Estimation of genetic parameters for milk and fertility traits within and between low,medium and high dairy production systems in Kenya to account for genotype-by-environment interaction

Dairy records from the Dairy Recording Service of Kenya were classified into low, medium and high production systems based on mean 305-day milk yield using the K-means clustering method. Milk and fertility records were then analysed to develop genetic evaluation systems accounting for genotype-by-environment interaction between the production systems. Data comprised 26,638 lactation yield, 3,505 fat yield, 9,235 age at first calving and 17,870 calving interval records from 12,631 cows which were descendants of 2,554 sires and 8,433 dams. An animal model was used to estimate variance components, genetic correlations and breeding values for the production systems. Variance components increased with production means, apart from genetic group variances, which decreased from the low to the high production system. Moderate heritabilities were estimated for milk traits (0.21–0.27) and fat traits (0.11–0.38). Low heritabilities were estimated for lactation length (0.04–0.10) and calving interval (0.03–0.06). Moderate heritabilities (0.25–0.26) were estimated for age at first calving, except under the high production system (0.05). Within production systems, lactation milk yield, 305-day milk yield and lactation length had high positive genetic correlations (0.52–0.96), while lactation milk yield and lactation length with age at first calving had negative genetic correlations. Milk yield and calving interval were positively correlated except under the low production system. The genetic correlations for lactation milk yield and 305-day milk yield between low and medium (0.48 ± 0.20 and 0.46 ± 0.21) and low and high production systems’ (0.74 ± 0.15 and 0.62 ± 0.17) were significantly lower than one. Milk yield in the low production system is, therefore, a genetically different trait. The low genetic correlations between the three production systems for most milk production and fertility traits suggested that sires should be selected based on progeny performance in the targeted production system.     

Heterosis effects in a black and white dairy cattle population under different production environments

The effect of the environmental level of production (ENV) on the expression of heterosis for 305-day milk, fat, protein, and fat plus protein (FP) yields, lactation average somatic cell score (LSCS), and age at first calving (AFC) was investigated in first lactation Black and White dairy cows in the Netherlands, and officially enrolled in the Dutch herd-book. Holstein Friesian (HF), Dutch Friesian (DF), and first generation (F₁) crosses obtained from the mating of HF sires and DF dams (HD) were involved in the study, and data from animals with a calving date between 1990 and 2000 were used. A total of 22,930 cows with production and AFC information distributed in 3549 herds and 11,055 cows with LSCS information distributed in 2071 herds, were available. Adjusted lactation yield of milk for each herd was obtained using a model that accounted for fixed effects of herd, year and month of calving, genotype, and AFC. The overall mean of all adjusted data was computed, and 3 ENV were defined on the basis of the overall mean ± 0.5 standard deviations. Once ENV was defined, traits were analysed with a model that included fixed effects of ENV, herd nested within ENV, AFC (only production traits and LSCS), year and month of calving, genotype, and the interaction between ENV and genotype. Least squares means for the interaction effect were used to estimate heterosis and to evaluate its magnitude across ENV. Holstein Friesian achieved higher productions than DF. First generation crosses showed productions close to HF, especially in the low ENV. Estimates of heterosis for yield traits ranged from 2.4% (milk) in the high to 5.3% (fat) in the low ENV, and reduced with increasing ENV. Estimates for LSCS and AFC were low, with the exception of LSCS in the high ENV. Results suggest that the highest non-additive genetic effects for yield traits and LSCS were expressed in the most stressful ENV, i.e., the low one for production and the high one for LSCS.     

Identification of genomic regions related to age at first calving and first calving interval in water buffalo using single-step GBLUP

In Brazil, water buffaloes have been used to produce milk for mozzarella cheese production. Consequently, the main selection criterion applied for the buffalo genetic improvement is the estimated mozzarella yield as a function of milk, fat and protein production. However, given the importance of reproductive traits in production systems, this study aimed to use techniques for identifying genomic regions that affect the age at first calving (AFC) and first calving interval (FCI) in buffalo cows and to select candidate genes for the identification of QTL and gene expression studies. The single-step GBLUP method was used for the identification of genomic regions. Windows of 1 Mb containing single-nucleotide polymorphisms were constructed and the 10 windows that explained the greatest proportion of genetic variance were considered candidate regions for each trait. Genes present into the selected windows were identified using the UOA_WB_1 assembly as the reference, and their ontology was defined with the Panther tool. Candidate regions for both traits were identified on BBU 3, 12, 21 and 22; for AFC, candidates were detected on BBU 6, 7, 8, 9 and 15 and for first calving interval on BBU 4, 14 and 19. This study identified regions with great contribution to the additive genetic variance of age at first calving and first calving interval in the population of buffalo cows studied. The ROCK2, PMVK, ADCY2, MAP2K6, BMP10 and GFPT1 genes are main candidates for reproductive traits in water dairy buffaloes, and these results may have future applications in animal breeding programs or in gene expression studies of the species.     

Genetic and phenotypic parameters and annual trends for milk production and fertility traits of the Sahiwal cattle in semi arid Kenya

Data comprising 7211 lactation records of 2894 cows were used to estimate genetic and phenotypic parameters for milk production (lactation milk yield, LMY and lactation length, LL) and fertility (calving interval, CI; number of services per conception, NSC and age at first calving, AFC) traits. Genetic, environmental and phenotypic trends were also estimated. Variance components were estimated using univariate, bivariate and trivariate animal models on based restricted maximum likelihood procedures. Univariate models were used for each trait, while bivariate models were used to estimate genetic and phenotypic correlations between milk production and fertility traits and between LMY, LL, CI and NSC within each lactation. Trivariate models were used in the analysis of LMY, LL, CI and NSC in the first three lactations. Heritability estimates from the univariate model were 0.16, 0.07, 0.03, 0.04 and 0.01 for LMY, LL, CI, AFC and NSC, respectively. The heritability estimates from trivariate analysis were higher for milk production traits than those from univariate analyses. Genetic correlations were high and undesirable between milk production and fertility traits, while phenotypic correlations were correspondingly low. Genetic trends were close to zero for all traits, while environmental and phenotypic trends fluctuated over the study period.     

Genetic aspects of productive and reproductive traits in a Murrah buffalo herd in São Paulo,Brazil

This study investigated genetic trends of some productive and reproductive traits in a herd of Murrah buffalo raised in São Paulo, Brazil. Variance components for milk production (MP), length of lactation (LL), calving interval (CI) and age of first calving (AFC) were estimated by the restricted maximum likelihood method, using an animal model. Estimated heritability values were 0.38; 0.01; 0.10 and 0.20 for MP, LL, CI and AFC, respectively. Estimated repeatability values were 0.50, 0.13 and 0.20 for MP, LL and CI, respectively. Means of predicted breeding values for cows, dams and sires according to calving year and the genetic correlations were presented.     

Estimation of genetic parameters for 13 female fertility indices in Holstein dairy cows

This study was aimed to assess genetic parameters for 13 traits in heifers and first-parity Holstein dairy cows. Data consisted of calving and insemination dates of 14,707 Holstein dairy cows in Isfahan province of Iran. Reproductive traits included age at first service (AFS), first service to conception (FSTC), gestation length (GL), age at first calving (AFC), calving to first service (CTFS), days open (DO), calving interval (CI), number of services per conception (NS), and non-return rate at 56 days (NRR). Model equations were optimized using GLM procedure in SAS package following genetic analysis using animal models in ASREML software. Minimum and maximum departure from normal distribution for phenotypic records belonged to AFS, NRR, GL, DO, CI and AFC, NS, FSTC, CTFS, respectively. Estimated heritability varied from 0.002 (NRR) to 0.184 (GL) in heifers and from 0.003 (NRR) to 0.153 (GL) in first-parity cows. AFS, CTFS, and GL were noticeably heritable compared to other assessed traits. Estimated absolute additive genetic correlations were in the range of 0.01 (NRR and AFS) and 0.99 (NRR and NS) in heifers and 0.07 (GL and CI) to 1 (FSTC and CI) in cows. Additive genetic correlations were antagonistic between AFS and other traits, except AFC. Interestingly, NRR which has been included in sire catalogs had the highest average absolute genetic associations with other traits.     

Estimation of Variances and Covariances of Milk Traits by REML with an Individual Animal Model

Abstract

Records form Finnish Ayrshire cattle were used to estimate variances and covariances of milk traits by the restricted maximum likelihood (REML) method using the individual animal model (IAM). Two data sets were analyzed. The first data set consisted of 1423 sires and 16363 cows, of which 11911 had records on first lactation. The heritabilities estimated from this data set for milk yield, protein yield, protein content and fat content were 0.40, 0.31, 0.63 and 0.68, respectively. The second data set was a subset of first data set with herds with less than ten observations excluded and consisted of 1335 sires and 11262 cows with 8140 first, 5688 second and 3717 third lactation records. The heritability estimates from the second data set under a repeatability model for milk yield, protein yield, protein content and fat content were 0.30, 0.26, 0.59 and 0.66, respectively. The repeatability estimates for the same traits were 0.53, 0.51, 0.67 and 0.76, respectively. The second data set was also used to estimate genetic and phenotypic correlations among milk traits in first lactation. Both genetic and phenotypic correlations among protein yield and protein and fat content traits were small. The genetic correlation between milk yield and protein content was -0.61, between milk yield and fat content -0.50 and between protein content and fat content 0.67. Absolute values of phenotypic correlations for the same pairs of traits were somewhat smaller than respective genetic correlations.     

Converting to organic dairy farming: Consequences for production, somatic cell scores and calving interval of first parity Holstein cows

This paper aims to describe the changes prompted by conversion to organic farming for milk production and fertility of first parity Holstein cows.

Data was collected for Dutch organic farms, with a distinction made between long-standing-organic farms, converted organic farms and a reference group of conventional farms. The percentage Holstein blood in the herds, milk production (kg milk, % milk fat, % milk protein), somatic cell scores (SCS), calving interval (CI) and age at first calving (AFC) were described over time. An animal model was used to estimate the effects of conversion on different traits based on data from converted organic farms.

Milk production was lower and somatic cell counts were higher on long-standing-organic farms than on conventional and converted organic farms. Interestingly, at pre-organic farms, i.e. before their conversion, the milk production level was already lower than at conventional farms.

The estimates from our statistical analysis showed a highly significant decrease in milk yield and protein percentage due to conversion. Also fat content decreased, SCS increased and AFC increased significantly.

It can be concluded that the conversion to organic farming is a gradual process over years. Dutch farmers who decided during the late 1990s to convert to organic farming, represented a specific group of farmers distinct from conventional farmers, which was reflected by lower milk yields, milk fat percentage and protein percentage before conversion as compared to conventional farms. During conversion, significant changes in milk production, protein and fat contents and somatic cell scores took place. Age of first calving is an important difference between organic and conventional farming.     

The Estimation of Genetic Parameters of Holstein Dairy Cows in Ningxia Region

The genetic parameters of milk fat percentage (FP), milk protein percentage (PP), somatic cell score (SCS), milk yield of 305 days (MYD), age at first calving (AFC),calving interval (CI) and linear classification scores (LCS) were estimated using the DHI data of 2008 to 2016 in Ningxia area of 27 444 Holstein dairy cows and type records. With the aid of DMU v 6.0 AI-REML software, DMU combined with EM algorithm and multi character animal model was used to model the influence factors of the birth season, herd, year, parity and individual additive genetic effect. The results showed that FP, PP, SCS, MYD, AFC, CI and LCS's heritability were 0.14, 0.19, 0.19, 0.31, 0.37, 0.10, 0.07, respectively. At the same time, the breeding value, genetic correlation and CPI2 values of different traits were calculated. The genetic evaluation for dairy cows in Ningxia, could be more in-depth understanding of the basic situation of the herd, to provide basic data for the construction of dairy cow breeding matching selection, planning and selection index.     

宁夏地区荷斯坦奶牛遗传参数估计

利用2008-2016年出生的27 444头宁夏地区荷斯坦奶牛生产性能（dairy herd improvement,DHI）数据及体型线性评分数据计算乳脂率（fat percentage,FP）、乳蛋白率（protein percentage,PP）、体细胞评分（somatic cell score,SCS）、305 d产奶量（milk yield of 305 days,MYD）、初产日龄（age at first calving,AFC）、产犊间隔（calving interval,CI）和体况评分（linear classification scores,LCS）的遗传参数。利用DMU v 6.0软件,采用AI-REML模块结合EM算法并配合多性状动物模型,以季节、场、年份、胎次和动物个体加性遗传效应作为模型的影响因素。计算结果表明,宁夏地区奶牛的FP、PP、SCS、MYD、AFC、CI和LCS的遗传力分别为0.14、0.19、0.19、0.31、0.37、0.10和0.07,同时得出了奶牛不同性状的育种值、遗传相关和奶牛生产性能指数2（China performance index 2,CPI2）值。本研究通过对宁夏地区奶牛DHI数据的深挖和遗传评估,准确地把握了宁夏奶牛群体结构特征,对于奶牛的选种选配、育种规划和选择指数的构建有重要意义。     

Genetic parameters and genetic trends for age at first calving and calving interval in an Angus-Blanco Orejinegro-Zebu multibreed cattle population in Colombia

Genetic parameters and genetic trends for age at first calving (AFC), interval between first and second calving (CI1), and interval between second and third calving (CI2) were estimated in a Colombian beef cattle population composed of Angus, Blanco Orejinegro, and Zebu straightbred and crossbred animals. Data were analyzed using a multiple trait mixed model procedures. Estimates of variance components and genetic parameters were obtained by Restricted Maximum Likelihood. The 3-trait model included the fixed effects of contemporary group (year-season of calving-sex of calf; sex of calf for CI1 and CI2 only), age at calving (CI1 and CI2 only), breed genetic effects (as a function of breed fractions of cows), and individual heterosis (as a function of cow heterozygosity). Random effects for AFC, CI1, and CI2 were cow and residual. Program AIREMLF90 was used to perform computations. Estimates of heritabilities for additive genetic effects were 0.15 ± 0.13 for AFC, 0.11 ± 0.06 for CI1, and 0.18 ± 0.11 for CI2. Low heritabilities suggested that nutrition and reproductive management should be improved to allow fuller expressions of these traits. The correlations between additive genetic effects for AFC and CI1 (0.33 ± 0.41) and for AFC and CI2 (0.40 ± 0.36) were moderate and favorable, suggesting that selection of heifers for AFC would also improve calving interval. Trends were negative for predicted cow yearly means for AFC, CI1, and CI2 from 1989 to 2004. The steepest negative trend was for cow AFC means likely due to the introduction of Angus and Blanco Orejinegro cattle into this population.     

Environmental factors affecting milk,fat and protein yields in Jersey cattle in Zimbabwe

A study was carried out to establish the factors affecting milk, butterfat and protein yields in Zimbabwean Jersey cattle. A total of 10,986 unedited 305-day lactation records were obtained from Zimbabwe Livestock Identification Trust containing 25 herds, with cows calving in the period 1996–2008. The general linear model procedure of the Statistical Analysis Systems version 9.1.3 was used to determine the environmental factors. Herd-year-season, calving interval, days dry and both the linear and quadratic effects of age at calving fitted as covariates significantly (P < 0.0001) affected the milk, fat and protein yields. Herd-year-season accounted for 36%, 36% and 35% to the total variation in milk, fat and protein yields, respectively. Milk, fat and protein yields increased with an increase in calving interval. The optimum dry period for milk, fat and protein yields obtained was 60–75 days dry. The relationship between the production traits and age at calving was both linear and quadratic, implying that milk, fat and protein yields increase with the age of the animal. It is thus necessary to preadjust data for these environmental factors when carrying out genetic evaluations of production traits in dairy cattle.     

中国荷斯坦牛乳房性状、体型总分与产奶性状的相关分析

研究利用武汉市58头公牛的971头女儿2006—2007年间的体型性状鉴定记录及2001—2007年间的生产性能测定记录,配合动物模型,采用REML方法进行参数估计,探讨了乳房性状、体型总分与产奶性状之间的关系。结果表明:乳房性状与产奶性状之间的表型相关较小。后乳房宽度与产奶性状之间存在强的遗传正相关(0.44～0.89)。后乳房高度与305 d产奶量(0.27)、305 d乳脂量(0.16)存在遗传正相关,而与305 d乳蛋白量(-0.32)存在遗传负相关。前乳房附着与产奶性状基本不存在相关。悬韧带与305 d产奶量存在遗传正相关(0.79)。乳房深度与305 d产奶量存在遗传负相关(-0.20)。体型总分与305 d产奶量、305 d乳脂量、305 d乳蛋白量存在较强的遗传正相关,故加强乳房性状和体型总分的选择对提高奶牛的生产性能有益。     

河北省中国荷斯坦牛产奶和体型性状遗传参数分析

旨在探究河北省中国荷斯坦牛产奶和体型性状的遗传参数,为育种提供参考.本研究收集了2012-2018年河北省133个牛场8 891头中国荷斯坦母牛第一胎次的3个产奶性状记录(产奶量、乳脂率和乳蛋白率)和26个体型性状记录,利用DMU软件,以场年季、产犊月龄、鉴定年季和鉴定员效应为固定效应,以个体的加性遗传效应为随机效应,...     

Genetic parameters for linear type traits in the Rendena dual‐purpose breed

The aim of the study was to estimate the genetic parameters for five composite traits and 20 individual type traits on 10 735 first‐parity Rendena dual‐purpose cows. Fixed effects included in the linear animal mixed models were herd‐year‐classifier, days in milk and age at first calving; the additive genetic effect of the animal was included as a random effect. Heritability estimates varied from 0.12 (feet) to 0.52 (stature). Genetic correlations between the individual body size traits were all ≥0.69; similar strong genetic correlations existed between traits describing similar morphological characteristics (e.g. mammary system, fleshiness). Many of the body size traits were negatively genetically correlated with animal fleshiness. Genetic trends showed that genetic merit for body size increased consistently over the last 10 years, while genetic merit for fleshiness declined. These results suggest that the characteristics of the dual‐purpose Rendena cattle are becoming more like specialized milk‐producing animals. Nonetheless, sufficient genetic variation exists to halt or reverse the deterioration in fleshiness.     

Genetic parameters of milk production traits and fatty acid contents in milk for Holstein cows in parity 1 – 3

The objective of this study was to estimate genetic parameters of milk, fat, and protein yields, fat and protein contents, somatic cell count, and 17 groups and individual milk fatty acid (FA) contents predicted by mid‐infrared spectrometry for first‐, second‐ and third‐parity Holstein cows. Edited data included records collected in the Walloon region of Belgium from 37 768 cows in parity 1, 22 566 cows in parity 2 and 8221 in parity 3. A total of 69 (23 traits for three parities) single‐trait random regression animal test‐day models were run. Approximate genetic correlations among traits were inferred from pairwise regressions among estimated breeding values of cow having observations. Heritability and genetic correlation estimates from this study reflected the origins of FA: de novo synthetized or originating from the diet and the body fat mobilization. Averaged daily heritabilities of FA contents in milk ranged between 0.18 and 0.47. Average daily genetic correlations (averaged across days in milk and parities) among groups and individual FA contents in milk ranged between 0.31 and 0.99. The genetic variability of FAs in combination with the moderate to high heritabilities indicated that FA contents in milk could be changed by genetic selection; however, desirable direction of change in these traits remains unclear and should be defined with respect to all issues of importance related to milk FA.     

Crossbreeding effects on milk yield traits and calving interval in spring‐calving dairy cows

The aim of the study was to assess crossbreeding effects for 305‐day milk, fat, and protein yield and calving interval (CI) in Irish dairy cows (parities 1 to 5) calving in the spring from 2002 to 2006. Data included 188 927 records for production traits and 157 117 records for CI. The proportion of genes from North American Holstein Friesian (HO), Friesian (FR), Jersey (JE) and Montbéliarde (MO) breeds, and coefficients of expected heterosis for HO×FR, HO×JE and HO×MO crosses were calculated from the breed composition of cows’ parents. The model used to assess crossbreeding effects accounted for contemporary group, age at calving within parity, linear regression on gene proportions for FR, JE and MO, and linear regression on coefficients of expected heterosis for HO×FR, HO×JE and HO×MO, as fixed effects, and additive genetic, permanent environmental and residual as random. Breed effects for production traits were in favour of HO, while for CI were in favour of breeds other than HO. The highest heterosis estimates for production were for HO×JE, with first‐generation crosses yielding 477 kg more milk, 25.3 kg more fat, and 17.4 kg more protein than the average of the parental breeds. The highest estimate for CI was for HO×MO, with first‐generation crosses showing 10.2 days less CI than the average of the parental breeds. Results from this study indicate breed differences and specific heterosis effects for milk yield traits and fertility exist in Irish dairy population.     

Effects of clinical mastitis on reproductive and milk performance of Holstein cows in Morocco

The aim of this study was to determine the influence of clinical mastitis and time of first mastitis occurrence on reproductive and milk performance of Holstein cows. Data were collected in a dairy farm from 2008 to 2012 on 1725 cows, among which 464 cows with mastitis. To determine the influence of clinical mastitis on reproductive and milk performance, models included fixed effects of parity, calving season, calving year, and group (cows with and with no mastitis). To determine the effect of time of 1st mastitis occurrence on reproductive performance, the mastitic cows group was further reclassified into three groups: prior to 60 days, between 60 and 90 days and greater than 90 days postpartum. For milk performance, the mastitic cows group was divided into two groups: before and after peak milk yield. Clinical mastitis had significant effects on calving to first AI interval, milk yield, and fat yield, but a non-significant effect on days open, number of inseminations per conception, and milk fat percentage. Mastitic cows had a calving to first AI interval 6.1 days longer and 549.6 kg milk and 20.4 kg fat per 305 days of lactation lower than those with no mastitis. Time of 1st mastitis occurrence did not have any significant effect on reproductive performance. Further, milk and fat yields of cows diseased before peak milk yield were 506 kg and 23.9 kg, respectively, lower than those of cows affected after peak milk yield. Extra attention needs to be paid to mastitis during the early postpartum period.

     

Heritability estimates and genetic correlations of various production and reproductive traits of different grades of dairy cattle reared under subtropical condition

Inheritance of economic traits and their genetic correlation was studied in different breeds and their various grades (crossbred’s cattle) under the subtropical condition. Data on principal parameters comprising 10 years, that is 2004–2014, were utilized for the present study. Different grades of dairy cows comprising Holstein Friesian (HF), Sahiwal x Friesian (SxHF), Jersey (J), Jersey x Achai (JxAC) and Achai (AC) were included in the study. Heritability estimates and genetic correlations of some important productive and reproductive traits were worked out. Heritability estimates of certain economic traits were found to be: birthweight, 0.32 ± 0.181; age at maturity, 0.11 ± 0.136; age at first calving, 0.19 ± 0.162; days open, 0.09 ± 0.121; calving interval, 0.14 ± 0.211; dry period, 0.11 ± 0.124; lactation length, 0.04 ± 0.212 and lactation yield, 0.46 ± 0.206. Genetic correlation showed that body weight was significantly and positively correlated with lactation length (0.30) and lactation yield (0.81), while negatively correlated with age at maturity, age at first calving, days open, calving interval and dry period (?0.09, ?0.07, ?0.16, ?0.34 and ?0.002, respectively). Calving interval was positively and significantly correlated with the dry period (0.56), lactation length (0.72) and lactation yield (0.37). Moderate to higher heritability estimates with adequate genetic variance was found for body weight and lactation yield. The moderate to higher heritability estimates of birthweight in the present study revealed that this important trait might be considered in selection criteria.     

Sire marbling score expected progeny difference and weaning weight maternal expected progeny difference associations with age at first calving and calving interval in Angus beef cattle.

Field records from the American Angus Association were used to study the associations of sire marbling score EPD and sire weaning weight maternal (milk) EPD with age at first calving (AFC) and calving interval (CI). Cows were selected based on the accuracy of their sire's milk (> or =.7) or marbling (> or =.6) EPD. The data were screened using biological constraints, and regression models were used to identify records that were greater than 5 SD from the mean. The AFC was modeled for both milk and marbling data sets to account for effects of year, sire EPD, and their interaction. The CI was subdivided into first, second, and mature calving interval traits and modeled to account for state, year, calf sex, calf birth weight (BW), calf weaning weight (WW), sire EPD, and interactions of EPD with year and state. Derivative-free REML was used to estimate heritability and genetic correlations for AFC and CI. Sire milk EPD and marbling EPD were predictors of AFC (P < .001); however, pooled estimates were unreliable because of state x EPD interactions (P < .001). Increases in sire milk EPD resulted in reductions in AFC; however, there was no consistent pattern to effects of marbling EPD increases. Models accounted for < 8% of variation in AFC. Sire milk EPD was not a predictor of first, second, or mature CI (P > .1). Sire marbling score EPD was not a predictor of second, or mature CI (P > .1); however, it was associated (P = .059) with first CI, although regression estimates varied across states and prevented pooling. The BW, sex, and WW were predictors of CI (P < .001). Increases in BW resulted in longer mature CI, and mature CI decreased as WW increased. The AFC was heritable (.22), and CI traits had heritabilities ranging from .01 to .03. The AFC was genetically correlated with first CI (-.6) and mature CI (-.93). Genetic correlations between CI traits were uninterpretable because of low additive genetic variances. In conclusion, sire marbling score and milk EPD do not seem to be reliable predictors of AFC or CI. The BW and WW have significant but small effects on AFC and CI. Selection for AFC is possible, but earlier calving heifers may have longer calving intervals.