Friday, 19 October 2018 07:55

Maintaining nutrition as pasture quality drops

Written by  Greg Jarratt, vet and director of Matamata Veterinary Services
Cows need more than pasture around this time of the season to maintain production. Cows need more than pasture around this time of the season to maintain production.

At this stage of the season, levels of Neutral Detergent Fibre (NDF) rise very rapidly in typical NZ pastures as ryegrass starts to form seed head.

NDF basically refers to the plant’s structural materials or cell wall components. The practical implication of this occurring is very important from the perspective of attempting to maintain a high level of nutrients available to a cow.

This is because the level of feed a cow can eat (Maximum DMI) is largely dictated by the amount of NDF she can physically ingest and ‘process’ through her rumen in 24 hours. Experimental evidence suggests that the maximum NDF a cow can eat in a day ranges from 1.2% - 1.5% of her live weight. 

Let’s consider a typical 500 Kg cow. Using the 1.2% - 1.5% limit, the maximum NDF she can process in 24 hours is 6.0 Kgs – 7.5Kgs. If we were to be offering her soft, leafy high quality pasture with a 35% NDF level, she would conceivably be capable of ingesting 17 – 21 Kgs DM. If we were to allow the pasture to form seed head with a 50% NDF level the amount she would be capable of ingesting would be between 12 – 15 Kgs DM. This represents a 40% reduction in the amount of feed she can physically ingest.

Strangely, it is about this stage that farmers start getting frustrated with cows falling off their peak coinciding with the girls entering what appears to be ‘plenty of tucker’ and baulking at what is on offer. Further, this change in pasture quality reinforces the widely accepted ‘myth’ of cows dropping in milk production as they fall pregnant.

So, what strategies can you practically employ to diminish this pasture quality effect on cow DMI? Pretty much there are two ‘levers’ you can pull. The first and most obvious is to attempt to lessen the effect of rising NDF or prolong pasture from heading through topping, shortening the round (dropping out silage) and trickling on Nitrogen based fertilisers to promote leaf growth. Another strategy is to limit the amount of poor quality high NDF feed being provided and consider increasing feeds with a more favourable nutrient profile with less NDF. One example would be reducing pasture DM on offer by 4 – 5 Kgs and providing a combination of protein and starch feeds (Canola and Tapioca for instance). 

To quote one of my clients who is far wiser than I ‘everything in farming is a compromise’. Yes attempting to utilise as much pasture as possible is definitely a low expenditure option, but at what cost to the cow’s production (and often fertility)? The counter-intuitive action of offering less pasture and boosting better quality feeds serves several purposes, chiefly providing her the opportunity to ingest more nutrients and less obviously banking more grass silage. This season, the extra grass silage may very well come in handy through summer and facing a 3Kg PKE limit!

Talk to your farm advisor, nutritionist or Vet if you want to change things up this month.

• Greg Jarratt is a vet and director of Matamata Veterinary Services.

This article is brought to you by J. Swap Stockfoods.

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