Milk yield and composition in dairy cows fed a diet with evening primrose { Oenothera paradoxa ) full fat seeds or oil cake

The experiment was carried out on 30 Black-and-White Lowland dairy cows divided into 3 groups of 10 to investigate the effect of feeding evening primrose {Oenothera paradoxa) full fat seeds or oil cake on milk yield and composition. The animals were fed a basic ration consisting of maize silage, sugar beet top silage, meadow hay or green pasture forage (in summer) and concentrate mixture (control group C) supplemented with evening primrose oil cake (group O) or full fat seeds (group S) from the beginning to 100th day of lactation. Average daily milk production was 31.4, 32.1 and 33.2 kg in the C, S and O groups, respectively, but differences between the groups were statistically insignificant. The fat content in milk from cows receiving oil cake (3.88 %) or full fat seeds (3.93 %) with their ration tended to be higher than in the control group (3.78 %) but the level of protein and lactose in milk was similar in all groups.


INTRODUCTION
Evening primrose (Oenothera paradoxa) seed fat contains a high level of unsaturated fatty acids, particularly of y-linolenic acid which is essential for animals.A deficiency of this acid causes disorders in some metabolic pathways (Hudson, 1984;Horrobin, 1990;Lammer-Zarawska, 1992) which could negatively affect animal production and feed efficiency.
Previous studies on the nutritive value and effect of feeding evening primrose oil cake as a diet component on beef quality, milk composition, calf performance and nutrient digestibility and utilisation have already been published (Stasiniewicz et al., 1998;Strzetelski et al., 1998 a, b,c).
The aim of the experiment was to compare milk yield and composition from cows fed diet supplemented with full fat evening primrose seeds or oil cake.

Animals and feeding
An experiment was carried out on 30 Black-and-White Lowland cows of average body weight 650 ± 50 kg, divided into 3 groups of 10 according to an analogue method based on HF blood share (av.58 %), lactation rank (2-5) and milk yield at the peak of last lactation.Groups of animals were completed successively at 3 weeks before calving over a period of three months.The experiment lasted from calving to day 100 of lactation.Daily milk production of each cow and content of fat, protein and lactose in samples representing 3-day periods during the whole experiment were determined.
All animals were individually fed a basic ration consisting of maize silage and sugar beet tops silage (70:30 % in DM, respectively), meadow hay or green pasture forage (in summer) and concentrate mixture (control group -C), supplemented with 10 % evening primrose oil cake (group -O) or with the addition of full fat seeds -350 g/day/cow (group -S) from the beginning to day 100 of lactation (Table 1).Feed intake was controlled.Cows were fed according to the INRA system (IZ-INRA, 1993).Proximate chemical analysis of feeds was carried out according to AO AC (1990) methods.Fat, protein and lactose in milk were determined with Milko-Scan 133B equipment.The nutritive value of feeds, concentrate mixtures and daily rations were set up using INWAR ver. 1.0 and INRAtion ver. 2.6 (1994) software systems.
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 Statgraphics Plus 6.0 (1992) software.

RESULTS
Concentrate mixtures contained about 17 % crude protein, but there was about 40 % less fat in the concentrate mixture for the control group than in the concentrate with evening primrose oil cake (Table 2).Average daily intake of nutrients was similar in all groups.Daily intake of DM was 18.6 ± 0.4 kg, crude protein Daily milk production and composition did not differ significantly between the groups, however, there was a tendency to higher milk yield in cows receiving evening primrose oil cake (by 5.7 %) and full fat seeds (by 2.2 %) than in control animals.A similar tendency was observed in the level of fat in milk of respective groups of animals, but the protein and lactose concentrations were similar in milk of all animals.Feed efficiency was slightly better, but not significantly, in animals of group O (Table 3).

DISCUSSION
Slightly higher milk yield in cows receiving the diet with evening primrose oil cake or full fat seeds in comparison with control animals suggests a stimulating influence of these feeds on milk production.The reason for that could be the high proportion of biologically active y-linolenic acid in evening primrose oil (Lammer-Zarawska, 1992) as metabolites of this acid affect tissue metabolism (Horrobin, 1990) and thereby could have a beneficial influence on animal production.
The advantageous tendency of supplementing diets for dairy cows with oil plant seeds to increase the level of milk fat has been reported, similarly as in the present experiment, by others (Palmquist, 1984;Murphy et al., 1990).
It is difficult to explain the lack of differences between groups in the level of protein in milk, as usually increased fat levels in the diet are associated with a decrease in the protein content in milk (Palmquist and Moser, 1981;Driver et al., 1990;Murphy et al., 1990).However, in the cited experiments the level of fat in diets was higher than in the present study.It is possible that the amount of fat introduced into diets O and S was too low to affect the hormonal status of cows and thereby amino acid transport and utilisation in the mammary gland (Palmquist and Moser 1981;Casper and Schingoethe, 1989).There is rather a small chance that the fat of evening primrose oil cake or full fat seeds inhibited microbial protein synthesis in the rumen, as the contribution of this fat in the diet was low.Hanczakowski and Szymczyk (1993) reported that evening primrose seeds and oil cake contain relatively high levels of tannins forming complexes with protein.Such complexes are poorly degraded in the rumen and protect fat from rapid release, saponification, biohydrogenation and conversion into the trans isomeric form of unsaturated fatty acids (Strzetelski et al., 1987).Having this in mind there is no reason to suppose that cellulolytic activity in the rumen was reduced by transacids, all the more so as the composition of concentrate mixtures fed to animals indicates that the content of PDIE and PDIN was similar in all mixtures.

CONCLUSIONS
In conclusion of this study it could be stated that both evening primrose full fat seeds and oil cake can be fed to lactating cows, increasing to some extent milk yield, and can also be considered a biologically active additive.

TABLE 2
Chemical composition and nutritive value of feeds g, 1850 g PDI (PDIE -PDIN = -37 g) and about 16.3 UFL.Average intake of evening primrose oil cake in group O was 764 g containing 92 g of oil, whereas cows of group S received 350 g full fat seeds containing 84 g of oil.