Search

Context: Length of productive life is defined as the number of days from first calving to the last day of milking records, when the cow is no longer sufficiently productive. Although it has economic implications, length of productive life has not yet been included in Brazilian dairy cattle breeding programs because it depends on other traits such as age at first calving, milk production level and disease occurrence. In addition, its evaluation occurs later in life, and heritability coefficients are low. Aims: The aim of this study was to identify the effects of both age at first calving and accumulated 305-day milk yield in the first lactation on length of productive life in Holstein cows. Methods: Official dairy control data of 31 562 Holstein cows, calved from 2010 to 2014, in 321 herds from Paraná state, Brazil, were analysed by using the Kaplan–Meier estimator and Cox regression model. Key results: First calving at <21 months was associated with shortest productive life (1197.01 ± 232.40 days), whereas first calving at 24 months was associated with the lowest hazard ratio (0.572), suggesting that this is the most suitable age of first calving for a longer productive life. Low-yielding cows (first lactation yield <6392 kg) had the second lowest survival probability (47.20%), the shortest productive life (1150.60 ± 234.51 days) and the highest voluntary hazard ratio (1.30) and were prematurely culled from the herds. High-yielding cows (first lactation yield >12 024 kg) had lower culling risk at the first lactation. Conclusions: Cows that started their reproductive life ∼16 months of age (first calving at 24 months) had the longest productive life and an average first lactation milk yield ∼9000 kg. Implications: Reproductive management practices could affect length of productive life through effects on age at first calving and first lactation milk yield. Most of the Holstein semen used in Brazil comes from countries where longevity has already been included in selection indexes; thus, early identification of cow longevity could be used for culling decisions. Having long-lived, more profitable and more functional cows in the herd is one of the biggest challenges in dairy farming in Brazil. We assessed the effects of age at first calving and accumulated 305-day milk yield in the first lactation on length of productive life in Holstein cows. Cows that started reproductive life at ∼16 months of age had the longest productive life and an average first lactation milk yield ∼9000 kg. [ABSTRACT FROM AUTHOR]

The objectives of this study were to assess the effects of heat stress on the milk yield and investigate the presence of genotype × environment interaction (G × E) in Brazilian Murrah buffaloes reared under tropical conditions. With this, 58,070 test‐day (TD) records for milk yield from 3,459 first lactations of buffaloes collected between 1987 and 2018 were evaluated. A mixed model considering days in milk (DIM) and temperature–humidity index (THI) was applied to quantify milk yield losses due to heat stress. The most detrimental effect of THI on TD milk yield was observed in the mid‐stages of lactation, after lactation peak, in DIM 105–154 and 155–204 days (−0.020 and −0.015 kg/day per THI, respectively). The least‐squares means of TD milk yield were used to identify a heat stress threshold using a piecewise linear regression model. A substantial reduction in TD milk yield due to heat stress was observed for THI values above 77.8 (−0.251 kg/day per increase of 1 THI unit). An analysis using a single‐trait random regression animal model was carried out to estimate variance components and genetic parameters for TD milk yield over THI and DIM values. Increased additive genetic variance and heritability estimates were observed for extreme THI values (THI = 60 and 80) combined with mid‐lactation stages. The lowest genetic correlation (0.50) was observed between TD records at opposite extremes of the THI scale (THI = 60 vs. THI = 80). The genetic trends observed for the regression coefficients related to the general level of production (0.02) and specific ability to respond to heat stress (−0.002) indicated that selection to increase milk yield did not affect the specific ability to respond to heat stress until the present moment. These trends reflect the low genetic correlation between these components (0.05 ± 0.14). In this sense, monitoring trends of genetic components related to response to heat stress is recommended. [ABSTRACT FROM AUTHOR]

Context: The estimation of genetic parameters for traits related to the production of milk, beef or both may assist in defining the selection criteria and objectives of the breeding program, as well as in the identification and selection of genetically superior animals. Aims: The objectives of this study were to estimate genetic parameters for body weight and 305-day milk yield of Guzera cattle and to perform cluster analysis on the basis of estimated breeding values for these traits, to identify groups of animals that could be selected for the production of beef, milk or dual purpose. Methods: Body weights (N = 253 012) of males and females were ecorded at 120 days of age (BW120), at weaning (WW), at 365 days (BW365), at yearling stage (YW) and at 24 months (BW24), and 6237 complete lactations (MY305) of 4723 cows were used to estimate the genetic parameters. The bi-trait animal models included direct additive genetic, maternal permanent environmental and temporary random effects for body weights and additive genetic, permanent environmental and temporary environmental random effects for MY305. The fixed effects for all the traits were contemporary group and age of cow at calving. Key results: The estimates of heritability ranged from 0.14 ± 0.01 for WW to 0.23 ± 0.01 for MY305. The genetic correlations between body weights at different ages and milk yield were positive and ranged from 0.27 ± 0.11 to 0.38 ± 0.19. Two principal components explained 86.74% of the total genetic variance among the traits. Conclusions: Cluster analysis identified four different clusters and showed that the Guzera breed had bulls with different genetic patterns that permits genetic selection for beef, milk or dual purpose. Implications: The genetic correlations of the present study suggest that selection to increase milk yield will lead to a slight genetic gain in the same direction for body weight at different ages, in contrast to reports from some other studies. The Guzera breed is in second position among Zebu breeds for milk production and is also used as a dual-purpose breed in some Brazilian production systems. The genetic correlations suggest that selection to increase milk yield will lead to selection in the same direction for body weight at different ages. The Guzera breed has the genetic potential to meet different selection objectives, either beef or milk production, or to produce dual-purpose animals as indicated by principal component analysis and cluster analysis. [ABSTRACT FROM AUTHOR]

Context: Lactation persistency (LP) is an economically important characteristic to include in the selection objectives of the Gyr breed. Two persistency measures were tested to establish their contribution to the genetic evaluation of milk production in this genotype. The second measure of persistency studied would be the more appropriate measure to use in the genetic evaluation of lactation persistency. Aim: The aim of this work was to study LP in Gyr cows by using a random regression model (RRM) in two-trait analysis. Methods: Test-day milk yields (TDMY) of the first two lactations of Gyr cows were analysed. RRM was performed by Bayesian inference using the GIBBS3F90 program. Fourth-order Legendre polynomials were used to describe the random additive genetic and permanent environmental effects of the animal. The fixed effects included in the model were contemporary group and, as covariates, age of cow at calving and the regression function according to the TDMY class of lactation as the average trajectories of lactation curve, distinguished by calving order. Two persistency measures (PS i , i.e. PS1 and PS2) were used in the analyses. Rank correlations were calculated between the predicted breeding values for PS i , 305-day lactation milk yield (MY305), and the regression coefficients a 0 and a 1, to determine the percentage of matching animals between rankings when different selection intensities are applied on the basis of the ranking for MY305. Key results: The heritability estimates for PS1, PS2 and for MY305 were 0.19, 0.12 and 0.41 respectively, in the first lactation, and 0.43, 0.27 and 0.38 in the second lactation. The genetic correlation between MY305 and PS1 was negative and of low magnitude. The rank correlation between breeding values for PS i , obtained for bulls with at least five daughters with production records, was higher than 0.80 in the two lactation periods. Conclusions: The results indicated that PS2 is the more suitable of the two persistency measures used in this work, for inclusion in genetic evaluations of lactation persistency in Brazilian Gyr cows. Implications: PS2 must be included as a selection criteria in a breeding program for the Gyr breed. The Gyr breed has been selected in Brazil for 40 years, mainly for total milk yield. The lactation persistency is closely related to the profitability of a milk production system. More persistent cows need less inputs, they get less sick, have more stayability and behave better reproductively. The results indicated that it is possible to make a selection for lactation persistency and that the second measure considered is better suited to the behavior of milk yield in Gyr breed. [ABSTRACT FROM AUTHOR]

The present study aims to estimate genetic parameters for dystocia, milk yield and age at first calving of Holstein cows reared in intensive production systems located in the southeastern region of Brazil. A total of 26,987 first-lactation records of Holstein cows were used. The following traits were analysed: 305-day cumulative first lactation milk yield (MY305), age at first calving (AFC) and dystocia. Dystocia was defined as a binary trait, with 0 indicating failure and 1 indicating success. Success was attributed to cows that had a normal calving, and failure was attributed to cows that had a difficult or human-assisted parturition. The (co)variance components were estimated using a Bayesian approach. The heritability estimates were 0.15 (0.01), 0.27 (0.02), and 0.17 (0.03) for MY305, AFC and dystocia, respectively. Dystocia showed genetic correlations of 0.30 (0.09) with AFC and −0.17 (0.11) with MY305. Early maturing heifers may be genetically prone to a more difficult first calving. [ABSTRACT FROM AUTHOR]

The present study evaluated the heat stress response pattern of dual‐purpose Guzerá cattle for test‐day (TD) milk yield records of first lactation and estimated genetic parameters and trends related to heat stress. A total of 31,435 TD records from 4,486 first lactations of Guzerá cows, collected between 1986 and 2012, were analysed. Two random regression models considered days in milk (DIM) and/or temperature × humidity‐dependent (THI) covariate. Impacts of −0.037, −0.019 and −0.006 kg/day/THI for initial and intermediate stages of lactation were observed when considering the mean maximum daily temperature and humidity to calculate THI. Heritability estimates ranged from 0.16 to 0.35 throughout lactation and THI values, suggesting the possibility to expect gains from selection for such trait. The variable trajectory of breeding values for dual‐purpose Guzerá sires in response to changes in THI values confirms that the genotype × environment interaction due to heat stress can have some effect on TD milk yield. Despite the high dairy performance of Guzerá cattle under heat stress, estimated genetic trends showed a progressive reduction in heat tolerance. Therefore, new strategies should be adopted to prevent negative impacts of heat stress over milk production in Guzerá animals in future. [ABSTRACT FROM AUTHOR]

This study evaluated 53 primiparous cows (36.8±1.23 months old and 484±40.9 kg of body weight) performance tested (GrowSafe® System) from 22±5 to 190±13 days of lactation in order to obtain daily dry matter intake (DMI). The animals received a high-forage diet (forage-to-concentrate ratio of 90:10). Milk production of the cows was evaluated three times by mechanical milking and the energy-corrected milk yield (ECMY) was calculated. Energy status (through the indicators glucose, cholesterol, triglycerides, and β-hydroxybutyrate), protein status (indicators albumin, urea, and creatinine), mineral status (indicators calcium, phosphorus, and magnesium), and hormonal status (indicators insulin and cortisol) were estimated four times throughout lactation. The residual feed intake (RFI) of cows was calculated considering DMI, average daily gain (ADG) and mid-test metabolic weight (BW0.75) obtained in early lactation (from 22±5 to 102±7 days), and the animals were classified as negative (most efficient) or positive RFI (least efficient). The RFI model explained 53% of the variation in DMI. The mean DMI, ADG, ECMY, and calf weight as a percentage of cow weight were 12.47±2.70 kg DM/day, 0.632±0.323 kg/day, 10.47±3.23 kg/day, and 36.6±5.39%, respectively. Negative RFI cows consumed 11.5% less DM than positive RFI cows, with performance and metabolic profile being similar to those of positive RFI cows, except for a lower milk protein content and higher blood cholesterol concentration. In conclusion, negative (most efficient) and positive RFI (least efficient) Nellore cows, fed an ad libitum high-forage diet, produced similar amounts of milk, fat and lactose and had similar subcutaneous fat thickness, weight, calf weight as a percentage of cow weight, and blood metabolite concentrations (except for cholesterol). Therefore, there are economic benefits to utilizing RFI in a cow herd since cattle had decreased DMI with similar overall performance, making them more profitable due to lower input costs. [ABSTRACT FROM AUTHOR]

• Milk lactoferrin concentration in milk is an indicator of udder health in primiparous Gyr cows. • Milk lactoferrin have a high association with somatic cells count in primiparous Gyr cows. • Stage of lactation influences the lactoferrin content in milk of primiarous Gyr cows. The objective of this study was to describe the variation in bovine lactoferrin (LF) content in milk from dairy Gyr heifers during lactation and to evaluate its relationship with milk components. Milk samples were collected between August to October 2013 for performance test 1 (25 first lactation cows) and August to October 2014 for performance test 2 (20 first lactation cows), coordinated by the Brazilian Association of dairy Gyr Breeders (ABCGIL), in Uberaba, MG, Brazil. Milk yield (MY) of 45 primiparous cows was measured daily. The milk samples for analysis of LF concentration and of the other milk components such as somatic cell count and percentage of fat (F%), protein (P%), lactose (L%) and total solids (TS) were collected monthly. The somatic cell count (SCC) was transformed to a somatic cell score (SCS). Pearson correlation coefficients between LF and the other milk components were calculated. Analyses of variance were performed by mixed models including the fixed effects of test (1 = calving 2013 and 2 = calving 2014) year-season of sampling, lactation month and age of cow at calving as classificatory effects, and the effects of SCS and MY as covariates (linear effect). The effect of cow was analyzed as a random effect considering repeated measures over time. The mean LF concentration was 16.80 ± 12.41 μg/mL milk and the values showed variation across lactation indicating that the lactation month influences milk LF concentration. Lactoferrin content was correlated with SCS (0.64, P < 0.01). The correlation between LF and MY was −0.47 (P < 0.01) and between LF and P% was 0.47 (P < 0.01). The trends of the LF and SCS mean curves were similar, while opposite trends were observed between LF and MY mean curves. The concentration of LF in milk from primiparous dairy Gyr cows showed a strong association with MY level and udder health. [ABSTRACT FROM AUTHOR]

Highlights • In Holstein cows, extreme milk yields are associated with a reduction in longevity. • Better udders and feet and legs conformation are associated with a lower SCS. • It is possible to promote early genetic gains in the longevity by correlated traits. Abstract Genetic associations were estimated between 305-day cumulative milk yield (MY305) and maximum somatic cell score (SCS) in the first lactation, stayability in the herd at 60 months of age (Stay60), and linear udder and feet and legs traits. First-lactation records of Holstein cows reared in intensive production systems in Brazil were used. The (co)variance components were estimated using a Bayesian approach. The heritability estimates were 0.24 ± 0.02, 0.08 ± 0.02 and 0.09 ± 0.03 for MY305, SCS and Stay60, respectively. The heritabilities of the linear traits ranged from 0.16 to 0.39 for udder traits and from 0.13 to 0.21 for feet and legs traits. Stay60 showed genetic correlations of -0.25 ± 0.12 with MY305, 0.11 ± 0.20 with SCS, 0.33 ± 0.16 with rear teat placement, and -0.47 ± 0.13 with a rear legs-side view. It is possible to promote early genetic gains in the longevity of animals by selecting for moderately correlated traits to obtain a good set of feet and legs, as well as well-positioned teats of medium length. Extreme milk yields are associated with a reduction in Stay60. SCS in the first lactation has practically no influence on Stay60. The maximum selection efficiency will be achieved by selecting directly by Stay60. [ABSTRACT FROM AUTHOR]

This study investigated the association of electrical conductivity (EC) of milk with milk production and composition traits in Dairy Gyr cows. Monthly milk samples were collected on the official milk recording day for laboratory analysis of somatic cell count, EC and milk composition. A total of 680 samples from 268 cows belonging to eight herds in the southeastern region of Brazil were collected between January and July 2012. Traits were analysed by the restricted maximum likelihood method using mixed models in order to associate EC and somatic cell score (SCS) with the other traits. Mean EC and SCS were 4.90 mS/cm and 4.66, respectively, and the correlation between these traits was 0.41. Linear regression of EC on SCS indicated an increase in EC of 0.094 mS/cm per SCS. Despite the relationship between EC and SCS, the former analysed only on the official recording day may not be a reliable method for the diagnosis of mastitis. However, EC could be used as an auxiliary trait in the analysis of mastitis resistance simultaneously with somatic cell count since, in addition to the association between these two traits, the measurement of EC is an inexpensive, simple and rapid method. [ABSTRACT FROM PUBLISHER]

In an attempt to determine the possible detrimental effects of continuous selection for milk yield on the genetic tolerance of Zebu cattle to heat stress, genetic parameters and trends of the response to heat stress for 86,950 test-day (TD) milk yield records from 14,670 first lactations of purebred dairy Gir cows were estimated. A random regression model with regression on days in milk (DIM) and temperature-humidity index (THI) values was applied to the data. The most detrimental effect of THI on milk yield was observed in the stage of lactation with higher milk production, DIM 61 to 120 (-0.099 kg/d per THI). Although modest variations were observed for the THI scale, a reduction in additive genetic variance as well as in permanent environmental and residual variance was observed with increasing THI values. The heritability estimates showed a slight increase with increasing THI values for any DIM. The correlations between additive genetic effects across the THI scale showed that, for most of the THI values, genotype by environment interactions due to heat stress were less important for the ranking of bulls. However, for extreme THI values, this type of genotype by environment interaction may lead to an important error in selection. As a result of the selection for milk yield practiced in the dairy Gir population for 3 decades, the genetic trend of cumulative milk yield was significantly positive for production in both high (51.81 kg/yr) and low THI values (78.48 kg/yr). However, the difference between the breeding values of animals at high and low THI may be considered alarming (355 kg in 2011). The genetic trends observed for the regression coefficients related to general production level (intercept of the reaction norm) and specific ability to respond to heat stress (slope of the reaction norm) indicate that the dairy Gir population is heading toward a higher production level at the expense of lower tolerance to heat stress. These trends reflect the genetic antagonism between production and tolerance to heat stress demonstrated by the negative genetic correlation between these components (-0.23). Monitoring trends of the genetic component of heat stress would be a reasonable measure to avoid deterioration in one of the main traits of Zebu cattle (i.e., high tolerance to heat stress). On the basis of current genetic trends, the need for future genetic evaluation of dairy Zebu animals for tolerance to heat stress cannot be ruled out. [ABSTRACT FROM AUTHOR]

• Persistency is important for dairy Zebu because they have short lactations. • Random regression is a suitable tool to model longitudinal traits like milk yield. • Cluster analysis identified group of animals suitable to attend the breeding goals. The aim of this study was to estimate genetic parameters for month test-day milk yields of dairy Gyr cattle and to explore the additive genetic pattern of the milk production curve using cluster analysis in order to choose subgroups of animals that can result in genetic gain for milk production. The dataset of dairy Gyr cows was provided by the Brazilian Association of Zebu Breeders (ABCZ) and contained 123,035 first-lactation test-day records from 16,318 cows and calvings between 1983 and 2014. Random regression under an animal model was used to predict the breeding values of animals for monthly milk yields from 30 to 305 days, as the sum of breeding values of each day in milk, for coefficients of the lactation curve (intercept, linear, quadratic, and cubic), for peak yield, persistency of lactation, and total milk yield. Two cluster analyses were used to describe the additive genetic structure of the population: the hierarchical (Ward method) and non-hierarchical (k-means method) cluster analyses using the predicted breeding values of the above traits. Cluster analysis were used to figure out the patterns of the additive genetic lactation curves within the population that matched up with pre-defined breeding goals (improve the milk production) to suggest potential selection candidates. The estimates of heritability for test day milk yields ranged from 0.14 ± 0.02 to 0.20 ± 0.02. The intercept of the random regression had strong genetic correlation with peak yield and total milk yield while the linear random regression coefficient had strong genetic correlation with the persistency, as defined in this study, of the lactation curve. Cluster analysis resulted in four groups. The animals from Cluster 1 could be used as selection candidates because their additive genetic pattern presented EBVs above the mean population for all the traits. So, those animals could help to increase the milk production, and the persistency of lactation. Cluster analysis was effective to identify groups of animals suitable to attend the breeding goals, i.e. increase the persistency of lactation and the milk production along the lactation curve in dairy Gyr cattle. [ABSTRACT FROM AUTHOR]