Rikke Fink

Energy intake and milk production in mink (MUSTELA vison)‐effect of litter size

Energy intake and milk production were measured in 12 mink dams raising litters of 3, 6 and 9 kits one to four weeks post partum by means of balance experiments and measurements of milk intake of the kits by the water isotope dilution technique. The dams were fed ad libitum on a conventional wet mink diet (DM: 323 g/kg; CP: 173 g/kg; ME: 4.4 MJ/kg). Milk samples collected from dams with corresponding litter sizes and lactation weeks, and body composition of kits nursed by these dams, were analysed for content of DM, ash, N and fat. The ME and drinking water consumption were higher in dams nursing 9 kits than in dams nursing 3 kits. The N and water balances as well as the live weight of dams were not affected by litter size. Daily milk production was higher in dams nursing 9 kits than in dams nursing 3 kits. The DM, N and fat content of the milk increased during lactation, but were not affected by litter size. Individual kit live weight was higher in litters of 3 than in litters of 6 and 9 kits four weeks post partum. The DM and fat content of the kits were lowest in kits from litters of 9 kits, whereas these kits had the highest protein content. Daily ME for maintenance of kits and the efficiency of utilisation of ME in milk for body gain were estimated to 356 kJ/kg0.75, kp ≈0.53 and kf ≈0.71, respectively. In conclusion, daily milk production increased with increasing litter size, but not in proportion to the number of kits, indicating that milk production limits the growth rate of the young. In the fourth week of lactation, milk production was not different between dams nursing 6 or 9 kits, indicating a maximum capacity.

Utilization of milk energy by suckling mink kits

A total of 36 mink dams and their litters of 3, 6 or 9 kits were used for determination of milk intake of the suckling young by means of deuterium dilution technique, and chemical composition of milk and of kit bodies. Measurements were performed during lactation weeks 1 – 4, each week with 3 dams with each litter size. Milk intake was determined over a 48 h measurement period, and by the end of this milk samples were collected and 2 kits (litters of 6 and 9) or 1 kit per litter (litters of 3) were killed for body chemical composition. Based on the results, different models were applied for calculation of the energetic efficiency of milk. Dam milk yield increased steadily from week 1 until week 3 but only slightly from week 3 to 4. The increase declined with increasing litter size, and for dams suckling 9 kits the increment from week 3 to week 4 was only 2 g. The dry matter content of milk increased significantly as lactation progressed, being reflected in crude protein increasing from 6.9% in lactation week 1 to 8.1% in week 4. Milk fat increased concomitantly from 5.6% to 8.0%. In kit bodies, crude protein content increased from 9.4% in week 1 to about 12% in weeks 3 and 4. Body fat content increased from week 1 (4.1%) to week 3 (8.4%) and then declined in week 4 (7.1%). Animals suckled in litters of 3 kits had the highest milk intake and live weight and kits suckled in litters of 9 had the lowest milk intake, live weight and daily gain. In terms of milk intake per g gain kits in litters of 6 were the most efficient, with 4.1 g milk per g body gain. The metabolizable energy requirement for maintenance (MEm) was estimated to 448 kJ/kg0.75 and the efficiency of utilization of ME for body gain (kg) to 0.67, the estimates being higher (MEm) or in good agreement with previous findings (kg) in suckling mink kits.

Oxidation of substrates and lipogenesis in pigs (Sus scrofa), mink (Mustela vison) and rats (Ratus norvegicus)☆

Abstract Data from experiments with 25 growing pigs at high feeding level, with 12 adult mink on a varied energy supply and with 36 rats on a maintenance level were used in a biological model of nutrient oxidation, lipogenesis and retention at the whole body level. Nutrient oxidation was calculated from gas-exchange measurements in respiration chambers working according to indirect calorimetry principles. Lipogenesis and nutrient retent retention were measured by means of carbon and nitrogen balances, in accordance with the demonstrated model. The results demonstrated that growing pigs had a high level of protein retention and low protein oxidation. Digested carbohydrates were oxidates were oxidized or used for lipogenesis. Oxidation of carbohydrate was the main energy source, while lipogenesis was the main source of fat retention. Independent of dietary fat level, pigs did not oxidize fat but used all dietary fat for body fat retention. The mink, being fed with high protein and fat levels but only a small amount of carbohydrate, use protein and fat as their main energy sources. Rats fed near-maintenance level used dietary carbohydrate as a main substrate for oxidation. It was demonstrated that the present model of nutrient oxidation, lipogenesis and retention in different animal species and at different dietary composition can be quantified by means of indirect calorimetry and measurements of carbon and nitrogen balances.

Can gas exchange measurements be used for calculation of nutrient oxidation in mink (Mustela vison) exposed to short-term changes in energy supply?

SummaryNutrient oxidation was calculated from gas exchange measurements for 6 control and 12 flush fed female mink, measured in six consecutive, one week periods. The energy supply to controls and flushed animals in periods 1 and 6 was ca 850 kJ ME/day, and during restriction and flush feeding, it was ca 450 kJ ME/day and ca 1300 kJ ME/day, respectively. Over the total experimental period the energy intake was similar in both groups, but it differed significantly between periods in the flushed group. Protein, fat, and carbohydrate oxidation averaged 39, 38, and 21%, of the total heat production (HP), respectively in the control group. During restriction, protein oxidation was ca 35% of HP in flushed animals, then increasing to 55% of HP during the first period of refeeding. High values for fat oxidation were recorded during restriction because of fat mobilization and values were low when feed supply was ample. It was concluded that the calculation method was a good indicative method, but some short-comings were discussed.ZusammenfassungBei Nerzen (6 Kontrollitere (Gruppe I) und 12 reichlich gefütterten weiblichen Tieren (Gruppe II) wurde die Nährstoffoxidation aus Respirationsmessungen berechnet. Die Gaswechselmessungen erfolgten in 6 aufeinanderfolgenden einwöchigen Versuchsperioden.Die Energieversorgung für die Gruppe I und II betrug in der Periode 1 und 6 ca. 850 kJ ME/d, während der Restriktion und der Fütterung auf hohem Niveau betrug sie 450 bzw. 1300 kJ ME/d. Während der gesamten Versuchsperiode war die Energieaufnahme für beide Gruppen vergleichbar. Es gab aber signifikante Unterschieded zwischen den Perioden bei der Gruppe II. Die Mittelwerte der Protein-, Kohlenhydrat-und Fettoxidation betrugen 39%, 38% und 21% von der totalen Wärmeproduktion (WP) in der Gruppe I. Während der Restriktion betrug die Proteinoxidation bei der Gruppe II ca. 35% der WP. Während der ersten Periode der Fütterung auf hohem Niveau wuchs dieser Wert auf 55%. Während der Restriktion wurde eine hohe Fettoxidation gemessen, weil die Fettmobilisierung anstieg. Die Fettoxidation war niedrig, wenn die Futterzufuhr reichlich war. Es wird daraus geschlußfolgert, daß die Berechnungsmethode geeignete Aussagen liefert. Einige Nachteile der Methode werden diskutiert.

Protein Turnover in Lactating Mink (Mustela vison) Is Not Affected by Dietary Protein Supply

The mink is a strict carnivore and may therefore serve as a model for the cat. Current recommendations for protein supply for lactating mink are based on production experiments with preweaning kit growth as a measure of dietary adequacy (1,2). Recently, nitrogen balance and substrate oxidation have been used to obtain a more detailed knowledge of the protein utilization of the lactating mink (3–5). These results have shown that lactating mink dams are able to regulate protein oxidation rate and that milk yield, during the first 4 wk postpartum, was improved, and dam weight loss reduced, when protein supply was reduced below current recommendations and replaced with readily digestible carbohydrates (5,6). The effect of reduced protein supply on protein turnover is, however, still unknown. Tracer methodology with N-labeled amino acids has been used to measure the whole-body protein turnover in humans (7), growing pigs (8), and growing rats (9). In adult cats, both protein synthesis and breakdown were lower when feeding a lowthan when feeding a high-protein diet [20 vs. 70% of metabolizable energy (ME) from protein] (10). The objectives of this study were therefore to develop a N-glycine endproduct method for measurement of protein turnover in lactating mink dams and to evaluate if it was affected by different levels of dietary protein supply. MATERIALS AND METHODS

Metabolic and growth response of mink (Neovison vison) kits until 10 weeks of age when exposed to different dietary protein provision

Growth performance and metabolism were investigated in mink kits (n = 210) exposed to the same dietary treatment as their dams (n = 30), i.e. high (HP; 61% of metabolisable energy, ME), medium (MP; 48% of ME) or low (LP; 30% of ME) protein supply, from birth until 10 weeks of age. The kits were weighed weekly, and were measured by means of balance experiment and indirect calorimetry, in weeks eight and nine post-partum (p.p.). At weaning (seven weeks p.p.) and 10 weeks p.p. one kit per litter was killed and blood, liver and kidneys were collected. Plasma amino acid profiles, and hepatic abundance of mRNA for phosphoenolpyruvate carboxykinase (PEPCK), fructose 1,6-biphosphatase, pyruvate kinase and glucose-6-phosphatase (G-6-Pase) by q-PCR, were determined. There were no differences in live weights among kits the first four weeks of life when kits solely consumed milk, but male LP kits were the heaviest. After transition to solid feed MP kits weighed most at nine weeks of age (p < 0.05). At eight weeks of age, the kits fed the LP diet retained less (p < 0.05) N than HP and MP kits. Heat production did not differ among kits, although protein oxidation was higher (p < 0.001) in HP kits than in LP kits. Kits fed the LP diet had lower (p < 0.05) plasma concentrations of lysine, methionine and leucine than MP kits. Dietary treatment was not reflected in the relative abundance of any of the studied mRNAs, but kits had significantly lower abundance of all studied mRNA than their dams, ranging from 83% less PEPCK abundance to 40% less for G-6-Pase. The kidney mass was smallest (p < 0.01) in kits fed the LP diet, and liver masses were largest (p < 0.001) in HP kits. The results indicate that the LP diet did not meet the protein requirements for mink kits in the transition period from milk to solid feed. The capacity to regulate the rate of gluconeogenesis was even more limited in young mink kits than in adult dams. However, young mink kits can regulate protein oxidation in response to dietary protein supply, probably by adapting the size of the liver and kidneys to the level of protein supply.

Utilization of milk amino acids for body gain in suckling mink ( Mustela vison ) kits

The efficiency of utilization of milk amino acids for body gain in suckling mink kits from small (n = 3), medium (n = 6) and large litters (n = 9) was investigated by using 36 mink dams and their litters for measurements during lactation weeks 1 through 4. Measurements on each dam and litter were performed once, hence three dams per litter size each week (n = 9). Individual milk intake of kits was determined, milk samples were collected and kits were killed for determination of amino acid composition. The most abundant amino acids in milk were glutamate, leucine and aspartate making up about 40% of total amino acids. Branched chained amino acids made up slightly more than 20% and sulphur containing amino acids less than 5% of total milk amino acids. In kit bodies the sum of glutamate, aspartate and leucine made up about 32% of amino acids, branched chain amino acids about 16% and sulphur containing amino acids about 4%. The amino acid composition of both milk and bodies changed as lactation progressed with decreasing proportions of essential amino acids. The ratio between body and milk amino acids was constantly over 1 only for lysine, suggesting that it was the most limiting amino acid in mink milk. Milk amino acids were efficiently utilized during week 1, ranging from 74.7% (lysine) to 42.1% (leucine), with an average for essential amino acids of 58.4%. Tendencies for improved utilization of lysine (74.7 – 78.2%), phenylalanine (61.0 – 70.0%), histidine (62.4 – 68.8%), arginine (61.3 – 70.4%) and all essential amino acids (58.4 – 60.2%) from week 1 to week 2 were recorded. During weeks 3 and 4, the efficiency declined, and for all essential amino acids the average utilization was 38.1% during week 4.

Glucose Metabolism and Regulation in Lactating Mink (Mustela Vison) - Effects of Low Dietary Protein Supply

Eighteen lactating mink raising litters of 6 to 7 kits were fed ad libitum from parturition on diets with 32% of ME derived from protein and decreasing fat:carbohydrate ratios [high fat:low carbohydrate (HFLC): 67:1, medium fat:medium carbohydrate (MFMC): 52:16, low fat:high carbohydrate (LFHC): 37:31]. Four weeks post partum the dams were fitted with a jugular vein catheter, and the experiment started with a 3 hours fasting period, after which the dams were fed 210kJ ME of the experimental diets. Blood samples were collected 10 and 5min before feeding and 30, 60, 90, 120, 150 and 180min postprandially. Two hours postprandially a single dose of 50µCi U-14C-labelled glucose was administered to each dam and blood samples were collected 5, 10, 20, 30, 45 and 60min after the tracer administration. Plasma concentrations of glucose and insulin 30 to 120min postprandially were higher in dams fed the LFHC diet, than in dams fed the HFLC diet, values for dams fed the MFMC diet being intermediate. Plasma glucagon concentrations were not significantly affected by dietary treatment. The glucagon:insulin ratios decreased postprandially in all dams, the response being significant in dams fed the LFHC diet. Plasma concentrations of urea were not significantly affected by dietary treatment. Plasma FFA concentrations tended to increase postprandially in dams fed the HFLC diet. Glucose turnover rates were approximately 4.0% permin in all dams, irrespective of dietary treatment. However, the daily glucose flux was lower in dams fed the HFLC diet than in dams fed the LFHC diet, and tended to be lower than in dams fed the MFMC diet. In conclusion, a dietary protein supply of 32% of ME simultaneously with a carbohydrate supply of 16% or 31% of ME had no adverse effects on glucose homeostasis or glucose metabolism in lactating mink.