Blood group polymorphisms and production and type traits in dairy cattle : after forty years of research

Abstract

Inconsistencies across studies and analytical designs emphasize a problem inadequately addressed in most recent theoretical studies on QTL detection and MAS: that posed by the intrinsic non-additivity of genetic/biological phenomena. To ignore this leads to inflated expectations regarding the usefulness of markers for selection purposes. Consistency of results across designs was emphasized as the strategy most likely to yield meaningful accomplishments in the short-term. Three associations fitted this criterion. The $rm Msb2Mspprime$ allele of the M locus was also found directly associated with reduced milk yield ($-$351.9 kg) and protein yield ($-$11.6 kg), and its frequency decreased with time. It is suggested that the M blood type can already be used as a complementary selection criterion in Holstein breeding. $rm Msb2Mspprime$ positive animals should be viewed as primary candidates for culling. The L group was associated with effects on milk yield/composition traits. Averages of the within-family differences associated with alternative sire alleles were: 4.5 kg for PTA-fat yield (after adjustment for PTA-milk yield); 2.6 kg for PTA-protein yield (after adjustment for PTA-milk yield); 1,122.0 kg for milk yield;.19% for protein percentage; and.61% for fat percentage. The null allele was predominantly associated with decreases in yields and increases in percentages due to linkage disequilibrium between the loci, and its frequency decreased with time. There is insufficient disequilibrium for the immediate application of this effect, but further research to facilitate its utilization is discussed. There is evidence that a major gene for fat yield lies in the chromosomal segment marked by the S group. The estimate of its magnitude is 78.6 kg (1.3 $rmsigmasb{p}$) for the average of the absolute values of within-family contrasts. QTL impacting rump angle appear to be present in the C group-marked segment. The economic importance of these effects in MAS schemes is not clear. Distortions of within-family allele segregation ratios for the F and Z systems are occurring and impacting allele frequencies. Although short-term applications should not be disregarded, an enhanced understanding of the biochemical/physiological basis of quantitative genetics should probably at this stage be formulated as the ultimate objective of this type of genetic analysis.