Thursday, March 28, 2024

How good is your hay?

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At the Stratford Demonstration Farm in the middle of February we had just finished getting in the last of the hay for the year.
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As usual we have done our best to ensure that this is harvested at the maximum quality (feed value) possible.

Paying attention to hay quality is a practice often questioned, especially when it involves extra costs and/or a reduction in yields. The thinking is that hay is only a maintenance feed, so if quality is down a bit give them a bit more to compensate and all will be the same in the long run.

While this argument does have some validity, it relies on the premise that the hay will be used only for maintenance feeding. This might be the intention, but farming is an unpredictable business and in a season of poor growth extra supplement might be required for productive animals for liveweight gain or milk production.

Having quality hay in the barn increases flexibility and provides more options.

While this could be discounted as too infrequent to worry about, there are circumstances where quality hay can be gainfully fed to producing animals where poor quality hay cannot, or at least to far less benefit. Feeding as a supplement to young calves is a good example but I think an even better one is feeding it strategically to milking cows.

By strategic feeding I am thinking particularly of early spring when pastures can naturally be of very low drymatter percentage, which is often exacerbated by heavy use of nitrogen fertiliser.

Early trial work at Ruakura showed that cows fed hay and pasture ad lib would increase drymatter intake over those fed just ad lib pasture, by up to 1kg DM/day.

This is quite logical. Spring pasture can be as low as 11% DM and on occasions even less, while hay will generally be 85% DM regardless of its quality. Pasture is much more bulky for the equivalent total drymatter, and where gut fill is the major factor limiting intake, as it generally is in early lactation, it makes sense that adding hay to the diet will increase drymatter intake. As the aim at this time of the year is to maximise intake to maximise production this can be seen as a good idea.

Or is it?

The problem is that it’s not the total kg DM that’s the vital factor, but rather the metabolisable energy (ME) contained in that DM, measured as megajoules (MJ) ME/kg DM. The critical factor is not the total DM intake/day, it’s the total MJME.

Spring pasture will generally have a ME value of 11-12 MJME/kg DM. If it’s really slushy, nitrogen-boosted pasture this could drop to 10.5 or less. Top quality hay will be 10-10.5 MJME/kg DM.

There won’t be much difference in feed value between mediocre spring pasture and top quality hay. Where this is the situation feeding the latter as a supplement can easily result in increased ME intake as well as increased DM intake.

However, this will not be the case when poor quality hay, which typically has an ME value of 7 MJME/kg DM, is being fed. In this case the total ME intake will be reduced.

A simple example will illustrate this.

Suppose cows are fed ad lib on pasture of 11MJME/kg DM and ingest 18kg DM/day. We offer them hay at a level of 5kg DM and this increases their intake to 19kg DM/day, but reducing the pasture component of this to 14kg DM. On pasture alone their ME intake will be 18kg DM x 11MJME = 198 MJME

For top quality hay at 10.5 MJME total ME will be hay 5 x 10.5 = 52.5 + pasture 14 x 11 = 154 = total intake of 206.5MJME, an increase of 8.5 or 4.3%.

Simplistically, at 80MJME/kg milksolids (MS) this represents a potential extra production of a little more than 0.1kg MS.

If the hay had a ME of only 7 then the figures would be 154 for pasture but only 7 x 5 = 35 for the hay giving a total of 189, a decrease of 9MJME or 4.5%, again equivalent to a potential reduction of 0.1125kg DM.

The lesson is simple. When cows are being ad lib fed slushy, low DM pasture in the spring, supplementing this with top quality hay can increase ME intake and hence production.

This might also have animal health benefits, particularly in contributing to prevention of metabolic diseases and in improving fertility. The paramount factor is that the hay must be of top quality.

In writing this I can hear a buzzing in my ears from people proclaiming the same results can be achieved by supplementing with palm kernel. This is likely to be true as palm kernel would be slightly superior to top quality hay as its DM is about 90% and its ME in the range of 11-11.5 MJME/kg DM.

Its cost would still put it well ahead of homegrown hay.

In any case this is sidestepping my main point – that is that having top quality hay in the barn gives far more options for its profitable use than having that of a mediocre quality or worse.

While I have, I hope, made a creditable case for putting maximum effort into achieving a top quality hay harvest, I have given no real detail on how to go about doing this, which I’ll save until the April issue.

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