Advances in methodology for utilizing sequential records

There have been substantial advances in recent years in methods for genetic analysis of traits that are expressed repeatedly over time, for example milk yield on successive test days during lactation. The background to the methods, notably random regression, covariance functions and splines, are outlined. The utility of these methods for analysing functional data on which individual records on cows are few but sire family records that span the lactation, is reviewed. Methods of analyses for measures of herd life are discussed and that being adopted in the UK is outlined.

An experimental comparison of selection methods

Five methods of selection each in five replicates were examined for single-generation response in high and low 21-day pupal weight of Tribolium castaneum. The methods of selection tested were individual (ID), dam family or full (DF), sire family or half-sib (SF), progeny test (PT), and index (IX). A selection intensity, involving as parents the top 25% of the individuals on any specific phenotypic scale, was applied throughout the experiment. Each replicate included a contemporaneous, randomly mated control line. Responses attained with each method were compared with predicted gains and with results observed for other methods. Differences in responses of males and females were also assessed. Response to selection was markedly asymmetrical with greater gains observed in the downward direction. In the lines selected for low pupal weight, males and females were found to respond similarly and actual responses did not differ from those predicted. Ranking of methods by responses obtained for downward selection yielded the order IX > ID > PT > DF > SF. Selection for high pupal weight yielded differences in responses of males and females and the observed responses were significantly less than those predicted in all cases except that of PT-selected females. Observed responses for males were ordered as IX > ID > PT > DF > SF, while those for females were PT > IX > DF > SF > ID. When the data from both sexes were combined, the order of responses was PT > IX > DF > ID > SF.Key words: asymmetrical response, selection, Tribolium, pupal weight.

Selection for prolificacy in pigs

Pigs can be bred at 6 months of age. By this time it is possible for their dams to have two litter records (at 12 months and 18 months of age) on which selection for litter size can be based. Hence, a generation interval of one year for both males and females can be achieved. Ollivier (1974), has shown that this system maximizes the rates of response. The accuracy with which replacements are chosen can be increased further by including information from other relatives (dam and sire family) in a selection index.

Environmental and genetic causes of variation in production traits of Damascus goats. 1. Pre-weaning and post-weaning growth

ABSTRACTData on 1542 Damascus kids, collected from 1977 to 1981, were used to study environmental and genetic factors influencing pre-weaning and post-weaning growth traits of kids. Season of birth, type of birth, sex of kid and dam lactation number were the environmental factors investigated. Phenotypic and genetic parameters were estimated from paternal half-sib correlations. The average sire family size was 17·2 kids. Single kids were heavier at birth, at weaning and at 140 days of age than twins or other multiples (P < 0·01). Male kids were heavier (P < 0·01) and grew faster (P < 0·01) than female kids from birth to 140 days of age (4·7 and 4·2 at birth, and 29·2 and 24·6 kg at 140 days, respectively). Dam lactation number significantly affected pre-weaning growth, but had no effect on the post-weaning growth rate of kids.Heritabilities for birth, weaning and 140-day weights, and pre-weaning and post-weaning growth rate, were 0·31 (s.e. 0·08), 0·27 (s.e. 0·07), 0·21 (s.e. 0·07), 0·16 (s.e. 0·06) and 0·22 (s.e. 0·07), respectively. Genetic correlations were mostly high and all positive, especially between weaning weight and 140-day weight (0·82 (s.e. 0·08)), and pre-weaning growth rate and 140-day weight (0·80 (s.e. 0·10)). The corresponding phenotypic correlations were also high and positive (0·71 and 0·67, respectively). No genetic antagonisms were found among the characters studied. Response to selection for post-weaning growth should be effective.

Close linkage between albumin and vitamin D binding protein (Gc) loci in chicken: a 300 million year old linkage group

SUMMARYEvidence for close genetic linkage between the structural loci for serum albumin (Alb) and serum vitamin D binding protein (Gc) in chicken is presented. The results are based on a study of a single sire family comprising 36 informative offspring. No recombinants have been observed. It is concluded that this linkage in the chicken is homologous to the close linkage of the albumin and Gc loci reported in man and the horse. Thus, this linkage group has most probably been conserved for at least 300 million years.