Pieter Gert Theron - Winner - SHARING Second runner up- Technical - 2023,
Hollard Insure and Farmingportal.co.za and Agri News Net - Young Agri Writers awards
Feed efficiency as selection trait: yes or no?
Despite feed conversion ratio (FCR) being a valuable tool for assessing feedlot performance it has severe drawbacks as selection criterion. An excessive focus on this trait during selection could negatively affect flock reproduction and inadvertently lead to decreased profitability.
Feed efficiency refers to how effectively an animal converts feed into a saleable product, most often meat. More efficient animals require less feed to produce the same amount of meat and are therefore more profitable to finish off in feedlots, making them desirable to producers. The most commonly used measure of feed efficiency is feed conversion ratio, calculated as the amount of feed an animal requires to gain one kilogram of live weight. Due to the focus placed on this trait in feedlots, great effort has been made to select breeding animals with favourable FCR. However, this focus on a single trait may have unintended consequences, particularly for extensive producers.
To be of use in selection for breeding, feed efficiency traits must be determined fairly early in an animals’ life, either before or shortly after sexual maturity. Animal growth follows a set pattern with accelerated growth prior to puberty and a decline in growth rate thereafter. This post-pubertal deceleration occurs partly because fat deposition increases after puberty which increases the maintenance requirement of the animal, leaving less energy available for growth. This increase in fat deposition, particularly in female animals, is necessary to prepare the animal for reproducing since the fat serves as an energy store. Conception will not occur if insufficient energy reserves are present in the animal.
Animals with less fat perform better in FCR tests due to their lower maintenance requirements. The problem with this is that animals, even within the same breed and flock, mature at slightly different rates. Later maturing animals will reach puberty later and therefore display higher growth rates and better feed conversion for a longer period of time than early maturing ones because early maturing animals start depositing fat at a younger chronological age. Later maturing animals are therefore selected for breeding based on FCR tests conducted at a fairly young age.
The biggest flaw in this approach is the unintended discrimination against early maturing animals. Later maturing animals generally have higher mature weights but less body fat at a given age. This leads to two significant problems. Firstly, larger animals have higher absolute feed requirements. Although they may be more feed efficient they will still require more feed per head due to their larger size. This means that producers will have to provide more feed to the same number of animals or keep fewer animals where grazing is a limiting factor.
Secondly, reproduction will be affected. Studies have shown that prolonged selection for feed conversion in dairy cattle led to delayed first calving and lower conception rates in heifers. This occurred because the onset of sexual maturity is delayed in later maturing animals. Thus these animals will have to be maintained for a longer period of time before they start reproducing while they will have a shorter reproductive lifetime if they are culled at a set age. Producers therefore have to spend more money on maintaining these animals while receiving less income from them.
Thirdly, there is a distinct possibility of breeding less drought tolerant animals. Because larger animals require more feed, they will be the first to start losing condition during periods of limited nutrition. They will also be less likely to build up adequate fat reserves under good grazing conditions which will affect both their reproductive capacity and ability to withstand short-term nutritional stress. Finally, studies have found that there is little correlation between feed efficiency at different ages and across different diets. Young animals selected for breeding based on feed efficiency tests conducted on concentrate diets may therefore not be the most efficient when maintained on grazing when they are older. This seriously calls into question the value of early life FCR tests as a selection criterion.
Therefore, while FCR can play an important role as part of the selection process for breeding animals, it should never be used as the sole criterion on which to base selection decisions due to the unintended negative consequences an excessive focus on this trait may have. It should only be utilized as part of a balanced selection program where its use can help to achieve specific breeding objectives. This is particularly important for extensive livestock producers in arid regions where grazing is often limited.
I grew up on a small sheep farm in the Karoo where my passion for livestock farming started.
I am currently engaged in research for my PhD project titled “Developing a climate-linked production prediction model for extensive South African sheep farming enterprises”. The research aims to determine what influence weather and climate patterns have historically had on sheep production conditions and to use the historic relationships to predict the effect of future climate change on production output. I am passionate about livestock agriculture and believe that we need to find innovative solutions to the ever increasing challenges we face in this sector.
