VISCERAL CHARACTERISTICS OF THREE BREEDS OF SWINE AND THEIR CROSSES

Two hundred and forty-nine pigs representing all possible two-breed crosses of Minnesota no. 1 (M), Pietrain (P), and Yorkshire (Y) breeds were slaughtered over five developmental stages (35 days of age, 22.5 kg, 45.0 kg, 67.5 kg, and 90 kg liveweight). The objectives were to determine how reciprocal differences and heterosis were affected by advancing maturity, to examine breed differences, and to determine growth curves for certain visceral measurements. Reciprocal differences were observed to show two distinct patterns. The first was characterized by an increase in magnitude relative to stage of development and the second was parabolic. Statistically significant heterosis estimates for these traits were the exception rather than the rule. The following breed differences were found: M > P > Y for large intestine length and leaf fat weight, (M = Y) > P for liver weight, P > Y > M for spleen weight, M > (P = Y) for kidney weight, M > Y > P for stomach weight and M > (P = Y) for small intestine wet weight. The growth curves for the viscera indicated that the intestinal tracts were the first to complete their growth, the internal organs grew relatively slower than liveweight increased, and the majority of leaf fat deposition occurred as the animals approached 90 kg live-weight. Key words: Reciprocal differences, heterosis, breed differences, viscera, growth curves, pigs