Restricted Maximum Likelihood Procedure Research Articles

The comparison of multilevel models, method of moment and restricted maximum likelihood in assessing population bioequivalence

The determination of bioequivalence is very important in the pharmaceutical industries because the regulatory agencies like the Food and Drug Administration (FDA) allow a generic drug to be marketed only if its manufacturer can demonstrate that the generic product is bioequivalent to the brand-name product. Up to date, there is a lack of widely accepted statistical procedure for assessing population bioequivalence. We propose multilevel models (MLMs) for evaluating and estimating parameters to assess population bioequivalence (PBE), and compare statistical properties of PBE estimators between MLMs and current approaches recommended by the FDA-the method of moment (MOM) and REML. The approach developed is illustrated using a real data set from the FDA. Statistical properties of MLM estimators are further explored using simulation studies as compared with MOM and restricted maximum likelihood (REML) estimators. The performance of MLM appeared to be much comparable to the existing REML procedure. The results suggest that MLM estimators that are fully comparable with REML estimators can be an adequate approach for assessing PBE. The MLMs approach proposed in the study provides an alternative and yet more flexible and powerful method than existing methods in assessing bioequivalence (BE) for complex study designs and data structures. Key words: Population bioequivalence, multilevel models, simulation, estimation procedure, restricted iterative generalized least square (RIGLS), restricted maximum likelihood (REML), method of moments (MOM), food and drug administration (FDA).

Genetic parameters for lameness and claw and leg diseases in dairy cows

Lameness in dairy cows is a serious welfare and economic problem in dairy production. The majority of all lameness cases seem to stem from claw and leg diseases. Indirect selection on claw health potentially might be feasible with lameness as indicator trait. Therefore, the genetic parameters for the 2 traits were estimated by applying both linear and threshold models. In addition, the impact of environmental effects, parity, and stage of lactation was analyzed. In total, 8,299 locomotion scores (1–5) of 326 dairy cows and 708 claw and leg disease diagnoses or treatments of 335 dairy cows from the dairy research farm Karkendamm (Institute of Animal Breeding and Husbandry, Christian-Albrechts-University, Kiel, Germany) were analyzed. Lameness was defined by a locomotion score of ≥3. Days in milk were limited to the range of 10 to 350d. To quantify the effect of the claw disease digital dermatitis, a second data set without this disease was built; 52.8 and 36.4% (without digital dermatitis) of the cows were treated at least once; 47.2% of the cows were clinically lame at least at one time. Genetic parameters were estimated bivariately using the average information restricted maximum likelihood procedure as implemented in the DMU software package. The heritability estimates derived from the threshold model were about twice as large as the values based on the linear model. For lameness, the threshold heritability increased from 0.15 to 0.22 and decreased for the diseases from 0.24 to 0.22 after exclusion of digital dermatitis. The genetic correlations were high and even increased from 0.60 to 0.72 after the exclusion of digital dermatitis, which suggests that lameness (locomotion score) seems to be a good indicator for claw and leg diseases. Digital dermatitis seems to affect the mobility of the dairy cow less strongly than other claw and leg diseases.

English

The aims of the study were to investigate the fixed effects which are considered to influence ewe productivity and to estimate the genetic parameters for ewe productivity traits of Lohi sheep. Genetic parameters were estimated by restricted maximum likelihood (REML) procedure using the GENSTAT program. The effects of year and age of ewe were significant for fertility, litter size at birth (LSB), litter size at weaning (LSW), litter weight at birth (LWB) and litter weight at weaning (LWW). The least squares means of fertility, LSB, LSW, LWB and LWW were 0.904, 1.422, 1.358, 6.689 kg and 41.577 kg, respectively. The means of total number of lambs born (TLB), total number of lambs weaned (TLW), total birth weight of lambs (TWB) and total weight of lambs weaned (TWW) per ewe over four lambing opportunities were 5.48, 5.25, 25.61 kg and 162.47 kg, respectively. Estimates of heritability for fertility, LSB, LSW, LWB and LWW were 0.0250, 0.0533, 0.0430, 0.0462 and 0.0255, respectively; and estimates of repeatability for these traits were 0.1242, 0.0787, 0.0772, 0.0882 and 0.0715, respectively. The low estimates of heritability and repeatability obtained in the current study for ewe productivity traits indicate that selection based on the ewe's own performance may result in slow genetic improvement. Key words: Genetic parameter, litter size, ewe productivity.

Estimation of genetic parameters for reproductive traits in shall sheep

The objective of this study was to estimate genetic parameters for reproductive traits in Shall sheep. Data included 1,316 records on reproductive performances of 395 Shall ewes from 41 sires and 136 dams which were collected from 2001 to 2007 in Shall breeding station in Qazvin province at the Northwest of Iran. Studied traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB), litter mean weight per lamb weaned (LMWLW), total litter weight at birth (TLWB), and total litter weight at weaning (TLWW). Test of significance to include fixed effects in the statistical model was performed using the general linear model procedure of SAS. The effects of lambing year and ewe age at lambing were significant (P<0.05). Genetic parameters were estimated using restricted maximum likelihood procedure, under repeatability animal models. Direct heritability estimates were 0.02, 0.01, 0.47, 0.40, 0.15, and 0.03 for LSB, LSW, LMWLB, LMWLW, TLWB, and TLWW, respectively, and corresponding repeatabilities were 0.02, 0.01, 0.73, 0.41, 0.27, and 0.03. Genetic correlation estimates between traits ranged from -0.99 for LSW-LMWLW to 0.99 for LSB-TLWB, LSW-TLWB, and LSW-TLWW. Phenotypic correlations ranged from -0.71 for LSB-LMWLW to 0.98 for LSB-TLWW and environmental correlations ranged from -0.89 for LSB-LMWLW to 0.99 for LSB-TLWW. Results showed that the highest heritability estimates were for LMWLB and LMWLW suggesting that direct selection based on these traits could be effective. Also, strong positive genetic correlations of LMWLB and LMWLW with other traits may improve meat production efficiency in Shall sheep.

Genetics of early conception and its relationship to growth traits in red deer (Cervus elaphus)

The genetics of early conception success and live-animal growth were studied in five herds of red deer in New Zealand. Conception date (CD) was used as the criterion of success in seasonally mated hinds, with 2493 mating records available. Liveweights analysed were weaning weight, yearling weight, 15-month weight and mature weight (hinds only). CD and liveweights were analysed using restricted maximum likelihood procedures with an animal model, including all available pedigree records. Under the management conditions applied, CD had a phenotypic standard deviation of 7.9 days, a repeatability across years of 0.29 ± 0.03 and a direct (univariate) heritability of 0.20 ± 0.06. Regression procedures using DNA markers to adjust the data for genetic differences resulting from an animal’s ancestral region of origin (mainly western vs eastern European) had little effect on the parameter estimates above. Direct heritability estimates for the four weight traits were 0.38 ± 0.03, 0.49 ± 0.02, 0.48 ± 0.04 and 0.46 ± 0.04, respectively, while the genetic correlations between CD and these traits (e.g. using 1763 paired records of CD with yearling weight) were –0.24 ± 0.11, –0.24 ± 0.09, –0.16 ± 0.10 and –0.04 ± 0.09, respectively. Selection for earlier CD would be successful and compatible with selection for higher juvenile weights.

Heritabilities and Genetic Correlations of Body Condition Score and Muscularity with Productive Traits and their Trend Functions in Italian Simmental Cattle

With the aim to study the genetics of energy and muscle balance in the Italian Simmental breed, the objectives of this study were: i) the estimation of the genetic parameters for body condition score (BCS) and muscularity (MU) score; ii) the estimation of genetic correlations of BCS and MU with productive traits; iii) the estimation of the expected patterns of BCS and MU over lactation. A total of 47,839 records of first-parity lactating cows, collected from 1999 to 2007 in 2794 herds, were used. Twotrait animal models were analyzed using restricted maximum likelihood (REML) procedures to estimate (co)variance components. The expected patterns of BCS and MU along the lactation of first parity cows were estimated from the solutions of DIM fixed effect obtained from an univariate mixed model for both the traits. The heritability estimated was 0.18 for BCS, 0.38 for MU, and ranged from 0.13 to 0.18 for yield traits. The genetic correlations between BCS, MU and yield traits were negative (-0.17 to -0.63). The genetic correlation between BCS and MU was strongly positive (0.88), indicating that cows that genetically tend to have high BCS are more likely to have high values of MU. The genetic parameters estimated suggested that selection for BCS and MU in dual purpose breeds may be possible, and BCS may indirectly improve MU. The expected patterns for BCS and MU showed the trend of these two traits along the lactation and can help farmers in planning the best management of the lactating cows.

Effects of feed intake on enteric methane emissions from sheep fed fresh white clover (Trifolium repens) and perennial ryegrass (Lolium perenne) forages

Published analyses of enteric methane (CH4) emissions from sheep and cattle show an inverse relationship between feed intake and CH4 yield (gCH4/kg dry matter (DM) intake), which suggests opportunities for reducing CH4 emissions from feed eaten and per unit of animal production. Most relationships between feed intake and CH4 yield have been based on animals fed conserved feeds, especially silages and grains. Our research is a series of experiments with fresh white clover (Trifolium repens) and perennial ryegrass (Lolium perenne; ryegrass) forages fed to sheep at a range of feed intake levels. This study was comprised of four experiments where good quality freshly harvested white clover or ryegrass were fed to sheep over a three-fold range in DM intake, and CH4 emissions were measured in respiration chambers for two consecutive days in each experiment. Measurements were made from 16 sheep in Experiment 1 (fed at 1.6×metabolizable energy requirements for maintenance; MEm), 28 sheep in Experiment 2 (at 0.8 and 2.0×MEm), eight sheep and two measurement periods in Experiment 3 (at 1.6×MEm), and 30 sheep in Experiment 4 (fed at 0.8, 1.2, 1.6, 2.0 and 2.5×MEm). Prior to each experiment, sheep had a 10d acclimatization period to diets. Apparent digestibility was measured over 7d from sheep in Experiments 1, 3 and 4, along with collection of rumen digesta for volatile fatty acid (VFA) determination. Although CH4 yields differed when sheep were fed white clover or ryegrass at similar intakes, the differences were inconsistent and mean values similar across all experiments. This, and a similar structure of all experiments, enabled combined analysis of data from all four experiments using the restricted maximum likelihood (REML) procedure to estimate effects of feed intake level on digestibility, digestible nutrient intake, gas emissions, and VFA concentrations in the rumen. The REML analysis showed that when DM intake increased from 0.40 to 1.60kg/d, the predicted responses were an increase in CH4 production (g/d) of 187% (12.4–35.6g/d; P<0.001), and a decline in CH4 yield of 21% (25.6–20.2g/kg DM intake; P<0.001). High feed intake levels were associated with increased molar proportions (mM of total VFA) of propionate from 0.17 to 0.21 (P=0.038). Single and multiple regressions were completed on the data from all experiments, with organic matter (OM) intake predicting 0.87 of the variation in CH4 production, and molar proportion of propionate predicting 0.60 of the variation in CH4 yield. Increasing feed intakes by 1kg/d of DM reduced CH4 yield by 4.5g/kg DM intake. Plant chemical composition was weakly related to CH4 yield. High intakes of fresh forages will lower CH4 yield from fermentation, but effects of feed composition on CH4 emissions were minor. The interaction between effects of feed intake and rumen function requires further investigation to understand relationships with CH4 emissions.

Genetic parameters for concentrations of minerals in longissimus muscle and their associations with palatability traits in Angus cattle1

The objective of this study was to estimate genetic parameters for concentrations of minerals in LM and to evaluate their associations with beef palatability traits. Samples of LM from 2,285 Angus cattle were obtained and fabricated into steaks for analysis of mineral concentrations and for trained sensory panel assessments. Nine minerals, including calcium, copper, iron, magnesium, manganese, phosphorus, potassium, sodium, and zinc, were quantified. Restricted maximum likelihood procedures were used to obtain estimates of variance and covariance components under a multiple-trait animal model. Estimates of heritability for mineral concentrations in LM varied from 0.01 to 0.54. Iron and sodium were highly and moderately heritable, respectively, whereas the other minerals were lowly heritable except for calcium, copper, and manganese, which exhibited no genetic variation. Strong positive genetic correlations existed between iron and zinc (0.49, P < 0.05), between magnesium and phosphorus (0.88, P < 0.05), between magnesium and sodium (0.68, P < 0.05), and between phosphorus and potassium (0.69, P < 0.05). Overall tenderness assessed by trained sensory panelists was positively associated with manganese, potassium, and sodium and negatively associated with phosphorus and zinc concentrations (P < 0.05). Juiciness assessed by trained sensory panelists was negatively associated with magnesium and positively associated with manganese and sodium concentrations (P < 0.05). Livery or metallic flavor was not associated with any of the minerals (P > 0.05). Beefy flavor was positively associated with calcium, iron, and zinc and negatively associated with sodium concentration, whereas a painty or fishy flavor was positively associated with sodium and negatively associated with calcium and potassium concentrations (P < 0.05). Beef is a major contributor of iron and zinc in the human diet, and these results demonstrate sufficient genetic variation for these traits to be improved through marker-assisted selection programs without compromising beef palatability.

Genetic evaluation of meat quality traits and their correlation with growth and carcase composition in Japanese quail

1. Estimates of heritability, genetic and phenotypic correlations of performance and meat quality traits were obtained in a population of Japanese quail using restricted maximum likelihood (REML) procedures. 2. The heritability estimates for body weight (BW) traits ranged from 0·15 at hatch to 0·42 at six weeks. For carcase composition traits, heritability estimates ranged from 0·12 for carcase yield to 0·26 for abdominal fat yield and for meat quality traits they ranged from 0·18 for drip loss to 0·54 for yellowness of the meat. 3. Negative genetic correlations were found between BW and carcase traits with ultimate pH and drip loss ranging from −0·01 (BW at hatch) to −0·40 (skin yield). Redness and yellowness showed negative genetic correlations with BW and carcase traits, whereas the genetic correlations with lightness were positive (from 0·04 to 0·43). 4. Shear force and cooking loss showed positive genetic correlations with carcase, breast, abdominal and skin yield. 5. In conclusion, meat quality traits have the potential to be improved through genetic selection but selection for higher BW and carcase composition may reduce the meat quality of Japanese quail through reducing redness, ultimate pH and intramuscular fat and increasing lightness, shear force and cooking loss of the meat.

Genetic relationship of body measurement traits at early age with carcass traits in Japanese black cattle

Estimates of genetic parameters were obtained for body measurement traits of 648 animals at 4 months of age, of 545 at 8 months and carcass traits of 14 972 animals with the use of an animal model by the restricted maximum likelihood procedure. The estimated heritabilities for carcass traits were high (0.41 to 0.54). At 4 months the estimated direct heritabilities for body measurement traits were moderate to high (0.28 to 0.64), except for chest width (0.19); at 8 months they were also moderate to high (0.23 to 0.49), except for chest depth and chest width (0.18 and 0.06, respectively). Maternal heritabilities for all body measurement traits were low at both ages. The results indicate that because of their moderate direct genetic correlations with body measurement traits, carcass weight, rib thickness and subcutaneous fat thickness can be improved; however, rib eye area and beef marbling standard show little such possibility considering their correlation with body measurement traits.

한우의 초음파 측정 형질과 도체 형질의 유전모수 추정

This study was conducted to estimate genetic parameters for ultrasound and carcass traits in Hanwoo. Heritabilities and genetic and phenotypic correlations were estimated for carcass and ultrasound measurements collected from Hanwoo cows (n=312) born at Hanwoo experiment station. Traits evaluated were eye muscle area (EMA), backfat thickness (BF), marbling score (MS) from carcass, and ultrasound eye muscle area (UEMA), ultrasound backfat (UBF), and ultrasound marbling score (UMS). Parameters were estimated using multi-trait animal models byderivative-free restricted maximum likelihood procedures. Estimated heritabilities for UBF, UEMA and UMS were 0.43, 0.23 and 0.32, while heritabilities for BF, EMA and MS were 0.33, 0.13 and 0.33 in fattened cows, respectively. Genetic correlations between ultrasound and carcass measurements were estimated to -0.19, -0.61, and -0.36 for UBF: UEMA, UBF: UMS, and UEMA: UMS in fattened cows, respectively. Phenotypic correlations between ultrasound and carcass measurements were 0.03, 0.13 and 0.26 for UBF: UEMA, UBF: UMS, and UEMA: UMS in fattened cows, respectively. As for the steer, genetic correlations between ultrasound and carcass measurements were 0.36, -0.80 and 0.27 for UBF: UEMA, UBF: UMS, and UEMA: UMS in steers, respectively. Phenotypic correlations between ultrasound and carcass measurements were 0.13, 0.07 and 0.41 for UBF: UEMA, UBF: UMS, and UEMA: UMS in steers, respectively. In conclusion, this finding would be very useful to implement into Hanwoo breeding program.

Genetic relationship of conformation traits with average somatic cell score at 150 and 305 days in milk in Holstein cows of Iran

Genetic, environmental, and phenotypic correlations among average somatic cell score (SCS) at different stages of lactation and conformation traits were estimated. Data consisted of the lactational average of SCS at 150 (SCS150) and 305 (SCS305) d in milk and 19 conformation traits recorded on 57,154 primiparous Holstein cows, that calved from 1996 to 2009 in 119 herds in Iran. Variance components were estimated using the restricted maximum likelihood procedure based on multiple-trait animal models. Udder depth (−0.32), fore udder attachment (−0.22), and udder width (0.34) showed moderate genetic correlation with SCS150. Heart girth (0.17), body depth (0.14), chest width (0.26), and angularity (0.19), showed modest genetic correlation with SCS150. The estimated heritabilities for SCS150 and SCS305 were 0.06 and 0.08, respectively. The heritability of the conformation traits ranged from 0.09 to 0.29. Genetic and environmental correlations between SCS150 and SCS305 were very high (means ± SE; 0.99±0.01 and 0.89±0.01, respectively), which indicates that recording SCS over a shorter period of lactation is an alternative approach for involving many herds in SCS data collection. The low heritability of SCS indicated that indirect selection for some of udder and body traits might be helpful to reduce the SCS. Additionally, selection for udder traits may help reduce SCS in developing countries where SCS data are sparsely recorded.

Genetic parameters for carnitine, creatine, creatinine, carnosine, and anserine concentration in longissimus muscle and their association with palatability traits in Angus cattle1

The objective of this study was to estimate genetic parameters for carnitine, creatine, creatinine, carnosine, and anserine concentration in LM and to evaluate their associations with Warner-Bratzler shear force (WBSF) and beef palatability traits. Longissimus muscle samples from 2,285 Angus cattle were obtained and fabricated into steaks for analysis of carnitine, creatine, creatinine, carnosine, anserine, and other nutrients, and for trained sensory panel and WBSF assessments. Restricted maximum likelihood procedures were used to obtain estimates of variance and covariance components under a multiple-trait animal model. Estimates of heritability for carnitine, creatine, creatinine, carnosine, and anserine concentrations in LM from Angus cattle were 0.015, 0.434, 0.070, 0.383, and 0.531, respectively. Creatine, carnosine, and anserine were found to be moderately heritable, whereas almost no genetic variation was observed in carnitine and creatinine. Moderate positive genetic (0.25, P < 0.05) and phenotypic correlations (0.25, P < 0.05) were identified between carnosine and anserine. Medium negative genetic correlations were identified between creatine and both carnosine (-0.53, P < 0.05) and anserine (-0.46, P < 0.05). Beef and livery/metallic flavor were not associated with any of the 5 compounds analyzed (P > 0.10), and carnitine concentrations were not associated (P > 0.10) with any of the meat palatability traits analyzed. Carnosine was negatively associated with overall tenderness as assessed by trained sensory panelists. Similar negative associations with overall tenderness were identified for creatinine and anserine. Painty/fishy was the only flavor significantly and negatively associated with creatinine and carnosine. These results provide information regarding the concentration of these compounds, the amount of genetic variation, and evidence for negligible associations with beef palatability traits in LM of beef cattle.

Genetic parameter estimates for subjectively assessed and objectively measured traits in South African Dorper sheep

Breed improvement in the Dorper sheep breed is based mainly on subjective assessment in the show ring. Information is limited about the genetic relationships between subjectively assessed and objectively measured traits in the breed. In an effort to establish genetic parameters as well as relationships amongst these traits, this study was conducted using Restricted Maximum Likelihood (REML) procedures. Live weight and growth traits were moderately to highly heritable ranging from 0.18±0.04 for post weaning weight to 0.54±0.15 for yearling weight using single-trait analyses. However, when multi-trait analyses were implemented, weaning weight and average daily gain to weaning assumed moderate h2 of 0.30±0.03 and 0.27±0.03 respectively. Maternal effects were significant, although of fairly low magnitude with the exception of estimates for post weaning weight and average daily gain to post weaning. Heritabilities of subjectively assessed traits were fairly low, ranging from 0.07±0.02 for Conformation and Type to 0.15±0.03 for Size using both single-trait and multi-trait analyses. It was established through multi-trait analyses that subjectively assessed and objectively measured traits had mainly positive genetic correlations. Five-trait analyses led the conclusion that there are some moderate to high maternal genetic correlations as well as dam permanent environmental correlations between live weight, growth, Size and Type. A few negative direct genetic correlations were found for trait combinations of Colour with yearling weight and average daily gain to yearling. It was concluded that despite most of the traits being positively correlated more emphasis should be put on breed improvement basing on objectively measured traits.

Estimates of Genetic and Phenotypic Trends of Growth Traits in Bali Cattle

The aim of this study was to estimate genetic and phenotypic trends for growth traits including birth (BW), weaning (WW) and yearling weight (YW) in Bali cattle. The number of cattle used to determine growth traits of BW, WW, and YW were 235, 215, and 178 heads, respectively. Estimation of breeding value, phenotypic and genetic correlation were calculated by Restricted Maximum Likelihood and General Linier Model (GLM) procedures, respectively. Genetic trends analysis was performed using the regression mean breeding values on birth year. Phenotypic and genetic correlation among BW and WW were 0.10 and 0.08 respectively and 0.90 and 0.70 for WW and YW respectively. The phenotypic trends for traits of birth and weaning weight were constant, whereas yearling weight was fluctuating from 2000 to 2008. Likewise, in the case of genetic trends, the birth and weaning weight were constant from 2000 to 2008 except for WW in 2005, whereas the genetic trends for yearling weight showed a fluctuation of wide range. According to the breeding value estimated for all traits, the best was the sire No. 0565, whose breeding value for BW, WW and YW were +0.07, +2.79, and +10.25 kg, respectively higher than the mean value of the population. The genetic trends showed that there have been a significant and positive genetic improvement in all growth traits and indicate that selection would be effective. Genetic correlation between WW and YW was high (0.70) which indicates that the selection on weaning weight might also increase yearling weight in Bali cattle.

Factors analysis and genetic parameter estimation of female repro-ductive traits in pigs

Reproductive performance of stock sows is one of the important factors of economic impact in pig farms. In this study, 8491 litter records from 2699 sows of Yorkshire, Landrace, and Duroc were analyzed using fixed model to determine the effect of parity, mating season, and breed on total number born (TNB), number healthy birth (NHB), litter birth weight (LWB), number weak birth (NWB), stillbirth, mummy fetus, and deform fetus by the least square analysis. Genetic parameters of the above traits were estimated by restricted maximum likelihood (REML) procedure. In addition, the effectiveness of pure-breeding and cross-breeding on litter performance were compared. The results showed that, parity, mating season, and breed had significant effect on TNB, NHB, and LWB(P < 0.001).The effects of parity and breed were significant on NWB(P < 0.001), while mating season had non-significant effect on NWB. Parity showed significant effect on stillbirth, while the effect of mating season and breed was not significant. Parity, mating season, and breed had no significant effect on mummy fetus and deform fetus. Landrace♂×Large White♀ showed the best litter performance, including TNB, NHB, and LWB. Moreover, LWB of Landrace depicted the highest heritability, while other traits were all bellow 0.2. The genetic correlation between TNB and NHB, NHB and LWB were higher than 0.96 in the three breeds. These results provided reference data for minimizing low-reproductive performance caused by non-infectious factors and improving sow reproductive performance in pig farms.

Direct and maternal (co)variance components, genetic parameters, and annual trends for growth traits of Makooei sheep in Iran

Genetic parameters and genetic trends for birth weight (BW), weaning weight (WW), 6-month weight (6MW), and yearling weight (YW) traits were estimated by using records of 5,634 Makooei lambs, descendants of 289 sires and 1,726 dams, born between 1996 and 2009 at the Makooei sheep breeding station, West Azerbaijan, Iran. The (co)variance components were estimated with different animal models using a restricted maximum likelihood procedure and the most appropriate model for each trait was determined by Akaike's Information Criterion. Breeding values of animals were predicted with best linear unbiased prediction methodology under multi-trait animal models and genetic trends were estimated by regression mean breeding values on birth year. The most appropriate model for BW was a model including direct and maternal genetic effects, regardless of their covariance. The model for WW and 6MW included direct additive genetic effects. The model for YW included direct genetic effects only. Direct heritabilities based on the best model were estimated 0.15 ± 0.04, 0.16 ± 0.03, 0.21 ± 0.04, and 0.22 ± 0.06 for BW, WW, 6MW, and YW, respectively, and maternal heritability obtained 0.08 ± 0.02 for BW. Genetic correlations among the traits were positive and varied from 0.28 for BW-YW to 0.66 for BW-WW and phenotypic correlations were generally lower than the genetic correlations. Genetic trends were 8.1 ± 2, 67.4 ± 5, 38.7 ± 4, and 47.6 ± 6 g per year for BW, WW, 6MW, and YW, respectively.

Direct and maternal genetic effects for body weight and price of calves sold for veal production1

The aim of this study was to estimate direct and maternal genetic parameters for age at sale (AS, d), BW (kg), price (PR, €/kg), and market value (MV, €/calf) of Brown Swiss male calves (Bos taurus) from first- (n = 6,719) and second- (n = 4,405) parity dams marketed at livestock auctions from 2003 to 2007, and destined for veal production. Market value was calculated as the product of PR and BW. Restricted maximum likelihood procedures incorporating multiple trait animal models were used to infer genetic parameters for AS, BW, and PR, whereas estimates for MV were from single trait models. Bivariate analyses treating performance of calves from first- and second-parity cows as different traits were also performed. Direct heritabilities for AS, BW, and cattle prices ranged from 0.046 to 0.090, 0.078 to 0.130, and 0.064 to 0.152, respectively, and the corresponding maternal heritabilities varied from 0.020 to 0.030, 0.036 to 0.079, and 0.020 to 0.045, respectively. Direct genetic correlations between the traits were generally moderate to high and negative, whereas direct-maternal relationships were moderate to low. Genetic correlation between the same trait recorded on calves from first- and second-parity dams was less than unity, but generally high and positive, suggesting that AS, BW, PR, and MV can be treated as the same traits across parities. As calf price is routinely collected at auctions and shows genetic variation, it can be genetically improved.

Genetic analysis of ewe productivity traits in Makooei sheep

This study reports genetic and environmental (co)variance components for productivity traits of Makooei sheep, using between 2647 and 3418 records obtained from 1429 ewes. Data were collected during 1996–2009 on the Breeding Station of Makooei sheep, located in Makoo in the west-Azerbaijan province of Iran. Genetic parameters were estimated for three basic and six composite traits. The basic traits were conception rate (CR), number of lambs born (NLB) and number of lambs alive at weaning (NLAW). The composite traits were number of lambs born per ewe exposed (NLBEE), number of lambs weaned per ewe exposed (NLWEE), total litter weight at birth per ewe lambed (TLBW), total litter weight at weaning per ewe lambed (TLWW), total litter weight at birth per ewe exposed (TLBWEE) and total litter weight at weaning per ewe exposed (TLWWEE). Genetic parameters were estimated with univariate and bivariate models using restricted maximum likelihood (REML) procedures. Random effects were explored by fitting additive direct genetic effects, permanent environmental effects due to the animal as well as service sire effects in different models for ewe productivity. The most appropriate model for each trait was determined based on likelihood ratio tests and Akaike's Information Criterion (AIC). Direct heritability estimates for CR, NLB, NLAW, NLBEE, NLWEE, TLBW, TLWW, TLBWEE and TLWWEE were 0.05±0.02, 0.11±0.01, 0.06±0.01, 0.08±0.02, 0.04±0.02, 0.17±0.03, 0.12±0.02, 0.13±0.02 and 0.10±0.02, respectively. The estimate for the permanent environmental variance due to the animal ranged from 0.03±0.02 for CR to 0.12±0.01 for NLAW, whereas service sire effects ranged from 0.02±0.01 for TLWW to 0.05±0.01 for TLBW. Genetic correlation estimates among studied traits ranged from −0.13 for CR with TLWW to 0.97 for NLAW with NLWEE. Phenotypic correlation estimates were generally smaller in magnitude than genetic correlations. Service sire effects were found to be important only for litter weight traits. These estimates of genetic parameters may provide a basis for deriving selection indexes for reproductive traits.

Genetic parameters and trends of production traits in Iranian Holstein population

The aim of the present study was to estimate the genetic parameters and trends of milk yield, fat yield and fat percentage in Iranian Holstein population using animal model (multiple-traits) and Derivative-Free Restricted Maximum Likelihood (DFREML) procedure. First lactation data of 1128, 1093 and 1093 Mazandaran Holstein cows were collected from National Animal Breeding Center from 1988 to 2004 for milk yield, fat yield and fat percentage, respectively. The numbers of the whole animals were 49776 from 12 generations of studied pedigree. The heritability of milk yield, fat yield and fat percent during 305 days of lactation were 0.22, 0.24 and 0.28, respectively. Genetic correlations between milk and fat yield, milk yield and fat percent, and fat yield and fat percent were 0.99, -0.98 and 0.52, respectively. The genetic trends of all three studied traits were calculated using regression of means of breeding values over the years. The genetic trends were positive for milk (6.791) and fat (0.139) yields and negative for fat percentage (-0.04). Key words: Production traits, genetic parameter, genetic trend, Iranian Holstein.