Post-Weaning Feed Efficiency


Post-Weaning Feed Efficiency and Growth in Brahman, Angus, and Brahman x Angus Crossbred Cattle

Feed costs represent the largest fraction of all costs in a beef cattle feeding operation. Any increase in feed efficiency will have a major economic impact on the beef cattle industry. On the other hand, Brahman cattle with its genetic ability to withstand hot and humid conditions is an essential component of multibreed or crossbred commercial beef herds in the Southern region of the US. Thus, evaluation of efficiency of feed utilization and post-weaning growth in Brahman and Brahman x Bos taurus crossbred cattle are areas of primary importance in beef cattle research.

Feed efficiency can be evaluated using several measurements, among them residual feed intake and feed conversion ratio. Residual feed intake is defined as the difference between the actual amount of feed that an animal consumes and an average amount of feed that this animal would be expected to consume given his weight and average daily. Animals that eat more feed relative to their expected feed consumption are less efficient than those animals that consume less feed. Feed conversion ratio is simply the ratio of daily feed intake to average daily gain. Both measurements aim at identifying animals that require less pounds of feed to produce one pound of beef. However, because of the way they are computed, estimates of residual feed intake are unrelated to growth measurements. Thus, selection of animals for residual feed intake is expected to have a smaller associated effect on growth, which will be an advantage if the selection objective is to increase feed efficiency while keeping change in cattle size to a minimum.

Prior to our study involving Brahman, Angus, and Brahman x Angus crossbred cattle, beef cattle research on residual feed intake and post-weaning growth had primarily been conducted in temperate regions using either purebred (Archer et al., 1997; Arthur et al., 2001a, b; Schenkel et al., 2004) or crossbred (Basarab et al., 2003; Nkrumah et al., 2004, 2007) Bos taurus cattle. Thus, the primary objectives of this research were to assess the effect of breed composition and temperament on residual feed intake (RFI), feed conversion ratio (FCR), daily feed intake (DFI), and post-weaning gain (PWG), and to estimate genetic parameters for these traits using bulls, heifers, and steers whose breed composition ranged from 100% Brahman (B) to 100% Angus (A).

Animals, Management and Data
A total of 581 bulls, heifers, and steers from 3 beef cattle herds in Florida (Brooksville: 100; Gainesville: 388; Marianna: 93) were used in the study. There were 31 bulls, 317 heifers, and 233 steers from 6 breed groups: A (n = 153), ¾ A ¼ B (n = 66), Brangus (5/8A 3/8 B; n = 107), ½ A ½ B (n = 115), ¼ A ¾ B (n = 49), and B (n = 91). Calves were born from December to March and weaned in August or early September in 2006 and 2007. After weaning, calves grazed on bahiagrass pastures, received a preconditioning diet for 3 to 6 weeks, and were then transported to the University of Florida (UF) Feed Efficiency Facility in Marianna, Florida, where they remained for the next 3 months.

The UF Feed Efficiency Facility is equipped with GrowSafe technology (GrowSafe Systems, Ltd., Airdrie, Alberta, Canada) that permits real-time measurements of individual feed consumption on large numbers of cattle housed in pens. Calves were grouped by sire breed and sex, and then randomly allocated to 24 pens (1162 square feet each; 17 calves per pen on average). Calves were identified with passive, half-duplex, transponder ear tags (Allflex USA Inc., Dallas-Fort Worth, TX) prior to entering the facility. Animals were fed a concentrate diet ad libitum twice daily. Calves went through a pre-trial adjustment period of 21 days followed by a 70-day trial period. The 2006 concentrate diet was composed of whole corn, soybean hulls, corn gluten feed, cottonseed hulls, and a protein, vitamin, and mineral supplement (FRM, Bainbridge, GA). The 2007 diet had a higher fiber content (chopped bermudagrass instead of soybean hull pellets). The concentrate had a DM, CP, NEm, and NEg of 91.2%,17.3%, 1.7 mcal/kg DM, and 1.2 mcal/kg DM in 2006, and 90.0%, 14.1%, 1.5 mcal/kg DM, and 0.9 mcal/kg DM in 2007. Feed consumption was measured in real time, and weights and exit velocity were taken every 2 weeks. Exit velocity measures how fast calves exit the working chute; it is used as an indicator of temperament in that faster animals are believed to have more excitable or nervous temperaments. Residual feed intake measurements were used to classify calves into 3 groups: high RFI (lowest efficiency), medium RFI (average efficiency), and low RFI (highest efficiency).

Main Results
Figure 1 shows that Brahman had a higher proportion of calves in the highest efficiency group (low RFI: 51.6%) than other breed groups (16.3 to 33.3%). Higher fractions of calves in the medium RFI group existed in Brangus (58.9%) and ¼ A ¾ B (55.1%) than in other breed groups, Brahman having the lowest percentage (25.3%). Brangus (18.7%), Angus (19.6%), and Brahman (23.1%) had lower percentage of calves in the high RFI group than the remaining 3 crossbred groups (28.6% to 32.2%).

Heifers were less efficient than steers (i.e., heifers had higher RFI than steers), and bulls had similar RFI to steers (this may have occurred because of the small number of bulls). However, another study (Nkrumah et al., 2004) found bulls to be more efficient than steers in a group of crossbred cattle composed of Angus, Charolais, Galloway, Hereford, and Holstein.

Residual feed intake in heifers tended to decrease as percentage of Brahman increased. Thus, Brahman and high percentage Brahman heifers tended to have better feed efficiency than Angus and high percent Angus heifers. On the other hand, residual feed intake for bulls showed a decreasing trend (but without much statistical support), and steers showed an increasing trend as Brahman percent increased, also without much statistical support. Additional data will be required to clarify these sex differences, particularly the estimate obtained for steers. However, results here indicated that Brahman cattle tended to be more efficient than Angus cattle for post-weaning growth under subtropical conditions in Florida.

Other feed efficiency studies involving Brahman and Bos taurus breeds were unavailable for comparison. Estimates of differences in feed efficiency between Bos taurus breeds in other studies have been smaller than the differences between Brahman and Angus found here for both bulls and heifers, suggesting that breed differences for residual feed intake between Brahman and Bos taurus breeds may be larger than differences among Bos taurus breeds.

Daily feed intake decreased as percent Brahman in calves increased, suggesting that Brahman and high percent Brahman calves consumed less feed than Angus and high percent Angus calves. On the other hand, feed conversion increased as Brahman percent in calves increased, indicating that Brahman and high percent Brahman calves needed more pounds of feed per pound of weight gain than Angus and high percent Angus calves. These results for feed conversion contradicted those for residual feed intake. This outcome may be explained using the results for post-weaning gain. Post-weaning gain tended to decrease as calf percent Brahman increased. Thus, Brahman and high percent Brahman calves gained less weight during the 70 day feed efficiency trial than Angus and high percent Angus calves. Thus, although Brahman calves consumed less feed during the 70-day trial, they also gained less weight, hence their larger feed conversion ratios.

Heterosis was not a significant factor for residual feed intake, feed conversion ratio, or post-weaning gain. However, it increased daily feed intake, i.e. Brahman x Angus calves ate more than either Brahman or Angus calves. Temperament (as measured by exit velocity) was not an important factor for any of the traits, with the exception of daily feed intake, where animals that consumed more feed exited the chute more slowly. This may be an indication of better temperament, or it may simply suggest that animals that ate more were more sluggish out of the chute.

Heritabilities were 0.19 for residual feed intake, 0.42 for daily feed intake, 0.24 for feed conversion ratio, and 0.40 for post-weaning gain. These heritabilities were reasonable and similar to estimates found in other studies. In particular, the heritability for residual feed intake reconfirmed that genetic variability existed in this Brahman, Angus, and Brahman x Angus population and that selection for residual feed intake would be feasible under subtropical conditions in Florida. However, the population of animals in this study was small, thus feed efficiency data needs to continue to be collected yearly in increasing numbers, particularly if cattle are to be genetically evaluated for feed efficiency and growth Graphsimultaneously. Considering the high cost of obtaining feed efficiency information, it would seem reasonable to link feed efficiency facilities across the Southern region to improve the accuracy of genetic evaluation of animals, particularly sires, to increase the rate of selection progress.

Conclusion
Brahman cattle tended to be more efficient, but to grow more slowly than Angus cattle under subtropical conditions in Florida. Although selection for feed efficiency and growth are feasible, collection of feed efficiency data would be the limiting factor in the foreseeable future.


This article was written by
Mauricio A. Elzo, Ph.D.
Animal Breeding and Genetics
Professor at University of Florida

Dr. Mauricio A. Elzo is an Animal Breeding and Genetics Professor in the Department of Animal Sciences at the University of Florida. He received his DVM from Austral University of Chile in 1974 and his Ph.D from the University of California, Davis in 1983. He has done research on genetic improvement of animals in multibreed populations of cattle and other domestic species of economic importance. Dr.Elzo has also been the principle or co-principle investigator in more than twenty national and international research projects.