ENERGY-METABOLISM DURING LATE-GESTATION AND LACTATION IN MULTIPAROUS SOWS IN RELATION TO BACKFAT THICKNESS AND THE INTERVAL FROM WEANING TO1ST ESTRUS

Ten crossbred, fourth or fifth parity sows were divided into 2 groups - high (H) and low (L) - according to their backfat thickness 9 days b efore parturition. Body weight, backfat thickness and litter weight we re recorded repeatedly during a 5 week lactation period. The length of the interval from weaning to first oestrus was also noted. All sows w ere fed a commercial diet (11.9 MJ/kg, 14.5% crude protein). During ge station, daily food intake was 2.2 kg/sow, while during lactation it w as 3.0 kg/sow plus 0.4 kg/piglet. Blood samples were drawn on day 9 be fore parturition and on days 2,7,14 and 21 of lactation. The samples w ere analysed to determine concentrations of glucose, urea nitrogen, cr eatinine, triglycerides, free fatty acids and beta-hydroxybutyric acid . In both groups, concentrations of free fatty acids and urea nitrogen were low on day 9 before parturition while those of triglycerides wer e high, indicating anabolism regardless of backfat thickness. During t he first week of lactation, concentrations of free fatty acids increas ed in the H-group but not in the L-group, and concentrations of urea n itrogen were higher in the H-group. These differences, together with t he greater loss of weight observed in the H-group, indicate that catab olism of maternal fat and protein depots was more pronounced in the H- group than in the L-group during this time. On day 14 of lactation, bo th groups showed equally tow concentrations of free fatty acids, decre asing creatinine concentrations and stable triglyceride and urea nitro gen concentrations. Furthermore, weight loss during the second and thi rd weeks of lactation was low in both groups. These facts, taken toget her, indicate that the catabolic rate was decreasing in both groups du ring this period. No differences in return to oestrus interval were no ted between the groups. The present study indicates that under a restr icted feeding regime the catabolic rate during the first week of lacta tion is higher in sows with higher backfat thickness in late gestation . As lactation progresses, a more balanced metabolism is achieved rega rdless of backfat thickness, which may tend to reduce differences in r eturn to oestrous interval.