Voi 6 (1997); SO5-312. Effect of feeding level during autumn and winter on breeding weight and result in single and pair-housed minks Hannu Korhonen, Paavo Niemelä Agricultural Research Centre ofFinland, Fur Farming Research Station, FIN-69100 Kannus, Finland. e-mail: hannu.t.korhonen@mll.fi The effect of feeding intensity (standard vs. restricted ration) and housing system (males and females kept singly vs. animals kept in male-female pairs) on breeding body condition and whelping was studied in farm standard mink ( Mustela vison). Dietary interventions lasted from 20 Septemberto 31 January. The maximum body weights of minks fed the standard ration were higher than those fed the restricted ration, and, the weights ofanimals housed in pairs were higher than those of animals housed singly. Daily feed intake was only slightly lower for singly-housed minks. Singly-housed females came on heat slightly later than females housed with a male. No statistically significant differences were found in whelping success due to feeding intensity orhousing system. Whelping results tended, however, to be best for the females on restricted feeding and housed with a male (4.1 kits/mated female), and poorest for the females fed the standard ration but housed singly (3.4 kits/mated fe- male), The conventional housing set-up, in which males and females are housed in pairs, is therefore recommended, but feeding from autumn onwards should be restricted. Key words', breeding performance, farm mink, feeding regulation, grouping, obesity ntroduction After weaning, farm-raised mink kits (Mustela vison ) are fed an energy-rich diet because high feeding intensity is usually considered necessary if they are to produce large furs of good pelt quality (Berg 1986). This practice often leads to obese animals in autumn and early winter. The reproductive success offat minks, however, tends to be poor. High pre-mating live weights would particularly increase the frequency of barren fe- males and kit losses, thereby leading to smaller litters (Sanne and Åhman 1966, Jorgensen and Glem-Hansen 1972,Tauson 1985). Animals in- tended for breeding are therefore usually slimmed before the breeding season to what is considered good individual breeding condition. This can, however, result in impaired reproduc- tive capacity, as observed in yearling mink fe- males (Tauson and Alden 1984). Furthermore, it is not necessarily easy to achieve the intended © Agricultural and Food Science inFinland Manuscript received December 1996 305 AGRICULTURAL AND FOOD SCIENCE IN FINLAND https://www.c-info.fi/en/info/?token=vPlvpqXcAxJYZUEY.QCki7FFYP7-lbWLeuNGOlQ.qJRx18t4jbYebO9CKySncgV79jEI1xrg-6ZL5ri7lTCEnyFcKXE0ts0KOuEie0YxtPe5Rsl4IImVbD8OVh6oJfJMYhFRG6WTSMak_i-oN6p-B81eF08QUtYr2mmPvzdmHyBBpUC7-HFSfJXZ4jqqzoedWm3PmOirhZ9JWA4RLvpB1w8obAkz-JROSnJogVayZiJoh4wYLWxw9LHpmIKNEZKxlNKbDi0RaqwF7OuSXLbmV7qmk83zMQ_O7Jmf1cd1OKWoLw1cSSKo5PgOWT-8j9Hu_HarXftvIQ Korhonen, H. & Niemelä, P. Effect offeeding on breeding weight and result in minks body condition as some animals respond poorly to rapid conditioning or flushing. The mink exhibits pronounced sexual dimor- phism, males being significantly larger than fe- males (Iversen 1972, Moors 1980, Korhonen et al. 1983). Consequently, males consume more feed than females (Korhonen and Niemelä 1993). Minks are conventionally housed in male-female pairs until pelting, a housing arrangement that has been thought to guarantee normal growth and fur development. On the other hand, animals housed singly do not have to compete against their cage partners for feed. One would also ex- pect it to be easier to regulate body condition by individual feeding ofsingly-housed animals (Kor- honen and Harri 1990, Korhonen et al. 1990). Thus, irrespective of feeding intensity, the body condition of farmed minks would be affected by the housing arrangement within a cage. The aim of our study was to establish, first, whether the need for intensive slimming before breeding could be eliminated by decreasing the feeding intensity offarmed minks from Septem- ber onwards and, second, whether this practice would improve the breeding result. The compar- isons were made between animals housed in pairs, that is, a male with a female, and animals kept singly. Material and methods General management The experiments were carried out at the Fur Farming Research Station of Kannus, western Finland. Juvenile dark minks (standard geno- type), all found to be plasmacytosis-negative according to the counter-immuno-electrophore- sis test (Hansen 1974), served as experimental animals. The minks were housed in standard rear- ing cages, measuring 40 cm wide x 60 cm long x 40 cm high, in two-row sheds. A wooden nest- box (22 cm wide x 30 cm long x 40 cm high) provided with sufficientbedding was connected to each cage. Water was freely available from an automat- ic dispenser system. The minks were weighed at monthly intervals. Experimental groups and feeding Two feeding intensity levels were used: (1) a standard ration (S), with the amount of feed ad- justedto conventional daily consumption (slight- ly lower than ad libitum), and (2) a restricted ration (R), amounting to 90% of the standard ration (see Fig. 1).The experimental feeding last- ed from 20 September to 30 January. Thereafter, the experimental groups were fed at the same level (males 230 g/animal/day; females 150 g/ animal/day). The freshly mixed mink feed was manufactured at a local feed kitchen (Kannus Minkinrehu Ltd.). The animals were fed 6 days a week at about 1 pm. Feeding was omitted on Sundays. Leftovers were collected and weighed on a groupbasis in order to calculate daily feed intake. The feed mainly consisted of slaughter- house offal, fish and cereals, and its composi- tion (Table 1) therefore met the conventional Scandinavian Standard Recommendations (Berg 1986). Three sub-groups were formed within above feeding intensity levels; (1) females (N=72) housed singly throughout the study period (cod- ed SI, Rl), (2) males (N=42) housed singly throughout (coded S2, R2), and (3) males and females housed in pairs (N=72 couples) until 10 December, but thereaftersingly (coded S3, R3). S in codes means standard feeding and R restrict- ed feeding. Mating routines The animals were mated between 7 and 23 March. Before the breeding season, the testicles ofall males were palpated. Those with hypopla- sia, that is, with very small or otherwise abnor- mal testicles, were excluded. All experimental females were left for breeding, but most of the males were pelted (only the number of males 306 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Vol. 6 (1997): 305-312. Table I. Dietary and chemical composition of feed in different months of the year (from September to March). DM=dry matter, ME=metabolizable energy. Sep Oct Nov Dec Jan Feb Mar Ingredient, % Baltic herring 25 30 30 10 15 10 10 Cod offal 5 5 5 25 20 35 35 Beef offal 21 10 10 10 22 10 10 Broiler offal 12 10 10 6 - - Cooked wheat/barley 19 25 25 15 10 10 10 Soybean oil I 1.5 1.5 - - Dried protein mixture 4.7 - - 6 5 5 5 Meat meal -44---- Vitamins” 1 I 1 1 1.5 1.5 1.5 1.5 Chemical composition DM, % 37.5 36.2 37.5 35.3 31.0 31.6 31.6 In DM, % Ash 7.5 8.5 7.7 8.6 9.1 11.0 10.9 Protein 31.4 31.4 28.7 32.1 37.0 37.7 41.1 Fat 18.0 17.5 17.9 15.0 14.1 16.7 16.8 Carbohydrates 43.1 42.6 45.7 44.3 39.8 34.6 31.2 ME, MJ/kgDM 17.2 16.9 17.2 16.3 16.1 16.4 16.8 Calculated % of ME from Protein 31.7 32.8 30.4 34.4 39.3 38.1 42.2 Fat 40.8 40.4 42.4 36.0 33.1 37.7 38.6 Carbohydrates 27.5 26.8 27.2 29.6 27.6 24.2 19.0 a> l kg mixture contains: vitamin A, 500 000 IU; vitamin D3, 50 000 IU; vitamin C, 6000 mg; vitamin E, 4000 mg; vitamin K, 10 mg; vitamin 81, 1500 mg; vitamin 82, 600 mg; vitamin 812, I mg; choline, 2500 mg; pantothenic acid, 500 mg; nicotinic acid, 1000 mg; pyridoxin, 400 mg; folic acid, 50 mg; and biotin, 3 mg. needed for breeding were left, i.e. 23 per group). Singly-housed animals were mated with each other, and, animals housed in pairs were mated only within the group. During the first weeks, females were mated according to the 1 + 8 sys- tem, but later they were remated the day after the first mating (Tauson 1985). For females that rejected mating, the date of exposure was record- ed and another attempt was made within a few days. At whelping, the date of parturition and the numbers of live born and stillborn kits were recorded. The whelping result was calculated at birth and at 4 weeks. Statistics Statistical analyses were made using procedures (GLM procedure, NPARIWAY procedure) de- scribed by SAS Institute Inc. (1990). Animal live weights were analysed for effect of treatment group. The effects of feeding level and housing system on whelping results were tested by two- way analysis of variance. The whelping results of two groups were compared using the Mann- Whitney U-test. The results are presented as means and standard deviation (SD). 307 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Korhonen, H. & Niemelä, P. Effect offeeding on breeding weight and result in minks Results Feed consumption The feed intake of the animals housed in cou- ples (from 20 September to 10 December) tend- ed to be slightly higher (S3: +1.8%, R3: +3.5%; not significant) than the calculated value of two separate individuals housed singly. The feed con- sumption of the treatment groups declined dur- ing a 2-week-long cold spell in November, but increased during a period of high ambient air temperatures from December to mid-January (Fig. 1). After mid-December when all experi- mental animals were kept singly in their cages, Table 2. Mating results of treatment groups. S = standard ration, R = restricted ration. 1 =singly-housed, 3 =housed in pairs. N = number of animals. Animals were mated be- tween 7 and 23 March. Group Mean mating date Breeding 9 Mated 9 N N % SI 15 March 69 65 94.2 S 3 13 March 71 70 98.6 Rl 15 March 70 69 98.6 R 3 13 March 69 68 98.6 no marked differences in feed consumption were detected between the groups. During the entire winter period, the feed consumption rates in the female groups, SI, S3, R 1 and R3, were 806, 803, 752 and 763 kJ ME/animal daily, respec- tively, and in the male groups, S2, S3, R 2 and R3, 1227, 1243, 1192 and 1203 kJ ME/animal daily, respectively. Body weight development Animal live weights are shown in Figs. 2 and 3. Males fed the standardration reached their max- imum body weights in October (8 Oct).The body weights of singly-housed males (S2) were then lower (2096 ± 151 g; mean ± SD) than those of males housed with females (2233 ± 164 g). Breeding body weights (March 3rd) were about equal in S 2 males (2060 ± 139 g) and S 3 males (2107 ±lB7 g). Males on restricted feeding were heaviest in November, when R 2 males were somewhat lighter (2027 ± 112 g) than R 3 males (2152 ± 201 g). At the beginning of March, the animals of both groups had similar live weights (R2: 1993 ± 141 g, R 3 1982 ± 167 g). The body weights of all the female groups were at a maximum in October (SI: 1096± 143 g and S3; 1150 ± 128 g, Rl: 1025 ± 92 g and R3: 1062 ± 122 g). Singly-housed females were slightly lighter than females housed with males. The breeding body weights (3 March) of females fed the standard ration were equal (SI: 1025 ± 136 g vs. S3: 1036 ± 130 g). A similar result was found between females in restricted feeding groups (Rl: 896 ± 136 g vs. R3: 909 ± 146 g). Reproductive performance Mating routines proceeded normally, and fe- males whelped at the end of April or in the first half of May. Singly-housed females (SI, Rl) came into oestrus slightly later than females housed with males (Table 2). The percentage of females mated was lowest in the S 1 group (Ta- ble 2). Fig. 1. Food intake of singly-housed minks. S= standard ration, R = restricted ration. I=9, 2 =cf. 308 AGRICULTURAL AND FOOD SCIENCE IN FINLAND AGRICULTURAL AND FOOD SCIENCE IN FINLAND 309 The reproductive performance of the animals was rather poor in general. There were no statis- tically significant differences in whelping results (kits/mated female) between dietary groups (S: 3.5 kits vs. R: 3.9 kits) or housing system (sin- gly: 3.5 kits vs. couples 3.9 kits). The best whelp- ing result was for females housed with a male and fed restrictively (R3; 4.1 kits); the poorest whelping result was for singly-housed females fed standard rations (SI: 3.4 kits) (Table 3). Discussion Regulation of the farm mink’s breeding body condition by feeding interventions may not be easy in practice. One crucial problem is the great variation in temperatures between months and between years under out door conditions. Cold winters are known (Korhonen et al. 1989) to cause eating problems from time to time. The Table 3. Numberof females and reproductive results. S = standard ration, R =restricted ration, 1 =singly- housed, 3 = housed in pairs. SI S 3 Total Rl R 3 Total Breeding g 65 70 135 69 68 137 Whelped 9 46 48 94 51 57 108 Kits lost 3-3 1 23 Barren 9 17 22 39 16 10 26 Kits: at 4 wks 223 255 478 249 282 531 per mated 9 3.4 3.6 3.5 3.6 4.1 3.9 per whelped 9 5.2 5.3 5.3 5.0 5.1 5.1 Fig. 2. Weight trend of male minks. S = standard ration, R = restricted ration. 2 =singly-housed, 3 =housed inpairs. Note that January is omitted from Figures 2 and 3 because there were no weighings. Fig. 3. Weight trend of female minks. S =standard ration. R =restricted ration. 1 =singly-housed, 3 = housed in pairs. Vol. 6 (1997): 305-312. Korhonen, H. & Niemelä, P. Effect offeeding on breeding weight and result in minks stomach volume of the male mink is about 50- 70 ml, and can hold no more than 75 g of fresh feed at once. In fact, the mink eats on average 13 times in a 24-hour period during the winter (Korhonen and Niemelä 1993). Thus, feed of- fered at temperatures below -10...-15°C quick- ly becomes so firmly frozen that the mink can- not consume it all (Korhonen 1990) and inevita- bly loses weight before breeding. Moreover, when the ambient air temperature falls to-10°C, the mink has to double its metabolic rate, which further increases the mobilization of body fat (Korhonen et al. 1983). If, however, the winter is mild, minks often become too fat despite ef- forts to restrict their daily feed intake. In the present study, the marked changes in ambient air temperatures (cold period in November vs. warm period in December-mid-January) clearly affect- ed the feed intake of the animals. The cold peri- od in November was also the main reason why maximumbody weights were already reached in October. During mild winters, maximum body weights are usually achieved later (Korhonen et al. 1989, Korhonen 1990). Thus, the outcome of conditioning farm mink varies because of yearly and short-term changes in climatic con- ditions. The energy expenditure of the mink has been shown to increase by about 40% when the ambi- ent air temperature falls from +2O to O°C (Chwali- bog et al. 1980). A nest is therefore necessary for the mink, particularly during the winter. It can decrease the lower critical temperature of the mink by about 10-15°C(Korhonen and Har- ri 1984), and so provides marked energy savings. The insulation provided by the nest depends on (1) the bedding material, and (2) the number of animals in the nest. The expected energy costs for singly-housed minks are thus higher than those for mink couples. The same assumption can be made on the basis of the results ofAlden and Tauson (1979), for instance, who found that animals housed alone used more energy for ther- moregulation and therefore less energy for growth than those housed in pairs. This conclu- sion was also confirmed by our present finding that minks housed in male-female pairs had markedly higher body weights than singly- housed animals during October-December. Weight loss, from maximum body weight to breeding weight, in female farm minks has been shown to vary from 9% to 25% (Charlet-Lery et al. 1984. Korhonen 1990). Excessively high weight loss before breeding can impair the whelping result (Backus 1982, Tauson and Al- den 1984). Moreover, females that are still obese at the onset of the breeding season, often tend to have poorer whelping results than normal size females. Wenzel and Schicketanz (1980) found that females fed restrictively from October on- wards had better whelping success than those fed intensively, a finding that was also supported by the results of Tauson and Alden (1984). In our study, no significant whelping difference was noted between animals on restricted and stand- ard feeding, although there was an observable tendency for a better whelping result on the re- stricted treatment. However, the weight loss of females on restricted feeding was higher (13.4%) than that of animals on the standard ration (8.2%). The most probable reason why the dif- ference in whelping results between our experi- mental groups was not significant was that feed was not restricted sufficiently from February onwards and/or the restriction was not total in- dividually. Thus, the planned goal for body con- dition was not fully achieved. According to normal farming practice, minks are raised in male-female pairs until pelting. Our results showed that minks grow best in this con- ventional housing arrangement. This conclusion is consistent with the findings of Shackelton et al. (1977) and Alden and Tauson (1979) that an- imalsreared singly do not grow as well as those kept in pairs. Furthermore, Möller (1991) found that separation of pastel kits from September onwards resulted in a lower weight at pelting and a shorter skin length than in animals raised in pairs. In our study the best whelping result was achieved with pair-housed females. A parallel conclusion was drawn in the study of Heller and Jeppesen (1980), namely, that the level of sexu- al performance was higher in group-housed than in singly housed females. It can therefore be 310 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Vol. 6 (1997): 305-312. concluded that the conventional housing set-up, in which males and females are housed in the same cage, can continue to be recommended for use on farms. Acknowledgements. We thank the staff of the research sta- tion (Pekka Toikkanen, Aimo Joki-Huuki, Jaakko Huuki, Pekka Eskeli, Terho Lindqvist, Sanna Moisio) for their val- uable assistance in carrying out these experiments. We are also grateful to Pekka Siirilä for assistance with the com- puter work. References Alden, E. & Tauson, A.-H. 1979. Varierende burstorlek till mink under uppfödningsperioden. NJF's Subsek- tion förpelsdyr, Kungälv, Sverige, 10-13 Okt, 26 p. Backus, C. 1982. Relation between change in body weight and reproduction performance of female mink. Sci- entifur 6: 34. Berg, H. 1986. Rehutietoutta Turkiseläinkasvattajille. Tur- kiselåintutkimuksia 23. STKL ry, Vaasa. 99 p. Charlet-Lery, G., Fiszlewicz, M., Morel, M. & Rougeot, J. 1984. Variation au cours du cycle annuel de I’etat nutritionnel du vison male adulte. Annales Zootech- nology 33: 73-98. Chwalibog, A., Glem-Hansen, N., Henckel, S. &Thorbek, G. 1980. Energy metabolism in adult mink in relation to protein-energy levels and environmental tempera- ture. In: Proceedings of the Bth Symposium on Ener- gy Metabolism, Cambridge, Butterworths, London. EAAP Publication 26: 283-286. Hansen, M. 1974. Ny og bedre metode til påvisning af plasmacytose. Dansk Pelsdyravl 37: 209-211. Heller, K. & Jeppesen, L.L. 1986. Effects of social stress on circulating eosinophil leucocytes and sexual be- haviour in ranch mink. Scientifur 10: 167-170. Iversen, J. 1972. Basal energy metabolism of mustelids. Journal of Comparative Physiology81 A: 341- 344. Jorgensen, G. & Glem-Hansen, N. 1972. Forsög med forskellig fordingsintensitet i perioden for parring. Årbog fra Landökonomisk Forsögslaboratoriums efterårsmöde, Copengahen, p. 219. Korhonen, H. 1990. Seasonal regulation of weight loss in female farm mink. Journal ofAnimal Physiology & Nutrition 63: 109-113. & Harri, M. 1984. Thermophysical properties of nests of farm mustelids: thermal insulation. Scientifur 8: 285-290. & Harri, M. 1990. Social influences on productive per- formance in farm-raised polecats. Scientifur 14: 89- 94. Harri, M. & Asikainen, J. 1983. Thermoregulation of polecat and raccoon dog: a comparative study with stoat, mink and blue fox. Comparative Biochemistry & Physiology 74A: 225-230. - , Harri, M. & Mononen, J. 1989. Regulation of weight loss in male farm mink. Comparative Biochemistry Physiology 92A: 355-357. - & Niemelä, P. 1993. Winter energetics and feeding ac- tivities in the male mink. Scientifur 17: 137-142. - , Tukiainen, H. & Harri, M. 1990. Effects of group and sex combination on productiveperformance of farmed polecats (Musteta putorius). Zeilschrift fur Ver- suchtstierkunde 33: 79-83. Möller, S. 1991, Weight gain and hair chewing in mink kits placed singly or in pairs from September. Scien- tifur 15: 21-27. Moors, P. 1980. Sexual dimorphism in the body size of mustelids ( Carnivora): the roles of food habits and breeding systems. Oikos 34: 147-158. Sanne, S. & Ahman, G. 1966. Undersökningar av hullets och upfödningsintensitetens inverkan på minkhonar- nas reproduktionsförmåga. Landtbrukshögskolans meddelanden, Uppsala, Sweden, Serie A, 56: 34. SAS Institute Inc. 1990. SAS Procedures Guide. Ver- sion 6, Fourth Edition, Vol. 1, SAS Insitute Inc., Cary, NC. 943 p. Shackelton, D.M., Eccles, T.R. &Witts, W.D. 1977. Acom- parison of the effects of rearing mink singly and in pairs on their growth and reproductive performance. Scientifur 1: 6-9. Tauson, A.-H. 1985. Effect of nutrition on reproductive performance and kit growth in mink. PhD. Disserta- tion. Rapport 143, Uppsala, Sweden. 30 p. - & Alden, E. 1984. Pre-mating body weight changes and reproductive performance in female mink. ActaAgri- culturae Scandinavica 34: 177-187. - & Alden, E. 1985. Different feeding intensity levels to Mink. Swedish Journal ofAgricultural Research 15: 97-107. Wenzel, U. & Schicketanz, W. 1980. Correlation between nutritional state, breeding condition and reproductive performance of female mink. Scientifur 4: 23-28. 311 AGRICULTURAL AND FOOD SCIENCE IN FINLAND Korhonen, H. & Niemelä, P. Effect offeeding on breeding weight and result in minks SELOSTUS Syys- ja talviruokinnan vaikutus yksin ja pareittain kasvatettujen minkkien lisääntymistulokseen Hannu Korhonen ja Paavo Niemelä Maalouden tutkimuskeskus Tutkimuksen tarkoituksena oli selvittää miten kaksi erilaista ruokintatasoa (normaali vs. 10 % rajoitettu) vaikuttaa yksin ja pareittain (uros ja naaras) kasva- tettujen minkkien siitoskuntoon ja pentutulokseen. Ruokintajärjestelyt kestivät syyskuun 20 päivästä tammikuun loppuun. Pareittain olleet eläimet siirret- tiin erilleen joulukuun 10 päivä. Tulosten mukaan normaalisti ruokittujen minkkien raaksimipainot oli- vat suuremmatkuin rajoitetulla ruokinnalla olleiden. Vastaavasti pareittain kasvatettujen minkkien painot olivat suuremmat kuin yksin kasvatettujen. Yksinkas- vatettujen minkkien rehunkulutus oli hieman alhai- sempi kuin pareittain kasvatettujen. Yksinkasvatetut naaraat tulivat kiimaan hieman pareittain kasvatettu- ja myöhemmin. Ruokintataso ja kasvatustapa eivät vaikuttaneet lisääntymistulokseen, mutta tiettyä suun- tausta kyllä ilmeni. Pentutulos oli paras rajoitetusti ruokituilla pareittain kasvatetuilla naarailla (4,1 pen- tua/paritettu naaras) ja huonoin normaaliruokituilla yksinolleilla naarailla (3,4 pentua/paritettu naaras). Tämän tutkimuksen perusteella paras lisääntymistu- los saadaan perinteisellä tarhaustavalla missä uros ja naaras kasvatetaan yhdessä nahkontaan saakka. 312 AGRICULTURAL AND FOOD SCIENCE IN FINLAND