Effects of sheep grazing and breeding strategies on animal performance and grass production, utilisation, and quality

A series of studies were undertaken to investigate the effects of sheep grazing strategies and genetics on animal performance and grass production, utilisation, and quality.

 Based on the knowledge gaps identified within the literature, the specific objectives of this thesis were to:

-Evaluate opportunities to improve herbage utilisation and animal performance by adopting rotational paddock grazing systems for lowland sheep production (Chapter 2 and 3).

-Identify the variability in grass growth, utilisation, and quality on commercial sheep farms in Northern Ireland (Chapter 3)

-Investigate the effect of sire breed and genetic merit on progeny performance in a temperate grass-based system (Chapter 3 and Chapter 4).

-Examine the effect of sward composition on digestibility and methane emissions of weaned lambs (Chapter 5).

Chapter Two assessed the effect of 4 vs. 8 paddock rotational grazing systems on animal and grassland performance in a mid-season lamb production system over two consecutive grazing seasons (April to November 2018 and March to November 2019). 

Chapter Three evaluated the effect of genetics and grazing strategies on lamb production efficiency across five commercial sheep farms in Northern Ireland during the 2018 and 2019 grazing seasons. It examined the effect of sire breed (Aberfield, Meatlinc and NZ Suffolk [SB]) and rotational grazing system (4 vs. 8 paddock rotational grazing system [PS]) on animal and grassland performance, providing estimates of grass growth, utilisation, and quality.

Chapter Four investigated the effect of sire breed (SB) and muscle depth estimated breeding value (EBV) on lamb performance and carcass quality. Ewes were artificially inseminated using terminal sires (Texel or Suffolk) with either a high or low EBV index for muscle depth.

 Chapter Five examined the effect of sward composition on feed intake, nutrient digestibility efficiency and CH4 emissions of weaned lambs. Thirty-six weaned lambs were used in a 3 diet (perennial ryegrass/white clover [PC] vs. meadow fescue/timothy/white clover [MTC] vs. composite mix [PMTC]) x 2 breed (Texel vs. Suffolk) study.