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<strong>AGRONOMIJAS</strong> VĒSTIS (Latvian Journal of Agronomy), No.10, LLU, 2008The main advantages of using TD models for genetic evaluation are: 1) individual test dateeffects can be included in the model, which affects the test day yield substantially; 2) the number ofrecords per cow and the interval between records can be accounted for; 3) the number of cows withrecords at the same test date exceeds the number of cows that enter a herd–year–season class in afull lactation model, which increases the accuracy of the adjustment for fixed effects; 4) TD modelscan account for individual differences in the shape of lactation curves of cows, which includes thepersistency of the lactation (Pool et al., 1999; Reents et al., 1996).The main objective of this study was to use a test day model to estimate the breeding valuesof the milk production traits of dairy cattle.Materials and MethodsTest day data for the study were obtained from the state agency ‘Agricultural Data centre’which organizes milk recording in Latvia and is responsible for the genetic evaluation.Latvian Brown (LB) is the main cattle breed in Latvia with an average milk yield of 4926kg, fat content of 4.45 % and protein content of 3.33 % in 305 days. A total of 362043 first 3lactation TD records were used from 23 949 LB cows (on average 15 TD records of 3 lactations percow). Cows TD data from 1995 – 2004 were used in the study. Included daughters of 687 sires (onaverage 35 daughters per sire) and cows of 1849 herds (on average 13 cows per herd) and 400districts (on average 60 cows per district). The main breeds of sires were Latvian Brown (LB),Danish Red (DS), Angler (AN), Swedish Red and White (ZS) and Holstein Red and White (HS).The average milk yield of cows in the test day was 14.9 kg, fat yield and protein yield wasrespectively 0.67 kg and 0.50 kg, fat and protein content was respectively 4.58 % and 3.37 %. Thelowest values are shown in 1 st lactation, but the highest in 3 rd lactation test day records for all traits.The average productivity results of cows of three lactations in different test days showedthat the highest milk yield (19.1 kg) is shown in the 1 st test day which decreases with the followingtest days to be in the lowest value (9.9 kg) in the 11 th test day (Table 1). The opposite situationwere present for fat and protein content. The lowest values were present in 2 nd TD (respectively4.22% and 3.01% for fat and protein content) which increases with the following test days to be inthe highest value in the last 11 th TD, respectively 5.10 % and 3.83 % for fat and protein content.Table 1. Phenotypic means and standard deviations for productivity traits of cows in the studyMilk yield, kg Fat content, % Protein content, %Testday x s x s x s1 19.1 4.97 4.55 0.953 3.23 0.4022 18.6 5.08 4.22 0.828 3.01 0.3203 17.3 4.88 4.26 0.795 3.11 0.3274 16.0 4.62 4.36 0.795 3.23 0.3285 14.9 4.40 4.49 0.808 3.33 0.3396 13.9 4.23 4.63 0.826 3.43 0.3487 12.8 4.09 4.75 0.844 3.52 0.3698 11.8 3.98 4.86 0.879 3.61 0.3999 10.8 3.90 4.97 0.901 3.70 0.43310 10.2 3.81 5.06 0.924 3.78 0.46611 9.9 3.76 5.10 0.937 3.83 0.481The following test day model was used for the breeding value estimation:y ijkl = µ + HT i or DT i + a j + pe j + LAYSI k + b k1 (D/c) + b k2 (D/c) 2 + b k3 ln(c/D) + b k4 [ln(c/D)] 2 + e ijkl , (1)wherey ijkl – n th test day observation (milk yield, fat yield, protein yield) for cow (j);µ – mean;HT i or DT i – fixed herd – test day (i) or fixed district – test day (i) effect;a j – random additive genetic effect (breeding value) of an animal (j);pe j – random permanent environment effect to account for repeated measures within a cow (j);LAYSI k – fixed (calving age*calving season*calving interval*calving year*lactation) effect;294
<strong>AGRONOMIJAS</strong> VĒSTIS (Latvian Journal of Agronomy), No.10, LLU, 2008b k1 and b k2 – regression coefficients on the linear and quadratic effect of the ratio D/c, in which D is the dayin lactation and c is a constant, in this case c = 380;b k3 and b k4 – regression coefficients on the linear and quadratic effect of ln(c/D);e ijkl – random residual effect (random error).There were built up the following a model groups with 2 fixed effects: I group) fixed HT iand LAYSI k effect with 108 defined lactation curves; II group) fixed DT i and LAYSI k effect with108 defined lactation curves; III group) fixed HT i and LAYSI k effect with 450 defined lactationcurves; IV group) fixed DT i and LAYSI k effect with 450 defined lactation curves.The results of TDM were compared with appropriate results calculated with LM used bythe state agency ‘Agricultural Data Centre’ in a routine genetic evaluation to analyze theimprovement of reliability and to show the changes in the rankings of bulls using different models.The data were processed using SAS 8.2. software [SAS, 1998]. PEST [Groeneveld, 1990]software was used to obtain the results of the genetic evaluation.Results and DiscussionEBV of productivity traits of bulls showed results with great variation (Table 2). EBV ofmilk yield ranged from -1013.9 to 1965.7 kg with the average values from 6.2 to 63.9 kg indifferent groups. The lowest and highest EBV was obtained by the model with the fixed DTDeffect. Using the model with the fixed the HTD effect EBV obtained ranged from -874.3 to 1074.4kg.Table 2. Estimated breeding values (EBV) of productivity traits of bulls, kgModel informationTrait ParameterI group II group III group IV groupMilk yield,kgFat yield,kgProtein yield,kgx ± s x6.2 ± 264.27 63.9 ± 424.51 7.5 ± 267.37 61.9 ± 427.01Min - 874.3 - 981.1 - 863.8 - 1013.9Max 1074.4 1965.7 1062.0 1955.9x ± s x0.18 ± 12.209 2.14 ± 18.237 0.25 ± 12.218 2.37 ± 18.927Min - 33.49 - 38.84 - 33.24 - 40.75Max 71.12 93.59 69.28 90.55x ± s x0.13 ± 8.155 1.86 ± 13.187 0.17 ± 8.995 1.99 ± 13.443Min - 33.39 - 33.33 - 37.33 - 33.70Max 35.49 58.41 37.33 59.86EBV of fat yield obtained in range from - 40.75 to 93.59 kg with the average EBV of eachgroup from 0.18 to 2.37 kg (Table 2). The highest average EBV obtained in II and IV group wherethe fixed DTD effect was included in the model, respectively 2.14 and 2.37 kg. Also results ofthese groups showed the larger variation of EBV, respectively 132.43 and 131.30 kg. EBV showedlower variation (104.61 and 102.52 kg) and the average EBV (0.18 kg and 0.25 kg) respectively inI and III group using the model with the fixed HTD effect.The results of protein yield showed that the average EBV ranged from 0.13 kg to 1.99 kg.Using the model with the fixed DTD effect results showed the highest variation of EBV(respectively 91.74 and 93.56 kg) and the average EBV (respectively 1.86 and 1.99 kg). The resultsshowed lower variation of EBV (respectively 68.88 and 74.66 kg) and the average EBV(respectively 0.13 and 0.17 kg) using the model with the fixed HTD effect.There was not significant differences between EBV of milk and protein yield where thesame fixed HTD or DTD effect included in the model and between all groups of fat yield (p
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