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1987). Growth and carcass characteristics of crossbred lambs by ten sire breeds, compared at the same estimated carcass subcutaneous fat proportion. Animal Production, 44, pp 83-98 ABSTRACT An evaluation was carried out over a 5-year period in 10 commercial flocks of Scottish Blackface, Scottish Half-bred and Mule ewes to evaluate 10 sire breeds: Border Leicester, Dorset Down, Hampshire Down, He de France, North Country Cheviot, Oxford Down, Southdown, Suffolk, Texel and Wensleydale. An average of 43 sires was used per sire breed.The analysis involved a total of 3360 lambs of which one-third had the left side dissected. Sire breeds were compared when their progeny were slaughtered at the same estimated carcass subcutaneous fat proportion (approx. 120 g/kg).Carcass weights were related to the adult body size of the sire breeds with a range of 4 kg between Southdown and Wensleydale crosses. Crosses by the conventional meat sire breeds tended to have higher daily carcass-weight and lean-tissue gains than those by Border Leicester and Wensleydale sires. Texel and Suffolk crosses did not differ significantly in carcass weight, daily carcass-weight gain, daily lean gain or age at slaughter (P > 0-05).Significant sire-breed x dam-breed interactions were recorded for daily carcass-weight gain and daily lean gain (P < 0-05). Dorset Down and Southdown crosses tended to grow relatively faster when from Mule dams; Texel crosses grew relatively faster when from Blackface dams.There was relatively little difference between sire breeds in visually assessed carcass conformation; all the means were within two points on a 15-point scale. Texel crosses had a higher carcass lean proportion than other crosses: their advantage over Suffolk crosses was 22 g/kg.

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SUMMARYDissection data from 643 carcasses of castrated male cattle (steers) of 15 breed-type × feeding system groups were used to examine the distribution of total fat (TF) between subcutaneous (SF), intermuscular (IF), kidney knob and channel (KKCF) and cod fat depots. The breed-type groups, which were from cereal or grass/cereal feeding systems, included Ayrshire, Simmental × Ayrshire, British Friesian and Friesian crosses with Aberdeen Angus, Hereford, Limousin, Charolais, South Devon and Simmental. Means for percentage TF in side ranged from 21·4 to 36·2 with a pooled within group SD of 3·87.The growth of each depot relative to TF was examined using the allometric equation. Significant but not large differences existed between groups for the growth coefficients of SF and IF while the coefficients for KKCF differed widely among groups. The coefficient for SF was greater than that for IF in every group (pooled within-group b values±SE were 1·20±·02 and 0·87±0·01 respectively).At constant TF weight, carcasses from Ayrshire and Ayrshire crosses tended to contain less SF and more IF+KKC F than those from Friesian and beef breed × Friesian. Important differences in distribution were recorded between the various beef breed × Friesian groups. The proportion of SF was lower for cattle fed on grass/cereal diets than for cattle of the same breed type fed on cereal diets.The differences in fat distribution led to substantial bias for some groups when the percentages of IF and TF in the side were predicted from percentage SF. The bias was less when both KKCF and SF were used as predictors.

Linear measurements and sample joint dissections were examined as predictors of carcass lean percentage using data from 1060 carcasses comprising 108 subgroups (nine genotypes × two sexes × two feeding regimes × three slaughter weights). The potential predictors were examined in terms of precision, cost and the stability of their regression equations.Probed fat thickness 6·5 cm from the dorsal mid-line at the last rib (P2) was the individual measurement giving the most precise prediction (residual s.d. pooled within subgroups = 2·21 percentage units; r = −0·72). The square root transformation (P2½) gave stable regression slopes over levels of all four factors, though there were important differences in intercepts between genotypes, sexes and slaughter weights.The precision of prediction from the lean percentage of sample joints was generally improved by including P2½ with each in multiple regression. Used in this way with current Meat and Livestock Commission costings, the ham joint offered the best compromise between cost and precision (pooled residual s.d. = 1·25 percentage units; R = 0·92). Regression slopes on each joint were stable for all factors except for those on the rump back and rib back joints which varied by feeding regime. Intercepts varied by genotypes for all joints except the ham, while intercept differences for feeding regimes were small or non-significant.The results confirm the value of the ‘sub-sampling with regression’ procedure for predicting carcass composition.

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