Variation In Milk Yield Research Articles

Impact of NDF degradability of corn silage on the milk yield potential of dairy cows

The neutral detergent fibre (NDF) degradability of corn silage samples, measured in vitro (ivNDFd) by a filter bag system, was used to examine (i) the relationship between the ivNDFd and that calculated from acid detergent lignin (L) content (NDFd) and (ii) the impact of ivNDFd variations on the predicted milk yield (MY) of dairy cows fed corn silage based diets. A total of 173 samples of corn silage were collected during a period of three years (2001-03) in different dairy farms of the Po Valley (Northern Italy). Each sample was analysed for chemical composition and was also tested in triplicate for the ivNDFd using the DaisyII incubator (Ankom, Tech. Co., Fairport, NY, USA) with incubation time of 48hs. Moreover, the NDFd of samples was calculated from the L contents, while the measured ivNDFd values were used to estimate the NEl, the potential dry matter intakes (DMI) and to predict the MY of cows.Corn silage samples of the three years were similar for NDF and starch contents (44.2 and 30.7% DM, on average, respectively) while samples from 2003, in comparison with 2001 and 2002, had lower crude protein (6.9 vs 8.3-8.4% DM, P<0.01) and L contents (3.3 vs 3.6-3.9% DM, P<0.01) and higher ivNDFd values (53.3 vs 45.6-47.8%, P<0.01). The relationship between ivNDFd and NDFd was weak (R2=0.09, not significant). The MY predicted from the NEl content and DMI of corn silage (5.5 MJ/kg DM and 8.9 kg/d) minus the maintenance energy costs, was 11.5 kg/d on average (coefficient of variation 20%). Our simulations indicate that a variation of ivNDFd by +1.0% changes the NEl of corn silage to have an expected variation in milk yield of +0.15 kg/d. If the ivNDFd is also used to predict the corn silage DMI then a +1.0% variation in ivNDFd of corn silage produces an overall +0.23 kg/d MY variation.The present results indicate that ivNDFd is highly variable in corn silage populations and differences in this nutritional parameter have an appreciable impact on the predicted milk yield from dairy cows.

Characterization of buffalo production of northeast of Italy

Aim of this study was to characterize the buffalo production in the Veneto region of Italy. Test day records of milk production traits (milk yield, protein, fat, and somatic cell count) of 845 buffalo cows from two herds were analyzed using a linear model. The effects included in the model were herd-test-day, days in milk, and parity. Days in milk was the most important source of variation for milk yield, protein, and fat. The patterns of milk yield traits across lactation followed the typical trend of buffalo cows. Results allowed a preliminary characterization of buffalo production in north of Italy.

Inferring Genetic Parameters of Lactation in Tropical Milking Criollo Cattle with Random Regression Test-Day Models

This study inferred genetic and permanent environmental variation of milk yield in Tropical Milking Criollo cattle and compared 5 random regression test-day models using Wilmink's function and Legendre polynomials. Data consisted of 15,377 test-day records from 467 Tropical Milking Criollo cows that calved between 1974 and 2006 in the tropical lowlands of the Gulf Coast of Mexico and in southern Nicaragua. Estimated heritabilities of test-day milk yields ranged from 0.18 to 0.45, and repeatabilities ranged from 0.35 to 0.68 for the period spanning from 6 to 400 d in milk. Genetic correlation between days in milk 10 and 400 was around 0.50 but greater than 0.90 for most pairs of test days. The model that used first-order Legendre polynomials for additive genetic effects and second-order Legendre polynomials for permanent environmental effects gave the smallest residual variance and was also favored by the Akaike information criterion and likelihood ratio tests.

The effect of different degrees of ‘positive’ human–animal interaction during rearing on the welfare and subsequent production of commercial dairy heifers

A 3-year study tested the hypotheses that brushing each heifer for 5 min per week in the weeks preceding calving (long term positive treatment: PT) while the heifers were unrestrained, is sufficient to improve subsequent parlour behaviour and production, and this could be influenced by the extent of the PT. Four intakes of commercial dairy heifers (total n148) managed under typical UK conditions were divided into treatment (T) and control (C) groups. The PT for the four treatment groups comprised of brushing each heifer for 5 min per week in the weeks preceding calving for either 30 min, 65, 155 or 245 in total for the different groups (equating to 6, 13, 31 and 49 weeks before calving). In the first 4 weeks after calving T heifers had 19% faster milk letdown ( P < 0.01) than C. Kicks in human presence accounted for 7.1% of the variation in milk yield ( r 2 = 0.071, P < 0.001) and 46% of C's kicks were in human presence compared to 38% of T ( P < 0.05). In the first week after lactation T heifers who had received 30 min of PT stamped 59% less at udder handling ( P = 0.017) compared to their respective C. The T heifers who had received 155 min of PT during rearing displayed violent kicks 74% less than their C ( P < 0.10). Heifers who had received 65 min PT had 75% less time spent on them during the milking routine ( P < 0.075). This was reflected in a significant difference in milker's score. Heifers appear to settle between Weeks 3 and 4 as there are no significant differences in behaviour of all heifers as a group. There was a treatment and week interaction for many variables and in Weeks 3 and 4 there are still differences in milking parlour variables between T and C at Week 4. This suggests that the PT quickened the T heifers’ acclimation to the milking routine. To conclude 30 min of PT in the 6 weeks prior to calving appears sufficient to reduce subsequent fear response to humans in the parlour demonstrated through improved behaviour when being milked.

Simulation Monte-Carlo pour évaluer l’impact des schémas MOET adultes chez les bovins Somba

L’impact de la technique de superovulation et du transfert d’embryons (MOET) sur la performance de la race Somba a été évalué à l’aide de simulations du type Monte-Carlo. Des schémas MOET adultes en noyaux fermés ont été simulés et soumis à 20 générations consécutives de sélection en supposant une capacité fixe de testage de 512 femelles connues pour leurs performances laitières, un taux de succès de 70 p. 100 pour le transfert, un taux de survie de 70 p. 100 chez les embryons et des tailles variables de familles (nD = 4, 8, 16). Les valeurs additives génétiques des candidats ont été estimées par la méthode BLUP utilisant le modèle animal réduit (RAM). Pour différents scénarios déterminés par le nombre de donneurs (D = 64, 128, 256) et le nombre de géniteurs (S = 4, 8, 16) à sélectionner, la réponse à la sélection a varié de 0,088 à 0,127 unités standard phénotypiques par an. Ces valeurs correspondaient à un progrès génétique annuel de 2,2 à 3,2 p. 100 par rapport à la moyenne de la population par an (le coefficient de variation de la performance laitière de la race Somba étant de 25 p. 100). Pour toutes les alternatives du point de vue de la structure de la population, le taux de consanguinité obtenu par simulation a varié de 1,32 à 2,93 p. 100 par an, contre une valeur estimée allant de 0,83 à 3,32 p. 100. Comparé au taux annuel de consanguinité de 0,1 à 0,2 p. 100 généralement admis pour le schéma conventionnel de testage sur descendance, les taux de consanguinité prédictibles pour les schémas MOET adultes ont été remarquablement élevés. Pour pallier ce handicap, des stratégies de réduction à court et à moyen terme du taux de consanguinité ont été examinées.

Evidence of Heterogeneity of Variance in Milk Yield among Holstein-Friesian Herds in Kenya

Three thousand, nine hundred and seventy five lactation records of Holstein- Friesian cows between 1968 and 1984 were used to investigate the existence of heterogeneity of variance in milk yield in Kenya. Coefficient of variation and standard deviations across herds were used to test heterogeneity of variance. Average herd standard deviation and coefficient of variation after correcting for the fixed affects were 672.2kg and 26.7% respectively, while scaled standard deviations between herds were 180.1kg and 3.4%.The scaling of observation s within individual herds by sample standard deviation minimized heterogeneity of variance of milk yield thereby increasing accuracy of selection. It was concluded that significant heterogeneity of variance in milk yield existed among herds and should be accounted for in sire and cow evaluation. The Kenya Veterinarian Vol. 25 2002: pp. 12-17

Non-genetic causes of the heterogeneity of variance in milk yield among Holstein-Friesian Herds in Kenya

Lactation records of Holstein- Friesian cows in Kenya made during the period 1968 to 1984 were analyzed for the cases of heterogeneity of variance in milk yield among herds using a fixed effect least squares model. Year, herd, herd class, parity, calving interval and lactation length all influenced milk yields significantly (p

Reduction in milk yield associated withMycobacterium aviumsubspeciesparatuberculosis(Map) infection in dairy cows

To assess the profitability of control schemes for Mycobacterium avium subspecies paratuberculosis (Map)-infection implemented in dairy herds, accurate estimates of its production effects are needed. This study aimed at quantifying the variation in milk yield of dairy cows according to their Map-infection status. The cow-status was determined by combining (i) its testing(s)-result(s) (serum ELISA, faecal culture (FC), PCR, Ziehl staining), (ii) the Map-status of its herd, and (iii) its possible vaccination against Map. A total of 15 490 cows in 569 herds located in western France was considered. The effect on test-day milk yield (TDMY) of the cow-status to Map was assessed separately in parity 1, 2 and 3 or more, using mixed linear models, after adjustment for herd-season (random), days in milk and breed. Average TDMY was significantly lower in cows from herds with at least one Map-infected cow (defined as positive herds). Individual TDMY showed a reduction ranging from 1.58 to 3.30, 2.03 to 2.51, 5.36 to 7.20 kg/day (P < 0.001) depending on parity for unvaccinated cows and testing ELISA-positive, PCR- or FC-positive, and Ziehl-positive, respectively, compared to cows in Map-free herds. The loss in milk yield increased with increased parity in ELISA-positive and Ziehl-positive cows. Cows that were both tested ELISA-positive and vaccinated had a smaller loss in TDMY than those that were unvaccinated. The estimates from this study can be used to further assess the economic impact associated with Map-infection in dairy herds or to help in the culling decisions regarding infected cows.

A simple statistical model to estimate precision of 300-day milk and fat production for dairy cows

In this paper we use a statistical model to examine the relative precision of lactation milk yield and milk fat yield, under various production recording regimes with different metering and sampling precision, recording frequencies combined with empirical daily variations in milk yield and fat composition. The analysis shows that if traditional monthly production recording was performed with devices of International Committee for Animal Recording (ICAR) precision, the resultant coefficient of variation (CV) for lactation yields of milk and fat would be 2.22 and 4.81%, respectively. These values are determined primarily by measurement frequency coupled with the natural daily biological variations in animal milk yield and fat composition. Meter and sampler precision play a relatively minor role. For example, our model shows that if the devices had double the CV prescribed by ICAR, the milk and fat yield CV would increase by only 0.20 and 0.19%, respectively. These are minute losses of precision. If the ICAR precision standards for meters and samples were relaxed, it could encourage development of innovative metering and sampling technologies that could provide much more cost-effective and convenient ways for farmers to conduct production recording.

Buffalos milk yield analysis using random regression models

Data comprising 1,719 milk yield records from 357 females (predominantly Murrah breed), daughters of 110 sires, with births from 1974 to 2004, obtained from the Programa de Melhoramento Genètico de Bubalinos (PROMEBUL) and from records of EMBRAPA Amazonia Oriental - EAO herd, located in Belèm, Parä, Brazil, were used to compare random regression models for estimating variance components and predicting breeding values of the sires. The data were analyzed by different models using the Legendre's polynomial functions from second to fourth orders. The random regression models included the effects of herd-year, month of parity date of the control; regression coefficients for age of females (in order to describe the fixed part of the lactation curve) and random regression coefficients related to the direct genetic and permanent environment effects. The comparisons among the models were based on the Akaike Infromation Criterion. The random effects regression model using third order Legendre's polynomials with four classes of the environmental effect were the one that best described the additive genetic variation in milk yield. The heritability estimates varied from 0.08 to 0.40. The genetic correlation between milk yields in younger ages was close to the unit, but in older ages it was low.

Genetic analysis of a purebred herd of Kundhi buffaloes in Pakistan

Kundhi is amongst the best dairy buffalo breeds of the world and main source of milk production in Sindh province of Pakistan. A Research and Development Kundhi Buffalo Farm was established at Rohri, Sukkur. Time series production performance data of 237 buffaloes, along with their pedigree, from 1976 through 2004 was collected and analyzed using Harvey Model-1 for fixed effects and DFREML for GLS solutions and genetic / phenotypic variances. The traits of economic importance studied were age at first calving (AFC), milk yield (MY), lactation length (LL), calving interval (CI) and dry period (DP). The fixed effects included year of birth (YOB), year of calving (YOC) season of calving (SOC) and lactation number (L No.). The data analyses revealed that among the fixed effect only YOC had significant effect (p < 0.05) on milk yield and all other traits. The average MY was 1356.48 ± 453.27 kg with mean lactation length 218.72 ± 122.97 days. The heritability of MY, CI, LL and DP was 0.209, 0.018, 0.009 and 0.024, respectively. Among the 5 sires used during this period, one sire contributed positively to milk production of the daughters. One hundred and three Kundhi buffaloes had positive and 134 negative breeding values for milk production. The genetic and phenotypic variance for milk yield was 35427.67 and 168521.94, respectively. The progeny testing program for Kundhi buffalos was initiated in August 2005. Under this program, more than 700 buffaloes are registered and ear tagged. The production and reproduction performance data recording at farmers doorstep has been initiated which will be used to identify bull mothers.

Random regressions models to describe the genetic variation of milk yield over multiple parities in Buffaloes

The objectives of this study were to estimate (co)variance functions for additive genetic and permanent environmental effects, as well as the genetic parameters for milk yield over multiple parities, using random regressions models (RRM). Records of 4,757 complete lactations of Murrah breed buffaloes from 12 herds were analyzed. Ages at calving were between 2 and 11 years. The model included the additive genetic and permanent environmental random effects and the fixed effects of contemporary groups (herd, year and calving season) and milking frequency (1 or 2). A cubic regression on Legendre orthogonal polynomials of ages was used to model the mean trend. The additive genetic and permanent environmental effects were modeled by Legendre orthogonal polynomials. Residual variances were considered homogenous or heterogeneous, modeled through variance functions or step functions with 5, 7 or 10 classes. Results from Akaike’s and Schwarz’s Bayesian information criterion indicated that a RRM considering a third order polynomial for the additive genetic and permanent environmental effects and a step function with 5 classes for residual variances fitted best. Heritability estimates obtained by this model varied from 0.10 to 0.28. Genetic correlations were high between consecutive ages, but decreased when intervals between ages increased

Results of the application of the technology of genetic improvement of Simmental cattle population in Serbia

Results of production traits obtained from first calving cows and evaluation of the breeding value of bull sires of Simmental breed in Serbia. Data was analyzed using the method of least squares and for evaluation of bulls' breeding value mixed model of random sire effect (BLUP method). Based on obtained results it was established in statistical analysis that breeding region had highly significantly affected (P&lt;0.01) the deviation of production traits from the general average. Considerable deviation from the general average was caused by the year and season of calving (P&lt;0.05), and interaction of breeding region and calving season contributed to high variation in yield of milk and milk fat (P&lt;0.01).

착유우의 연속유량, 유량변이, 유성분, 체세포수, 비유지속시간, 비유속도에 대한 산차, 착유시간, 유기 및 착유간격의 효과

This study was carried out to estimate the effects of parity, milking time, milking interval and days in milk(DIM) on variation in milk yield between consecutive milkings(am to pm to am), morning and evening milk yield and its components, somatic cell counts(SCS), milking duration, milk flow rate and peak milk flow in Holstein dairy cattle. Records from one hundred and twenty two heads of Holstein cattle at National Livestock Research Institute, Korea were used for this study from July 1 to August 8, 2005. The experimental herd had average 1.6±0.9 parities, 199.8±109.1 DIM and 12.26±4.06 kg milk yields at each milking. Milking yield, percent milk fat and SNF, milking duration and average milk flow were significantly varied by parity, milking time and DIM. Percent milk protein and lactose were varied by parity and DIM, however SCS and average milk flow were affected by parity and milking time. Milking interval significantly affected the consecutive, morning and evening milk yield and average milk flow. However, MUN was not affected by parity, milking time, DIM and milking interval. Milk yield was decreased with increasing parity. Milk yield in the morning was higher than that of in the evening. Milk yield between consecutive milking was not affected by parity, however, affected by milking time. Percent milk Fat, SNF and SCS were higher at in evening milk than those of in morning milk. Milk protein, lactose, SNF, SCS, milking duration and peak milk flow rate were influenced by parity. This study suggested that milk yield variation between consecutive milking, milking flow rate, and milking duration could be important traits for enhancing Holstein cattle productivity however, and more study is needed to estimate genetic parameters for such traits.

Comparison of Random Regression Test-Day Models for Polish Black and White Cattle

Test-day milk yields of first-lactation Black and White cows were used to select the model for routine genetic evaluation of dairy cattle in Poland. The population of Polish Black and White cows is characterized by small herd size, low level of production, and relatively early peak of lactation. Several random regression models for first-lactation milk yield were initially compared using the “percentage of squared bias” criterion and the correlations between true and predicted breeding values. Models with random herd-test-date effects, fixed age-season and herd-year curves, and random additive genetic and permanent environmental curves (Legendre polynomials of different orders were used for all regressions) were chosen for further studies. Additional comparisons included analyses of the residuals and shapes of variance curves in days in milk. The low production level and early peak of lactation of the breed required the use of Legendre polynomials of order 5 to describe age-season lactation curves. For the other curves, Legendre polynomials of order 3 satisfactorily described daily milk yield variation. Fitting third-order polynomials for the permanent environmental effect made it possible to adequately account for heterogeneous residual variance at different stages of lactation.

Some Factors Affecting Variation in Milk Yield in Crossbred Dairy Cows on Smallholder Farms in North-East Tanzania

A 2-year longitudinal survey was carried out to investigate factors affecting milk yield in crossbred cows on smallholder farms in and around an urban centre. Sixty farms were visited at approximately 2-week intervals and details of milk yield, body condition score (BCS) and heart girth measurements were collected. Fifteen farms were within the town (U), 23 farms were approximately 5 km from town (SU), and 22 farms approximately 10 km from town (PU). Sources of variation in milk yield were investigated using a general linear model by a stepwise forward selection and backward elimination approach to judge important independent variables. Factors considered for the first step of formulation of the model included location (PU, SU and U), calving season, BCS at calving, at 3 months postpartum and at 6 months postpartum, calving year, herd size category, source of labour (hired and family labour), calf rearing method (bucket and partial suckling) and parity number of the cow. Daily milk yield (including milk sucked by calves) was determined by calving year (p < 0.0001), calf rearing method (p = 0.044) and BCS at calving (p < 0.0001). Only BCS at calving contributed to variation in volume of milk sucked by the calf, lactation length and lactation milk yield. BCS at 3 months after calving was improved on farms where labour was hired (p = 0.041) and BCS change from calving to 6 months was more than twice as likely to be negative on U than SU and PU farms. It was concluded that milk production was predominantly associated with BCS at calving, lactation milk yield increasing quadratically from score 1 to 3. BCS at calving may provide a simple, single indicator of the nutritional status of a cow population.

Genetics and physiology of leptin in periparturient dairy cows

In dairy cattle, the increase in milk yield has been accompanied by a more negative energy balance (EB) during early lactation and a decrease in fertility. As the hormone leptin is involved in regulation of nutritional status and reproductive function this hormone is an interesting protein to investigate during the periparturient period in dairy cattle. This study was performed to get insight into the function of leptin during the periparturient period and to perform an association study between polymorphisms in the bovine leptin gene and leptin receptor gene and fertility as well as production traits. Leptin concentrations in the periparturient cow undergo remarkable changes; leptin concentrations were high during late pregnancy and declined to a nadir at parturition. Genetic analysis of the leptin gene indicated that a combination of three polymorphisms located at a 135 bp region of the leptin promoter explained most of the variance in prepartum leptin concentrations. The two extreme genotype combinations could be used to investigate the function of leptin concentrations in pregnant cows. A polymorphism located on intron 2 of the leptin gene explained a significant part of the variation in milk yield. On the promoter region of the leptin gene an SNP was detected that was associated with first postpartum luteal activity (FPLA). This SNP could be a candidate marker for fertility in dairy cows. Another SNP on the leptin promoter was associated with energy balance and dry matter intake (DMI) where a higher dry matter intake occurred together with a higher energy balance. Two genotype combinations of the aforementioned three associated SNPs were defined which had a good milk yield together with a good energy balance and fertility. Calculations of an economical value per trait have to validate if one of these genotype combinations would be a possible candidate to be used in selection.

Evaluation of the breeding strategy for milk yield of Holstein Friesian cows on large-scale dairy farms in Malawi

Over the last two decades, dairy cattle management in Malawi has been oriented towards increasing milk yield per animal. One consequence of this process has been reliance on Holstein Friesian bull semen from temperate regions. The aim of the current study was to evaluate the performance of Holstein Friesian cows on large-scale farms in Malawi. A data set of 60640 test-day records from Holstein Friesian cows in first, second and third lactation from three large-scale dairies in Malawi were utilized. Fixed effects of herd, year and season of calving were tested. (Co)variance components were estimated through the restricted maximum likelihood (REML) procedure. Heritability, genetic and phenotypic correlations for milk yield, lactation length, age at first calving, and calving interval were determined. In general, milk yield decreased over the years and there was significant (P&lt;0·001) variation in milk yield between herds. The genetic base, as indicated by the genetic trend, remained almost constant in the studied period. This entails genotype by environment interaction, culminating in the additive genetic effect not expressing itself fully in the phenotype. It is therefore apparent that considerable improvement could be achieved by improving the production environment.

Heterogeneidade de (Co)variância para as produções de leite e de gordura entre vacas puras e mestiças da raça Gir

Registros de produção de leite e de gordura de 5086 vacas puras e mestiças da raça Gir de rebanhos de diferentes Estados do Brasil, ajustados para idade adulta, rebanho, ano e estação de parto, foram utilizados para estimar componentes de (co)variância por análises bicaráter e multicaráter com modelo animal pelo método REML. O modelo multicárater para a predição de valores genéticos (VG) para as produções de leite (PL) e de gordura (PG) de vacas puras e mestiças foi comparado com o modelo bicárater (leite e gordura) como alternativa para o ajuste da heterogeneidade de variância da PL (características distintas) entre grupos genéticos (vacas puras e mestiças). As estimativas dos componentes de (co)variância para as produções de leite e de gordura foram heterogêneas entre vacas puras e mestiças. As variâncias genéticas aditivas para leite (115.536,4 kg²) e para gordura (214,8 kg²) de vacas puras foram o triplo das estimadas para leite (39.080,4 kg²) e para gordura (60,8 kg²) em vacas mestiças. As correlações genéticas entre as produções de leite e de gordura variaram de 0,73 a 0,99 e foram maiores para as produções de leite (0,86) do que para as produções de gordura (0,76) entre vacas puras e mestiças. As herdabilidades (h²) das produções de leite e de gordura foram respectivamente maiores nas vacas puras (0,23 e 0,20) do que nas vacas mestiças (0,08 e 0,07). As estimativas de correlação genética (r g) entre as produções de leite e de gordura foram 0,95 e 0,99, respectivamente para as vacas puras e mestiças. A estimativa de covariância genética entre as produções de leite e de gordura de vacas puras (4.742,9 kg²) foi o triplo da obtida para vacas mestiças. As estimativas dos componentes de variância genética para as produções de leite (99.104,92 kg², h² = 0,20) e de gordura (181,21 kg², h² = 0,18) do modelo bicaráter corresponderam, respectivamente, a 85,9 e 84,4% dos valores obtidos em vacas puras da raça Gir com o modelo multicaráter. A estimativa de covariância genética foi 4.071,14 kg², com r g igual a 0,96 entre as produções de leite e de gordura. As correlações de ordem entre os VG para PL de animais Gir e VG para PL e PG de animais mestiços estimados com o modelo multicaráter e os VG para PL e PG obtidos com o modelo bicaráter foram superiores a 0,96. Alterações observadas na ordem de classificação de touros e vacas indicam maior precisão na seleção e maior potencial de progresso genético com a utilização do modelo multicaráter nas avaliações genéticas.

Evaluation of age of dam effects on maternal performance of multilactation daughters from high- and low-milk EPD sires at three locations in the southern United States.

Angus bulls (n = 16) selected for either high- or low-milk EPD but similar growth EPD were mated within location at random to Angus cows. Daughters were bred to calve at 2 yr of age and annually until 6 yr of age. Milk yield was measured four times during lactation with a portable milking machine to estimate 12-h milk yield. Milk was collected for analysis of the percentage of fat and protein. A mixed model procedure was used to analyze the weaning weight, milk yield, and milk component data. The model for weaning weight included location, genetic line of sire, gender of calf, and age of dam. Calf age at weaning was used as a covariate. The model for the milk yield and components included location, genetic line of sire, gender of calf, period, and age of dam. Random effects for all models included sire of dam nested within line, sire of calf, and year. Genetic line was a significant source of variation for milk yield (P < 0.01) and weaning weight (P < 0.01) but not for percentage of fat or protein. Location was significant for milk yield (P < 0.01), fat (P < 0.01), protein (P < 0.01), and weaning weight (P < 0.01). The interaction of line with location was not significant except for percentage of protein (P < 0.01). Age of dam was significant for milk yield (P < 0.01), weaning weight (P < 0.01), and percentage of protein (P < 0.01), but not for percentage of fat (P = 0.29). Line difference for mean weaning weight was 18.1 kg, which is similar to the difference between lines for milk EPD (19 kg). Weaning weights from high-milk EPD line daughters were heavier (P < 0.01) than low-milk EPD line daughters at each age of dam evaluated. Cows nursed by males had higher milk yields (4.33 kg/12 h) than cows nursed by heifers (4.0 kg/12 h). The difference in yields for gender was significant for 2-, 3-, and 5-yr-old cows, but not for 4- (P < 0.052) and 6-yr old (P < 0.15) cows. Correlation coefficients between weaning weight and weaning EPD, milk EPD, and total maternal EPD were greater than zero (P < 0.01) (0.76, 0.65, and 0.89, respectively). Daughters of sires with high-milk EPD produced more milk at each age and weaned heavier calves than daughters of sires with low-milk EPD. These results confirm the value of milk EPD for improvement of weaning weights in beef cattle and also validate age of dam effects on milk yield and the associated effects on weaning weights.