Use of CAT scan to determine mammary gland development of sows injected with growth hormone releasing factor during gestation and (or) lactation

Abstract

Fifty-two Yorkshire × Landrace gilts were allotted to: (1) saline injections (CTL; n = 17) thrice daily during gestation (day 100 to parturition) and lactation (days 3 to 29); (2) s.c. injections of 12 mg of GRF (1-29)NH2 thrice daily from day 100 of gestation to parturition (GEST; n = 12); (3) s.c. injections of 12 mg of GRF thrice daily from days 3 to 29 of lactation (LACT; n = 11); and (4) s.c. injections of 12 mg of GRF thrice daily during gestation (day 100 to parturition) and lactation (days 3 to 29) (GEST-LACT; n = 12). All sows were slaughtered on day 30 of lactation and mammary glands were excised and stored frozen at -20°C. Mammary development was measured on half of the thawed mammary gland with CAT scanning, and standard dissection and previously published biochemical measurements of mammary development were used to assess the contralateral half; correlation analyses were used to compare the two approaches. Volume of parenchymal tissue of GEST-LACT sows was 19% smaller than that of sows subjected to other treatments (GEST × LACT interaction, P = 0.01). Total mammary gland volume (r = 0.68; P = 0.002) and extraparenchymal tissue volume (r = 0.77; P < 0.001) measured by CAT scanning were correlated with extraparenchymal tissue weight obtained by tissue dissection. However, none of the CAT scan measurements were correlated with parenchymal tissue weight (P > 0.1). In conclusion, exogenous GRF given to sows during lactation affected cell volume/differentiation of the mammary gland. For mammary gland assessment in lactating sows, the CAT scan technique accurately measured the weight and volume of extraparenchymal tissue but not parenchymal tissue mass. Key words: Sows, mammary gland, mammary development, CAT scan, growth hormone-releasing factor, lactation