Inbreeding in populations with incomplete pedigrees

Inbreeding has detrimental effects on a number of economically important traits. W iggans et al. (1995) estimated inbreeding depression of ?29 kg, ?1.08 kg and ?0.97 kg for each 1% increase of inbreeding for the traits milk, fat and protein yield, respectively, across several dairy cattle breeds. For post-weaning gain in Hereford cattle, the depression was ?0.24 kg (G engler et al. 1998). For the number of piglets born alive, 21-day litter weight, and days to 104.5 kg, it was ?0.023, ?0.052 and 0.21, respectively (C ulbertson et al. 1998). Inbreeding also adversely impacts reproductive traits, such as delayed puberty, reduced conception rates, higher likelihood of losing established pregnancies, increased mortality of calves and lowered bull fertility (Y oung et al. 1969). National genetic evaluations involve animals with incomplete pedigrees. Regular inbreeding algorithms (RA) based on the definition of W right (1922), such as those by Q uaas (1976), calculate the inbreeding of animals with at least one parent missing as zero. Even if an animal has both parents known, its inbreeding will be underestimated if some of its ancestors are unidentified. If the proportion of missing parents is large, the inbreeding trend in a population could be seriously underestimated. Subsequently, losses from inbreeding would be underestimated, and steps to slow the increase of inbreeding, such as using sires that are less related to the general population or mating less-related animals (T oro and P erez -E nciso , 1990; G rundy et al. 1994; M euwissen and S onneson 1998; V an R aden and S mith 1999), may be delayed. In particular, use of a mating system can result in matings adjusted for both inbreeding and dominance (M isztal et al. 1999). In populations that use AI substantially, unidentified parents may not differ genetically from identified parents, on average. Therefore the real average inbreeding in animals with unidentified parent(s) may be similar to their contemporaries with both parents known. V an R aden (1992) proposed an algorithm (VRA), where the inbreeding of animals whose parent(s) are unknown is equal to the mean inbreeding of their contemporaries with known parents. Contemporaries are stratified along unknown parent groups (UPG). VRA has been applied to a few US dairy breeds (V an R aden 1992; W iggans et al. 1995). The calculated inbreeding for the youngest Holstein animals was 3.7% with RA and increased to 4.2% with VRA (V an R aden 1992). The increase was small because the number of unidentified animals was small. However, the performance of VRA in recovering inbreeding lost for a range of incomplete pedigrees has not been evaluated. The objectives of this study were (i) to determine average inbreeding coefficients when pedigrees are increasingly more incomplete; (ii) to assess the efficacy of VRA in recovering these inbreeding coefficients; and (iii) to determine the mean inbreeding using the two inbreeding algorithms in a large beef population.     

Deposition rates and accretion patterns of intramuscular fat, loin muscle area, and backfat of Duroc pigs sired by boars from two time periods

A study was conducted to evaluate differences in performance and in carcass composition and tissue deposition rates between purebred Duroc pigs sired by boars currently available and those sired by boars from the mid-1980s. Two lines were developed by randomly allocating littermate and half-sib pairs of females to matings by current time period (CTP) or old time period (OTP) boars. Pigs from 2 replications were placed on test at a group mean BW of 63.5 kg. Serial ultrasonic measurements of the 10th-rib LM area (LMA), off-midline backfat (BF10), and intramuscular fat percentage (IMF) were collected every 2 wk in the first replication and used to assess deposition rate differences. Off-test ultrasonic LMA, BF10, and IMF measurements from a total of 557 pigs from 23 CTP sires and 232 pigs from 15 OTP sires across 2 replications and at a mean BW of 109 kg were evaluated. All available barrows and randomly selected gilts (n = 277) were sent to a commercial abattoir, and carcass measurements of 10th-rib backfat, last-rib backfat, last lumbar backfat, and LMA were collected. Analysis of serial backfat measurements revealed a linear relationship between back-fat and BW between 73 and 118 kg for pigs from both time periods. Pigs sired by OTP boars deposited more backfat (P < 0.05) at a faster rate than pigs sired by CTP boars over the entire test period. A curvilinear cumulative tissue deposition pattern was revealed for ultrasonically estimated LMA and IMF within both time periods. Significant linear and quadratic regression coefficient differences between lines indicated that pigs sired by CTP boars deposited more LMA and less IMF per kilogram of BW gain than pigs sired by OTP boars. Pigs sired by CTP boars had more LMA and less BF10 (P < 0.05), whereas pigs sired by OTP boars had more IMF (P = 0.04). Carcass evaluation revealed more (P < 0.01) carcass measurements of LMA and less (P < 0.05) carcass measurements of 10th-rib backfat, carcass measurements of last-rib backfat, and carcass measurements of last lumbar backfat for pigs sired by CTP boars. No difference (P > 0.05) between the time periods was found for ADG over the entire test period. Results from this study illustrate that significant progress in carcass composition has been realized within the Duroc breed since the mid-1980s. The long-term selection response in carcass leanness has also resulted in changes in deposition rates of correlated traits such as LMA and IMF.     

Comparison of two insulin protocols for diabetic dogs undergoing cataract surgery

Objective To evaluate the effectiveness of two insulin doses to maintain an acceptable range of blood glucose concentrations (70–200 mg dL^?1) in the peri‐operative period in diabetic dogs. Animals Twenty‐four diabetic dogs with a median weight of 20.6 kg and a median age of 8 years old. Methods The dogs were randomly assigned to receive either 25 or 100% of their normal insulin dose subcutaneously on the morning of surgery. The anesthetic and feeding protocols were standardized. On the day before surgery, venous blood was collected for measurement of β‐hydroxybutyrate, cholesterol, glucose, glycosylated hemoglobin, hematocrit, total plasma protein and urea nitrogen. On the day of surgery, blood glucose concentrations were measured prior to anesthesia, prior to the start of surgery, 1 and 2 hours after beginning of surgery, 1 hour after extubation, at 16 : 00 hours and at 20 : 00 hours. β‐hydroxybutyrate concentrations were measured at 20 : 00 hours that day. At 08 : 00 hours the following day, β‐hydroxybutyrate and glucose concentrations were measured. The significance of differences between groups was tested with Wilcoxon's two‐tailed rank‐sum test, Chi‐square test and Fisher's exact test. Results There were no differences in insulin treatments, clinical signs, concurrent diseases and most clinicopathological parameters between the two groups of dogs at entry to the study. The 25% dose group had blood glucose values of 296 (102–601) mg dL^?1 at 16 : 00 hours and 429 (97–595) mg dL^?1 at 20 : 00 hours on the day of surgery. The 100% insulin dose group had lower corresponding values of 130 (55–375) mg dL^?1 (p = 0.04) and 185 (51–440) mg dL^?1 (p = 0.004). No other differences (p < 0.05) were detected between the two groups. Conclusions The administration of a full dose of insulin is only marginally advantageous for reducing glucose to normal (70–120 mg dL^?1) after anesthesia but neither dose consistently induced glycemic values in an acceptable range (70–200 mg dL^?1) or normoketonemia. Clinical relevance Blood glucose should be measured immediately before anesthesia and periodically throughout the peri‐operative period in all diabetic dogs because presurgical subcutaneous administration of 25 or 100% of the normal insulin dose resulted in unpredictable blood glucose concentrations.     

Estimation of direct and maternal heritability and genetic correlation for backfat and growth rate in swine using data from centrally tested Yorkshire boars.

The purpose of this study was to estimate components of variance and covariance for backfat and growth rate in swine tested in central test stations in the United States. Data were collected from 26 central boar test stations from 1984 through 1990. The traits analyzed were backfat adjusted to a 104.5-kg basis and ADG adjusted to a 36-kg on-test weight. Records from 7,951 purebred Yorkshire boars were analyzed. Contemporary groups were defined as boars of a breed that were tested and sold as a common group in a test station. Variance components were estimated using a pseudo-expectation method with a multiple-trait, sire-maternal grandsire model. Direct heritabilities for backfat and ADG were estimated to be .56 and .24, respectively. Direct maternal effects were significant for both backfat and ADG; they accounted for 11 and 23% of the variance, respectively. The additive genetic correlation between backfat and ADG was approximately zero. Within this population of centrally tested Yorkshire boars, heritability seems to be high for backfat and moderate for ADG, with a significant maternal effect on each trait.     

Prevalence of the causes of fleece derangement among sheep flocks in New South Wales

SUMMARY An investigation of sheep flocks with unknown histories of fleece derangement, selected at random from the main sheep raising areas of New South Wales, showed that Psorergates ovis was present in 53 of the 177 flocks surveyed and In 162 of the 3495 sheep examined. Of the single causes of fleece derangement, the most prevalent was grass seed contamination (15.7%) followed by Infestation with sheep body lice, Bovicola ovis, (14.7%) and Infestation with Itch mite (7.8%). The prevalence of fleece derangement was significantly higher on sheep In which lice were the only ectoparasites found than on those In which Itch mites were the only ectoparasites present. The greatest prevalence of P ovis was In flocks In the Young, Yass, Mudgee and Tenterfield districts. In most affected flocks, more than one potential cause of fleece derangement was present. Itch mite Infestation was more prevalent in flocks that received no treatment for ectoparasites than in those that had been treated in the year preceding the survey. Our results did not support a commonly held belief among farmers that arsenical compounds control Infestations of Itch mites more effectively than other types of pesticides. There was no significant difference in prevalence of fleece derangement between flocks treated with different pesticide groups and those that received no treatment, but mean fleece derangement score was significantly lower in sheep treated with organophosphates than in untreated sheep. Infestations of lice were significantly more prevalent in sheep from flocks treated with synthetic pyrethroids than from those treated with organophosphates or those that received no treatment.     

Genetic parameters and trends for lean growth rate and its comvonents in U.S. Yorkshire,Duroc, Hampshire,and Landrace pigs

Records on 361,300 Yorkshire, 154,833 Duroc, 99,311 Hampshire, and 71,097 Landrace pigs collected between 1985 and April of 2000 in herds on the National Swine Registry Swine Testing and Genetic Evaluation System were analyzed. Animal model and REML procedures were used to estimate random effects of animal genetic, common litter, maternal genetic, and the covariances between animal and maternal for lean growth rate (LGR), days to 113.5 kg (DAYS), backfat adjusted to 113.5 kg (BF), and loin eye area adjusted to 113.5 kg (LEA). Fixed effects of contemporary group and sex were also in the statistical model. Based on the single-trait model, estimates of heritabilities were 0.44, 0.44, 0.46, and 0.39 for LGR; 0.35, 0.40, 0.44, and 0.40 for DAYS; 0.48, 0.48, 0.49, and 0.48 for BF; and 0.33, 0.32, 0.35, and 0.31 for LEA in the Yorkshire, Duroc, Hampshire, and Landrace breeds, respectively. Estimates of maternal genetic effects were low and ranged from 0.01 to 0.05 for all traits across breeds. Estimates of common litter effects ranged from 0.07 to 0.16. A bivariate analysis was used to estimate the genetic correlations between lean growth traits. Average genetic correlations over four breeds were -0.83, -0.37, 0.44, -0.07, 0.08, and -0.37 for LGR with DAYS, BF, and LEA, DAYS with BF and LEA, and BF with LEA, respectively. Average genetic trends were 2.35 g/yr, -0.40 d/yr, -0.39 mm/yr, and 0.37 cm2/yr for LGR, DAYS, BF, and LEA, respectively. Results indicate that selection based on LGR can improve leanness and growth rate simultaneously and can be a useful biological selection criterion.     

Genetic parameters for pork carcass components

Data from 456 homozygous halothane normal purebred Yorkshire, Duroc, and Other-breed pigs from two national progeny testing and genetic evaluation programs were utilized to estimate genetic parameters for carcass components in pigs. Carcass components were cut and weighed according to Institutional Meat Purchase Specifications. Primal cut weights evaluated included 401 Ham (HAM), 410 Loin (LOIN), 405 Picnic shoulder (PIC), 406 Boston Butt (BB), and 409 Belly (BELLY). Individual muscle weights included the inside (INS), outside (OUT), and knuckle (KNU) muscles of the ham, the longissimus dorsi (LD) and psoas major (TEND) of the loin, and the boneless components of both the Boston Butt (BBUTT) and picnic (BPIC). Muscle weights from each primal were summed to yield a boneless subprimal weight (BHAM, BLOIN, BSHLDR), and all boneless subprimals were summed to yield total primal boneless lean (LEAN). Heritability estimates for HAM, LOIN, and BELLY were 0.57, 0.51, and 0.51, respectively. Heritability estimates for BB and PIC were 0.09 and 0.21, respectively. Heritability estimates for the boneless components of each primal were higher than those for the intact primals. Genetic correlations for HAM, LOIN, and PIC with loin muscle area (LMA) were 0.53, 0.78, and 0.70, respectively, and-0.62, -0.51, and -0.60, respectively, with 10th rib off-midline backfat (BF10). Boneless subprimal components were highly correlated with LEAN. Gilts had heavier weights (P < 0.01) than barrows for all boneless subprimals, individual muscles, LEAN, and for all primal cuts except BELLY. Gilts also had less BF10 and more LMA (P < 0.01) than barrows. Duroc pigs had a heavier (P < 0.01) weight for HAM and PIC when compared to Yorkshires. Yorkshire pigs had more (P < 0.01) LOIN weight than did the Durocs. Results suggest primal, boneless subprimal, and individual muscle weights in pigs should respond favorably to selection.