M. D. MacNeil

Genome-wide scans for QTL affecting carcass traits in Hereford x composite double backcross populations

A genome-wide scan for chromosomal regions influencing carcass traits was conducted spanning 2.413 morgans on 29 bovine autosomes using 229 microsatellite markers. Two paternal half-sib families of backcross progenies were produced by mating Hereford x composite gene combination (CGC) bulls to both Hereford and CGC dams. Progeny of the first sire (n = 146) were born in 1996 and progeny of the second sire (n = 112) were born in 1997. Each year cattle were fed out and slaughtered serially when they were between 614 and 741 d of age. Phenotypes measured at harvest were: live weight; carcass weight; fat depth; marbling; percentage kidney, pelvic, and heart fat (KPH); and rib eye area. Dressing percentage and USDA Yield Grade were calculated from these data. The phenotypes were adjusted to age-, live weight-, and fat depth-constant endpoints using analysis of covariance. The resulting residuals were analyzed by interval mapping to detect QTL. Within family, nominal significance was established by permutation analysis. Approximate genomewide significance levels were established by applying the Bonferroni correction to the nominal probability levels. Regression and error sums of squares and degrees of freedom were pooled across families when suggestive linkage identified in one family was confirmed in the other. The results indicate promising locations for QTL affecting live weight on BTA 17 and marbling on BTA 2 that segregate in Bos taurus. Also, previously identified linkage between central markers on BTA 5 and USDA Yield Grade was confirmed in one family. Greater marker saturation in these regions coupled with refined methods for data analysis will lead to more precise determination of QTL positions.

Variation in Mitochondrial DNA and Microsatellite DNA in Caribou (Rangifer tarandus) in North America

Abstract Genetic variation of caribou (Rangifer tarandus) at 18 microsatellite DNA loci and the cytochrome-b gene of mitochondrial DNA (mtDNA) was quantified in 11 herds of 3 North American subspecies: Alaskan barren ground caribou (R. t. granti), Canadian barren ground caribou (R. t. groenlandicus), and woodland caribou (R. t. caribou). Phylogenetic analysis of 1,194 nucleotides of cytochrome-b sequence resulted in a clade of 52 genotypes in R. t. granti, R. t. groenlandicus, and in 1 herd of R. t. caribou, and a clade of 7 genotypes in R. t. caribou. mtDNA sequence divergence is approximately 1% between these clades and 0.3–0.6% within these clades. The subspecies do not have monophyletic mtDNA, but do have different frequencies of mtDNA genotypes. Microsatellite allele frequencies also are differentiated between the woodland (R. t. caribou) and barren ground (R. t. granti and R. t. groenlandicus) subspecies. An exception is the George River herd in Labrador, which is classified as R. t. caribou but has mtDNA and microsatellite allele frequencies intermediate between the other herds of R. t. caribou and R. t. groenlandicus. Within subspecies, there is relatively low differentiation of microsatellite allele frequencies and mtDNA genotypes among herds of R. t. granti and R. t. groenlandicus, and relatively high differentiation of microsatellite alleles and mtDNA genotypes among herds of R. t. caribou in 4 geographically separate areas in Canada. The extent of differentiation of mtDNA genotype frequencies and microsatellite allele frequencies within and among each subspecies reflects past and present gene flow among herds. Issues related to subspecies, populations, ecotypes, and herds are discussed.

Genetic Variation and Differentiation of Bison (Bison bison) Subspecies and Cattle (Bos taurus) Breeds and Subspecies

The genetic relationship of American plains bison (Bison bison bison) and wood bison (Bison bison athabascae) was quantified and compared with that among breeds and subspecies of cattle. Plains bison from 9 herds (N = 136), wood bison from 3 herds (N = 65), taurine cattle (Bos taurus taurus) from 14 breeds (N = 244), and indicine cattle (Bos taurus indicus) from 2 breeds (N = 53) were genotyped for 29 polymorphic microsatellite loci. Bayesian cluster analyses indicate 3 groups, 2 of which are plains bison and 1 of which is wood bison with some admixture, and genetic distances do not show plains bison and wood bison as distinct groups. Differentiation of wood bison and plains bison is also significantly less than that of cattle breeds and subspecies. These and other genetic data and historical interbreeding of bison do not support recognition of extant plains bison and wood bison as phylogenetically distinct subspecies.

Suppression of annual bromes impacts rangeland: vegetation responses.

Presence of invading annual bromes (Bromus spp.) can alter seasonal patterns of forage production and quality and require management changes for efficient use of infested rangelands in the Northern Great Plains. We studied biological impacts of the presence of brome by comparing brome infested rangeland to similar sites in which brome had been suppressed with autumn applications of atrazine [6-chloro-N-ethyl-N’-(1-methylethyl)1,3,5-triazine-2,4-diamine] at 0.56 kg ha in 1992 and 1993. Each treatment was randomly assigned to three, 12-ha pastures. Vegetation was measured for 5 months (May to September) each year from 1993 to 1995. Each pasture was stocked with 8 crossbred steers (Bos taurus) from mid-May to mid-September 1993 and 1995 and to mid-August 1994. The forage base varied temporally by date and year, but generally was not less than 800 kg ha. Brome suppression increased (P ≤ 0.05) crude protein concentration for western wheatgrass (Pascopyrum smithii Rydb. [Love]) in July (7.1 vs. 9.1%) and August (6.0 vs. 7.1%). With the variation in annual brome stands among years, as influenced by growing conditions, this experiment demonstrated that improvement in forage nutritional quality can be expected from suppression of annual bromes on semiarid rangelands.

Effects of preovulatory estradiol on embryo survival and pregnancy establishment in beef cows.

The role of preovulatory estradiol on post-fertilization embryo survival and pregnancy establishment has not been well characterized in beef cows. We hypothesized that preovulatory estradiol is important for embryo survival and pregnancy establishment in beef cows. Twenty-four ovariectomized multiparous cows were used in a replicated 3×3 Latin Square design. Cows received estradiol cypionate (ECP) 36h, estradiol benzoate (EB) 12h, or no estradiol (CON) before a gonadotropin-releasing hormone (d 0) induced LH surge. Luteal phase progesterone was mimicked with twice daily progesterone injections from d 3 to 6. On d 7 cows received one embryo and progesterone was supplemented with progesterone-releasing devices (CIDR). Expression of interferon stimulated genes, ISG15, MX2, and OAS1, in leukocytes was determined on d 17, 19, 21, and 28 to determine capability of embryonic signaling. Pregnancy specific protein B concentrations were measured in serum samples from d 17 through 29 to determine embryonic attachment. Transrectal ultrasonography was performed on d 29 and 32 to determine pregnancy viability (heartbeat). Serum estradiol profiles during simulated proestrus/estrus were different (P<0.001) between treatments. Mean serum progesterone concentrations from d 17 to 24 were decreased (P=0.05) in EB and ECP cows compared to CON. Transrectal ultrasonography indicated that fewer CON (4%) cows had a viable embryo present compared to estradiol treated cows (25%). Embryonic loss in cows that did not receive estradiol during the simulated preovulatory period occurred following maternal recognition of pregnancy, indicating that its impact was likely on uterine receptivity and embryonic attachment.

Effect of reduced heifer nutrition during in utero and post-weaning development on glucose and acetate kinetics.

Energetic efficiency was evaluated in composite bred heifers born from dams receiving 1·8 or 1·2 kg/d winter supplementation for approximately 80 d before parturition. Heifers were then developed post-weaning and randomly assigned to heifer development treatments of either control (100 %; ad libitum; n 8/year) or restricted (80 %; fed 80 % of supplementation fed to controls adjusted to a common body weight: n 8/year) in a 2-year study. A glucose tolerance test (GTT) and acetate irreversible loss test (AILT) were administered to heifers at the termination of a 140 d development period when the heifers were approximately 403 d of age and consumed a silage-based diet, and again at 940 d of age when pregnant with their second calf and grazing dormant forage. No differences were measured (P>0·08) for dam winter nutrition or heifer development treatment for baseline serum metabolites or measures in either the GTT or the AILT. However, changes in baseline serum concentrations (P>0·05) were different between metabolic challenges, which occurred at different stages of development. No difference in acetate disappearance (P = 0·18) and half-life (P = 0·66) was measured between the two metabolic challenges. A trend for glucose half-life to be shorter in heifers born from dams receiving in utero winter treatments that supplied 1·2 kg/d of winter supplementation was observed (P = 0·083). Heifers developed with lower total DM intake during a 140 d development period had similar glucose and acetate incorporation rates as ad libitum-fed heifers when evaluated at two different production stages.