Preparing for weaning lambs at Athenry

The Ireland and New Zealand Across Country (INZAC) flock was established in Teagasc Mellows campus, Athenry, Co Galway, during 2015. The 180-ewe flock, comprised of Suffolk and Texel ewes, is divided and managed as three sub-flocks with 60 New Zealand ewes with elite genetics, 60 Irish ewes with elite genetic merit (HGM) and 60 Irish ewes of low genetic merit (LGM).

The aim of the trial is to compare elite New Zealand genetics with Irish-bred ewes and determine the suitability of such genetics for use in Irish grass-based production systems.

Fiona McGovern is a post-doctoral researcher and is responsible for the day-to-day running of the flock.

When I met with her, she was quick to remind me that the trial is still in its first year of a five-year term. Therefore, preliminary findings must be seen as such, with more definite results becoming available as the database increases over the coming years.

A large number of measurements are being recorded from the flock from lambing traits to flock health and grassland intakes. Fiona receives additional support in running the flock from technician Henry Walsh and farm staff member Martin Ward, as well as various third-level students, both from Ireland and abroad.

Results

Scanning results showed a lower in-lamb percentage for New Zealand ewes (83%) compared with the Irish ewes of HGM (90%) and the LGM group (94 %). Fiona says there are two potential reasons for the lower conception rates in the New Zealand ewes.

“Firstly, the ewes were imported in May 2015 and so were mated outside of their natural breeding season. Furthermore, semen quality from some of our New Zealand rams was poor at the time of mating, as they weren’t inclined to jump and release semen for AI.”

This is something they hope will not be a recurring problem in subsequent years. When barren ewes are excluded, litter size was 1.74 lambs/ewe for New Zealand females, compared with 1.57 lambs/ewe for the HGM group and 1.58 lambs/ewe for the LGM group.

Lambing commenced on 27 February, with 82% of ewes lambed within three weeks, giving a mean lambing date of 11 March. Average birth weight was 5.1kg for New Zealand lambs, 5.4kg for HGM lambs and 5.5kg for LGM lambs. Lambing mortality ran at 11% for New Zealand ewes and 14% across both Irish ewe groups. Lambing to six-week mortality was 6% for New Zealand and 9% for Irish groups.

Post-lambing, there were some instances of mastitis and eye infections across all groups,which is being put down to the cold and wet weather in early April. Ewes were shorn in December. Ewes and lambs were treated with pour-on for blowfly strike last week.

All lambs were dosed at six weeks of age for nematodirus with a levamisole drench. Faecal egg count (FEC) samples were taken 10 weeks after lambing. New Zealand lambs had an FEC score of 480, HGM lambs had 510, while LGM lambs had 570.

Although an FEC score of 500 is the threshold for dosing, the decision was made to dose all groups so as not to create a bias within the experiment. Lambs were sampled again in week 12 and results came back zero for all groups.

Lamb performance

From weeks 0–10 of age, New Zealand lambs averaged 307g/day, with Irish HGM and LGM lambs averaging 300g and 294g/day respectively. In terms of liveweight gain, this meant New Zealand lambs weighed on average 26.2kg, Irish HGM lambs 25kg and Irish LGM averaged 24.4kg at 10 weeks of age.

Commenting on lamb performance, Fiona said: “We must remember this is a purebred flock, so there is no hybrid vigour. Also, as part of a research trial, the ewes and lambs are handled much more often than in a commercial setting, which may affect lamb thrive slightly.”

The grazing platform extends to 15ha, which is run as three farmlets (5ha per sub-flock). Stocking rates are 12 ewes/ha. Each farmlet consists of four permanent paddocks.

Fiona has laid down some strict rules when it comes to grassland management. Groups enter paddocks with pre-grazing covers of 1,100kg to 1,200kg DM/ha (8cm to 9cm grass height). For the first rotation, these paddocks were grazed out to 3.5cm to ensure high-quality regrowth for subsequent grazing rotations.

After the first rotation, the four paddocks per group were sub-divided using four strands of electrified temporary fence.

This simple way of doubling the number of paddocks makes management during the main grass-growing season much easier and provides greater flexibility in terms of grassland management.

The groups are currently on their fourth rotation and grazing paddocks out to 4cm.

In an earlier update this spring, weather conditions had been very poor and grass growth was slow. Things have picked up significantly since then.

Grass management

Grass growth has rocketed since the first week of May. At this stage, 55% of paddocks have been taken out as surplus grass, with paddocks having received 85kg/ha of nitrogen this year.

“At the beginning of the latest good spell of weather, we were getting grass growth in excess of 120kg DM/ha/day.

“Last week, growth was back to 65kg DM/ha/day and we were actually starting to dry up slightly, as we had missed the heavy thunder storms that were going around,” said Fiona.

Growth is expected to pick up again this week after the rain over the last couple of days.

Weaning is taking place this week (week 14) and lambs will be FEC sampled again. After weaning, lambs will graze ahead of the ewes. Target pre-grazing sward heights will remain at 8cm to 9cm, with lambs grazing down to 5cm. Ewes will then come in and take it down to 4cm.

Lambs will be taken out of the system as they reach 45kg liveweight. As they are purebred animals, only some will be slaughtered. The remainder will be retained as replacements and rams for breeding.