Throughout the literature there were no indication that feed intake decreased as a result of pea supplementation. In fact, DM intake of oat hay and grain by four lactating Friesian cows was higher (P < 0.05) when the cows were given legume grains rather than barley grain (8.6 0.32 kg/day-peas vs. 6.6 0.71 kg/day-barley) (Valentine and Bartsch 1987 {652}).
There have been few studies on the effect of feeding peas to dairy cattle, and the results vary. Due to the lower effective degradability of crude protein in peas compared to soybean/canola meal (12 vs. 28% Khorasani et al. 1992 as cited by Corbett et al. 1995 {562}) and a lower undegradable protein content relative to soy/canola meal (22 vs. 35 and 28%), milk production may decrease in early lactation when the demand for undegradable protein is high (NRC 1989) (Corbett et al. 1995 {562}). In some studies this finding has been confirmed and the reduction in milk production is attributed to the greater degradation of pea protein in the rumen (Khasan et al. 1989 {633}).
Studies have reported that peas can be substituted for soy/canola meal as a protein source for late-lactation cows (Khorasani et al 1992 as cited by Corbett et al. 1995 {562}; Corbett et al. 1995 {562}) and in a commercial dairy herd with moderate milk production (23 kg/d) (Ward et al. 1989 as cited by Corbett et al. 1995 {562}; Valentine and Bartsch 1990 {612}; Jutz and Leitgeb 1989 {636}). A study using Holstein Friesian cows (n=8 for 60 d) with a high daily milk yield (29 kg) were supplemented with peas, sunflower oilmeal and brewer's residues as the main protein source. Mean daily milk yield were 27.7, 27.9 and 29.5 kg/d, milk protein 3.13, 3.14 and 3.17 % and milk protein yield was 866.0, 878.5 and 938.3 g/d for peas, sunflower oilmeal and brewer's yeast (Grigorova et al. 1990 {618}). Results from feeding peas to a high producing Holstein dairy herd (31.3 kg/d) are located in table 5 (Corbett et al. 1995 {562}).
Milk production for the entire experimental period was higher (P < 0.05) for cows fed the soy/canola meal supplement (32.1 kg/d) than for cows fed the pea supplement (30.5 kg/d), but fat corrected milk was equivalent for both groups. In early lactation, fat corrected milk was lower for cows fed the soy/canola supplement (29.7 kg/d) compared to the cows fed the pea (31.3 kg/d) concentrate diet (Corbett et al. 1995 {562}). In mid-lactation, milk production was higher for cows fed the soy/canola supplement compared to cows fed peas. This may be due to decreased milk production (17% decrease) of the primiparous cows fed peas compared to those fed the soy/canola supplement. It was suggested that the primiparous cows' requirements for growth could be the cause for the depressed milk production in mid-lactation (Corbett et al. 1995 {562}). Another study using 80% first time lactating cows (n=21) fed a control concentrate based on maize silage and an experimental concentrate based on peas. Milk yield (23.5 kg), milk fat (948 g) and milk protein yield (692 g/d) was similar for both groups. However, the most productive cows had a decrease in 4%-fat corrected milk (FCM) yield (P < 0.07), fat yield (P < 0.02) and fat content (P < 0.02) when they received the pea diet. They concluded that the use of peas in dairy rations is possible up to production levels of 25-30 kg of milk/day, but higher production rates will require a higher quality protein (Hoden et al. 1992 {588}).
When the requirement for bypass protein is low (for late lactating cows or a herd with moderate milk production) peas can be the sole source of protein for dairy cows. In southern Australia feeding peas instead of cereal grains to cows supplemented with a cereal hay based diet in early lactation resulted in an increase in milk yield and improved rumen pH and ammonia levels (NH3)(Bartsch and Valentine 1986 {658}; Valentine and Bartsch 1987 {652}). Peas can be used in the diets of high producing dairy cows or in early lactation as long as the ration is balanced for bypass protein (Jans 1993 {577}; Corbett et al. 1995 {562}; Hoden et al. 1992 {588}). Dairy production studies from the University of Saskatchewan reported no differences in high producing dairy cows (41 kg/d) fed raw pea, SBM, or micronized pea rations. The rations consisted of 47% concentrate and 53% forage (DM) and the forage contained 75% barley silage and 25% second cut alfalfa hay. Barley was the only grain in the concentrate (48-64%). The concentrate also consisted of 3% molasses, 1.3% canola oil, and mineral and vitamin premixes. Soybean meal was used to adjust the protein content of the ration to exceed the NRC (1989) requirements by 10%. Milk yield was maintained at 41 kg over three months with no difference between treatments in milk fat % or milk fat yield or protein % or yield. In a similar study using a raw vs. micronized pea/canola blend and SBM, milk production was maintained at 40 kg/d for all groups with similar milk protein and fat yields and percentages (Christensen et al. 1998). Peas can be used in combination with other protein sources or as the sole protein source in well balanced diets for high producing dairy cattle.
Milk fat percentage was higher (P < 0.05) in cows fed a pea concentrate in all stages of lactation compared to cows fed a soy/canola concentrate. This was attributed to the low degradation rate of non-structured carbohydrates in peas. Previous reports suggest this prevents a depression in rumen pH (Valentine and Bartch 1987 as cited by Corbett et al. 1995 {562}; Valentine and Bartsch 1987 {652}). This maintains a more stable rumen, resulting in increased cellulolysis and a higher acetate:propionate ratio, leading to an increase in milk fat (Valentine and Bartch 1987 as cited by Corbett et al. 1995 {562}). Robinson and McQueen (1989 as cited by Corbett et al. 1995 {562}) reported low pea starch degradation rate of 3.9-5.3%/hr compared to barley starch (21.3-34.2%/hr) when peas were fed in a high concentrate:low forage diet. However, the University of Saskatchewan trials reported similar milk fat percentage and yield in dairy cattle fed SBM, micronized or raw peas (Christensen et al. 1998).
Milk protein percentage and yield were not affected by diet at any stage of lactation when peas were substituted for soy/canola in the concentrate and the diets were balanced for undegradable protein. This may be a reflection of a similar amino acid profile and supply to the small intestine between the two protein sources (Corbett et al. 1995 {562}).