MOLECULAR STRUCTURE FEATURES AND NUTRIENT AVAILABILITY AND UTILIZATION OF BARLEY SILAGE VARIETIES WITH VARYING DIGESTIBLE STRUCTURAL CARBOHYDRATE IN COMPARISON WITH A NEW SHORT-SEASON CORN SILAGE IN HIGH-PRODUCING DAIRY CATTLE
Refat, Basim 1987-
Barley silage is a main crop forage source that used by the dairy producer in Western Canada. There are many barley forage varieties that used for silage production. However, there is limited information in their nutritional characteristics and utilization in dairy cows, meanwhile new corn forages that developed to Western Canada that required less crop heat units to reach the maturity stage for silage production. The objectives of the Experiment 1 and 2 were: (1) to assess the magnitude of difference among barley silage varieties in comparison with short-season corn silage in terms of their chemical composition, energy values, protein and carbohydrates fractions, rumen degradation kinetics, and intestinal absorbed true protein supply to dairy cattle and (2) to define the interactive association between molecular structure of silages and carbohydrates or protein utilization in dairy cows. The two experiments were complete randomized design with four treatments: corn silage (P7213R), CDC Cowboy barley silage, CDC Copeland barley silage, and Xena barley silage. The barley silage varieties were selected based on varying rate of in vitro neutral detergent fiber digestibility (ivNDFD). Five cannulated lactating dairy cows were used for measuring in situ rumen degradation kinetics. Intestinal digestibility of rumen undegraded feed protein was estimated using three-step in vitro procedure. The protein and carbohydrates related-molecular structure spectral data was collected using attenuated total reflectance Fourier transform infrared (ATR-FT/IR) molecular vibrational spectroscopy. Corn silage showed the highest total digestible nutrient and energy content. Cowboy showed lower energy content and lower dry matter (DM) degradation in the rumen relative to other barley varieties. All studied silages exhibited the same level of metabolizable protein supply to dairy cows. Molecular structural analysis showed significant modifications in protein or carbohydrates related molecular spectral intensity. The protein structure α-helix to β-sheet ratio are correlated to total intestinally absorbed protein supply. The spectral intensities of carbohydrates were highly correlated with the digestible carbohydrate content of silages. The objective of the Experiment 3 was to evaluate the effect of barely silage varieties selected for varying rates of ivNDFD on DM intake (DMI), milk production, and total chewing activity of high-yield dairy cows in compared with short-season corn silage. Four mid-lactating multiparous Holstein cows (DIM = 101 ± 25; parities = 2.75 ± 0.83) were used in a 4 × 4 Latin square design. The CDC Cowboy with higher ivNDFD did not result in improvements in milk yield, feed efficiency, or total chewing activity compared with other barley silage varieties. Cows fed P7213R corn silage-based diet tended to have higher DMI (28.1 vs. 25.7; P = 0.10) and produce more milk (40.1 vs. 35.3 kg/d; P = 0.01) than those fed barley silage-based diets. This implies that the cows fed corn silage-based diet improved feed efficiency compared with those fed barley silage-based diets. The objective of the Experiment 4 was to investigate the effects of barely silage with varying ivNDFD in comparison to short-season corn silage on rumen fermentation characteristics and microbial protein synthesis using a rumen simulation technique. The experiment was a randomized complete block design with four treatments that previously used in the dairy trial. The experiment consisted of 10 d of adaptation and 6 d of data collection. The main results of this study are: Cowboy barley silage did not affect rumen fermentation characteristics when compared with other barley silage varieties. On the other hand, the short-season corn silage had lower ruminal pH, a greater molar proportion of propionate, and lower acetate to propionate ratio relative to the average of all barley silage varieties. Nutrients digestibility of total mixed ration were not affected by the treatments. The corn silage had higher DM digestibility (DMD) compared with the average all barley silage varieties. There was no significant effect of barely silage variety on the bacterial protein production, whereas the diet containing corn silage had exhibited higher bacterial protein production compared to barley silage. To sum up, the results indicate that the new short-season corn silage had a higher energy content than barley silage. Feeding the new short-season corn silage would increase the milk yield, microbial protein synthesis, and feed efficiency in dairy cows relative to barley silage. The FT/IR could be used as a rapid potential tool to predict the ruminal degradation of fiber and the rumen degradation kinetics of CP by using molecular spectral bands intensities in structural carbohydrates and protein regions, respectively. The short-season corn silage could be used as an alternative to other conventional forages in Western Canada. Selecting barley silage varieties based on ivNDFD level is not a satisfactory approach to improve the milk production and DMI in dairy cows. Thus, for the next two experiments (5 and 6) it was intended to improve ivNDFD of barley silage or barley silage-based diet using an exogenous fibrolytic enzymes derived from Trichoderma reesei to enhance ivNDFD, and to correlate this increase with dairy cows’ performance during mid-lactation or early-lactation, ultimately to see whether or not the effects on lactation performance in high producing dairy cows. In the experiment 5, effects of fibrolytic enzymes on lactation performance, digestibility, and feeding behavior of dairy cows during mid-lactation were assessed. Dairy cows were fed barley silage-based diet pre-treated with a new fibrolytic enzymes derived from Trichoderma reesei (FETR, mixture of xylanase and cellulase; AB Vista, UK). Two studies were conducted to evaluate the effect of this product on barley silage and barley silage-based diet. Before starting the dairy trial, in vitro incubations were conducted to predict whether this product would have a positive effect before proceeding to animal experiments. The dairy trial was performed using eight Holstein dairy cows. The cows were blocked by their parity and assigned randomly to one of 4 treatments: 0, 0.5, 0.75, and 1 mL of FETR / kg DM of diet in a replicated Latin square design. The application of FETR linearly (P = 0.02) increased in vitro DM digestibility and tended to improve (P = 0.08) ivNDFD in barley silage. The diet supplemented with an intermediate dosage level of FETR (0.75 ml FETR/ kg of TMR) had exhibited a higher milk fat (1.2 vs. 1.4 kg/cow/day) and fat-corrected milk (38.9 vs. 36.4 kg/d) compared to control. Increasing FETR levels resulted in a quadratic effect (P < 0.05) on feed efficiency. There was no effect (P > 0.10) of FETR level on feeding behavior. Based on the findings in this study, the optimal dosage of FETR was the 0.75 mL / kg DM of TMR. Adding this level of FETR to TMR, increased the digestibility of NDF, milk yield and milk fat yield in dairy cows. In experiment 6, effects of pre-treating barley silage-based diet with a fibrolytic enzyme derived from Trichoderma reesei on lactation performance, omasal nutrient flow and digestibility, rumen fermentation characteristics, and rumen pH profile in Holstein dairy cows during early lactation were estimated. The application of FETR tended to decrease the DM intake compared to control (32.8 vs. 33.7; P = 0.08). There was no effect of FETR (P > 0.10) on rumen fermentation characteristics, ruminal pH profile, omasal nutrient flow. There was a significant decrease (P = 0.05) in milk urea nitrogen as a consequence of adding FETR to the diet. In conclusion, dairy cows fed barley silage-based diet pre-treated with FETR had maintained milk yield with less amount of feed during early lactation. The positive effect of FETR may depend on diet composition, lactation stage and milk yield level.
DegreeDoctor of Philosophy (Ph.D.)
DepartmentAnimal and Poultry Science
CommitteeMcKinnon , John J; Christensen , David; Beattie , Aaron; Yang, WenZhu; Mutsvangwa , Tim
Copyright DateApril 2018
vibrational molecular spectroscopy