August 2021 Monthly Management

TCMS & Chlorine Free; Autumn Grazing; What are the Target Weights for Heifers; Weeds of Reseeds; Grass & Grazing

23 August 2021

TCMS & Chlorine Free

The move to chlorine free is almost complete with over 90% of samples now coming back below the Trichloromethane (TCM) threshold of 0.0012mg/kg. The focus now is to get 100% of samples under the TCM threshold.

Total bacteria count (TBC) issues in relation to the changeover to chlorine free are very few but where an issue did arise there was a general trend towards one of three areas. Either the frequency of descaling, hot washing, or the addition of peracetic acid was not completed regularly or had ceased. What usually happens if descaling is stopped/ reduced is that TBCs start to rise slowly over weeks and months until a more serious problem develops. Regular descaling, hot washing, and the use of peracetic acid are all key components of consistently maintaining good milk quality in a chlorine free routine.

Autumn Grazing

For anyone not regularly measuring grass a general guideline for autumn grazing management is rotation length. Milking platforms stocked between 2.5 – 3.5 LU/Ha should be aiming for the following:

Date Rotation length
Mid-August 25 days
September 1st 30 days
Mid-September 35 days

For those measuring grass, using their average farm cover as a guide will give greater accuracy. Targets are below:

Average Farm Cover Targets (kg/DM/Ha)

Date 2.5 LU/Ha 3.0 LU/Ha 3.5 LU/Ha
Mid-August 450 750 770
September 1st 500 990 980
Mid-September 750 1100 1200

Whether growth and rotation length are running ahead or behind target it is best to act as soon as possible during August to address surpluses or shortfalls.

What are the Target Weights for Heifers

Once the mature weight of the herd has been established, target weights can be calculated for heifers, by using a proportion of mature bodyweight (BW) e.g. 30% mature BW at 6 months, 60% mature BW at 15 months or breeding and 90% mature BW at calving.

Research has shown that maiden heifers who achieve target weight at the start of the breeding season will have higher survivability in the herd during their first three lactations compared to those who fail to make targets, i.e. heifers that calve in early February on target weight and correct body condition will produce more milk than their later calving comrades and also have a far better chance of going back in calf early and calving again the following February. For this reason, heifers should be weighed prior to the first winter to ensure that they are on track to achieve the desired body weight at mating start date. If the group is below-target weight, a good response to autumn supplementation can be achieved, and pre-grazing covers for calves should be maintained between 1,000 to 1,400 kg DM/ha. The worming program should also be reviewed to ensure that calves are not carrying any underlying stomach or lungworm issue.

In-calf Heifers: 4 months to reach target.

In January the last month of pregnancy, heifers will gain no actual body weight. As a result, we have 4 months to ensure that heifers reach target weight from September to December. Weigh the group and draft out the heifers that need to be fed now prior to housing. Due to housing restrictions, it is much easier to divide the heifers now and target the lighter heifers.

For anyone interested in weighing stock, scales are available to rent in most Drinagh branches. The rental fee is €50 per day and scales must be pre-booked on

Mature BW 6 Months 15 Months Calving
% Mature BW 30% 60% 90%
Holstein Friesian (HF) 580 kg 175 kg 350 kg 525 kg
NZ or Br Friesian 550 kg 165 kg 330 kg 495 kg
Jersey x HF 500 kg 150 kg 300 kg 450 kg

Weeds of Reseeds

Grass reseeding will nearly always require a post emergence spray to control both perennial and annual weeds. Seedling weeds that come up at this stage can be destroyed before they have time to develop strong roots. Timing is key for post emergence spraying especially when using clover safe products.

perennial weeds

Seeding docks should be sprayed when the leaf is the size of a €2 coin

Chickweed can be a problem particularly where regular grazing is not expected to take place (silage fields), therefore herbicide choice is important.

Can be controlled but timing is key on getting a good kill.

annual weeds

High populations of other weeds such as fat hen, redshank, creeping buttercup, sheperds purse and mayweed can cause problems. These weeds can be hard to control if they get too strong. In such cases grazing/ topping will help provide control.

The post emergence spray should be applied approx. four to six weeks after seeding before the first grazing. Docks, chickweed and thistles are the most critical weeds to control in reseeds Most annual weed seedlings as well as docks and chickweed can be controlled by a broad-spectrum herbicide such as Envy at 1.5l per hectare. (Envy is not clover safe and has poor control of thistles. Herbicides such as Clovermax or DB Plus Underclear are clover safe and offer good control of weed seedings. The rate is 7l per hectare and timing is key to getting good control. Bear in mind that these clover safe products do not control chickweed.

Grass & Grazing

This month’s feature farm is Donal & David O’Connor, Reavouler, Drinagh

Date 13/08/2021
Average farm cover (AFC) 842 kg/DM/Ha
Cover/ LU 259 KG/DM
Growth/ Day 92 KG/DM
Demand 49 KG/DM
Stocking Rate 3.25 LU/Ha
Rotation 26 days
Yield (litres/cow) 17.5 litres
Butterfat% 4.49%
Protein % 3.84%
Kgs Milk Solids / cow 1.50kg
Supplement fed (kg/cow) 2kg

Thankfully grass has taken off here again after the dry spell. We measued a growth of 92 for the last 7 days up from 51 on the previous walk. The aim is to build an AFC of 1100kg/dm/ha by September 30th. If good growth continues we may have to bale a paddock or two which is always a tough decision at this time of year. We are currently following cows with 25 units of nitrogen in the form of either 18.6.12 or urea.

Reseeding: we set around 6.5 acres of D74 with clover on the 19th of June. The post emergence (Clovermax) was applied on the 15/07/2021. When we started grazing the reseed in early August the cows were pulling the young grass roots out of the ground. The paddock was left for a few days more and we tried again but the same problem persisted. I’m not sure why this was happening as the field was rolled after setting but it may have been linked to the dry weather. We ended up pre-mowing the paddock on August 7th and it worked well. The paddock was cleaned off by the cows and no grass was pulled up. After grazing 3000 gallons of dirty water were applied and we hope to graze the reseed again this weekend.