Use of different forms of soybeans in dairy cows feeding / Utilização da soja em diferentes formas na alimentação de vacas leiteiras

Ângela Maria de Vasconcelos Corrêa

The research was carried out to evaluate the in situ ruminal degradation and the intestinal digestibility of raw and roasted soybeans and the effect of diets containing different forms of soybeans on the consumption, nutrient digestibility, production and milk composition, variation in pH and ruminal N-NH3 concentration, urea excretion in urine, concentrations of ureic nitrogen compounds in milk and plasma, nitrogen compound balance, microbial production and thermal environment effect on physiological and productive variables. Twelve pure and crossbred Holstein cows were used in the experiments II, III and IV. The cows were grouped according to milk production and lactation days, used in three simultaneous 4x4 Latin squares and fed the following isoproteic diets: only soybean meal (SM- control diet), raw soybean (RS), roasted soybean (RTS) and soybean meal plus 5% urea (SMU), and total diet consisting of 50% of roughage. The experimental periods were 21 days, the first 14 days for adaptation to the diet and the last 7 for data collection. Experiment I, using the in situ nylon bag technique, evaluated the ruminal degradation kinetics of dry matter (DM) and crude protein (CP) at 2, 4, 8, 16, 24 and 48 hours and the intestinal digestibility of crude protein that is not degraded in the rumen by the three-step method. The following six treatments were applied: raw soybeans - T1; soybeans heat-treated at 125 oC for 3 min with and without steeping -T2 and T3; at 145 oC for 1 min with steeping -T4; at 115 oC for 4 min with steeping - T5; and at 110 oC for 5 min without steeping -T6. The roasted soybeans, independently of the temperature and roasting procedure (with and without steeping), showed lower means of DM and CP effective degradability (ED) than the control diet. Treatment four (T4) was the least degraded with 61.33% of DM effective degradability and 52.23% of CP. The intestinal digestibility of raw soybeans was higher and showed significant effect (P <0.05) when compared to roasted soybeans, except for the T5 - 115 oC for 4 min with steeping.T4 gave the lowest protein degradation, 67.72%, corresponding to 52.33% more PNDR than the control diet. Soybeans roasted at 145oC for 1 min and potentialized by the steeping process contributed to a lower CP ruminal degradability and higher PNDRD escape. The experiment II evaluated the effect of different forms of soybeans on the consumptions and digestibilities of DM, OM, EE, CP, NDF, NFC, TDN consumption, milk production and composition and its economic viability. DM, NDF and NFC consumptions were not different (P>0.05) among the different diets. CP consumption was affected (P <0.05) by the diets and the highest EE means (P <0.05) were found for the treatments with raw and roasted soybeans, whereas TDN consumptions were lower (P <0.05) for the raw and toasted soybeans. The digestibility coefficients of DM, OM, CP, EE and NDF were not affected by the addition of different protein sources (P>0.05). NFC digestibility was lower (P <0.05) for the diet containing roasted soybeans and TND decreased (P <0.05) in the treatments with raw (RS) and roasted (RTS) soybeans. Total milk production (TMP) and production of 3.5% fat-corrected milk (FCM), milk efficiency per kilogram of dry matter (MKGDM) and/or crude protein (MKGCP) were not affected (P>0.05). The tested diets added with 50% of corn silage (DM basis) replacing soybean meal can be fed to high production cows without compromising milk production and composition. The experiment III evaluated the effect of different forms of soybeans on variation in pH and ruminal ammonia, urea excretion in urine (UEU), concentration of ureic nitrogen in milk (UNM) and in plasma (UNP), nitrogen compound balance (NB) and microbial synthesis and efficiency. There was effect (P <0.05) of the diets on urine volume (UV) and urea excretion in urine (UEU). The smallest UV (P <0.05) was found in the diet with SMU. UEU was similar among the diets containing RS and RTS and differed (P <0.05) from SM and SMU. The concentrations of UNP were not different (P>0.05) among the diets, whereas the secretion of UNM was significant (P <0.05) with the diet with raw soybeans showing the highest means. Nitrogen compound balance (NB) was not affected (P>0.05) and significant differences were neither found (P>0.05) in the excretion of total purine derivatives (PD) nor in the ruminal microbial synthesis and efficiency, which was expressed as g of CP/kg of consumed TDN for the different diets. It was concluded that the tested diets did not affect nitrogen balance nor microbial production, however the addition of raw soybeans increased nitrogen levels in the milk. The experiment IV evaluated the thermal environment effect on the following physiological variables: respiratory frequency (RF), cardiac frequency (CF), rectal temperature (RT), sweat rate (SR); and the productive variables: dry matter consumption (DM), total milk production (TMP), protein (P%) and fat (F%). Significant differences were found (P <0.05) for all the physiological variables, except for SR. When DM consumption was analyzed, the lowest value was found (P <0.05) in the period 1 (P1) and total milk production (TMP) and fat percentage (F%) were not affected (P>0.05). Protein content was lower (P <0.05) for P1. There was no effect between the diets and the physiological variables, however RF and CF differed (P <0.05) at collection times. It is therefore concluded that the physiological variables were not changed by the diets. They were nevertheless affected by the thermal environment, resulting in reduction of DM consumption in the hottest period, but without change in milk production. The protein content was affected by the experimental periods.

Use of different forms of soybeans in dairy cows feeding / Utilização da soja em diferentes formas na alimentação de vacas leiteiras

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