Individual Test Day Research Articles

CSN1S1, CSN3 and LPL: Three Validated Gene Polymorphisms Useful for More Sustainable Dairy Production in the Mediterranean River Buffalo.

The search for DNA polymorphisms useful for the genetic improvement of dairy farm animals has spanned more than 40 years, yielding relevant findings in cattle for milk traits, where the best combination of alleles for dairy processing has been found in casein genes and in DGAT1. Nowadays, similar results have not yet been reached in river buffaloes, despite the availability of advanced genomic technologies and accurate phenotype records. The aim of the present study was to investigate and validate the effect of four single nucleotide polymorphisms (SNP) in the CSN1S1, CSN3, SCD and LPL genes on seven milk traits in a larger buffalo population. These SNPs have previously been reported to be associated with, or affect, dairy traits in smaller populations often belonging to one farm. A total of 800 buffaloes were genotyped. The following traits were individually recorded, monthly, throughout each whole lactation period from 2010 to 2021: daily milk yield (dMY, kg), protein yield (dPY, kg) and fat yield (dFY, kg), fat and protein contents (dFP, % and dPP, %), somatic cell count (SCC, 103 cell/mL) and urea (mg/dL). A total of 15,742 individual milk test day records (2496 lactations) were available for 680 buffalo cows, with 3.6 ± 1.7 parities (from 1 to 13) and an average of 6.1 ± 1.2 test day records per lactation. Three out four SNPs in the CSN1S1, CSN3 and LPL genes were associated with at least one of analyzed traits. In particular, the CSN1S1 (AJ005430:c.578C>T) gave favorable associations with all yield traits (dMY, p = 0.022; dPY, p = 0.014; dFY, p = 0.029) and somatic cell score (SCS, p = 0.032). The CSN3 (HQ677596: c.536C>T) was positively associated with SCS (p = 0.005) and milk urea (p = 0.04). Favorable effects on daily milk yield (dMY, p = 0.028), fat (dFP, p = 0.027) and protein (dPP, p = 0.050) percentages were observed for the LPL. Conversely, the SCD did not show any association with milk traits. This is the first example of a confirmation study carried out in the Mediterranean river buffalo for genes of economic interest in the dairy field, and it represents a very important indication for the preselection of young bulls destined for breeding programs aimed at more sustainable dairy production.

Significance of environmental factors that influence on fortnightly test days milk yield of Sirohi goat

The data of 22,630 fortnightly test day milk yield of 2,263 Sirohi does at different lactations were used and subjected to least square analysis to study the effect of various non-genetic factors like cluster, periods of kidding, season of kidding, parity, type of birth and regression of dam’s weight. The overall least-squares means of different individual fortnightly test day milk yields increase from 0.820±0.04 kg on TD1 (15th day of lactation) to a peak yield of 1.070±0.06 kg on TD2 (30th day of lactation) and subsequently declined to 0.348±0.01 kg on TD10 (150th day of lactation). Cluster and period wise variation were highly significant on all stages of fortnightly test day milk yields. The significantly higher test day milk yield were observed in winter kidded does as compared to summer and rainy kidded, it could be milk climatic conditions. The parity had statistically highly significant effect on fortnightly test day milk yields, in which seemed that milk yields increase as parity increase, thereafter declined slowly. The effect of type of kidding was non-significant on overall fortnightly test day milk yield under this study. The regression of dam’s weight at kidding was positive and highly significant (P≤ 0.01) on all fortnightly test day milk yield. In order to increase goat milk production, goat keepers need to be focused on nutritional and others environmental conditions as it affect their flock.

Test day variability in yield and composition of Surti and Mehsani buffaloes milk at day 15 and 60 postpartum.

Aim:To estimate individual test day variability in yield and composition of Surti and Mehsani buffaloes milk at day 15 and 60 postpartum (pp).Materials and Methods:A total of 13 normally calved Surti and Mehsani buffaloes each maintained at Livestock Research Stations of Navsari and Sardarkrushinagar Dantiwada Agricultural Universities, respectively, were selected for the study. Milk sample was collected from each selected buffalo at day 15 and 60 pp to study milk yield and composition variability between these two breeds. Buffaloes were categorized for the ease of data analysis and comparisons into four groups, viz., S15 (Surti buffaloes 15th day pp), S60 (Surti buffaloes 60th day pp), M15 (Mehsani buffaloes 15th day pp), and M60 (Mehsani buffaloes 60th day pp).Results:There were 37.20% and 25.03% significant (p≤0.05) increase in mean test day milk yield (TDMY) of S60 and M60 as compared to S15 and M15 groups, respectively. The mean TDMY of Mehsani buffalo was 99.19% and 81.53% significantly (p≤0.05) higher than Surti buffaloes at day 15 and 60 pp, respectively. The mean fat and protein corrected test day milk yield (FPCTDMY) of all the groups was found to be significantly different (p≤0.05) from each other. There was significant (p≤0.05) increase of 1.94 and 3.45 kg in mean FPCTDMY with the progression of lactation between day 15 and 60 pp in Surti and Mehsani buffaloes, respectively. Similarly, the mean FPCTDMY of Mehsani buffaloes were approximately double with 103.27% and 96.36% higher yield as compared to Surti buffaloes at day 15 and 60 pp, respectively. Among milk composition, significant differences were observed for solid not fat (SNF) and protein%, whereas fat and lactose% were steady among four groups. The only significant (p≤0.05) difference was observed for SNF in M60 group, which was 8.29%, 6.85%, and 10.70% higher as compared to S15, S60, and M15 groups, respectively. The mean protein% in milk of Mehsani buffaloes was 21.01% and 33.05% significantly (p≤0.05) higher than Surti buffaloes milk at day 15 and 60 pp, respectively. However, there was a significant difference in protein% observed with the advancement of lactation in Mehsani buffaloes, but it was not so in the case of Surti buffaloes.Conclusion:Major consistent finding of the present study reveals that milk yield and protein% of Mehsani buffalo was significantly higher than Surti buffalo at day 15 and 60 pp.

Reaction norm model to describe environmental sensitivity across first lactation in dairy cattle under tropical conditions.

Reaction norm models have been widely used to study genotype by environment interaction (G × E) in animal breeding. The objective of this study was to describe environmental sensitivity across first lactation in Brazilian Holstein cows using a reaction norm approach. A total of 50,168 individual monthly test day (TD) milk yields (10 test days) from 7476 complete first lactations of Holstein cattle were analyzed. The statistical models for all traits (10 TDs and for 305-day milk yield) included the fixed effects of contemporary group, age of cow (linear and quadratic effects), and days in milk (linear effect), except for 305-day milk yield. A hierarchical reaction norm model (HRNM) based on the unknown covariate was used. The present study showed the presence of G × E in milk yield across first lactation of Holstein cows. The variation in the heritability estimates implies differences in the response to selection depending on the environment where the animals of this population are evaluated. In the average environment, the heritabilities for all traits were rather similar, in range from 0.02 to 0.63. The scaling effect of G × E predominated throughout most of lactation. Particularly during the first 2 months of lactation, G × E caused reranking of breeding values. It is therefore important to include the environmental sensitivity of animals according to the phase of lactation in the genetic evaluations of Holstein cattle in tropical environments.

Prediction of 305-day lactation milk yield based on bimonthly test day values in Karan Fries cattle

The present investigation was carried out using data of first lactation bimonthly (BTDY) test day milk yields and 305-day milk yield records of 1345 Karan Fries cows sired by 84 bulls from 1984-2006 maintained at NDRI, Karnal. The test day milk yields recorded from 6th to 305th day at bimonthly intervals were used to predict 305 day milk. Based on simple linear regression analysis with only one independent variable, the regression coefficients showed a consistently increasing trend up to BTDY-3 and thereafter a consistently declining trend up to BTDY-7 test day milk yield was noticed. The accuracy of prediction (R2) of 305-day milk yield based on individual bimonthly test day milk yields varied between 19% (BTDY-1) and 59% (BTDY-4). However, slightly higher estimates of accuracy of prediction in the middle portion of lactation in bimonthly test day milk yields were observed. The absolute error, percent error and error variance showed continuously declining trend from BTDY-1 to BTDY-3 but then increasing trend from BTDY-3 to BTDY-6. Based on fitting of stepwise multiple regressions, the regression equation with 3 variables viz. BTDY-2, BTDY-3 and BTDY-5 was considered more appropriate for prediction of first lactation 305-day milk yield with 83 % accuracy and 7.54 per cent error of prediction in 305-day milk yield.

Estimation of genetic parameters for daily milk yields of primiparous Iranian Holstein cows

Abstract. Applying a multiple trait random regression (MT-RR) in national level and for whole test day records of a country is a great advance in animal breeding context. Having reliable (co) variance components is a critical step in applying multiple traits genetic evaluation especially in developing countries. Genetic parameters of milk, fat and protein yields were estimated for Iranian Holstein dairy cows. Data included 276 692 test day (TD) production traits records collected of 30 705 primiparous cows belonging to 619 sires. An animal multi-trait random regression model was employed in the analyses using the restricted maximum likelihood (REML) method. The model included herd-test-date, age-season of calving (by applying a fixed regression for each subclass of this effect) and year of calving as fixed effects and random regression (RR) coefficients for additive genetic (AG) and permanent environmental (PE) effects. Obtained results showed that daily heritabilities ranged from 0.10 to 0.21 for milk, from 0.05 to 0.08 for fat and from 0.08 to 0.18 for protein yield. Estimated heritability for 305-d milk, fat and protein yields were 0.25, 0.20 and 0.25, respectively. Correlations between individual test day records within traits were high for adjacent tests (nearly 1) and decreased as the interval between tests increased. Correlations between yields of milk, fat and protein on a given test day are also high and greater during late lactation than during early or mid-lactation. Genetic correlations between 305-d yield traits ranged from 0.75 to 0.92. The largest genetic correlation, as well as permanent environmental correlation, was observed between milk and protein yield.

Association of season and herd size with somatic cell count for cows in Irish, English, and Welsh dairy herds

The aims of this study were to describe associations of time of year, and herd size with cow somatic cell count (SCC) for Irish, English, and Welsh dairy herds. Random samples of 497 and 493 Irish herds, and two samples of 200 English and Welsh (UK) herds were selected. Random effects models for the natural logarithm of individual cow test day SCC were developed using data from herds in one sub-dataset from each country. Data from the second sub-datasets were used for cross validation.Baseline model results showed that geometric mean cow SCC (GSCC) in Irish herds was highest from February to August, and ranged from 111,000cells/mL in May to 61,000cells/mL in October. For cows in UK herds, GSCC ranged from 84,000cells/mL in February and June, to 66,000cells/mL in October. The results highlight the importance of monitoring cow SCC during spring and summer despite low bulk milk SCC at this time for Irish herds. GSCC was lowest in Irish herds of up to 130 cows (63,000cells/mL), and increased for larger herds, reaching 68,000cells/mL in herds of up to 300 cows. GSCC in UK herds was lowest for herds of 130–180 cows (60,000cells/mL) and increased to 63,000cells/mL in herds of 30 cows, and 68,000cells/mL in herds of 300 cows. Importantly, these results suggest expansion may be associated with increased cow SCC, highlighting the importance of appropriate management, to benefit from potential economies of scale, in terms of udder health.

Estimation of adjustment factors for standardizing age and season corrected 305 day milk yield and estimation of heritability and repeatability of stadardized milk yield of Red Chittagong cattle

Adjustment factors for lactation milk yield to mature age and season corrected 305–day were calculated and heritability and repeatability of 305-day and test day (TD) milk yields were estimated from the nucleus herd of Red Chittagong Cattle (RCC) reared during 2005 to 2009. Lactation records (116) of 50 lactating cows were used for estimation. The factors for standardizing incomplete lactations to projected 305-day were estimated by taking 4 calving age groups (<4, 4–5, 5–6, and 6+ years of age) and 3 seasons (mid Feb to mid June, summer; mid June to mid Oct, rainy and mid October to mid Feb, winter) with the ratio factors. The heritability estimates for TD and 305-day milk yield were found as 0.41±0.08 and 0.35±0.08, respectively. Heritability estimates of individual TDs ranged from 0.24±0.33 to 0.64±0.06. Heritability of individual TD milk yield was highest in the first three months (TD2 to TD6) whereas, lowest in first few days and later after 3 months. The repeatability of 305-day and TDs milk yield were estimated as 0.28±0.12 and 0.49±0.04, respectively using intra-class correlation.

Genomic associations with somatic cell score in first-lactation Holstein cows

This genome-wide association study aimed to identify loci associated with lactation-average somatic cell score (LASCS) and the standard deviation of test-day somatic cell score (SCS-SD). It is one of the first studies to combine detailed phenotypic and genotypic cow data from research dairy herds located in different countries. The combined data set contained up to 52 individual test-days per lactation and thereby aimed to capture temporary increases in somatic cell score associated with infection. Phenotypic data for analysis consisted of 46,882 test-day records on 1,484 cows, and genotypic data consisted of 37,590 single nucleotide polymorphisms (SNP). Using an animal model, the associations between each individual SNP and the phenotypic data were estimated. To account for the risk of false positives, a false discovery rate threshold of 0.20 was set. The analyses showed that LASCS was significantly associated with a SNP on Bos taurus autosome (BTA) 4 and a SNP on BTA18. Likewise, SCS-SD was associated with this SNP on BTA18. In addition, SCS-SD significantly associated with a SNP on BTA6. Relatively few associations were found, suggesting that LASCS and SCS-SD are controlled by multiple loci distributed across the genome, each with a relatively small effect. Increased knowledge on genetic regulation of LASCS and SCS-SD may aid in identification of genes that play a role in mastitis resistance. Such knowledge helps us understand the genetic mechanisms leading to mastitis and in discovery of targets for mastitis therapeutics.

Genetic and environmental dispersion parameter estimation by test interval method in dairy sheep

Genetic and environmental parameters for 38 983 test-day records of daily milk yield (DMY), fat (FC) and protein (PC) content, collected between 1994 and 2002, were estimated on 3,068 dairy ewes of the three Slovenian breeds. A multivariate restricted maximum likelihood method was used for estimation, where every test-day record was treated as a different trait. Fixed part of the multitrait animal model for DMY, FC, and PC included breed and lambing season as classes, while stage of lactation, parity, and litter size were covariates. Random part of the model contained additive genetic effect and the effects of flock test month and permanent environment over lactations. Heritability estimates for individual test-days were between 0.10 and 0.23 for DMY, 0.09 and 0.18 for FC, and 0.19 and 0.28 for PC. The flock test month effect explained most of the phenotypic variance: 0.18 to 0.41 for DMY, 0.26 to 0.45 for FC, and 0.24 to 0.44 for PC. A lower variance ratio was explained by the permanent environment effect over lactations: 0.09 to 0.15 for DMY, 0.02 to 0.11 for FC, and 0.02 to 0.09 for PC. Additive genetic correlations between individual test-days were high in all three milk traits for adjacent months of lactation. They decreased when the interval between months of lactation increased. The structure of additive genetic correlations showed that the observed milk traits in the different stages of lactation were genetically not the same trait, since the correlations between distant months of lactation were lower than one.

La propuesta reducción del límite máximo permitido de células somáticas en leche cruda y su posible efecto sobre la industria lechera en Puerto Rico.

Se analizaron datos de 302,995 pesajes individuales de leche de vacas de hatos acogidos al Programa de Mejoramiento de Hatos Lecheros de Puerto Rico (PRDHIP, por sus siglas en inglés) y 8,833 resultados de análisis de recuentos de células somáticas (RCS) de muestras de tanque de todas las operaciones lecheras de Puerto Rico durante los años 2004 y 2005 para determinar el efecto potencial que tendría la aplicación de la propuesta del Concilio Nacional de Mastitis (NMC) de reducir el límite máximo actual de 750,000 células por mililitro de leche cruda. Los promedios de producción diaria de leche por vaca y de los recuentos de células somáticas expresados en la escala lineal (RLCS) en este conjunto de datos fueron 17.2 kg y 3.9, respectivamente. Basado en los registros del DHIP, se estimó en un 20% la proporción de pesajes de vacas individuales, equivalentes a 920,290 kg de leche cruda, que estaría fuera de norma si el límite máximo permitido se redujera a 600,000 células somáticas por mililitro. Los meses de mayor producción promedio de leche fueron febrero, marzo y mayo (18.4, 18.2 y 18.2 kg/día, respectivamente), mientras que las producciones menores se registraron en los meses de agosto, septiembre y octubre (16.3,15.6 y 15.8 kg/día, respectivamente). Los meses con los menores promedios de RLCS correspondieron a febrero y abril (ambos en 3.5) y los mayores a agosto, septiembre y octubre (4.2, 4.2 y 4.3, respectivamente). El promedio de los RCS de muestras de tanque de los hatos acogidos o no al DHIA difirieron poco (461,656 y 473,096, respectivamente; P mayor que 0.05).

Comparison of Fitting Performance of Random Regression Models to Test Day Milk Yields in Holstein Friesians

Recently, test day models have been suggested for genetic evaluation of test day milk yields, instead of using 305 day milk yields . Since the correct description of factors for each individual test day milk yield is possible, a higher genetic progress should be expected . Accuracy of genetic evaluations depends on the amounts of information used and methods. For analysis of test day milk yields, several types of models are applied such as Kafkas Univ Vet Fak Derg 15 (2): 261-266, 2009 DOI:10.9775/kvfd.2008.138-A RESEARCH ARTICLE

Heterogeneity of variance components for production traits in large‐scale dairy farms

The aim of this study was to estimate genetic parameters applying fixed regression and random regression test day models for protein yield using subsets stratified by herd size, average production level of herds in test day protein yield, and average age at first calving within herds. The data consisted of 64,394 Holstein cows located in one region in Eastern Germany including 690,553 first lactation test day production records. Estimates of variance components revealed heterogeneity of genetic variances across subsets and the highest additive genetic variances and heritabilities were found in larger herds with high production level and low age at first calving. Special cooperator herds for dairy cattle progeny testing programs will be a common practice in the near future. Suitable selection criteria for cooperator herds should consider genetic parameters, e.g. genetic variances and heritabilities within herds or subsets, to identify genetically superior sires as accurately as possible. As shown in the present study, the two‐step cluster analysis is an appropriate method to combine all desirable effects of herd parameters for a final selection of cooperator herds. One cluster included 44 large‐scale dairy farms with an average of 638 cows per farm and was also characterised by the highest protein yield, the lowest age at first calving, the highest heritability, and the highest additive genetic variance for test day protein yield within herds. A cluster analysis can be implemented in the work routine of dairy cattle breeding programs and delivers results in acceptable time. Rank correlations of estimated breeding values of bulls in different subsets as well as in different clusters were greater than 0.90, and therefore disprove any concerns for possible genotype by environment interaction between the test and the production environment. The permanent environment variance was slightly increased in strata indicating a better environment, whereas the residual variance component was similar for all subsets. There were no remarkable differences in genetic correlations between individual test days and test days 25 and 150, when analysing different subsets.

Gastrointestinal responses following acute and medium term intake of retrograded resistant maltodextrins, classified as type 3 resistant starch

Study part 1 was executed as a randomized double-blind placebo-controlled crossover study and study part 2 as a longitudinal study. Forty-one healthy adult volunteers aged 18-24 years were recruited from the student population of the University of Salford. All subjects enrolled and completed study part 1 and 39 subjects enrolled and completed study part 2. In study part 1, individuals consumed, in random order 0, 20, 40, 60, 80, 100 or 120 g of a RRM containing starch product incorporated in pre-prepared foods on individual test days. Assuming a minimum content of 50% RRM in the starch product this delivered respectively 0, 10, 20, 30, 40, 50 or 60 g of RRM. All foods were prepared and coded by personnel not involved in carrying out the tests. Test days were separated by 7 day washout periods. In study part 2, consumption of RRM was increased from 3.6 g at day 1 in incremental doses up to each subject's MNED as determined in study 1, to be achieved at day 14. Subsequently, RRM intake was from day 15-21 in a way that the final intake at day 21 was at least 10 g above the individual MNED. In both parts of the study, subjects reported the prevalence and magnitude of GI symptoms. No significant change was observed in either defecation frequency and faecal consistency or the number of subjects experiencing any GI symptoms, following consumption of foods containing 0-60 g RRM. The individual MNED at which an increase in symptoms did not occur was determined as 60 g RRM for 71% of the subjects who participated in study part 1. Regression analysis showed that consumption of gradually increasing doses of RRM in food products over 21 days was associated with a significant increase in the mean symptom score for flatulence (P=1.5 x 10(-4)), total bowel movement frequency (P=0.023) and bowel movement frequency to pass watery faeces (P=0.0157). Increasing the ingested dose of RRM by 10 g above the predetermined MNED, however, did not provoke significant increases in GI symptoms. In both studies, the majority of symptom responses were classified by the subjects as 'little more than usual'. Consumption of up to 60 g RRM is tolerated well by most individuals with no evidence of any significant dose-dependent increase in the magnitude of symptoms or the occurrence of multiple GI symptoms. However, a mild laxative effect when consuming >60 g RRM is suggested. Although there was no change in GI responses following consumption of increasing doses of RRM over 21 days, generally a dose of 10 g RRM above the MNED level was tolerated well during medium term intake.

Gastrointestinal tolerance of erythritol and xylitol ingested in a liquid

To determine and compare the gastrointestinal (GI) responses of young adults following consumption of 45 g sucrose, 20, 35 and 50 g xylitol or erythritol given as a single oral, bolus dose in a liquid. The study was a randomized, double-blind, placebo-controlled study. Seventy healthy adult volunteers aged 18-24 years were recruited from the student population of the University of Salford. Sixty-four subjects completed the study. Subjects consumed at home without supervision and in random order, either 45 g sucrose or 20, 35 and 50 g erythritol or xylitol in water on individual test days, while maintaining their normal diet. Test days were separated by 7-day washout periods. Subjects reported the prevalence and magnitude of flatulence, borborygmi, bloating, colic, bowel movements and the passage of faeces of an abnormally watery consistency. Compared with 45 g sucrose, consumption of a single oral, bolus dose of 50 g xylitol in water significantly increased the number of subjects reporting nausea (P<0.01), bloating (P<0.05), borborygmi (P<0.005), colic (P<0.05), watery faeces (P<0.05) and total bowel movement frequency (P<0.01). Also 35 g of xylitol increased significantly bowel movement frequency to pass watery faeces (P<0.05). In contrast, 50 g erythritol only significantly increased the number of subjects reporting nausea (P<0.01) and borborygmi (P<0.05). Lower doses of 20 and 35 g erythritol did not provoke a significant increase in GI symptoms. At all levels of intake, xylitol produced significantly more watery faeces than erythritol: resp. 50 g xylitol vs 35 g erythritol (P<0.001), 50 g xylitol vs 20 g erythritol (P<0.001) and 35 g xylitol vs 20 g erythritol (P<0.05). When consumed in water, 35 and 50 g xylitol was associated with significant intestinal symptom scores and watery faeces, compared to the sucrose control, whereas at all levels studied erythritol scored significantly less symptoms. Consumption of 20 and 35 g erythritol by healthy volunteers, in a liquid, is tolerated well, without any symptoms. At the highest level of erythritol intake (50 g), only a significant increase in borborygmi and nausea was observed, whereas xylitol intake at this level induced a significant increase in watery faeces.

Avaliação genética de caprinos da raça Alpina utilizando-se a produção de leite no dia do controle

Com os objetivos de estimar os parâmetros genéticos e predizer os valores genéticos para produção de leite no dia do controle (PLDC) e para produção acumulada (PAC), utilizaram-se dados de 356 cabras da raça Alpina, com 825 lactações e 26.389 controles semanais efetuados entre os anos de 1997 e 2004. A PLDC foi analisada considerando-se o efeito fixo de grupo contemporâneo (ano-mês de controle), a idade da cabra ao parto, como covariável, e os efeitos aleatórios genético aditivo e de ambiente permanente. Para PAC, o modelo incluiu os mesmos efeitos aleatórios, o efeito fixo de grupo contemporâneo (ano-mês de parto) e as covariáveis idade da cabra ao parto e duração da lactação. Em geral, as herdabilidades estimadas foram de maiores magnitudes na primeira lactação, nos controles intermediários, indicando possibilidade de resposta à seleção. As correlações de ordem entre os valores genéticos para a produção até 305 dias de lactação e as PLDC intermediárias foram maiores que as do início e do final da lactação. Apesar de a correlação de ordem ter sido alta, houve alterações na classificação dos reprodutores para produção até 305 dias de lactação quando a seleção foi praticada com base na PLDC aos 90 dias. A seleção pela PLDC e PAC no meio da lactação pode ser indicada como critério de seleção, em substituição à produção até 305 dias.

Genetic Parameters of Milk Yield and Milk Fat Percentage Test Day Records of Iranian Holstein Cows

Genetic parameters for first lactation milk production based on test day (TD) records of 56319 Iranian Holstein cows from 655 herds that first calved between 1991 and 2001 were estimated with restricted maximum likelihood method under an Animal model. Traits analyzed were milk yield and milk fat percentage. Heritability for TD records were highest in second half of the lactation, ranging from 0.11 to 0.19 for milk yield and 0.038 to 0.094 for milk fat percentage respectively. Estimates for lactation records for these traits were 0.24 and 0.26 respectively. Genetic correlations between individual TD records were high for consecutive TD records (>0.9) and decreased as the interval between tests increased. Estimates of genetic correlations of TD yield with corresponding lactation yield were highest (0.78 to 0.86) for mid-lactation (TD3 to TD8). Phenotypic correlations were lower than corresponding genetic correlations, but both followed the same pattern. For milk fat percentage no clear pattern was found. Results of this study suggested that TD yields especially in mid-lactation may be used for genetic evaluation instead of 305-day yield. (Asian-Aust. J. Anim. Sci. 2005. Vol 18, No. 9 : 1231-1236)

Mobility of a lightweight tracked robot over deep snow

We designed and built a 24-kg tracked robot, named SnoBot, based on the performance of a 1400-kg manned vehicle scaled using Bekker mobility theory. We then documented the mobility of the robot for 10 cases of deep snow and four cases of shallow snow. The scaled predictions agreed well with average sinkage, resistance and traction measured in deep snow and thus gave useful design guidance. Nevertheless, large differences occurred between measured and predicted snow-compaction resistance on individual test days. The behavior of actual snow packs is difficult to capture using simple Bekker theory. Most deep-snow packs showed a linear relationship between pressure and sinkage for small indentation, followed by a steep rise in pressure as indentation compacted the snow against the ground. Also, small strength variations due to icy layers were important. SnoBot traveled easily over ice crusts that were much too weak to support foot travel. The results indicate that a lightweight tracked robot can display excellent deep-snow mobility when ground clearance, motor torque and energy storage allow for proportionally high sinkage and motion resistance compared with larger vehicles.

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

Test-day milk yield records of 11,023 first-parity Holstein cows were used to estimate genetic parameters for milk yield during different lactation periods. (Co)variance components were estimated using two random regression models, RRM1 and RRM2, and the restricted maximum likelihood method, compared by the likelihood ratio test. Additive genetic variances determined by RRM1 and additive genetic and permanent environmental variances estimated by RRM2 were described, using the Wilmink function. Residual variance was constant throughout lactation for the two models. The heritability estimates obtained by RRM1 (0.34 to 0.56) were higher than those obtained by RRM2 (0.15 to 0.31). Due to the high heritability estimates for milk yield throughout lactation and the negative genetic correlation between test-day yields during different lactation periods, the RRM1 model did not fit the data. Overall, genetic correlations between individual test days tended to decrease at the extremes of the lactation trajectory, showing values close to unity for adjacent test days. The inclusion of random regression coefficients to describe permanent environmental effects led to a more precise estimation of genetic and non-genetic effects that influence milk yield.

Estimation of genetic and environmental parameters of milk production traits in Slovak purebred sheep using test-day model

Covariance matrices and genetic parameters for milk production traits in sheep were estimated for the Improved Valachian and Tsigai breeds. These multipurpose breeds are of local importance, and are bred for milk, meat and wool. The traits under study were daily milk yield and fat and protein content. Genetic analyses were based on test-day records gathered over the period from 1995 to 2001. Each breed was analyzed separately. Only purebred animals with at least four test days per lactation were considered. The data set for the Improved Valachian consisted of 117,959 test-day records of 28,753 lactations belonging to 18,867 ewes. The corresponding pedigree comprised information on 32,804 animals. For the Tsigai breed, the data set consisted of 52,191 test-day records of 12,382 lactations belonging to 8,132 ewes and the pedigree comprised 14,576 animals. The three-trait animal model was used for analyses. To account for different lactation stage, a fixed regression on individual test days was employed. In addition to the function describing, effects of days in milk, effects of lactation, litter size, number of milkings per day, age at lambing, and flock-test day as well as additive genetic and permanent environmental effect of the animal were included in the model. Of these, flock-test day, additive genetic and permanent environmental effects were treated as random. Restricted maximum likelihood (REML) algorithm was used to estimate genetic parameters and covariance matrices. Heritabilities were 0.10 and 0.19 for daily milk yield, 0.06 and 0.12 for fat content, 0.07 and 0.17 for protein content for the Improved Valachian and Tsigai breeds, respectively. Genetic correlations between milk yield and fat content for the two breeds were −0.29 and −0.23 and those between milk yield and protein content were −0.30 and −0.27. Genetic correlations between fat and protein content were 0.58 and 0.57. Higher values (either positive or negative) were found for the breed with the larger number of records. Variance ratios and correlations were also estimated for nongenetic effects for both breeds. Variance ratios for the flock-test-day effects were rather high, ranging from 0.34 to 0.48. Higher values for these effects were found in the Improved Valachian sheep, reflecting more variability in management conditions in this breed. The genetic parameters estimated in this study should be used in routine genetic evaluation of milk production traits of local sheep breeds to replace present selection criteria based on phenotype values of dam milk yield.