Growth performance of yearling horses grazing bermudagrass pastures at different grazing pressures.

The study focuses on understanding how different grazing pressures affect the growth performance of yearling horses consuming bermudagrass pastures. There is a noticeable influence of stocking rate on the daily gain of body weight but not on the increase in height.

Study Design and Methodology

• The researchers conducted the study on yearling geldings (young neutered male horses) kept on pastures of bermudagrass without any additional energy or protein feed supplementation. The stocking rates, which refer to the number of yearlings per hectare, tested were 6.7, 8.0, 9.5, and 12.4.
• The investigators collected weekly forage samples from the pastures to assess both the quality and quantity of the available grass. These samples were divided into three equal parts to represent the upper, middle, and lower parts of the grass canopy. This procedure was meant to establish any relationships between the available forage and the growth rate of the yearlings.

Results and Findings

• The study revealed a clear connection between the average daily gain (ADG) – the rate at which a horse increases its weight daily – and the stocking rate. However, there was no impact of stocking rates on the height increase of the yearlings.
• The ADG varied between -0.31 kg/day and 0.37 kg/day. Interestingly, a higher stocking rate correlated with a lower ADG, implying the horses gained less weight when more horses were present in a given area.
• The relationship between the available forage and the ADG was found to be quadratic, meaning that as the amount of available forage changes, the ADG does not increase or decrease at a constant rate but accelerates or decelerates.
• When considering only the top layers of the grass canopy, the forage quantity appeared to linearly affect the ADG. Hence, the authors speculated that the performance of the yearlings may have been hindered by a lack of available forage in the top layers in lightly grazed pastures.

Implications

• The findings from this research could be used to guide decisions about appropriate stocking rates for horses grazing bermudagrass pastures, with a view to optimizing their growth rates, particularly their weight gain.
• Further, knowing that the availability of the upper layers of grass could limit animal performance may influence future pasture management strategies.
• While the study findings suggest that increasing the stocking rate may decrease the individual body weight gain of yearlings, other factors (like cost and space efficiency) should also be considered when deciding on optimal stocking rates.