The range in maize crops means careful fine-tuning of diets will be needed this winter

26 November 2015

Regular analysis is the key to getting most from maize.

While early harvested maize crops are analysing well and should help support good milk yields, a significant number of crops have been harvested late and may present nutritional challenges, according to Trouw Nutrition GB who have already analysed over 1000 samples this year.

Dr Liz Homer, the company’s Ruminant Technical Development Manager reports that early crops have produced a similar quality feed to 2014 which suggests some well-made, good quality forages.

“The average 2015 maize silage is 30.1% dry matter which is 1.4% lower than last year. However, the average ME is higher at 11.6MJ which is combined with marginally higher starch, lower NDF and lignin. Intake potential is virtually identical to last year too.

“To achieve a typical intake of 5kg DM/cow/day it will be necessary to feed 0.7kg more freshweight per day.There should be no problem achieving the extra intake, however, it is important to be vigilant with regard to rumen health.”

Dr Homer explains that several aspects of the average analysis indicate that rumen health could be an issue, although careful management can reduce the risk. She says that the low NDF levels have resulted in a fibre index 9 units below last season while the acid load is considerably higher than last year’s early analysed samples. But the biggest difference is in starch degradability.

“The extent of starch degradability determines how much of the total starch will be fermented in the rumen. The higher the degradability, the greater the rumen fermented starch and more starch being fermented in the rumen increases the rate of VFA production which in turn can increase the risk of acidosis.

She says starch degradability increases with time in the clamp as a result of the action of acids in the clamp on the starch granules in the forage. Last year mature maize crops had a starch degradability of 69.8%, where this year’s early analysed crops already have a starch degradability of 69.9%. The rapidly fermentable carbohydrate (RFC) level at 205g/kg is the same as last year’s more mature feeds which Dr Homer says confirms the effect this year’s crops could have on the rumen.

“This means that in terms of starch degradability, this year’s early cut crops are as good as last year’s later analysed feeds, implying there is already a high level of rumen available starch which will only continue to rise. Nutritionists must look carefully at other energy sources in the diet to limit the acidosis risk, especially given the lower NDF content. The effect of feeding particular cereals on the rumen should be considered, and fed alongside high fibre energy sources.

“It will also be essential to keep a close eye on glucogenic energy, the type of energy which drives milk production. As starch degradability increases it may be necessary to add more glucogenic energy to the diet, by feeding treated cereals or other sources with decreased rumen fermentation and increased levels of bypass starch, in order to maintain milk yield. I would advise farmers to get clamps analysed regularly during the winter so changes in starch degradability can be reflected in diet formulation.”

Dr Homer says in any year there will always be considerable variation around the average, making individual clamp analysis essential and she believes the range in analyses will be increased as a result of the difficult maize season. She says the early maize crops should support good levels of milk production provided they are well-balanced. 

However, a significant proportion of crops have been harvested late either due to harvest conditions or difficulty getting crops to mature due to the low sunlight hours this summer.

“Where crops have been harvested late because they were slow to mature it is likely that overall starch levels will be increased as more sugars are converted to starch, leading to a higher potential ME level provided crops do not get over ripe. However, if the stalk becomes increasingly lignified then the crop will have lower digestibility which will impact on both energy content and intakes.

“If crops are harvested late due to the weather, then increased lignification will be a serious risk and starch content may be reduced as a result of a higher proportion of vegetative material in the crop. The other threat in this situation will be the increased risk of soil contamination which will make it difficult to achieve stable fermentation.

“With farmers looking to maximise contribution from forage and to ensure all litres are produced as efficiently as possible, maize silage will have a large role to play. Regular analysis of quality and close attention to diet formulation to maximise rumen health will be essential to exploit the potential this winter,” Dr Homer emphasises.

For further information, contact the Trouw Nutrition GB Ruminant Team.