Planning for Winter Diets Starts Now

27 July 2020

With over 600 first cut grass silage samples now analysed, early indicators are that quality is good, but as ever the key to making the most of grass silage will be regular analysis throughout the season combined with careful balancing of the diet.

Our Ruminant Technical Development Manager, Dr Liz Homer says that as expected there is a range in quality reflecting the disruptive winter and spring weather which impacted on cutting dates and grass growth over the winter.

 “Most grass continued to grow over the winter meaning some crops contain a high proportion of older grass which will impact on quality, in particular resulting in higher lignin content.  However, on average farmers have made some good feed to act as the foundation for winter diets,” she says.

 “At 35.5% dry matter, crops are at the higher end of the target range, reflecting the warm, dry weather in April and May.  When clamps are open, care will need to be taken with face management to minimise wastage and heating in the drier feeds.”

 Generally, she says silages submitted are well fermented with a pH of 4.2, moderate sugars, ammonia and VFAs.  As expected with a drier crop, lactic acid is slightly lower.

 “The ME content at 11.4MJ/kgDM is high, reflecting good levels of NDF at 44%DM.  We saw an increased use of pre-cut testing this year, suggesting more farmers are looking to time cutting more precisely and are seeing the benefits of this attention to detail.

 “Dynamic energy, which is the energy actually available to the cow is also good at 6.3MJ/kgDM  While energy content is good, the silages have a low fibre index and high acid load which means rumen health could be an issue needing to be managed when diets are formulated.”

 She says overall crude protein is lower than usual at 14.6%.  She suggests this reflects the disruptive season and the difficulties in applying fertiliser initially followed by a prolonged dry period which resulted in reduced nitrogen uptake.  However, while some feed advisors may use this as a need to increase crude protein in the rest of the diet, she believes this may be ineffective and costly explaining it is important to look at the types of protein.

 “The make up of protein will affect how silages may feed out.  While levels of metabolisable protein (NDIP) are good, fermentable protein levels are low with more bypass protein.  This means diets may benefit from some fermentable protein such as soya, rape or distillers.

 “When formulating diets, it will be important energy and protein are in balance to ensure an efficient rumen.  This means looking closely at the total energy and protein and also the rates at which they are fermented in the rumen, looking at both total and rapidly fermented carbohydrates and proteins. 

 “Overall, across the samples analysed so far, the balance of fermentable carbohydrates and protein is at the lower end of the scale. In grass silage-based diets we may need to increase fermentable carbohydrates, perhaps with more cereals, but if maize silage is included then fermentable protein will be essential in the total diet.

 “The key in every case will be to get individual silages analysed and then formulate rations to be the most efficient by balancing the rumen as effectively as possible.”

 Dr Homer stresses that while the first cuts are encouraging on average, there is a tremendous range in the samples seen and the quality of forage.  She also emphasises that the on-farm challenges will depend on the total forage available and the mix of silages that can be fed.

 “While these early results are encouraging, it is important to remember that forage is only around 50% of the total diets, that farms feed different combinations of forages and that no farm has the average silage.  We know second cut has been affected by the dry weather, while the recent rain will be helpful for third cut and also maize.

 “As the forage picture develops through the season, so farmers and their advisors will be able to formulate diets to make best use of forage by supplementing diets carefully.  But the early indications are that many farmers can look forward to first cuts being a good foundation for diets.

 “With pressure on the milk price: feed price ratio, it will be particularly important that all clamps on the farm are analysed regularly and that the diet is carefully balanced and routinely reviewed to ensure forage is used as efficiently as possible to help support margins,” Dr Homer emphasises.

Nutrient analysis for early first cut silages 2020 (Source TNGB)

Nutrients

Minimum

Average 2020

Maximum

Dry Matter (%)

19.1

35.5

60.9

Protein (%DM)

8.1

14.6

20.4

D Value (%)

58.0

71.5

76.1

ME (MJ/kgDM)

9.3

11.4

12.2

NDF (%DM)

36.2

44.1

58.8

Fermentation Quality

 

 

 

pH

3.5

4.2

5.4

Sugars (%DM)

0.2

3.4

9.7

NH-3 N (%DM)

1.1

3.1

9.0

VFA (g/kgDM)

0.7

15.1

59.5

Lactic Acid (g/kgDM)

12.0

71.2

147.1

NutriOpt Analysis

 

 

 

RFC (g/kgDM)

135.6

202.6

247.9

TFC(g/kgDM)

362.1

457.5

578.1

RFP (g/kgDM)

44.9

90.5

129.1

TFP (g/kgDM)

51.9

110.3

156.5

Acid Load

32.7

49.5

57.4

Fibre Index

145.5

176.9

238.1

DyNE (MJ/kgDM)

4.7

6.3

7.4