RFI's effect on feed efficiency of mature beef cow

RFI's effect on feed efficiency of mature beef cow

*Phillip Lancaster is with the University of Florida Range Cattle Research & Education Center in Ona, Fla.

RECENTLY, considerable research has focused on evaluating residual feed intake (RFI), also referred to as net feed intake or net feed efficiency, as a trait for use in selection programs.

Typically, feed conversion ratio (FCR), i.e., feed-to-gain, has been used as the measure of feed efficiency in beef cattle. However, more-efficient animals can have either lower feed intake for the same gain or faster gain for the same feed intake, indicating that selection pressure may not be consistently placed on either feed intake or rate of gain, which makes genetic improvement difficult.

FCR shares a strong negative correlation with growth rate, so selection for faster growth rate will significantly increase mature weight, thereby increasing the amount of feed required to maintain the cow herd. Given that the cow herd accounts for 65% of feed required to produce a pound of beef, selection for improved feed efficiency based on FCR or growth rate may be detrimental to the feed efficiency of beef production.

RFI is an alternative trait to feed:gain that is independent of growth rate and mature weight and will not result in greater maintenance requirements of the cow herd. RFI is calculated as actual feed intake minus expected feed intake based on growth rate and bodyweight; animals that consume less than expected have a low RFI and are more efficient.

The use of RFI to measure feed efficiency identifies animals that consume less feed for the same growth rate and bodyweight, putting selection pressure directly on feed intake. Therefore, consistent genetic improvement in feed efficiency can be made using RFI.

Selection for improved RFI typically occurs in young growing bulls measured shortly after weaning in performance test stations utilizing high-energy diets. However, mature cows consume a low-energy diet and produce milk rather than deposit nutrients into tissue.

This raises a significant question: Will selection of young growing bulls with superior RFI on high-energy diets translate into improved feed efficiency in mature cows consuming low-energy diets?

Recently, Basarab et al. (2011) found that low-RFI heifers had lower pregnancy and calving rates than high-RFI heifers, but other studies have found no differences in pregnancy or calving rates between low- and high-RFI heifers. Additionally, previous research has found no difference in age at puberty between low- and high-RFI heifers.

In an Australian RFI selection project, Arthur et al. (2005) found no differences in pregnancy, calving or weaning rates among cows from the low- and high-RFI selection lines. These authors did report a tendency for cows from the low-RFI line to calve five days later in the year, which indicates that these cows were bred later in the breeding season compared with cows from the high-RFI selection line.

Additional studies have indicated that low-RFI females may calve later in the calving season, which suggests that these females may be achieving puberty later or breeding later.

No difference in milk yield, weaning weight or pounds of calf weaned per cow exposed was reported between cows from the low- and high-RFI selection lines (Arthur et al., 2005).

Collectively, these results suggest that selection for more-efficient cattle using RFI may negatively affect the age at puberty and pregnancy rates of heifers but have little effect on reproductive performance and productivity of mature cows.

A recent study (Durunna et al., 2011) found that the rank correlation between RFI measured in steers fed a growing diet followed by a finishing diet was 0.33, compared with 0.44 and 0.42 between RFI measured in steers fed either the growing or finishing diet for the entire study, respectively.

Several other studies have reported genetic and phenotypic correlations of 0.45 to 0.55 between RFI measured in the growing and finishing phases in cattle fed a moderate-energy growing diet followed by a high-energy finishing diet. These results indicate that diet may have a small effect on the correlation of RFI between growing bulls and mature cows, but the stage of maturity may have a large impact on feed efficiency.

A recent study (Black et al., 2013) at the University of Florida North Florida Research & Education Center reported no significant relationship (0.13) between RFI measured in growing heifers and again as three-year-old non-pregnant, lactating cows fed a different diet.

Additional studies have reported moderate to strong genetic correlations (0.58 and 0.98) between RFI measured in growing heifers and again as young cows fed similar diets, which suggests that the physiological state (growing versus pregnant or lactating) has only a small effect on genotype.

However, several studies have observed that the phenotypic correlation between RFI measured in growing heifers and again as young cows is weak to moderate (Table). When young cows are not pregnant or lactating, the phenotypic correlation is approximately 0.40 — similar to that seen when comparing growing versus finishing steers. However, when young cows are lactating, the phenotypic correlation averages only 0.17, which indicates that physiological state has a significant impact on expression of genetic potential for feed efficiency and that the most-efficient growing cattle are not the most-efficient lactating cows.

Collectively, these results suggest that different physiological states and diets can combine to drastically reduce the relationship with feed efficiency of growing cattle, which indicates that selection for improved RFI in young growing bulls fed high-energy diets will most likely result in a minimal improvement in feed efficiency of mature lactating cows.

 

The Bottom Line

In conclusion, limited research indicates that selection for improved RFI in growing cattle will have a minimal impact on cow productivity. However, several studies have reported a weak relationship between RFI measured in growing cattle and again as mature, pregnant, lactating cows.

This suggests that even though selection for RFI will not negatively affect cow productivity, it likely will not result in much improvement in feed efficiency of the mature cow either.

 

References

Arthur, P.F., R.M. Herd, J.F. Wilkins and J.A. Archer. 2005. Maternal productivity of Angus cows divergently selected for post-weaning residual feed intake. Aust. J. Exp. Agric. 45:985-993.

Basarab, J.A., M.G. Colazo, D.J. Ambrose, S. Novak, D. McCartney and V.S. Baron. 2011. Residual feed intake adjusted for backfat thickness and feeding frequency is independent of fertility in beef heifers. Can. J. Anim. Sci. 91:573-584.

Black, T.E., K.M. Bischoff, V.R.G. Mercadante, G.H.L. Marquezini, N. DiLorenzo, C.C. Chase, S.W. Coleman, T.D. Maddock and G.C. Lamb. 2013. Relationships among performance, residual feed intake and temperament assessed in growing beef heifers and subsequently as three-year-old, lactating beef cows. J. Anim. Sci. 91:2254-2263.

Durunna, O.N., F.D.N. Mujibi, L. Goonewardene, E.K. Okine, J.A. Basarab, Z. Wang and S.S. Moore. 2011. Feed efficiency differences and reranking in beef steers fed grower and finisher diets. J. Anim. Sci. 89:158-167.

 

Relationships of RFI measured in growing and mature cattle

 

-Cattle description-

 

Study

Age 1

Age 2

rp*

Nieuwhof et al., 1992

Growing dairy heifer

Non-pregnant, lactating first-calf heifer fed similar diet

0.07

Arthur et al., 1999

Growing heifer

Non-pregnant, non-lactating cow fed same diet

0.36**

Archer et al., 2002

Growing heifer

Non-pregnant, non-lactating cow fed same diet

0.40**

Herd et al., 2006

Growing heifer

Non-pregnant, non-lactating cow fed same diet

0.39**

Adcock et al., 2011

Growing heifer

Non-pregnant, lactating cow fed same diet

0.30**

Black et al., 2013

Growing heifer

Non-pregnant, lactating cow fed different diet

0.13

Hafla et al., 2013

Growing heifer

Pregnant, non-lactating first or second-calf heifer fed different diet

0.42**

*rp = phenotypic correlation coefficient.

**Correlation coefficient is different from zero (P < 0.05).

 

Volume:86 Issue:03

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