Field peas as a protein source for high-production dairy cows on grass silage and hay based feeding

Twenty-four dairy cows were used in an experiment in which 1) soybean meal, 2) rapeseed meal and 3) rapeseed meal plus urea were compared for feeding value, when given as protein sources in grass silageand hay-based feeding. About 25 % of the digestible crude protein required for milk production was replaced with these protein sources. The rapeseed meal was mainly of the Span variety. The rapeseed meal composed 13 %of a concentrate mixture also containing barley, oats and molassed beet pulp. The daily consumption of rapeseed meal was up to 1.2 kg/cow, the average being 1.0 kg/cow. As a protein source the rapeseed meal was almost equivalent to the soybean meal. There were no significant differences between the groups in the intake or utilization of the feeds, milk production or milk composition, or liveweight changes. The replacement of silage protein with rapeseed meal or with soybean meal improved the utilization of the protein of the whole ration for milk production.


Introduction
In practical feeding the protein requirement of the dairy cow is covered up to a daily milk yield of 20 kg by a diet consisting of equal parts of grass silage and hay (SYRJÄLÄ 1981).At higher milk production levels protein concentrates are necessary, because of difficulties caused by the bulk of the diet.The crude protein fraction of silage is generally in a very soluble form, which decreases its utilization (SYRJÄLÄ 1977).Inportancc thus attaches to the quality of the protein and energy supplements, and in this case soybean meal has proved to be a valuable source of protein (e.g.GORDON 1980), since its protein is not degrared as much or as rapidly in the rumen as the protein of silage (SETÄLÄ and SYRJÄLÄ-QVIST 1982).
In countries like Finland, where soya is an imported feed, it is desirable to find domestic alternatives to this supplement.One of these is field peas (Pisum sativum and Pisum arvense).The amounts of peas recommended earlier for dairy cows have been I-2 kg per day (ANON.1965, ERIKSSON et al. 1972), but supplements of 3-4 kg have also given promising results (UOTILA 1959, OLSSON and LINDELL   1975, PELLETIER and BOUCHARD 1975, THOMKE 1979).In those experiments, however, the milk production levels were generally less than 20 kg per day.The main purpose of this investigation was to study the value of peas when they replaced soybean meal as a protein source for high production cows on silage and hay based feeding.    1 The feeding values were calculated by using the digestibility coefficients and value numbers presented by ANDERSEN and JUST (1979) and ANON. (1969).

Experimental procedures
The experiment was performed with 24 dairy cows, 21 of which were Ayrshire and 3 of Friesian breed.The animals were brought into the experiment in three blocks.At the beginning of the experiment the average time that had elapsed from calving was 56 days.In the case of all the blocks the experiment lasted 14 weeks.
The two first weeks formed a standardization period, when all the animals received the same feed, comsisting of hay, grass silage, grain concentrates, soybean meal and minerals.The feeding was adjusted to their nutrient requirements (BREIREM 1969).
At the end of this period the cows were divided into 3 groups that were as similair as possible in respect of their fat-corrected milk (FCM) yields, days after calving, liveweights and breed.During the following two weeks the animals were changed to the experimental feeds.Feeding was still according to the nutrient requirements.
The test period lasted 10 weeks.The basic feeds during this period were hay, grass silage, barley, oats, sugar-beat pulp and minerals (Table 1).The concentrate mixture of the different groups contained (Table 2): Soybean meal 14 %, group 1 Soybean meal 7.5 % plus ground field peas 15 %, group 2 Ground field peas 35 %, group 3 These protein feeds were intended to supply 35 -4O % of the protein needed by the animals for milk production.Fresh grass silage was given ad libitum and concentrate mixture at the rate of 0.3 feed unit per kg FCM.The concentrate allowences were corrected after a 2-kg decrease in milk production.The sampling, analyses, calculations and statistical treatments were as described by SYRJÄLÄ et ai.

Results and discussion
Intake of feeds and nutrient supply The average intake of feed varied slightly between the groups (Table 3, Fig. 1).It was lower in the soybean-pea group than in the other groups.The differences in the supply of energy and protein between the groups were not, however, statistically significant (P > 0.05).In all the groups the total net energy supply was near the corresponding feeding standard (BREIREM 1969).The protein supply exceeded the standards, however, being 115 % of the corresponding standard in the soybean group, 109 %in the soybean-pea group and 11 3% in the pea group.The reason for the protein overfeeding lies mainly in the protein content of both silage and hay, which chanced to be unexpectedly high during the test period.
The average daily intakes of soybean meal and/or peas were; group 1, 1.1 kg soybean meal; group 2, 0.6 kg soybean meal and 1.1 kg peas; group 3, 2.8 kg peas.The maximum pea intake was 3.6 kg per day.In the different groups these protein feeds gave respectively, 31 %, 34 % and 38 % of the protein needed for milk production.

Production of cows
The milk production of the cows was at the same level in the different groups (Table 3, Fig. 2) and no statistically significant differences existed (P > 0.05).The average decrease in milk yield from the standardization period to the test period was about the same in the two groups receiving soybean, 3.4-3.5 kg FCM, but in the pea group it was a little greater, 5.1 kg FCM/day.There were no significant differences in the fat and dry matter content of the milk between the groups (P > 0.05), but the protein content of the milk was significantly lower (P < 0.01) in the soybean-pea group than in the other groups, although the differences in the daily milk protein production were not significant (P > 0.05).
The reason for the lower milk protein content in the soybean-pea group than in the other groups is not clear.Perhaps the cows were suffering from an energy deficit, although this was not evident from the energy supply values.At least the cows in this group lost weight during test period, which was not found in the other groups   (Table 3).It has been shown that lack of energy can cause decrease in milk protein content (REID et al. 1966, KAUFMANN 1976, 1979, OLDHAM and SUTTON  1979).

Utilization of feeds
The feed unit and digestible crude protein consumption per kg of fat-corrected milk was used as a measure of feed utilization (Table 3).The f.u. and DCP needed for maintenance were substracted from the total supply.The maintenance values used were 4 f.u. per 500 kg liveweight and 7 5 g DCP/maintenance f.u.(BREIREM 1969).The energy requirements for a change in liveweight (Table 3) were taken as 2.2 f.u./kg liveweight decrease and 2.6 f.u./kg liveweight increase.No corrections were used in the protein calculations.
There were no significant differences between the groups in energy and protein utilization (P > 0.05).In the test period the consumption of production f.u. per kg FCM was near the corresponding requirement standard, as follows: soybean group 0.39, soybean-pea group 0.38 and pea group 0.41.The digestible crude protein consumed for milk production was higher than the standard by 18 %in the soybean group, by 11 %in the soybean-pea group and by 17 %in the pea group, the values being 71, 67 and 70 g DCP/kg FCM, respectively.

Compisition of blood
There were no significant differences between the three groups in the concentration of the blood constituents determined (Table 4).All the values fall within the normal ranges (RAUEN 1964, HEWETT 1974).The changes in urea- nitrogen could be explained by the increased level of protein feeding during the test period (PRESTON et al. 1965).It has been suggested by PAYNE et al. (1972) that soybean meal increases the level of blood glucose, which agrees with the increase observed in this experiment. (1978).

Fig. 2 .
Fig. 2. Milk yield and composition in the different groups.
The men chemical composition and feeding value of the feeds 1

Table 2 .
The percentages of different feeds in the concentrate mixture.

Table 3 .
The mean intake and milk yields in the different groups

Table 4 .
Haematological criteria and chemical constituents of the blood of the cows.The change during the test period.