By: Monty Kerley, Ph.D.
My association with GrowSafe Systems® began over a decade ago when the University of Missouri became the site of the first installation in the United States. As a professor at the University of Missouri in the Animal Sciences department focused in ruminant nutrition, I was uniquely interested in GrowSafe Feed Intake technology. My interest in the Feed Intake technology stemmed from wanting to study the genetic potential for energetic efficiency in cattle and to identify if a relationship of mitochondrial function to energetic efficiency existed. It was already known that other species had substantial variation in metabolic efficiency. The poultry and swine industry used genetic outliers for metabolic efficiency to increase feed efficiency of production animals. We hypothesized that ruminants would follow suit. With GrowSafe’s technology and analytics we were able to conduct various trials related to natural feeding behavior, feed efficiency and performance in a research environment.
We first studied mitochondrial function (respiration rate) among beef calves with differing residual feed intake (RFI) phenotypes. We found that low RFI (metabolically efficient) calves had more rapid uptake of oxygen by mitochondria than high RFI calves. This finding gave support to our hypothesis that RFI was a trait that did measure metabolic efficiency, or energetic efficiency of cellular metabolism not influenced by growth rate (mature size) or composition of growth (muscle vs. protein).
Our research identified differences in complex I – a primary entry point for electrons to the respiratory chain – of the mitochondria, which plays a role in energy metabolism, to demonstrate differences among RFI phenotypes. We believe more metabolically efficient animals have the ability to take up oxygen faster and replenish ATP pools quicker than less efficient animals. By being quicker to maintain phosphorylation ratio, and therefore replenishing the required levels of ATP, satiety is reached sooner thus requiring less feed intake. If intake is reduced for this reason, because mammals cannot uncouple respiration, then less carbohydrate is consumed and less must be deposited as lipid. This is what happens when inefficient calves are contrasted to efficient calves, inefficient calves have more subcutaneous fat depot than low RFI calves.
Most important to us was that RFI differences among calves had a biological reason for the differences; differences in cellular energy metabolism between low and high RFI calves. We also measured repeatedly in calf populations studied a 1.4-fold difference in dry matter intake by calves but with similar body weight gains. The range in feed efficiency of the population, without selection, was 40 percent. Assuming a herd of cattle have a normal distribution for RFI, selection for RFI could improve efficiency by 20 percent. There is no other single technology that holds this much promise to reduce feed costs. A producer that had made genetic selection for RFI a priority for sires used and heifers retained as cows reduced feed to gain of his calves in the feedlot by one pound of feed per pound of gain, an approximate 17 percent reduction in feedlot feed cost.
We conducted a series of experiments to better understand RFI throughout various stages of production.
- The first experiment was to measure the impact of RFI phenotype on forage intake by grazing cows and the effect of using RFI as a selection criterion on calf energetic efficiency. Beef cows with a low RFI (efficient) were compared to high RFI cows for forage intake on pasture. Forage intake was measured on pasture using forage growth and digestibility estimates. As a result, forage intake by negative RFI cows was 20 percent lower than high RFI cows. The potential to reduce hay requirements by 20 percent would have great impact on annual cow production costs and potential to reduce pasture forage requirement would be beneficial for pasture costs and improve condition when forage was limiting such as drought conditions.
- We measured milk production in beef and cross-bred dairy cows comparing negative to positive RFI cows. Cows in each group had similar dry matter intakes with negative RFI cows having 15 percent greater milk production.
- The improvements in efficiency that have been measured in feedlot calves can also occur in the beef cow herd. A producer that has selected for RFI over multiple generations saw improvements in calves retained through the feedlot, with economic gains in reduced feed costs being greater than carcass premiums he received. Production of these calves was accomplished by placing selection pressure for RFI on heifers retained into his cow herd. The producer noted that he used to hunt for hay to feed the cow herd and now has more meadow grass than his cows can consume. We concluded selection for RFI will reduce winter hay costs and result in cows that can maintain body condition better when feed is limited, such as during drought conditions.
- We measured growth performance of calves generated from negative RFI sire and dam matings. We measured RFI in the dam as a calf post-weaning, mature nonlactating cow and lactating cow. The RFI value that best predicted progeny performance was from testing the dam as a heifer, which is fortunate since this is the easiest point to test females.
GrowSafe has proven that RFI is a valid trait to measure and select. RFI, like any trait, should not be viewed as a single-selection strategy. RFI is a measure of energetic efficiency of the cell, or how efficient the cell is at converting consumed feed to energy that can be used for maintenance and growth. The selection for low RFI cattle (efficient) can have great dividends for the cow herd by reducing hay costs, maintaining body condition during feed restriction, such as drought, and producing more valuable offspring. Selection for RFI-proven genetics and using RFI EPD information should be no different than other traits producers target. Most importantly, RFI emphasis is as important for the cow herd if not more so than it is for calves in the feedlot.