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Feed Conversion Efficiency in Beef Production Systems

Associate Professor Stephen T. Morris
Nutritional Management of Pastoral Animal Production and Health
Institute of Veterinary, Animal & Biomedical Sciences, Massey University

(Paper for Angus Cattle Breeders Canterbury 16 May 2003)

Providing feed to animals is a major cost in most animal production systems. This has been recognised by the pig and poultry industries, where the cost of feed is easily quantified. These industries have made significant improvements in feed efficiency through genetic and non-genetic means. The cost of providing feed is more difficult to quantify in grazing systems. It includes the capital cost of land, costs of pasture improvement, irrigation, supplementary feed, operating and capital cost of plant, machinery and labour.

Traditionally, and still today beef producers have improved their herds by selection for growth. Growth is an easy and economical trait to measure and is moderately heritable. Selection for growth traits has resulted in faster growing cattle, however it has also resulted in the introduction of some correlated undesirable traits such as increased birth weights leading to calving difficulties, delayed sexual maturity and increased herd maintenance requirements associated with the feed costs of larger animals.

In most beef cattle production systems, researchers have established that 65-85% of total feed intake is required by the breeding cow herd and that half of that total feed intake is required just to maintain cow liveweight. In contrast to beef cattle, pigs and poultry breeding feed costs represent only around 10% of the total feed costs. Therefore the costs of maintaining the breeding cowherd is clearly an important factor determining the efficiency of beef production.

Despite its economic importance farmers in New Zealand do not usually assess the cost of feed for their farming operation. The complimentary roles of beef cattle on sheep farms complicate the economic assessment of feed efficiency in New Zealand’s mixed livestock farming systems. However as profitability is a function of both inputs and outputs, there is a need to consider avenues for reducing inputs in order to improve efficiency of production and increase profits.

Selecting to improve the efficiency of feed conversion in a herd has been proposed as an alternative to selecting for growth rate. Here the producer is striving to improve the efficiency of converting feed to gain, rather than concentrating on growth alone. Different measures of the efficiency of growth have evolved over the years because of the complex nature of feed use in the animal. The most commonly used definitions to describe the efficiency of growth are:

Feed Conversion Ratio (FCR)
Feed conversion ratio (FCR) is a measure of the amount of feed eaten per unit of bodyweight gain or carcass weight gain. Since feed is the numerator, FCR should be minimised. Common values for growing ruminants grazing pasture are around 7-10 whereas pigs and poultry aim for values less than 2. For a production system some people measure the feed conversion ratio for the system as output of beef (kg liveweight or carcass weight) per tonne of dry matter consumed. The term Feed Conversion Efficiency (FCE) is also often used but the more correct term is FCR as it is a ratio (i.e. feed eaten per unit of gain)

Efficiency of Feed Utilisation
Efficiency of feed utilisation is simply the reciprocal of Feed Conversion Ratio and since feed is the denominator, it should be maximised. The important point to remember is that more efficient cattle will have a lower FCR and a higher efficiency of feed utilisation. When comparing efficiency from different studies, farms or calculations it is important to not only be clear about which term is being used, but to be also clear about the measures (units) of inputs and outputs used.

Intensive Finishing Systems and Feed Conversion Ratio
In theory intensive finishing systems should utilize cattle that are capable of efficiently converting pasture to liveweight or carcass weight. There are a number of factors that influence feed conversion ratio or the efficiency of feed use such as liveweight, sex, liveweight gain and breed of the animal.

Liveweight affects FCR through its effect on maintenance requirement. The heavier the animal the greater its maintenance requirements and, all other things being equal, the lower its FCR. For example, a rising two-year-old steer at 350 kg liveweight has a maintenance requirement of around 4.4 kg DM per day while a rising one-year old steer at 200 kg LW requires around 3.1 kg DM per day for maintenance.

On a given feed supply, such as a 4-hectare (ha) paddock with 600 kg/ha of available dry matter, only 180 rising two year old steers can be provided with a maintenance ration for three days compared with 260 rising one year steers.

Heavier animals also require more feed above their maintenance requirements to grow at the same rate as lighter animals, i.e. their production requirements are higher.

To grow at a rate of 1 kg liveweight gain per day, a 350 kg steer requires 8.6 kg DM/day of which 4.4 kg DM is the maintenance requirement and 4.2 kg DM the production requirement. However, a 200 kg steer requires 5.9 kg DM/day of which 3.1 kg DM is required for maintenance and 2.8 kg DM to produce 1 kg of growth.

Therefore, lighter animals with lower maintenance and production requirements need less feed to grow at the same rate as heavier animals; i.e. they use feed more efficiently.

So, on the same 4 ha. paddock with 600 kg DM/ha available, 136 rising one year steers can gain 1 kg/head/day over three days while only 93 rising two year steers can be grown at the same rate because they cannot match the efficiency of the lighter animals.

Therefore, intensive beef production systems that start with lighter (younger age) animals have a potential advantage over those that start with heavier and older cattle. Another important point is that the greater the liveweight gain, the quicker the animal reaches slaughter weight and less time required to maintain that animal. There is also greater output over which the maintenance costs can be spread and hence the higher the FCR.

Sex of animal and FCR
The sex of an animal can influence FCR through the higher (about 15%) maintenance requirement of bulls than that of steers, with little difference between steers and heifers. At maintenance or at low liveweight gains (below about 0.3 kg/day) the feed requirement of bulls is actually greater than that of steers of the same liveweight.

Note also that the feed intake of bulls and steers of the same liveweight is often not very different. For an intake of 60 MJ ME or 5 kg DM, bulls will grow at 0.80 kg/day and steers at 0.60 kg/day. This difference is not much more than the 15-20% extra liveweight gain expected from the entire male over the castrate.

A second way in which sex has an effect on FCR is through the composition of liveweight gain. The liveweight gain of bulls contains more protein and less fat than that of steers and a similar difference exists between steers and heifers. The cost of depositing lean is much less than that of fat. Consequently, on this basis, the FCR of bulls, at higher liveweight gain, will be better (less feed per kg of gain than that of steers).

The third difference between the sexes is their potential for liveweight gain, with entire males having a greater potential than castrates or females. Much of this difference is really due to the composition of gain effect and mature body weight.

Breeds and Feed Conversion Ratio
Faster growing breeds have leaner gain and therefore a higher FCR although some claim they may pay a slight penalty in terms of a higher maintenance requirement, somewhat like bulls. On the other hand, faster growing breeds also become heavier and this counts against FCR.

In summary it can be said that lighter cattle of the same breed and sex, growing at the same rate, as heavier ones will require less feed per kg gain. Similarly, if animals are of the same weight, the faster growing ones will be the more efficient.

Efficiency of feed use on a herd basis
There is however a need to go a step further and look at feed efficiency across the whole production system. To compare the feed conversion efficiency of systems of beef production, the total feed required over the entire finishing period needs to be divided by the total beef output of the system.
Although FCR is an important component of intensive beef production, the seasonal pattern of the feed demand is also of significance. The lower the winter feed demand and the higher the spring demand, the lower the need for expensive pasture conservation as silage or hay or for winter feed crops. Systems buying calves in November have the advantage of doubling the number of stock over the late spring-early summer period when herbage growth usually increases.

Selecting animals that are more efficient in their Feed Utilisation
The major disadvantage of selection for FCR is that it increases mature weight and this is a highly undesirable correlated response in the breeding cowherd. In response to this other measures of the efficiency of feed use have been sought.

An issue that is of considerable practical interest is the extent to which individual animals are more or less efficient than would be expected for an animal of their weight and growth rate. This trait has been termed the net feed conversion efficiency or the residual feed intake. More efficient cattle can theoretically be found within any desired cattle weight range, and selection for improved net feed conversion efficiency (hereafter referred to, as Net Feed Efficiency) will not increase mature size.

Net Feed Efficiency (NFE)
Net feed efficiency (NFE) refers to variation in feed intake between animals beyond that related to differences in growth and liveweight. Consequently it is expected that selection for improved NFE may reduce herd feed costs with little or no adverse changes in growth performance. Ranking animals on NFE requires measuring differences in their feed intake, liveweight and growth rate over a defined test period. A high NFE bull will consume less feed than expected over the test period and have a lower (negative) net feed intake. A low NFE bull will consume more feed than expected over the test period and have a higher (positive) net feed intake. An animal’s expected feed intake is predicted from the test groups’ average feed requirements for a particular growth (say 1 kg/head/day) and liveweight maintained (say 300 kg). An animals net feed intake is simply the difference between its predicted feed intake and its actual feed intake.

An example of how feed intake is a function of liveweight is shown in the following conceptual data (Figure 1). In figure 1, as expected, feed intake increases with animal liveweight so that bigger animals eat more. However, there is variation and although heavier animals eat more, there are some that are eating much less than expected (shown below the line). Also small animals may eat more or less than expected. This difference from expectation is termed residual feed intake and used as the net feed efficiency term. The units are kg feed per day, the values are likely to be normally distributed, and by definition the mean is zero.

What is happening here is that feed intake is effectively partitioned into two components 1) the fed intake expected for the given level of production; and 2) a residual portion. The residual portion can then be used to identify those animals, which deviate from their expected level of feed intake, and they can be classified as high efficiency (negative residual intake) or
lower efficiency (positive residual feed intake). Since “residual” is a statistical term which may be confusing, the term Net Feed Efficiency is used.

graph Figure 1. Example of net feed efficiency (residual feed intake)

If genetic improvement for net feed efficiency is undertaken in New Zealand then it will generate profit when steers are finished for slaughter sooner or at heavier liveweights when slaughtered at the same time, however, greater gains may come from the improvement in NFE when it is applied to beef breeding cows.

EBV’s for net feed efficiency have been developed by Breedplan and are available for industry use. The Australians have some industry guidelines for conducting NFE tests. These tests are either conducted on-farm or at central locations where animals from different properties are tested together in uniform conditions. A feeding system that gives accurate measurement of individual animal feed intake is required. The test usually lasts for 70 days and uses automated self feeders (with a ration of grain and hay) and cattle with electronic ID.

We need to be sure this is cost effective for our New Zealand grass-fed conditions and that is the purpose of a MeatNZ funded trial at Massey University. Firstly evaluating if selection for NFE using Australian derived EBV’s is valid under our grazing conditions and secondly if it is to then devise systems of testing. We are using the n-alkane method and the before and after grazing pasture measurements to estimate animal intakes The difference in EBV’s between the high NFE and low NFE bulls used in our 2001 matings translated to an expected 13% difference when there progeny weighed 300kg, grew at 1.0 kg/day and consumed 8 kg of dry matter per day.

Selection for improved NFE needs to be assessed in conjunction with improvement in other traits such as liveweight gain (for example 600 day weight EBV) and maternal traits (for example 200 day milk EBV). At the same time as NFE is being assessed selection for high and low 600-day liveweight EBV and 200 day milk EBV are being evaluated. Although not part of the original objectives of the trial we will be able to make an estimation of the value of using high 600 day EBV bulls (i.e. bulls in the top 10% for that particular trait) over commercial cows and then recording the performance of steer and heifer progeny under normal farming conditions.

In year one only the high and low 600 day and 200 day milk EBV lines were generated and in the second year (calving 2002) the high and low Net Feed Efficiency progeny (and the appropriate link bulls with year one) were generated and will be moved to Massey in May 2003.

The 2001 born steers arrived at an average liveweight of 255 kg and the heifers weighed 244 kg. The steers have been split into two - one group to be finished at 20 months and the other at 30 months of age. The liveweight gain of the 20-month group of steers has averaged 0.85 – kg/head /day from arrival until 25 February 2003 when they weighed 511 Kg. The 30-month groups liveweight gains have been 0.60 kg/head/day since arrival and they weighed 433 kg on 25 February 2003. We have been measuring intakes on these animals but the laboratory analyses of these intakes have yet to be processed.

The heifers are being run together and have been monitored for onset of puberty with tailpainting and weekly blood sampling to assess progesterone levels, an indication of when first oestrus occurs. Onset of oestrus was quite slow last spring and some animals had not cycled (as indicated by progesterone assay) when the bull went in on 25 November. There was no difference in onset of puberty between the selection lines (i.e. high or low 600 day or milk EBV’s). The heifers were mated to four yearling Angus bulls all of which had similar EBV figures for growth and all were fewer than 3.5 for birthweight EBV. Pregnancy rates were 90% in these heifers over three cycles of mating with no difference between selection lines

The first feed intake measurements on the heifers were made in late June and a second measurement was made in October. We are using two techniques here, n- alkanes an indirect marker technique and a before and after grazing technique. The latter involves splitting the selection lines so that each group and placing them into individual lanes within a paddock and then allocating each line the same daily allowance per kg of liveweight (i.e. daily break size is dependent on liveweight of group) to grow at the planned liveweight gain (in this case 1 kg/head/day). Early results indicate no differences in intake between selection lines.

Conclusion

If we accept that an objective of breeding programs might be to increase the efficiency of production and irrespective of how efficiency is defined; the efficiency of feed utilisation will form a major component of the breeding program objective. Feed conversion ratio although important in a beef systems context (i.e. more efficient systems have lower FCR) when we select for animals on FCR or efficiency of feed use we may be increasing mature size, which is detrimental to a cow-calf system. Selection programmes might be better to use Net Feed Efficiency to select for efficient animals however this has yet to be evaluated under New Zealand pasture conditions.

References

Nicol, A.M. 1999. Principles of Intensive Beef Finishing. New Zealand Beef Council Publication BC4. Intensive Beef Production, P6-16.

McRae, A.F. 1999. Beef Finishing – some profitability issues. A paper presented to Central Districts/Wairarapa Beef Council. New Zealand Beef Council Publication, BC 31

Smeaton, D.C. 2003. Profitable Beef Production. A New Zealand Beef Council Publication.


Contact Information

Steve Morris
Institute of Veterinary, Animal & Biomedical Sciences (IVABS)
Mail Code 411
Massey University
Private Bag 11-222
Palmerston North

Phone: 06 350 5364
Fax: 06 350 5616
Email: S.T.Morris@massey.ac.nz
Web: www.beef.org.nz or
ivabs.massey.ac.nz

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