Ultrasonic Backfat Thickness Research Articles

Genetically lean and fat sheep differ in their growth hormone response to growth hormone-releasing factor

The aim of this study was to compare the ovine growth hormone (oGH) responses of 5 genetically lean and 5 genetically fat 9 month old ram lambs (selected on the basis of their ultrasonic backfat thickness) given two 0.3 μg kg −1 liveweight intravenous injections of synthetic human pancreatic GH releasing factor analogue Nle 2 hGHRF 29 -NH 2 (GRF-29) 150 minutes apart. Plasma oGH response curves were analysed using an exponential 2 compartmental model and comparisons made through parallel curve analysis. Plasma oGH levels over 200 ng ml −1 were detected in response to GRF-29. Exponential model parameters indicated that lean lambs had a significantly higher rate of oGH release into the plasma after both consecutive GRF-29 injections, and a significantly lower rate of oGH clearance from the plasma after the second GRF-29 injection only. Significantly smaller peak oGH responses to the second GRF-29 injection were shown by the fat lambs. These results suggest that oGH release is impaired in genetically fat lambs and that either the synthesis of releasable oGH is reduced or the inhibitory tone is greater in the fat lambs. The lean and fat sheep may provide a useful model for the study of hormonal control of factors affecting leanness and fatness.

The influence of index selection for improved growth and carcass characteristics on appetite in a population of large white pigs

ABSTRACTCorrelated genetic changes in the level and pattern of average daily food intake (ADFI) were evaluated n i a population of pigs under index selection over an 11-year period. Performance testing was carried out in single sex groups of two or three full-sibs over the live-weight range 27 to 87 kg on an ad libitum feeding regime. The selection index incorporated live-weight gain, ultrasonic backfat thickness and a group food conversion ratio. Samples of boars from a contemporary control line were used to measure genetic change over time. Cumulated correlated responses in ADFI for boars and gilts showed considerable variation between years but the values were always negative and tended to increase up to year 7 but increased no further from then on. Thus, in year 11 the cumulated responses for ADFI in boars and gilts were -0·25 (s.e. 0·06) kg (P < 0·001) and -0·19 (s.e. 0·05) kg (P < 0001) respectively, the corresponding regressions of cumulated response on year number being — 0012 and — 0·017 kg. The relationship between food intake and live weight was compared in samples of boars and gilts from the selection line (S) and boars from the control line (C) during the final year of the study. The regression of ADFI on live weight for the two boar lines differed in intercept but not in slope with S line boars consuming, on average, 0·23 kg/day less meal than the C line boars over the test period. The regression equations for S line boars and gilts differed in slope and elevation with gilts consuming relatively more food daily up to around 60 kg live weight and less subsequently.

Sire × testing regime interactions in growing pigs

ABSTRACTCentral test data of two pig breeding companies were analysed to estimate sire × testing regime (S × T) interaction for ultrasonic backfat thickness (BT), life-time growth rate (GL) and growth rate during test (GT). Testing regime consisted of a combination of sex, test period and housing system (individual v. group housing). Data were analysed within five lines, with 5417, 8331, 3427, 2413 and 1263 records of progeny of 97, 162, 64, 69 and 33 sires, respectively. The data were collected from May 1983 until May 1987 (lines 1, 2 and 3) and from June 1985 until May 1987 (lines 4 and 5). Testing regime had a significant effect on BT (in three lines) and on GL and GT (in five lines). S × T interaction was significant only for BT in three lines and for GT in one line. Genetic correlations between identical traits, measured under the two testing regimes, varied from 0·64 to 1·00 for BT, from 0·65 to 1·00 for GL and from 0·62 to 1·00 for GT. Conclusively, within central test S × T interactions were relatively unimportant for BT, GT and GL.

Evaluation of cytoplasmic genetic effects in beef cattle using an animal model.

Mixed model techniques were used to evaluate the importance of cytoplasmic genetic effects on beef cattle performance. Birth weight (BWT), preweaning average daily gain (ADG), weaning weight (WT205), postweaning gain (PG), ultrasonic backfat thickness (FAT) and predicted milk yield (MILK) data were collected in two herds of Hereford cattle located at Plymouth and Raleigh, North Carolina. Cytoplasmic lines were determined based on the foundation female in the maternal lineage of each animal. An animal model was used to account for all nuclear genetic variation among animals within herds. Direct breeding values were estimated for all animals with records and their parents for all traits. For MILK, permanent environmental effects were estimated for animals with multiple records. For preweaning traits, maternal breeding values and permanent maternal environmental effects also were estimated. In all analyses, F-tests for cytoplasmic effects were not significant. Probability values approached significance (P = .15 to P = .10) only for PG and FAT at Plymouth. Assumptions regarding the ratios of genetic and environmental variances and covariances had no effect on F-tests. Results contrast with earlier analyses of the same data in which nuclear genetic effects were accounted for by including sire and maternal grandsire in the statistical model. This study failed to show that cytoplasmic genetic effects were important sources of variation in performance; residual additive genetic effects were confounded with cytoplasmic lines for these herds. Because cytoplasmic sources may be regarded as founder effects, further research is needed in other populations.

Effect of average daily food intake on production performance in growing pigs

ABSTRACTEffects of daily food intake (FI) on daily gain (DG), food conversion ratio (FCR), ultrasonic backfat thickness (BF), proportion of lean parts (LP), proportion of fatty parts (FP), lean tissue growth rate (LTGR), fatty tissue growth rate (FTGR) and lean tissue food conversion (LTFC) were investigated in 687 barrows and 98 gilts, slaughtered at a mean live weight of 108 kg and fattened in seven batches. In the range of food intake from about 1·7 to 3·2 kg/day (22 to 42 MJ digestible energy) a continuous distribution of data was available.Body composition was linearly related to FI. Most regressions of BF and all of LP and of FP on FI were linear, showing fatter animals at higher food intake. For FTGR, BF, LP and FP, parameter estimates based on linear regression were given. Although the response of DG and of LTGR on increasing FI was not always significantly different from linearity, the second degree polynomials indicated diminishing returns in all batches. FTGR had a high linear correlation with FI (0·85 to 0·95), indicating that in the present range of FI a rather fixed proportion of the food was used to deposit fatty tissue.For DG and LTGR a non-linear model of the type a(FI -fo)bwas fitted, wherefowas interpreted as maintenance requirement. For FCR and LTFC the corresponding model was FI/(α(FI —fo)b). Both models were preferred over second degree polynomials because of better interpretation of parameters. FCR and LTFC showed minima at about 2·6 and 2·2 kg/day food intake, but especially for FCR the increase at increasing FI was low. Results were not consistent in demonstrating or refuting a plateau in LTGR, which in any event appears to lie near to or beyondad libitumFI for most pigs.

Genotype × environment interactions in pig breeding programmes. I. Central test

In this first paper of a series, Dutch central test results are examined for genotype × environment interaction (G × E) and the data are further used to estimate genetic correlations between the various evaluations of growth and carcass quality, as used in the distinct environments of the breeding programme. G × E in pig breeding programmes is outlined as genotypes expressing different phenotypes in the distinct levels of the breeding programme or even in different environments within a level (e.g. herds). In most studies on G × E, the expectation of genetic correlation between similar traits measured in different environments has been taken to be one. Estimated correlations between similar traits measured on central tested pigs in this study indicate however, that expectations should be smaller, especially for carcass characteristics. Genetic correlations of carcass backfat thickness (CB) with ultrasonic backfat thickness (UB), normally used in on-farm tests, were 0.61 and 0.57 for Dutch Landrace (NL) and Dutch Yorkshire (GY), respectively. Correlations of UB with backfat class, as used in commercial fattening, were 0.25 and 0.42. Genetic correlations of ham + loin % with type class were 0.60 and 0.94. In future analyses of G × E these differences in genetic background of the traits should be taken into account. Genotype × batch and genotype × sex interactions were investigated for daily gain and feed conversion ratio. No significant interactions were found. However, for daily gain between arriving at the station and the end of the test, as well as for weight for age at the end of the test, genotype × batch interaction was significant ( P < 0.05). The possible causes of these interactions are discussed. For slaughter characteristics genotype × month interactions were not of significance.

Relationships between blood groups, isozymes and halothane reaction in pigs from a selection experiment.

German Landrace pigs (n = 1500) were halothane-tested and blood samples were taken for the determination of A-O and H blood types as well as for the determination of PHI and 6-PGD isozymes. The pigs originated from two generations (7th and 8th) of a selection experiment 'selection for activity of NADPH-generating enzymes in backfat of pigs'. The selection lines are E-, E+ (selection for low and high enzyme activity), U- (selection for low ultrasonic backfat thickness) and K (control). Preliminary results show an average proportion of halothane-susceptible animals of 49%. The frequencies of halothane-positive pigs amount to 60%, 46%, 70% and 30% in lines E-, E+, U- and K, respectively. The investigation shows a non-random combination of the marker genes caused by linkage disequilibrium, especially in line E-. Recombination frequencies between the loci vary from 0% to 18%.