What’s happening with Grass this Spring?

Grass coming through the winter this season both visually appeared and tested of a higher quality than last season. Even as we closed on the end of the first round the grass quality on most farms has appeared significantly better.

Last season we conducted a study with Dr Jim Gibbs of Lincoln University to understand both the cause and effect of low milk urea nitrogen (MUN) values which were growing trend in the previous few seasons. Jim found that the main driver of the low MUN were high NDF contents (i.e. the grass was over mature and tough). It was thought that this may have been due to the reduction in nitrogen use in the autumn.

This season, almost across the board, those farms that had low MUN values last season have been higher this year. This may be reflective of both a more consistent phase of growth since late June and strategic nitrogen use. The higher MUN indicate that digestibility of the grass and the crude protein values have been higher this spring. Expensive high protein supplements are probably of less value this spring.

With the consistent and recent rains, we can expect that the dry matter percentages of grass will be a lot lower for at least the next couple of weeks. There are two main considerations that need to be taken into consideration.

1. Low dry matter feeds take up more space and are less energy dense. Studies have shown a reduction of dry matter intake of 0.2-0.3kg DM for each percentage drop in dry matter below 15-18%.

• After a period of wet weather and good growing conditions this might see voluntary intakes drop from 18kgDM/day to 16kgDM/day if the dry matter percentage dropped from e.g. 18% to 12%.

• Mowing high quality, low dry matter grass several hours before grazing in the right conditions will lift the DM percentage and increase intakes.

2. Low dry matter grass also leads to higher urine output. This can cause a washout of sodium. Sodium is essential to draw Volatile Fatty Acids across the rumen. Sodium deficient cows will have a lower appetite and reduce milk production.

• Cows will typically require/consume 30grams of salt per day. This may increase to 50grams in some situations. Look to provide cows free access salt on a daily basis.

The First Month of Lactation - Minimising Negative Energy Balance

The management of the first month of lactation beyond the colostrum period very critical for herd level performance. Most cows will spend this period in negative energy balance (NEB). This is why providing consistently high feed quality is imperative. What we have learnt from cow collars is that farms that are having low rates of pre-mate heats four weeks before planned start of mating will still be low just before mating.

Cows in significant negative energy balance may develop clinical or sub-clinical ketosis. Fats mobilised (NEFAs) will also damage and therefore reduce the fertility of developing eggs on the ovaries.

Cows which are well fed/have a good appetite in the first month of lactation will lose less weight and have better mating performance. Consider the following:

• Optimal pre-graze covers of 3,000 to 3,400 kgDM/ha in the first round will ensure good quality and easy harvest for the cow, while maintaining a residual at 1,550-1,600kgDM/ha.

• Know what your daily cow requirement is and calculate your allocation every day - where feed deficits exist on any given day fill it with appropriate supplement.

• If the herd or part of the herd is skinny and there are large feed deficits ahead, production may be best sacrificed by OAD milking for up to 3 weeks to maintain BCS leading into mating.

• Use monensin (Rumenox), to increase feed conversion efficiency, by driving propionate production. Clinical trials show boost in milk protein production and far less BCS loss. Use strategically from calving up until end of mating.

• Internal parasites – the biggest impact these have is on appetite suppression. Almost all farms will have high levels of over-wintered larvae this year. Aim to drench your herd by early/mid-September.

• Vitamin B12 – is a requirement for energy extraction. Deficient cows will lose appetite. We see B12 levels drop at the same time as spring grass goes lush. This is partly due to rapid transit times through the gut impeding B12 absorption. Rule of thumb “when faeces start becoming loose look to give Vit B12”.

Emergency Treatment of Lice in Spring

Cows with heavy lice infestation are up to 10% less productive due to eating less, because they are distracted or itching.

Lice are the most important winter parasite of cattle; you will see a lot of scratching and hair loss over the neck and shoulder. I strongly believe that severe lice infestations do cause milk production and BCS loss in dairy cattle. Furthermore, lice burdens are often highest in cattle which are in poor condition and have been tight for feed over the winter.

While it would have always been better to have treated cattle for lice in early winter a salvage treatment can still be used in the spring. The critical thing is to dose all cattle with an effective dose and product.

Product choice becomes vitally important as we head into spring due to both the milk and bobby calf with holds.

Pour on “Mectin” treatment options- These treat both lice and internal parasites:

• Cydectin is the logical choice in this situation as it achieves good control of both lice and internal parasites. It has the advantage of both a nil milk and meat withhold. The bobby calf meat withhold is also nil.

• While pour-on drenches containing Abamectin are great options for controlling lice MPI implemented a new milk and meat with holding time of 35 days in Sept 2022. This means Reflex and Topline are largely restricted to being used as dry off treatments in the autumn.

Pour on lice only treatment options:

• Blaze is a synthetic pyrethroid pour-on which has a nil milk withhold and 28-day meat withhold. There is no bobby calf withholding period.

• Destruct is a pour-on organophosphate which has a 3-day meat withhold and 5-day milk withhold.

It is important to be aware that when any of these pour on products are applied to cattle that have come straight off crop and have thick coats covered in mud or faeces, then efficacy may be compromised. Lice numbers will rebuild again over 8 weeks, often requiring another treatment.

The Winter Diet in the Last Month of Gestation

Over the last 10 years, management of the dry cow to attain optimal condition has been much improved. This has been mainly facilitated by setting realistic figures on crop utilisation (90% for FB and 80% for Kale in good conditions) and ME requirements for condition gain (70MJME/kg liveweight gain), maintenance (60MJME) and pregnancy (30-50MJME – 6 to 2 weeks from calving). Also factor in the increased requirements due to wet, wind chill and mud which can add an additional 10-30MJME/day.

Ensure that cows are not getting over-fat or are at risk of not achieving target. A BCS (from your vet) at the start of July can tell you whether intakes need to be increased or decreased.

The winter diet for a pregnant cow, through until about the last 3 weeks of pregnancy, requires about 11% crude protein in the diet (or 1.2-1.4kg of crude protein). As well as cow’s normal base protein requirements, she has the demands of a rapidly growing calf, the development of new udder tissue and production of colostrum antibodies. Cows under protein stress for significant periods of time will break down their own tissues to meet foetal demands, but the end result may be muscle loss (calving difficulty), poor udder development, poor colostrum quality and poor cow immunity (placing her at greater risk of mastitis or metritis).

Optimal crude protein requirements increase to >16% in the last 3 weeks before calving. Typically Fodder beet bulbs have crude protein levels less than 10%, whereas the leaf is in the 15-20% range. If the crop you are feeding is losing leaf yield in July, ensure that cows are receiving an additional supplement that has higher protein content.

Brassica Feeding over the Dry Period – The Good, the Bad and the Ugly

Next to fodder beet, brassicas (rape, kale, turnips and swedes), are the other mainstay of the winter diet. It helps to understand some of their properties to get the best from them.

The Good

• In kale, the upper 2/3rd of the plant has quite good ME – being about 12.5MJ. The lower part of the plant (the stalk) will be lower and is only about 7ME close to the ground. The overall ME is about 11-11.5MJ/kgDM. The ME of all other brassicas are closer to 12MJME.

• Generally speaking, brassicas have good levels of crude protein for a dry cow – 14- 18%. This makes it quite a good crop to finish the winter on if you have had cows on a low crude protein fodder beet through the early part of the dry period.

• Kale/Rape have high levels of calcium – about 3 times what is in grass and 9 times what is in fodder beet bulbs. This makes it handy for replenishing bone stores in dairy cows.

• A tall grazing face can form good shelter for cows if being grazed in a southern direction.

The Bad

• Kale crops often have bad utilisation in bad weather – it can be as low as 50%. Make sure you allow for this.

• Best practice is to work on 80% utilisation in good conditions. If it is higher than this, cows are probably being underfed. Make sure you factor this in on your daily allocation.

• All brassicas are low in effective fibre (and yes that includes those chewy looking stalks). This is the reason that as a minimum 25% of the diet needs to have a long fibre source – e.g. straw, hay or baleage.

• Animals often ingest quite a bit of mud while on crop – this will deplete copper stores. Selenium is also consumed/depleted soaking up ‘free radicals’ created by a high content of poly-unsaturated fatty acids.

• Swedes can be quite hard, making it tough for calves and heifers to eat. It can tend to be lower in crude protein as well.

The Ugly

• The lack of effective fibre and if fed frozen can make cattle prone to frost bloat (a free gas bloat). The cold temperature shocks the rumen disabling the ability to belch. Wait for the frost to come off before feeding.

• Brassicas will bind up Iodine which can result in still births in calves – particularly out of heifers. Dosing a trough with stock iodine on a daily basis in the last month of gestation may reduce this risk.

• Nitrate poisoning is a real danger - particularly in rape followed next by kale. Its most likely to occur after periods of cold, low light conditions, where leaf loss has occurred from previous breakouts, and when animals go onto a frozen crop with an empty belly.

• Like fodder beet, swedes can cause acidosis. A transition period is also important.