Heritability and correlation among first lactation traits in Holstein Friesian cows at Holeta Bull Dam Station , Ethiopia

Records of 433 cows from 48 sires that had at least four daughters were used to study genetic parameters for age at first calving, 305 day milk yield, first lactation milk yield, first lactation length, first service period, first dry period and first calving interval. Data were analyzed by the procedures of Restricted Maximum Likelihood Method with animal model. Age at first calving had highest heritability of 0.53±0.116, and the estimate for all other traits found to be medium in magnitude ranged from 0.23 to 0.28. Very low phenotypic correlations of age at first calving with all other traits were observed. The phenotypic, genetic and environmental correlations of first lactation milk yield with 305 day milk yield were high and positive. All correlations of first lactation milk yield with first service period, first dry period and first calving interval were negative. High phenotypic, genetic and environmental correlations were found for service period with dry period and calving interval; and dry period with calving interval.


INTRODUCTION
The economy of Ethiopia is largely dependent on livestock.According to CSA (2010) report, the nation has 50.8, 25.9, 21.9, 7.2 and 0.8 million heads of cattle, sheep, goat, equines and camel, respectively.However, productivity of cattle in terms of milk and meat is very low.Lactation yield of cows is within the range of 300 to 600 kg and average carcass weight of mature cattle is only 112 kg (Azage et al., 1993).To improve the supply of milk and milk products cattle breeding has been implemented for several years.This demands continuous evaluation of breeding centers for reproductive and productive performances.Genetic parameters are important tools for improving quantitative traits by selection.
The potential for genetic improvement of a trait largely depends upon genetic variation existing in the population of interest.The genetic variability for a particular trait in a herd or population is measured by heritability estimate of a trait under given environmental conditions.The genetic composition of a population can be studied by considering the relative importance of heredity and environmental factors affecting the performance of individual in that population.
The estimates of genetic parameters are helpful in *Corresponding author.E-mail: ggoshu2000@yahoo.com.Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License determining the method of selection to predict direct and correlated response to selection, choosing a breeding system to be adopted for future improvement as well as in the estimation of genetic gains.If genetic correlation between the two traits is high, the selection for one trait would result in an improvement/deterioration for the other trait as a correlated response.The phenotypic correlation is an expression of observed relationship between the phenotypic performances of different traits while the degree of association between genes responsible for the additive variance of different traits is measured through genetic correlation.The genetic correlations give the information how genes affecting one trait also affect the other traits.The effectiveness of selection and net genetic progress can be measured when selection is made for more than one trait (Javed et al., 2004).The Holeta Bull Dam Station was established for improving milk production.So far, genetic parameters for first lactation traits at this station have not yet been studied.These traits are expressed early in the life time of the cow hence important for genetic improvement.Therefore, the objective the study was to estimate heritability, and phenotypic, genetic and environmental correlations for first lactation traits.

Description of the study area
The site is characterized by cool sub-tropical climate with mean maximum and minimum temperatures of 22.3 and 6.2ºC, respectively and a mean relative humidity of 59%.The mean annual rainfall ranges from 818 to 1247 with an average of 1014 mm.The three seasons are classified into dry, short rainy and long rainy which last from October to February, March to May and June to September, respectively.

Herd management
Lactating cows were allowed to graze on native pasture from 8:00 am to 3:00 pm and were provided with native grass hay on return to the barn in the afternoon.The herd was supplemented with cultivated green vetches from December to January and also allowed to graze on irrigated pasture from February to May.Most of the cows were served at first observed heat after calving.Heat detections were routinely followed three times a day, that is, early in the morning after milking; in the resting period at noon; and in the afternoon before milking.Calves were separated from their dams immediately after birth and allowed to receive 5, 4, 3, and 2 L of milk per day from 5 to 65; 66 to 85; 86 to 105; and 106 to 120 days of ages, respectively.Regular vaccinations against contagious bovine pleura-pneumonia, lumpy skin disease, anthrax, and blackleg, foot and mouth disease and pasteurellosis were given and treatments provided when incidence of cases were observed.

First service period (FSP)
The time interval (days) between date of calving and date of successful conception.

First dry period (FDP)
The time interval (days) between the date on which the animal was dried off and the date of next normal calving.

Age at first calving (AFC)
The difference (days) between the date of birth and date of first calving.

First lactation milk yield (FLMY)
Milk yield (kg) from the day of first calving to the day on which cows dried off.This was calculated from monthly records.

day milk yield (DMY)
Adjusted first lactation milk yield (kg) to 305 day.

First lactation period (FLP)
The difference (days) between date of calving and date of drying off an animal.

First calving interval (FCL)
The time interval (days) between dates of first two successive calving.

Data source and statistical analysis
Data collected during 1984 to 2009 from records of 433 pure bred Holstein Friesian cows from 48 sires that had at least four daughters were employed for the study of genetic parameters.Heritability for age at first calving (AFC), 305 day milk yield (305 DMY), first lactation milk yield (FLMY), first lactation period (FLP), first service period (FSP), first dry period (FDP) and first calving interval (FCL) were estimated using univariate analysis of the Restricted Maximum Likelihood Method (REML) with animal model.y = Xß + Zu + e Where y = a vector of n×1 records; ß = a vector of fixed effect (season and year); u = a vector of random animal effect; e = vector of residual animal effects, X and Z were incidence matrices relating to records to fixed and random animal effects, respectively.The expected values of a and e were E (a) = E(e) = 0.The (co)variance structure assumed to be was V(a) = Aσ 2 a; V(e) = Iσ 2 e, and cov(a,e) = cov(e,a) = 0; cov(y,a) = ZAI σ 2 a, where A is the numerator relationship matrix.
Where σ 2 ai= additive genetic variance for i th trait; σ 2 pi = phenotypic variance for the i th trait; σ 2 ei = residual variance for the i th trait; Covpi, pj = phenotypic covariance for trait i and j; Covai, aj = genetic covariance for trait i and j and Covei, ej = residual covariance for trait i and j.Co variances, heritability and genetic correlations were estimated using DMU (Derivative free Multivariate analysis by restricted  (Madsen and Jensen, 2008).

Heritability of first lactation traits
The descriptive statistics first lactation traits in Table 1 showed that the estimates for AFC, 305 DMY and FCL were closer to the values obtained from study animals.
There was high variability among cows in FDP, FSP and FLMY.
The heritability estimates for first lactation traits were as shown in Table 2.The highest h 2 value was found for age at first calving.The heritability estimate for FLMY, 305 DMY, FLP, FSP, FDP and FCL were found to be medium in magnitude from range 0.23 to 0.28.

AFC with other traits
Age at first calving had very low phenotypic correlation with all other traits (Table 2).The genetic correlation was low (0.19±0.26) with 305 DMY but negative with FSP, FDP, and FCI.Moreover, the environmental correlation was small (less than 0.11).

FLMY with other traits
The phenotypic, genetic and environmental correlation with 305 DMY was very high and positive.Optimum correlations were observed with FLP.All correlations of FLMY with FSP, FDP and FCI were negative.

DMY with other traits
Low phenotypic (0.23±0.05) was observed between 305 DMY and FLP.All genetic correlations of 305 DMY with FLP, FSP, FDP and FCI were negative and the value estimated were -0.87 and -0.66 with FSP and FDP, respectively.

FLP with other traits
The phenotypic correlation of FLP with FSP and FCI were very close, 0.16 and 0.20, respectively.However, it had negative correlation with FDP.

FSP and FDP with other traits
High phenotypic, genetic and environmental correlations were found for FSP with FDP and FCI, and FDP with FCI.

Heritability of first lactation traits
The heritability (Table 2) for AFC was high in magnitude (0.53±0.116) and this indicates sufficient additive genetic variance for affecting the selection to reduce the AFC.Therefore, it is important to consider this trait when recruiting sires for breeding program.The result agreed with Gill and Allaire (1976) who observe almost similar h 2 estimate (0.51) for AFC in Holstein cows.However, the present h 2 estimate was lower than the report of Suresh and Sharma (1985) who found 0.75±0.12for AFC, but this h 2 value was higher than the results of Sachdeva and Gurnani (1989) and Singh et al. (1996) who have reported h 2 values of 0.42, and 0.46, respectively.These reports showed that there was wide genetic variation for AFC in different cattle breeds.Early study (Allaire and Lin, 1977) (Schneider and Van Vleck, 1985).Higher h 2 estimates for FLMY were reported by Suresh Chand and Sharma (1985), Sachdeva and Gurnani (1989), Tajane and Rai (1989), Rao and Nagercekar (1992) and Tomar et al. (1996).They found 0.89, 0.51, 0.48, 0.48 and 0.77 for Holstein Friesian crosses, respectively.Lower h 2 of 0.17 and 0.16 to 0.22 for FLMY were reported for Holstein cows in Mexico (Montaldo et al., 2010) and USA (Lofgren et al., 1985), respectively.
The h 2 estimate for FLP was 0.28±0.124indicating presence of additive genetic variance to affect the individual selection and the value was higher than that found by Berhanu and Chakaravarty (2013).Medium estimates of 0.36 and 0.43 for h 2 of FLP were reported by Tomar et al. (1996) and Gaur (2003) for Friesian crosses.Extremely estimates of 0.01 and 0.02 were reported by Tajan and Rai (1989) and Dalal et al. (1993) indicted environmentally controlled nature of the trait.
The service period is the period between calving to conception and is economically very important in dairy cattle, as it determines the length of calving interval.The h 2 for FSP was 0.26±0.113.This h 2 indicates some that additive genetic variance is available to affect the selection to improve the trait genetically and appears to be against the non-genetic environmentally controlled nature of the trait.However, as per the nature of the trait it is largely controlled by feeding, management and post partum health care of the cow.This finding was in agreement with Kumar et al. (2003) for Jersey with Sahiwal cross.Guar et al. (1999) and Guar (2003) reported 0.65 and 0.49, respectively for Friesian×Sahiwal crosses.Much lower h 2 value of 0.02 was found for Frieswal cattle (Bharti, 2004).
Heritability for the length of first dry period was 0.24±0.117indicating that some additive genetic variance was available to affect selection for optimizing the dry period.Tomar et al. (1996), Guar et al. (1999) and Guar (2003) found h 2 estimates of 1.0, 0.67 and 0.43, respectively for Friesian crosses with Sahiwal.Very low h 2 estimates of 0.09 and 0.10 were reported for the same genetic group by Butte and Desphande (1987), Singh et al. (1990), respectively.
The h 2 for FCI was 0.28±0.141.This h 2 value also indicated that additive genetic variance exist to affect the selection for the improvement of first caving interval.Higher h 2 estimates of 0.52 than the present study was reported by Gaur (2003).Very low h 2 estimates were found by Suresh and Sharma (1985), and Montaldo et al. ( 2010) that noted 0.07 and 0.01, respectively.

Age at first calving with other traits
The phenotypic and genetic correlations of AFC with FLMY (0.06±0.05 and 0.234 ±0.26) and 305 DMY (0.04±0.05 and 0.19±0.26)were positive while environmental correlations were negative and small (-0.04 and -0.04).These correlations indicated that higher AFC were related with higher FLMY and 305 DMY due to genetic reasons, though at environmental level high AFC were found related with lower first lactation milk yield on total as well as 305 day lactation basis.This could be due to the reason that cows sexually maturing and calving at higher age because of genetic reasons will attain bigger body size and hence is likely to produce more milk than cows maturing and calving at a lower age.However, cows attaining maturity and calving at a higher age due to environmental reasons, especially due to poor feeding and management, will possibly have poor body condition and will produce lower milk yield.Similar positive phenotypic and genetic relationships were between AFC and FLMY have been reported by Jadhav et al. (1996), Suresh and Sharma (1985), Jain et al. (1995), Gaur et al.(1999) and Bharti (2004) in various crossbred cattle herds.
The phenotypic, genetic and environmental correlations (Table 3) between AFC and FLP were all positive but very small (0.03±0.05, 0.01±0.25 and 0.06) and agreed with Jadhav et al. (1996) who has reported almost similar correlations between these traits.However, Gaur et al. (1999) and Bharti (2004) observed negative phenotypic and genetic correlations between these traits.
The phenotypic, genetic and environmental correlations of AFC with FSP were estimated as 0.01±0.05,-0.15±0.26,and 0.11, respectively, indicating that phenotypically higher AFC were associated with longer FSP due to environmental reasons while on genetic scale reverse was true and higher AFC were related with  Gaur et al. (1999) and Bharti (2004).The observed positive phenotypic correlation was in conformity with the report of Jain et al. (1995) but contrary to the observation of Gaur et al. (1999) who has found negative relationship between AFC and FSP in crossbred cattle.
The correlations of AFC with first dry period were -0.01±0.05,-0.20±0.27and 0.10 for phenotypic, genetic and environmental, respectively.These negative phenotypic and genetic correlations revealed that higher AFC were related to shorter FDP essentially due to genetic reason while on environmental level higher AFC were associated with longer FDP in Holstein Friesian cows.These correlations indicate that cows with higher AFC due to genetic causes might have attained optimum body weight by first calving age which in turn has reflected in terms of better lactation performance including low service period, longer lactation period and shorter dry period.However, higher AFC due to environmental reasons might have resulted from poor growth rate and suboptimum body weight in turn lowering the performance for all first lactation traits including longer FDP in such cows.These negative genetic and phenotypic correlations can be supported with the findings of Singh et al. (1996) and Bharti (2004) in crossbred cattle.
The negative genetic correlation between AFC and FCI in Holstein Friesian cows indicate that lower AFC due to genetic reasons were associated with longer FCI, but on environmental level lower AFC were related to longer FCI.The possible reasons may be that cows maturing and first calving at a younger age due to genetic reasons may not attain optimum body size and weight and hence is likely to suffer with reproductive problems at the time of parturition and also during first lactation performance, including prolonged first service period vice-a-versa prolonging FCI in such cows.While cows maturing and calving at a higher age genetically, will have optimum body weight/condition and well developed reproductive system, such cows are likely to perform better for first lactation traits, including smaller FSP resulting into smaller FCI.The small and positive phenotypic correlation indicates that cows with higher AFC had longer FCI and it was because of environmental reasons, as indicated by positive environmental correlation.This could be due to the fact that cows maturing and calving late at higher age due to poor environmental conditions viz.inadequate feeding, management and disease control etc. may not have good body condition resulting into poor performance for first lactation traits including longer FCI.Similar positive phenotypic and negative genetic correlations between AFC and FCI have been observed by Bharti (2004).However, Suresh and Sharma (1985), Jain et al. (1995) andJadhav et al. (1996) have reported positive genetic and phenotypic correlations.

First lactation milk yield with other traits
The phenotypic, genetic and environmental correlations of FLMY with 305 DMY were 0.90±0.02,0.79±0.12and 0.89, respectively which were all positive and highly significant indicating that higher FLMY were associated with higher 305 DMY on phenotypic scale essentially due to both genetic and environmental reasons.Very high correlations of FLMY with 305 DMY showed that sires can be evaluated for milk yield on either of the trait and improvement on one trait could bring a concomitant increase on the other.
The positive and significant correlations between FLMY and 305 DMY indicated that higher first lactation milk yields on total lactation length as well as on 305 day lactation basis were associated with longer lactation period in Holstein Friesian cows and selection for higher FLMY will increase length of lactation period.These results can be supported with the similar findings of Berhanu and Chakaravarty (2013), Taneja et al. (1978), Gaur et al. (1999), Suresh and Sharma (1985), and Bharti (2004) reported in various crossbred cattle.However, negative genetic correlation of 305 DMY with FLP can be explained with the reasons that when milk yield of lactations of more than 305 days is adjusted to 305 day lactation period using per day average yield than on genetic basis it take reverse trend and milk yield is reduced as the length of lactation period increases.So it can be concluded that on genetic scale higher 305 DMY was related to optimum lactation length.
The phenotypic and genetic correlations of FLMY and 305 DMY with FSP negative and indicating that higher FLMY on total as well as on 305 lactation basis were associated with lower FSP on phenotypic scale essentially due to both genetic and environmental reasons and cows with higher FLMY or 305 DMY conceived early and have shorter FSP.These observations were contrary to the findings of Gaur et al. (1999), Jain et al. (1995) and Bharti (2004), as they all have reported positive relationships between these traits in crossbred cattle at all levels.
The correlations of FLMY and 305 DMY with FDP were all negative indicating that higher FLMY were related with shorter FDP and selection for higher FLMY or 305 DMY will reduce the FDP or selection of sires for short dry period which could further improve the milk yield.These correlations were in complete agreement with the reports of Singh and Tomar et al. (1996) but did not agree with Jain et al. (1995), Gaur et al. (1999) and Bharti (2004) as they have found positive genetic and phenotypic relationships between these traits in various crossbred cattle.
The negative, significant phenotypic and genetic correlations between FLMY and 305 DMY with FCI indicated that higher FLMY and 305 DMY were associated with shorter FCI, on phenotypic scale due to genetic reasons.These correlations as expected were in accordance with the above observed correlations of FLMY and 305 DMY with FSP in Holstein Friesian cattle because length of FCI is determined by the length of FSP and so relationships with both traits also behave in similar way.The observed negative genetic and phenotypic correlations between these traits were observed by Kaul (1987) in Friesain×Sahiwal cattle, Suresh and Sharma (1985), Jain et al. (1995), Gaur et al. (1999) in different crossbred cattle herd and have reported both as positive relationships.

First lactation period with other traits
The phenotypic, genetic and environmental correlations of FLP with FSP were found as 0.16±0.05,0.44±0.23 and 0.06, respectively.These correlations were all positive and showed that cows with longer FLP associated with longer FSP on phenotypic scale due to both genetic and environmental reasons.These positive correlations completely agreed with the report of Bharti (2004).
The phenotypic, genetic and environmental correlations of FLP with FDP were estimated at -0.42±0.04,-0.15±0.34 and -0.52, respectively.These correlations were all negative and significant and reveal that observed negative phenotypic relationship between FLP and FDP was due to both genetic and environmental reasons and any efforts in the direction of reducing FDP through improvement in management/environmental conditions will improve the FLP in the herd.This finding was in agreement with the observation of Bharti (2004).However, Suresh and Sharma (1985), and Gaur et al. (1999) have observed negative genetic but positive phenotypic correlations between these traits in different cross bred cattle herds.
The phenotypic, genetic and environmental correlations between FLP and FCI were all positive.These correlations indicated that longer FLP were associated with longer FCI on phenotypic scale and this was due to both genetics and environmental reasons and any increase in FLP of cows either due to genetic or environmental reasons will increase FCI.The observed relationship of these traits agreed with the reports of Deshpande andBonde (1983), Suresh Chand andSharma (1985) Gaur et al. (1999) and Bharti (2004).

First service period with other traits
The phenotypic, genetic and environmental correlations of FSP with FDP were high and positive which showed that longer FSP were associated with longer FDP and FCI.The high positive correlations of FSP with FDP and FCI showed that reducing the FSP either due to genetic or environmental reasons will shorten the duration of both traits.These results were in agreement with the reports of Jain et al. (1995), Gaur et al. (1999) and Bharti (2004) for different crossbred cattle herds.

First dry period with FCI
The correlations between FDP and FCI were found to be positively correlated on phenotypic, genetic and environmental scales and their coefficients were 0.73±0.03,0.94±0.12and 0.65 respectively, which presumably indicated that longer FDP on phenotypic scale were associated with longer FCI due to both genetic and environmental reasons.This suggested that both the traits are controlled by similar genetic and environmental conditions and improvement in one trait will automatically improve the other trait.These results agreed with the reports of Desphande and Bonde (1983) and Bharti (2004) as they all have observed positive correlations between these traits in different crossbredcattle herds.

Conclusions
The high heritability of age at first calving showed the importance of including the trait in the selection index when genetic improvement is sought.Increase in the length of first service period, first dry period, and first calving interval will reduce first lactation milk yield and 305 day milk yield.High and positive correlations existed among length of service period, dry period and calving interval and reduction of the length of one trait would have subsequent result on the others.performance in Holstein×Sahiwal crossbred.Indian J. Dairy Sci.15:3-9.Tomar SS, Rawal SC, Singh RB (1996).Population analysis for certain demographic parameters in Tharparkar herd.Indian J. Dairy Sci.49(9):562-566.

Table 2 .
Estimates of heritability of first lactation traits in Holstein Friesian cows.
maximum likelihood) packages