Meat quality study favours castrates over ram lambs

The results of a Teagasc/University College Dublin study comparing meat quality attributes of ram and wether lambs fed on a short-term all-concentrate diet prior to slaughter were presented by Teagasc’s Michael Diskin at Tuesday evening’s Teagasc lowland sheep conference in Loughrea.

In terms of sensory attributes, the differences between wethers and rams were highlighted. These were statistically significant but numerically small in favour of wethers for 11 meat quality sensory descriptors.

However, of equal importance, the study found that while lower in number, wether lambs also produced meat samples with undesirable sensory attributes, with lamb castration not eliminating this risk.

The results of the study also confirmed the many production efficiency benefits ram lambs can deliver and Michael said this is an element that must also be considered when farmers are making decisions on lamb castration.

He said decisions should ultimately be taken in light of a farm’s production system and market signals, which is discussed in greater detail later in the article.

The study

The foundation for the study was put in place at lambing, with 120 Scottish Blackface (SB) and 120 Texel-cross-Scottish Blackface (TSB) lambs identified, tagged and birth recorded on six commercial farms.

Every second male lamb was castrated within 48 hours of birth using a scrotal rubber ring. Lambs were inspected on all farms at five months of age and all sheep underwent a quarantine programme on entering the Teagasc Research Centre at Mellows Campus, Athenry.

Five slaughter points were selected (October, November, January, March and April), with lambs assigned according to weight and grazed ahead of indoor finishing. In total, 100 SB and 100 TSB lambs were put through the trial. Half of each breed type were wether lambs.

Lambs were finished in a 36-day intensive period and offered concentrate ad libitum, along with 100g/day silage dry matter and free access to water.

Lambs were allowed tactile, olfactory and visual contact with each other through pens, while also having visual and tactile contact with non-pregnant cyclic ewes in adjoining pens.

The meat quality attributes analysed were broken down into three areas including carcase and meat composition; meat tenderness and collagen content; and post-slaughter muscle pH, temperature profile, colour attributes, aroma, flavour and texture attributes.

The study was designed to evaluate three-way and two-way interactions among breed, sex and slaughter age.

Michael reported that no three-way interactions and few two-way interactions were detected, which indicated that the effect of sex was largely consistent across both breed types and age of slaughter.

Meat sensory results

Intramuscular fat (IMF), as described by Michael, is a key indicator of meat-eating quality. SB lambs had higher IMF compared with TSB lambs, while no difference was observed between genders.

Meat colour, which is an import visual attribute for consumers, is preferred as bright and red rather than dark. Meat from SB lambs was statistically lighter in colour, but the difference was very small and Michael said meat from both breeds was very acceptable.

He said redness and yellowness of meat colour was statistically higher in meat from wether lambs, but again differences were small and both were very acceptable.

The pH value, as recorded at 25 hours post-mortem, indicated that high pH levels were not an issue across breed type or gender.

In terms of tenderness, meat from SB lambs was more tender than meat from TSB lambs, while wether lambs tended towards delivering more tender meat than ram lambs, with differences described as very small. Meat from castrates or rams was not deemed as unacceptably tough.

Sensory analysis was collected from taste tests in grilled loin muscle from ram and wether lambs, with the results summarised by Michael as follows.

“Twenty-two out of 38 sensory descriptors were affected by breed type and gender treatments. Differences between rams and wethers, although numerically small, were statistically different for 11 descriptors. Lamb from rams had higher average scores for intensity of lamb aroma, animal /farm smell, woolly aroma, rancid aroma, manure/faecal aroma, sweaty aroma, rancid flavours, off-flavours, and fattiness/greasiness, while ram lambs also had lower mean scores for intensity of roast meat aroma and intensity of roast meat flavour.”

Michael added that there were close to statistically significant differences for soapy aroma, soapy flavour and fatty/greasy aftertaste, with ram lambs having higher scores than wether lambs.

A measure called the median absolute deviation (MAD) was applied to seven sensory attributes considered undesirable to identify how many samples exceeded the standard cut-off point. The results of this is detailed in Table 1.

Michael highlighted that it is very noteworthy that there were some castrates among the animals exceeding the cut-off point, which indicates that undesirable attributes are not confined to ram lambs.

He concluded that the risk of avoiding problematic meat samples cannot be eliminated by castration and that other factors, such as slaughter age, diet and consumption habits, are worthy of investigation.

Production performance

Along with looking at meat quality, the study also compared the performance of ram lambs versus castrates and breed differences. Ram lambs had higher growth rates (314g/day v 272g/day), produced heavier carcases and had a better food conversion efficiency (5.58kg concentrate/kg gain v 6.31kg).

Feed intake was similar for both at an average of 1.5kg to 1.6kg concentrate daily, while wether lambs had a higher kill-out of 47.6% (over 45.7%).

Wether lambs also had a slightly higher carcase conformation score (2.92 v 3.10 with 5, 4, 3, 2, 1 = EUROP), but were much fatter (fat class 3.91 v 3.07). This, Michael said, could be a reflection of the high-energy diet during finishing. Not surprisingly, the TSB lambs performed better in all production parameters.

Michael also reviewed a number of comparable studies from other countries, which found negligible differences in the meat-eating quality of ram versus wether lambs.

“The study shows there is a greater likelihood of obtaining a problematic sample with meat from ram lambs, but it should be stressed that it is only a proportion of rams that produce such problematic samples and while castration helps to lower this number, it does not eliminate it. The study also confirms the well-established production and efficiency benefits associated with leaving male lambs entire,” concluded Michael.

Take-home message

This fed into Michael’s take-home message of whether sheep farmers should castrate lambs or not.

“A decision on lamb castration needs to take into account the farm’s production system, time of lamb finishing, flock size, ability to separate ewe and ram lambs in the autumn and signals returned from the market.”

For example, difficulty in achieving the desired fat cover on ram lambs late in the season was identified as one constraint regularly highlighted by producers.

Michael said that given the production benefits of leaving ram lambs entire, it is not surprising that non-castration has become more frequent in recent years. “If processors require more wether lambs, it is likely they will have to reward producers by paying a premium for such lambs.”