Ration balance critical to benefit from multi-cut grass silages

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Length: 950 words; 3–4 minutes

Recent years have seen a steady increase in the number of dairy units switching from the traditional 2–3 cuts of grass silage to so-called ‘multi-cut’ systems taking five cuts or more. However, despite the potential benefits of increased overall silage feed value, higher protein levels can pose a significant challenge when it comes to ration formulation.

“Many farms are now regularly taking five cuts of grass silage, typically closing the gap between cuts to around four weeks, depending on the season,” KW nutritionist Dr Anna Sutcliffe explains. “The younger sward produces silage with higher digestibility, higher intake potential and an energy content up to 1MJ ME/kg DM higher, yet still give similar total silage yields for the season.”

Reducing feed costs

The claimed benefits include more milk from forage, lower feed costs and a higher margin over purchased feeds. Some reports have suggested the reduction in feed costs can be as high as 2ppl.

“But the multi-cut approach also raises the level of silage crude protein (CP), all of which is rapidly available rumen degradable protein (RDP),” Dr Sutcliffe continues. “Compared to the typical 9–16% CP levels for traditional 2–3 cut systems, we’re seeing ranges of 15–20% and higher (table 1).

“The challenge is that if cows are consuming 10–12kg DM of grass silage each day, it’s difficult to create a balanced winter ration that’s below 19% CP, once additional feed ingredients such as soyabean meal or rapeseed expeller have been added to meet the cow’s requirements for higher quality protein. The result is an oversupply of RDP, leading to excess nitrogen in the rumen.”

Excretion of this nitrogen not only represents a loss of nutrients, but also wastes energy that could instead be going into milk production. In addition, oversupply of RDP has been strongly linked to increased embryo mortality. 

“Together, these issues can quickly undermine the potential benefits of a multi-cut system,” adds Dr Sutcliffe. “The extra cost for a full season has been shown to be as much as £2,500, so if a good proportion of the additional protein and energy are wasted, the advantages become much less clear.”

Balancing rumen nitrogen

According to Dr Sutcliffe, the challenge is greatest where there’s insufficient low protein, high starch maize or wholecrop cereal silage to help counter the higher grass silage CP levels. To be effective, these silages need to make up at least 35% of the forage mix (on a freshweight basis), and for many that isn’t achievable year round, or at all.

“Research carried out at CEDAR has shown that there’s little benefit, in terms of milk output, from having an overall ration CP levels above 16%. In fact, doing so both reduces nitrogen use efficiency and increases nitrogen excretion and subsequent pollution risk,” she adds.

“The key is to match the supply of nitrogen in the rumen sufficient fermentable energy…”

“The key is to match the supply of nitrogen in the rumen from RDP with sufficient fermentable energy (FME) to maximise the conversion of that nitrogen into microbial protein. And if low protein, high energy forages like maize silage aren’t available, or supplies are limited, alternatives need to be found.”

The target is to ensure no more than a 20% oversupply of RDP, with milk urea concentration a useful guide – around 0.020-0.025% is ideal, and levels above 0.030% indicatie that more FME is needed to balance excess RDP. Table 2 shows examples of balanced rations to support M+38 litres where different forages are available, and the challenge will be even greater at lower production levels, warns Dr Sutcliffe.

“Start by making sure there’s at least 5% sugars in the ration to drive rapid microbial growth, using one of the high sugar molasses-based liquid feeds like Molale or Economol,” she explains. “Additional FME required should then come from a balance of starch and digestible fibre to promote good rumen function and avoid sub-acute ruminal acidosis (SARA).

“For starch, use feeds like Soda Wheat, maize germ or ground maize, all of which release starch more slowly in the rumen. Other options include the confectionery blends, such as SweetStarch and SugaRich Dairy, which contain a mix of starch, sugars and oil, so pose a much lower risk of SARA than rolled cereals.

“For digestible fibre, avoid diluting the overall energy density of the ration by using sugar beet feed, soya hulls or Traffordgold wheat-gluten moist feed (table 2).” 

Careful protein choice

The balance of the ration will also be improved by minimising the additional RDP contained within feed ingredients used to supply rumen-bypass protein (digestible undegraded protein, DUP). Careful feed choice here can make a substantial difference, claims Dr Sutcliffe.

“Soyabean meal, for example, has a RDP:DUP ratio of 1.56, which means that for every 1kg of DUP you get another 1.56kg of RDP you probably don’t need. In contrast, that same 1kg of DUP from SoyPass rumen-protected soyabean meal will come with just 0.35kg of RDP, and for NovaPro heat-treated rapeseed expeller it’s around 0.61kg of RDP.

UK-produced NovaPro is a highly cost-effective source or rumen-bypass protein.

“The quality of that DUP also has an impact on both nitrogen capture and milk production. Rapeseed-based feeds, for example, have an amino acid profile more closely matching that of milk than soyabean meal.”

According to Nottingham University research, using heat-treated rapeseed expeller instead of soyabean meal not only increased daily milk yield by 1.7kg/cow and dry matter intake by 1.2kg/day, but also cut milk ureas by 11%, a clear indication of improved nitrogen utilisation.

“The increased pollution risk from excretion of excess nitrogen is also becoming a much bigger issue, with consumer – and governmental – pressure on how we produce milk on the increase,” Dr Sutcliffe concludes. 

“That includes where feed ingredients are sourced. The new Brazilian president’s commitment to deforestation and the use of pesticides banned in the UK, for example, is casting a shadow over the use of soyabean meal in dairy rations.“Fortunately we now have UK-sourced alternatives like rapeseed expeller – in both standard and heat-treated (NovaPro) form – that we can use when looking to improve ration balance, and make the most of the forages produced on-farm.”

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