Growth of nursing pigs related to the characteristics of nursed mammary glands

The purpose of this study was to determine growth performance of nursing pi gs in relationship to teat order and to observe teat preference by pigs. In the first experiment, litter size of 13 primiparous sows was adjusted to 9 (8.7 +/- 1.5) pigs and teat order of each litter was observed on the day b efore slaughter. Another group of eight sows was killed on d 0 (within 12 h after farrowing). In the second experiment, litter size was adjusted to 9 (8.9 +/- 1.4) pigs for 20 primiparous sows and teat order for each litter w as observed 1 d before slaughter. The weights of sows and individual pigs w ere recorded at farrowing, weekly, and on the day before slaughter. Mammary glands were collected at slaughter on d 21 of lactation and trimmed of ski n and the extraneous fat pad. Individual glands were separated, weighed, an d ground for measurement of dry matter, dry fat-free tissue, protein, fat, ash, and DNA contents. Middle mammary glands had the greatest wet weight am ong glands obtained within 12 h after weaning (P < .05). For sows completin g the 21 d lactation, only glands known to have been nursed were included i n the data sets. Greater than 60% of the first four pairs of mammary glands were nursed, and less than 40% of the seventh and eighth glands were nurse d by pigs during lactation. Pigs that nursed the first five pairs of anteri or glands gained faster than pigs nursing the remaining glands. The first f ive pairs of anterior glands had greater wet and dry weights, and greater p rotein and DNA contents compared with the remaining glands. Pigs that nurse d heavier glands gained weight faster (r = .68, P = .0001), and those heavi er glands contained greater amounts of protein (r = .98, P = .0001) and DNA (r = .66, P = .0001). Variation in weight gain of pigs nursing the anterio r and middle glands was not statistically significant. The functional super iority of anterior and middle glands was positively correlated with body we ight gain of nursing pigs.