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UDC 636.2.082.2
THE FEATURES OF SELECTION AND GENETIC PARAMETERS OF THE ECONOMICALLY USEFUL TRAITS OF HIGHLY PRODUCTIVE COWS IN CONNECTION
WITH THE TERM OF INDUSTRIAL USE
Molchanova N.V., Leading Resercher Seltsov V.I.*, Researcher Filipchenko A.A., Post-graduate student All-Russia Research Institute for Animal Husbandry named after Academy Member L.K. Ernst, Moscow, Russia *E-mail: [email protected]
ABSTRACT
The impact of industrial use of cows on following genetic parameters: phenotypic variability, correlation, repeatability and heritability of economically useful traits in the high producing dairy cows herd of black-motley breed with the high level of holsteins has been studied. With the increasing the period of use cows up to 7 or more lactations, coefficients of variation of all monitored indicators declined in connection with the removal of cows with extreme indicators of productivity and longevity during first 3-4 lactations. The correlation coefficients of milk yields during the first, highest lactation and in lifetime, regardless of the period of use is closely related to the life-long milk yield, milk yield per day of productive life and milk yield per day of life. The heritability coefficients (h2) of the indicators of longevity with increasing period of use cows up to 5 or more lactations has tended to increase: by the age of first calving from 0.01 to 0.16, by the number of highest lactation from 0.18 to 0.33, by milking days from 0.10 to 0.30, by lifetime milk yields from 0.18 to 0.32, and by days of life from 0.01 up to 0.21. The highest repeatability of indicators of milk yield, milk fat, body weight of cows regardless of the duration of their use was for the adjacent lactations (1 and 2, 2 and 3, 3 and 4, 4 and 5, 5 and 6). With increasing distance of lactations from each other the coefficient of repeatability of these traits is lowered.
KEY WORDS
Cow; Productivity; Longevity; Variability; Correlation; Repeatability; Heritability.
Efficiency of selection work, the definition of the breeding value of the animals and the establishment of breeding programs depend on the population-genetic parameters. The pace of animal improvement increases if the genetic situation in the herd is regularly taken into account. For developing effective breeding program the following parameters used: variability, heritability, repeatability and interdependence of indicators. Efficiency of selection determined by the value of variability. The variability of trait is determining the genetic shift of sampled trait in the herd. Small degree of variation and overly big in any herd is undesirable, since the first leads to the fact that cannot be found in a herd of cows for its further improvement on one or another trait, and the second degree can lead to the large value of the regression, that is, return to the average indicators of herd in the offspring of animals. Variability characterizes the possibility of selection, the parameters of livestock reproduction. Heritability coefficient reflects the share of variability, caused by the heredity of animals, in the total variability of trait. Reliability of assessment methods of animals' qualities characterized the coefficient of repeatability. The higher the coefficient of repeatability, the more effective selection on this trait [2, 4, 6, 7].
Individual traits of animals vary with age, this cause to make adjustments when selecting cows. Due to the fact that in available literature is not enough information regarding the data on breeding and genetic parameters of productive and other economically valuable traits of dairy cows in relation to the period of production use, the goal was, on the example of high-yielding herd, to determine the actual breeding and genetic parameters of the traits of
the productive longevity of cows in connection with the different periods of their productive use [1, 3, 5].
MATERIALS AND METHODS
The material for the study is based on data from the primary zootechnical and veterinary accounting (program «SELEX»), plans for the selection of bulls to the herd of farm «Dubrovitsy» of breeding plant «Klenovо-Chegodaevо» for the last 13 years. On the farm are bred holsteins black-spotted cattle. Over the past 10 years milk productivity of mature cows was 7118 - 9016 kg with 4.34% fat, 3.12% protein. The database included 388 cows with the term of removal from 1 to 11 lactations. In overall analysis included the indicators of development, milk productivity, reproduction and working lifespan by 34562 primary accounting records 1420 lactations.
Research methods: comparative, statistical and zootechnical analyzes. Biometric data processing and calculation of the criterion of difference validity between the average indicators of the different groups of animals were carried out using the software package MS Excel 2003.
RESULTS OF ESEARCH
In the study of the variability of productive longevity and economically valuable traits of cows with different useful lives the highest values of the coefficient of variation of cows who completed only 1 lactation on the following parameters: the number of calving, the number of calves, dairy days, lifetime milk yield, milk yield and milk fat on 1 day (from 27.4% to 35.5%) are set (Table 1).
Depending on the term of using animals, period of service was characterized by greatest variability both on 1 lactation, and the average for all lactations (from 49.6% to 63.3% and from 25.9% to 59.3%, respectively).
Milk yield in the first, the highest lactation, milk yield of a lifetime, the number of milking days, days of life changed as well, depending on the age of the animals. Cows that have lived 1-3 lactation have higher indicators than those used for more than 4 lactations. In the first three lactation cows with extreme variants of indicators are eliminated from the herd: unproductive - by culling, highly productive - because of the lack of appropriate level of feeding. And so the animals who have lived 7 or more lactations have milk yield in the first lactation 5592 kg (Cv = 14,5%), and who have lived 2 lactation - 6295 kg at Cv = 19,4% (P <0,001).
On average, around all livestock, coefficients of the indicators variability of productive longevity and economically useful traits indicate their sufficient variability for effective selection in highly productive herd.
Economically useful traits of dairy cattle are linked and between them there is a complex relationship which is the result of the interaction of hereditary factors and the environment.
In the literature, information relating to the establishment of regular relations between milk yield and other economically valuable traits of cows due to the different periods of their use is not enough, and the knowledge of such regularities could significantly improve the efficiency of selection in the direction of increasing milk yields, the term of the productive use of animals and their lifetime productivity.
Attracting the attention of researchers to the problem of correlation is due, first of all, the necessity to improve animals not one by one trait, but on a range of key indicators without compromising their health. On the other hand, knowledge of the nature and extent of the correlation between desired traits affect the specific methods of selection breeding pairs in order to generate offspring with the best combination of these traits.
Table 1 - The variability of the indicators of productive longevity and economically useful traits of cows with the different periods of production use
Indicators - Term of use (number of lactations)
1 (n=21 ) 2 (n=93) 3 (n=104) 4 (n=68) 5 (n=38) 6 (n=31) 7 or more (n=33) Average (n=388)
Age of first calving, days M 881,6 837 862 875 875 845 880 861
Cv, % 15,1 12,8 13,8 14,8 13,5 12,1 13,0 13,7
Milk yield (1 lactation), kg M 4606 6295 6160 5837 5360 5190 5592 5848
Cv, % 21,5 19,4 15,9 17,1 18,6 18,7 14,5 19,3
Average service-period, days M 125 161 168 160 146 138 135 156
Cv, % 49,3 59,3 46,8 36,1 25,9 29,1 26,6 45,9
Average period between calving, days M 396 445 449 439 425 409 412 436
Cv, % 14,1 21,5 17,9 13,0 16,1 10,8 10,5 16,8
Milk yield (highest lactation), kg M 4606 7332 7689 7745 7719 7627 7416 7421
Cv, % 21,5 18,8 18,3 15,8 26,2 19,8 13,9 20,9
Dairy days, all lactations M 363 769 1157 1483 1845 2194 2745 1363
Cv, % 33,8 24,0 18,8 17,5 12,5 14,1 18,7 49,8
Lifetime milk yield, kg M 6023,4 16477 24704 31724 37667 44984 54807 28402
Cv, % 34,7 28,1 23,4 23,8 23,0 23,9 21,7 50,9
Milk yield per 1 day of productive life, kg M 16,8 21,5 21,5 21,4 20,4 20,5 20,1 20,9
Cv, % 16,2 18,1 16,8 15,1 20,0 10,7 14,8 18,0
Days of life M 1282 1743 2234 2642 3076 3448 4136 2477,5
Cv, % 13,6 12,4 12,7 13,4 9,8 7,7 13,6 33,0
Milk yield per 1 day of life, kg M 4,63 9,4 11,1 11,9 12,4 13,0 13,2 10,96
Cv, % 27,4 23,7 19,7 19,9 23,1 21,8 14,6 27,6
Number of lactations M 1 2 3 4 5 6 7,64 3,66
Cv, % - - - - - - 14,5 49,2
Note: M - average value of trait; Cv - coefficient of trait variation
Population genetics distinguishes two interrelated forms of correlations: phenotypic, which characterizes the relationship between economic-useful traits of animals that is generated during ontogenesis and genetic, which means the degree of connection between the traits in close relatives (parents - descendants and others).
We determined the phenotypic correlation of the economically valuable traits of cows in relation to the timing of their use and showed it in Table 2, from which follows that the value of the correlation coefficient between the individual traits change dynamically.
So the correlation of milk yield per the first lactation with fat was insignificant and negative in cows lived 1-4 lactation (r = -0,09: -0,13); cows with the 5th and 6th finished lactation it was positive (r = 0,15 and r = 0,22), and with 7 - negative (r = -0,20). Correlation of milk yield per 1 lactation with the production of milk fat, with a service period, with term of use, with a yield for the highest lactation, life-long milk yield and complex indicators of longevity - milk yield on day of life and on the day of productive life - become less close with increasing the term of use animals.
A similar situation is observed with the correlation coefficients of milk yield for the highest lactation and lifetime milk yield with indicators of productive longevity and economically useful traits.
Thus, based on the results of the conducted correlation analysis found that the increase in the period of industrial use of cows from 1 to 7 lactations leads to weakening of the linkages between milk yield with indicators of longevity and other economic-useful signs.
The proportion of variability trait caused by the influence of genetic factors, that is, the heritability (h2) is very important for breeding. It is known that at a high heritability trait (h2> 0,6) selection by phenotype or mass selection are effective, and at a low (h2 <0,2) breeding in herds should be carried out with the involvement of additional sources of information about the productive and breeding qualities of animals.
Heritability coefficients characterize the genotypic diversity of traits, depending on factors such as the degree of hereditary conditionality of trait, genetic heterogeneity of the study group and the influence of environmental factors operating in each population differently.
Therefore the coefficients of heritability have not only a specific value for each herd but for each group of cows with different periods of use (see Table 3).
Highest h2 by age of first calving in cows, that have completed 5 or more lactations is observed (h2 = 0.16), for the other age groups, and the average for all animals - it is small (0.01 to 0.06). By milk yield for 305 days of the first and highest lactations, milk yield per 1 day of productive life, heritability coefficients are significantly reduced in cows with 5 and more finished lactations compared to animals with two lactations.
Signs of longevity: dairy days, days of life, by contrast, has a higher heritability coefficient in connection with the term of use (5 or more lactations). Consequently, with the increase of the term of use cows up to 5 or more lactations, heritability coefficients of milk yield are reduced and signs of longevity, on the contrary, are increased.
Average heritability coefficients for the entire sample indicates that the influence of mothers on economically useful traits and the longevity of cows at farm «Dubrovitsy» are small. Therefore, the main factor affecting the longevity of cows this analysis did not reveal.
For proper breeding use of cows it is necessary to detect their potential capacity for high productivity as earliest as possible. Therefore degree of traits repeatability by lactations in cows has great importance.
Investigated herd is characterized by repeatability coefficients between milk yield, fat content in milk, body weight, and service period that are given in Table 4. Analysis of the periodicity of milk traits for a number of lactations shows that by milk yield and milk fat for the adjacent lactations, regardless of the period of economic use, positive and statistically significant coefficients of repeatability are received. So repeatability of milk yield per 1-2 lactations ranged from 0.43 to 0.53, per 2 and 3; 3 and 4; 4 and 5; 5 and 6 lactations 0.520.66; 0.44-0.64; 0.36-0.52; 0.27 respectively.
Table 2 - Phenotypic correlations of (r) milk yields with indicators of productive longevity and economic-useful traits in cows
with different periods of production use
Pairs of traits Term of use (number of lactations)
1 (22 heads) 2 (92 heads) 3 (104 heads) 4 (68 heads) 5 (38 heads) 6 (31 heads) 7 and more (33 heads) In average N=388 heads
Milk yield (1 lactation), kg:
- fat, % -0,013 -0,039 -0,01 -0,09 0.15 0,22 -0,20 0,05
- production of milk fat, kg 0,97 3) 0,94 3) 0,91 3) 0,92 3) 0,86 3) 0,97 3) 0,87 3) 0,98 3)
- service-period (1 lactation), days 0,31 0,29 2) 0,03 0,12 -0,27 0,371J 0,12 0,15 2)
- milk yield (highest lactation), kg 0,89 3) 0,71 3) 0,63 3) 0,64 3) 0,71 3) 0,68 3) 0,53 2) 0,62 3)
- lifetime milk yield, kg 0,85 3) 0,57 3) 0,53 3) 0,56 3) 0,49 2) 0,57 3) 0,48 2) 0,40 2)
- milk yield per 1 day of life, kg 0,83 3) 0,68 3) 0,64 3) 0,66 3) 0,64 3) 0,63 3) 0,41 " 0,65 3)
- milk yield per 1 day of productive life, kg 0,50 " 0,77 3) 0,65 3) 0,69 3) 0,49 2) 0,71 3) 0,66 3) 0,67 3)
- age of retirement, calvings 0,21 0,11 0,09 0,19 -0,12 0,28 2) 0,24 -0,09
- days of life 0,18 0,01 -0,02 0,04 -0,35 " 0,36 0,14 -0,14 "
Milk yield (highest lactation), kg:
- service-period (average), days 0,35 0,18 0,21 " 0,37 3) 0,09 0,23 -0,24 0,19 2)
- lifetime milk yield, kg 0,85 3) 0,71 3) 0,75 3) 0,74 3) 0,77 3) 0,62 3) 0,52 2) 0,49 3)
- milk yield per 1 day of productive life, kg 0,50 " 0,84 3) 0,78 3) 0,83 3) 0,84 3) 0,85 3) 0,70 3) 0,80 3)
- milk yield per 1 day of life, kg 0,83 3) 0,81 3) 0,84 3) 0,86 3) 0,82 3) 0,93 3) 0,79 3) 0,81 3)
Lifetime milk yield, kg:
- age of first calving, days -0,01 -0,23 1 -0,24 " -0,28 -0,36 " -0,29 -0,17 -0,06
- service-period (average), days 0,31 0,59 3) 0,56 3) 0,65 3) 0,38 1 0,55 2) 0,05 0,13 1
- days of life 0,65 1) 0,52 3) 0,46 3) 0,47 2) 0,73 3) 0,48 2) 0,43 3) 0,49 3)
- milk yield per 1 day of productive life 0,22 0,53 3) 0,57 3) 0,66 3) 0,81 3) 0,81 3) 0,45 2) 0,78 3)
- milk yield per 1 day of life 0,94 3) 0,88 3) 0,83 3) 0,80 3) 0,80 3) 0,93 3) 0,73 3) 0,80 3)
Note:1) P < 0,05; 2) P < 0,01; 3) P < 0,001
The farther into the rank row are lactations, the lower the coefficient of repeatability of milk yield. For example, between the milk yield in the first and sixth lactations it was only 0.12, with the sixth and second - 0.22, for the third and sixth - 0.10.
Table 3 - The heritability of the indicators of productive longevity and economically valuable traits of cows with the different periods of production use (h2 = 2rM-D)
Term of use (number of lactations)
Indicators 2 (n=80 3 (n=74 4 (n=36 5 and more In average
pairs) pairs) pairs) (n=36 pairs) (N=226 pairs)
Age of first calving, days 0,14 0,01 0,06 0,16 0,06
Milk yield (1 lactation), kg 0,31 0,22 0,01 0,04 0,25
Service-period (1 lactation), days 0,21 0,07 0,10 0,28 0,19
Average service-period, days 0,24 0,25 0,01 0,20 0,27
Average period between calving, days 0,30 0,24 0,02 0,21 0,19
Number of highest lactation 0,18 0,26 0,32 0,33 0,21
Milk yield (highest lactation), kg 0,36 0,52 0,50 0,17 0,28
Dairy days 0,16 0,11 0,18 0,30 0,19
Lifetime milk yield, kg 0,18 0,18 0,01 0,32 0,18
Milk yield per 1 day of productive life 0,39 0,20 0,57 0,22 0,30
days of life 0,05 0,10 0,05 0,21 0,13
Milk yield per 1 day of life, kg 0,07 0,25 0,34 0,18 0,04
Table 4 - The repeatability of the economically valuable traits of cows
Compared lactations The sample size (n) Milk yield for 305 days, kg Milk fat, % Live weight, kg Service-period, days
Lim. Lim. Lim. Lim.
First - second 546 0,43J)-0,53J) 0,41J)-0,67J) 0,38J)-0,82J) 0,12 - 0,272)
First - third 426 0,30"- 0,443 0,33J)-0,47J) 0,25J)-0,55J) 0,01 - 0,222)
First - fourth 276 0,292)-0,403) 0,343)-0,483) 0,232)-0,563) 0,07 - 0,07
First - fifth 150 0,11 - 0,11 0,50J)-0,53J) 0,322)-0,49j) 0,02 - 0,04
First - sixth 68 0,12 0,36 2) 0,19 0,02
Second - third 426 0,603J-0,663J 0,383)-0,523) 0,443)-0,703) 0,07-0,252)
Second - fourth 276 0,332)-0,40j) 0,36J)-0,60J) 0,36J)-0,73J) 0,05 - 0,14
Second - fifth 150 0,15 - 0,14 0,14 - 0,513 0,08 - 0,483 0,06 - 03 92)
Second - sixth 68 0,22 0,24 1 0,26 0,16
Third - fourth 276 0,443)-0,523) 0,211)-0,413) 0,453)-0,893) 0,02 - 0,07
Third - fifth 150 0,25i)-0,362) 0,322)-0,52j) 0,02 - 0,643 0,02 - 0,17
Third - sixth 68 0,10" 0,40 0,281) 0,28
Fourth- fifth 150 0,362)-0,523) 0,453)-0,493) 0,01 - 0,73 0,13 - 0,26
Fourth - sixth 68 0,18 0,473) 0,27 0,10
Fifth - sixth 68 0,27 1 0,433) 0,352) 0,04
Note: Lim. - extreme variants;1) P < 0,05; 2) P < 0,01; 3) P < 0,001
Repeatability of fat content in the milk of cows with different terms of use proved to be more stable than milk yield; it may be due to the higher indicator of the heredity of butterfat compared with milk yield. Repeatability of live weight of cows with different term of use is similar to the repeatability of milk yield and the fat content of milk.
From the above it follows that the traits of milk production and live weight has in most cases very high and reliable coefficients of repeatability, allowing with a sufficient degree of reliability predict them by initial measurements.
CONCLUSIONS
Thus, the selection of cattle by economically valuable traits, evaluation of the results of breeding, forecast of its efficiency and definition of breeding value of animals should be
carried out with the use of population genetic parameters, to predict the effect of selection on
these traits. When selecting breeding animals you need to be sure that these animals have a
high genetic superiority, which will be inherited by the next generation.
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