Initial maize analysis good but expect issues with late crops

17 December 2015

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

The company’s ruminant technical development manager, Dr Liz Homer says 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, 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, particularly lower fibre and increased starch degradability although careful management can reduce the risk.

“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 which 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. 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%. 

“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.

“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. Clamps should be analysed regularly so changes in starch degradability are reflected in diet formulation.”

She also comments that this year a significant proportion of crops have been harvested late which can have consequences for feeding value so these crops will need to be analysed and diets formulated carefully.

“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 were 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. 

“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.