Starting at field level there will be soil type and also the


composition of the sward which will influence heading dates and timing of harvest. Then there is timing of fertiliser application across different fields and the ability of the sward to assimilate the nitrogen into protein which in turn will influence effectiveness of fermentation. Weather conditions during the main growing period will also


affect maturity, while weather at harvest will potentially delay cutting date and influence the rate of drying down and the number of times the crop is moved in the field. Then there is the management at harvest. Does the contractor


arrive on time and are all fields at the optimum cutting stage? Does harvest plough on regardless of weather etc. Is clamp filling and sealing adequate? “Multiply all these factors by the number of cuts taken


especially if cuts are mixed in the clamp and it is easy to see why the composition of feed in the clamp will vary significantly over the course of feedout. Unless clamps are analysed sufficiently regularly and with a representative sample, accuracy of diet formulation will be compromised and the impact on performance and costs of production will be considerable. Dr Homer says a study at Ohio State University set out to define


the optimal analysis frequency for forages which will depend itself on a number of factors including herd size, size of clamp etc. “The study introduces the concept of ‘out of control days’, which


is the number of days between their being a change in the clamp and the next regular analysis at which time a problem can be solved. In simple terms the less frequent the analysis, the longer the potential out of control days and the greater the potential consequences. “Table 3 looks at the variation in a clamp of solely first cut silage


made in 2020 which was analysed more regularly than many we see and clearly demonstrates the consequences of variability. “There are variations in all the key parameters and if the diet is


not adjusted milk from forage feeding 10kgDM varies by 1.5 litres/cow/ day. Cows need more supplementary feed or would lose condition


and potentially fertility would suffer. “Freshweight required to supply 10kgDM varies hugely. As silage


gets wetter, if the fresh weight fed is not adjusted then performance would fall. In the worst case if the farmer still feed 2673kg/day assuming the silage was 37.5%DM when actually it was 32.6%DM meaning he actually needed to feed 3067kg, the difference is 1.5kgDM/cow down which is over 2 litres on energy. “Between October and December, dry matter and ME fall so


diets need adjusting. But by February, dry matter and energy have increased and RFC are higher suggesting diets needed rebalancing to maintain consistent rumen fermentation characteristics. At this time there was a bigger interval between analyses. “More regular analysis allows you to be proactive and to


take account of changes in fermentability and ensure the rumen environment stays as stable as possible. As the acid load varies, you would need to consider what to supplement the forage with. Do you stay on same compound/blend? Do you need a rumen buffer?” According to Dr Homer the key with out of control days is the


change from being reactive to proactive and getting farmers to value silage analysis. She emphasises the need to analyse to be sure nothing has changed. If anything has changed then adjustments can be made to limit the financial consequences. “The more cows you have the more it will cost you when silage


varies throughout the clamp. On this basis, the recommendation is that herds of 500 cows should be analysing the clamps closer to once every 11 days. For herds of 250 cows the optimum is every seventeen days while for 120 cows it is every 26 days. “But this is a big change as currently typically the average for a


500-cow herd is 30 days for 250 it is 45 days and for 120 it is 60 days. However, increasing frequency is the only way to ensure forages are used effectively and deliver the best return on investment. “The portable, handheld NOA could have a huge role to play in


facilitating more regular analysis and deliver a higher level of customer support,” she concludes.


Table 3: Variation in analysis of a single clamp of first cut grass silage as a typical representation of analysis pattern


DM (%) ME (MJ


/kgDM)


CP (%DM) NDF (%DM) Acid load


Fibre Index


RFC (g/kgDM) DyNE (MJ


/kgDM) NDIP (g/kgDM)


MJ difference in ME supply if feeding 10kgDM/day


kg freshweight required to supply 10kgDM/day to 100 cows


PAGE 26 JULY/AUGUST 2021 FEED COMPOUNDER


26/8/2020 37.4 10.9 12.5 45.8 46.7 185 201 6.14 60.3


109 2673


6/10/2020 43.0 11.0 12.4 45.7 46.1 186 202 6.12 63.5


110 2325


29/10/2020 36.4 10.4 13.4 46.4 45


188 184 5.86 56


104 2747


2/12/2020 32.6 10.2 14.2 48 43


194 171 5.69 55


102 3067


19/2/2021 41.3 10.6 12.9 45 48


184 212 5.77 63.5


106 2421


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