Pre-weaning Traits Research Articles

Heritabilities of pre-weaning traits in a multibreed beef cattle herd fitting models with or without a sire genotype x dam genotype interaction

Animal breeders are concerned with unbiased estimation of genetic parameters, since it also has aninfluence on the accuracy of predicted breeding values. In many studies, additive genetic variances are often eitherover- or under-estimated. In multibreed (crossbred or composite breeds) evaluations these parameters aresometimes overestimated when it is assumed that non-additive differences are absent. Estimates will especially bebiased if the correct covariance structure is not employed ( Komender & Hoeschele, 1989), such as where there is anon-random distribution of sires across genotypes, i.e. if certain sires are more frequently used within certaingroups than in others. Animal (or sire) effects are then confounded with group effects, thus resulting in the biasedestimates. The objective of this investigation was to compare heritabilities where the sire genotype x dam genotypeinteraction was fitted into the model to account for non-additive variances and the non-random distribution of siregenotypes compared to where it was not fitted.

Genetic parameters for direct and maternal effects on weights and ultrasonic muscle and fat depth of lambs

Genetic parameters were estimated for liveweights, total weight gains and ultrasonic muscle and fat depth of lambs at two different ages using a single trait animal model including direct and maternal genetic effect, and an environmental effect. Records of 972 lambs descending from 60 rams and 295 ewes were analysed by DFREML procedures. The approximate sampling correlation between the estimates indicated that the variance components of the maternal genetic effect and the covariance between the direct and maternal genetic effects were the most difficult parameters to estimate precisely. The correlation between the direct and maternal genetic effects was close to zero (−0.10–0.04) for all traits. Direct heritability estimates for weight declined slightly according to age from 0.22 at birth to 0.12 at weaning. The heritability estimate on maternal effect was very high for birth weight (0.42), and slightly lower for pre-weaning weight (0.14) than for weaning weight (0.17). The direct and maternal heritability estimates for ultrasonic measurements were generally low, except for the direct heritability for muscle depth at weaning (0.32). The results indicate that selection for maternal ability will not be more efficient by including pre-weaning traits in the selection index.

Effects of inbreeding and heterozygosity on preweaning traits in a closed population of Herefords under selection.

Records of five inbred lines at the Livestock and Range Research Laboratory were used to evaluate effects of inbreeding and heterozygosity on preweaning traits. Members of each line were descendants of a single founder Hereford bull. A total of 8,065 records of birth weight and 7,380 records of preweaning daily gain and weaning weight were analyzed by derivative-free REML using a model that included fixed effects of sex, combination of year and month of birth and parity of dam, with covariates for direct and maternal genetic fractions of inheritance from the genetic groups, inbreeding, and heterozygosity fractions. Heterozygosity fractions were computed for crosses between lines. The random model effects were direct and maternal genetic and uncorrelated maternal permanent environmental and temporary environmental. Direct inbreeding and heterozygosity fractions averaged .098 and .343, and maternal inbreeding and heterozygosity fractions averaged .075 and .294. Regression coefficients of traits on direct and maternal inbreeding fractions were -5.8 +/- 1.1 and -4.7 +/- 1.3 for birth weight, -.189 +/- .031 and -.252 +/- .039 for preweaning daily gain, and -44.5 +/- 6.6 and -56.1 +/- 8.4 kg for weaning weight. Estimates for direct heritability, maternal heritability, and direct-maternal genetic correlations were .37, .12, and -.01 for birth weight; .16, .25, and -.27 for daily gain; and .17, .26, and -.21 for weaning weight. Results suggest that heterosis represents recovery of accumulated inbreeding depression. Results also indicate that selection can overcome inbreeding depression and antagonism exists between direct and maternal genetic effects for preweaning traits.

Genetic and phenotypic parameters for birth and weaning weights of purebred and crossbred Ndama and West African Shorthorn cattle

Calf records for a 30 year period (1965–1995) on purebred and crossbred Ndama and West African Shorthorn (WASH) cattle and their crosses with Santa Gertrudis or Red Poll were analyzed to determine factors affecting birth and weaning weights and to estimate genetic parameters. Male calves weighed heavier ( P < 0.05) at birth and at weaning. Similarly period (year grouping) significantly influenced birth and weaning weights of calves. Season of birth did not influence calf weight at birth but significantly affected calf weaning weights. Purebred calves were similar in weight at birth and at weaning. Santa Gertrudis crossbreds weighed heavier than Red Poll crossbreds at birth only but not at weaning. Generally the poor level of nutrition of the natural pasture did not permit improved weaning weights in calves which were heavier at birth. Additive direct heritability estimates were 0.45 ± 0.08 for birth weight and 038 ± 0.18 for weaning weight. Moderate genetic correlation (0.48) between birth and weaning weights indicates that selection for one trait would lead to moderate positive correlated response in the other trait. Due to negative genetic correlation (−0.29 ± 0.16) between direct and maternal effects for weaning weight, and moderate heritabilities for both traits, selection for both the direct and maternal components of preweaning traits is advised.

Lactational performance of Giza White rabbits and its relation with pre-weaning litter traits

AbstractAn experiment was carried out in Egypt using Giza White rabbits to investigate their lactational performance and to estimate the repeatabilities of milk yield and other litter traits. Data on 325 litters from 115 does fathered by 40 sires were used. Lactation traits involved milk yields during the first 7 days, 21 days and 35 days. Litter traits included litter size and weight at birth, number born alive, litter weight and gain at 21 days, litter size and weight at weaning and pre-weaning litter gain. Linear mixed models were used for analysing such data.Phenotypic variation in milk yield was relatively high during the first 7 days, and decreased thereafter with advance of lactation stage. Year-season effects were significant for most litter traits, while month of kindling affected litter weight and gain at 21 days and milk yield during the first 7 days (P &lt; 0·05 or P &lt; 0·001). Litters kindled during winter had the highest milk yield compared with litters kindled in the other seasons. Milk production, litter size and weight and litter gain had curvilinear relationship with parity (P &lt; 0·05 or P &lt; 0·001). Sire of doe had no significant effects on litter traits studied. Repeatabilities of all traits were low and ranged from 0·001 to 0·134. Litter size and weight at birth were residually correlated with milk yield. Litter weight and gain at 21 days were significantly correlated with the lactational performance of the doe (P &lt; 0·001).

Contribution of breed, cow weight, and milk yield to the preweaning, feedlot, and carcass traits of calves in three beef breeding systems.

Data were obtained from 1980 to 1987 on animals belonging to one of three breeding systems: Hereford, small rotation, and large rotation. Differences among Angus-, Gelbvieh-, Pinzgauer-, and Tarentaise-sired calves within the small rotation system were generally not detected as significant for the preweaning traits of gestation length, calving ease, birth weight, gain to weaning, or creep feed intake with the exception of a longer gestation length for Gelbvieh-sired calves. Similarly, differences for feedlot gain, days on feed, feedlot intake, and the carcass characteristics of carcass weight and marbling, and lean, fat, and bone percentages were generally nonsignificant. Gelbvieh- and Pinzgauer-sired calves had higher growth rate, market weight, and longissimus muscle area than Angus- or Tarentaise-sired calves with a corresponding tendency for increased feed intake. Differences among Charolais-, Maine Anjou-, and Simmental-sired calves within the large rotation were not significant for any of the traits studied. Increased cow weight was positively associated with birth weight, significantly so for the small rotation. No patterns of association with cow weight were found for other preweaning traits. Increased milk yield was positively, but not always significantly, associated with gestation length and all weights and was negatively associated with creep intake. Neither cow weight nor milk yield showed any consistent association with feedlot or market traits, although increased milk yield was shown to be associated with higher daily gains for Hereford and small rotation and with higher carcass and market weights for Hereford. In general, associations of traits of calves with weight and milk yield of their dams were not detected as being different among breeding systems; except the effect of increased milk yield on gain to weaning was greater in Hereford than in large rotation cows.

Crossbreeding Ayrshire, Friesian, and Sahiwal Cattle for Milk Yield and Preweaning Traits of Progeny in the Semiarid Tropics of Kenya

Individual and maternal additive genetic and heterotic effects were estimated for preweaning, reproductive, and lactation traits of the Sahiwal breed and its crosses with Bos taurus (Ayrshire and Friesian). The individual additive genetic breed effect influenced all cow traits except annual milk yield, and the maternal additive genetic effect influenced all yield traits. The individual and maternal genetic effects between B. taurus and Sahiwal breeds for lactation milk yield were 746 and –601kg, respectively. Individual heterosis for lactation milk yield of 73kg (5%), estimated using the mean of the reciprocal F1 crosses, was not significant but increased to 374kg (28%) when estimated using only the F1 cross sired by B. taurus, showing the important influence of maternal effects. Individual additive genetic effects influenced preweaning daily gain and weaning weight. Maternal additive genetic and heterotic effects affected birth weight, and individual heterosis significantly influenced all calf traits. Maternal additive genetic effects may have biased the estimation of individual heterosis for milk yield in other tropical studies. When stratification is not possible or when reproductive rates are low, two-breed rotational crossbreeding is an efficient system to exploit additive and nonadditive genetic variation for tropical dairy production.

Genotype x environment interactions in preweaning traits of purebred and reciprocal cross Angus and Brahman calves on common bermudagrass and endophyte-infected tall fescue pastures.

Preweaning data on 486 Angus, Brahman, and reciprocal cross calves (AB, BA) managed on common bermudagrass or endophyte-infected tall fescue were used to evaluate the interactions of forage type and sex of calf with direct effects, individual heterosis, and maternal effects. Calves were spring-born in 1988, 1989, 1990, and 1991 to five sires of each breed. Male calves were castrated at birth, and calves were not creep-fed. Average values of heterosis for birth weight, 205-d weight, weaning hip height, and weaning weight:height ratio (WT/HT) were important (P < .01) and consistent across forage environment. Heterosis for birth weight was larger in bull calves than in heifer calves (P < .05), whereas heterosis for other preweaning traits were consistent across sex of calf. Average maternal effects for WT/HT (P < .10) were important and consistent across forage environment. Maternal effects for birth weight were larger with bull calves than with heifer calves (P < .01). Maternal effects for weaning hip height favored the Angus dam managed on bermudagrass (P < .05) but not managed on fescue. A similar but nonsignificant trend occurred in maternal effects for 205-d weight. Direct effects for birth weight were larger in bull calves than in heifer calves (P < .01). Direct effects for weaning height were larger in calves managed on bermudagrass than in calves managed on tall fescue (P < .07). A similar but nonsignificant trend was evident in direct effects for 205-d weight. Direct effects for WT/HT were relatively small and unimportant.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of breed of sire, breed of dam, pasture program and of their interactions on preweaning performance of crossbred beef calves

Angus (A), Hereford (H), Jersey (J), Simmental (S) and Brahman (B) bulls (202), were mated to A and H cows (855 cow-years) to produce F 1 calves. Cows were randomly assigned within age and breed to two pasture programs. The two pasture programs were expected to differ in particular with respect to the energy level offered to the cows during winter (tall fescue hay versus corn silage). Effects of genotypes, pasture program and of their interactions on preweaning traits were studied. Differences ( P< 0.05) between pasture programs were found only for frame and muscle scores. Marginal means for A dams were higher ( P<0.05) than those for H cows for all traits, except birth weight. Calves sired by B bulls were heavier ( P<0.01) at birth than those sired by S, A and H, and J bulls. For the other traits, S-sired calves tended to have the largest estimated means, followed by calves of B bulls, then by the average of calves sired by A and H bulls and finally by J-sired offspring. Significant ( P< 0.05) breed of sire × breed of dam interactions involved only extreme sire breeds. All hypotheses involving pasture program × breed of sire interactions were not significant. Muscle score was the only trait affected ( P< 0.05) by a pasture × breed of dam interaction. However, its effect was only magnitudinal. Birth weight was the only trait not affected at all by the pasture program × breed of sire × breed of dam interaction. In the other traits, significant interactions reflected changes in the magnitude of the response rather than in the ranking of genotypes across pasture programs.

Sire × pasture program interaction effects on preweaning performance of crossbred beef calves

Records on crossbred calves from the eight crosses between Angus (A) and Hereford (H) cows, and A, H, Jersey, Simmental and Brahman sires, and raised in two pasture programs were used to assess sire × pasture interactions on preweaning traits. There were 518–734 calves from 252–318 dams and 122–166 sires in the data set; numbers vary by traits. Sires, AI or natural service, constituted a representative sample of the breeds. Pasture programs differed principally in the winter period (tall fescue hay vs. corn silage). Heritabilities across and within pastures were: 0.28±0.19 and 0.28 ± 0.19 for birth weight (BW ); 0.08 ± 0.58 and 0.58 ± 0.19 for weaning weight (WW); 0.30 ± 0.41 and 0.71 ± 0.19 for weight adjusted to 205 days (W205); 0.00 ± 0.00 and 0.36 ± 0.15 for daily gain (DG); 0.61 ±0.35 and 0.94±0.25 for frame score (FRAM); 0.14±0.38 and 0.53±0.22 for muscle score (MUSC); and 0.00±0.00 and 0.14±0.21 for conformation score (CONF), respectively. Correlations between progenies of the same sire in different pasture programs are: 1.00±0.00 for BW; 0.13±0.99 for WW; 0.42±0.58 for W205; 0.00±0.00 for DG; 0.65±0.34 for FRAM; 0.27±0.71 for MUSC; and 0.00±0.00 for CONF. Except for birth weight, estimates (although imprecise) suggest that changes in the ranking of sires should be expected to occur between the two environments, possibly in part from incomplete adjustment for changes in season of calving between pasture environments for calves sired by the same sire.

Estimation of genetic and phenotypic parameters for growth and reproductive traits for red deer on an upland farm

AbstractGenetic and phenotypic parameters were estimated for farmed red deer (Cervus elaphus) in an upland environment in the north-east of Scotland. Genetic parameters were estimated using restricted maximum likelihood analyses. Heritabilities of pre-weaning traits associated with growth were moderate for birth weight (0·27 (s.e. 0·04)), weaning weight, generally in September at 3 months of age (0·21 (s.e. 0·06)) and growth rate from birth to weaning (0·15 (s.e. 0·03)). Heritabilities for post-weaning traits were 0·10 (s.e. 0·05) for turn-out weight in April/May, 0·14 (s.e. 0·06) for September weight, at 15 months of age, 0·08 (s.e. 0·05) for growth rate weaning to turn-out and 0·12 (s.e. 0·06) for growth rate turn-out to September. Correlations between weaning weight and post-weaning traits were high indicating the usefulness of weaning weight as a selection criterion for red deer on upland farms. While Wapiti (Cervus elaphus canadensis) crosses grew faster than pure red deer they also tended to have higher mortality rates pre-weaning. Older dams were more likely to have a successful pregnancy and also tended to calve earlier. Date of calving was found to show no heritable variation in this study.

Estimation of crossbreeding parameters between Large White and Meishan porcine breeds. II. Growth before weaning and growth of females during the growing and reproductive periods

Summary - A crossbreeding experiment using Large White (LW) and Meishan (MS) pig strains was conducted. Direct, maternal and grand-maternal additive genetic effects together with direct, maternal and paternal heterosis effects were estimated for traits during the preweaning, growing and reproductive periods. Weight at birth (WB) and at 21 d of age (W21) was recorded in 3731 male and female piglets. After weaning at 28 d, 543 females were weighed at 73 (W73) and 154 (W154) d of age. From these, 148 sows were weighed before farrowing from 1st to 5th parity. Average daily gains were computed from birth to 21 days of age (ADG 0-21), 21 to 73 days of age (ADG 21-73) and 73 to 154 days of age (ADG 73-154). The genetic influence on preweaning traits was mainly maternal in origin. Maternal additive differences between breeds significantly increased with parity of the dam. Average values were 0.33 ± 0.05 kg (26%) and 1.24 dh 0.22 kg (26%) in favour of LW for WB and W21 respectively. Maternal heterosis effects were 0.05 ± 0.02 kg (6%) for WB and 0.65 t 0.09 kg (14%) for W21. Significant grand-maternal additive and direct heterosis effects were also observed on WB. Adjustment of data for litter size slightly increased additive and heterosis maternal values. After weaning, direct effects became important. Additive differences between breeds rapidly increased during the growing period and averaged 4.1 f 1.0 kg (18%), 22.9 ! 3.3 kg (36%) and 231 ::I:: 33 g/d (47%) in favour of LW for W73, W154 and ADG 73-154 respectively. Direct heterosis effects for these traits were 3.7 =L 0.7 kg (15%), 19.2 + 2.3 kg (25%) and 187 t 24 g/d (30%) respectively. Direct additive differences in favour of LW increased from 58 ! 9 kg at the first farrowing to 111 t 10 kg at the fifth one. Direct heterosis effects were similar throughout reproductive life and averaged 27 ! 3 kg (11%). The other crossbreeding

Performance of crosses among Hereford, Angus and Simmental cattle with different levels of Simmental breeding: IV. Maternal heterosis and calf production by two-year-old dams.

The performance of 264 contemporary 2-yr-old straightbred and crossbred dams during 1978 to 1981 was studied and maternal heterosis was estimated. Dam breed groups were Hereford (HH), Angus-Hereford (AH), 25% Simmental-75% Hereford (1S3H), 50% Simmental-50% Hereford (1S1H) and 75% Simmental-25% Hereford (3S1H). Differences among dam breed groups were nonsignificant for length of gestation, calving difficulty and late milk production but were important (P less than .01) for calf weights (birth, early and late milking periods and weaning), calf average daily gains during various intervals from conception to weaning, early milk production and other calf traits at weaning (height, weight/height and visual condition score). Dam breed group means (HH, AH, 1S3H, 1S1H and 3S1H, respectively) for representative calf traits were .37, .39, .39, .42 and .42 kg/d for estimated average daily gain the last 3 mo of gestation; 33.6, 34.7, 35.7, 37.6 and 37.1 kg for birth weight; 191, 205, 209, 228 and 228 kg for weaning and 7.5, 8.4, 8.3, 9.5 and 10.0 kg for 24-h early milk production. Therefore, 2-yr-old crossbred dams raised calves that were generally larger for the preweaning gain traits than HH dams. Differences among dam breed groups were significant for traits involving reproduction; means (HH, AH, 1S3H, 1S1H and 3S1H, respectively) were .58, .92, .72, .91 and .79 for proportion calving and 105, 179, 126, 182 and 154 kg for actual calf weaning weight per cow exposed to breeding. Estimates of percentage maternal heterosis were 6.3, 12.9, 9.0 and 7.6% for calf weights at birth, 40 d, 130 d and weaning, respectively; 1.8, 5.7 and 5.7% for calf hip height, height/weight and condition score at weaning, respectively; and 43.1 and 34.6% for proportion calving and actual calf weaning weight per cow exposed to breeding. The dominance model explained most (greater than 95%) of the variation observed among dam breed group means for most traits.

Effects on maternal performance and litter preweaning traits in doe rabbits

Effects on maternal performance and litter preweaning traits in doe rabbits

Genetic parameter estimates for postweaning traits of beef cattle in a stressful environment.

Postweaning growth data, collected from a Hereford herd located in the Southwest, were used to estimate genetic parameters for weights and gains. The herd was maintained on unsupplemented range forage, and average weight losses from weaning to yearling age were 9% for bulls and 12% for heifers. Data were grouped into years with poor and good environments based on contemporary group means for gain from 8 to 12 mo. Postweaning growth data (12- and 20-mo weights, 8- to 12-mo gain and 12- to 20-mo gain) were analyzed by least squares methods with a model that included year of birth, sire within year of birth, age of dam and a covariate of age for 12- and 20-mo weights. Heritability estimates of 12- and 20-mo weights for bulls were .58 +/- .15 and .55 +/- .22 in good environments vs .32 +/- .11 and 1.09 +/- .15 in poor environments; for heifers these estimates were .19 +/- .08 and .35 +/- .12 in good environments vs .38 +/- .07 and .47 +/- .09 in poor environments. Heritability estimates of 8- to 12-mo and 12- to 20-mo gain for bulls were .32 +/- .14 and .51 +/- .24 in good environments vs .16 +/- .11 and .09 +/- .14 in poor environments; for heifers these estimates were .21 +/- .08 and .14 +/- .10 in good environments vs .10 +/- .06 and .44 +/- .10 in poor environments. Genetic correlations among the preweaning traits of birth and weaning weight and postweaning weight traits were positive and of a moderate to large magnitude, with the exception of birth and 12-mo weight in a poor environment (-.06 +/- .49). Genetic correlations between 8- to 12-mo gain and birth weight in poor environment and weaning weight in all environments were negative (range from -.06 +/- .33 to -.53 +/- .41). Genetic correlations among 12- and 20-mo weights were large and positive in all environments. Relationships among gains were more variable.

INFLUENCE OF BIRTH DATE, SEX OF CALF, BREED GROUP AND AGE OF DAM ON PREWEANING PERFORMANCE OF RANGE BEEF CALVES

Preweaning data on 2856 calves covering a 14-yr period in three breed groups of range beef cattle: Hereford (HE), Beef Synthetic (SY) and Beef Crossbred (XB) were analyzed for birth weight, weaning weight and preweaning average daily gain (ADG). Year of birth, age of dam, sex of calf and breed group were considered as main effects. Calf birth date was used as a covariate in the least-squares analyses. Year of birth was a significant source of variation. The correlation coefficients between the least-squares constants for years and year of birth indicated a steady improvement in the preweaning traits over the 14-yr period. Bull calves exceeded heifers (P &lt; 0.05) in all traits except for ADG in HE. Preweaning performance peaked in calves from 5- to 6-yr-old dams. Though heavier at birth, XB calves were excelled by SY calves at weaning primarily because of superior ADG recorded in SY, while HE was the lightest of the breeding populations. Breed group by sex of calf interactions for weaning weight and ADG were significant. In addition, declining multiplicative sex adjustment factors from birth to weaning in the HE and XB populations suggested that in view of their greater potential for growth, male calves might have been marginally disadvantaged by the poor nutritional environment provided by the dams. In the HE and SY populations, calf birth weights significantly increased with the progression of the calving season, but the stage of the calving season did not affect calf birth weights in XB. The linear effects of age of calf were generally significant for weaning weight while quadratic effects were significant only in the XB population. Key words: Beef cattle, preweaning traits

Additive and heterosis effects on preweaning traits, maternal ability and reproduction from crossing of the Angus and brown Swiss breeds in Florida.

Angus (A), Brown Swiss (S) and A X S reciprocal F1 (AS) dams were mated to A, S and AS (also reciprocal F1) sires resulting in nine breed groups of progeny with varying proportions of Angus and Brown Swiss breeding. Breed group of dam and of sire significantly influenced birth weight, preweaning daily gain, weaning weight, 205-d weight, condition score and frame size. The means for birth weight and weaning weight were 33 and 213 kg, respectively. Brown Swiss bulls sired calves with the heaviest birth and weaning weights. Calves produced by S dams likewise were heavier at birth and weaning. Pregnancy rates were influenced significantly by year, age and breed of dam and averaged 79, 95 and 92% for S, AS and A cows, respectively. Survival rate averaged 97% and was not influenced significantly by any of the effects examined. Because survival rates were similar for all breed groups, the results for weaning rate paralleled those for pregnancy rate. Genetic influences on preweaning growth traits and survival rate were partitioned into additive breed differences (B) and heterosis (H) effects for direct (d) and maternal (m) components. Pregnancy and weaning rates were examined using similar analyses except that genotype of service sire of dam replaced that of the offspring for the direct additive breed and direct heterosis components. The Bd values indicated that the Angus breed was inferior (P less than .01) to the Brown Swiss breed for all preweaning growth traits except for condition score, in which the Angus breed surpassed (P less than .01) the Brown Swiss. The Bm values also showed an advantage for the Brown Swiss breed for all preweaning growth traits. The additive maternal effect (the genotype of the females exposed), Bm, was important for pregnancy rate and weaning rate (P less than .001 and P less than .05) but not for survival rate (P greater than .10). The direct additive breed effect was not important for any reproductive trait. Direct heterosis did not affect any of the preweaning or reproduction traits; however, maternal heterosis (Hm) significantly affected all traits except birth weight, frame score and survival rate. The Hm estimates were 12.0 and 8.4 kg for weaning weight and 205-d weight, respectively. The Hm estimates for pregnancy rate, survival rate and weaning rate were 10, 2 and 13%, respectively.

Selection for weaning weight and postweaning gain in Hereford cattle. III. Correlated responses to selection in milk yield, preweaning and postweaning traits.

Single trait selection was practiced in three lines of Hereford cattle. Bulls were selected within sire families for increased weaning weight (WW) in the WW line (WWL), for postweaning gain (PG) in the PG line (PGL) and at random in the control line (CTL). Correlated responses to selection indicated that predicted milk yield in cows and preweaning daily gain and yearling weight in bulls and heifers were genetically improved in both WWL and PGL. Larger correlated responses were observed in PGL than in WWL. Birth weight in bulls and heifers increased in PGL but no genetic change was observed in WWL. Feed efficiency, feed intake and fatness were evaluated in bulls on postweaning feedlot test. No significant correlated responses in feed efficiency were observed in either line. Larger correlated responses in feed intake were observed in PGL bulls than in WWL bulls, while fatness was significantly increased in both selection lines.

Genetic effects on maternal performance and litter pre-weaning and post-weaning traits in rabbits

AbstrtactFlemish Giant (FG) and New Zealand White (NZW) purebreds and terminal crossbreds (TX) (Flemish Giant sires × Florida White-New Zealand White dams) were evaluated during a 10-month period for maternal and litter pre-weaning and post-weaning performance. For the doe traits studied, teat number was greatest and litter interval was shortest, while body weight at breeding age (154 days), litter weight at 21 days and day 1 to 21 food intake were lowest for crossbred does. These traits were similar for pure doe groups, with the exception of body weight, for which FG does were heavier. For the preweaning litter traits examined (no. = 101 litters), litter size born was smallest in the TX group (the purebred groups being similar) and was largest at weaning (28 days) for NZW. Proportion of kits born alive was lowest in FG litters, while the NZW and TX groups were comparable. Litter and average birth and weaning weights, litter daily gain, and doe and litter food intake (1 to 28 days) were all highest in FG litters and lowest in TX litters. Repeatability estimates (t) were low (t &lt; 0·05) for litter size and birth weight traits, and were moderate to high (0·18 &lt; t &lt; 0·58) for the remaining maternally influenced characters. For the post-weaning litter traits studied (no. = 86 litters), NZW litters were larger in number and heavier at market age (56 days), and consumed more food from 28 to 56 days than FG and TX litters. Purebred FG litters, however, had heavier average market weights per rabbit, while purebred NZW and TX litters were similar. Mortality due to respiratory disease was higher in FG litters than in NZW and TX litters. Total mortality incidence was lowest in the TX group.

Characterization of straightbred and crossbred rabbits for milk production and associative traits.

Two hundred twenty-five lactation and litter performance records from 82 does representing four genetic groups and two diets were analyzed to quantify breed, heterosis, reciprocal F1 cross and diet effects for milk production and associative traits. Doe genetic groups were New Zealand White (NN) and Californian (CC) straightbred and Californian X New Zealand White (CN) and New Zealand White X Californian (NC) reciprocal crossbreds. Pelleted diets fed to does and litters were either a commercial control or a 74% alfalfa diet. Three sire breeds of litters included NN, CC and Flemish Giant (FG) straightbreds. Doe genetic group and diet were important sources of variation (P less than .05) for all traits examined except for litter milk efficiency (litter gain/milk intake) and doe feed efficiency (milk yield/feed intake). The sire breed of litter effect did not influence (P greater than .05) lactational performance of does nor associative preweaning traits. Straightbred NN does were heavier at kindling, yielded more milk, reared a heavier litter by 21 d and were more efficient in converting feed into milk than were straightbred CC does (P less than .01). Significant heterosis was detected for milk production and for litter size and weight at 21 d. Reciprocal differences between crossbred doe groups were observed (P less than .05) for litter milk efficiency and doe feed intake. The 74% alfalfa diet was superior to the commercial control diet for effects on milk production and litter size and weight at 21 d, although doe feed intake was increased.(ABSTRACT TRUNCATED AT 250 WORDS)