By Chris McCullough

IT’S been five years since Greenmount Agricultural College in Northern Ireland officially opened its new £2.5m dairy unit to act as a centre of excellence for both students and dairy farmers alike.

Today, the unit is home to 200 Holstein cows thanks to the addition of the CREAM herd that was kept separate at the college until recently when it was integrated into the main herd.

The CREAM herd consists of 30 high genetic merit cows managed separately by foundation degree and honours degree students on a daily basis.

However, the herd concept was 25-years-old and due to changes in course requirements by the awarding bodies and a problem getting students to stay at the college over weekends, it was decided to end the project.

A few months ago, the college staff held two open days to update dairy farmers on the herd’s latest production figures and management systems.

The herd is currently averaging 8777 litres per cow per year, with feed amounting to 2729kg per cow per year. Cows are achieving a milk solids yield of 658kg and are producing 2712 litres per cow from forage and all that equates to a margin over concentrates figure of £1863 per cow per year.

The milking cows are currently being fed in three groups to achieve good feed efficiency. The herd is split into fresh calved cows and heifers, high yielders and late lactation cows.

First and second cut silage is being fed to the fresh calved and high yield cows together with a maize silage and dairy blend. Late lactation cows are being fed on second cut silage plus in parlour concentrates fed according to yield.

Greenmount’s breeding season started on November 22, 2017, and achieved a submission rate of 89% in the first three weeks with 65 cows inseminated.

The first group of cows inseminated were pregnancy diagnosed on December 27 and January 3, with 27 of 34 cows presented PD’d positive.

Heifer rearing

Heifer rearing on any dairy farm is important as it accounts for around 20% of milk production costs.

The average age for dairy heifers calving in Northern Ireland in 2016 was 27.5 months with only 7% of heifers calving at the 'ideal' age of 24-months.

Data from Northern Ireland milk recorded herds shows that heifers calving at 24 months have the highest lifetime yield compared to heifers calving at any other age. Also, for every one month delay in calving beyond 24 months, on average a loss of 570 litres of lifetime milk is incurred per month.

Milk recording data shows that heifers in Northern Ireland are calving on average at 27 months, which represents an additional rearing cost of approximately £258 compared to calving at 24 months. By improving heifer rearing practices, this should also have a positive effect on the carbon footprint of the farm.

Analysis of milk recording data indicates that there is a strong correlation between heifer age at first calving and lifetime yield and longevity. Heifers calving at 24 months produce approximately 7000 litres more milk in their lifetime than heifers calving at 36 months.

Rearing replacement heifers to calve at 24 months, at approximately 90% of mature body weight, is recognised internationally as a key target to minimise rearing costs and greenhouse gas emissions from dairy farming.

Target weights for weaning at two-months-old is 75kg, service at 14 months at 390kg, and a post-calving weight of 570kg. To achieve these weight targets requires an average growth rate of 0.75kg per day. The aim at the college is to have all its replacement heifers calve at 24 months.

Dry cows

Within the Greenmount herd significant emphasis is placed on body condition scoring, particularly in the 8-12 weeks before drying off.

Nutrition during the dry period is another critical aspect as it can determine the level of metabolic diseases post calving, like milk fever.

Cows are divided into two feeding groups (close up and far off) and fed accordingly at Greenmount.

Feed is the single largest cost for any dairy herd and CAFRE's benchmarked farms, purchased feed accounts for 65% of variable costs and so within the Greenmount herd, strong emphasis is placed on conserving high quality forages for winter feeding to optimise milk from forage. Forage is fed to the cows through a diet feeder with diet composition monitored through the Keenan inTouch service.

Slurry application

The majority of cattle slurry produced by the dairy herd is spread on swards used for silage making using trailing shoe or band spreading.

Prior to first cut, approximately 39m3/ha (3500 gallons per acre) is spread in February or March depending on weather and ground conditions. A further 28m3/ha (2500 gallons per acre) is spread after each cut.

Cows are grazed from mid-March to mid-November most years and in spring, the first cows grazed are the autumn calving cows with numbers increased as grass growth increases. In autumn, spring calving cows are the last cows to be fully housed.

Rotational paddock grazing is practised, with grass covers monitored weekly. Any grass surpluses identified are quickly removed as baled silage for feeding later in the season.

Ammonia

Approximately 50% of the nitrogen in typical dairy cow slurry is in the form of ammonia and this is readily lost to the air from the surfaces of livestock buildings, from slurry storage and during slurry spreading.

The slurry management systems employed at Greenmount Campus has been designed to reduce this loss of ammonia N, so flooring systems within the milking and dry cow sheds and the heifer rearing accommodation are of a Dutch design aimed at reducing ammonia loss and provide good gripping surfaces for the cattle.

The majority of slurry is stored in covered above ground stores to reduce ammonia loss and the accumulation of rainfall.