The effects of cold stress, as measured by minimum ambient temperatures at day(s) of mating, on conception rate (CR), and litter size were studied in purebred Yorkshire and Lacombe swine populations maintained at the Canada Agriculture Research Station, Brandon, Manitoba (49°50′N, 99°57′W). One hundred and sixty-nine Yorkshire and 160 Lacombe boars were used to hand mate 406 Yorkshire gilts (505 estruses) and 460 Lacombe gilts (558 estruses). All gilts were bred on the 1st day of standing estrus, and gilts still in estrus the next day were mated a second time with the same boar. All matings were carried out in December and January over an 8-year period. Gilts and boars were housed separately in outside pens with wooden cabins as shelter. The data were grouped on the basis of minimum temperature on day(s) of mating into the following arbitrarily chosen temperature ranges: < −25, −25 to −18, −17 to −10 and > −10 C. The CR for gilts mated once were 81, 73, 58, and 56%, respectively, for the four temperature ranges. Corresponding values for the gilts mated more than once were 88, 81, 73, and 65%. Chi-square analyses indicated that CR were dependent (P < 0.01) on ambient temperatures. Repeat mating per estrus increased CR of the Yorkshire gilts by 12.5% (77.9 vs. 65.4%) and of the Lacombe gilts by 11.3% (80.4 vs. 69.1%) as compared with single mating. In both breeds, repeat mating increased litter size by 0.3 piglets (9.2 vs. 8.9, P = 0.10) over single matings. Litter size was not influenced by cold stress at time of mating.
Reduced reproductive performance associated with warmer ambient temperatures during incubation in a winter-breeding, food-storing passerine
