Research

Background

Improving feed efficiency can help both reduce feed costs and reduce the environmental impact of feed cattle. There is a large variation between animals when it comes to feed efficiency. Residual feed intake (RFI) is one way to measure efficiency in cattle, but doesn’t work as well on grazing animals. RFI is also influenced by diet and stage of production, with re-ranking occurring depending on these factors. These researchers want to better understand why some animals are more efficient at digesting forages than others.

Objective

The objectives of this study are to:

• Determine if the microbial ecology of the rumen and/or hindgut varies between animals that differ in forage digestion efficiency
• Identify key genes and/or microbes in high efficiency animals that are not present in low efficiency animals
• Determine if animal physiology and host metabolism is a bigger factor in feed digestion efficiency than the microbial processes in the gut.
• Determine if efficiency rankings in animals change as a result of changes in feed composition and how might this relate to animal and/or microbial factors.\

What they Did

Two detailed animal studies (called metabolism trials) were conducted to understand why some heifers fed the same diet are better than others at breaking down the fiber in their feed. In the first trial, all eight heifers were on a high-forage diet and how much they ate, how well they digested it, how much methane they produced, and microbial activity in the gut were measured. In the second trial, the same animals were tested on four different diets – two high in forage and two high in grain – to see how diet affected digestion efficiency, feed intake, and the gut microbiome (the microbes that live in the digestive tract, which are important for feed digestion and animal health). Feed, feces, urine, and rumen contents were sampled, and chewing behavior, fermentation patterns, and microbial communities in the rumen and feces were monitored. DNA and RNA sequencing was used to understand which microbes were present, what enzymes they were producing, and to see if this was affecting the genes produced in the gut. The goal was to determine if the ability to digest fiber is determined solely by the animal itself, by the microbes in the gut, or a combination of both.

What they Learned

The results showed that heifers classified as ‘efficient’ on the basis of their ability to digest forage generally ate more, digested their feed more efficiently, and tended to gain more weight, even when their diet changed. Surprisingly, these animals also produced less methane per unit of feed. However, when we looked at the microbes in the rumen, we found only small differences in microbial populations between animals classified as high and low based on their ability to digest fibre. This suggests that gut microbes alone may not explain why some animals are more efficient. In some cases, shifts were seen in particular groups of microbes, but these differences were usually minor and varied depending on the diet.

Instead, bigger differences were seen in how the animals behaved. High digestibility cattle spent more time chewing and ruminating, which likely helped them break down fiber more thoroughly. They also had larger rumen volumes and may have kept their feed in the rumen longer, giving microbes more time to work. These physical and behavioral traits may play a bigger role in fibre digestion efficiency than the microbial community itself.

We also tested new DNA sequencing approaches to study rumen protozoa and fungi, microbes from the rumen that are less well understood than bacteria. These early findings revealed that the protozoa and fungi populations were more related to fibre digestibility ranking than the bacteria and archaea, and suggest that these types of microbes could be a promising future target for improving feed efficiency.

What it Means

This research shows that selecting cattle based on how well they digest fiber could improve productivity and reduce environmental impact. While microbes in the gut are important, the most efficient animals also had unique physical and behavioral traits like greater rumination time and larger rumen capacity, which may play a bigger role in digesting fiber. Understanding these traits could help breeders select more efficient animals. It also highlights that fiber digestion is a complex trait, shaped by both the host animal and its gut microbes. While most microbiome differences were subtle, ongoing work integrating microbial gene function with animal performance may reveal new ways to enhance efficiency and sustainability in beef production.