BREEDING AND GENETICS - American Society of Animal Science

292 Quantitative trait locus (QTL) analysis of the
bovine butyrophilin gene. A. Zegeye* 1 , M. Ashwell 2 , C.
Rexroad 2 , and I. H. Mather 1 , 1 University of Maryland, College Park,
2 ARS-USDA, Beltsville, MD.
Bovine butyrophilin (bBTN) is a mammary specific protein that is expressed
during late pregnancy and lactation. It localizes to the apical
surface of secretory epithelial cells, and is enriched in the milk-fatglobule
membrane. It possesses two exoplasmic Ig-like loops that share
significant homology with the B7 immune molecules. Moreover, the
gene encoding bBTN is found in the MHCI cluster. The cytoplasmic
tail contains the conserved domain called B30.2 that is also found in
other proteins. The tissue specificity of bBTN, the structural homology
with other proteins, and the chromosomal localization of the gene point
to possible roles for bBTN in lactation: in milk secretion and/or immunity.
The allelic substitution effects of bBTN on milk production and
udder health traits were investigated. Five intragenic molecular markers
in the form of PCR restriction fragment length polymorphisms (RFLPs)
were first identified: three within introns A and D, and two within exons
4 and 7. These markers were used to genotype grandsires and their sons
from a granddaughter design. A QTL analysis was conducted to identify
associations between bBTN and milk production and health traits
as per the model described by Ashwell et al. (Ashwell, M. et al., 1997,
Anim. Genet., 28, 216–222). Three grandsire families with a minimum
of 56 sons were used in the analysis. Seven traits were considered: milk
yield, milk fat yield, protein yield, % fat, % protein, somatic cell score
(SCS) and productive herd life. Most of the alleles showed no statistically
significant effect (P.05) between MFPD or PTA M values of the groups. Group 3 was
excluded from analysis because only one individual had this haplotype.
Even though the MspI site in intron 3 is located near a transcription
factor binding site and the MspI (+−) is associated with a .9 kb insertion/deletion
in the 3’ flanking region, potentially carrying transcription
regulator sites, neither this, nor the AluI(+−) or the presence of both
MspI(+−)/AluI(+−) in the current study resulted in difference in indicators
of genetic merit.
Key Words: Selection Marker, RFLP, Genetic Marker
J. Anim. Sci. Vol. 76, Suppl. 1/J. Dairy Sci. Vol. 81, Suppl. 1/1998 75