Milk Production, Milk Quality and Behaviour of Dairy Cows Grazing on Swards with Low and High Water-Soluble Carbohydrates Content in Autumn: A Pilot Trial

Grazing ruminant systems can be sustainably intensified by improving efficiency while reducing their environmental impact. The objective was to examine the potential of pastures differing in water soluble carbohydrate (WSC) and crude protein (CP) contents, to affect milk production and composition, and behaviour of cows grazing perennial ryegrass (PRG) swards. By modifying the nitrogen (N) fertilisation rate (83 and 250 kg/ha per year) and the defoliation frequency (3 or 2 leaves per tiller), combined with cultivars selection (high sugar vs. standard cultivars) we obtained two swards differing in WSC and CP contents. The two contrasting swards were grazed by 6 dairy cows each in 9 daily strips in autumn. Pasture samples were collected to determine herbage mass and quality. Cows behaviour was recorded by direct observation. Forage offered and apparently consumed was similar between swards (averaging 37.3 and 18.2 kg/cow, respectively), although the residual was lower in the high sugar sward (1735 vs. 2143 kg/ha). Cows spent less time grazing in the high sugar sward (66.9 v. 71.6%) but with similar rumination times (14.6 %). Milk production and composition were similar between groups, suggesting that high quality pastures would require a greater difference in nutritional composition to affect animal performance.