Water content of feed and livestock performance issues

Ag Advice - August 2022

Brett Littler, Senior Land Services Officer - Livestock

Over the last few months, I have been responding to a lot of enquiries about moisture content of feeds and the ‘feed is just to wet’ for their animals to perform. So, what does the moisture content of the feed mean for livestock and when is it too wet?

When livestock performance is broken down to its basics, it’s all about intake. The more the animal eats the faster they grow. There are several factors that influence intake and therefore performance on pasture or crop including: quality/digestibility of the pasture/crop, the height/availability of the feed, legume content and what species are they eating. Dry matter percentage of the feed or how much water is in that feed can also influence intake and therefore performance.

Generally, we know that high quality pasture or crops will be low in dry matter or have higher moisture content, but at what levels will this moisture content have an influence on livestock performance. There are a number of nuances that will dictate at what levels moisture content will start to have an influence on intake such as the size of the animal, their pregnancy status, the level of neutral detergent fibre (NDF) of the feed, etc, all influence when moisture content will become an issue and reduce intake.

Unfortunately, there are no hard and fast rules, but the following is a guide to when high moisture content or low Dry Mater (DM) percentages becomes an issue. At levels below 20% DM we know that moisture content is starting to become a physical barrier and starts to have an influence on intake. When DM declines to around 17-18% livestock are getting all their water requirements from the pasture or crop. At 14% DM the overall amount of feed that an animal has to consume increases significantly and has a significant influence on dry matter intake. At 10% DM the amount of fresh forage an animal needs to consume to meet daily energy and protein requirements is enormous and is no longer possible.

Below are 2 examples of a 50kg ewe in early lactation with a single lamb at foot and a 550kg cow also in early lactation with a calf at foot. Both animals are on pasture which is a 11ME/Kg DM. To meet the high energy requirement of lactation the ewe needs to consume 1.68kg DM/day (orange bars in Figure 1) and the cow 11.36kg DM/day (orange bars in Figure 2). Figures 1 and 2 show the overall quantities of fresh pasture or crop that the cow and ewe would be required to eat per day to meet energy requirements.

Figure 1: The impact of moisture content in pasture/crop on the amount of fresh forage that needs to be consumed by a 50kg lactating ewe. Assumes energy content of forage is 11ME.

Figure 2: The impact of moisture content in pasture/crop on the amount of fresh forage that needs to be consumed by a 550kg lactating ewe. Assumes energy content of forage is 11ME.

In looking at Figure 1 and 2 is becomes clearly evident how much feed a cow and ewe are required to eat when the DM percentage drops below 20%.

It also highlights the intake issues we see when DM percentages fall to 10% and just how much feed stock need to consume to meet nutritional requirements. At these levels it is no longer possible.

When is high moisture content likely to be an issue and what should I do about it? Generally, feed generally sits between 18 and 30% in high quality green feed and feed test that we have conducted recently backs this up, so in most cases it’s not an issue. It tends to be more of an issue when high quality pastures are wet after rain and also in grazing crops, especially brassicas. In these situations, putting out a good quality hay or silage can help balance things up a bit without being detrimental to performance.

For more information on this and current pasture conditions in the Central and Southern Tablelands please go to the ‘Pasture quality and livestock performance’ webinar recording here.

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