AFBI Research demonstrates improved performance within a 'multi-cut' silage system

Improving the quality of grass silage offered to dairy cows can improve profitability by increasing cow performance and enabling lower concentrate inputs.

Given that silage digestibility (D-value) declines by an average of 3.3% for each one-week delay in harvest date, silage quality can be improved by harvesting herbage earlier, or more frequently.

A recent AFBI survey indicated that 12.7% of Northern Ireland farmers now use a 4-cut system (‘multi-cut’) in an attempt to improve silage feed value. However, few studies have compared cow performance within a ‘traditional’ 3-cut system compared to a 4-cut system. The current study examined cow performance and the whole system impact of offering silages produced within either a 3- or 4-cut system. 

The study

Grass silage was produced within either a 3-cut or 4-cut system during 2018.  When possible, grass was tedded to facilitate wilting, and grass within all harvests was treated with a bacterial inoculant at ensiling. The silages were then offered to 80 Holstein cows (including 24 heifers) during a 25 week feeding study, with silages within each system offered in order of harvest. Cows were offered a basal diet comprising silage plus 8 kg concentrate per day, mixed using a mixer wagon. Cows were also offered additional concentrates on a ‘feed-to-yield’ basis using an out-of-parlour feeding system. Concentrate levels where reviewed weekly and adjusted according to milk yields during the previous 2 weeks. Average ‘maintenance plus (M+)’ values (i.e. the quantity of milk the basal ration was calculated to support) within the 3-cut system were 24 and 19 kg milk/day for cows and heifers, respectively.  Due to the higher intake potential and higher quality of silages made within the 4-cut system, average M+ values were 26 and 21 kg milk/day for cows and heifers, respectively. Concentrates were offered at a rate of 0.45 kg for each kg of milk produced in excess of the assumed M+ values.  

Outcomes

Impact on silage yield and quality

Total silage dry matter (DM) yields for the 3-cut and 4-cut systems were 13.4 t DM/ha and 12.3 t DM/ha, respectively. Mean silage composition across all harvests is presented in Table 1. Mean silage DM contents were 31.9 and 34.4 % with the 3-cut and 4-cut systems respectively, although across all harvests DM content ranged from 22.5 to 49.1%. Silage crude protein and metabolisable energy content were higher in the 4-cut system, reflecting the shorter re-growth intervals (average, 39 v. 54 d, respectively).

Table 1: Mean composition (across all harvests) of silages produced within the 3- and 4-cut systems

Impact on cow performance

Cows on the 4-cut system had a higher silage DM intake than those on the 3-cut system, although concentrate intake did not differ between systems (Table 2).  Cows on the 4-cut system also had a higher milk yield, and produced milk with a higher protein content, than those on the 3-cut system, although cows on the 3-cut system produced milk with a higher fat content (Table 2).  The higher milk yield of cows offered the 4-cut silages is likely due to their higher energy intakes (a consequence of higher DM intakes and the silage having a greater metabolisable energy content).  The cumulative effect of the differences in milk yield and milk composition was that cows on the 4-cut system had a higher milk fat + protein yield. Silage production system had no effect on average body condition score (average 2.5) or on any of the fertility parameters measured.

Table 2. Cow performance when offered silages produced within either a 3- or 4-cut silage system.

Margin over feed costs

The impact on margin-over-feed costs of moving from a 3-cut to a 4-cut system will be largely dictated by silage cost, concentrate cost and the value of milk produced.  Silage production costs (per t DM) will be higher within a 4-cut system, as many field operations (fertiliser application, mowing, tedding, rowing, harvesting) and yard operations (filling, rolling, sealing of silos) have to be repeated an extra time, and many contractors charge ‘per acre’, irrespective of yield.

Full economic costs of silages produced were assumed to be £114 and £135/t DM within the 3-cut and 4-cut systems, respectively (excluding feed-out costs). This cost takes into account a ‘land charge’, reseeding costs, variable costs of growing a grass crop, the reduced DM yield associated with multi-cut systems and assumes contractor charges for the complete harvesting operation. Concentrates were assumed to cost £250/t, while a milk price of 28p per litre (adjusted for compositional bonuses) was also assumed.   

While total feed costs were 23 pence per cow/day higher with the 4-cut system, the value of milk produced was also higher (71 pence per cow/day), resulting in an increase in margin-over-feed costs of 48 pence per cow/day with the 4-cut system. Extrapolating these figures for a 100 cow dairy herd over a 180 d winter period, offering silage made within a 4-cut system will increase margin-over-feed costs by £8,640. This simple calculation illustrates that there can be an economic benefit of moving from a 3- to a 4-cut system, despite the higher silage production costs incurred.

Table 3. Calculated margin-over-feed cost within the 3-cut and 4-cut systems¹

¹_{Costs of 3- and 4-cut silages are currently under review by CAFRE and AFBI}

Practical Implications

The reduction in herbage yield, together with the higher intakes associated with the 4-cut system, will have an impact on land requirements. Based on the results of the current study, feeding a 100 cow dairy herd over a 180 d winter period would require 15 ha of land with a 3-cut system, compared to 18 ha with a 4-cut system, a 19.3% increase.

While performance can be higher within a 4-cut system, the system is not without its challenges. Firstly, producing high digestibility silages in a 4-cut system means that grass must be harvested within a relatively narrow time-window, something which can be challenging given the high reliance on contractor usage. Secondly, in order to achieve a satisfactory fermentation, which can be challenging in grass harvested at an earlier growth stage due to higher nitrogen levels, adequate wilting is necessary. Therefore, the short-time window for harvesting to maintain digestibility must also be balanced with suitable weather conditions for wilting. On a positive note, herbage harvested within a 4-cut system will have a faster rate of wilting than herbage harvested within a 3-cut system due to the lower yield at each harvest. 

Conclusion

Offering silage produced under a 4-cut system increased silage DM intake, milk yield, and milk fat + protein yield, compared to silage produced under a 3-cut system. Despite the lower herbage yields and higher silage costs with the 4-cut system, margin-over-feed costs were 8% higher within this system.

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