Research Article
Studies on the Genetic Constitution of Black and White Dairy Cattles Raised in Tahirova State Farm
Department of Animal Science, Agricultural Faculty, Trakya University 59030 Tekirdag, Turkey
Milk yield and reproductive performance are crucial factors that have important effects on the profitability in dairy farms[1]. Records of this traits are also important for the breeding programs conducted a national level. Such records are not completely done in Turkey condition except for some private dairy farms that have large herd size. On the other hand, data recording regarding milk yield and reproductive traits has been done for many years in state farm of Turkey, but unfortunately these data have not been used to a greater extent in national breeding programs[2].
In this study genetic constitution of Black and White cattles raised in Tahirova State Farm were evaluated.
In this study 1504 individual milk yield records of 468 Black and White cattles raised Gönen-Tahirova State Farm were evaluated. Data were obtained from the period of 1978-1995.
First breeding age (FBA), first calving age (FCA), calving interval (CI), days in dry (DID) and service period (SP) data were used as a reproductive traits and lactation length (LL), 305 day milk production (305d-MY) were used as a milk yield trait. Descriptive values of animal materials of Tahirova State Farm were given in Table 1 with the reported average values by Kaymakçi[3] for each traits.
Following linear models were used to the estimation of genetic parameters for reproductive and milk yield traits, respectively.
Table 1: | Descriptive values of animal materials |
*Reported values by Kaymakçı[3] |
Yijk | = | + Si + YLNj +eijk |
Yijk | = | + Si + YLNSj + eijk |
Yijk | = | observed value, |
μ | = | estimated population mean, |
Si | = | random sire effect, |
YLNj | = | fixed year, lactation number effect |
YLNSj | = | fixed year, lactation number, season effect |
Eijk | = | residual |
Heritability: Estimated heritability coefficiencies of reproductive and milk yield traits were given Table 2.
Heritability of growth rate is high[4] and FBA and FCA are related traits to growth rate. So it is normally expected that heritabilities of FBA and FCA would also be high in this study, heritability of FBA and FCA were estimated as 0.74±0.14 and 0.81±0.15, respectively. CA, SP and DID traits on the other hand are more affected by environmental factor then the FBA and FCA traits.
Heritabilities of CA, SP and DID traits were estimated as 0.60±0.04; 0.06±0.04; 0.0, respectively in this study. These results of the present study are consistent with those of published studies[5-12,18,19].
Table 2: | align="justify">Estimated heritability coefficiencies for the reproductive and milk yield traits of Black and White cattles raised Tahirova State Farm |
Table 3: | Phenotypic correlation between the reproductive traits |
Heritability of milk yield was estimated as 0.27±0.07 in this study. Miglior et al.[13] reported that the heritability of milk yield for Black and White cattle was between 0.29-0.30, however Dong and Van Vleck[18,19] found the heritability of milk yield for same dairy breed in first lactation period as 0.27. In a study which was previously conducted in Tahirova State Farm, heritability of milk yield was found as 0.17[14].
Heritability of lactation length was found to be low in this study (0.05±0.03). this is not an unexpected finding because it is largely determined by environmental factors.
Phenotypic correlations: Determination of first breeding age (FBA) for heifers is highly crucial in dairy production as this age is closely related to growth and future milk yield potential of heifers. The delay in the we of heifers for the first breeding age also affects the genetic progress at the same time[15,16]. Thus the delay in FBA results in the delay in FCA which is directly related to FBA. Correlation coefficiencies between FBA and FCA and between SP an CI were found as 0.95 and 0.99, respectively (Table 3).
High correlation between SP and CI is an expected case because service period length is used for calculating for calving interval[17].
It can be seen from Table 4. That the correlation coefficiency between LL and 305d-MY is low (0.021). This two parameters are heavily affected by environmental factors rather than genetically ones. This has major influence on this relationship.
High genetic variance in respect to FBA and FCA suggest that FBA and FCA can be reduced and this reduction would be possible to some extend. However the use of heifer for breeding at on early stage could have a negative effect on their future milk yield potential. The reason for high heritability of these traits may not be directly based on genetically factors.
The expectation of similar body size in first breeding from the sire families which have low and high mature body weight may cause this variation. Thus the average mature body weight of sire families should be known. In order to reduce economic losses due to the delay of first breeding, first breeding should be performed in view of mature body weight of sire families.
The environment is known to have a major influence on CI, SP and LL. This features are mainly controlled by the former. Service period is a measure of fertility in animal, thus it is expected that genetic variance of this traits is probable it is not suppressing that there was no genetic variance in DID trait which is only controlled by the farmer under conventional condition.
As a result, estimated heritability coefficiencies of different traits in this study should be evaluated with care and the results of this study should be subjected to further studies.