INDEX EVALUATION OF PIGS AND DETERMINATION OF SELECTION LIMITS

The main goal of modern pig breeding is increasing the genetic potential of animals and obtaining the maximal number of products. Global experience demonstrated that the introduction of the system of breeding and fi nishing hybrid stock with the organization of the relevant system of estimating animals may be used to increase the profi tability of this industry. The increase in the productivity of animals is related to the progress of population in general, and the latter is considerably dependent on the accuracy of estimating genotypes [1–4].


INTRODUCTION
The main goal of modern pig breeding is increasing the genetic potential of animals and obtaining the maximal number of products. Global experience demonstrated that the introduction of the system of breeding and fi nishing hybrid stock with the organization of the relevant system of estimating animals may be used to increase the profi tability of this industry. The increase in the productivity of animals is related to the progress of population in general, and the latter is considerably dependent on the accuracy of estimating genotypes [1][2][3][4].
Index estimation is widely used in the whole world. The BLUP method was elaborated in the 1980-s and is currently used for almost all the animal species. Nearly all the countries estimate pigs using selection indexes, different in their composition. For instance, in Australia the estimation of pigs is conducted at the holdings, the obtained data (average daily gain, fat thickness, live bodyweight at the time of estimation) are used to calculate the index of selection value [5][6][7][8][9][10]. In Germany (Bavaria), the index estimation includes the indices of the fat thickness at the point of reaching the live bodyweight of 85-95 kg for sows and 130-150 kg -for sires. Exterior data are estimated additionally. The animals with the highest index, complying with minimal exterior requirements, are used in further selection work. In the USA, the estimation of a group of progeny for each sire is conducted with the estimated index, in which the trait of fat thickness takes 30 %, the area of "loin eye" -10 %, average daily gain -30 %, meat quality -20 %, composition steadiness -10 % [11][12][13].
Scientists suggested an approach to estimating animals by the indices of reproductive ability, fattening traits and comprehensive evaluation of fi nishing and meat traits [14][15][16]. The structure of these indices is the same for all the breeds and holdings, there are some changes only in average data of productivity in holdings and the estimated actual weight coeffi cient, which allows using these indices in any country of the world.
It is relevant to estimate the weighing coeffi cients of traits, composing the index structure separately for each herd (breed). The index estimate allows isolating the best animals in the herd for further use [1].
The selection of parental pairs by the value of progeny index involves a so-called lower limit of development for each trait under selection. The animals, which have reached and exceeded the set minimal limit, are recommended for further reproduction. The minimal selection limit sets minimal requirements to the development of the trait under selection [1,15].
In modern conditions of intense pig breeding, the hybridization system is based on using maternal and paternal breeds for two-breed and multibreed crossing. Thus, our studies were aimed at estimating genetically and mathematically grounded target limits of selecting pigs for further generations. They were used as a basis to select local progeny with the best value of selection index for further increase in productive traits of animals.
The conditions of feeding and keeping were identical for all the groups of animals within each experiment and corresponded to zootechnic norms with the consideration of age, live bodyweight, and physiological state. The animals were fed with concentrates. The gender ratio of animals in groups was ♀50 % and ♂50 %, the number of pigs in each group for studies was proportional.
To enhance the effi ciency of selecting pigs of different breeds, selection indexes of reproductive, fattening, and fi nishing and meat traits (J 1 -J 3 ) were used, which were built by the method of standardized deviations according to M.V. Mykhailov with the consideration of selective-genetic parameters in the estimation of productive traits of pigs: by the reproductive ability: where: k 1 -k 2 -actual weighing coeffi cients of traits; x 1 -multiple pregnancy, animals; x 2 -weight of pen at the moment of weaning, kg; by fattening traits: where: k 1 -k 3 -actual weighing coeffi cients of traits; x 1 -age of reaching the live bodyweight of 100 kg, days; x 2 -expenses for fodder per 1 kg of gain, fodder units; by fi nishing and meat traits: where: k 1 -k 3 -actual weighing coeffi cients of traits; x 1 -age of reaching the live bodyweight of 100 kg, days; x 2 -expenses for fodder per 1 kg of gain, fodder units; x 3 -fat thickness above 6-7 thoracic vertebra, mm; х 4 -area of "loin eye", sq.cm.
Actual weighing coeffi cients, included into selection indexes, were estimated by the ratio of the selection weight trait to the selection effect.
The productivity indices of pigs, included to the estimation of selection indexes, were determined by common methods, elaborated by the Institute of Swine Production n.a. O. V. Kvasnytsky, NAAS in 2005. The reproductive ability of sows in terms of multiple pregnancy was estimated by the number of live newborn piglets per littering, the weight of pen at the time of weaning was estimated after 30 days.
The fattening traits of pigs were estimated by the age of reaching the live bodyweight of 100 kg and the expenses for fodder per 1 kg of gain.
During the control slaughter of pigs with the live bodyweight of 100 kg, fat thickness was measured INDEX EVALUATION OF PIGS AND DETERMINATION OF SELECTION LIMITS between 6 and 7 thoracic vertebrae of a cooled semicarcass in vertical position. The area of "loin eye" was determined on the cross section of the longest spine muscle between 1 and 2 loin vertebrae. The contour of a "loin eye" was transferred to the tracing paper to estimate the value of this index, multiplying width by length and coeffi cient 0.8.
Young sows and emasculated boars were used while slaughtering four-breed progeny.
To achieve more accurate differentiation of pigs by productivity indices of progeny, target limits of selecting animals were defi ned by the formula [15,17]: where M X -average value of the traits in the studied herd; d -standard deviation for the experimental herd; TR -table value according to Le Roy with the given percentage of animal selection.

RESULTS AND DISCUSSION
To select highly productive two-breed animals for further use in the crossing, we estimated selection indexes with the weighing coeffi cients of traits for each group of pigs (Table 1-3).
Constructing three kinds of indexes for estimation and fi nal selection of two-breed pigs by the results of littering and control fi nishing and slaughter is conditioned by changeable priorities of modern pig breeding, thus, they may be used both in the complex and individually as an independent instrument of estimating the initial parental forms with the purpose of obtaining progeny with desired level of productivity.
In addition, the estimation of animals by indices J 2 and J 3 is comprehensive, and, depending of the index structure, weighing coeffi cients for the trait (%) are different. Their increase in index J 3 was observed for meat indices of productivity.
Taking into consideration average values of productivity for the leading groups, we estimated selectivegenetic parameters by the main traits of reproductive ability, fi nishing and meat productivity.
All the selective-genetic parameters for further indexes were estimated in the same way.
The average values for the herd by the age of reaching the live bodyweight of 100 kg were in the range of 173.96-183.54 days, by the expenses per 1 kg of gain -from 3.55 to 3.42 of fodder units. The selection relevance was from 30.98 % in the group ♀D × ♂P to 49.03 % in pigs of the group ♀WL × ♂WL.
The average values for the herd in terms of the age of reaching live bodyweight of 100 kg were in the range of 175.25-180.25 days, in terms of the expenses for fodder per 1 kg of gain -from 3.55 to 3.50 of fodder units, in terms of fat thickness above 6-7 thoracic vertebra -from 20.50 to 16.25 mm, in terms of the area of "loin eye" -from 33.93 to 40.33 sq.cm. The selection relevance by all the indices was from 2.41 % in the group ♀WL × ♂WL to 63.09 % in pigs of the group ♀P♂D.
The selection indexes for the evaluation of pigs by the reproductive ability were estimated, the index J 1 looks as follows for interbred combinations: The comparative analysis of the evaluation of productivity of sows confi rmed that high reproductive ability in terms of all the indices was demonstrated by sows of the group ♀WL × ♂WL, and sows on the combination ♀WL × ♂L.
The traits of fattening and meat productivity of pigs are determined by the amount and quality of meat, obtained from them. It is important to produce maximally possible volumes in the shortest period of time. High gains become the prerequisite of success on this way. Thus, while estimating the fattening productivity, it is relevant to pay attention to average daily gains and expenses for fodder.
The estimation of four-way progeny by selection indexes allowed ranging them depending on the level of productivity with the consideration of genotype and selecting the most effi cient parental forms. The evaluation of the reproductive ability involved the indexes, developed for the maternal form ♀WL × ♂WL and ♀WL × ♂L, and that of fattening and meat traits of the progeny -indexes, developed for local boars ♀D × ♂P and ♀P × ♂D.
Ranging of animals by the value of indexes allowed calculating the minimal target limits at different intensity of selection with the purpose of selecting boars and sows with anticipated indices of productivity for further use in pork production. The results of estimates at different percentage of selection are presented in Table 4. At 20 % selection, the minimal value of the reproductive ability index for the control group was 238.7 points. The animals of group ♀(WL × L) × × ♂(D × P) and ♀(WL × L) × ♂(P×D) had 369. 16  It is reasonable to use the sows, which correspond to the estimated target limits by the indices of reproductive abilities at the set level, while crossing the suggested combinations.
The minimal target limit while selecting sires by the fattening traits of progeny within the 20 % selection was from 50.57 to 255.65 points. Therefore, a group of purebred animals included 8 animals, the group ♀(WL × L) × ♂(D × P) -9 animals, and ♀(WL × L) × × ♂(P × D) -13 animals. Taking the obtained data into consideration, it is reasonable to select White Large boars, the progeny of which reached the weight of 100 According to the indices of the index estimation by meat and fattening traits, it is reasonable to select White Large boars, the progeny of which reached the weight of 100 kg at least after 170 days with the expenses for fodder of 3.6 fodder units, fat thickness of 27 mm, the area of "loin eye" of 30.5 sq.cm. These productivity indices of the progeny for boars of the combination ♀D × ♂P should be at least 178 days, 3.1 fodder units, 15 mm, 44.5 sq.cm. respectively. As for the animals of the crossing variant ♀P × ♂D -174 days, 3.5 fodder units, 14 mm, 39 sq.cm.

CONCLUSIONS
Index evaluation of pigs in the crossing, based on the indices of reproductive, fattening, fi nishing and meat traits of the progeny, allowed ranging them by the index values. The estimates allowed setting minimal target limits of selecting animals and optimizing the selection of parental pairs with estimated productivity: in case of 20 % selection by multiple pregnancy with at least 11 animals, the area of "loin eye" -30.5-44.5 sq.cm. It would be reasonable to select the animals, the productivity of progeny of which is above the determined limit, for further breeding from 238.70 to 606.94 points. This selection should be performed in each specifi c population.

ACKNOWLEDGMENT
The authors would like to thank the staff and the head of Freedom Farm Bacon Limited Liability Company, Oleksandr Pokhvalenko.

This article does not relate to any studies using humans and animals as investigation subjects.
Confl ict of interests. The authors deny any confl ict of interests.