Results on the body and carcass composition of 7885 lambs sired by 371 rams of 15 different breeds mated to Romney cast-for-age ewes are given. Trials were run at the Ruakura Agricultural Centre and the Manutuke Research Station from 1963 to 1972. Lambs of the different breeds were slaughtered at the same average age so that differences between breeds/crosses in liveweight and carcass weight reflected differences in growth rate. Ranked from heaviest to lightest mean age-adjusted carcass weights, lambs sired by the Dorset Horn, Poll Dorset, Hampshire, Border Leicester, Suffolk, Dorset Down, South Suffolk, and South Dorset Down produced the heaviest carcasses, and those sired by the Cheviot, Southdown, English Leicester, and Ryeland were intermediate. The Lincoln, Merino, and Romney sired carcasses were lighter. The longer-woolled Romney, Merino, and Lincoln had lowest dressingout percentages based on full liveweights and the short finer-wooled breeds such as the Southdown, Dorset Down, and Poll Dorset/Dorset Horn dressed 2-3% higher. When compared at the same carcass weight, lambs sired by the Southdown followed by the Ryeland had the fattest carcasses and those A94091Received 26 September 1994; accepted 27 April 1995 1 Deceased sired by the Suffolk, Cheviot, and Dorset Horn produced the least fat, leanest carcasses. The Southdown, Dorset Horn, South Dorset Down, and Poll Dorset crosses had the largest eye muscle areas for carcasses of similar weight.

Angus (A) and Hereford (H) cows at one location and A cows at a second location were used to generate purebred controls and six first-cross (FI) types of calf. Foundation sires were A, H, Friesian (F), Jersey (J), and South Devon (Sd) at Location 1, generating FH, FA. JA, SdA, and HA (plus AH) FI calves, and at Location 2 sires were A and Blonde d' Aquitaine (Ba), generating BaA Fis. Sire breeds were selected as potentially contributing to productive crossbred cows, based on previous FI cow comparisons. In subsequent years F2, F3, and F4 calves were produced from each of the two-breed crosses, with overlapping generations and contemporary controls providing balanced comparisons of breed types and generations. The experiment consisted of 395 unique sires and 5243 calves born in 1973-88 at Location 1 and 105 different sires and 2404 calves born in 1976-86 at Location 2. Growth, reproductioQ, maternal, and carcass traits were studied. Heterosis was estimated from HA (plus AH) and purebred A and H animals, but only breed x A 93009 generation effects were estimated from the other two-breed crosses because of the absence of reciprocal FI matings. Heterosis from HA crosses was 3.5 and 6.3% for direct effects on weaning and yearling weights respectively, and 9.0% for the maternal (i.e. Fl cow) effect on weaning weight. For reproduction of FI HA cows, heterosis was 15.2% for calf crop weaned per cow joined, 25.4% for productivity (calf weaning weight per cow joined), and 18.1 % for an efficiency ratio (i.e. productivity/ average cow weight). Over all six two-breed crosses, relative to purebred controls, advantages of Fis averaged 4.4 and 8.1 % for direct effects on weaning and yearling weights respectively, and 13.3% for the . maternal (FI cow) effect on weaning weight. For reproduction, the FI cow advantage over controls averaged 9.7% for calf crop weaned per cow joined (range -7.3 to +15.2%), 24.7% for productivity (range -8.9 to 47.3%), and 16.8% for the efficiency ratio (range -15.7 to +36.3%). For the efficiency ratio, breed types were ranked FH (greatest), JA, FA, HA, SdA, A, H, and BaA. On average, the F3 and F4 calves out-perfonned the Fls by 6.3% in weaning weight but were similar to Fls in yearling weight, whereas for maternal weaning weight the means for F3 cows' calves were 3.4% below those for FI cows. For reproduction, averages of F3s were below those of Fls but superior to the purebreds by 7.2, 17.7, and 16.3% for calves weaned per cow joined, productivity, and the efficiency ratio respectively. There were also significant breed-group differences in carcass composition.

The proportions of cuts from 7885 lamb carcasses sired by 15 different ram breeds, reared on pasture at two locations over 10 years, were measured and examined for breed differences. Although highly significant breed differences were found, their magnitude was small reaching a largest difference between crosses of 1.22% for the leg and 1.26% for the loin compared at the same carcass weight. Compared at the same time of slaughter (age), the maximum differences between the progeny of different ram breeds were 1.02% for the leg and 1.06% for the loin. Wether lambs had a slightly higher proportion of forequarter cuts. Sire breed had a major effect on the proportion of lambs reaching the fatter P grade (class) with the meat breeds Southdown, Dorset Down, South Dorset Down, Hampshire, and South Suffolk sires producing 68-76% P carcasses and the wool breeds such as the English Leicester, Merino, Romney, and Lincoln producing 18-23% of P carcasses. Lambs sired by the Poll Dorset, Dorset Horn, Suffolk, Ryeland, Border Leicester, and Cheviot produced 49-62% P carcasses.

Four lines of mice were formed from a common base population and selected for 37 generations for either increased 3-week weight (weaning weight), 6-week weight, 3-6 week gain, or maintained as a randomly bred control line. Realised heritability estimates for short-term (long-term) responses were 0.33±0.20 (0.07±0.10), 0.46±0.14 (0.26±0.09), 0.36±0.14 (0.24±0.11) for 3-week weight, 6-week weight and 3-6 week gain, respectively. Realised genetic correlations estimated from short-term (long-term) responses were 0.23±0.08 (0.35±0.10) between 3-week weight and 3-6 week gain; 0.82±0.04 (0.58±0.08) between 3-week weight and 6-week weight; and 0.81±0.04 (0.97±0.04) between 3-6 week gain and 6-week weight. The genetic correlation between 3-week weight and 6-week weight was asymmetric with a greater correlated response for 3-week weight when selecting for 6-week weight (1.06) than vice versa (0.63).

Two selection herds with Angus cattle were maintained at Waikeria near Te Awamutu, New Zealand, from 1964 to 1981, with experimental calvings comprising 3355 recorded calves. The selection criterion was yearling weight in one herd (the YW herd) and postweaning weight gain in the other (the PWG herd). In the absence of a control herd, genetic responses were estimated using best linear unbiased prediction (BLUP) methods. Annual direct selection differentials averaged 6.45 kg in the YW herd and 5.00 kg in the PWG herd, respectively 0.90 and 0.79 phenotypic standard deviations of selection per generation. The average generation intervals were 3.23 and 2.88 years respectively. Direct responses were estimated to be 1.96 and 0.97 kg/year respectively (both P < 0.01), whereas correlated responses in yearling weight (pWG herd) were 1.52 kg/year and in postweaning gain (YW herd) were 0.68 kg/year. Significant increases were obtained in birth and weaning weights in the YW herd but not in the PWG herd. Paternal half-sib heritabilities ofdirect selection traits were estimated from the selection herds at 0.34 for yearling weight and 0.22 for postweaning gain, using a technique including a numerator relationship matrix. *Deceased.Estimates from 56 of the selection herd bulls used in a progeny test herd were 0.36 and 0.26 respectively. The genetic response calculated from BLUP analyses of yearling weight was less than the preliminary estimate obtained in another selection experiment using Angus cattle at Waikite,New Zealand, carried out with a contemporary control herd.