Investigation of virginiamycin to improve health of growing and finishing steers: II. Animal growth and development, and intake dynamics

Objective

Our objective was to determine the inter- relationship between rumen health dynamics and animal growth and development characteristics of growing and finishing steers receiving virginiamycin (VM). A companion article was published previously (Rivera et al., 2024).

Materials and Methods

A total of 120 Angus-crossbred steers (304 ± 27 kg) were assigned randomly to 1 of 20 pens equipped with a Calan gate feed system from which animals within a pen received VM (240 mg/d) or not as follows: no VM (T₀₀₀); VM in the last 50 d (T₀₀₁); VM for the last 100 d (T₀₁₁); VM in the first 50 d (T₁₀₀); VM in the first 100 d (T₁₁₀); and VM for 150 d (T₁₁₁). At slaughter, the 9th to 11th rib section was collected from the right side of each animal’s carcass to estimate carcass and empty body composition. Data were analyzed using a random coefficients model with the pen as a random effect and animals within treatment as the subject.

Results and Discussion

Dry matter intake was less for T₁₁₁ compared with T₀₀₀; however, ADG was not different. Thus, VM improved G:F. The T₀₁₁ had greater DMI compared with T₁₁₀, which resulted in greater ADG with no difference in G:F. Apparent total-tract NDF digestibility was greater for T₁₁₁ than T₀₀₀, which was confirmed by an improved diet growth-adjusted ME for T₁₁₁ than T₀₀₀. The T₀₁₁ tended to have a greater carcass and final shrunk BW than T₁₁₀. Ether extract content of the 9th to 11th rib section tended to be decreased for animals that consumed VM regardless of the period or length of feeding, resulting in a tendency to have less empty body fat content.

Implications and Applications

In this experiment daily inclusion of VM during the overall feeding phase increased feed energy utilization, and its withdrawal during the end of the finishing phase (T₁₁₀) decreased DMI and ADG. Continuous VM feeding enhanced fiber digestion and energy utilization, likely due to it promoting ruminal health.