Test-day Milk Yield Research Articles

Genetic Polymorphism in Prolactin Gene and its Effect on Test Day Milk Production Traits in Sahiwal Cattle

Background: The selection of genetically superior animals at an early stage of life, the molecular markers are used along with traditional selection. The study was carried out to identify the genetic polymorphism in the exon3 region of the Prolactin and enumerate its effect on milk production performance in Sahiwal cattle. Prolactin plays an imperative regulatory role in mammary gland development, milk emission and lactogenesis. Analysed the sequence of this gene to explore whether mutations in this sequence and it could be accountable for quantitative variations in milk production and its composition traits.Methods: Total DNA was isolated from the blood samples of 98 pedigreed Sahiwal population. Using PCR-RFLP method and direct sequencing, noticed a single-nucleotide polymorphism in exon3 region of the Prolactin gene in 156bp and also the effect of non- genetic factors on each trait was assessed by least-squares analysis for non-orthogonal data by a fixed model.Result: PCR-RFLP was done with RsaI restriction endonuclease for the identification of different genotypes. The frequency of G and A alleles of the Prolactin gene was evaluated as 0.575 and 0.425, whereas the frequencies of GG, GA and AA genotypes for the Prolactin gene were 0.45, 0.25 and 0.30, respectively. SNP (G55A) conferred an increase in test-day milk yield around 321.5g, in test day fat yield around 13.9g and in test day SNF yield increase was 19.4g, respectively. High correlation was perceived from test day (TD2) onwards between test day traits and lactation milk yield indicating that selection based on identified SNP in TD2 increased test day milk yield, fat yield and SNF yield by 1.1472 kg, 29.6gm and 45.4gm, respectively.

Postcalving udder health and productivity in cows approaching dry-off with intramammary infections caused by non-aureus Staphylococcus, Aerococcus, Enterococcus, Lactococcus, and Streptococcus species

The objective of this prospective cohort study was to explore associations between intramammary infection (IMI) in late-lactation cows and postcalving udder health and productivity. Cows (n = 2,763) from 74 US dairy herds were recruited as part of a previously published cross-sectional study of bedding management and IMI in late-lactation cows. Each herd was visited twice for sampling. At each visit, aseptic quarter milk samples were collected from 20 cows approaching dry-off (>180 d pregnant), which were cultured using standard bacteriological methods and MALDI-TOF for identification of isolates. Quarter-level culture results were used to establish cow-level IMI status at enrollment. Cows were followed from enrollment until 120 d in milk (DIM) in the subsequent lactation. Herd records were used to establish whether subjects experienced clinical mastitis or removal from the herd, and DHIA test-day data were used to record subclinical mastitis events (somatic cell count >200,000 cells/mL) and milk yield (kg/d) during the follow-up period. Cox regression and generalized estimating equations were used to evaluate the associations between IMI and the outcome of interest. The presence of late-lactation IMI caused by major pathogens was positively associated with postcalving clinical mastitis [hazard ratio = 1.5, 95% confidence interval (CI): 1.2, 2.0] and subclinical mastitis (risk ratio = 1.5, 95% CI: 1.3, 1.9). Species within the non-aureus Staphylococcus (NAS) group varied in their associations with postcalving udder health, with some species being associated with increases in clinical and subclinical mastitis in the subsequent lactation. Late-lactation IMI caused by Streptococcus and Streptococcus (Strep)-like organisms, other than Aerococcus spp. (i.e., Enterococcus, Lactococcus, and Streptococcus spp.) were associated with increases in postcalving clinical and subclinical mastitis. Test-day milk yield from 1 to 120 DIM was lower (-0.9 kg, 95% CI: -1.6, -0.3) in late-lactation cows with any IMI compared with cows without IMI. No associations were detected between IMI in late lactation and risk for postcalving removal from the herd within the first 120 DIM. Effect estimates reported in this study may be less than the underlying quarter-level effect size for IMI at dry-off and postcalving clinical and subclinical mastitis, because of the use of late-lactation IMI as a proxy for IMI at dry-off and the use of cow-level exposure and outcome measurements. Furthermore, the large number of models run in this study (n = 94) increases the chance of identifying chance associations. Therefore, confirmatory studies should be conducted. We conclude that IMI in late lactation may increase risk of clinical and subclinical mastitis in the subsequent lactation. The relationship between IMI and postcalving health and productivity is likely to vary among pathogens, with Staphylococcus aureus, Streptococcus spp., Enterococcus spp., and Lactococcus spp. being the most important pathogens identified in the current study.

Genomic evaluation of Brown Swiss dairy cattle with limited national genotype data and integrated external information

This study demonstrated the feasibility of a genomic evaluation for the dairy cattle population for which the small national training population can be complemented with foreign information from international evaluations. National test-day milk yield data records for the Slovenian Brown Swiss cattle population were analyzed. Genomic evaluation was carried out using the single-step genomic best linear unbiased prediction method (ssGBLUP), resulting in genomic estimated breeding values (GEBV). The predominantly female group of genotyped animals, representing the national training population in the single-step genomic evaluation, was further augmented with 7,024 genotypes of foreign progeny-tested sires from an international Brown Swiss InterGenomics genomic evaluation (https://interbull.org/ib/whole_cop). Additionally, the estimated breeding values for the altogether 7,246 genotyped domestic and foreign sires from the 2019 sire multiple across-country evaluation(MACE), were added to the ssGBLUP as external pseudophenotypic information. The ssGBLUP method, with integration of MACE information by avoiding double counting, was then performed, resulting in MACE-enhanced GEBV (GEBVM). The methods were empirically validated with forward prediction. The validation group consisted of 315 domestic males and 1,041 domestic females born after 2012. Increase, inflation, and bias of the GEBV(M) reliability (REL) were assessed for the validation group with a focus on females. All individuals in the validation benefited from genomic evaluations using both methods, but the GEBV(M) REL increased most for the youngest selection candidates. Up to 35 points of GEBV REL could be assigned to national genomic information, and up to 17 points of GEBVM REL could additionally be attributed to the integration of foreign sire genomic and MACE information. Results indicated that the combined foreign progeny-tested sire genomic and external MACE information can be used in the single-step genomic evaluation as an equivalent replacement for domestic phenotypic information. Thus, an equal or slightly higher genomic breeding value REL was obtained sooner than the pedigree-based breeding value REL for the female selection candidates. When the abundant foreign progeny-tested sire genomic and MACE information was used to complement available national genomic and phenotypic information in single-step genomic evaluation, the genomic breeding value REL for young-female selection candidates increased approximately 10 points. Use of international information provides the possibility to upgrade small national training populations and obtain satisfying reliability of genomic breeding values even for the youngest female selection candidates, which will help to increase selection efficiency in the future.

Multiple linear regression analysis using monthly test day milk yield predicting the first lactation production performance for sire evaluation in Murrah buffaloes

A total of 9071 first lactation monthly test-day milk yield records of Murrah buffaloes were used to predict the first lactation 305-day milk yield (FL305DMY) by using stepwise backward regression analysis. For the prediction of FL305DMY best combination of monthly test-day milk yields were selected based on adjusted R 2 and RMSE values. The objective of the study was to compare various methods of sire evaluation viz., least squares (LSQ), simple regressed least squares (SRLS), best linear unbiased prediction sire model (BLUP-SM) and best linear unbiased prediction animal model (BLUP-AM) in terms of accuracy and efficiency. The methods were compared on the basis of error variance, coefficient of determination, coefficient of variation and rank correlations among the methods. The accuracy of prediction of FL305DMY from monthly test-day milk yields were observed to be best for TD-2 (45 th day), TD-4 (105 th day) and TD-6 (165 th day) combination with BLUP-AM as the most efficient method for sire evaluation. Individual, key monthly TD-6 (165 th day) milk yield has high rank correlation with EBVs obtained from actual 305-day milk yield. It was concluded that the optimum combination of TD-2 (45 th day), TD-4 (105 th day) and TD-6 (165 th day) or individual TD-6 (165 th day) can be used for genetic evaluation of Murrah sires.

Heterosis effects on 305-day milk yield in a Girolando dairy cattle population in different lactation orders

The aim of this study was to evaluate the heterosis effects for 305-day milk yield (305MY) in different lactation orders of Girolando cows, by fitting test-day milk yield records to Wood's, Mixed Log, and Wilmink's non-linear models. A total of 400,328 test-day milk yield records of 39,077 Holstein (H), Gyr (G), and Girolando (1/2 H, 1/4 H, 3/4 H, 3/8 H, 5/8 H, and 7/8 H genetic groups) cows from 822 herds were collected in the state of Minas Gerais, Brazil, from 1998 to 2014. The pedigree file comprised 36,640 animals, including 3677 sires and 24,472 cows. Genetic parameters were obtained by single-trait analysis using the AIREMLF90 software. Heritability estimates of 305MY and of 305MY fitted to the different non-linear models were higher in the first lactation and ranged from 0.10 to 0.29. We observed a greater heterosis effect for 305MY (and 305MY fitted) verified in cows of genetic group 1/2H, which presented average production superior to the average of their parents (of pure breeds) in the first (1034.33 kg) and second (1303.94 kg) lactation, respectively. Both Wood's and Wilmink's models stood out in quality of fit, presenting the best estimates for 305MY adjusted for different lactation orders. Wood's model is the most suitable to estimate 305MY of cows with a higher proportion of H genes. However, Wilmink's model allows estimating heterosis effects for 305MY and components of the lactation curve more similar to those observed in 305MY in the different genetic groups. The results indicate that local breeders can promote an improvement in milk production through exploitation of the heterosis effect, making choices of genetic combinations (breeders) more suitable for mating to obtain greater economic and productive efficiency of their herds during lactations.

Estimation of genetic parameters for test-day milk yield in Girolando cows using a random regression model

ABSTRACT The objective of this study was to estimate the components of variance and genetic parameters of test-day milk yield in first lactation Girolando cows, using a random regression model. A total of 126,892 test-day milk yield (TDMY) records of 15,351 first-parity Holstein, Gyr, and Girolando breed cows were used, obtained from the Associação Brasileira dos Criadores de Girolando. To estimate the components of (co) variance, the additive genetic functions and permanent environmental covariance were estimated by random regression in three functions: Wilmink, Legendre Polynomials (third order) and Linear spline Polynomials (three knots). The Legendre polynomial function showed better fit quality. The genetic and permanent environment variances for TDMY ranged from 2.67 to 5.14 and from 9.31 to 12.04, respectively. Heritability estimates gradually increased from the beginning (0.13) to mid-lactation (0.19). The genetic correlations between the days of the control ranged from 0.37 to 1.00. The correlations of permanent environment followed the same trend as genetic correlations. The use of Legendre polynomials via random regression model can be considered as a good tool for estimating genetic parameters for test-day milk yield records.

Selection for Test-Day Milk Yield and Thermotolerance in Brazilian Holstein Cattle

Simple SummaryInterest in selection for milk yield and thermotolerance in cattle has grown, since heat stress has caused great losses in milk yield. However, few studies on how to carry out concurrent selection are available. Milk yield was analyzed by traditional methods, including heat stress indicators, in genetic evaluation. The results showed that the best sires for milk yield are not the best for heat tolerance, and only a small proportion of individuals have the aptitude for joint selection. Despite a small population fraction allowed for joint selection, sufficient genetic variability for selecting more resilient sires was found, which promoted concomitant genetic gains in milk yield and thermotolerance.Intense selection for milk yield has increased environmental sensitivity in animals, and currently, heat stress is an expensive problem in dairy farming. The objectives were to identify the best model for characterizing environmental sensitivity in Holstein cattle, using the test-day milk yield (TDMY) combined with the temperature–humidity index (THI), and identify sires genetically superior for heat-stress (HS) tolerance and milk yield, through random regression. The data comprised 94,549 TDMYs of 11,294 first-parity Holstein cows in Brazil, collected from 1997 to 2013. The yield data were fitted to Legendre orthogonal polynomials, linear splines and the Wilmink function. The THI (the average of two days before the dairy control) was used as an environmental gradient. An animal model that fitted production using a Legendre polynomials of quartic order for the days in milk and quadratic equations for the THI presented a better quality of fit (Akaike’s information criterion (AIC) and Bayesian information criterion (BIC)). The Spearman correlation coefficient of greatest impact was 0.54, between the top 1% for TDMY and top 1% for HS. Only 9% of the sires showed plasticity and an aptitude for joint selection. Thus, despite the small population fraction allowed for joint selection, sufficient genetic variability for selecting more resilient sires was found, which promoted concomitant genetic gains in milk yield and thermotolerance.

Forticept® innovative products’ effectiveness for complex udder hygiene

The quality of cow’s milk and the spread of mastitis greatly depend on the level of udder hygiene. Our author’s research was conducted to evaluate the effects of Forticept® Udder Wash and Forticept® Udder Forte, used before and after milking, on the treatment and prevention of subclinical mastitis and hyperkeratosis of cows’ udders. A total of 6880 milk samples were taken from 430 cows, 3-4 years old, 470-490 kg weight, at 60 ± 15 days of lactation. The therapeutic efficacy coefficient (EC) of Forticept® polymers based on benzetonium and benzalkonium chloride, against the subclinical form of mastitis was 73.8% compared to iodine-containing agents; preventive EC - 32.4%. Dipping hygiene of the udder using Forticept® on the 30th day reduced the number of 1-3 stage teat hyperkeratosis cases from 78.8% to 41.3%. Also, during this period, a significant (P<0.05) improvement in the chemical parameters of the milk was observed - an increase in fat (up to 3.94 ± 0.08%), protein (3.35 ± 0.07%), casein (3.15 ± 0.09%) and dry matter (14.91 ± 0.28%). After using Forticept®, the total bacteria count (TBC) of the milk decreased to 3×105 CFU/cm3, and the somatic cell count (SCC) - to 130 thousand/cm3 (P<0.05). Test day milk yield (TDMY) increased by 1.15% due to efficient dipping with Forticept® (P<0.05).

Polymorphisms of the ACSL1 Gene Influence Milk Production Traits and Somatic Cell Score in Chinese Holstein Cows.

Simple SummaryMilk production traits of cows are important economic indicators of the livestock industry. Many dairy farms strive to improve the quality of their milk. Long-chain acyl-CoA synthetase 1 (ACSL1) is a gene related to lipid metabolism. It is widely found in various organisms and can affect fat content and protein content in milk. Single nucleotide polymorphisms (SNP) refers to the polymorphism of DNA sequence caused by a single nucleotide variation at the gene level, which plays a vital function in the genetic study of milk production traits in dairy cows. Our study identified six SNPs of the ACSL1 gene in Chinese Holstein cows, which were related to milk yield, milk fat content, milk protein content and somatic cell score (SCS) to some extent. In summary, the pleiotropic effects of bovine ACSL1 for milk production traits were found in this paper, which will provide a reference for Chinese Holstein cow breeding selection and high economic benefits.Improving the quality of milk is a challenge for zootechnicians and dairy farms across the globe. Long-chain acyl-CoA synthetase 1 (ACSL1) is a significant member of the long-chain acyl-CoA synthetase gene family. It is widely found in various organisms and influences the lactation performance of cows, including fat percentage, milk protein percentage etc. Our study was aimed to investigate the genetic effects of single nucleotide polymorphisms (SNPs) in ACSL1 on milk production traits. Twenty Chinese Holstein cows were randomly selected to extract DNA from their blood samples for PCR amplification and sequencing to identify SNPs of the bovine ACSL1 gene, and six SNPs (5’UTR-g.20523C>G, g.35446C>T, g.35651G>A, g.35827C>T, g.35941G>A and g.51472C>T) were discovered. Then, Holstein cow genotyping (n = 992) was performed by Sequenom MassARRAY based on former SNP information. Associations between SNPs and milk production traits and somatic cell score (SCS) were analyzed by the least-squares method. The results showed that SNP g.35827C>T was in high linkage disequilibrium with g.35941G>A. Significant associations were found between SNPs and test-day milk yield (TDMY), fat content (FC), protein content (PC) and SCS (p < 0.05). Among these SNPs, SNP 5’UTR-g.20523C>G showed an extremely significant effect on PC and SCS (p < 0.01). The SNP g.35446C>T showed a statistically significant effect on FC, PC, and SCS (p < 0.01), and also TDMY (p < 0.05). The SNP g.35651G>A had a statistically significant effect on PC (p < 0.01). The SNP g.35827C>T showed a highly significant effect on TDMY, FC, and SCS (p < 0.01) and significantly influenced PC (p < 0.05). Lastly, SNP g.51472C>T was significantly associated with TDMY, FC, and SCS (p < 0.05). In summary, the pleiotropic effects of bovine ACSL1 for milk production traits were found in this paper, but further investigation will be required on the intrinsic correlation to provide a theoretical basis for the research on molecular genetics of milk quality traits of Holstein cows.

Influence of Panamin Animal and Panamin Detox on milk coagulation properties of dairy cows

Abstract. The aim of the study was to evaluate the differences in milk coagulation properties in three groups of dairy cows receiving the dietary supplements Panamin Animal and Panamin Detox. The present group production experiment was conducted in the experimental cattle farm of the Agricultural Institute – Stara Zagora with three groups (two experimental and one control) each comprising 11 lactating dairy cows between November 2016 and March 2017. The cows are kept freely, the milking is in a hall “Fish bone”, and the groups were fed balanced rations compliant with milk yield and live body weight of cows, supplemented with 0.50 g/day of two natural dietary additives – Panamin Animal and Panamin Detox in line with recommendations of the manufacturer. The following parameters were monitored: rennet coagulation time (min) – RCT and curd firmness (mm) – a30. The analysis of individual milk coagulation properties was done on 436 milk samples from cows. Individual milk samples were obtained during the morning milking without adding preservative. The analysis of milk coagulation ability was evaluated at the laboratory of the Agricultural Institute – Stara Zagora by means of Computerized Renneting Metter – Polo Trade, Italy. The obtained phenotypes were corrected for main factors influencing test-day milk yield. The used model considered each test day milk yield as independent observation and unbiased estimates of traits were obtained by a linear mixed-effects model. The supplementation of cows’ ration with dietary supplements Panamin Detox and Panamin Animal had a statistically significant beneficial effect on milk coagulation properties of milk (p&lt;0.001). The statistical analysis of group differences in RCT and curd firmness showed highly significant differences between Panamin Animal and control groups for both traits (p&lt;0.001). There was also a highly relevant difference in curd firmness of milk from cows given Panamin Detox supplement and control cows (p&lt;0.001). Data were processed with statistical software products Systat 13 and Pest (Groeneveld), and graphs were generated in MS Excel.

Estimates of genetic parameters and cluster analysis of the lactation curve of dairy Gyr cattle

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.

Evaluating the impact of heat stress as measured by temperature-humidity index (THI) on test-day milk yield of small holder dairy cattle in a sub-Sahara African climate

This study evaluates the effect of heat stress on milk production and describes the pattern of response of milk yield to increasing heat load, using temperature-humidity index (THI) on test-day milk records of small holder dairy cattle herds in the sub-Saharan African climate of Tanzania. Climate data obtained from aWhere, an agricultural weather data platform (http://www.awhere.com) was analysed with 14,367 first lactation test day milk records of 3511 dairy cows collected between 2016 and 2019. THI was calculated from daily maximal temperatures and daily minimum humidity. Three sets of analysis were performed. In the first and second analysis, two mixed effect repeatability models were fitted with THI treated as a categorical variable grouped into 5 classes (THI1= [61 - 66], THI2= [67 - 71], THI3= [72 - 78], THI4=[79 - 81], THI5=[82 - 86]), to obtain least squares estimates of THI effect on milk production, and as a continuous variable within THI classes to identify THI thresholds at which milk yield started to decline. In the third analyses, one quadratic polynomial regression (POL) and three regression spline functions namely piecewise linear spline function (PLF), natural splines function (NSF) and cubic splines function (CSF) were fitted to determine the average effect of THI on milk yield in the population and describe the pattern of response of milk yield to increasing head load.The results show that heat stress reduced milk yield by 4.16% to 14.42% across THI groups, with daily milk yield being the highest in THI1 (7.40±0.39 litres) and the lowest in THI4 (6.33±0.32).Regression coefficients within groups showed significant daily milk yield decrease in THI2 (-0.09) and THI3 (-0.06), but not for other THI classes, indicating that cows experienced heat stress between THI values of 67 and 76 and milk loss plateaued afterwards, suggesting that the animals acclimatized to heat stress conditions beyond THI value of 76. At the population level, THI and its squared term were significantly negatively and positively (-0.61, 0.004) associated with milk production, indicating a non-linear relationship between milk yield and THI. The CSF model showed better goodness of fit and predictive ability than other models for predicting future population response of milk yield to heat stress in small holder dairy farms in Tanzania.Herd management strategies and animal husbandry measures are needed in small holder dairy farms in Tanzania to minimize the impact of heat stress on milk yield and income of the farmers.

Genetic parameters for test-day milk yield, lactation persistency, and fertility in low-, medium-, and high-production systems in Kenya

Genetic parameters for test-day milk yield, lactation persistency, and age at first calving (as a fertility trait) were estimated for the first 4 lactations in multiple-breed dairy cows in low-, medium-, and high-production systems in Kenya. Data included 223,285 test-day milk yield records from 11,450 cows calving from 1990 to 2015 in 148 herds. A multivariate random regression model was used to estimate variance and covariance components. The fixed effects in the model included herd, year, and test month, and age as a covariate. The lactation profile over days in milk (DIM) was fitted as a cubic smoothing spline. Random effects included herd, year, and test month interaction effects, genetic group effects, and additive genetic and permanent environmental effects modeled with a cubic Legendre polynomial function. The residual variance was heterogeneous with 11 classes. Consequently, the variance components were varied over the lactation and with the production system. The estimated heritability for milk yield was lower in the low-production system (0.04-0.48) than in the medium- (0.22-0.59) and high-production (0.21-0 60) systems. The genetic correlations estimated between different DIM within lactations decreased as the time interval increased, becoming negative between the ends of the lactations in the low- and medium-production systems. Low (0.05) to medium (0.60) genetic correlations were estimated among first lactation test-day milk yields across the 3 production systems. Genetic correlations between the first lactation test-day milk yield and age at first calving ranged from 0.27 to 0.49, 0 to 0.81, and -0.08 to 0.27 in the low-, medium-, and high-production systems, respectively. Medium to high heritabilities (0.17-0.44) were estimated for persistency, with moderate to high (0.30-0.87) genetic correlations between 305-d milk yield and persistency. This indicates that genetic improvement in persistency would lead to increased milk yield. The low to medium genetic correlations between test-day milk yield between production systems indicate that sires may be re-ranked between production systems. Therefore, we conclude that sires should be selected based on a genetic evaluation within the target production system.

Comparison of daughter's performance of progeny tested sires with pedigree selected sires in Holstein Friesian crossbred cattle

The present study was conducted to compare the estimated breeding values of progeny tested sires and pedigree selected sires for test day milk yield of crossbred Holstein Friesian cattle. First lactation milk yield records (1,20,198) of 12,971 daughters sired by 267 sires were collected from INAPH database maintained by NDDB. Variance and covariance components for test-day milk yield (TDMY) were estimated by different random regression test day models (RRTDM), viz. Cubic B- Spline function, Quadratic B-Spline function, Legendre polynomial (LP) function and Wilmink function using Average Information Restricted Maximum Likelihood (AIREML). Considering various criteria for comparison of different orders of TDMs, LP of 6th order for TDMY was the best fitted model for further estimation of breeding values. The heritability estimates ranged from 0.15 to 0.39 for TDMY using Leg_2 model. The additive genetic correlations were higher than the phenotypic correlations among different TDs. The additive genetic correlations between test day yields varied from 0.73 to 0.99. The expected progeny difference (EPD) for TDMYcalculated based on dam’s yield for the top ten and bottom ten PS bulls was 2,662.5 kg; whereas, the actual progeny difference (APD) for these bulls was -28.47 kg. While, EPD for top 10 and bottom 10 PT bulls selected based on EBVs was 2,820.52 kg whereas the APD for PT bulls was 890.48 kg. The difference in expected and actual MY of progeny was higher in PS bulls as compared to PT bulls indicating that the pedigree information for EPDs had a poor association with APDs and sire superiority is not reflected in progeny’s actual performance. The rank correlation between ranks of all PS and PT bulls were very poor and non-significant. The bulls selected based on estimated breeding values will give faster genetic progress and decision to select replacement bulls based on breeding values instead of dam’s yield will have positive effect on genetic progress.

Estimation of genetic parameters for milk yield using a random regression test-day model in first parity dairy cows under pasture-based systems of Los Ríos region in Chile

In dairy cattle, genetic selection for milk yield was generally based on 305 days lactation records that were calculated from available monthly test-day milk yield records. A test-day milk yield record, multiplied by the number of days between the current and following test-day, was the monthly milk yield and summed to all other monthly milk yields represented a 305 days lactation yield. Cows that for any reason did not complete their lactation got a 305 days yield via correction factors assuming a common lactation curve. Random regression models allow individual deviation from a common curve. The objective of this study was to estimate genetic parameters for daily milk yield using a random regression model (RRM) in Chilean dairy cows. A data set containing 97,683 monthly test-day records of 10,528 cows from 15 commercial dairy herds of Los Rios Region in southern Chile was used. Days in milk (DIM) were modelled using the fourth-order Legendre polynomials and the model also included, as fixed effects, contemporary group and cow age at test-day as a covariate. The average daily milk yield was 17.83 ± 5.25 kg. Average estimated heritability and repeatability from five to 305 DIM was 0.26 ± 0.02 and 0.61 ± 0.04, respectively. The heritability estimate varied from 0.23 to 0.31. Both parameters did not vary dramatically except after 270 DIM when repeatability increased while heritability decreased. Although the estimated genetic parameters did not seriously depart from the most recent results available in the Chilean literature, they are mathematically more precise for estimating the true parameters than those calculated using adjustment factors, suggesting that the model used could be the starting point to develop a genetic evaluation system for dairy cattle in Chile.

Effect of Non-Genetic Factors on Test-Day Milk Yields and First Lactation Milk Yields in Holstein Friesian × Sahiwal Cattle

Effect of Non-Genetic Factors on Test-Day Milk Yields and First Lactation Milk Yields in Holstein Friesian × Sahiwal Cattle

Effect of Season, Parity and Stage of Lactation on Productive Performance of Sahiwal Cattle

The study was conducted to understand the effect of season, parity and stage of lactation on productive performance of Sahiwal cattle. The data of productive traits of 133 Sahiwal cattle from 2016 to 2018 maintained at the Livestock Research Center, Karnal, Haryana, were used for this study. The production data were analyzed using least-square procedures based on season, parity and stage of lactation. Results indicated that the parity had significant (p less than 0.05) influence on monthly milk yield (MMY) whereas, the stage of lactation had highly significant (P less than 0.01) influence on monthly milk yield (MMY) and test day milk yield (TDMY). However, there was no significant effect of season on different productive performance traits in Sahiwal cattle. The phenotypic parameter estimates indicated that the parity and stage of lactation of cattle can be used as a selection tool for improvement of productive traits considering its high positive phenotypic correlations with succeeding productive traits in Sahiwal cows.

Randomized controlled trial investigating the effect of 2 selective dry-cow therapy protocols on udder health and performance in the subsequent lactation

The objective of this study was to compare culture- and algorithm-guided selective dry-cow therapy (SDCT) programs with blanket dry-cow therapy (BDCT) in a multi-site, randomized, natural exposure clinical trial for the following cow-level outcomes: clinical mastitis, removal from the herd, and Dairy Herd Improvement Association (DHIA) test-day milk yield and SCC measures during the first 120 d in milk (DIM). Two days before planned dry-off, cows in each of 7 herds were randomly allocated to BDCT, culture-guided SDCT (cult-SDCT), or algorithm-guided SDCT (alg-SDCT). At dry-off, BDCT cows received an intramammary antibiotic (500 mg of ceftiofur hydrochloride) in all 4 quarters. Antibiotic treatments were selectively allocated to quarters of cult-SDCT cows by only treating quarters from which aseptically collected milk samples tested positive on a rapid culture system after 30 to 40 h of incubation. For alg-SDCT cows, antibiotic treatments were selectively allocated at the cow level, with all quarters receiving antibiotic treatment if the cow met at least one of the following criteria: (1) any DHIA test with a somatic cell count >200,000 cells/mL during the current lactation, and (2) ≥2 clinical mastitis cases during the current lactation. All quarters of all cows were treated with an internal teat sealant. Clinical mastitis and removal from the herd events (i.e., culling or death) and DHIA test-day data from dry-off to 120 DIM were extracted from herd records. Hazard ratios (HR) for the effect of treatment group on clinical mastitis and removal from the herd during 1 to 120 DIM were determined using Cox proportional hazards regression. The effects of treatment group on test-day loge-transformed SCC and milk yield were determined using linear mixed models. Final models indicated that either SDCT program was unlikely to increase clinical mastitis risk (HRcult-SDCT/BDCT = 0.82, 95% CI: 0.58, 1.15; HRalg-SDCT/BDCT = 0.83, 95% CI: 0.63, 1.09) or test-day logeSCC (cult-SDCT minus BDCT = 0.05, 95% CI: -0.09, 0.18; alg-SDCT minus BDCT = 0.07, 95% CI: -0.07, 0.21). Risk of removal from the herd and test-day milk yield were similar between treatment groups. Findings from this study indicate that culture- or algorithm-guided SDCT can be used at dry-off without negatively affecting cow health and performance in early lactation.

Polymorphisms in Fatty Acid Desaturase 2 Gene are Associated with Milk Production Traits in Chinese Holstein Cows.

Simple SummarySearching for causative polymorphisms underlying the variability of milk production traits and then incorporating them into breeding programs are very effective ways to improve the efficiency and reliability of conventional dairy cattle breeding. Fatty acid desaturase 2 (FADS2) plays a pivotal role in the biosynthesis of polyunsaturated fatty acids. Previous studies provided evidence that FADS2 was one of the most downregulated genes during negative energy balance in the liver of postpartum dairy cattle. Genes involved in the energetic pathways may influence other production traits, such as protein, fat and milk yields. Therefore, in the present study, we investigated the common genetic variants of the FADS2 gene in Chinese Holstein cows. Our results provided direct evidence that FADS2 was an interesting candidate for selection to increase milk production and improve resistance against mastitis.This study investigated the single nucleotide polymorphisms (SNPs) of Fatty acid desaturase 2 (FADS2) gene and further explored their genetic effects on conventionally collected milk production traits in Chinese Holstein cows using 18,264 test-day records of 841 cows. One missense mutation c. 908 C > T (SNP site in the complementary DNA sequence), which caused an amino acid change from alanine to valine (294Ala > Val), and two 3’ untranslated region (UTR) SNPs, c.1571 G > A and c.2776 A > G were finally identified. The SNP c.908 C > T was significantly associated with test-day milk yield, fat percentage and 305-day milk, fat and protein yield. In particular, the T allele of the SNP c.908 C > T showed a significant association with decreased somatic cell score (SCS) in the investigated population. Significant relationship between the SNP c.1571 G > A and 305-day milk yield showed that genotype GG was linked to the highest milk yield. Substituting the allele G for A at the c.2776 A > G locus resulted in a decrease of protein percentage. Our results demonstrated that FADS2 was an interesting candidate for selection to increase milk production and improve resistance against mastitis.

Randomized equivalence study comparing the efficacy of 2 commercial internal teat sealants in dairy cows

The use of an internal teat sealant (ITS) at dry-off has been repeatedly shown to improve udder health in the subsequent lactation. However, almost all ITS research conducted in North America has evaluated one product (Orbeseal, Zoetis, Parsippany, NJ). The objective of this study was to evaluate a new ITS product (Lockout, Boehringer-Ingelheim Animal Health, Duluth, GA), by comparing it directly to Orbeseal in a multi-site, randomized, positively controlled equivalence trial for health indicators during the dry period [quarter-level new intramammary infection (IMI) risk, IMI cure risk, and IMI risk at 1 to 13 d in milk, DIM] and during the first 100 DIM [clinical mastitis and culling or death risk and test-day milk somatic cell count (SCC) and milk yield]. At dry-off, cows were randomly allocated to be treated with Orbeseal or Lockout after blanket administration of a cloxacillin dry cow therapy product. Cows were then followed from dry-off until 100 DIM. Intramammary infection status at enrollment and at 1 to 13 DIM was determined using standard bacteriological methods, allowing for the measurement of IMI dynamics during the dry period (i.e., IMI cures and new IMI). The effect of ITS group on dry period IMI cure, dry period new IMI, and IMI risk at 1 to 13 DIM was determined using generalized linear mixed models (logistic). Marginal standardization was used to derive risk difference estimates. An equivalence hypothesis test was conducted to compare ITS groups for dry period new IMI risk (margin of equivalence was ±5% units). The effect of ITS group on clinical mastitis and culling or death was determined using Cox proportional hazards regression. The effect of ITS group on test-day SCC and milk yield was determined using linear mixed models. Final models indicated that measures of quarter-level IMI dynamics were similar between ITS groups (i.e., risk difference estimates and 95% confidence intervals all close to zero). Furthermore, Lockout was found to be equivalent to Orbeseal for dry period new IMI risk using an equivalence hypothesis test. Hazard ratio estimates for clinical mastitis and culling or death were close to 1 and differences in SCC and milk yield between ITS groups were close to 0, indicating negligible effects of ITS group on test-day SCC and milk yield. In most cases, these effect estimates were relatively precise (i.e., narrow 95% confidence intervals). We conclude that producers using blanket dry cow therapy could consider including Orbeseal or Lockout treatment in their programs.