Chemical, Physical, and Degradation Characteristics of Ryegrass Cultivars Grown in Autumn and Winter for Dairy Cows.

Simple Summary: New Zealand has a temperate climate, and dairy farming relies on ryegrass pasture-based systems, normally with a winter-calving system. Although there is adequate pasture growth in some regions during winter, dairy farmers use autumn-saved pasture to sustain cows for one to two months before and after calving. During the transition period at calving, dairy cows have major changes in both physiology and nutritional requirements. The knowledge of ryegrass cultivars would enable the most appropriate selection to benefit cows pre- and post-calving. However, studies on Winter ryegrass are scarce. In this study, we measured nine ryegrass cultivars, including perennial, hybrid, and Italian types grown in late autumn and winter and harvested after seven or nine weeks of regrowth. The crude protein concentration was similar across types, but perennial ryegrasses contained the most fibre. Italian ryegrasses had the greatest proportion of soluble nutrients. The degradation rate of insoluble (fibrous) nutrients was the highest in Italian and the lowest in perennial grasses. Ryegrasses grown during winter had lower crude protein and fibre and higher non-fibre carbohydrate concentrations than that grown in late autumn. In conclusion, this study′s insights into the characteristics of nine ryegrass cultivars, grown in different seasons, offer valuable guidance for selecting the most suitable options to support the nutritional requirements of dairy cows during the transition period around calving. During winter and early spring, pasture supply is usually lower than the demand in New Zealand dairy farming systems and thus the 'autumn saved pastures' (stockpiling) are introduced to fill the gap. This study aimed to investigate the chemical, physical, and degradation characteristics of ryegrass pastures, the predominant forage in New Zealand, grown in autumn and winter. To serve as 'autumn saved pasture', nine ryegrass cultivars, comprising three types (three perennial, three hybrid, and three Italian), were grown in late autumn (Autumn) and early winter (Winter) and harvested after 7 and 9 weeks of regrowth, respectively. The experiment had two experimental factors: ryegrass type (or cultivar) and harvest season. These experimental factors were in a randomised block design with the forage plot as the experimental unit. The degradation characteristics were assessed in the rumen of fistulated cows using the in situ incubation technique. Perennial ryegrass had a greater neutral detergent fibre (NDF) concentration (468 g/kg dry matter (DM)) than the hybrid (435 g/kg DM) or Italian (414 g/kg DM) ryegrasses. Italian ryegrasses had the greatest soluble fraction of DM (64.2% vs. 46.7% and 40.7%) and the greatest degradation rate of an insoluble but degradable fraction of DM (0.221 vs. 0.189 and 0.145/h) than the hybrid and perennial ryegrasses. Compared with the Winter ryegrass, the Autumn ryegrass had a greater crude protein concentration (246 vs. 208 g/kg DM) and a greater NDF concentration (486 vs. 392 g/kg DM) but a lower calculated soluble carbohydrate concentration (152 vs. 263 g/kg DM). It is concluded that there are notable variations among the cultivars, highlighting distinctions in parameters, such as NDF concentration, soluble fractions, degradation rates, and nutrient content among the perennial, hybrid, and Italian ryegrasses, as well as the seasonal variations observed between autumn and winter growth. These findings will not only facilitate enhanced nutrition for dairy cows as they undergo the transition phase but also have practical implications for future research and dairy cow nutrition. [ABSTRACT FROM AUTHOR]