Whilst developed several decades ago, research into high sugar grasses and their proposed benefits has been continual. But where do they differ from normal grasses? Firstly, their “higher sugar” levels are delivered through greater water-soluble carbohydrate (WSC) levels within the grass. These WSC’s are present within the plant’s cells as opposed to the cell walls, where they take longer to be broken down for energy in the rumen. Higher WSC content within the grasses offers a greater amount of readily available energy within the cow’s diet, allowing for more efficient utilisation of dietary proteins in the rumen.
Research has demonstrated that feeding dairy cows with High Sugar Grasses has several benefits to production, economics and the environment. In relation to productivity, High Sugar Grasses (HSG) have been shown to significantly increase the digestible dry matter intake of grazing herds by up to 2kg/head per day (Miller et al.,2001; Lee et al., 2002). Thus, allowing for maximum nutrient uptake with minimal additional dietary inputs. HSG’s have also been shown to improve diet digestibility levels by 3%, leading to further dietary dry matter gains (Miller et al.,2001; Moorby et al., 2006).
These dietary benefits, combined with increased milk production efficiencies from greater grass protein utilisation, have been found to increase output. This is particularly noticeable in late-lactation cows, with improved milk yields over a grazing season of 6% or 2.5 litres/day per cow (Miller et al.,2001), and 2.3 litres/day per cow during early-lactation without a reduction in milk quality. Milk solids have also been shown to achieve a marked improvement of up to 10% from cows fed on an HSG based diet (Cosgrove, 2007).
Whilst re-seeding with a new HSG lay may be costly, the economic case in its support is strong as it is advised to re-seed at least 10-15% of your lays annually to maintain productivity. As discussed above, several studies have shown marked production performance in cattle, from improved dietary efficiency to increased milk yield output. Increased feed conversion efficiency in turn reduces the amount of supplementary feed required which results in improved margins. If higher daily dietary requirements can be achieved by grazing cattle on HSG pasture and silage, then feed cost savings can be achieved all year round. It must however be noted that to retain the HSG’s benefits in the form of silage, the following steps are advised: use an inoculant to assist with fermentation, ensure your silage isn’t too wet (i.e. 28-32% DM target) so as not to reduce dry matter value and take your silage cut during the afternoon to ensure maximum WSC content in the grass.
Alongside these productive and cost benefits, it must also be noted that HSG’s have been found to provide environmental benefits in the form of reduced environmental N losses (Keim and Anrique, 2011; Foskolos and Moorby; 2017). As discussed in a previous article on crude protein (CP) in dairy diets, improving protein utilisation in the rumen reduces nitrogen (N) losses in the urine. This in turn, reduces environmental impacts through the decrease in nitrous oxide emissions from converted volatile ammonia in urine. Whilst in the case of reducing CP, where N losses are shifted from urine to less volatile faecal form, with HSG’s this shift differs. A proportion of the N usually lost through urinary excretion is shifted to the milk in the form of protein, due to more efficient N utilisation in the rumen (Miller et al.,2001; Moorby et al., 2006).
So, we see that HSG’s, whilst an investment, will payback relatively quickly. They can offer improved feed conversion and efficiency to the herd, reduce feed costs and an increase in milk yields without affecting composition. On top of this there are, of course, the environmental benefits of reduced N emissions. With subsidies, support mechanisms and the public view shift further towards lowering agriculture's environmental footprint, HSG’s really could be a source of green money.
Sian Rowlands BSc (Hons), MSc
Dairy Technical Specialist Coordinator
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