Search

Selection for feed efficiency is crucial for improving economic and environmental sustainability in beef cattle production. Residual feed intake (RFIfat) is a commonly used measure of feed efficiency and is determined in a drylot setting by calculating the difference between observed and expected dry matter intake (DMI), where expected feed intake is adjusted for metabolic body weight (BW), average daily gain (ADG) and body fatness. Lower RFIfatcattle are more efficient animals as they eat less than predicted for the same growth, body size and body fatness. Limited studies have been conducted evaluating the role of RFIfaton the subsequent performance of cow-calf pairs on native range. Kinsella Composite cows and calves (n = 120) grazed native pasture from July 11 to Sept 12 (summer) and from Sept 13 to Nov 2 (fall) of 2023 were included in this study. All dams had previously been evaluated for RFIfatas a heifer (8 to 12 mo of age) using the GrowSafe Feed Intake System (Vytelle, Canada). Cow and calf ADG were subjected to an analysis of covariance using lm function from stats R core package (R Core Team, 2024), with cow age (2 to 8 yr of age) as the fixed effect and RFIfatas the covariate, analyzing separately by season. An unbalanced Tukey HDS post-hoc were applied for age and p-values < 0.05 were considered significant. Weight gain was assessed on cows with an initial BW on pasture of 598.4 ± 68.4 kg, and 2 to 8 yr of age, and on calves having an initial on pasture BW of 106 ± 21.5 kg, and 65 ± 14 d of age. Cow age affected (P < 0.01) cow ADG during summer, with the youngest dams (2 yr old) gaining more weight than older animals (7 yr old; Figure 1A). No effect of RFIfatwas found on cow weight gain during summer grazing. However, during fall grazing, RFIfataffected (P < 0.01) cow ADG (Figure 1B). Low-RFIfatcows (efficient) had increased weight gain during fall grazing as compared with high-RFIfatcows (inefficient: Figure 1B). Calf ADG was not affected (P > 0.1) by cow age, cow RFIfat and cow ADG during summer and fall. We conclude that cows with low RFIfatexhibited superior body weight gain, during fall grazing on native range when forage nutrient quality and quantity become limiting. [ABSTRACT FROM AUTHOR]

The rumen harbors a complex symbiotic microbiome (bacteria, archaea, protozoa, fungi and viruses), which degrades plant cell walls and ferments sugars to the volatile fatty acids that provide energy to host. Extensive recent research has revealed that variation in rumen microbiome composition and function can directly and in directly influence many phenotypes in cattle such as feed efficiency, methane emission, metabolic health, milk and meat quality. Such findings highlight the opportunity to intervene rumen microbiome for improved productivity, health and reduced environmental footprint. More and more evidence revealed the individualized rumen microbiome and host genetics could be one of the factors in colonizing of selective rumen microbiome. This presentation will focus on to date knowledge on “heritability” of rumen microbes and explore the opportunities to breed cattle with a desired rumen microbiome for improved feed efficiency and lower emission of greenhouse gases. [ABSTRACT FROM AUTHOR]