R. L. Baker

Genetic and phenotypic relationships among anti-Trichostrongylus colubriformis antibody level, faecal egg count and body weight traits in grazing Romney sheep

Serum levels of an antibody (Ab) and immunoglobulin G, (IgG,) to the larval (L3) stage of the internal parasite, Trichostrongylus colubrifomis, were determined in 3 years in Romney lambs. Animals from two pairs of selection flocks, bred for increased or reduced resistance to internal parasites, were compared for Ab or IgG, levels, and a progeny test flock was recorded to provide data for genetic parameters (n = 64 sires). Lambs were exposed to a natural parasite challenge on pasture, following an anthelmintic drench treatment at weaning. Blood and faecal samples from 4- to 6-month-old lambs (January samples) were taken when the mean FEZ of a monitor group reached 800 to 1500 eggs/g. Lambs were again drenched with anthelmintic and a further cycle of the protocol was carried out (March samples). Selection flock differences in March (High flock minus Low flock means) averaged - 0.73, - 0.93 and 1.27 phenotypic standard deviations for log,Ab, log, IgG, and log, (FEC + 100) at one site, and -0.89, - 0.94 and 1.89 phenotypic standard deviations at the other. Repeatabilities and he&abilities of log,Ab, log, IgG,, and log, (FEC + 100) were estimated. For data collected in March, the genetic correlations between log,Ab or log IgG, and log, (FEC + 100) were - 0.56 f 0.18 and - 0.35 f. 0.19 respectively, whilst they were -0.48 f 0.17 and -0.47 + 0.15 between log,Ab or log, IgG, and the average of log, (FEC + 100) in January, March and May. The results suggest that ram selection based on serum antibody levels in March would result in 51-67s of the genetic gain in reducing FEC that could be achieved by using FEC directly.

Heritability of and genetic correlations among faecal egg counts and productivity traits in Romney sheep

Abstract A total of 2611 spring-born Romney ewe lambs, the progeny of 60 sires over 3 years, were studied on a Hawkes Bay farm to estimate the heritability of faecal egg count (FEC), and correlations between FEC and production traits. Weaning weight, an autumn weight, the weight gain between these 2 times, and yearling fleece weight were recorded in each of 3 years. A dag score was obtained in the final 2 years. An anthelmintic drench was administered to 1987-born lambs in mid January after which further treatment was withheld until April. In the 2 subsequent years, drench treatment was administered in the first week of December and further treatment withheld until the mean FEC in a small monitor group reached a target value of 1000-1500 eggs/g. Once the target value was reached, a faecal sample was obtained from all animals for an FEC, the dag score and autumn liveweight were taken, and routine drenching was then resumed. Variance components were estimated using a multivariate restricted maximum likelih...

Responses of Romney sheep to selection for resistance or susceptibility to nematode infection

Divergent breeding lines of Romney sheep, selected as lambs for consistently low or high faecal worm egg count (FEC) following natural multispecific challenge by nematode parasites, have been maintained at Wallaceville Animal Research Centre since 1979. From the start of the trial until 1992, 821 and 736 experimental lambs in lines selected for increased resistance (R) and increased susceptibility (S), respectively, were generated, with the use of 44 different sires. In order to assess genetic responses to selection, FEC and productivity data were analysed using restricted maximum likelihood procedures. By 1988 the two lines had diverged in average loge (FEC+100) by 0·67 log units, and by 1992 divergence had increased to 1·48 log units, representing 2·90 genetic standard deviations of divergence. No significant correlated responses were observed in live weights. However, by 1992 the mean score for breech soiling (dags) in the R line was proportionally 0·41 greater than in the S line (F v. 0·92, respectively). It is concluded that selective breeding can change the degree of resistance or susceptibility to nematode infection in Romney sheep, and selection for productivity needs to be continued at the same time in any practical breeding programme.

Maternal effects for growth traits in beef cattle

Abstract Estimates of direct and maternal heritabilities, the genetic correlation between direct and maternal additive effects, and the permanent environmental variance as a percentage of the phenotypic variance (c2) were reported for weights of beef cattle at birth, weaning, yearling and 18 months. The data consisted of one Hereford and two Angus weight selection herds, analysed separately, recorded from 1969 to 1987 with a grand total of 7291 records. A univariate animal model was used. Direct and maternal heritabilities averaged 0.30 and 0.07 respectively for birth weight, 0.14 and 0.13 for weaning weight, 0.29 and 0.04 for yearling weight, and 0.32 and 0.04 for 18-month weight, whilst c2 terms averaged 0.05, 0.15, 0.03 and 0.01 respectively. Genetic correlations between direct and maternal genetic effects in the Angus data averaged 0.20, 0.03, 0.09 and 0.27, respectively. Genetic correlations in the Hereford data were 0.37, −0.35, 0.97 and 0.95, respectively. Animal models which ignored maternal effects tended to overestimate direct heritability.

Genetic correlations between pubertal traits in bulls and heifers

Abstract Records from a crossbreeding experiment were analysed to estimate the genetic correlation between scrotal circumference in bulls and pubertal traits in heifers, using paternal half-sib relationships. There were 234 sire groups in common. Bull and heifer calves were selected at random at weaning to comprise about five and six potential replacements respectively per sire group. In total 1307 bulls (born in 1980–1985) were each recorded for scrotal circumference in May (8 months of age), August and October, and 1302 heifers (born in 1981–1985) were checked for puberty for a 7-month period (using chinball harnesses on bulls) from about the beginning of May until mid-December. The pubertal traits in heifers were age at first oestrus (AFO), standardised age at first oestrus (SFO) and weight at first oestrus (WFO). Live weights were recorded monthly on heifers and WFO was interpolated from these weights. The heritabilities and genetic correlations were estimated using restricted maximum likelihood. Heritabilities for scrotal circumference were 0.50 ± 0.11, 0.33 ± 0.10 and 0.29 ± 0.10 in May, August and October respectively (0.29 ± 0.07 for all ages combined), whilst those for AFO, SFO and WFO were 0.33 ± 0.12, 0.32 ± 0.10 and 0.40 ± 0.13, respectively. Genetic correlations between scrotal circumference and heifer puberty traits averaged −0.39 ± 0.22 for AFO, −0.19 ± 0.20 for SFO and −0.39 ± 0.20 for WFO.

Correlated responses to selection for yearling or18-month weight in Angus and Hereford cattle

Abstract Correlated responses to selection for yearling (AS1 herd) or 18-month weight (AS2 herd) wereevaluated against a control (AC0 herd) in a progeny test herd using 2294 calves born in 1975–1988. A sample of privately-owned Angus bulls, available by artificial insemination (AI), were compared with them for eight liveweight or gain traits up to 18 months, with four carcass traits on steers. Cows of known pedigree in the progeny test herd were also evaluated for seven maternal traits. Other correlated responses were evaluated directly in the ACO and selection herds (three puberty traits, daily food intake, cow weight, and survival and reproduction traits). Realised genetic correlations to selection for yearling weight (AS1 herd) averaged 6% higher (forgrowth and carcass traits) than published paternal half-sib estimates, whilst those with 18-month weight (AS2 herd) were about 10% lower than with yearling weight. The sign of maternal genetic effects for live weights up to weaning varied among selection herds. Realised genetic correlations with selection weight averaged 0.51 (carcass fat depth), 0.93 (food intake), 0.16 (scrotal circumference in bulls), 0. 18 (age at puberty) and 0.37 (weight at puberty in heifers), 0.38 (cow weight, AS I herd) and 0.92 (cow weight, AS2 herd). The selection herd differences from control were not significant for cow or calf mortality or reproductive traits (6501 mating records), but tended to be negative for cow and calf death rates, and variable for overall reproductive rate.

Heritabilities and genetic correlations for live weight and fibre traits in New Zealand Cashmere goats

Abstract Data were obtained at Whatawhata on the growth of goats to the yearling stage and on their cashmere production as hoggets. There were 884 animals recorded from the 1985 to 1989 birth years, comprising the progeny of 60 sires. Records from kid shearings were also obtained in the last two years. Mixed-model restricted maximum likelihood (REML) models were fitted. Heritabilities from yearling fleece records were 0.42±0.13 for fleece weight, 0.57±0.15 for yield, 0.62±0.15 for down weight, 0.35±0.12 for guard hair weight, 0.99±0.19 for down fibre diameter and 0.57±0.15 for mean down length; corresponding values from kid fleeces (23 sires only) were smaller in most cases than from yearlings, being respectively 0.14±0.06, 0.19±0.07, 0.20±0.07, 0.04±0.04, 0.19±0.07 and 0.87±0.29. The phenotypic and genotypic correlations between down weight and fibre diameter in yearlings were 0.50±0.03 and 0.81±0.08 respectively, representing an unfavourable relationship when selecting for heavier but finer down. The genetic correlations of yearling weight with down weight and down fibre diameter were slightly negative (−0.34 and −0.25), but the estimates were non-significant.

Results of selection for yearling or 18-month weight in angus and hereford cattle

Abstract A selection experiment was carried out in Angus cattle to compare the effectiveness of selection on 13-month weight (with first mating at 14 months of age — AS1 line) or on 18-month weight (with first mating as 2-year-olds — AS2 line), alongside a control Angus herd (AC0 line). A yearling mated Hereford herd, selected on 13-month weight (HS1 line) was also established. Data from calves born in 1972–1986 were analysed for birth weight (BW), weaning weight (WW), 9-month weight (9W), yearling weight (YW) and 18-month weight (18W). By 1986 there had been an average of 3.4, 3.8, 4.9 and 4.6 generations of selection in the AC0, AS2, AS1 and HS1 lines, respectively. Corresponding generation intervals were 4.4, 4.4, 3.2 and 3.3 years, respectively, and selection differentials (standard deviations per generation) averaged 1.04 and 0.86 for YW in the AS1 and HS1 lines and 1.02 for 18W in the AS2 line. The AS1 annual response was about twice the AS2 response, for all traits analysed. Realised heritabilities when responses were obtained as deviations from control were 0.31±0.04 (YW: AS1 line), 0.33±0.06 (YW: HS1 line), and 0.23±0.05 (18W: AS2 line). Corresponding values after adjusting for genetic trend in the control were 0.40±0.05, 0.45±0.06 and 0.35±0.05, respectively. The realised genetic correlation between YW and 18W, derived from the direct and correlated responses in the AS1 and AS2 lines, was 0.96±0.12.

Reciprocal crossbreeding of Angus and Hereford cattle 3. Cow weight, reproduction, maternal performance, and lifetime production

Abstract Dam breed, sire breed, and heterosis effects on cow weight, reproduction, maternal performance, and lifetime production were estimated from purebred Angus (A × A), purebred Hereford (H × H), and crossbred (H × A and A x H) cows bred at the Waikite Land Development block near Rotorua over a 3-year period (1970 – 72). They were first mated as yearlings and the experiment lasted until the calves born in 1982 were weaned. The 273 cows represented 57 sire groups. The sire breed effect on cow weights was significant; Herefords were 5 – 11 kg (1 – 3%) heavier than Angus. The dam breed effect was in the same direction but not always significant. Heterosis, taken here as the crossbred value divided by the average purebred value, was 5 – 6% for cow weight. Surviving cows remained in the experiment for an average of six joinings, with sire breed and dam breed effects on survival (neither significant) favouring Angus. There was 9.6% heterosis for cow survival, with 29 crossbred cows (20% of those entering th...

Reciprocal crossbreeding of Angus and Hereford cattle 2. Steer growth and carcass traits

Abstract Breed and heterosis effects for growth and some carcass characteristics were estimated from purebred Angus (A x A), purebred Hereford (H x H), and crossbred (H x A and A x H) steers bred at the Waikite Land Development Block near Rotorua over a 4-year period. Data from 477 steers alive at 5-month weaning and 445 steers slaughtered at 20 monthsof- age were analysed. Age of dam and age of calf were significant non-genetic effects for all liveweights, 20-month carcass weight, and eye muscle area. The age of dam effect was not significant for average fat depth over the 12th rib of the ~arcass, but age of calf showed a significant effect. At a constant slaughter age (618 days) steers by Hereford sires had a higher slaughter liveweight, carcass weight, and dressing-out percent than those by Angus sires. Steers out of Hereford cows relative to those from Angus cows were heavier at slaughter and had heavier carcasses but there was no significant effect of cow breed on other carcass traits. At a constant ...