Understanding and Improving Feed Efficiency of Beef Cows

Background

Feed costs are the largest expense in beef production and reducing them as much as possible while improving productivity is essential to keep operations in business. Therefore, feed efficiency is an important selection trait, especially in seedstock herds. However, to select animals with high feed efficiency, they must be identified. This can be done by using individual feed intake data. However, recording individual feed intake is expensive, time-consuming and difficult to conduct under field conditions. Additionally, the relationship between feed efficiency and other important selection traits, such as reproduction and health, remains poorly understood.

This research project focused on potential ways to improve feed efficiency estimation in cattle by examining its relationship with other variables (proxies). These included physiological and metabolic factors, including heart function, blood metabolites, reproduction and rumen physiology. By understanding how these proxies relate to feed efficiency, this group of researchers sought to select proxies that could help replace individual feed intake measurements, enabling continued selection for feed efficiency while considering their relationships with other important traits. The long-term goal is to develop technologies that can rapidly, accurately and cost-effectively predict feed efficiency in herds, especially seedstock and research herds.

Objectives

• Understand why some cattle are naturally more feed efficient than others by studying how their health, digestion, metabolism and reproduction data relate to feed efficiency
• Develop simple, practical ways to measure feed efficiency more quickly and cost-effectively

What they did

Residual feed intake (RFI; kg/day) is the metric calculated for individual animals from this project, serving as the measure for feed efficiency. RFI is defined as the difference between an animal’s actual feed intake and its expected feed intake, based on its body size and growth rate over a specified period. A negative RFI indicates that an animal consumes less feed than expected for its size and growth rate, making it more feed efficient. On the contrary, a positive RFI indicates that an animal consumes more feed than expected and is therefore less feed efficient.

For this study, the team used data from cow-calf pairs, young bulls and feedlot steers from both the Maritime Beef Test Station (Nappan, NS) and the University of Guelph’s Ontario Beef Research Centre (Elora, ON). Individual feed intake was recorded for all animals, and potential proxy measures of feed efficiency, including blood metabolite profiles, rumen physiological parameters, tissue histology, heart rate monitoring, feeding activity and behaviour, reproductive and fertility assessments and infrared thermography (for some animals).

Also, the replacement beef heifer calves (107) and pregnant yearlings (36) at Nappan were enrolled in a standardized stress test study. Their responses to stress were assessed by examining blood cell profiles, immune responses, plasma metabolites, heart rate patterns, activity and behaviour.

Besides this, steers (95) and yearling bulls (16) at Elora were evaluated for daily rumen pH and temperature patterns, rumen fluid fatty acid composition, rumen microbiology and rumen tissue thickness. A separate group of 34 yearling bulls at Elora were evaluated for fertility-related traits, including scrotal infrared thermography, scrotal circumference, testicular ultrasound, semen quality, post-slaughter carcass characteristics and histological evaluation of the testes and epididymis. Seminal plasma protein concentrations (“fertility-associated proteins”) and blood parameters were also measured. Additional beef bulls from the Maritime Beef Test Station and 51 from the Ontario Beef Research Centre were assessed for indicators of sexual maturity.

What They Learned

Heifers and Cows

Understanding the biology of feed efficiency in heifers:

• More feed-efficient heifers showed differences in mineral and metabolic indicators compared to those with lower efficiency. This suggests that efficient ones use nutrients better.
• Improved feed efficiency does not appear to negatively affect immune function, suggesting that selecting heifers for high feed efficiency should not affect health.
• More feed-efficient heifers appear to require less oxygen and energy to support growth and development than those with lower efficiency.

Heart rate and stress response as proxies of feed efficiency:

• Heart rate measurements collected overnight and during mild stress events show potential as proxies of feed efficiency.
• More feed-efficient animals may differ in how they respond to and recover from stress.

Bulls and Steers

Activity, rumen function and animal health:

• Rumen temperature and activity monitoring show potential as proxies of feed efficiency and overall animal health.

Rumen function and feed efficiency:

• More feed-efficient males show differences in rumen function compared to less efficient ones. This can explain differences in performance.
• More feed-efficient males tend to maintain a healthier rumen environment and spend more time within optimal rumen pH ranges compared to those that are less efficient.
• Feed-efficient males showed differences in rumen microbial populations, including fewer methane-producing microorganisms compared to less efficient ones.

Understanding potential trade-offs in bull fertility and feed efficiency:

• More feed-efficient bulls exhibit several desirable production traits but may reach sexual maturity later than less feed-efficient bulls.
• More feed-efficient bulls exhibited changes in sperm characteristics and reproductive tissue structure. More feed-efficient bulls arrive at puberty at an older age, have reduced sperm motility, had more sperm abnormalities and have less temperature difference between their scrotal and body temperature than those with lower efficiency. Overall, this suggests that reproductive aspects should be monitored alongside feed efficiency during breeding decisions.

What it Means

This project investigated potential proxies for measuring feed efficiency when individual measurements using traditional approaches cannot be obtained. These findings could potentially be used in future technologies developed for monitoring research and seedstock herds.

Studies in heifers found that more feed-efficient animals tend to use oxygen and nutrients more efficiently while maintaining healthy immune function and normal growth compared with less efficient animals. Heart rate monitoring, both under normal conditions and in response to mild stress, also showed potential as a proxy. Similarly, measurements of rumen function (including rumen temperature, activity, pH, composition and microbial populations) revealed important differences between more and less efficient cattle. More efficient animals tended to have rumen environments more favourable for certain microbial communities that suggest improved nutrient absorption and reduced methane production. These findings suggest that technologies such as heart rate monitoring, rumen sensing and others could eventually help identify individual feed-efficient animals.

Studies conducted in bulls showed reproductive variables should be considered alongside feed efficiency. This is because more feed-efficient bulls exhibit several desirable production traits but may reach sexual maturity later than less feed-efficient bulls.