D. R. Notter

Heritabilities and genetic correlations of body weight, testis growth and ewe lamb reproductive traits in crossbred sheep

Heritabilities (h2) and genetic correlations (rc) involving body weights, measures of testes size and ewe lamb reproduction were calculated using 953 spring-born lambs produced during formation of a three-breed composite population containing 0·50 Dorset, 0·25 Rambouillet and 0·25 Finnish Landrace breeding. The h2 of body weight ranged from 0·2 to 0·3 between 45 and 150 days of age, but increased to 0·41 at the start of breeding of ewe lambs at about 6 months of age. Additive maternal effects were not important, perhaps because intensive housing encouraged cross-suckling. Testes size was measured as scrotal circumference (SC), SC with linear adjustment for weight (SCW) and SC divided by the one-third power of body weight (RSC). The h2 of SC traits was highest at 90 days (0·52 for SC, 0·62 for RSC and 0·57 for SCW), and h2 for age at maximum SC growth rate (i.e. TI, the inflexion point of a logistic SC growth curve) was 0·49. The h2 of ewe lamb fertility in autumn was 0·09 but the h2 for frequency of remating the following spring was 0·41. The h2 for ewe lamb litter size in these data was zero. At 90 days, rc between alternative measures of testes size exceeded 0·86; rG with body weight were 0·67 for SC, 0·53 for RSC and –0·74 for TI. The rG with ewe lamb fertility for 90-day weight, SC, RSC and SCW and for TI were –0·25, 0·20, 0·25, 0·38 and –0·32, respectively. The rc for these traits with spring remating were 0·34, 0·34, 0·26, 0·10 and –0·48, respectively.

Microarray analysis reveals difference in gene expression profiles of hair and wool sheep infected with Haemonchus contortus.

Sheep infected with the abomasal parasite, Haemonchus contortus, have reduced growth rates, decreased wool production, and anemia, and heavy infections may result in death. Anthelmintic treatment can remove worms, but the cost of treatment and prevalence of drug-resistant worms has led to greater focus on genetic resistance of the host to parasitism. Variation in parasite resistance exists within and among sheep breeds, and Caribbean hair sheep have greater resistance than most conventional wool breeds. Our objective was to investigate differences in gene expression between 24 parasite-resistant hair and 24 susceptible wool lambs to determine genetic mechanisms involved in resistance to H. contortus. Half of the animals of each breed were infected and sacrificed at 3 or 27 days post-infection; the remaining animals were uninfected controls. Breed differences in abomasum and abomasal lymph node tissue gene expression were assessed using bovine cDNA microarrays. Over 60 transcripts differed between breeds for each tissue and infection status. Genes differentially expressed between hair and wool sheep 3 days PI were assessed for gene function and mechanisms for greater immune cell infiltration, abomasal tissue repair, Th17 response, and anticoagulation were present in parasite-resistant hair sheep. By 27 days PI, hair sheep had greater expression of genes involved in gut motility, inflammatory cytokines, and cell proliferation and differentiation compared to wool sheep. Changes in these processes indicate Caribbean hair sheep have a stronger inflammatory response when infected with H. contortus which may facilitate the increased parasite resistance observed in these sheep.

Mitochondrial DNA-based analysis of genetic variation and relatedness among Sri Lankan indigenous chickens and the Ceylon junglefowl (Gallus lafayetti)

Indigenous chickens (IC) in developing countries provide a useful resource to detect novel genes in mitochondrial and nuclear genomes. Here, we investigated the level of genetic diversity in IC from five distinct regions of Sri Lanka using a PCR-based resequencing method. In addition, we investigated the relatedness of IC to different species of junglefowls including Ceylon (CJF; Gallus lafayetti), a subspecies that is endemic to Sri Lanka, green (Gallus varius), grey (Gallus sonneratii) and red (Gallus gallus) junglefowls. A total of 140 birds including eight CJF were used to screen the control region of the mitochondrial DNA sequence for single nucleotide polymorphisms (SNPs) and other variants. We detected and validated 44 SNPs, which formed 42 haplotypes and six haplogroups in IC. The SNPs observed in the CJF were distinct and the D-loop appeared to be missing a 62-bp segment found in IC and the red junglefowl. Among the six haplogroups of IC, only one was region-specific. Estimates of haplotype and nucleotide diversities ranged from 0.901 to 0.965 and from 0.011 to 0.013 respectively, and genetic divergence was generally low. Further, variation among individuals within regions accounted for 92% of the total molecular variation among birds. The Sri Lankan IC were more closely related to red and grey junglefowls than to CJF, indicating multiple origins. The molecular information on genetic diversity revealed in our study may be useful in developing genetic improvement and conservation strategies to better utilize indigenous Sri Lankan chicken resources.

B-mode, real-time ultrasound for estimating carcass measures in live sheep: Accuracy of ultrasound measures and their relationships with carcass yield and value,

Accuracy and repeatability of live-animal ultrasound measures, and the relationships of these measures with subprimal yields and carcass value, were investigated using data from 172 wethers. Wethers were F(1) progeny from the mating of 4 terminal sire breeds to Rambouillet ewes and were finished in a feedlot to a mean BW of 62.9 kg (SD = 9.5 kg). Before transport to slaughter, LM area, LM depth, and backfat thickness were measured from transverse ultrasound images taken between the 12th and 13th ribs. After slaughter, these measures were taken on each carcass. Carcasses were fabricated into subprimal cuts, and weights were recorded. Ultrasound accuracy and repeatability were assessed using bias, SE of prediction, SE of repeatability, and simple correlations. Relationships among ultrasound and carcass measures, and between these measures and carcass yield and value, were evaluated using residual correlations and linear prediction models. Ultrasound bias approached 0 for LM area, and backfat thickness was overestimated by only 0.69 mm. The SE of prediction and r were 1.55 cm(2) and 0.75 for LM area, and 1.4 mm and 0.81 for backfat thickness, respectively. The SE of repeatability was 1.31 cm(2) and 0.75 mm for LM area and backfat thickness, respectively. At a standardized BW and backfat thickness, wethers with larger LM area and LM depth yielded larger and more valuable carcasses, and these relationships were detectable with ultrasound. For each SD increase in carcass LM area, dressing percentage increased 1.57 percentage points, gross carcass value increased US

Genetic parameters for direct and maternal effects on body weights of Muzaffarnagari sheep

5.12, and boxed carcass value increased US

Managing the risk of comparing estimated breeding values across flocks or herds through connectedness: a review and application

6.84 (P < 0.001). For each SD increase in ultrasound LM area, dressing percentage increased 0.95 percentage points, gross carcass value increased US

Phenotypic and genetic associations between lamb growth traits and adult ewe body weights in western range sheep

3.15, and boxed carcass value increased US

Evaluation of Columbia, USMARC-Composite, Suffolk, and Texel rams as terminal sires in an extensive rangeland production system: I. Ewe productivity and crossbred lamb survival and preweaning growth

3.86 (P < 0.001). When LM area effects were adjusted for carcass weight, the response in boxed carcass value attributed to disproportionate increases in high-value subprimal cut weights was small. Associations of dressing percentage and carcass value with ultrasound and carcass LM depth were significant (P < 0.01) but smaller than corresponding associations with LM area. These data indicate biological and economical incentives for increasing LM area in wethers, and live-animal ultrasound can provide reliable estimates of carcass measures. These results are applicable to terminal sire breeders and producers who market sheep using carcass-merit pricing systems.

Direct and maternal (co)variance components and heritability estimates for body weights in Chokla sheep

Estimates of co(variance) components were obtained for weights at birth, weaning and 6, 9 and 12 months of age in Muzaffarnagari sheep maintained at the Central Institute for Research on Goats, Makhdoom, Mathura, India, over a period of 28 years (1976 to 2003). Records of 5530 lambs out of 169 rams and 1631 ewes were used for the study. Analyses were carried out by restricted maximum likelihood (REML), fitting six animal models, including various combinations of maternal effects. Heritability estimates for weight at birth, weaning and 6, 9 and 12 months of age were 0·09, 0·21, 0·06, 0·10 and 0·14, respectively. Maternal heritability of body weight declined from 0·07 at birth to 0·02 at weaning. The maternal permanent environmental component contributed 10 to 11% to the total variance for all traits except weight at 12 months. A significant large negative genetic correlation was observed between direct and maternal genetic effects on weaning weight, suggesting the presence of antagonistic environmental, as well as perhaps genetic, effects in daughter and dam. Results suggest that maternal additive effects were only important in early stages of growth, whereas a permanent environmental maternal effect existed at all ages up to 9 months, probably as a carry-over effect of maternal influences present at weaning. Modest rates of genetic progress appear possible for all weights, but the presence of an antagonism between direct and maternal effects on weaning weight would complicate attempts to improve both by selection.

Effects of ewe age and season of lambing on prolificacy in US Targhee, Suffolk, and Polypay sheep

Comparing predicted breeding values (BV) among animals in different management units (e.g. flocks, herds) is challenging if units have different genetic means. Unbiased estimates of differences in BV may be obtained by assigning base animals to genetic groups according to their unit of origin, but units must be connected to estimate group effects. If many small groups exist, error of BV prediction may be increased. Alternatively, genetic groups can be excluded from the statistical model, which may bias BV predictions. If adequate genetic connections exist among units, bias is reduced. Several measures of connectedness have been proposed, but their relationships to potential bias in BV predictions are not well defined. This study compares alternative strategies to connect small units and assesses the ability of different connectedness statistics to quantify potential bias in BV prediction. Connections established using common sires across units were most effective in reducing bias. The coefficient of determination of the mean difference in predicted BV was a perfect indicator of potential bias remaining when comparing individuals in separate units. However, this measure is difficult to calculate; correlated measures such as prediction errors of differences in unit means and correlations among prediction errors are suggested as practical alternatives.