Wendy Stewart (nee Faulkner) 1995. Factors affecting gastrointestinal development in growing ranched silver foxes. Supervisor: Dr. D. M. Anderson.
A study of young growing ranched foxes (birth to 170 d) was conducted to examine factors affecting gastrointestinal development in animals maintained under typical commercial farm conditions. Very little is currently known of the development of the digestive system of this species. To achieve more effective and economical feeding of growing silver foxes, additional information is required. A total of 64 silver foxes (32 per sex) were sampled over 16 time periods by serial slaughter technique. Four animals were sacrificed per timing. Sampling occurred at 10 d intervals beginning at birth and continuing to 120d. Three additional sampling occurred to investigate the effects of early and late weaning and to verify gut maturity at 170 d. All feed (commercial pellets with 20% meat byproducts for foxes under 40 d) and water ad libitum. Chromic oxide was used (1%) as an inert feed marker for the purposes of digestibility calculations. Sexual dimorphism in body weight was evident at 50 d with the males generally being heavier than the females. Body growth and growth of the organs increased most rapidly during the first 30 d. During this time, body length and weight increased by 3.43 and 22.7% per day. Between birth and 170 d, the foxes grew from 13.8 to 69.0 cm in length from 92.8 to 6106 g in weight. The organs approximated adult size by 90 d. The relative size of all abdominal organs (except the stomach) compared to body size was reduced as the foxes approached maturity. Even with body weight used as a covariant, the effect of sex was significant for the weights of the stomach, kidney and liver. These organs in the male foxes tended to be heavier than those in the females. Measured activity of pancreatic trypsin (per gram of pancreas) was the same for all age groups studied. Relative activity of trypsin (expressed as units per gram of body weight or per gram of metabolic body weight) was significantly higher in foxes at birth than at any other age studied. Foxes weaned at 30 d and reared to 40 d on exclusive non-milk feed suffered from no obvious setbacks and tended to grow better than the regularly weaned 40 d foxes left with their dams. Body size and size of abdominal organs were somewhat higher in these foxes than in regularly weaned animals of the same age. Activity of pancreatic trypsin (per gram pancreas) was not affected by this early weaning. Apparent digestibility in the stomach and jejunum did not differ among age groups studied. Across all age groups apparent digestibility in the stomach averaged 43.4, 16.2, 16.8 and 15.8 % for dry matter (DM), organic matter (OM), crude protein (CP) and the energy fraction (EF) respectively. In the jejunum, apparent digestibility averaged 70.5, 38.2, 51.7 and 30.7 % for DM, OM, CP, and EF respectively. Apparent digestibility of DM in the ileum, CP in the caecum as well as DM and CP in the colon were significantly different among the age groups studied, however these differences occurred in foxes less than 100 d of age and mainly concerned comparisons with the early weaned 40 d foxes. Apparent digestibility of DM had neared completion (97.9 %) in the jejunum and digestibility of CP was essentially complete in the ileum. Apparent digestibility of OM and EF were further increased in the colon. Significant reductions in apparent digestibility of CP in the caecum indicate that endogenous protein secretions and microbial action in the caecum of the foxes may have been substantial. Although body and organ size changed greatly between birth and maturity, trypsin activity per gram of pancreas was unchanged. Apparent digestibility of DM, OM, CP and EF differed in certain sites within the tracts but only for a select few age groups. This study was successful in providing valued baseline data regarding gastrointestinal development in the young silver fox.