Brown adipose tissue function in short-chain acyl-CoA dehydrogenase deficient mice

Brown adipose tissue is a highly specialized organ that uses mitochondrial fatty acid oxidation to fuel non-shivering thermogenesis. In mice, mutations in the acyl-CoA dehydrogenase family of fatty acid oxidation genes are associated with sensitivity to cold. Brown adipose tissue function has not previously been characterized in these knockout strains. Short-chain acyl-CoA dehydrogenase (SCAD) deficient mice were found to have increased brown adipose tissue mass as well as modest cardiac hypertrophy. Uncoupling protein-1 was reduced by 70% in brown adipose tissue and this was not due to a change in mitochondrial number, nor was it due to decreased signal transduction through protein kinase A which is known to be a major regulator of uncoupling protein-1 expression. PKA activity and in vitro lipolysis were normal in brown adipose tissue, although in white adipose tissue a modest increase in basal lipolysis was seen in SCAD−/− mice. Finally, an in vivo norepinephrine challenge of brown adipose tissue thermogenesis revealed normal heat production in SCAD−/− mice. These results suggest that reduced brown adipose tissue function is not the major factor causing cold sensitivity in acyl-CoA dehydrogenase knockout strains. We speculate that other mechanisms such as shivering capacity, cardiac function, and reduced hepatic glycogen stores are involved.     

Trait association of a genetic marker near the IGF-I gene in egg-laying chickens

The insulin-like growth factor I (IGF-I) gene was screened for genetic variants associated with trait means and trait correlations. Analysis of an unselected randomly mated White Leghorn population revealed a PstI restriction fragment length polymorphism (RFLP) in the 5' region of the gene which segregated at a frequency of 0.83 for the PstI(+) allele (presence of a PstI restriction site). A comparison of the three genotypic classes revealed that the PstI(-/-) genotype was associated with a significantly lower egg weight measured in three different time periods, while the PstI(+/-) genotype was significantly associated with a higher eggshell weight estimated from the egg weight and egg specific gravity. For eggshell weight, the effect was age dependent and significant only for the last two periods of egg laying. No genotype associations were found for body weight, feed consumption, and egg laying rates. Significant dominance effects of the IGF-I genotype were observed for two of the egg weight measurements and three of the eggshell weight estimates. Partial correlation analyses in the two most frequent genotypic classes, PstI(+/+) and PstI(+/-), revealed the presence of a regulatory loop between feed consumption, body weight, egg weight, and the rate of egg laying. Several aspects of this regulatory loop were different between the two genotypic classes. In particular, for the PstI(+/+) genotype, feed consumption was positively associated with egg weight, while there was no significant association for the PstI(+/-) genotype. Further, the degree of association of body weight with egg weight decreased with age in the genotypic class PstI(+/-), while it was constant for the PstI(+/+) genotype. The results indicated that the marker in the IGF-I gene was not only associated with changes in some trait means, but also with changes in the stability of the coordination between feed intake, body weight, and egg production traits.     

The effect of simultaneous selection on the genetic correlation

The theoretical effect of simultaneous selection on the genetic correlations between two traits over 20 generations was examined using simulation. For each generation, a population of 50 male and 50 female diploid gen otypes with 15 loci, each with two alleles, was synthesized. None of the loci exhibited dominance. Five loci affected only trait 1, 5 loci only trait 2 and 5 were pleiotropic (affected both traits). Initial allelic frequencies were equal at each locus. Phenotypes were created by adding a random normal deviation for each trait to the genotype. The size of this deviation for each trait determined its heritability (h²). Index selection with h² combinations of (0.15, 0.15), (0.15,0.45) and (0.45,0.45) and relative economic weights of (1, 1) and (1, 3) for each h² combination was employed. In each generation, the highest ranking 25 genotypes of each sex were used to generate the next generation with single-pair matings, each producing two male and two female offspring. One hundred replicates were run for both negative and positive correlations. With a positive initial value, the genetic correlation tended to decline (toward zero). The rates of change were moderately affected by index weights and h². With a negative initial value, the genetic correlation tended to decrease (towards -1). However, unequal heritabilities and unequal relative economic weights slowed the rate of change with the greatest imbalances tending to hold the correlation constant or move it toward zero. These simulations illustrate that changes in parameters over time can affect the selection practiced. Under some of the conditions simulated, the use of initial genetic parameter values without change could have potentially negative effects on overall genetic gain.     

The effects of rapid cooling (cold shock) of ram semen, photoperiod, and egg yolk in diluents on the survival of spermatozoa before and after freezing

The effects of rapid cooling of semen (cold shock) from 30 degrees C to various temperatures above 0 degrees C on survival of ram spermatozoa suspended in diluents with or without egg yolk were assessed before and after freezing. Rapid cooling of extended semen from 30 to 15 degrees C had little or no effect on spermatozoa survival before or after freezing. Rapid cooling of extended semen from 30 degrees C to 10, 5, or 0 degrees C was accompanied by a progressive decrease in percentage of motile spermatozoa and percentage of intact acrosomes before freezing and a decrease in percentage of motile spermatozoa and after freezing. The ability of spermatozoa motile after cold shock to survive freezing and thawing, evaluated as cryosurvival, was not significantly (P greater than 0.05) affected by the temperature to which semen was cooled. The addition of egg yolk to the initial extender had a beneficial effect on percentage of motile spermatozoa particularly after rapid cooling of semen to 10 and 5 degrees C. Although egg yolk had little effect before freezing on semen rapidly cooled to temperatures above 15 degrees C and therefore not actually cold shocked, it substantially improved the subsequent survival of spermatozoa after freezing and thawing. Percentage of motile spermatozoa after cooling and after freezing was generally higher when the semen was collected during a decreasing photoperiod than during an increasing photoperiod.     

Evaluation of a new diluent and different processing procedures for cryopreservation of ram semen

Ram semen was processed for freezing after initial dilution with a modified Tris-fructose diluent. Two aliquots were processed by cooling gradually to 5 degrees C, further dilution, equilibration and freezing in 0.5 ml straws either in pressurized liquid nitrogen (LN(2)) vapor (Method A) or on a block of dry ice (Method B). A third aliquot was cooled rapidly to 16 degrees C and then slowly to 5 degrees C, diluted further, equilibrated and frozen in straws in pressurized LN(2) vapor (Method C). The second dilution was carried out using a new diluent based on dextran-lactose. The diluted semen was equilibrated for 2 h before freezing. Semen was evaluated by artificial insemination (AI). The fertility of ewes bred by a double insemination with frozen-thawed semen processed by Methods A, B and C was 73% (n = 33), 67% (n = 30) and 80% (n = 30), respectively. In comparison, the fertility of ewes inseminated with fresh semen was 93% (n = 31). These preliminary data indicate an acceptable fertility can be achieved by AI with frozen-thawed semen processed using improved procedures.     

DNA polymorphisms in the chicken growth hormone gene: response to selection for disease resistance and association with egg production

Analysis of the growth hormone (GH) gene in 12 strains of White Leghorn chickens revealed restriction fragment length polymorphisms (RFLPs) at three Msp I sites and at a Sac I site. Based on linkage disequilibrium analysis, they gave rise to eight different alleles (i.e. combinations of RFLPs), with five occurring at frequencies above 5% in at least one strain. Pairs of GH–RFLPs were at near maximal linkage disequilibrium, suggesting either a lack of recombination or the presence of selection pressure during evolution of the GH gene. Allele frequencies were determined in 12 non-inbred strains derived from three different genetic bases. These strains had been selected either for an array of egg production traits, resistance to Marek's disease or resistance to avian leukosis. Selection for disease resistance was consistently correlated with an increase in the frequency of one of the alleles. One strain segregated for only two alleles, which differed by three RFLPs. Analysis of variance in this strain indicated that the GH allele co-selected with resistance was associated with a delayed onset of ovulation but a higher persistency of ovulation as age progressed, resulting in an overall increase of egg production by 15% (age at first egg to 497 days). The resistance-associated GH allele was dominant for the onset of ovulation and recessive for the persistency of egg production. There was no significant effect of the GH genotype on juvenile body weight, egg weight or egg specific gravity.     

The effect of glycerol-related osmotic changes on post-thaw motility and acrosomal integrity of ram spermatozoa

Ram semen, collected by artificial vagina, was diluted and processed for long-term storage as described by P. S. Fiser, L. Ainsworth, and R. W. Fairfull (Canad. J. Anim. Sci. 62, 425-428, 1982). The concentration of the cryoprotectant, glycerol, was adjusted to 4% in the diluted semen prior to freezing by a one-step addition at 30 degrees C (Method 1), by cooling the semen to 5 degrees C and addition of the glycerol gradually over 30 min (Method 2), by one-step addition of glycerol prior to equilibration for 2 hr (Method 3), or by cooling to 5 degrees C, followed by a holding period of 2 hr at 5 degrees C, and the one-step addition of glycerol just prior to freezing (Method 4). After thawing, the glycerol concentration of the semen was reduced by stepwise dilution from 4 to 0.4% over 15 or 30 min or by a one-step ten-fold dilution. The average post-thaw percentage of motile spermatozoa was significantly lower after addition of glycerol by Method 1 (39.9%) than when the glycerol was added by the other three methods (range, 44.0-46.4% averaged over the glycerol dilution). The average post-thaw percentage of intact acrosomes (61.2%), highest in semen in which the glycerol was added by Method 2, was not significantly different from those in which glycerol was added to semen by Methods 3 and 4, but it was significantly higher than that found in semen in which the glycerol was added by Method 1 (54.4%). However, when averaged over the method of glycerolation, the post-thaw percentage of motile spermatozoa (range, 43.7-44.2%) and the percentage of intact acrosomes (range, 56.8-59.5%) did not differ significantly in semen subjected to gradual decrease in glycerol concentration and diluent osmolality (over 15 and 30 min) or by a one-step, 10-fold dilution. These data indicate that post-thaw survival of spermatozoa can be influenced by the way in which glycerol is added prior to freezing. However, post-thaw spermatozoa motility and acrosomal integrity can be maintained even after a rapid decrease in glycerol concentration such as that which accompanies insemination or dilution of semen for assessment of motility.