Renewed interest in hogget mating

01-04-2009 | Gerard Hall

A better summer and autumn this year in most parts of the country and the higher prices being paid for lambs means wider smiles are returning to sheep farmers' faces.

As a result, there is renewed enthusiasm for sheep and greater interest this year in putting ewe hoggets to the ram.

Country-Wide spoke with Massey University's Dr Paul Kenyon to update the findings from the Meat & Wool New Zealand and C. Alma Trust funded study that is developing practical ‘best practice' hogget mating strategies.

While there are some risks, research by Kenyon and his Massey team illustrates when done well, lambing hoggets adds to the sheep enterprise's efficiency and is profitable.

Kenyon recommends ewe hoggets should be as heavy as possible by mating. Onset of puberty is correlated to liveweight and increases rapidly as liveweight exceeds 36kg, although bodyweights around the 40kg mark are recommended.

To induce more hoggets to reach puberty and exhibit oestrus, he says vasectomised rams should be run with ewe hoggets for just 17 days immediately prior to the planned start of mating. When doing so, teaser ratios as high as 1:70, are proving to be effective.

The use of teaser rams has a synchronising effect which will result in more hoggets cycling and cycling earlier.

Teasers should be out for exactly 17 days, no more, no less. This is because if puberty is induced, the hogget will cycle again 17 to 18 days later.

Leaving teasers in longer than 17 days will result in some of the induced hoggets cycling before the entire rams go out.

As result they will be mated two to three weeks after entire rams have been introduced, resulting in a spread lambing. This defeats the whole idea of using teasers, which is to have more hoggets mated earlier.

Another advantage is the earlier hoggets lamb, the more flexibility there is in terms of weaning and timing of weaning.

Kenyon says lamb weights are not being penalised by earlier weaning and 10 weeks of age appears to be an optimal time.

A benefit of weaning lambs earlier is the additional time to get the ewe hogget to the desired two-tooth mating weight.

Being shy breeders, the ram: ewe hogget ratio is important during mating.

While the 2002 Massey survey suggests hogget lambing percentage was 8% higher at a ratio of 1:30 compared to 1:100, a field study in 2007 found there to be no significant difference.

However Kenyon says in a field study last year, pregnancy rates after 17 days of mating were lower at 1:75 compared to when hoggets were mated at a ratio of 1:60, (45% compared to 57%). Ratios around the 1:60 are optimal. Lower ratios may improve results slightly but they are unlikely to be cost effective

He believes there can be risks using ram hoggets and their use should be avoided.

Studies show using ram hoggets at similar ratios to mature rams results in fewer ewe hoggets getting in-lamb. If they are to be used, he suggests a very low ratio of about 1:30.

If farmers are concerned about ram costs, another option that has been successful in two field studies is to reuse mature rams that have been taken out of the mixed-age ewe mobs at the end of their first cycle of mating.

Fewer rams are needed for the mature ewes in their second cycle. In other instances maternal rams are being replaced with terminal sires around day 17 of mating so they become a viable option also.

Farmers should ensure ewe hoggets are 40kg LW, or heavier, when the ram goes out.

With feeding levels during pregnancy, Kenyon says the aim should be to put on a liveweight gain of about 150g/day from the time the ram goes out until day 100 of pregnancy. This appears to be optimal in terms of the weight of lambs and the hoggets when weaned.

During the first 100 days of pregnancy most liveweight gain is going into the hogget and not into foetal growth. Liveweight gain in the last 50 days will be going to foetal growth.

Kenyon says their research shows hoggets putting on 150g/day during the first 100 days of pregnancy will be 7.5kg heavier (conceptus free) by lambing time.

In the last third of pregnancy hoggets should still be gaining 150g/day, but this gain will be going into the foetus, so the young dam herself will not be gaining. This is why it is important to feed her well in early pregnancy if poor two-tooth weights are to be avoided.

He believes liveweight gains as high as 200g/day during mating and through pregnancy would be safe and are actually virtually impossible to achieve in winter anyway.

Mid-pregnancy shearing has been shown to increase lamb birthweight but any affect on lamb survival is dependant on weather at lambing time.

The research estimates an additional 50-70kg drymatter of feed is required for every hogget put to the ram. The additional feed requirement is over and above the yearly feed requirement of an unmated hogget. Therefore it is important adjustments are made within the farming system to ensure hoggets are fed adequately.

Referring to the long-term effects of hogget lambing. Kenyon acknowledges it is likely there will be a small liveweight check at two-tooth mating. However, by the time they lamb again as two-tooths they have caught up.

As well as developing best practice, the research investment is providing opportunities for young NZers to broaden their knowledge and research skills. So far, two Massey University students have successfully completed agricultural honours degrees, another two their masters' studies and a current PhD student is well on the way towards completing his research project.

Part of the Massey research includes studying the long-term effects of mating hoggets. Now in its sixth year, the lifetime study shows ewes first lambed as hoggets are not burning out, their reproductive performance has remained the same and their lifetime performance is higher.

The ewe's overall performance is ahead because they have had a lamb as a hogget.

However, the lifetime reproductive performance of those failing to get pregnant is consistently worse.

Reproductive performance is a combined measure of the ability to get in-lamb, pregnancy scanning percentage and number of lambs weaned.

Often overlooked is the value of hogget lambing as a selection tool for identifying ewes with poor reproductive potential.

Kenyon says this mirrors the earlier research in the 1980s that showed hogget oestrus is a good indicator of a ewe's future reproductive performance.

Campylobacter and toxoplasma vaccinations should be moved forward to cover ewe hoggets. Farmers should discuss with their veterinarian internal parasite issues and the merits or otherwise of supplementing with trace elements such as cobalt, vitamin B12 and iodine before lambing.

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