No abstract

Estimates of heritability, repeatability, and phenotypic and genetic correlations were calculated from data involving about 1050, 720, and 250 dam-daughter pairs for Merino, Corriedale, and Polwarth breeds respectively; data on daughters were taken at both 18 and 30 months of age. Phenotypic and genetic correlations in general were of the same order of magnitude and similar between breeds; the estimates substantiated the results obtained by other workers. Estimates of repeatability of most fleece traits between 18 and 30 months of age were significantly lower than estimates based on later ages. However, the differences were not large, and the use of a single figure for repeatability, either the younger age estimate or a pooled estimate, would give a reliable prediction for subsequent performance. Estimates of heritability of all traits in each breed were high; however, the heritabilities of greasy and clean wool weights of Merino and Polwarth ewes were about 40% smaller at 18 months than at 30 months, the estimates at 30 months being generally similar to previous estimates at 18 months. Relative to selection at 18 months, wool production, either greasy or clean, would increase at a greater rate per annum with selection of Merinos and Polwarths at 30 months; for Corriedales, selection at 30 months is more efficient for greasy, but not for clean wool production.

The effects of year of birth, age of dam, sex, and litter size upon birth weight of lambs were examined by least squares analysis in eight flocks in Western Victoria (4 Merino, 3 Corriedale, and 1 Polwarth). Male lambs were approximately 0.8 lb heavier (P<0.01) than female lambs, single lambs about 1.6 lb heavier (P<0.01) than twin lambs. Lambs, born of 5-year-old ewes, were generally heavier (P<0.01) at birth than lambs from ewes of other ages. A general set of adjustments of birth weight for these sources of variation are presented for each breed. The effects of the same sources of variation on survival of lambs to weaning were calculated by least squares analysis. Regressions of survival on birth weight (BW), BW2 and BW3 were included in the analysis. Male lambs did not survive as well as female lambs and a higher proportion of twin lambs died than single lambs. Lambs from primiparous ewes generally did not survive as well as those from multiparous ewes. Maximum survival occurred at birth weights of about 10 lb (Merino), 11 lb (Corriedale), 8 lb (Polwarth).

Sex ratios have been the subject of numerous investigations, particularly in studies with humans. In general, however, the literature relating to sex ratio in sheep is limited (Chapman & Lush, 1932;Henning, 1939;Rasmussen, 1940; Karam, 1957).Population studies have generally been based on an expected sex ratio of 0\m=.\5, and any factor causing marked divergence from this ratio is important. Although the proportion of entire males used in domestic animal populations in very much smaller than for females, production from castrated males is a significant proportion of the total production of wool and meat from sheep. Hence, studies of population dynamics and flock structure need to take account of factors causing variation in sex ratios. This paper examines the influence of some factors, breed and strain, age of mother, year of birth and type of birth (single or twin) on the sex ratio of sheep at birth and weaning.The data used in these analyses were collected as part of a wider study, which has been previously reported (Mullaney, 1966; Mullaney 8c Hyland, 1967). Sex ratio at birth was defined as the proportion of males born, either dead or alive; sex ratio at weaning was the proportion of males present at weaning (approximately 150 days of age). Each ewe for each breed (Merino and Corriedale) was classified according to year of birth of offspring, age of ewe, birth type of offspring (single or twin) and strain (property). The method of least squares was used to obtain estimates of the effects of each of these factors on sex ratio at birth and weaning.The overall sex ratio at birth was 0-508 (11,962 lambs) and at weaning was 0-501 (9746 lambs) (Table 1). These estimates are slightly higher than those quoted previously (Chapman & Lush, 1932;Henning, 1939;Rasmussen, 1940; Karam, 1957) and are based on larger numbers.There was a trend for the sex ratio in single births for both breeds to be higher than in twin births (0-516 versus 0-489, Merino; 0-503 versus 0-486, Corriedale), but this trend was not significant. This supports previous work which suggested a preponderance of females among twin births, probably resulting from differential intrauterine mortality of males in multiple births.The sex ratio of single lambs decreased at weaning because of the higher survival rate of females (85-6%) than of males (82-4%) ( Table 2). The survival rate of the two sexes was similar for twin lambs (both 65-7 %) and the sex ratio of this group remained constant between birth and weaning. Differential 391

Fifty-four pigs weaned at 3 weeks of age were allocated at an average weight of 5-4 kg to two experiments to examine the effects of diets having digestible energy (DE) concentrations ranging from 2910 to 3940 kcal/kg. In the first experiment pig growth performance and the dry-matter digestibility of the experimental diets were measured between 3 and 8 weeks of age. The composition of the carcass at 8 weeks of age was correlated with the composition of various carcass joints. In the second experiment pig growth performance was measured over the live-weight range 5-4 to 20 kg. The findings were: 1. Growth rate was linearly related to DE intake. 2. The optimum DE level for maximum growth was 3640 kcal/kg. 3. The efficiency of utilization of DE for growth did not vary in the first experiment but was poorest at a DE concentration of 3245 kcal/kg in the second. 4. The DE content of the diet had no significant effect on carcass characteristics at 8 weeks of age in the first experiment or at 20 kg live weight in the second. 5. The proportion of fat and lean in the 8-week carcass was significantly (P< 0-01) correlated with that of the shoulder joint.