First-lactation Yield Research Articles

Observational study on associations between resilience indicators based on daily milk yield in first lactation and lifetime profitability.

Resilience is the ability of cows to be minimally affected by disturbances, such as pathogens, heat waves, and changes in feed quality, or to quickly recover. Obvious advantages of resilience are good animal welfare and easy and pleasant management for farmers. Furthermore, economic effects are also expected, but these remain to be determined. The goal of this study was to investigate the association between resilience and lifetime gross margin, using indicators of resilience calculated from fluctuations in daily milk yield using an observational study. Resilience indicators and lifetime gross margin were calculated for 1,325 cows from 21 herds. These cows were not alive anymore and, therefore, had complete lifetime data available for many traits. The resilience indicators were the natural log-transformed variance (LnVar) and the lag-1 autocorrelation (rauto) of daily milk yield deviations from cow-specific lactation curves in parity 1. Good resilience is indicated by low LnVar (small yield response to disturbances) and low rauto (quick yield recovery to baseline). Lifetime gross margin was calculated as the sum of all revenues minus the sum of all costs throughout life. Included revenues were from milk, calf value, and slaughter of the cow. Included costs were from feed, rearing, insemination, management around calving, disease treatments, and destruction in case of death on farm. Feed intake was unknown and, therefore, lifetime feed costs had to be estimated based on milk yield records. The association of each resilience indicator with lifetime gross margin, and also with the underlying revenues and costs, was investigated using analysis of covariance (ANCOVA) models. Mean daily milk yield in first lactation, herd, and year of birth were included as covariates and factors. Natural log-transformed variance had a significantly negative association with lifetime gross margin, which means that cows with stable milk yield (low LnVar, good resilience) in parity 1 generated on average a higher lifetime gross margin than cows that had the same milk yield level but with more fluctuations. The association with lifetime gross margin could be mainly attributed to higher lifetime milk revenues for cows with low LnVar, due to a longer lifespan. Unlike LnVar, rauto was not significantly associated with lifetime gross margin or any of the underlying lifetime costs and revenues. However, it was significantly associated with yearly treatment costs, which is important for ease of management. In conclusion, the importance of resilience for total profit generated by a cow at the end of life was confirmed by the significant association of LnVar with lifetime gross margin, although effects of differences in feed efficiency between resilient and less resilient cows remain to be studied. The economic advantage can be mainly ascribed to benefits of long lifespan.

Impacts of Prepubertal Rearing Intensity and Calf Health on First-Lactation Yield and Lifetime Performance

Abstract The objective of the present study was to investigate possible long-term effects of calf and heifer feeding intensity on first-lactation milk yield and lifetime efficiency (milk per day of life). Detailed records from a total number of 2,252 female German Holstein calves from one commercial farm were obtained from birth to culling. Data regarding all information about calf’s birth, rearing time until first insemination, first calving, first-lactation yield and lifetime performance were collected over a 12-year period. This large data volume was merged, handled, checked for plausibility, classified and evaluated. Analyses revealed that body weight at an age of six months was significantly influenced by the average daily gain in the first two weeks of life (P<0.0001) and by the duration of treatment for respiratory diseases (P=0.0080). Moreover, first-lactation yield was affected by average daily gain in the whole first year of life (P=0.0013) and particularly in the period of month nine to twelve (P=0.00187). Lifetime efficiency was significantly influenced by body weight at first insemination (P=0.0051), average milk yield (P<0.0001) and reason for culling (P<0.0001). The results of this long-term study confirm that growth is important in general, but as shown by the negative correlation between average daily gain from month nine to twelve and the first lactation milk yield, nutrient intake (energy and protein) should be adapted to enable a controlled growth especially at certain periods of life. After six months of age, daily gain has to be controlled to avoid fat accumulation for a healthy and effective start of lactation. In addition, this analysis revealed that after passing first lactation, particularly health and fertility are the keys for a long efficient lifetime of dairy cows.

Association of rumination time and health status with milk yield and composition in early-lactation dairy cows

The objective of this study was to determine the associations of rumination time (RT) and health status with milk yield and milk composition. This study used 339 dairy cows from 4 commercial dairy farms in Ontario, Canada (first lactation, n = 107; second lactation, n = 112; ≥third lactation, n = 120). Rumination time was monitored (24 h/d) using an automated system from 1 to 28 d in milk (DIM). Cows were milked 3×/d on each farm, and 2 farms recorded milk weights at each milking to determine daily milk yield (n = 170). Cows were also monitored for milk composition (fat and protein content) 1×/wk. Last, subclinical ketosis (SCK) was diagnosed 1×/wk; cows with at least one blood sample with β-hydroxybutyrate ≥1.2 mmol/L postcalving were diagnosed with SCK. Cases of retained placenta, metritis, milk fever, or mastitis during the study period were also recorded. Cows were categorized into 1 of 4 groups: healthy cows that had no SCK or any other health issue (HLT; n = 139); cows that were treated for at least one health issue other than SCK (HLT+; n = 50); SCK cows with no other health problems during transition (HYK; n = 97); or cows that had SCK and one or more other health problems (HYK+; n = 53). All data were summarized by week across cows, and the associations between rumination time and milk yield (n = 170) and milk composition (n = 339) were modeled. Across all lactations, and including all health categories, milk yield increased by week, whereas fat and protein content both decreased by week. A positive association was found between summarized RT and milk yield in first-lactation (+0.006 ± 0.003 kg/min of RT) and second-lactation (+0.015 ± 0.004 kg/min of RT) cows from 4 to 28 DIM, as well as in ≥third-lactation cows; however, the relationship between RT and milk yield differed across weeks in those cows. A negative association between RT and milk fat content was found in ≥third-lactation cows (-0.002 ± 0.00059 percentage points/min of RT). From 4 to 28 DIM, ≥third-lactation HYK and HYK+ cows produced less protein (0.11 ± 0.051 and 0.13 ± 0.056 percentage points, respectively) than HLT cows. Over the 4-wk observation period, first-lactation HYK+ cows tended to deposit 0.11 ± 0.056 percentage points less protein in their milk compared with HLT cows. Second-lactation HYK+ cows produced less milk than HLT cows each week during early lactation. In summary, RT was positively associated with milk yield in early-lactation dairy cows, across all lactations, and negatively associated with milk fat content in ≥third-lactation cows. Further, the results showed that early-lactation cows that experience SCK, particularly with one or more other health problems, might have decreased milk yield and milk protein content.

The relationship between Norwegian Red heifer growth and their first-lactation test-day milk yield: A field study

Today's Norwegian Red (NR) is markedly different from the one that existed 25 yr ago due to the continuous genetic improvement of economically important traits. Still, current national recommendations on replacement heifer rearing largely are based on results from Danish studies from the late 1980s to the mid 1990s. The objectives of the present study were to gain information on (1) growth and growth profiles of modern NR replacement heifers in commercial dairy herds and (2) how growth during the rearing period affects the heifers' milk yield during their first lactation. To this end, we conducted a field study on 5 high-producing and 5 low-producing commercial dairy farms from each of 3 geographical regions in Norway. On these 30 farms, we combined repeated onsite registrations of growth on all available females from newborn to calving with registrations deriving from the Norwegian Dairy Herd Recording System. Each herd was visited 6 to 8 times over a period of 2 yr. At each visit, heart girth circumference on all available young females was measured. Registrations were made on a total of 3,110 heifers. After imposing restrictions on the data, growth parameters were estimated based on information from 536 animals, whereas 350 of these animals had the required information needed to estimate the relationship between growth and test-day milk yield. Our findings pointed toward an optimal ADG of 830 g/d from 10 to 15 mo of age that would optimize first-lactation yield of heifers in an average Norwegian dairy herd. The optimum will likely increase from selection over time. Utilizing simple proportionality, the ADG between 5 and 10 mo of age ideally should be 879 g/d, taking into account the fact that animal growth rate is higher at low ages and that a high prepubertal growth rate had no negative effect on first-lactation yield. When such a rearing practice is used to meet the requirements of today's genetically improved NR heifer, heifers can both optimize production in their first lactation and enter the milking herd earlier than the current average age of 24.8 mo.

Drinking regime evaluation with continuous ruminal monitoring boluses

Drinking regime evaluation with continuous ruminal monitoring boluses

A meta-analysis of the effects of preweaned calf nutrition and growth on first-lactation performance

Several studies and a 2013 meta-analysis have proposed that increased feeding of milk or milk replacer to neonatal calves may improve subsequent milk production. However, data from individual studies are conflicting, and the meta-analysis was unable to assess the influence of calf starter intake. The objective of the current meta-analysis was to review newly published data and evaluate the effects of preweaning diet (including calf starter intake) and growth rate on first-lactation milk, fat, and protein yield. Data from 9 studies representing 21 treatment groups were included in the analysis. We created separate models for each outcome variable using regression methods in SAS (version 9.4, SAS Institute Inc., Cary, NC) to determine the effects of intake and growth rate. We then selected the best-fitting models using Akaike’s information criterion. The effect of study explained 98, 85, and 96% of the variance in 305-d milk, fat, and protein yield in first lactation, respectively, indicating that other aspects of management are more important for determining first-lactation production than preweaning intake and growth rate. However, we found a synergistic relationship between preweaning liquid and starter dry matter intake for improving milk, fat, and protein production, and a positive relationship between first-lactation performance and preweaning average daily gain. These data indicate that provision of adequate nutrients from liquid and solid feeds and maintaining average daily gain above 0.5kg/d can enhance the first-lactation performance of heifers when combined with proper postweaning practices.

Genetic analysis of twinning rate and milk yield using a threshold‐linear model in Japanese Holsteins

The objective of this study was to estimate genetic parameters and breeding values for the twinning rate of the first three parities (T1, T2 and T3) and 305-day milk yield in first lactation (MY), using a four-trait threshold-linear animal model in Japanese Holsteins. Data contained 1 323 946 cows calving between 1990 and 2007. Twinning was treated as a binary character: 'single' or 'twin or more'. Reported T1, T2 and T3 were 0.70%, 2.87%, and 3.73%, respectively. Individual 305-day milk yield was computed using a multiple trait prediction for cows with at least eight test-day records. (Co)variance components were estimated via Gibbs sampling for randomly sampled subsets. Posterior means of heritabilities for T1, T2 and T3 were 0.11, 0.16 and 0.14, respectively. Genetic correlations between parities were 0.92 or greater. Genetic correlations of MY with twinning rate were not 'significant' (i.e. their 95% highest probability density intervals contained zeros). Multiple births at different parities were considered as the same genetic trait. The average evaluations of T1 (T2) for sires born before 1991 was 0.48% (2.25%) compared with a mean of 0.76% (3.37%) for sires born after 1992. A recent increase in the reported twinning rate reflects the positive genetic trend for sires in Japanese Holsteins.

Genetic correlations between milk production traits and somatic cell scores on test day within and across first and second lactations in Holstein cows

The genetic correlations between milk production traits (daily milk yield, 305-day milk yield, and lactation persistency as the difference between milk yields at days 240 and 60) and daily somatic cell score (SCS) within and across first and second lactations in Holstein cows were estimated by using a multiple trait test day (TD) animal model. The data set consisted of 200,095 TD milk and SCS records from 21,238 cows in their first lactations and 143,051 records from 15,281 cows in their second. Data were analyzed by using a two-trait, two-lactation random regression animal model. Genetic correlations between daily SCS and milk production traits were estimated from additive genetic variance component estimates of random regression coefficients. Genetic correlations between daily milk yield in first lactation and daily SCS in both lactations were positive and peaked in early lactation stage. In contrast, the genetic correlations between persistency and daily SCS in both lactations were negative, except in very early lactation stage. These correlations suggested that focusing selection on increasing milk yield early in the first lactation would likely increase SCS, whereas selecting for increased persistency would decrease SCS during both lactations. The genetic correlations between 305-day milk yield and persistency were positive within and across the first and second lactations. These results suggested that selection for lactation persistency could help to increase lactation yield overall in the first and second lactations without increasing SCS.

Comparison of different lactation curve models in Karan Fries cattle of India

The first lactation weekly test day milk yield (WTDMY) records (57233) and monthly test day milk yield (MTDMY) records (11970) spread over a period of 23 years (1984– 2006) sired by 82 bulls of Karan Fries cattle were used to develop the best lactation curve model. The lactation curve parameters of Quadratic cum log model (QCLM), Gamma function (GF), Cobby Le Du model (CLDM), Polynomial regression function (PRF) and Multiphasic logistic function (MLF) were estimated. The average weekly test day milk yield was predicted with high degree of accuracy (R2 > 85%) by all the models with the maximum accuracy (R2 = 99.50%) obtained by polynomial regression function (PRF) and the least fit (R2 = 87.90%) was obtained by Gamma function (GF). However Quadratic cum log model (R2 = 99.20%) was almost equal to polynomial regression function and was better than Cobby Le Du model (R2 = 92.80%). The average root mean square error (RMSE) was found to be minimum with PRF (0.0121 Kg) followed by MLF (Triphasic). Thus the best fit model was polynomial regression function, which was better than other functions for prediction of first lactation WTDMY. The average monthly test day milk yield was predicted with high degree of accuracy (R2 > 75%) by all the models with the maximum accuracy (R2 > 99.41%) obtained by polynomial regression function (PRF) and the least fit was obtained with gamma function (R2 = 79.05%). However, quadratic-cum-log model (R2 = 99.28%) was almost equal to polynomial regression function and was better than CLDM (R2 = 89.50%). The average root mean square error (RMSE) was found to be minimum with PRF (0.0061 kg) followed by QCLM (0.0620). Thus the best fit model was polynomial regression function for prediction of both weekly and monthly test day milk yield of first lactation in Karan Fries cows.

Preweaning milk replacer intake and effects on long-term productivity of dairy calves

The preweaning management of dairy calves over the last 30 yr has focused on mortality, early weaning, and rumen development. Recent studies suggest that nutrient intake from milk or milk replacer during the preweaning period alters the phenotypic expression for milk yield. The objective of this study was to investigate the relationship between nutrient intake from milk replacer and pre- and postweaning growth rate with lactation performance in the Cornell dairy herd and a commercial dairy farm. The analysis was conducted using traditional 305-d first-lactation milk yield and residual lactation yield estimates from a test-day model (TDM) to analyze the lactation records over multiple lactations. The overall objective of the calf nutrition program in both herds was to double the birth weight of calves by weaning through increased milk replacer and starter intake. First-lactation 305-d milk yield and residuals from the TDM were generated from 1,244 and 624 heifers from the Cornell herd and from the commercial farm, respectively. The TDM was used to generate lactation residuals after accounting for the effects of test day, calving season, days in milk, days pregnant, lactation number, and year. In addition, lactation residuals were generated for cattle with multiple lactations to determine if the effect of preweaning nutrition could be associated with lifetime milk yield. Factors such as preweaning average daily gain (ADG), energy intake from milk replacer as a multiple of maintenance, and other growth outcomes and management variables were regressed on TDM milk yield data. In the Cornell herd, preweaning ADG, ranged from 0.10 to 1.58kg, and was significantly correlated with first-lactation yield; for every 1kg of preweaning ADG, heifers, on average, produced 850kg more milk during their first lactation and 235kg more milk for every Mcal of metabolizable energy intake above maintenance. In the commercial herd, for every 1kg of preweaning ADG, milk yield increased by 1,113kg in the first lactation and further, every 1kg of prepubertal ADG was associated with a 3,281kg increase in first-lactation milk yield. Among the 2 herds, preweaning ADG accounted for 22% of the variation in first-lactation milk yield as analyzed with the TDM. These results indicate that increased growth rate before weaning results in some form of epigenetic programming that is yet to be understood, but has positive effects on lactation milk yield. This analysis identifies nutrition and management of the preweaned calf as major environmental factors influencing the expression of the genetic capacity of the animal for milk yield.

Phenotypic effects of calving ease on the subsequent fertility and milk production of dam and calf in UK Holstein-Friesian heifers

The effect of calving ease on the fertility and production performance of both dam and calf was studied in approximately 50,000 and 10,000 UK Holstein-Friesian heifers and heifer calves, respectively. The first objective of this study was to estimate the effect of a difficult calving on the subsequent first-lactation milk production by estimating lactation curves using cubic splines. This methodology allows the estimation of daily milk, protein, and fat yields following calvings of differing degrees of difficulty. Losses in milk yield after a difficult calving have been quantified previously; however, estimates are generally restricted to the accumulated yields at specific days in lactation. By fitting cubic splines, gaps (in which the shape of the lactation curve can be merely guessed) between estimations were avoided. The second objective of this study was to estimate the effect of a difficult birth on the subsequent performance of the calf as an adult animal. Even though the calving process is known to involve cooperation between dam and calf, the effect of a difficult calving has, until now, only been estimated for the subsequent performance of the dam. Addressing the effects of a difficult birth on the adult calf strengthens the importance of calving ease as a selection trait because it suggests that the benefit of genetic improvement may currently be underestimated. The effect of calving ease on the subsequent reproductive performance of dam and calf was analyzed using linear regression and with calving ease score fitted as a fixed effect. Dams with veterinary-assisted calvings required 0.7 more services to conception and 8 more days to first service and experienced a 28-d longer calving interval in first lactation compared with dams that were not assisted at calving. Effects of calving ease on the reproductive performance of the adult calf in first lactation were not detected. Losses in milk yield of the dam were significant between d 9 to 90 in milk subsequent to a veterinary-assisted calving, creating a loss of approximately 2kg of milk per day, compared with a nonassisted calving. Calves being born with difficulties showed a significant reduction in milk yield in first lactation, demonstrating the lifelong effect of a difficult birth. Compared with nonassisted calves, veterinary-assisted calves showed a loss of 710kg in accumulated 305-d milk yield, which was significant from 129 to 261 d in milk. This suggests that from birth to production, physiological effects of a bad calving are not negated. Results furthermore suggest a beneficial effect of farmer assistance at calving on the milk yield of both dam and calf, when moderate difficulties occurred.

Fatores genéticos e ambientais sobre a probabilidade de prenhez precoce em bovinos Caracu

Em bovinos, critérios de seleção, associados à precocidade sexual, vêm sendo atualmente pesquisados para a sua inclusão em programas de seleção, visando à diminuição da idade de entrada dos animais em reprodução, com conseqüências positivas sobre a receita do rebanho. O objetivo deste trabalho foi estimar a herdabilidade da probabilidade de prenhez precoce (PPP) de fêmeas Caracu, característica associada à puberdade e que pode ser considerada como indicadora do início da atividade reprodutiva, usando para isso, um arquivo com 5.273 observações. A significância dos efeitos da produção de leite da mãe na primeira lactação, da idade da mãe ao parto e da idade à desmama das novilhas sobre a PPP, foi analisada por meio do procedimento logístico de regressão. Empregou-se a análise Bayesiana para a estimação de herdabilidade da PPP mediante um modelo de touro, onde foram incluídos os efeitos de grupo de contemporâneos, produção de leite na primeira lactação, touro e resíduo. A média a posteriori da herdabilidade da PPP foi de 0,13, que, embora baixa, evidenciou a presença de ação gênica aditiva na determinação desta característica, o que possibilitaria a obtenção de progresso genético na mesma.

Effect of age at first calving on some productive and longevity traits in Iranian Holsteins of the Isfahan province.

Production and pedigree data of Iranian Holsteins were collected from 1991 to the end of 2001 on 45 herds in Isfahan province. Data on culled cows (birth and culling dates) were used to estimate the effect of age at first calving on total lifetime and productive life; and the effect of age at first calving on first-lactation yields was estimated from corrected (2x 305 d) first-lactation records of 12,082 dairy heifers that calved between 1995 and 2001. The estimate of heritability of age at first calving obtained in this study was 0.086. This low heritability indicates the importance of using available information on relatives for selection on this trait. Age at first calving significantly affected all the traits investigated, including: milk yield, fat yield, fat percentage, lifetime, and productive life. Results indicated a positive effect of reducing age at first calving on milk yield and productive life, although reducing age at first calving to 21 mo of age had a negative effect on yields of milk and milk fat. Lifetime did not show a similar trend with age at first calving. However, a slight positive phenotypic correlation (0.052) was detected between age at first calving and lifetime. We conclude that due to negative effects of age at first calving on productive life and because of optimum age at first calving for milk yield was 24 mo in this study, the reduction of age at first calving to 24 mo of age could be an effective management practice.

Disposal Pattern and Its Impact on Milk Production and Herd Size in Karan Fries and Karan Swiss Cows

Data on 958 Karan Fries (KF) and 780 Karan Swiss (KS) cows, born during 1974 to 1992 at National Dairy Research Institute, Karnal were evaluated for causes of culling and their impact on milk performance and herd strength. Causes of culling were classified as voluntary culling (low milk yield) and involuntary culling (other than milk yield). The milk yield of cows was evaluated inretrospectively by estimating expected breeding value (EBV) on the basis of first lactation yield (FLY) and all available lactation yield (ALY). The culling rate of KF cows over the years varied from 10.89 (1988) to 33.92% (1991) with an overall average of 20.96% and in KS from 19.91 (1984) to 33.74% (1989) with an overall average of 25.01%. Reproductive disorders, teat and udder problems, low milk production, health and locomotive disorders were the major reasons of culling accounted respectively for 5.56, 4.97, 4.61, 3.18 and 2.24% of herd strength in KF cows. The corresponding causes of culling were 6.20, 6.26, 7.69, 1.49 and 2.67% of herd strength in KS cows. The involuntary culling of cows accounted for 82.4% in K F and 76.1% in KS cows of total culling. The average annual disposal rate in KF and KS was 26 and 30% whereas annual replacement rate was 24 and 26% respectively. The EBV of involuntary culled cows on the basis of FLY and ALY was 3,111 and 3,515 kg in KF; and 2,669 and 2,940 kg in KS cows respectively. The EBV of selected cows on the basis of FLY and ALY was 3,242 and 3,549 kg in KF and 2,893 and 3,245 kg in KS cows respectively. The average breeding value of involuntary culled cows was not significantly different from selected cows in both the herds. The high rate of involuntary culling of potential cows might be major factor responsible for declined performance and size in these herds. The results indicated that higher genetic gain (2.14% of herd average in KF and 3.49% of herd average in KS) could be obtained by restricting the involuntary culling (50% of total culling) through improved management practices and increasing replacement rate.

Genetic and Phenotypic Evaluation of Milk and Fat Production Traits and Their Interrelationship in (Zebu×European) Crossbred Cattle Using Parent Group Mixed Model

Data pertained to 335 crossbred cows comprising of 1/2 Friesian (F) + 1/2 Hariana (H), 1/2 F + 1/4 Jersey (J) + 1/4 H, 1/2 F + 1/4 Brown Swiss (BS) + 1/4 H, 1/2 F + 1/4 Red Dane (R) + 1/4 H, FR (I) and FRH (I) genetic groups extending over a period of 21 years (1970-1990) maintained at Animal Farm of CCS HAU, Hisar. The averages for first lactation milk yield was 2,486.24±80.26 kg and peak yield of first three lactation were 11.35±0.72 kg, 13.97±0.60 kg and 16.02±0.42 kg, respectively. The lifetime milk production was observed as 11,305.16±1,004.52 kg in crossbred cattle. The average first lactation fat yield was observed as 102.06±0.01 kg and peak fat yield of first three lactation were 0.458±0.01, 0.490±0.01 and 0.500±0.02 kg, respectively. The lifetime fat production was estimated as 502.31±45.90 kg. LTMP and LTFP had reasonably good additive genetic variance which could be exploited either through mass selection/combined with family or pedigree selection. FLMY, peak yields and LTMP had significant positive phenotypic correlation with FLFY and LTFP and the correlation at the genetic level were also higher and positive for these traits. Finally, peak week milk yield of first lactation (PMY1) was the earliest available trait having desirable and significant correlation at phenotypic and positive at genetic level with FLFY, PFY1 and PFY2, PFY3 and LTFP and selection for this trait will help in early evaluation of sires and dams and will increase genetic advancement per unit of time. (Asian-Aust. J. Anim. Sci. 2003. Vol 16, No. 9 : 1242-1246)

Estimation of (Co)Variance Functions for Test-Day Yields During First and Second Lactations in the United States

(Co)variance components for milk, fat, and protein yields during first and second lactations were estimated from test-day data from 23,029 Holstein cows from 37 herds in Pennsylvania and Wisconsin using a multitrait test-day model. Canonical transformation was used with an expectation-maximization algorithm. To allow description of (co)variances within and across yield traits and parities, four lactation stages of 75 d were defined6 for each parity, and the test day nearest the center of each interval was used. Prior to analysis, data were adjusted for lactation curves within lactation stages using all records from all available cows. Data from cows with missing values were excluded to allow a canonical transformation to be used for estimation of (co)variance matrices. Data from 9110 cows were available for canonical analysis of lactations with test days in all lactation stages. (Co)variance functions were used to describe (co)variance structure within and across yield trait and parity. (Co)variance components of biological functions (305-d yield, persistency defined as difference between yields on d 280 and 60, and maturity rate defined as difference between second- and first-lactation yields) were developed from (co)variance functions. Heritabilities ranged from 0.09 to 0.22 for test-day yields, from 0.21 to 0.23 for 305-d yields, from 0.03 to 0.11 for persistencies, and from 0.05 to 0.07 for maturity rates. Phenotypic correlations between first- and second-lactation persistencies were low, but genetic correlations were high. Genetic correlations with maturity rate ranged from 0.11 to 0.61 for 305-d yields and persistencies.

Evaluation of the Impact of Parasite Control With the IVOMEC® SR Bolus Given at Breeding Age on First-Lactation Yield in Holstein Heifers

A sustained-release ivermectin bolus (IVOMEC® SR bolus) has been proven efficient for the treatment and prevention of nematode infections in growing beef and dairy cattle. However, its effects on growth in breeding-age dairy heifers, as well as on first-lactation yield, have not been demonstrated. This field trial was designed to test the effect of treatment with a sustained-release ivermectin bolus on average daily gain and total weight gain in breeding-age Holstein heifers under commercial pasture conditions in southern Quebec during summer 1995. A follow-up pilot study was undertaken to test the effect of the IVOMEC® SR bolus on first-lactation milk production (projected to 305 days) and milk composition (% fat and protein) in heifers that calved between October 1995 and August 1996.

Relationship of Fertility to Milk Yield in Swedish Cattle

Data consisted of 48,830 and 21,136 records of Swedish Red and White and Swedish Black and White cattle. Fertility in virgin heifers and in first lactation cows was measured by first service pregnancy rate and number of services per pregnancy. Production trait considered was FCM produced in first 100 d of lactation. The heritabilities for fertility traits in virgin heifers and first lactation cows were about .05 in both breeds. The genetic correlations between fertility measures within parity were close to one in both breeds, suggesting that these were measures of the same trait. The genetic correlations between fertility in virgin heifer and in first lactation were about .88 for Swedish Red and White breed and between .6 and .7 for Swedish Black and White breed. The association between fertility and production in first lactation cows was antagonistic, with genetic correlations between first service pregnancy rate and milk yield of –.13 and –.32 for Swedish Red and White and Swedish Black and White breed, respectively. The association between first service pregnancy rate in virgin heifers and milk yield in first lactation was also antagonistic, with genetic correlations of –.14 and –.41 for Swedish Red and White and Swedish Black and White breed, respectively.

Relationships Among Proofs for Survival, Culling, and Yields in First and Later Lactations

Sire evaluations for survival to 84 mo and age at last record from unregistered cattle were regressed on combinations of the following: BLUP summaries for percent culled in first lactation (from unregistered cattle) and PD milk from all, first, later, and later minus first lactations. Correlations between sire summaries for survival and the other traits were all favorable. Of the yield variables, PD from later lactations had the largest correlations with the summaries for survival. Predicted Difference based on first lactations had a low correlation with survival to 84 mo. Partial regressions indicated that PD for yield in first lactation was of little value to predict survival rates after percent culled. Predicted Difference for yield in later lactations and the difference in PD (later minus first) were significant when fitted after percent culled. The difference in PD was significant when fitted along with percent culled and PD milk from all lactations. Low early culling, high later lactations, and large increases in yield from first to later lactations were associated with greater survival rates to older ages. Higher yields in later lactations may be associated with cows that are able to maintain their health.

Genetic and Phenotypic Parameters for Production and Days Open in the First Three Lactations of Swedish Dairy Cattle

Abstract The material consisted of completed 305-day records of daughters of Al bulls. The analyses were carried out for each of the two predominant breeds where one of the breeds was divided into two separate geographical areas. The material was further divided into five years of first calving (1977–81) giving a total of 15 data sets. The traits were 305-day lactation milk (M) or fat (F) yield and days open (DO) in the first three lactations (1, 2, 3). All traits were preadjusted for month and age of calving, production was also adjusted for days open. The multiple trait mixed model used had the same effects for all traits analyzed simultaneously. These were effects of herd (fixed), group (fixed) and sire within group. The latter was random if the sire was a young bull and fixed for old progeny-tested bulls. The fixed sires were not used for estimating variance components. A triangular transformation was applied which made the residual variance-covariance matrix an identity matrix. The EM-algorithm was used to get approximate REML estimates of the variance components. Forty rounds of iteration were carried out. Overall average h 2 for milk yield were 0.268, 0.246 and 0.248 for the first three lactations respectively. The genetic correlations between the lactations were high, 0.855, 0.836 and 0.966 for r g12, r g13 and r g23 respectively. Heritabilities for fat yield were somewhat lower: 0.250, 0.213 and 0.228 respectively. Genetic correlations were 0.920, 0.846 and 0.938 respectively. For days open low heritabilities were found: 0.040, 0.050 and 0.066 respectively. Fairly high genetic correlations were found between these traits, however: 0.582, 0.493 and 0.220. Genetic correlations between milk yield in first lactation (Ml) and days open in first and second lactations (DO1, DO2) were moderately high and unfavourable: 0.414 and 0.335 respectively. There were no systematic trends in the estimated parameters over the different production years. The unfavourable genetic correlations obtained in this study between milk production and days open was not reflected in the estimated genetic trends for days open in a previous study.