Challenges and opportunities: A closer look at first cut silage analysis

Commenting on the results of crops analysed so far this year, Dr Liz Homer, ruminant technical development manager says that samples have been received considerably earlier this year, reflecting both the growing season and a swing towards multi-cut production systems.

“The season is roughly two weeks ahead of 2018, with the first samples arriving in late April. Numbers dropped back during June,” she explains. “The good weather and better early growth will have contributed to this and we know more farmers have opted for more cuts, bringing the date of first cut forward.”

Dr Homer says the very early samples were well fermented but characterised by higher NDF and lignin compared to the general dataset, an indicator of a higher proportion of more mature grass. This will affect how these silages will feed as they will be less fermentable.

Fermentation

Overall she says first cuts analysed so far are well fermented with higher dry matters, a result of optimal harvesting conditions. At the same time, sugar content is higher.

She adds: “While dry matter is higher at 34.1 per cent compared to 31.2 per cent last season, lactic acid is lower which is what we would expect with a drier crop. There is a significant range in lactic acid content, indicating some poorer fermented crops compared to the average.

“Farmers should be aware that a combination of higher dry matter and increased sugars are indicators of a greater risk of heating when clamps are opened, particularly if clamps were not adequately consolidated which is an added risk with drier crops.”

Looking at the nutritional analysis (see table), Dr Homer says that average ME content is higher at 11.5MJ/kgDM. Crude protein is marginally lower at 15.4 per cent. However, a concern is that while NDF content is similar to 2018, lignin content is elevated.

“This is indicative of the rapid growth at the start of the season resulting in a more mature crop despite an earlier harvest. The consequence is that this will affect how silages will perform in the rumen.

Diet balance

“The combination of increased dry matter and lignin means that both rapidly and slowly fermentable carbohydrates are lower than in 2018. Overall, fermentable carbohydrate averages are low when compared to fermentable protein. This means that there is an excess of rumen fermentable protein which could impact on rumen balance in the total diet.

“To balance this, it may be necessary to increase the proportion of rapidly fermentable energy sources in supplementary feeds, possibly feeding more cereals to optimise rumen energy and microbial protein levels.

“The good news is that we are seeing lower acid loads than in 2018 and are generally seeing a higher fibre index than last year. Together these mean it should be possible to formulate diets containing more cereals safely, without increasing the acidosis risk.”

Dr Homer says the overall picture is that the average silage has a ‘dynamic energy’ content down from 6.7MJ/kgDM to 6.2MJ/kgDM. While this still indicates a good energy level, the reduced fermentability could affect milk production potential. A cow eating 10kgDM/day would be expected to produce maintenance plus 8.1 litres from silage provided the total diet is correctly balanced in terms of rapidly and slowly fermentable carbohydrate and protein.