No abstract

The objective of this study was to evaluate and quantify the genetic progress achieved in a New Zealand Angus nucleus herd through long-term selection for an economically based, multi-trait breeding objective. A 4-trait breeding objective was implemented in 1976 and selected on through 1993 with traits consisting of slaughter weight and dressing percentage of harvest progeny and cull cows, and the number of calves weaned in the lifetime of each cow. These traits were related to gross income with none related to costs of production. To overcome this, economic weights were adjusted down for increased feed requirements of faster growing (and generally larger) animals. Performance and pedigree information was recorded on 16,189 animals from 1976 through 1993 and included weaning, yearling, and mature cow weights along with the lifetime number of calves weaned by each cow. These traits were used in the phenotypic selection indexes developed to predict the defined breeding objective. Individual performance was adjusted by least squares for major environmental fixed effects and deviated from contemporaneous means. Genetic and residual (co)variances were re-estimated for each of the traits using REML techniques and used to calculate EBV for each trait. These EBV were in turn used to calculate annual genetic changes. The average annual genetic changes for weaning weight direct and maternal breeding value were 0.43 +/- 0.05 and 0.03 +/- 0.22 kg/yr, respectively. Corresponding annual genetic changes for postweaning BW gain, yearling weight, harvest weight, and mature BW were 0.29 +/- 0.03, 0.72 +/- 0.06, 1.7 +/- 0.13, and 0.13 +/- 0.09 kg, respectively. The annual change in number of calves weaned per cow lifetime was 0.006 +/- 0.001 calves/cow and the change in dressing percentage was estimated to be -0.035 +/- 0.003 %/yr. At the end of the program, 3.21 generations of selection had occurred with a mean accumulated selection differential of 3.87 SD. Change in objective traits due to selection was similar to or exceeded change predicted at the onset of the program with the exception of mature BW and dressing percentage. Genetic change in mature BW was not different from zero, whereas the predicted change was 29.3 kg. The overall genetic trend in the breeding objective exceeded that predicted at the onset of the program. Results of this study showed that selection on indexes developed to predict an economically based, multi-trait breeding objective will produce genetic change.

Weaning weights of 7771 Hereford (18 herds) and 16666 Angus calves (37 herds), from <) years' records of the Beef Cattle Weight Gain Performance Recording Scheme, were analysed within breeds by least squares to investigate the main effects of herd, year of birth, age-of-dam group, and sex, with age at weaning as a covariate, and the first-order interactions among herd, year, age-of-dam group, and sex effects. Only the herd X year interaction for Hereford, and the herd x year and herd x sex interactions for Angus, were important. Within sub-class linear regression coefficients of weight on age at weaning for Hereford and Angus calves were 0.70 ± 0.01 and 0.62 ± 0.01 kg/day, respectively. Hereford and Angus males were heavier (P < 0.01) than females at weaning by 29.8 and 25.6 kg respectively. Weights of Hereford calves out of dams 2, 3, 4, 5, and 10 years of age and older deviated from those of calves out of mature dams (6 to 9 years) by 33.3,17.6,8.7,3.8, and 2.2 kg, respectively, and of Angus calves l-y 22.7,15.2,7.9,5.4, and 1,4 kg. Age-of-dams effects were also estimated by best linear unbiased procedures from similar numbers of calves; effects so estimated generally differed little from those derived by least squares. Additive and multiplicative applications of the linear regression coefficients of weight on age for each breed, to adjust for age at weaning, reduced the dependence of adjusted weight on age more effectively than the procedure used in the National Beef Recording Service (NBRS). Apart from factors for Angus calves out of 3-year-old dams, adjustments determined for age-of-dam effects by least squares and by best linear unbiased estimation did not differ significantly from adjustments used in NBRS. Variances within age-of-dam groups indicated that additive, rather than multiplicative, adjustment factors should be used for each breed. Multiplicative adjustment factors for sex were more appropriate in equalising variances within sex groups. 269Recording Service warranted study and perhaps some reap-

Sixty pl egnant beef cows of Friesian, 7/8 Friesian X Jersey, and Angus genotypes 3 years of age and older were used. At 56 days before calving, each cow was allocated to 1 of 2 daily pasture DM allowance levels: 20 ("20") and 8 ("8") kg DM per cow. At calving cows were re-assigned to daily pasture allowances of 20 ("20-20" and "8-20") or 8 ("20-8" and 8-8") kg DM per cow for 56 days post-partum. At 56 days after calving, the cows were grouped into a single mob and given a daily allowance of 18 kg DM per cow throughout mating and until weaning. Despite similar pre-calving weights, "20" cows were 36 kg heavier (P < 0.01) immediately after calving than "8" cows. Forty-two days after calving the visually assessed condition scores of "20" cows remained consistently higher (P < 0.05) than the score of "8" cows. Mean DM intakes (kg/cow/day) for "20" and "8" cows before calving were 9.5 and 6.3 respectively. Mean DM intakes (kg/cow/day) (and % DM utilisation rates) for "20" and "8" cows before calving were 9.5 kg (47.6%) and 6.3 kg (78.2%) respectively. At 56 days after calving, "20-20" and "8-20" cows weighed 520 kg and ')02 kg respe('tively and were heavier (P < 0.01) than "20-8" and "8-8" cows (340 kg and 392 kg); condition scores were significantly different (P < 0.05) at 6.8, 6.0, 3.4, and 2.5 respectively. Treatments did not affect calf weights until 56 days of age when calves of "20-20" (76 kg) and "8-20" (81 kg) cows were heavier (P < 0.05) than those of "8-8" cows (67 kg) ; calves out of "20-8" cows (74 kg) were intermediate. Intakes (kg DM/cow/day) for " 20-20", "8-20", "20-8", and "8-8" cows during the 56 days after calving were 10.5, 11.7, 6.8, and 7.0 kg respectively. From 56 days post-partum until weaning, gains in cow live weight (and condition score) were -5 kg (-0.2) , 44 kg (2.0), 4 kg (-0.1), and 58 kg (2.7) for " 20-20", "20-8", "8-20", and "8-8" cows respectively. Corresponding calf weight gains (kg) were 81, 83, 83, and 83. The mean intervals (days) from calving to first oestrus were 72, 80, and 69 for "20-20", "20-8", and "8-20" cows respectively, shorter (P < 0.05) than the 97 days of "8-8" cows. Pre-calving pasture allowance had no effect on interval from calving to first oestrus or pregnancy rate, but both these traits were affected by post-calving allowance.417

of 80.8%. Lambs were born between 1997 and2000. Fixed effects fitted in the model included sex and contemporary group, defined as the interaction of age of dam, flock, and birth date class. Median heritabilities were 0.106 ± 0.010 for direct, 0.082 ± 0.005 for maternal, and a median proportion of phenotypic variation 0.098 ± 0.003 for permanent environmental effects. The direct-maternal correlation was -0.75 ± 0.03. Estimated breeding values on the underlying scale were back-transformed to the phenotypic probability scale. For direct lamb survivability, the highest performing sire's lambs had a 14.8% greater chance of survival than the lowest performing sire's lambs for flocks with an average lamb survivability of 80%. Although heritabilities for both components of lamb survivability are low, selection for this trait can be accomplished and is of economic importance for the sheep breeder.Keywords lamb survival; sheep; estimated breeding values; heritability; threshold model Abstract Lamb survivability is a major determinant of the reproductive efficiency of the flock. The objective of this study was to estimate variance components for direct, maternal, and permanent environmental components of lamb survivability. Threshold model procedures were used to estimate variance components from 25 362 lamb survival observations representing 136 sires from two Romney flocks in New Zealand with an average lamb survival A06028;