Genetic Evaluation of Cattle Raised Under High Vs. Low Input Winter Feeding Systems

Background

Feed efficiency in a growing feedlot steer is a different trait than feed efficiency in a mature range cow, so selecting for one will not necessarily improve the other. An animal will not fully express its genetic potential unless it is in a favorable environment. A favorable (high input) wintering environment may compensate for inferior genetics in heifers and cows that have above-average needs or below-average efficiency and allow them to regain condition and rebreed quickly enough to maintain a 365-day calving interval. In a tougher (low input) wintering environment, only the easy keeping, more efficient cows will be able to extract enough nutrition from their feed to maintain body condition, rebreed and maintain a 365-day calving interval. 

In Canada and the US, the percent of calves born to exposed females has remained constant at 82-84% for over 30 years despite huge advances in nutrition and health management. It is likely that this is not a “biological limit” in the North American beef herds but rather, lack of genetic diversity in beef herds, meaning producers are losing the benefits of heterosis, as well as lack of selection for productivity traits in females and selective breeding for replacement heifers.

Objectives

• Estimate genetic and phenotypic relationships of feeding behaviour, dry matter intake (DMI), feed efficiency with heifer fertility, longevity, and lifetime productivity (LTP) of cows reared under two winter feeding systems 
• Determine the relationships between mature cow DMI per pound of calf weaned over 5 calvings and heifer performance. 
• Predict heifer fertility and cow LTP using additive (inherited traits) and non-additive (genomic retained heterozygosity or genetic diversity) genetic effects. This objective will create a Replacement Heifer Profit Index Score which will be used for sorting heifers from top to bottom in terms of fertility and lifetime productivity. 
• Quantify the economic value differences among heifers using feed intake, fertility, LTP and longevity. 
• Evaluate 2000 commercial heifers for feed intake and efficiency using Growsafe Feed Intake System™ and generate RHPI Scores™ for each heifer. The RHPI Score™ includes genomic retained heterozygosity, and molecular breeding values (MBVs) for nine growth, feed efficiency and fertility traits, including accuracy and ranking values.

What They Did

Data collected from the Lacombe Research and Development Centre and Roy Berg Kinsella Research Station between 2005 and 2022 allowed the team to evaluate the feed intake, feed efficiency and reproductive performance from 2697 heifers and 689 cows which had 9500 mating opportunities. Data was also collected from Olds College yielding an additional 200 crossbred heifers from 10 Alberta cow-calf herds which were tested for feed efficiency between 2018 and 2023. All the animals were genotyped to quantify heritability of traits and if any phenotypic correlation could be found, specifically for traits that influence pre-weaning calf performance, feed efficiency, fertility, and longevity. This information was used to develop and train the Replacement Heifer Profit Index Score (RHPI Score™).  

This team also looked at the whole genome to see if they could identify genetic markers that influence cow feed intake, feed efficiency and fertility. The lifetime energy intake and associated feed costs per individual cow was also calculated. These calculations were based on cow, heifer and calf body weight using feed/maintenance requirement models set by the NRC (2001) and NASEM (2016).

What They Learned

This team found that selecting for RFI in beef heifers should result in mature cows who are more feed efficient, with every 1kg DM/day in RFI measured as a heifer being equivalent to 0.66 kg DM/day when measured again as a mature cow. Further (and keeping in mind that a lower RFI = more efficient), everyone additional unit of RFI resulted in $38.60/cow increase in feed costs, $76.40/cow increased in total costs, a $168.50/cow decrease in marginal return and a $163.80/cow decrease in net return every year.  

Cows with a low RFI reduced feed intake by 30.4% compared to those with a high RFI. This meant low RFI cows reduced the feed bill by $60/cow/year and $52/heifer/year. When everything is said and done, the reduced feed costs seen by more efficient cows and heifers showed a net return of $261/cow after five production cycles. However, this number is reliant on feed prices and therefore could be much higher should the cost of silage, hay, barley, corn, and supplements stay high.  

The Replacement Heifer Profit Index Score™ (RHPI Score™) was able to be developed from the findings of this study to make more informed and profitable replacement heifer selections. 

What It Means

A well-designed and managed heifer replacement program that favors replacements from early calving cows that have produced more daughters in the herd, while avoiding calving difficulty and twin births are important to cow longevity and the profitability of a cow-calf operation. All too often, commercial producers pick the biggest and prettiest heifer in the pen. The Replacement Heifer Profit Index Score™ (RHPI Score™), made available to commercial cow-calf producers through Livestock Gentec, aims to optimize heifer selection by incorporating both additive and non-additive genetic effects. Early results show that high indexing heifers produce nine more calves and require nine fewer replacement heifers per 100 heifers exposed to breeding. Increased income from more weaned calves and lower costs of r