Effects of dietary supplement of methionine and lysine on blood parameters and fur quality in blue fox during low-protein feeding

. Four groups of blue fox (AlopexLagopus) were fed from weaning to pelting with feed of two different protein levels. The metabolizable energy (ME) from protein amounted to 35/30 % in the control group and to 22/18 % in three low-protein groups during the early and late growthperiod, respectively. One of the low-protein groups received an unsupplemented diet. The second low-protein diet was fortified with methionine, and the third with methionine and lysine to the same level as in the control diet. Hematological values, urea and creatinine were lower in all low-protein groups as compared to the control group. The activities of amino acid metabolizing enzymes ASAT, ALAT and GOT in plasma were lower in the low- protein groups although the relative sizes of the liver and kidneys were greater. The lowered protein content in the feed was sufficient for growth, and only a slight negative effect on fur characteristics was observed. The dietary supplementation of methionine and lysine yielded no improvement in the fur quality or other parameters as compared to the unsupplemented low-protein feed, indicating that there was no deficiency of these amino acids in these low- protein feeds.


Introduction
In order to produce high-quality furs the feeds for fur-bearing animals contain a relatively high proportion of energy as protein.
At the same time, protein is a decisive price factor in feeds. Moderately decreased protein content in mink feed has reduced feeding expenses without affecting the quality of the fur (Glem-Hansen 1980, Berg et ai. 1983, Työppönen et ai. 1986). Attempts to compensate a markedly lowered protein content in mink feed by the addition of some essential amino acids have not been very successful (Milovanov 1963, Jorgensen & Glem-Hansen 1970, Skrivan 1977, Työppönen et ai. 1987). The present paper describes an experiment where the possible beneficial effects of supplemental 355 JOURNAL OF AGRICULTURAL SCIENCE IN FINLAND methionine and lysine were studied in blue fox fed with diets of low protein content.

Animals and diets
Four groups of healthy weaned male blue fox (Alopex lagopus) were used in the experiment. The groups consisted of 30 foxes, housed individually in cages. The control group was fed with a diet of standard protein content, i.e. 35 % of metabolizable energy (ME) from protein, from weaning to the end of August and 30 % from September to pelting (Table 1). The three low-protein groups received 22/18°7o of ME from protein during the early/late growth period. One of the low-protein groups received an un-supplemented diet, the second diet was supplemented with methionine (DL-Methionine, Feed Grade, 98 %), the third with methionine and lysine (L-Lysine, Monohydrochloride, 98 %). The levels of methionine and lysine added in the low-protein feeds shown in Table 2 were calculated to be equivalent to the control diet as based on the methionine and lysine content in the raw materials (Berg 1986).
At pelting time, in the beginning of December, blood was collected by cardiac puncture into heparinized tubes, and hematological parameters were determined. For chemical analyses, plasma samples were stored at -2O°C until analysed. After blood sampling, the foxes were killed, weighed and the pelt length was measured. The quality and colour of the fur were graded at Finnish Fur Sales Ltd. Hemoglobin (Hb), hematocrit, and leukocyte count were determined by standard methods (Schalm et al. 1975).
Plasma urea was analysed according to Gutmann & Bergmeyer (1974), creatinine with Jaffe reaction (Slot 1965), albumin as described by Gindler & Westgard (1973) and total protein according to Weichselbaum (1946). Aspartate aminotransferase (ASAT), alanine aminotransferase (ALAT) and gamma-glutamyl transferase (GGT) were determined according to the Committee on enzymes (1974). All the chemical analyses described above were performed with a Gilford System 3500 Computer Directed Analyzer.
Between-group comparison was performed using Student's t-test.

Results and Discussion
Blood hemoglobin and hematocrit were significantly reduced in fox fed a low-protein feed as compared to the control group (Table 3). Low-protein feeding in mink has resulted in decreased (Työppönen et ai. 1986) or unchanged (Työppönen et ai. 1987) hema-tological parameters. Leukocyte counts were similar in all groups of blue fox (Table 3).
The content of urea and creatinine in plasma tended to be lower in low-protein groups as compared to the control group (Table 4). The lowered plasma urea concentration reflects the smaller amount of protein available for energy production in these animals.
A similar decreasing tendency in plasma urea has previously been observed in mink on lowprotein rations (Työppönen et ai. 1986, Työppönen et ai. 1987. Plasma creatinine content correlates with muscle mass of the body. Thus, the slightly lowered creatinine content in low-protein groups probably reflects the slower rate of muscle protein synthesis and turnover as compared to the control group (Table 4).
Albumin and total protein content in plasma were similar in all groups except for the low-protein group supplemented with methionine and lysine where a significant decrease of albumin and an increase of total protein content were observed (Table 4). The reason for this phenomenon remained unknown, but increased content of plasma proteins has previously been observed also in P<o.ol, as compared to control group mink during low-protein feeding (Työppönen et ai. 1986). The plasma activities of three enzymes involved in amino acid metabolism (ASAT, ALAT and GGT) are presented in Table 5.
The activity of ASAT is high in liver and muscle tissue, but a considerable ASAT activity is also found in other tissues (Työppönen et ai. 1982). ALAT is relatively liver specific in blue fox, and GGT activity is strongly concentrated in the kidneys (Työppönen et ai. 1982). The activity of amino acid metabolizing enzymes, especially ALAT and GGT, was reduced during low-protein feeding (Table 5). This is probably due to metabolic adaptation to lowered dietary protein content as previously shown to occur in rats (Das & Waterlow 1974). Strict carnivores like cat or mink have only a limited ability to this kind of enzymatic adaptation (Rogers et al. 1977, Työppönen et ai. 1986). In the present study, the lowered enzyme activities in low-protein groups become even more evident if the increased relative sizes of the liver and kidney are taken into account (Table 6). A similar negative correlation between body weight and liver and kidney weights has previously been observed in Raccoon dog during restricted feeding (Korhonen & Harri 1985).
The final body weights were similar in all groups (Table 7), but as discussed earlier, the decreased muscle mass, as indicated by the lowered creatinine content in plasma, was probably compensated by the increased amount of body fat. The higher fat and energy contents of the low-protein diets also contribute to such a conclusion ( Table 1). The fur characteristics of the animals are shown in Table 7. There were only slight differences in the presented parameters be-  (Työppönen et ai. 1987). As previously observed in mink, also in the present study the dietary supplements of methionineand lysine had no beneficial effect on fur quality or other parameters as compared to animals fed with low-protein feed without supplemental amino acids.