RFID readers and feedbunks equipped with antennae and load cells. Whenever a bull visits a feedbunk, the data-acquisition system identifies the bull based on its RFID ear tag, and records how much feed it consumes by automatically comparing the “before and after” weight of feed in the bunk. In addition to recording daily feed intakes, the data-acquisition system also records feeding behavior traits for each bull like frequency of feedbunk visits and total time spent eating. The researchers also weigh bulls every two weeks, allowing them to combine feed-intake data with average daily gains to calculate net feed intake for each bull.

This graph illustrates the relationship between dry-matter intake (DMI) and body weight for 120 bulls in the test conducted by Texas A&M University and The Beef Development Center of Texas. While there is considerable variation in DMI, on average, heavier bulls consumed more feed than lighter bulls. However, within any particular weight range, you can see that some bulls consumed significantly less and others significantly more feed than the contemporary average (represented by green line). For example, bulls 818 and 616 had similar body weights at the end of the test, but bull 616 consumed 4.2 pounds less feed per day than bull 818.

This graph shows the relationship between dry-matter intake and average daily gain. Again, the faster-gaining bulls ate more feed than slower-gaining bulls. But at a given ADG, some bulls ate more than the contemporary group average, represented by the green line, while some ate less. Here we see that bulls 818 and 616 gained weight at similar rates, but bull 818 consumed 4.2 pounds more feed per day than bull 616.

This graph illustrates the relationship between the feed:gain ratio and average daily gain. The downward (negative) slope between F:G ratio and ADG is typical in that bulls with the fastest gain usually also have lower (more efficient) F:G ratios. Selection for improved feed efficiency using F:G ratio will concurrently result in selection of faster gaining bulls and/or bulls with larger mature sizes.

Net feed intake is determined by subtracting a bull’s expected feed intake from its actual feed intake. Because bulls 818 and 616 had similar gains and final weights during the test, their expected feed intakes were also similar at 18.4 pounds per day. Bull 616 was more efficient during the test because on a daily basis he consumed 2.1 pounds of feed less than expected (NFI = 16.3 - 18.4 = -2.1), while bull 818 was less efficient as he consumed 2.1 pounds of feed more than expected (NFI = 20.5 - 18.4 = +2.1). The graph shows that net feed intake is phenotypically unrelated to average daily gain. Research with beef cattle has demonstrated that selection for low NFI will improve feed efficiency with minimal effects on growth rate and mature body weights. Selection for lower feed:gain ratio will also improve feed efficiency, but will be associated with increases in growth rates and mature body weights.

The table shows the average performance and feed efficiency data for the 42 most efficient and 37 least efficient bulls based on NFI during the first test at the BDCT involving 120 bulls. The least efficient bulls ate 17 percent more feed then the most efficient bulls even though growth rates and final weights were similar for both groups of bulls. There were no differences in ultrasound measurements of ribeye area, backfat and intramuscular fat, or in scrotal circumference between the bulls with low and high NFI during this test.

Beef Development Center of Texas

For more information about the BDCT contact:
Shawn Woods, General Manager

Gordon Carstens
Department of Animal Science
Texas A&M University

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