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

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


INTRODUCTION
The first lactation milk and fat yield reflects the real economic worth of the cow and is considered as a selection criterion for the improvement of genetic potential of dairy animals by using different progeny testing programme in which superior germplasm can be identified on the basis of performance of their progeny under farm and field condition.In the recent past the main thrust in breeding in India has been emphasized on crossbreeding to improve genetic potentiality for milk and milk products by introducing exotic inheritance in purebred locals.By introducing the exotic inheritance at different levels in purebred locals the milk and their products have been increased many folds however, the estimates of heritability of milk production traits in crossbred population, using mixed models with breed group effects (Meyer, 1987;Wilmink et al., 1986) were higher than published value from purebreds (Maijala and Hanna, 1974;Hill et al., 1983).Among other factors, non-additive might have inflated the heritability estimates.Vander Welf and De Boar (1989a) proposed a mixed model for analysis of such data in which care has been taken for fixed effects of heterosis and recombination for the estimates of variance components from crossbred population.They also used parent group model and found that estimates of additive variance were unbiased using this model, however, the estimates of residual variance was slightly higher.In the present study it was not possible to include the effect of heterosis and recombination in the model due to lack of proper data structure/records, hence parent group model was used to utilize the available records.Keeping this in view the above facts and to plan a sound-breeding programme for further propagation of these crossbred animals having different levels of exotic inheritance, it is essential to know the extent of genetic variability and co-variability among different milk and fat production traits.

MATERIALS AND METHODS
The records utilized for this investigation pertained to 335 crossbred cows comprising of 1/2 Friesian (F)+1/2 Hariana (H), 1/2 F+1/4 Jersey (J)+1/4 H, 1/2 F+1/4 Brown Swiss (BS)+1/4 H, 1/2 F+1/4 Red Dane (R)+1/4 H, FR (I) and FRH (I) genetic groups extending over a period of 21 years  maintained at Animal Farm of CCS HAU, Hisar.FR (I) and FRH (I) are interse crosses.The animals that completed their first 300 days lactation were included in the study.The records like those resulting from abortions, premature birth, stillbirth and incomplete lactations due to death and culling were excluded from the study.The data were grouped according to genetic groups of the grand parents of the animal, season of calving and period of calving to quantify the effects of these factors.The genetic group was divided into two sire groups (SG l ) and (SG 2 ) and four dam groups (DG 1 , DG 2 , DG 3 and DG 4 ).Total duration of 21 years was divided into four periods i.e.P 1 (1970-1976), P 2 (1977-1981), P 3 (1982)(1983)(1984)(1985)(1986) and P 4 (1987)(1988)(1989)(1990).On the basis of climatic conditions, each year was further sub-divided into four seasons viz.S l (Winter), S 2 (Summer), S 3 (Rainy) and S 4 (Autumn).The seasons were made on the basis of fluctuations of atmospheric temperature, relative humidity, rainfall and sunshine hours over a period of 21 years .The four periods were classified on the basis of preliminary year wise analysis of records and the years that did not differ significantly from each other were included into different periods to overcome the differences in managemental practices.The average numbers of female progenies per sire were 8.8.The first lactation milk yield (FLMY) and fat yield (FLFY) was calculated by summing up the milk and fat yield of first 300 days of lactation (excluding colostrums during first three days).Total milk and fat production in the first four and above lactations were considered as lifetime milk yield (LTMY) and fat production (LTFP) of the animal.The maximum milk (PMY) and fat yield (PFY) in a day during lactation were considered as peak milk and fat yield of that lactation.The peak milk (PMY 1 , PMY 2 and PMY 3 ) and fat yield (PFY l , PFY 2 and PFY 3 ) were taken for first three lactations of the animal.
To study the effect of certain important factors such as sire, sire group, dam group, season and period of calving and to overcome the problems of non-orthogonality for these effects due to disproportionate frequencies and to estimate the genetic and phenotypic parameters the mixed model technique as explained by Harvey (1987) was applied.The age at first calving was used as a covariate and statistical model used for each trait was: Where, Y ijklmn =observation on n th animal calving in m th period and l th season belonging to k th dam and j th sire group and of i th sire µ=population mean S i =random effect of i th sire (i=1, 2------38) SG j =effect of j th sire group (j = 1, 2) DG k =effect of k th dam group (k= 1, 2, 3, 4) S l =effect of l th season of calving (l = 1, 2, 3, 4) P m =effect of m th period of calving (m = I, 2, 3, 4) b 1 and b 2 =linear and quadratic regression coefficient of Y ijklmn on age at first calving A ijklmn =age at first calving corresponding to Y ijklmn Ā=arithmetic mean of age at first calving e ijklmn =random error associated with Y ijklmn observation assumed to be NID (0, σ e 2 ) The differences of means were tested by Duncan's multiple range tests.The data were adjusted for significant effects of sire, sire group, dam group, seasons, periods and age at first calving.The heritability estimates for different traits were obtained by the paternal half-sib correlation method on adjusted data.The standard errors of heritability estimates were obtained by using the formula given by Swiger et al. (1964).Genetic and phenotypic correlations among different traits were calculated from sire components of variance-covariance analysis.The standard errors of genetic and phenotypic correlations were estimated by Robertson (1959) and Snedecor and Cochran (1968), respectively.

Averages
The adjusted means and their standard errors for different traits have been presented in Table 1.The averages for first lactation milk yield was 2,486.24±80.26kg and peak yield of first three lactation were 11.35±0.72kg, 13.97±0.60kg and 16.02±0.42kg, respectively.The lifetime milk production was observed as 11,305.16±1,004.52kg in crossbred cattle.The average first lactation milk yield of Friesian×Hariana reported by Stepanov and Zhamerkov (1983) as 1,811 kg whereas Dalal et al. (1991) reported as 3,009.33±31.28kg.Moreover, Jadhav and Bhatnagar (1984) observed the highest first lactation milk yield as 3,505.20±59.86kg in Friesian×Tharparkar crossbreds.The average peak yield of first lactation reported by Mudgal et al. (1986) was 18.43±0.47kg in Sahiwal×Friesian crossbreds.Koul et al. (1977) estimated second lactation peak milk yield as 11.05 ±0.46, 10.21±0.47 and 8.93±0.28kg in Friesian×Hariana, Brown Swiss×Hariana and Jersey×Hariana crossbreds.Singh (1981) observed as 14.73±0.41and 17.08±0.40kg peak milk yield in second and third lactation of Brown Swiss×Hariana and Friesian×Hariana crossbred animals.The attainment of higher FLMY and peak yields reflects the manifestation of maximum milk secretion in lactation and there is a high probability that it will influence future shape of the lactation.The average first lactation fat yield was observed as 102.06±0.01kg and peak fat yield of first three lactation were 0.458±0.01,0.490±0.01and 0.500±0.02kg, respectively.The lifetime fat production was estimated as 502.31±45.90kg.Saxena (1982) observed first lactation fat yield as 81.26, 84.26 and 87.00 kg in Brown Swiss×Hariana, Friesian×Hariana and Jersey×Hariana crossbreds.Moreover, Jadhav and Bhatnagar (1984) reported as 152.50±577, 141.16±2.06,141.45±4.14 and 135.99±2.95kg in Holstein ×Sahiwal, Holstein×Tharparkar, Brown Swiss×Tharparkar and Brown Swiss×Sahiwal crossbred heifers.Godara et al. (1990) reported that lactation fat yield was higher in Jersey ×Hariana followed by Friesian×Hariana crossbreds and the lowest yield was observed in Brown Swiss×Hariana crossbreds.The variability in the performance of different herds of crossbred cattle for fat yield suggested that there is scope for improvement in this trait.
The heritability estimates of first lactation fat yield was reported as 0.16±0.10 by Norman et al. (1988) in Ayreshire cattle and 0.76±0.12by Saxena et al. (1982) in European× Zebu crossbred cattle.The medium to higher estimates of heritability for fat production traits were reported by Vander Welf and De Boer (1988), Godara et al. (1990) Harris and freeman (1991), Welper and Freeman (1991) and Pander et al. (1992) in different crossbreds and exotic breeds of cattle.
From the perusal of the estimates obtained for milk and fat production traits, it could be inferred that LTMP and LTFP have heritability of more than 20 percent.The estimates of heritability of FLFY, PMY 3 and PFY 3 were ranged from 5-11 percent whereas these estimates of heritability of FLMY, PMY 1 , PMY 2 , PFY 1 and PFY 2 less than 5 percent.
The results obtained in the present study are suggestive of the fact that the improvement in these traits may be brought out by exploiting the genetic variability present in some traits with little emphasis on pedigree and progeny testing programme.

Estimation of phenotypic and genetic correlations
The phenotypic and genetic correlations along with their standard errors are presented in Table 2.The phenotypic correlations of FLMY with FLFY and LTFP were significant (p<0.05) and moderate to high (0.33 to 0.99).The correlations with PFY 1 , PFY 2 and PFY 3 were either negative or with low magnitude.The phenotypic correlations of PMY 1 to other fat production traits i.e.FLFY, PFY 1 , PFY 2 , PFY 3 and LTFP ranged from 0.09 to 0.67 with 5 per cent standard error.Similar phenotypic correlations were also obtained between PMY 2 and PMY 3 with other fat production traits except PMY 2 and PFY 1 ; PMY 3 with PFY 1 and PFY 2 , having low and negative phenotypic correlation.The phenotypic correlation between LTMP with FLFY, PFY 2 , PFY 3 and LTFP ranged from 0.03 to 0.98 and the correlation with PFY 1 was observed higher but in negative direction.The genetic correlations of FLMY with FLFY, Similarly high genetic correlations were obtained between LTMP with FLFY (0.92±0.88) and LTFP (0.98±0.02).The estimates of inter-relationship among other traits of this study had very high standard error at genetic level and in many cases they have crossed even the statistical limit for the defined range of such estimates and no conclusion can be drawn from such parameters.High genetic and phenotypic correlations for milk and fat yields were also reported by Batra (1969), Saxena (1982), Godara (1984) and Norman et al. (1988) in different crossbred cattle.The positive and high genetic and phenotypic correlations between milk yield and fat yield were also reported by Vander Welf and De Boer (1988), Godara et al. (1990), Harris and Freeman (1991) and Pander et al. (1992) in different breeds of exotic and crossbred cattle.
The overall picture of the results of the present investigation leads to the findings that FLMY, peak yields and LTMP had significant positive phenotypic correlation with FLFY and LTFP and the correlation at the genetic level were also higher and positive for these traits.This kind of relationship is an indicator of improving lactation milk and fat yield through the improvement in one of its component trait like peak yield of first lactation.The standard errors of phenotypic correlation of this trait with others are not high and hence precise.Finally, peak week milk yield of first lactation (PMY 1 ) was the earliest available trait having desirable and significant correlation at phenotypic and positive at genetic level with FLFY, PFY 1 , PFY 2 , PFY 3 and LTFP.This will help in early evaluation of sires and dams and will increase genetic advancement per unit of time.

Table 1 .
Averages and heritability estimates of first lactation milk and fat yield Parameters No. obs.

Table 2 .
Genetic and phenotypic correlations among various traits