Results from one such study, in which steers and bulls were slaughtered at 17 months, showed that, relative to steers, bulls produced carcasses that were 43kg (14pc) heavier, leaner and with better conformation.
In all of these studies, bulls had a higher feed conversion efficiency (grams of carcass per 1kg food dry matter consumed).
Rearing male lambs entire increases performance
Two studies have been undertaken at Athenry to evaluate the effects of castration on the performance of lambs.
Study 1: The first study involved 157 sets of all-male twins. One member of each set of twins was castrated at birth, while the other was left entire. The ewes and their lambs were put to pasture and managed as one flock in a mid-season grazing system.
The effects of castration on animal performance are presented in Table 1. The lambs that were left entire grew faster and thus were 1.8kg heavier at weaning.
The increase in lamb weight at weaning due to leaving the lambs entire was similar to the response expected from supplementing each lamb with 12kg of creep concentrate.
Due to their higher growth rate, the entire male lambs were slaughtered 16 days earlier than their castrated brothers to achieve the same carcass weight. Entire males had a lower kill-out percentage (due to their scrotal contents).
The reduced age at slaughter due to leaving male lambs entire is similar to the response obtained from supplementing with 17kg creep concentrate.
The improvement in animal performance due to leaving male lambs entire occurred for no extra cost or labour input.
Given the growth response obtained, the financial gain from leaving male lambs entire, under current market conditions, is equivalent to approximately €4.50 per male lamb.
In addition, carcasses from the entire lambs were leaner. Carcass conformation did not differ between the castrated and entire lambs.
Study 2: The second study involved 43 all-male sets of twins. One member of each set of twins was castrated at birth, while the other lamb was left entire. The ewes and their lambs were managed as one flock until weaning.
Post weaning, the lambs grazed as part of a larger flock of lambs, managed on an all- grass system, received no concentrate supplementation, and were all drafted for slaughter prior to the end of the grazing season.
The effects of castration of male lambs on performance are presented in Table 2. The entire male lambs grew faster to slaughter and were heavier at weaning by 1.3kg.
At slaughter the entire males had a lower kill-out percentage (due to their scrotal contents) as occurred in study 1. Entire males also produced leaner carcasses.
At Athenry male lambs have not been castrated in the research flocks for the last 10 years. At drafting, entire males are drafted at a heavier weight (1kg) than the females. Entire male lambs are drafted earlier than females. On average for 2015 and 2016, 72pc and 53pc of male and female lambs were drafted by mid-September, respectively.
Effects on meat eating quality
There is a perception, supported by some industry commentators, producer groups, marketers and meat processors, that rearing male lambs entire has a negative impact on eating quality.
A study to address this issue was undertaken, in collaboration with Vanessa de Campos and Professor Torres Sweeney of UCD, to examine in detail the effects of castration on lamb meat eating quality.
Twenty lambs (10 sets of twins; 1 castrate and 1 entire) were slaughtered at six months of age. Cooked meat from these lambs was evaluated, by a panel of 10 trained assessors, for texture, tenderness, juiciness, lamb flavour, flavour liking and presence of abnormal flavour.
A score for "overall liking" was also assigned. The main results are summarised in Table 3. The evidence shows that leaving male lambs entire had no negative effect on flavour or overall-liking score.
Furthermore, meat from the entire male lambs was more tender. The study concluded, therefore, that there was no evidence for any negative effect on meat-eating quality of meat from entire male lambs relative to meat from castrates. The results of this study are in line with the conclusion from an extensive review of the international literature by Dr JP Hanrahan that "where lambs are reared on an all-grass diet and slaughtered by the end of the grazing season, leaving male lambs entire has no negative effect on meat quality, whether assessment is laboratory based or through in-home consumer testing".
Managing entire lambs
When male lambs are left entire, they should be managed with the intention of having them all drafted for slaughter prior to the end of the grazing season (mid-December). Entire male lambs should be separated from ewe lambs from early September, otherwise energy is spent following females, performance declines and unwanted pregnancies may occur.
Dr Tim Keady is principal research scientist at the Animal and Grassland Research and Innovation Centre, Teagasc, Athenry, Co Galway
Leaving male lambs entire increases lamb performance and reduces age at slaughter.
Consumers have an aversion to fat, therefore, the leaner carcasses from entire males is good for the image of lamb at the butchers counter.
Leaving male lambs entire has no negative impact on meat-eating quality relative to meat from castrated males.
So why castrate?
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