Selection For Weaning Weight Research Articles

Genetic association between mature weight and early growth and heifer pregnancy traits in Nellore cattle

In order to determine whether selection for traits included in the selection index used in a breeding program would increase the mature weight (MW) of females, this study analyzed the association between MW and four traits composing the index: weaning weight (WW), post-weaning weight gain in 345 days (PWG), scrotal circumference (SC), and muscling score (MUSC). Additionally, the genetic relationship of MW with probability of pregnancy at 14 months (PP14) was analyzed to evaluate the association between MW and sexual precocity. The database included 480,000 Nellore animals from Agropecuária CFM born between 1984 to 2012 on farms in the states of São Paulo, Mato Grosso do Sul, and Goiás. The heritability for the six traits and the correlations between them were estimated, with special importance being given to the correlation of MW with the other five traits. The (co)variance components were estimated by the restricted maximum likelihood method. The heritability coefficients were 0.22 ± 0.01, 0.19 ± 0.01, 0.50 ± 0.01, 0.22 ± 0.01 and 0.50 ± 0.01 for WWd, PWG, SC, MUSC and PP14, respectively. The genetic correlations between MW and the growth traits were positive: 0.55 ± 0.04 (WWd), 0.68 ± 0.03 (PWG), 0.07 ± 0.02 (SC), and 0.46 ± 0.01 (MUSC). Selection for WW, PWG and MUSC might be related to an increase in MW of cows. The correlation between MW and PP14 was negative and of low magnitude (−0.03). However, selection for increasing MW in this population of Nellore cattle should not cause genetic change in fertility. The scientific literature on correlation estimates between MW and the PP14 are scarce. Further investigation on the same topic, using different data sets and other approaches are recommended.

한우의 이유시 체중과 도체형질과의 유전적 관계

ABSTRACT The objective of this study was to evaluate the genetic relationship between weaning weight (WW) and carcass traits. Carcass traits were eye muscle area (EMA), back fat thickness (BFT), marbling score 1 (MS1) in 21 grade scales, marbling score 2 (MS2) in 7 grade scales and meat color scores (Mcolor). Parameters were estimated by REML procedure with MTDFREML package. Models included contemporary group as defined by the same year-season-sex at birth, linear covariates of age (days) at weaning, age of dam (days) and age at slaughter (days) as fixed effects and animal random effects for all the traits. Heritability estimates of WW, EMA, BFT, MS1, MS2 and Mcolor were 0.25, 0.20, 0.20, 0.32, 0.32 and 0.22, respectively. Genetic(phenotypic) correlation coefficients of WW with EMA, BFT, MS1, MS2 and Mcolor were 0.75(0.16), 0.18 (0.05), 0.41 ( 0.09), 0.40 (0.11) and 0.07 (0.05), respectively. Results from this study suggest that single trait selection for weaning weight would lead to progeny population having carcass with large EMA, thick BFT and decreased MS.(

Selection to improve birth and weaning weight of Javanese Fat Tailed Sheep

Abstract. In Indonesia, the Javanese Fat Tailed Sheep is a very popular domestic animal for its meat production However selection to increase body weight has never been done by local farmers. As a result the variability of body weight is high, and expected that application of a selection program can improve this trait Two Steps of selection were done in order to improve birth and body weight. In the first selection, the elite group was established by selecting the best 40 females and 3 males from 12500 sheep reared by local farmers based on their mature body weight and tail length. The control group was established by randomly selecting 40 females and 4 males In the second step of selection, the best 50 % females and 5 % males of the progeny of the elite group was selected based on their weaning weight and tail size. The first selection results indicate that there was a positive genetic progress in both birth and weaning weight. Selection had increased 7.17 % and 5.48 % of male and female birth weight respectively and 9.48 % and 9.78 % of male and female weaning weight, respectively. Positive genetic progresses of birth and body weight were also found after the second selection. Birth weights of males and females were 6.75 % and 7.20 % higher than those in the control group. Male and female weaning weights were 5.60 % and 8.19 % higher than those in the control group, however, selection for weaning weight did not affect reproductive traits.

Protein metabolism in lambs from lines divergently selected for weaning weight

SUMMARYThe physiological consequences of selection for weaning weight were investigated using 14-month-old castrated male Merino lambs from lines selected for (W +) and against (W – ) weight at weaning for over 10 generations. The selection experiment commenced in 1953 and was conducted at Trangie, NSW, Australia. Lambs from these lines now differ by 42% in weight at weaning and maturity, and have a proportionately similar composition of protein, fat and ash in their bodies at similar stages of maturity. In the whole body, there were no apparent between-strain differences in protein synthesis, but W + lambs had lower (P < 0·05) rates of phenylalanine oxidation than W – lambs. In hind limb muscle, protein metabolism of W + lambs was more responsive to food intake than in W – lambs. In particular, the rate of change of protein degradation differed (P < 0·05) between the lines in response to food intake per unit liveweight with protein degradation decreasing with increased feed intake in W + lambs. W + lambs had lower (P < 0·05) rates of blood flow to, and used less (P < 0·05) oxygen per kg hind limb muscle than W— lambs. Endocrine differences between the lines included increased (P < 0·05) plasma insulin-like growth factor-I (IGF-1) concentration in W + compared to W— lambs and, from regression analysis, an indication that there was a higher (P < 0·01) response in hind limb protein gain to insulin in the W + lambs.These results suggest that selection for weaning weight has altered the dynamics of protein metabolism in lambs, principally through alterations in protein breakdown in muscle. Moreover, they suggest that there are associated genetic differences in endocrine control of protein metabolism which involve insulin and possibly IGF-I.

Effect of divergent selection for weaning weight on liveweight and wool growth responses to feed intake in Merino ewes

During a 6-week experiment, the feed requirements for maintenance of liveweight (LW) by adult Merino ewes were measured in 2 flocks selected over 32 years for divergent weaning weight. Also examined were the net efficiency of LW gain and wool growth in response to change in feed intake, and the ability to digest dietary organic matter. Ewes selected for high weaning weight (W+) were 31% heavier than those selected for low weaning weight (W-) at the start of the experiment. To maintain LW, W+ ewes ate 24% more digestible organic matter (DOM) per day than W- ewes. There were no differences (P>0.2) in the net efficiency of feed use for LW gain. The W+ ewes digested more (P<0.01) dietary organic matter, by 1.8 percentage units, than W- ewes and, consequently, required only 22% more dry feed to maintain their heavier LW. Ewes from the 2 flocks did not differ (P>0.4) in the amount of wool grown, and as W+ ewes were larger, they produced less (P<0.01) wool per kg LW for the same DOM intake.

An alternative to restricted BLUP based on mate selection

A new application of mate selection is presented in this study that maximizes the expected genetic progress of a selected trait while holding a correlated trait unchanged. The proposed method combines the use of BLUP evaluation and linear programming techniques and its properties have been analyzed by Monte Carlo simulation on a numerical example from beef cattle with selection for weaning weight and restriction on birth weight. With respect to restricted index or BLUP selection, this alternative method allows: (a) a similar response for both the selected and restricted traits, (b) lower variances of the responses and (c) greater robustness against errors in the genetic correlation estimate.

Consequences of selection for weaning weight in zebu, Bos taurus and zebu × Bos taurus cattle in the tropics

Direct and correlated responses to a single generation of divergent selection for weaning weight per day of age (WA/A) were examined in Bos taurus, zebu and zebu crossbred cattle in a tropical environment. Selection for high WW/A resulted in increased liveweights at all ages in all genotypes, with the exception of birth weight in the Bos taurus genotype. Preweaning daily gains were higher in all genotypes selected for high WW/A, but postweaning daily gains did not differ in two zebu crossbred genotypes. Overall parasite and heat resistance did not change significantly as a result of selection. However, selection within the more resistant genotype/sex populations resulted in higher tick and worm burdens, while in the more susceptible populations tick and worm loads decreased. An examination of lifetime cow fertility showed that cows with high preweaning growth reared more calves to weaning (P < 0.05), had fewer neonatal mortalities (P < 0.10) and also calved earlier (P < 0.01) than cows with low preweaning growth, leading to the conclusion that cows with high WW/A have improved lifetime fertility. Heritability of birth weight, WW/A and 18 month weight per day of age over all genotypes was estimated by parent-offspring regression to be 0.46, 0.21 and 0.22 for each of the traits respectively. The realized heritability of WW/A was 0.17 over all genotypes.

Effect of selection for growth traits on age and weight at puberty in bovine females.

This 20-yr study, using 584 beef heifers born in the spring of 1984 or 1985, was conducted to determine whether selection for growth traits affected age and weight at puberty. Heifers were from three Hereford lines selected for weaning weight, final weight, and final weight plus muscling score, a control line and a line of Angus cattle. In addition, heifers from reciprocal crosses among the selection lines, control and Angus groups were evaluated. Intact bulls and androgenized heifers fitted with marking harnesses were used to aid in detection of estrus for heifers born in 1984 and 1985, respectively. The time of puberty was identified by the first behavioral estrus. During both years, heifers were weighed at 56-d intervals; these weights were used to calculate weight at puberty. Mean age at puberty was determined using survival analysis; percentages of heifers that were pubertal by the end of the study were transformed to logits for analysis. Heifers born in 1985 were heavier (P less than .05) at puberty than those born in 1984. Heifers in lines selected for growth traits were younger at puberty (P less than .05; 20 d) than were heifers in the control line because of combined direct and maternal genetic effects. Heifers from the final weight, control (P less than .05) and weaning weight lines (P less than .10) weighed less at puberty than Angus heifers; selection line x Angus crossbred heifers were heavier at puberty (P less than .05) than their respective pureline or purebred contemporaries due to heterotic effects. Selection for weaning weight, final weight or final weight plus muscling score did not have a detrimental effect on age at puberty in heifers.

Growth of Mashona cattle on range in Zimbabwe. II. Estimates of genetic parameters and predicted response to selection.

For 1,456 Mashona calves sired by 88 bulls heritability estimates from paternal half-sibs were 0.44 +/- 0.11 for birth weight, 0.38 +/- 0.10 for 205-day weaning weight, 0.39 +/- 0.10 for 18-month weight, 0.37 +/- 0.10 for pre-weaning daily liveweight gain and 0.41 +/- 0.11 for daily gain from weaning to 18 months of age. Genetic correlations were relatively low for birth weight with weaning weight (0.42 +/- 0.18), 18-month weight (0.56 +/- 0.16), pre-weaning gain (0.33 +/- 0.19) and post-weaning gain (0.36 +/- 0.19). Higher genetic correlations were observed for pre-weaning gain with weaning weight (0.98 +/- 0.01) and 18-month weight (0.59 +/- 0.14) and for 18-month weight with weaning weight (0.67 +/- 0.12) and post-weaning gain (0.73 +/- 0.10). Post-weaning daily gain was not significantly correlated genetically with both pre-weaning gain (-0.11 +/- 0.22) and weaning weight (-0.03 +/- 0.22). With 10% retention of males and 60% of females expected genetic improvements per generation from direct selection for weaning weight or 18-month weight were 8.11 kg and 12.12 kg respectively. These improvements would be reduced by 18% and 35% if selection indices were used to produce no correlated change in birth weight.

Selection for Weaning Weight and Postweaning Gain in Hereford Cattle. II. Response to Selection

Single trait selection was practiced in three lines of Hereford cattle at two locations. 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). Data include the performance of 2,467 calves produced from 1967 to 1981. Environmental effects were estimated from CTL (method I) and from multiple regression procedures (method II). Phenotypic and environmental time trends were negative for WW and generally were positive for PG. Estimated genetic gains for WW in WWL were 1.07 +/- .51 kg/yr in bulls and .62 +/- .36 kg/yr in heifers using method I and .50 +/- .31 kg/yr in bulls and .10 +/- .17 kg/yr in heifers using method II. Corresponding values for PG in PGL were .85 +/- .40 and 1.03 +/- .24 kg/yr in bulls and .30 +/- .28 and .37 +/- .12 kg in heifers. Correlated genetic gains for WW in PGL were larger than direct WW gains, whereas genetic gains for PG in WWL were smaller than direct PG gains. From method I, estimates of realized heritability (h2R) for WW were .31 +/- .18 in bulls and .22 +/- .13 in heifers. For PG, h2R was .31 +/- .13 in bulls and .06 +/- .12 in heifers. Using method II, h2R for WW was .09 +/- .08 in bulls and .02 +/- .07 in heifers. Corresponding values for PG were .29 +/- .10 and .11 +/- .08. Joint estimates of the realized genetic correlation between WW and PG were .69 +/- .18 and .46 +/- .31 for methods I and II, respectively. Variation in selection response was evaluated using quasi-replicates. Results of this study indicate that selection for PG improved both WW and PG faster than selection for WW.

Direct and correlated responses to selection for weaning weight, post-weaning weight gain and six-week weight in mice

Four lines of mice were formed from a common base population and selected for 37 generations for either increased 3-week weight (weaning weight), 6-week weight, 3-6 week gain, or maintained as a randomly bred control line. Realised heritability estimates for short-term (long-term) responses were 0.33±0.20 (0.07±0.10), 0.46±0.14 (0.26±0.09), 0.36±0.14 (0.24±0.11) for 3-week weight, 6-week weight and 3-6 week gain, respectively. Realised genetic correlations estimated from short-term (long-term) responses were 0.23±0.08 (0.35±0.10) between 3-week weight and 3-6 week gain; 0.82±0.04 (0.58±0.08) between 3-week weight and 6-week weight; and 0.81±0.04 (0.97±0.04) between 3-6 week gain and 6-week weight. The genetic correlation between 3-week weight and 6-week weight was asymmetric with a greater correlated response for 3-week weight when selecting for 6-week weight (1.06) than vice versa (0.63).

COMPARISON OF SINGLE AND MULTIPLE TRAIT BEEF SIRE EVALUATIONS

Beef bulls of 13 breeds were evaluated from progeny records for calving ease, weaning weight and yearling weight using single and multiple trait best linear unbiased prediction techniques. Multiple trait procedures allowed more bulls to be evaluated for all traits and gave slightly greater variances to sire evaluations than the single trait method. The correlations of proofs between single and multiple trait methods were above 0.9 for the majority of the breeds for each trait, with the lowest correlations being between yearling weight proofs from the two methods. The correlations of proofs between traits within the multiple trait analysis were greater in absolute magnitude than within the single trait analyses. Multiple-trait procedures seem to be advantageous for lowering the standard errors of prediction for young bulls with their first proof, and for removing the effects of selection for weaning weight from the yearling weight proofs.

The effect of correction factors on response to selection in beef cattle

ABSTRACTProgeny of younger dams grow more slowly than those of older dams. When the environmental effects of dam age are not allowed for in selection for growth rate, selection differentials and genetic responses to selection are reduced.In a model herd, with cows aged 2 to 8 years, it was found that neglecting the dam age effects reduced genetic gains by about 15% when selection is for weaning weight, and by 11 to 7 % when selection is at an age of 12 to 20 months. Much of the reduction occurs because of the selection of higher proportions from genetically inferior groups.If genetic differences among dam age groups are small the reduction is only 7% at weaning and less at older ages. The effect of ignoring calf age was also estimated. It was found that if calves born within a period of 33 days were compared and calf age was neglected, the response to selection for weaning weight would be reduced by about 6%.

Reproductive performance of ewe lambs: genetic correlation with weaning weight and subsequent reproductive performance

The reproductive performance of Merino ewe lambs was examined in flocks with different selection histories for growth to weaning and net reproductive rate. These ewes were drawn from selection flocks maintained at the Agricultural Research Station, Trangie. There was evidence of a positive genetic correlation between weaning weight and reproductive performance of ewe lambs. Selection for weaning weight had a significant effect on the percentage of ewes lambing (P < 0.05). This appeared to be a function of a higher level of fertility (P <0.05) and a higher proportion of ewes mating (n.s.). The proportion of ewes apparently in oestrus during a 39 day teasing period, prior to joining, was significantly influenced by selection for weaning weight (P < 0.05). Simultaneous selection for increased net reproductive rate, weaning weight and clean fleece weight did not result in higher ewe lamb performance than that achieved by selection for increased weaning weight alone. No conclusion could be drawn from these data about the correlation between net reproductive rate and reproductive performance of ewe lambs.

Selection for weaning weight in Merino sheep. 3. Maintenance requirements and the efficiency of conversion of feed to wool in mature ewes

Net and gross efficiencies of wool growth have been estimated for ewes from three Trangie selection flocks, one selected for high weaning weight (Weight Plus), one for low weaning weight (Weight Minus), and a random control flock. Weight Plus ewes had 15 and 11 per cent heavier body weights than Weight Minus ewes at maintenance and unlimited levels of feeding respectively. At each level, feed intake was proportional to body weight both between and within flocks. In addition, the feed costs of a unit gain and loss of body weight were the same for each flock at each level of feeding. The Weight Plus ewes grew 7 and 10 per cent more wool than Weight Minus ewes at maintenance and unlimited levels of feeding. Consequently, there was only a small difference between the flocks in efficiency of conversion of feed to wool at maintenance, and there was no difference on unlimited intake. These results indicate that there is no genetic correlation between weaning weight and efficiency of conversion of feed to wool. At the three levels of controlled feeding (543, 725, 902 grams of dry matter a day) there were no differences in gross efficiency of wool growth, either between flocks or between levels within flocks, despite differing changes in body weight. During unlimited feeding, gross efficiency of wool growth was lower than that during controlled feeding. This was due to a reduced response in wool growth, as feed costs per unit body weight change were constant. As both production and feed intake changed in proportion to body weight, it is concluded that attention to weaning weight has little place in a Merino breeding program aimed at increasing wool production. However, selection for high weaning weight may be a useful tool in selecting ewes for crossbreeding because of the associated increases in milk production and lamb growth rate.

Selection for weaning weight in Merino sheep. 2. Correlated responses in other production characters

The heritabilities of seven production characters of Merino Sheep and their phenotypic and genetic correlations with corrected weaning weight have been calculated using half-sib and dam-daughter correlations. Realized genetic correlations calculated from responses in Weight Plus and Weight Minus selection flocks, which showed broad agreement with these correlations, were : 17-month body weight, 0.72 ; yield, 0.22 ; clean fleece weight, 0.24 ; and staple length, 0.17. There was zero relationship with greasy fleece weight and crimps per inch, and a large negative relationship between folds and high weaning weight. There were strong phenotypic correlations between lamb growth and milk production through the total weight of milk protein produced. The lamb's genotype was the most important contributor to the difference in weaning weight between the flocks. There were no differences in reproductive performance or survival rates between the flocks but twice as many twin rams and 20 per cent more twin ewes were mated in the Weight Minus flock over the selection period.

Selection for weaning weight in Merino sheep. 1. Direct response to selection

The heritability of corrected weaning weight has been estimated by dam-offspring and paternal half-sib correlations in a random-bred, medium-wool Peppin Merino flock. All weights were corrected for age and type of birth within each year. The dam-off-spring heritability estimates were 0.28 � 0.10 for ewes and 0.32 � 0.11 for rams. The paternal half-sib estimates were 0.18 � 0.07 for ewes and 0.19 � 0.13 for rams. Responses in flocks selected for high and low weaning weight for four generations (1951 to 1961) were used to calculate realized heritabilities. These were 0.33 � 0.03 and 0.18 � 0.06 for ewes and rams respectively in the high weaning weight flock, and 0.22 � 0.10 and 0.23 � 0.19 for ewes and rams in the low weaning weight flock. The average increases in inbreeding coefficients since selection commenced were 3.97 per cent in the high weaning weight flock, 3.58 per cent in the low weaning weight flock and 0.39 per cent in the randomly selected control flock. The regressions of weaning weight on inbreeding, independent of the effects of selection, ranged from -0.076 to -0.387 with an average of -0.191 lb weaning weight per one per cent inbreeding.