A. L. Rae

Genetic and phenotypic parameter estimates for selection to improve lamb carcass traits

Abstract The variance components needed to calculate genetic and phenotypic parameters for selection to improve carcass composition in white-faced sheep were estimated from a sire model using REML on data from 1602 Romney and Romneycross lambs. The sires were either Romney (n = 60), Border Leicester (n = 18), Poll Dorset (n = 14), or Coopworth (n = 10) with approximately 16 progeny per sire and all dams were Romney. Lambs had an average liveweight of 31.0 kg at an average age of 205 days. Carcasses were dissected into lean, subcutaneous fat, intermuscular fat, bone, and waste. The multivariate mixed linear model included birth date of the lamb as a linear covariate, year-rearing group, breed of sire, sex of lamb, birth rank, and slaughter group as fixed effects, and sire as a random effect. Traits were categorised as either lean, fat, or skeletal dimension indicators. Heritability estimates for lean indicator traits obtained by dissection averaged 0.36. The lean indicator trait with the highest heritabili...

Carcass characteristics of Southdown rams from high and low backfat selection lines

Abstract Carcass characteristics of Southdown rams from lines selected for high or low backfat depths (assessed ultrasonically at Position Cover the longissimus dorsi muscle at the last rib) were compared. Rams were 15-18 months old and average carcass weight was 29.5 kg fot the High-line (n = 36) and Low-line (n = 42) groups. When adjusted by covariance to the same carcass weight, animals from the High-line had higher dressing-out percentages, lighter weights of several internal organs, and shorter carcasses. At a constant side weight, the High-line sides contained 18% more dissectible fat and significantly lighter weights of muscle and bone. However, muscle to bone ratio and muscularity in terms of muscle weight per unit length were greater for the High-line group. The High-line carcasses contained a greater proportion of their weight in the rack and loin cuts. The greater weights of four dissectible fat depots in the High-line carcasses were the result of larger rather than more adipocytes. The results...

A note on liveweight gains of sheep grazing different ryegrass pastures

Abstract Three trials are described in which the liveweight gains, of sheep grazing different strains of ryegrass with and without white clover were compared. In the first trial, the pastures were: perennial ryegrass (P), perennial ryegrass plus white clover (P + C), short-rotation ryegrass (S), and short-rotation ryegrass plus white clover (S + C). The ranking of the pastures in order of decreasing liveweight gains was: S + C, P + C, Sand P. In the second trial, the pastures investigated were: Ariki ryegrass (A), Ariki rye grass plus white clover (A + C), P and S. A + C gave the greatest liveweight gain, followed by S, while A was intermediate between Sand P. The pastures in the third trial were: A, P, A + C, and Italian rye grass (I). I gave the greatest liveweight gain, followed by A + C. P and A, which were similar, gave the poorest liveweight gains, A separate comparison indicated no difference in liveweight gains between I and S.

Meat quality and muscle fibre type characteristics of Southdown Rams from high and low backfat selection lines.

Characteristics of the meat of 15-18-month Southdown rams from lines selected for high or low backfat depths (assessed ultrasonically at position C over the last rib) were compared. Half of the carcasses were electrically stimulated (ES) and within each carcass post-mortem treatments chosen to produce effects on meat tenderness were ageing periods of 1 or 15 days (Semimembranosus), early or delayed chilling (Biceps femoris), and trimming of the s.c. fat cover (Longissimus dorsi). These treatments had the expected effects on shear values, but the sizes of the effects were little affected by selection line or ES treatment. Selection line did not have any direct effects on shear values, reflectance values at several wavelengths, waterholding capacity, cooking loss or sarcomere length. The Semitendinosus muscle had a higher proportion of predominantly oxidative fibres for the high-backfat line, based on succinic dehydrogenase activity (P < 0·05), but there was no line difference in alkaline-stable ATPase activity in the same muscle. Muscle fibre diameter was similar for the two lines.

Resistance to cold stress in the newborn lamb 1. Responses of Romney, Drysdale × Romney, and Merino lambs to components of the thermal environment

Abstract Newborn lambs aged 1-30 h were exposed to a range of environmental conditions (5-30°C ambient temperature|0.0-1.9 mls air speed|wet or dry) and their metabolic rates, rectal temperatures, and hind-limb skin temperatures examined. Wet lambs exhibited substantially greater metabolic rates (by 3.8-7.0 W/kg) than those tested when dry. The results indicate that wet Romney lambs may attain their summit metabolic rate of 12-22 W Ikg and become hypothermic at ambient temperatures as high as 15°C. Conversely, dry lambs are unlikely to become hypothermic unless air temperatures are well below freezing point. Lambs exposed to air movement (1.0-1.9 m/s) had elevated metabolic rates (by 0.8-1.5 W/kg) compared with those in still air. Drysdale x Romney lambs were better able to conserve body heat than Romneys. Wet Romney and Drysdale x Romney lambs exposed to a series of declining ambient temperatures were able to minimise the hind-limb skin temperature-air temperature gradient but dry lambs generally failed ...

Selection responses in New Zealand Romney sheep: 2. Selection for yearling greasy fleece weight

Data from a flock selected for high yearling greasy fleece weight and a randomly selected control group, derived from the same base flock, were analysed. Each flock contained 70-80 mixed-age breeding ewes mated to 4 rams each year. Data from yearlings born in the flocks from 1956 to 1979 were analysed. On average, they represented 8.5 generations. The accumulated selection differential in the selection flock was about 5 kg, and this resulted in a genetic response to selection of 0.7-0.8 kg in yearling greasy fleece weight. Estimates of the realised heritability of greasy fleece weight ranged from O. 10 to 0.17. Several significant correlated responses occurred in the yearling data. Relative to control flock means: clean fleece weight, staple length, mean fibre diameter, clean scoured yield, weaning weight, and liveweight increased; whereas quality number and crimp frequency decreased. Mean date-of-birth became earlier. Lifetime averages of the performance of ewes born between 1956 and 1971 indica...

Selection response in New Zealand Romney sheep

Abstract Data from a flock selected for wool-free faces, and a random-selected control group derived from the same base flock were analysed. Each flock consisted of 70–80 breeding ewes, mated usually to 4 rams each year. Estimates of the realised heritability of face-cover grade ranged from 0.44 to 0.68. Correlated responses derived from yearling data were generally negligible. Relative to control group means: liveweight, staple length, and fibre fineness increased slightly in both the yearling ewes and rams; clean scoured yield and fibre uniformity increased in the yearling ewes; and fleece weights were slightly lower in both sexes. Data on the lifetime averages of ewes born between 1956 and 1971 indicated that, relative to the control group, staple length and fibre fineness showed small increases.

Resistance to cold stress in the newborn lamb 2. Role of body weight, birth rank, and some birth coat characters as determinants of resistance to cold stress

Abstract The effects of body weight and birth rank on resistance to cold stress were examined in Romneytype and Nd-type lambs. Twins exhibited lower coat depths than singles and they also appeared to have a lower summit metabolic rate per kg body weight. These effects were, however, small and the greater rate of body cooling experienced by twin lambs was principally a function of their low body weights. Sire of .the lamb exerted a small influence on its body weight and coat depth but these differences were not translated into a corresponding effect on the rate of decline in rectal temperature. Nd-type lambs had significantly greater coat depths and midside wool weights (per unit area of skin) than Romney-type lambs. The metabolic rate required by the lamb to maintain deep-body temperature was significantly related to coat depth (b = - 0.14 W Ikglmm) but not to midside wool weight. Rate of decline in rectal temperature was also low in deep-coated lambs. Most of the difference between Romney-type and Nd-typ...

Analysis of records of a Perendale flock

Abstract Genetic parameters for weaning and yearling (14-15 months) traits were estimated using 3313 half-sib records from 62 sires and 1720 daughter-dam pairs. The estimates of heritability by paternal half-sib and daughter-dam regression analyses were respectively: weaning weight (WW) 0.20 and 0.16, hogget body weight (BW) 0.27 and 0.44, greasy fleece weight (FW) 0.32 and 0.30, quality number (ON) 0.26 and 0.13, fibre diameter (FD) 0.54 and 0.47, staple length (SL) 0.49 and 0.35, and fleece character (FC) 0.23 and 0.23. Estimates of genetic correlations were in the following ranges: Medium negative (−0.4 to −0.6) BW × FC, ON × SL; Low negative (−0.2 to −0.4) WW × ON, FD × FC, ON × FW, ON × FD; Low positive (0.2 to 0.4) BW × WW, BW × ON, SL × FC; Medium positive (0.4 to 0.6) FW × FD, FW × FC; High positive (0.6 and over) FW × SL. Phenotypic correlations generally agreed with the genetic correlations. Important exceptions were BW × FW and BW × FD. Among the environmental factors studied, age-of-dam and re...

Repeatability of weight-corrected ultrasonic fat-depth measurements made on ewes at intervals of one year

Abstract The repeatability of ultrasonically measured fat depths in Southdown and Romney ewes was investigated by making these measurements shortly before mating in each of four successive years.Animals were allocated to fat or meaty groups within each breed based on the first weight-corrected measurement,and group differences were effectively maintained over the duration of the experiment.The fat groups of both breeds had shorter average body lengths at a set weight than the corresponding meaty groups, but the groups did not differ significantly in withers height.Intra-class correlations indicated that weight-corrected assessments of fat depth,body length, and withers height were only moderately repeatable over the four years, with the values for fat depth of Southdowns (n = 68) and Romneys(n = 71) being 0.36 and 0.54 respectively.