Reproductive qualities and the manifestation of different forms of heterosis in sows of English origin of different breeding directions during purebred breeding, crossing, and hybridization

The work evaluated the productivity indicators of the maternal breeds of Large White and Landrace pigs under the conditions of their purebred breeding and crossing, the results of purebred breeding of pigs of the synthetic line PIC-337, and the productivity of crossbred animals of the maternal breeds of Large White and Landrace when hybridized with boars of the artificial line PIC-337. It was found that sows of maternal genotypes outperformed their counterparts selected for paternal traits in the total number of piglets born by 29.2–56.8 %, multiparity by 32.3–59.9 %, litter weight at birth by 27.3–46.1 %, number of piglets in the litter at weaning by 28.8–51.6 %, litter weight during this period by 10.7–27.9 %, and had a 1.8–4.0 % lower proportion of non-viable piglets at birth. At the same time, they were inferior to sows of the terminal line in terms of high fertility – 5.0–8.6 %, average daily and absolute gains - 17.0–29.8 %, and the weight of one piglet at weaning – 15.6–25.4 %, but they were superior to them in terms of complex indices of reproductive qualities – 22.2–49.9 %. It has been proven that sows of maternal genotypes-half in their direct and backcrossing surpassed their counterparts in their purebred breeding: by 5.5 % in the total number of piglets born, by 3.2 % in multiparity, by 1.9 % in large-scale fertility, by 5.2 % in the mass of the piglet nest at birth, by 1.9 % in their number at farrowing, by 3.2 % in average daily and absolute gains, by 3.0 % in the mass of one piglet and by 4.9 % in the mass of the nest at this time. At the same time, they had 1.1 % worse piglet survival during the suckling period and a 2.1 % higher share of stillborn piglets. In terms of complex indicators of reproductive qualities, they surpassed their purebred counterparts by 2.5–3.6 %. The advantages of hybrid piglets over inbred ones were established in terms of the total number of piglets born by 5.1 %, in terms of multiparity by 5.0 %, in terms of the weight of the piglet nest at birth by 1.0 %, in terms of the number of piglets at weaning by 5.9 %, in terms of the weight of one piglet by 2.8% and by 8.9 % in terms of the weight of their nest at this time, by 4.3 % in terms of average daily and absolute gains. At the same time, they were inferior to the first in terms of high fertility by 3.8 % and had a 2.1 % higher share of stillborn piglets. When hybridizing crossbred sows of the Large White breed and Landrace breeds of accessions (♀WB×♂L) and (♀L×♂WB) with boars of the synthetic terminal line RIS-337, higher values of hypothetical heterosis and specific heterosis were established for most signs of reproductive performance. In contrast, the proper and general form of heterosis with this breeding method was manifested less frequently and was less pronounced.