ESTIMATION OF GENETIC TRENDS FOR ECONOMIC TRAITS IN CROSSBRED CATTLE BY USING REGRESSION METHODS

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1 Indian J. Anim. Res., 48 (6) : , 214 doi:1.5958/ AGRICULTURAL RESEARCH COMMUNICATION CENTRE / ESTIMATION OF GENETIC TRENDS FOR ECONOMIC TRAITS IN CROSSBRED CATTLE BY USING REGRESSION METHODS M. Chaudhari, R. Kumar*, A.S. Khanna, D.S. Dalal, S. Khanna and J. Goyal Department of Animal Genetices and Breeding Lala Lajpat Rai University of Veterinary and Animal Sciences, Hisar-125 4, India Received: Accepted: ABSTRACT The present study was conducted on 782 crossbred cows sired by 35 bulls, maintained over the period from to. The data were analyzed to estimate genetic, phenotypic and environmental changes in characters of economic importance which might have taken place during the several years of selective breeding practiced in the herd. The economic traits studied were first lactation milk yield, first lactation milk yield per day of lactation length and first lactation milk yield per day of calving interval in kg and age at first calving, first lactation length, first calving interval, first service period and first dry period in days. The average genetic changes in a given trait were estimated by four methods. Phenotypic trends were negligible for all the traits except age at first calving while, genetic trends were in desirable direction. Comparison of methods of estimation of genetic trend showed that adjustments for biases due to non-random allotment of dams with respect to their age and merit suggested by Powell and Freeman were useful for increasing the precision of the estimates. This method showed lower magnitude of standard error in comparison to other methods. Method- III showed lower standard error than method-iv. Hence, method III was the best method of estimation of genetic trends. Key words: Age at first calving, First lactation, Genetic trends, Milk yield INTRODUCTION Crossbreeding of indigenous cow (Bos indicus) with exotic (Bos taurus) bulls was started to enhance genetic potential of milk production in the subsequent crossbred programmes. The basic theme was to confluence the milk yield potential of exotic breeds and stress sustainability and disease resistance capabilities of indigenous breeds within the crossbred progenies, which would be desirable to maintain them under tropical climatic conditions. The appraisal of selection in breeding programme can be done by estimating change per year. The observed change in the performance of a population for an economic trait per year, i.e. phenotypic trend consist of two components viz. genetic trend resulting from change in mean breeding value due to selection and environmental trend due to cumulative change in various non-genetic factors. The estimates of the trends are essential because they permit comparison of realized trends with expected one in the experimental situation and assessment of progress * Corresponding author s sihagmahi@gmail.com in a particular trait. Magnitude of genetic trends must be known for comparison of sires. Several methods have been developed to measure the genetic trend in the animal population (Smith, 1962; Powell and Freeman, 1974). Hence, there is need to know which is more precise. MATERIALS AND METHODS The data were collected on crossbred cattle from the history-cum-pedigree sheets maintained over the period from to in the Department of Animal Genetics and Breeding, CCS HAU, Hisar (Now LLRUVAS, Hisar). The economic traits studied were first lactation milk yield (FLMY), first lactation length (FLL), first lactation milk yield per day of lactation length (FLMYLL), first lactation milk yield per day of calving interval (FLMYCI), age at first calving (AFC), first calving interval (FCI), first service period (FSP) and first dry period (FDP). A total of 786 lactation records of cows sired by 35 bulls, spread over 25 years were collected. Abnormal

2 528 INDIAN JOURNAL OF ANIMAL RESEARCH lactation records due to specific causes like abortion, culling and pre-mature birth were excluded. The entire duration of 25 years from to was divided into 8 periods each having three years duration except 8 th period (-88).Year to year variation within period were assumed to be nonsignificant. Each year was divided into four seasons on the basis of fluctuations in atmospheric temperature and relative humidity. Phenotypic trend for each trait was calculated as regression of performance of population on year (b P.T ). The methods of estimating genetic trends were obtained by procedure suggested by Smith (1962) i.e. method I and II and its modification by Powell and Freeman (1974) i.e. method III and IV: Method-I ĝ = 2 (b P.T. b P.T/S ) Method-II ĝ = -2 [b ( p p ] ).T/S Where, b P.T is regression of population performance on time b P.T/S is within sire regression of progeny performance on time [b ( p p ] is within sire regression of progeny ).T/S performance deviated from annual population mean on time. Environmental trends were obtained by subtracting genetic trend estimates from phenotypic trend for each trait. The four methods of estimation of genetic trends were compared on the basis of their standard errors. RESULTS AND DISCUSSION The year-wise means for production and reproduction traits are presented in the Fig 1-4. The estimates of coefficients of various regressions utilized for estimation of genetic trends for production and reproduction traits are presented in Table 1 and Table 2, respectively. The estimates of phenotypic trends are presented in Table 3 and estimates of genetic and environmental trends are presented in Table 4. First lactation milk yield: The rates of phenotypic changes in this trait obtained were kg per year, which was associated with high standard error that makes it negligible. Negative phenotypic changes in milk production were reported by Frietas et al. () and Peixoto et al. (26). All the methods exhibit positive genetic improvement in the trait. Present study indicated that considerable genetic improvement was achieved in milk yield Method-III ĝ = 2(b P.T b P.T/S + ½ D 1 ) / (1 + b DA.T/S b DA.T ) FLMY FLL 45 Method-IV ĝ = -2[b ( p p - ½ D ]/(1 + b b ) )T/S 2 DA.T/S DA.T D 1 is within sire trend in additive genetic merit of dams as compared to all available mates. b DA.T is regression of dam performance on time b DA.T/S is within sire regression of dam s performance on time. b ( p p ) is within sire regression of dam s ).T/S performance on time, records being deviated from corresponding annual population means. First lactation milk yield (kg) FIG 1: Year-wise means for FLMY and FLL First lactation length (days) TABLE 1: Different coefficients of regression for estimation of genetic trends for production traits Regression FLMY (kg) FLL (days) FLMYLL (kg) FLMYCI (kg) P.T (4.4).95 (.4) -.3 (.1) -.3 (.1) P.T./S (17.81) (1.71) -.24 (.4) -.26 (.4) ( p p).t -. (4.3) -. (.37).1 (.1).1(.1) ( p p).t/s (16.83) (1.62) -.18 (.3) -.2 (.4) DP.T (4.45).15 (.43).4 (.1).1 (.1) DP.T/S (18.91) 2.73 (1.88) -.14 (.4) -.11 (.4).7 (4.23) -.1 (.42).1 (.1).1 (.1) ( DP P ).T ( DP P ).T/S (18.4) 2.6 (1.81) -.6 (.3) -.3 (.4)

3 Vol. 48, No. 6, FLMY/FLL FLMY/FCI 8 AFC FCI Lactation milk yield per day of lactation length (kg) Lactation milk yield per day of calving interval (kg) Age at first calving (days) First calving interval (days) 4 FIG 3: Year-wise means for AFC and FCI FIG 2: Year-wise means for FLMYLL and FLMYCI TABLE 2: Different coefficients of regression for estimation of genetic trends for reproduction traits (in days) Regression AFC FCI FSP FDP P.T (1.24) 1.83 (.42) 1.51 (.38).88 (.36) P.T./S (4.1) 6.2 (1.85) 5.96 (1.65) 5.17 (1.55) ( p p).t -. (1.2). (.4).15 (.37).1 (.34) ( p p).t/s (3.92) 3.85 (1.78) 3.63 (1.59) 4.33 (1.5) DP.T (1.44) 1.47 (.43) 1.88 (.4) 1.76 (.39) DP.T/S 7.4 (5.81) 1.28 (1.94) 1.64 (1.77).8 (1.74) -.33 (1.4) -.13 (.42) -.21 (.39) -. (.38) ( DP P ).T ( DP P ).T/S (5.62) 1.78 (1.87) -.31 (1.7) (1.67) P = Performance; T = Time; S = Sire; D Dam and P = Population mean Figures in parentheses are standard error. TABLE 3: Phenotypic trends for different economic traits during a period of 25 years. This improvement was, however, nullified by negative environmental trends for the characters. So, genetic potential may be better exploited by improving managemental practices. The present estimates of genetic trends for the trait are higher than those reported by Rehman (28) and Bakir et al. () in Sahiwal and Holstein Friesian cattle, respectively. First lactation length: Phenotypic trend for FLL was days/year. However, Singh () and Rehman (28) reported negative phenotypic changes in indigenous cattle. Positive genetic trend by all the four methods show slight genetic improvement in the trait. This might have resulted due to correlated response to selection for milk yield due to high positive genetic correlation ( ) between the traits. First lactation milk yield per day of lactation length: Estimate of phenotypic trend for this trait was kg/year. This estimate indicated no significant change in this trait. Estimates in the present study showed considerable genetic Traits Phenotypic trends S.E. AFC (days) FLMY (kg) FLL (days).95.4 FCI (days) FLMYLL (kg) FLMYCI (kg) FSP (days) FDP (days) improvement in this trait. However, environmental trend in negative direction, nullified the genetic trend. Thereby no significant phenotypic progress in the trait was observed. Considerable genetic progress in the trait could be the result of a correlated response to selection for milk production due to high genetic correlation between milk production and yield per day of lactation length (.9+.7). First lactation milk yield per day of calving interval: Phenotypic trend estimated for the trait was kg/year. This revealed almost negligible trend in this trait over a period of 25 years. The positive genetic progress in the trait which might have resulted as correlated response to selection for

4 53 INDIAN JOURNAL OF ANIMAL RESEARCH First service period (days) FSP TABLE 4: Genetic and environmental trends for various economic traits by different methods Trait Trend Without adjustment With adjustment Method-I Method-II Method-III Method-IV AFC(days) ĝ 31.27± ± ±.21.86± ± ± ± ±5.6 FLMY(kg) ĝ ± ± ± ± ± ± ± ±7.7 FLL(days) ĝ 4.28± ± ±.8.17± ± ± ±.41.77±5.48 FCI(days) ĝ -8.74± ± ± ± ± ± ± ±5.48 FLMYLL(kg) ĝ.41±.4.37±.3.2±..1± ±.4 -.4±.4 -.5±.1 -.5±5.46 FLMYCI(kg) ĝ.45±.4.41±.4.2±..2± ± ±.4 -.5±.1 -.5±5.46 FSP(days) ĝ -8.88± ± ± ± ± ± ± ±5.47 FDP(days) ĝ -8.58± ± ± ±5.46 FIG 4: Year-wise means for FSP and FDP milk yield in view of high positive genetic association between the two traits (.9+.3). The negative environmental trend for the character has produced non-significant phenotypic change. However, Singal () and Singh () found negative genetic trend. Age at first calving: Estimate of phenotypic trend was days/year, which was significant. The decreasing trend in AFC as observed in present study is in desirable direction. Rehman (28) reported contrary phenotypic trend for AFC in Sahiwal cattle.estimates indicate favourable genetic FDP First dry period (days) trend and environmental trends being in the opposite direction. However, significant phenotypic change in desirable direction could be observed in this trait. Present results are contrary to Singal () and Singh () at genetic level. First calving interval: Estimate of phenotypic trend for the FCI was days/year. Similar results were obtained by Singh () in Hariana cattle. However, negative phenotypic changes were observed by Singal () in Sahiwal and Vergera et al. () in Angus-Blanco multi-breed cattle. Results indicate negative genetic trends for FCI, which is desirable but due to positive environmental trends nullified the effect at phenotypic level. As the trait is mainly governed by non-genetic factors, hence managemental practices may be improved for lowering the FCI. First service period: Estimate of phenotypic trend for the trait was days/year, which is not in desirable direction. The estimate showed desirable genetic progress in the trait but because environmental trends were in opposite direction, that resulted into undesirable phenotypic changes. As the trait governed by non-genetic factors, hence 9.46± ± ± ±5.47

5 managemental practices may be improved for lowering the FSP. First dry period: The estimate of phenotypic trend in FDP was days/year, which is not in desirable direction. Present study indicates desirable genetic trend for the trait but influences of nongenetic factors nullified the desirable impact. However, larger standard error in the phenotypic trend makes it imprecise. Comparison of the estimates of genetic trends obtained by different methods: Comparison of Method-I and II of Smith (1962): As the standard errors of all the traits studied are lesser for the estimates of genetic trends by method- II than by method-i, hence method-ii may be superior to method-i. These results are in conformity with Powell and Freeman (1974), Hingane (198), Singal () and Singh (). Comparison of method-iii and IV of Powell and Freeman (1974): The estimates and standard errors by method-iii are lower than method-iv; hence, method-iii was better over method-iv. Similar inferences were drawn by Singh (). However, Vol. 48, No. 6, contrary results were reported by Powell and Freeman (1974), Hingane (198) and Singal (). Comparisons among methods of Smith (1962) and Powell and Freeman (1974): In general, the estimates of genetic trends by methods of Powell and Freeman (1974) have lower standard errors than by methods of Smith (1962). The same was expected because methods of Powell and Freeman (1974) removed biasness due to non-random allotment of dams to the sires with respect to their age and merit. Hence, estimation of genetic trends from Powell and Freeman (1974) methods is better than from Smith (1962) methods. The method-iii showed lower standard error than method-iv. It may, therefore, be inferred on the basis of the present study that method-iii (Powell and Freeman, 1974) is the most precise and best method for estimation of genetic trends for economic traits. Although it is inferred by several workers (Powell and Freeman, 1974; Hingane, 198; Singal, ) that method-iv is best but due to limitation of size of data in present study method-iv was associated with higher standard error than method-iii. REFERENCES Bakir, G. and Kaygisiz, A. (). Estimates of trends components of 35 day milk yield at Holstein Friesian cattle. J. Ani. Vet. Advance 8: Frietas, A. F. D., Wilcox, C. J. and Costa, C. N. (). Genetic trends in the production of Brazilian dairy crossbreds. Rev. Brasil. Genet., 18: Hingane, V. R. (198). Estimation of genetic and environmental trends for economic traits in Hariana cattle. Ph.D. Dissertation, Haryana Agric. Univ., Hisar, India. Peixoto, M. G. C. D., Verneque, R. S., Teodoro, R. L., Penna, V. M. and Martinez M L. (26). Genetic trends for milk yield in Guzerat herds participating in progeny testing and MOET nucleus. Genetc. Mol. Res., 5: Powell, R. L. and Freeman, A. E. (1974). Genetic trends estimators. J. Dairy Sci. 57: Rehman, Zia. Ur. (28). Factors affecting first lactation performance of Sahiwal cattle in Pakistan. Arch. Tierz Dummerstorf, Summer Story, 5: Singal, D. K. (). Estimation of genetic trends for economic traits in Sahiwal breed of dairy cattle. M.V.Sc. Dissertation, CCS Haryana Agric. Univ., Hisar, India. Singh, K. (). Phenotypic and genetic trends of economic traits in Hariana cattle. M.V.Sc. Thesis, HAU, Hisar India. Smith, C. (1962). Estimation of genetic change in farm livestock using field records. Anim. Prod. 4: 239. Vergera, O. D., Elzo, M. A. and Ceron-Munoz, M. F. (). Genetic parameters and genetic trends for age at first caving and calving interval in an Angus-Blanco Orejinegro Zebu multibreed cattle. Livestock Science. 126: