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Biomedical subjects

G L Bennett

Publications and source records attributed to G L Bennett.

114 records · Page 7Linked to original sources
PubMed1986

Birth weight, dystocia and calf mortality in some New Zealand beef breeding herds.

Calf mortality data were summarized from four experiments, including a total of 15,694 birth records over 39 herd-years. Two experiments at Waikite and Waikeria were long-term, straightbred Angus and Hereford selection trials and the other two, at Goudies and Tokanui stations, were comparisons of 11 sire breeds mated to Angus and Herefore cows. The objective of the analyses was to study the relationship between birth weight (BW) and calf mortality for both calf sexes and for different dam age or parity groups. Overall calf death rates from birth to weaning were greater (P less than .01) from 2-yr-old than from older dams at Waikite (13.4 vs 5.3%) and Waikeria (14.7 vs 5.2%). Sex differences in death rate within 2 d of birth were small for calves from older dams. Death rate of males vs females from 2-yr-old dams were 9.1 vs 3.2% (Waikite) and 17.7 vs 10.5% (Waikeria). Mature Angus dams at Goudies had 3.7% calf deaths at birth (4.9 vs 2.4% for males vs females), a further 1.8% calf deaths to weaning and 4.6% assisted births. The BW of calves at Waikite from Angus 2-yr-old vs older dams averaged, respectively, 6.8 and 6.5% of their dam's precalving live weights. Corresponding figures for Waikeria Angus were 7.8 and 6.6% and for Waikite Herefords, 7.3 and 6.9%. Quadratic regressions revealed that, on a whole-herd basis, a small increase in BW would have no effect on total mortality at Waikeria and would decrease total mortality at Waikite; regression lines were different in shape and minimum value for calves from the two dam age groups. Quadratic models also provided an adequate fit to data from Goudies and Tokanui. There was no particular threshold BW.

Animals↗
PubMed1983

Expected relative responses to selection for alternative measures of life cycle economic efficiency of pork production.

Relative genetic responses to selection for alternative measures of economic efficiency of pork production were examined. The analysis was based on results from a deterministic bio-economic model of lifecycle pork production. Alternative aggregate breeding values considered were based on cost (+)/unit of live weight or of carcass output lean for different production systems and for different breeding roles of the selected stocks. For cost/unit of lean, changes in leanness (or fatness) dominated the index. For cost/unit of live weight, however, no one trait dominated the index, and changes in growth and reproductive traits as well as the breeding role of the stock (purebred, maternal or paternal) were important in defining selection objectives. Management and production systems were less important than breeding role for cost/unit live weight output, except that importance of growth rate was increased by marketing at the mean weight reached at a fixed age rather than at a fixed weight irrespective of age. Implications of these results for goals and systems of pig improvement are discussed.

Adipose Tissue↗
PubMed1983

Use of repeated matings to estimate environmental and genetic trends and effects of relaxing selection in a selected strain of Leghorn chickens.

Response from index selection for egg production traits in a Leghorn strain over 7 years was partitioned into estimates of total (delta T), temporary (delta R), and net genetic (delta G) response, by producing progeny from selected (A) and unselected (D) first year breeders and from second year breeders (B) and first year full-sisters of previous years A breeders (C). In A, B, C, and D populations, average yearly number of full-sib families was 121, 47, 37, and about 50 and of birds with complete records was 824, 287, 258, and 298. Restricting A to repeated B families added positive bias in delta G for viability, age at first egg, and rate of lay. Estimates of delta G and delta R from B and C populations were similar. Yearly environmental change (delta E) was over three times the phenotypic change (delta P) for egg numbers, emphasizing necessity for intra-year estimates of delta G and delta R. Temporary response (delta R) approached or exceeded total response (delta T) for mortality and accounted for 40% of delta T for rate of lay and 60% for economic index, suggesting adverse maternal environmental effects from relaxing selection (D). Net yearly genetic change (delta G) was 1.5% for rate of lay, $.18 per bird, and in desired direction for most traits. Estimated net yearly response for rate of lay exceeded that predicted from .64 sigma male and .92 sigma female index selection differentials and sire-component genetic parameters (.6%) but agreed ($.16) for economic index. Efficiency and bias for the repeat-mating design are handicapped by mortality and health-related maternal effects.

Animals↗
PubMed1980

Genetic variance and correlation after selection for two traits by index, independent culling levels and extreme selection.

Three two-trait selection methods were analyzed for their effects on genetic variance and correlation by multivariate methods, two-locus methods and computer simulation. The two-trait selection methods studied were independent culling levels (ICL), index (IND) and extreme (EXT) selection. The effects of the selection methods on genetic variance and correlation were partitioned into permanent effects due to changes in gene frequencies and temporary effects due to nonrandom association of alleles at different loci. Multivariate methods were used to predict temporary effects from a single generation of selection by each method and from several generations of index selection. Two-locus theory was used to determine the stability and rank of temporary effects on genetic correlation for all three methods. Predictions were compared to computer simulation results. When selection increased the means of both traits, EXT had the lowest (closest to -1.0) genetic correlation and highest variances, while ICL tended to have the highest (closest to 1.0) genetic correlation. When selection increased the mean of one trait and decreased th mean of the other, EXT had the highest genetic variances and correlation, while ICL had the lowest genetic variance and correlation.

Alleles↗
PubMedDate not supplied

Surgical treatment of symptomatic accessory tarsal navicular.

We report a retrospective review of 50 consecutive patients (75 feet) with chronically symptomatic accessory tarsal naviculars that failed to improve with conservative treatment. Surgical treatment consisted of excision of the accessory tarsal navicular or medial protuberance of a prominent cornuate-shaped navicular combined with simple replication of the tibialis posterior tendon without altering its course. Good and excellent results were obtained in 45 (70 feet) of the 50 patients (90%). The procedure has a low rate of minor complications, is easy to perform, and is extremely well accepted by the patients.

Adolescent↗