Brian Reidy: Keeping herds performing through summer grass deficit

As we all know, June and July are difficult months to manage grass in normal conditions, never mind when the crop comes under the heat and moisture deficit stress, like it is now, writes ruminant nutritionist Brian Reidy

The dry conditions are getting serious on dairy farms where, even with excellent grassland management, grass quality and availability have deteriorated over the last two to three weeks. 

July is upon us and some are now experiencing near-drought conditions. Most of the country now has a 30-60mm soil moisture deficit. The forecast is not promising a downpour anytime soon, and grass is disappearing rapidly.

The dry conditions are getting serious on dairy farms where, even with excellent grassland management, grass quality and availability have deteriorated over the last two to three weeks. 

Good grassland managers had been wrapping surplus grass and/or grass which had gone too strong and was not suitable to feed to cows for optimum performance. Unfortunately, after wrapping the surplus, we have had a significant reduction in growth rates.

As we all know, June and July are difficult months to manage grass in normal conditions, never mind when the crop comes under the heat and moisture deficit stress, like it is now.

There is poor density or substance to most swards at present, with stem and seed head dominant in many paddocks.

Herd performance

Well one thing is for sure — if you allow dramatic drops in milk yield at the moment, you won't be getting that milk back for the rest of the year.

If a 100-cow herd drops three litres per cow due to not getting sufficient dry matter and energy from the supplied feed, what are the possible consequences?

We are now in the second week of July, so most cows have about 140 days left in their lactation. That equates to 42,000 litres less milk produced from that farm.

Yes, that milk is not produced for free, but when grass growth and quality recover, if the cows are still milking well, then they can produce it predominantly from grass.

The question is, can you afford to let your cows drop off this early in their lactation?

So how are herds dealing with the grass deficit?

Many herds are feeding up to 6kg of concentrates in the parlour and bridging any remaining deficit with silage while remaining out day and night.

This silage can be fed once per day in the morning or evening. The morning is best where possible. Some are feeding this in the paddock by day where all cows will have access. 

Many yards don't have enough headspace for a morning snack where all cows would need to eat at the same time.

If feeding 6kg in the parlour, where possible feed a bigger proportion in the morning.

Housing cows by day and supplying 50% or more of total dry matter required indoors.

In the intense heat, cows are happier indoors by day and grazing by night. If cows are in by day in winter accommodation, they will have access to several water troughs as opposed to the typical one trough per paddock. This will keep them hydrated, cooler, and encourage better appetite to maintain milk yields.

The forage supplied in this scenario varies from maize silage, wholecrop, straw, bale silage, brewers' grains, distillers' grains, hay, previous years' pit silages, 2026 first-cut silage, and zero grazing of either outside heifer blocks or grass intended for second-cut silage.

While all of these options will do the job of supplementing the remaining supplies of grazed grass on farm, some will need to be managed more carefully than others.

Maize silage, wholecrop, brewers' grains and distillers' grains clamps must be well managed with the current temperatures so they do not heat. These materials, when heating, can easily form moulds and toxins which can cause digestive upsets and scours. All are excellent energy sources and will complement the scarce grass very well in the current climate.

For recently made bale silage, it is important it has fermented properly before it is fed. A high acid loading during the fermentation process can again induce digestive upsets and scouring.

Silages in both pit and bale made more than three weeks ago are much more stable and a better option where possible.

Where zero grazing is bridging the grazing deficit, a few things need to be considered.

Grass mown in the afternoon will have higher sugar and dry matter content, so will be more valuable to the cow per kilo of fresh weight consumed.

If zero-grazed grass has been fertilised for second-cut silage, what is its nitrogen content like? Will you be supplying a very high nitrogen grass which could be detrimental to animal performance? Excesses of protein in grass have to be processed before being excreted and this will use up energy.

Those who have milk urea data from their milk collection can monitor this to make sure excessive levels of total dietary protein are not being supplied.

Low covers of leafy grass will have very little fibre content and could potentially run through cows, inducing acidosis if not complemented with a bit of fibre. Straw, hay or dry bale silage will do this effectively.

Some are strip grazing second-cut silage ground if close to the grazing platform.

The same grass quality concerns apply as above with zero grazing.

Is it a better option to make your second-cut silage and, in the meantime, continue to fill the grass deficit with silages already in stock? 

Advanced crops of second-cut silage are not growing much these days, and many will cut them soon or already have done. 

Crops will begin to melt away with the heat and lack of moisture. Once we do get rain, these fields will grow rapidly, and a good third cut can be saved to help replenish stocks.

Milk quality — the best indicator

Watching milk protein in particular is an excellent indication as to whether your cows are consuming and digesting their energy efficiently.

Protein in milk produced today is a reflection of the herd's energy status seven to 10 days ago.

Butterfat production is a reflection of the amount of fibre being digested by the herd in recent days. The more cud chewing, the better for butterfat.

I always find it better to calculate kilos of solids produced rather than talk about percentages. That means that we are all speaking the same language.