A note on rearing calves on diets supplemented with evening primrose { Oenothera paradoxa ) oil cake

The effect of substitution of soyabean oilmeal with evening primrose (Onothera paradoxa) oil cake was investigated on 60 bull calves from days 7 to 120 of age, divided into three groups: control, C, fed with soyabean oilmeal as the main source of protein in the concentrate mixture; PI , 50% soyabean oilmeal protein was substituted with the equivalent of evening primrose oil cake; P2, total protein of soyabean meal was substituted with protein of evening primrose oil cake. In the respective diets, the feed mixtures contained 0, 16.5 or 33% of evening primrose oil cake. The calves were given about 350 kg of whole milk from days 7 to 56 of life. The increased level of evening primrose cake in the diet augmented feed intake but was not reflected in body gains (P>0.05), and significantly decreased feed efficiency (P<0.01).


INTRODUCTION
The nutritional value and effectiveness of feeding evening primrose oil cake as a component of the diets for fattened bulls and lactating cows was reported in previous papers (Stasiniewicz et al., 1998;Strzetelski et al., 1998a,b).The results of these experiments indicated that evening primrose oil cake can be used as an alternative complementary source of protein in beef and milk production having in mind its high content of methionine and cystine but low level of lysine.The high level of essential unsaturated fatty acids and, particularly, of biologically active y-linolenic (C 18 .3n6 ) acid which is an intermediate metabolite of linoleic (C 18 .2n6 ) acid (Horrobin, 1990), in evening primrose oil cake makes this feed interesting as an additive to the diet for reared calves.Experiments on rats suggest that evening primrose oil cake is of limited significance in monogastric feeding as it contains antinutritive substances decreasing protein digestibility (Hanczakowski and Szymczyk, 1993).New-born calves could be considered as monogastric animals but the development of forestomachs and fermentation processes and nutrient digestibility in the rumen start relatively early.Rumen fermentation can modify antinutritive substances into less harmful compounds decreasing their negative effect on nutrients utilization in calves (Dixon and Hosing, 1992).
The aim of the present study was to assess the effectiveness of feeding rearing calves diets containing evening primrose oil cake.

Animals and feeding
The experiment was carried out on 60 Black-and-White Lowland bull calves from 7 days of age at the beginning to 120 days of age at the end of the experiment.The animals were divided into 3 groups of 20 animals in each, allocated to the  1) was according to INRA system (IZ, 1993).
The main source of protein in the diet for calves of the control group (C) was soyabean oilmeal, in the second group (PI) 50% of soyabean oilmeal protein was substituted with respective amounts of evening primrose oil cake protein, and in the third group (P2) all of the protein of soyabean was substituted with the appropriate amount of evening primrose oil cake protein.
Feed intake was controlled daily and body liveweight of calves was controlled for two successive days at the beginning of the experiment (7 day of age), at the end of milk period (56 day of age) and at the end of experiment (120 days of age).

Chemical analysis and statistics
Proximate chemical analysis of feeds was carried out according to AO AC (1990) methods.The nutritive value of feeds and experimental feed mixture composition were set up using INWAR ver.1.0, and INRAtion ver.2.62 (1993) software systems.The coefficient of protein degradability in the rumen deg = 0.39 and intestinal digestion of protein undegraded in the rumen dsi = 0.65 were determined according to the method of Michalet-Doreau et al. (1987).
The results were subjected to statistical analysis using one way analysis of variance estimating the significance of differences between groups with multiple interval test according to the Statgraphics Plus 6.0 (1992) software system.

RESULTS
The level of crude protein was similar in all mixtures, but that of PDI and energy in the mixture was higher in the experimental feed mixtures (PI and P2) than in the control (C).The fat, crude fibre content and feed intake increased with the higher proportion of evening primrose oil cake in feed mixtures (Tables 2 and 3).The daily intake of nutrients and concentrate mixtures was the highest in group P2 and the lowest in group C, but intake of UFL, PDI and difference between PDIE and PDIN were similar (P>0.05) in all groups.Differences in body liveweight gain both in the milk period as well as in the whole period of rearing were statistically insignificant (Table 4).However, the body gain of calves of group P2 in the entire experimental period was about 4% less than of these in groups C and PI.Feed utilization for body gain was the best in C and worst in group P2.

DISCUSSION
The beneficial influence of increasing the proportion of evening primrose oil cake in the concentrate mixture on its intake in calves is difficult to explain.May be evening primrose, classified as an herb, contains some aromatic substances or other components advantageously affecting feed palatability and intake.Preparations of herb aroma and taste or herb mixture additives to the diet for animals are Daily intake of feed and nutrients 381 sometimes used to stimulate feed intake (Bradley, 1978;Rys and Urbanczyk, 1983;Wojcik et al., 1984).As compared with the control group, increased feed intake in calves fed diets with evening primrose oil cake did not cause significant differences in calf liveweight gains but worsened feed efficiency, particularly in group P2 with the 33% proportion of evening primrose oil cake in the diet.In spite of higher feed intake in this group, the body liveweight gains were similar in all groups but feed efficiency worse than in remaining groups.
The lack of differences in body liveweight gain between groups of calves in spite of the low content of lysine in evening primrose oil cake could probably be explained by a complementary amount of amino acids in the diets -the lysine-rich but methionine-deficient soyabean oil meal and evening primrose oil cake, which is low in lysine but high in methionine (Stasiniewicz et al., 1998).May be the high y-linolenic acid content in evening primrose oil cake, a biologically active component, had some influence on improving the performance of calves in group PI and P2 (Horrobin, 1990).
The protein of evening primrose has a low solubility and digestibility (Szymczak and Drzewicka, 1992;Stasiniewicz et al., 1998) and, as a consequence of that, the physiological availability of such a protein might be low.The higher proportion of fat in the concentrate mixture with 33 % of cake could also negatively effect crude fibre digestibility (Kowalczyk et al., 1977;Murphy et al., 1990;Strzetelski et al., 1993).

TABLE 2
Chemical composition and nutritive value of feeds according to INRA system IZ, 1993: UFL -unit for milk production; PDI -protein truly digestible in the small intestine; PDIN -PDI dependent on ammonia-N amount; PDIE -PDI dependent on energy amount