Feeding stubble turnips can improve winter lamb meat quality
Take Home Message: Finish lambs on stubble turnips to produce meat of a consistently high eating quality that is attractive to consumers.
Stubble turnips provide a consistent diet that delivers a high level of, and consistency in, lamb eating quality through the winter months. These were just some of the positive findings of trials, carried out by ADAS and the University of Bristol, to investigate the dietary effects of finishing rations on lamb meat.
“…We found that, although later slaughter tended to reduce the assessors’ overall liking for grass silage and concentrate fed lambs, UK lamb compared favourably with our sample of New Zealand lamb,” ADAS’s Kate Phillips told delegates at this year’s British Society of Animal Science’s annual conference.
Consumer purchasing decisions are, to a large part, governed by the level and consistency of meat quality and there is a need to identify systems of production that deliver consistent lamb eating quality through the winter months that will restore retailer confidence in British lamb outside the main grazing season.
A recent report on lamb eating quality highlighted the deterioration in lamb flavour post-Christmas and recommended that dietary effects be investigated.
So Dr Phillips and her team set up an experiment involving 180 Texel cross Mule lambs from one Shropshire farm. These were allocated to a ‘three feed treatment and two finishing period’ study to investigate variation in meat quality by diet and date of slaughter.
Lambs were finished in groups of 30 after a six- to seven-week finishing period in either November 2007 or March 2008. The feed treatments were; grass or grass silage, with compound supplementation where necessary; stubble turnips; or ad-lib compound feed.
Lambs were weighed fortnightly until sale, aiming to finish at between 18kg and 21kg carcass weight and fat class 2/3L. Loins of 16 wether lambs from each treatment were compared with lambs from two control groups: grass-only fed British lamb, from the same Shropshire-based farm and slaughtered in November; and New Zealand lamb delivered, vacuum-packed and chilled, in May.
Fresh samples were assessed for pH and colour with the remainder being vacuum packed and frozen until required. Sensory analysis was carried out by trained assessors who ranked samples on eight-point category scales for tenderness, juiciness, lamb and abnormal flavour intensity, flavour liking and overall liking.
“We found that lambs fed the ad-lib compound feed ration grew significantly faster, resulting in both heavier lambs at sale – 44.8kg compared to 41.7kg and 41.1 kg for stubble turnip fed and grass or grass silage fed lambs respectively,” said Dr Phillips.
“This reduced average days to sales to just 50.5, compared to 56.2 and 57.0 for the other two feed treatments.
“Although slaughter date did not affect carcass conformation or fatness significantly, grass or grass silage fed lambs were leaner with poorer conformation.”
Overall growth rates and days to sale were unaffected by slaughter date. Mean loin muscle pH varied between 5.5, for grass or grass silage fed lambs in March, to 6.1 for New Zealand lamb – an atypically high value usually caused by glycogen depletion pre-slaughter.
“The meat from the two control groups was significantly darker than the other groups and the NZ lamb had a significantly lower hue value – it was ‘redder’ – than lamb from all the other groups and a significantly lower chroma, in other words it was ‘duller’ than UK lamb. New Zealand lamb was, however, the most tender,” she said.
For grass and compound fed lambs, there was deterioration in some quality attributes between November and March, most notably in abnormal flavour (which increased) and flavour liking and overall liking (which decreased).
“Compared with the UK controls, both groups of grass and compound fed lambs had weaker lamb flavour and, apart from the November-slaughtered grass-fed lambs, a significantly more pronounced abnormal flavour. The UK controls were preferred overall to any of these groups.
“On the other hand, both stubble turnip fed groups had quality ratings on a par with the UK controls and, moreover, there were no significant effects of season of slaughter on this diet. In terms of overall liking, the most preferred were the two stubble turnip groups and the UK controls; the least preferred groups were grass or grass silage fed and compound feed ration fed lambs slaughtered in March,” she added.
“The flavour changes were more important in determining overall liking than the changes in tenderness and juiciness between the two slaughter times, some of which favoured the March slaughtered groups. But it is noteworthy that all lamb groups produced meat that was tender.”
Presented to the British Society of Animal Science Annual Meeting, March 30 to April 1, 2009, Southport, UK.
Full details: Phillips K, Wheeler KPA, Fisher AV, Nute G: “Investigation of the variation in lamb meat quality on three winter finishing systems.”
Summary (pdf) Presentation_046phillips (pdf)
To view proceedings of all summaries presented at the Annual Conference http://www.bsas.org.uk/Publications/Annual_Conference_Proceedings/ To view Powerpoint presentations http://www.bsas.org.uk/Members_Area/ For further information contact: BSAS on 0131 445 4508 or bsas@sac.ac.uk
