The first lactation records of 1450 Gir cattle progeny of 290 dams and 41 sires maintained over the period from 1987 to 2010 at Cattle Breeding Farm, Junagadh Agricultural University, Junagadh, Gujarat were used to estimate the phenotypic, genetic and environmental trends of traits viz. first lactation total milk yield (FLTMY), first lactation total milk yield per day of first calving interval (FLTMY/FCI), first lactation total milk yield per day of first lactation length (FLTMY/FLL). The phenotypic trends were estimated as: 90.70 ± 6.44 kg, 0.24 ± 0.01 kg and 0.32 ± 0.02 kg for FLTMY, FLTMY/FCI and FLTMY/FLL respectively. The genetic trends were compared by five methods as Smith method1 (SM1), Smith method 2(SM2), Powell and Freeman method 1 (PM1), Powell and Freeman method 2 (PM2) and BLUP. The annual genetic trends for FLTMY were found to be positive by SM1 (2.88 ± 39.58 kg), PM1 (2.21 ± 37.34 kg) and BLUP (9.17 ± 1.94 kg). The annual genetic trends for FLMY/FCI were positive by SM1 (0.43 ± 0.03 kg), SM2 (2.69 ± 0.03 kg), PM1 (0.38 ± 0.02 kg) and PM2 (2.06 ± 0.02kg) while negative by BLUP (-0.05 ± 0.01 kg). The annual genetic trends for FLMY/FLL were found to be positive by SM1 (0.51 ± 0.06 kg) and PM1 (0.45 ± 0.03 kg) methods while negative by SM2 (-2.37 ± 0.05 kg), PM2 (-1.79 ± 0.03 kg) and BLUP (-0.06 ± 0.01 kg). However, the estimates obtained by BLUP method had the lowest standard errors and were more reliable compared to other methods.
The aim of an animal breeder is to maximize the genetic gain per unit of time for various traits of economic importance in a breed improvement programme. High production efficiency in livestock is an economically desirable attribute that targets ultimately for genetic up gradation (Dangar and Vataliya, 2015a). In dairy cattle breeding, this implies maximizing genetic gain mainly for milk yield and production efficiency traits. This calls for evaluation of a breeding programme in terms of assessing change in the genetic constitution as well as environmental (managemental) conditions over time in organized herds of a particular breed. The magnitude and direction of production trends in a herd indicate effectiveness of breeding programme and help in developing or modifying appropriate strategies for bringing further improvement. Therefore, the genetic trends in production traits are important in that they allow for the evaluation of the efficacy of selection and management schemes (Nehara et al., 2013). Many studies have examined genetic trend by regression of estimated breeding values on time (Powell et al., 1985; Lee et al., 1985) or regression of production on time for estimation of phenotypic trends (Burnside and Legate, 1967; Powell and Freeman, 1974).
In India, annual genetic in first lactation 305day milk yield were estimated by Singh (1995); Singh et al. (2002); Raja (2004) and Mukherjee (2005) in Karan Fries, Hariana, Sahiwal and in Frieswal. In the present study an attempt has been made to compare the genetic and environmental trends of first lactation milk yield and production efficiency traits viz. first lactation total milk yield per day of first calving interval and, first lactation total milk yield per day of first lactation length by five methods as Smith method1 (SM1), Smith method 2(SM2), Powell and Freeman method1 (PM1), Powell and Freeman method2 (PM2) and BLUP methods in Gir cattle.
Materials and Methods
The records of Gir cattle’s on production traits were collected from history-cum pedigree sheets maintained at Cattle Breeding Farm, JAU, Junagadh during the period of 24 years from 1987 to 2010. The animals with lactation length less than 100 days and with abnormal calving like still birth, abortion were excluded from the study. The data were grouped in three seasons, summer (March to June), monsoon (July to Oct.) and winter (Nov. to Feb.). Six periods viz. period-1 (1987-1990), period-2 (1991-1994), period-3 (1995-1998), period-4 (1999-2002), period-5 (2003-2006), period-6 (2007-2010) and six age groups viz. age group-1(d”875days), group-2 (876- 950days), group-3 (951-1025 days), group-4 (1026-1100 days), group-5 (1101-1175 days) and group-6 (>1175 days).
Estimation of Phenotypic Trends
The phenotypic trends for each trait were estimated by taking regression of performance of the population on the year as b (P.T.).
Estimation of Genetic Trends
Genetic trends were estimated as the pooled intrasire regression of progeny performance on time as per method I and method II of Smith (1962) using the following formulae-
Method I: ĝ = 2(bPT – bPT/S)
Method II: ĝ = – 2(b (P-P̅) T/S)
Where, ĝ = Genetic trends, bPT = is regression of population performance on time, b P.T/ S = is within sire regression of progeny performance on time, b (P-P̅) T/S = is within sire regression of progeny performance on time record being deviated from population mean.
Powell and Freeman’s Methods
This procedure was given by Powell and Freeman in 1974. It is a modification over Smith method (1962) procedure for estimation of genetic trend because this method removes the bias due to non-random allotment of dams to sires with respect to age. Considering this, the estimators of genetic trends would improve as follows-
Method I: ĝ = 2(bPT – bPT/S) / (1 + bDAT/S – bDAT)
Method II: ĝ = – 2(b (P-P̅) T/S) / (1 + bDAT/S – bDAT)
Where, bDAT = is regression of dam’s age on period, bDAT/S = is within sire regression of dam’s age on period
The genetic trends were estimated by calculating the transmitting ability (ETA) of sires. The transmitting ability of sire is half of additive genetic value and therefore genetic trends was obtained as 2 times regression of weighted average of sire’s transmitting abilities (WAETA) for each year on year as (Hintz et al., 1978)-
WAETA = Σ nik si / n.k
Where, nik = Number of daughter of sire i (i= 1, 2, … .., m ) in kth year, Si = Estimated Transmitting ability (ETA) of sire ith, n.k = Number of daughters of m sires in the kth year.
Transmitting ability is half of the additive genetic value and additive genetic value calculated by BLUP (best linear unbiased prediction) method (Henderson, 1975) as-
Y= Xb + Zu + e
Where, Y is the vector of observations for ith trait (I = 1, 2, 3), b is the vector of observations of unknown ith fixed effects (Season, period and age group), u is a vector of observations of unknown ith random effect (Sire), X and Z are the incidence matrices pertaining for fixed and random animal effect respectively and e is the vector of random error.
G-1 is inversely of sire relationship matrix. The mixed model equation is-
By solving the mixed model equations the BLUP of breeding values of the sires were obtained.
Estimation of Environmental Trends
Environmental trend (ΔE) was obtained by subtracting the genetic trend (ΔG) from the overall phenotype trend (ΔP).
ΔE = ΔP – ΔG
The standard error of environmental trend S.E. (ÄE) was estimated as-
Where, is linear regression of population performance (P) on time (T), N is number of observations.
Standard errors of different regression and genetic trends were calculated using the following general formulae assuming covariance between regressions to be zero.
V (byx) =
Where, S is number of subclasses (Van Vleck et al., 1961).
Results and Discussion
Phenotypic, Genetic and Environmental Trends in First Lactation Total Milk Yield (FLTMY)
The phenotypic trend of first lactation total milk yield (FLTMY) was 90.70 ± 6.44 kg and was statistically significant (P< 0.05). The overall average FLTMY of Gir cattle was 2347.63 ± 187.76 kg. Sadana and Tripathi (1986) in HF crosses cattle at Hisar; Gupta (1992) in Red Sindhi cattle at Hosur and Puddukkottai farms; Singh (1995) and Nehara et al. (2013) in Karan Fries cattle at NDRI, Karnal and Singh and Nagarcenkar (2000) in Sahiwal cattle at Durg farm also reported positive phenotypic trends for FLTMY. The genetic trends for FLTMY estimated using SM1, SM2, PF1, PF2 and BLUP methods are shown in Table 1. The genetic trends were positive by SM1 and PF1 but standard error was relatively low in BLUP method with positive genetic trend.
Negative genetic trend for FLTMY were reported by Gupta (1992) in Red Sindhi cattle at Chiplima Farm and by Tripude et al. (1995) in Sahiwal cattle at Nagpur Farm. Singh (1995) in Karan Fries cattle at NDRI farm and Mukherjee (2005) in Frieswal cattle at various military dairy farms also reported negative genetic trends. While positive genetic trend for FLTMY was reported by Nehara et al. (2013) in Karan Fries cattle. The estimated environmental trends were estimated using SM1, SM2, PF1, PF2 and BLUP methods (Table1). Environmental trends were in positive direction. Desirable environmental trend was also reported by Desraj (1987) in Kankrej cattle at Mandavi Farm; Murdia and Tripathi (1991) in Jersey cattle and by Tripude et al. (1995) in Sahiwal cattle; Herbert and Bhatnagar (1988) at NDRI in KS cattle; Singh (1995) and Nehara et al. (2013) at NDRI in Karan Fries cattle. Period of 24 years was affect significantly (p < 0.05) to lactation milk yield in Gir Cattle by Dangar and Vataliya (2015b).
Table 1: Phenotypic, genetic and environmental trends in total milk yield and milk production efficiency traits in first lactation records estimated using different methods
|Traits||Trends||Smith Methods||Powell and Freeman Methods||BLUP|
|FLTMY (Kg)||90.7 ± 6.44||2.88±39.58||-21.85±38.16||2.21±37.34||-16.7±35.17||9.17±1.94|
|FLMY/FCI (Kg)||0.24 ± 0.01||0.43±0.03||2.69±0.03||0.38±0.02||2.06±0.02||-0.05±0.01|
|FLMY/FLL (Kg)||0.32 ± 0.02||0.51±0.06||-2.37±0.05||0.45±0.03||-1.79±0.03||-0.06±0.01|
Phenotypic, Genetic and Environmental Trends in First Lactation Milk Yield per Day of First Calving Interval (FLMY/FCI)
The mean FLMY/ FCI in Gir cattle was 1.57 ± 0.05 kg. The changes in yearly means were quantified by the phenotypic trend which was 0.24 ± 0.01 kg and was statistically significant. Dangar and Vataliya (2015c) had reported non-significant genetic and environmental correlation between SLMY and AFC in Gir cattle. Dangar and Vataliya (2015c) had also reported 0.006 ± 0.178 genetic correlation in Gir cattle. The genetic trends estimated by SM1, SM2, PF1, PF2 and BLUP methods are shown in Table1. The genetic trends for the FLMY/FCI estimated by SM1, SM2, PF1 and PF2 were found to be positive, while genetic trend was found to be negative by BLUP method. The environmental trends were estimated shown in Table1 by SM1, SM2, PF1, PF2 and BLUP method which were negative except BLUP method. Nehara et al. (2013) reported phenotypic trend which was 0.05 ± 0.04 kg (0.57% of HA) and was statistically non-significant, genetic trends were found to be negative and statistically significant (P< 0.05) by SM2 and PF2 methods and The environmental trend in FLMY/ FCI by BLUP method was found to be positive whereas negative trends were observed by other methods in Karan Fries. Murdia and Tripathi (1991) reported significantly negative genetic trend for FLMY/FCI in Jersey cattle at Bhiwani, Bidaj and Anand Farms. The environmental trend was in desirable direction at Bhiwani and Bidaj Farms. Period of 24 years was affect significantly (p < 0.05) to age at first calving in Gir cattle by Dangar and Vataliya (2014).
Phenotypic, Genetic and Environmental Trends in First Lactation Milk Yield per Day of First Lactation Length (Flmy/Fll)
The average FLMY/FLL in Gir cattle was 7.15 ± 0.05 kg. The changes in yearly differences are quantified by the phenotypic trend which was 0.32 ± 0.02 kg per year. The genetic trends for FLMY/FLL were estimated using SM1, SM2, PF1, PF2 and BLUP methods (Table1). The genetic trends by SM1 and PF1 methods were observed to be positive. Narain and Garg (1972) reported positive and non-significant phenotypic and genetic trends for FLMY/FLL in Red Sindhi cattle at Bangalore and Hosur Farms. However, Murdia and Tripathi (1991) observed negative and significant genetic trend for this trait in Jersey cattle at Bhiwani Farm. Nehara et al. (2013) reported genetic trends by SM1, PF1 and BLUP methods were observed to be positive in Karan Fries. The environmental trends for FLMY/FLL were estimated using SM1, SM2, PF1, PF2 and BLUP methods and were observed positive by using SM2, PF2 and BLUP methods (Table 1). Nehara et al. (2013) reported environmental trends for FLMY/FLL were observed positive and statistically significant (P< 0.05) by SM2, PF2 and BLUP methods in Karan Fries.
Based on the present investigation, it was found that the Smith method-2 and Powell and Freeman method-2 were superior to Smith method-1 and Powell and Freeman method-1 but inferior to BLUP method because of low sampling variance in the BLUP method. The positive phenotypic trends in milk production trait FLTMY could be due to desirable environmental trends during the period under study, though the standard errors of these environmental trends were quite high. Therefore, it is suggested that the BLUP method should be used for estimation of genetic trends of economic traits because it gave relatively lower sampling error compared to other methods and corrected for environmental factors more efficiently than other methods.