In Part A of Study I, six groups of female standard mink were fed (once daily) either 5, 10, or 15 mcgm. of DES/mink/day or a forage antiestrogen extract at levels of 5, 10, or 15 gm. equivalent of alfalfa/mink/day. In Part B, seven groups of female pastel mink were fed (once daily) 15 mcgm. of DES/mink/ day prior to and at various stages of the gestation period. Also, the antiestrogen extract was again fed (once daily) at levels of 5, 10, or 15 gm. equivalent of alfalfa to three groups of female pastel mink after implantation of the fertilized egg had occurred. From the results of Part A and B of Study I it is evident that DES at levels as low as 5 to 15 mcgm/ mink/day caused complete reproductive failure. At the 15 mcgm. level it is possible to prevent or disrupt pregnancy if the hormone is administered for at least one week during the period starting one week before breeding and ending 30 days prior to parturition. The forage antiestrogen at levels between 5 and 15 gm. equivalent of alfalfa reduced the number of kits per litter from 5.8 to 1.6. The feeding of various levels of DES or the antiestrogen extract did not adhere to a dose/response relationship either in interrupting pregnancy or reducing the number of kits per litter. The DES, fed at levels of 5, 10, or 15 mcgm./mink/ day was a more potent antifertillty agent than the forage antiestrogen fed at levels equivalent to 5, 10, or 15 gm. of alfalfa. In Part A of Study II, 200 mature male and female mink of a variety of colour phases were divided into five groups. The groups were fed (twice daily) rations varying in crude protein (36.6 to 44.8%, on a d.m. basis) and gross fat (21.3 to 28.9%, on a d.m. basis). In Part B, 280 pastel and standard kits (6-7 wks. old) were fed (twice daily) rations varying in crude protein (39.0 to 54.3%, on a d.m. basis) and gross energy (5.20 to 5.52 Kcal/gm. dry feed). From the results of Part A and B of Study II it is evident that rations containing 35 to 40% crude protein and 20 to 25% fat, on a dry matter basis, are satisfactory for the late growth and maintenance requirements of mink. The mean apparent digestibility coefficients obtained in these studies for dry matter, protein, fat, and energy are 66.38, 74.05, 87.20, and 73.74%, respectively. As the apparent digestible energy (A.D.E.) was raised from 353.4 Kcal/100 gm. dry matter to 426.0 Kcal/100 gm. and as the apparent digestible nitrogen (A.D.N.) level reached 4.980 gm/100 gm dry matter, the early growth of both male and female mink was improved. Maximum early growth rate was obtained in kits when the ration contained 85.54 Kcal of A.D.E./gm A.D.N. (13.6 Kcal gross energy/gm gross protein). Also, increasing A.D.E. content in the diets had a definite protein-sparing effect. Maximum nitrogen retention was obtained when the diet contained 426.0 Kcal of A.D..E./100 gm. of dry feed. Finally the results suggest that the growing male kits (from 6-28 weeks of age) were capable of utilizing feeds more efficiently than female kits of the same age. / Land and Food Systems, Faculty of / Graduate

Lead, cadmium, zinc and copper concentrations were determined in bone, kidney and liver samples of mink (Mustela vison) trapped during 1981-83 in Virginia. Ages were determined to obtain population information. The literature on delayed implantation in mink was reviewed. Lead and cadmium concentrations in all tissues were generally low. Approximately 50% of bone samples and less than 10% of kidney and liver samples had detectable lead concentrations (>1 ug/g). Mean detectable bone lead concentrations (ug/g d.w.) were 2.90 and 2.48 during 1981-82 and 1982-83, respectively. Cadmium was detected (>0.1 ug/g) in all kidney samples. Mean kidney cadmium concentrations (ug/g d.w.) were 1.21 and 1.02 in 1981-82 and 1982-3, respectively. Lead and cadmium accumulated (p < .05) with age. Cadmium concentrations were higher (p < .05) in Southwest Virginia than in other areas. Mean zinc and copper concentrations were comparable to those in other mammals and do not appear to pose any toxic threat. Bacula, femurs, radiographs of canine teeth, and cementum annuli of second premolars were examined for aging purposes. The first 3 methods were confusing in many samples, apparently due to transition from juvenile to adult characteristics. A systematic method for aging winter-trapped mink was developed. Approximately 60% of mink trapped during both seasons were juveniles. The age-specific survival rate was very low (0.292) for juveniles, increased for 2 year-olds (0.719) and then declined quickly for subsequent years. The male to female ratio was very high (approximately 3:1) probably reflecting trapping bias. / Master of Science