Multispecies swards: effects on animal performance, meat nutritional composition and indicators of rumen function of co-grazed cattle and sheep

Grazing systems can impact the environmental sustainability and nutritional composition of ruminant products. Multispecies swards (MSS) can deliver higher agronomic and animal performance at lower nitrogen (N) fertilisation rates compared to perennial ryegrass monoculture, while including forage herbs and legumes in animal diets can alter the fatty acid profile of ruminant meat, the rumen microbiome and subsequent rumen fermentation. The aim of this thesis was to investigate the effect of grazing four different sward types on the animal performance of co-grazed cattle and sheep; the intramuscular fatty acid (FA), vitamin E, zinc and selenium composition of beef and lamb; and the rumen microbiome and subsequent rumen fermentation in beef heifers throughout the grazing season. In 2019, a grazing experiment was established comprising four sward types: a perennial rye grass monoculture (PRG) (receiving 170 kg N/ha/y); a permanent pasture (PP) (receiving 135 kg N/ha/y); a 6 species sward (6SP) with 2 grasses, 2 legumes, and 2 herbs (receiving 70 kg N/ha/y); and a 12 species sward (12SP) with 3 grasses, 4 legumes, and 5 herbs (receiving 70 kg N/ha/y). In 2020 and 2021, each sward type was rotationally grazed from April to November by dairy cross heifers (n= 20 per treatment per year) and ewes plus lambs (n=22 ewes per treatment per year). Average daily gain (ADG) from turnout to slaughter was higher for heifers grazing the 6SP sward (1.09 kg/day) compared to all other sward types (12SP (0.99 kg/day), PRG (0.92 kg/day), and PP swards (0.92 kg/day); P<0.001)). Lamb ADG from birth to slaughter of lambs grazing the 6SP (393 g/day) and 12SP (363 g/day) swards were greater than lambs grazing the PP (305 g/day; P<0.001) or PRG swards (292 g/day; P<0.001). Lambs grazing the 6SP and 12SP had a reduced number of grazing days from turnout to slaughter (82 and 93 days respectively) compared to the lambs grazing the PPG and PP swards (133 and 127 days respectively; P<0.01). Raw muscle from heifers grazing the 6SP and 12SP swards had higher concentrations of C18:2n6c, C18:3n3c and total polyunsaturated FA (PUFA) compared to raw muscle from heifers grazing the PRG and PP swards (P<0.05). Cooked muscle from heifers grazing the 6 SP and 12SP had a higher proportion of C18:3n3c compared to cooked muscle from heifers grazing the PRG and PP swards (P<0.01). Lambs grazing both MSS had a higher proportion of C18:3n3c in raw muscle than in the PRG and PP swards (P<0.05). Cooked muscle from lambs grazing the 12SP sward had a higher proportion and concentration of C18:3n3c and concentration of total PUFA compared to cooked muscle form the lambs grazing the PP sward (P<0.01). There was no effect of sward type on the α-tocopherol concentration of heifer or lamb muscle. Selenium concentration of bovine muscle was lower in heifer grazing the PRG sward compared to the three other sward types (P<0.001), while concentrations of Se were higher in muscle from heifers grazing the PP compared to the 12SP sward (P<0.01). Lambs grazing the PRG sward had lower concentration of Se in muscle compared to lambs grazing the 6SP (P<0.001), 12SP (P<0.001), and PP (P<0.05) swards. Sward type had no effect on the concentration of Zn in muscle from either heifers or lambs. The analysis of the rumen microbiome in heifers showed that the alpha diversity was higher in the PP sward compared to the 6SP sward in September (P<0.05). There was an effect of sward type (P<0.05) and measurement date (P<0.001) on beta diversity. Between the four sward types at the three measurement dates where the abundance of 11 phyla, 86 families, and 161 genera significantly differed (P<0.05). Overall, co-grazing MSS improved heifer and lamb production performance at lower N fertiliser rates, while marginally improving the FA and selenium composition of beef and lamb muscle. Finally, grazing different sward types changed composition of the rumen microbiome in grazing heifers.