Effect of Post-Grazing Sward Height, Sire Genotype and Indoor Finishing Diet on Steer Intake, Growth and Production in Grass-Based Suckler Weanling-to-Beef Systems.

Peter R Doyle,Mark Mcgee,Edward G O’Riordan,Alan K Kelly,Aidan P Moloney

doi:10.3390/ani11092623

Abstract

Simple SummaryGrass-fed beef is becoming popular; however, there is little research information on optimising beef cattle performance in such production systems. In grass-forage-only beef systems, the removal of dietary concentrates increases the difficulty in achieving target live-weight performance and carcass fatness. Post-grazing sward height can potentially influence animal live-weight gain at pasture, whilst sire breed maturity (genotype) can potentially influence carcass fatness and, therefore, the duration required to achieve a commercially acceptable carcass fat score. Therefore, contrasting post-grazing sward heights and beef steer genotypes were evaluated within a grass-forage-only and grass-forage + concentrate production system. The high post-grazing sward height (6 cm) increased intake and live-weight gain at pasture and resulted in a heavier carcass after an indoor finishing period compared to the low post-grazing sward height (4 cm). The early-maturing genotype had a greater intake, live-weight gain and carcass fatness, but similar carcass weight and lower conformation score compared to the late-maturing genotype. Although concentrate supplementation indoors increased carcass weight and fatness, grass-forage-only steers still achieved a commercially-acceptable fat score when slaughtered at 24 months of age. In conclusion, grazing higher sward residuals and utilising early-maturing animal genotypes can increase live-weight pasture gain and carcass fatness, respectively, in grass-forage beef production systems.This study evaluated the effects of post-grazing sward height (PGSH, 4 or 6 cm) on herbage production, its nutritive value, dry matter (DM) intake, grazing behaviour and growth of early- (EM) and late-maturing (LM) breed suckler steers (n = 72), and the subsequent effect of indoor finishing diet (grass silage + 3.8 kg concentrate DM/head daily (SC), or grass silage only (SO)) on performance and carcass traits. Animals rotationally grazed pasture for 196 days, followed by indoor finishing for 119 days. At pasture, daily live-weight gain (LWG) was 0.10 kg greater for PGSH-6 than PGSH-4, resulting in a tendency for carcass weight to be 11 kg heavier. Although EM had a 0.10 kg greater daily LWG at pasture than LM, carcass weight did not differ between the genotypes. There was a genotype × PGSH interaction for carcass fat score, whereby there was no difference between EM-4 (8.83, 15-point scale) and EM-6 (8.17), but LM-6 (7.28) was greater than LM-4 (6.33). Although concentrate supplementation during indoor finishing increased carcass weight (+37 kg) and fat score (1.75 units), the majority of steers (83% of EM and 78% of LM) achieved a commercially-acceptable carcass fat score (6.78) at slaughter in the grass-forage-only system.

Highlights

Maximising herbage production and animal live-weight gain (LWG) at pasture, optimising stocking rate and minimising purchased concentrates are identified as key drivers of profitability in suckler beef systems [1]
Grass-based suckler beef production systems in temperate climates entail spring-calving cows rearing their own calves until weaning at the end of the grazing season [2]; these calves are usually sold for subsequent finishing
Herbage allowance measured above 4 cm only was greater (p < 0.01) for Post-grazing sward height (PGSH)-6 than PGSH-4

Summary

Introduction

Maximising herbage production and animal live-weight gain (LWG) at pasture, optimising stocking rate and minimising purchased concentrates are identified as key drivers of profitability in suckler beef systems [1]. Grass-based suckler beef production systems in temperate climates entail spring-calving cows rearing their own calves until weaning at the end of the grazing season [2]; these calves are usually sold for subsequent finishing. Such weanling-to-beef steer systems typically involve a post-weaning indoor ‘store’ feeding period, where animals are offered a restricted-energy diet based on grass silage and limited concentrates, which is followed by a grazing season exploiting compensatory growth [3].

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