Roberts: cow efficiency will be most influenced by environment interactionsWritten by Christy Martinez
There are four ways to express feed efficiency, through ratios – pounds consumed per pound gained and pounds gained per pound consumed – and residual feed intake (RFI) and residual gain.
“One problem with feed efficiency data is that any time we try to use one number to demonstrate a relationship between two traits, it usually doesn’t work very well,” says Roberts.
“A limitation in the industry today is that most feed intake data is collected on an individual trial basis, and you really can’t make comparisons across studies, or even across feeding trials at the same location,” he says. “In contrast to many other traits, where we standardize some of the known sources of variation, that’s not happening well for the feed efficiency trials in the country at this time.”
Cowherd efficiency and economics
Speaking of feed efficiency in cowherds, from an economic standpoint, Roberts says feed sources should be considered.
“If we look at efficiency with respect to the amount of energy input per amount of edible pound output, we stand no chance to ever compete with other livestock species on a one-to-one basis,” he says.
However, he says cattle can use feed sources that won’t work in the other livestock species.
“Rather than look at efficiency in respect to feed efficiency, let’s look at efficiency in terms of what type of feed we’re putting in those animals, and use the economic driver rather than a biological driver,” he says.
Also, he says lifetime production becomes important in minimizing the impact of overall energy needed.
“For efficiency in the cow, we need to look at the input – maximizing utilization of inexpensive resources – and the output, which is lifetime productivity,” says Roberts.
Compared to other meat species, Roberts says that cowherd inputs vary due to season, location and management, and that requirements will differ due to genetics and their impact on mature size, as well as the stage of production through the annual cycle and the environment.
“All those things considered, efficiency of the cow, more than any other trait, will be influenced by an interaction with the environment,” he says. “A bull might have a better EPD in Nebraska than Montana for growth, because of the environmental effects. The genotype-by-environment interaction isn’t very significant in most things we measure for EPDs at this point in time.”
“I would propose that, if we get a cow efficiency EPD, it would be important to consider the environmental interaction, and some cows will be better for some environments than other cows,” he states.
Pushing the system
Roberts cites data that indicates the age of a cow accounts for variations in weaning weights more than any other factor.
“We’re losing a lot of our animals way before they reach their maximum efficiency,” he says. “There is a 20 percent difference in output between cows and heifers, with little difference in input. Twenty percent is a big number, and probably way larger than the impact we’ll see with any changes in feed efficiency.”
To make that happen, Roberts says a manifold system should be used.
“A finite amount of feed goes into the animal, and if they’ve been selected for RFI they may not eat much, but if we select for a larger input, they have the opportunity to push the system and make all the possibilities work. Deciding which traits to select for can become daunting.”
Taking the EPD for mature size and milk production, Roberts says he thinks the EPD is good, but he says it’s limited because it assigns the maintenance energy requirement on the average of animals at a given mature size and milk production.
“Very few animals are average,” he says. “The EPD does not account for the biological variation around the average for a mature size and level of milk production,” he notes.
Roberts says some breeds do have an EPD for stayability and longevity.
“To me, that may be an indicator of longevity due to sustained reproductive function,” he explains. “I’m not aware of research to see how much genetic progress can be make selecting for this, because not many people want to dedicate the lifetime it will take to get that done.”
“We need to make use of the technologies we have available,” says Roberts, giving 25 percent greater lifetime production as an example. “How will selection for feed efficiency compare to that? I’d be interested to see how much progress we could make that would equate to that. We need to think about prioritization.”
“In addition to genetic mechanisms chasing efficiency, we have an opportunity to improve efficiency through looking at the alternatives management strategies we could use,” he says.
RFI: one number, two traits
USDA Agriculture Research Service research scientist Andy Roberts says that, in his opinion, the RFI scale is backwards.
“Biologically, we usually put the factor having the effect on the bottom, and the response variable on the side,” he states. “Residual feed intake looks at that backwards, asking ‘At a given level of gain, do the animals eat more or less than average?’ In this case, a negative number is more desirable, and a positive number is less desirable.”
“Something that really scares me about RFI is that it’s strongly correlated with how much an animal eats,” says Roberts. “Anyone who has anything to do with a feedlot doesn’t want an efficient animal that won’t eat. If you look at RFI data, keep in mind that, for a slaughter or market animal, you have to have an endpoint. Efficient animals that don’t eat much won’t reach that endpoint very fast, and the total feed put into them will be high because they use a lot of feed for maintenance.”
In evaluating animals by the four approaches to measure feed efficiency, Roberts says they can end up with very different results, depending on the strategy.
“It boils down to the problems with trying to use one number to account for variation in two traits,” he explains. “We need to use feed intake as one trait, and growth as another, not try to use the two together to come up with a magic number.”