1a. Objectives (from AD-416):
The objectives of the proposed research are: 1) to determine the nutritional value of canola meal as a protein supplement for lactating dairy cows; 2) to develop improved methodology for quantifying protein utilization in cattle; and 3) to improve N efficiency and reduce urinary N excretion during milk production.
1b. Approach (from AD-416):
Preliminary in situ assessment of variation in ruminal protein degradation in canola meal will be carried out with samples collected from a range of canola production plants. Samples will be chemically analyzed for DM, ash, NDF, NDIN, ADIN, total N, buffer-soluble N, NPN, and amino acid (AA) composition. Initial degradability screening of canola samples (plus standard soybean meals) will be conducted by incubating replicates in the in situ rumen for 12 hr in ruminally cannulated cows. Based on these results, a subset representing the range of in situ degradabilities in the sample set will be incubated with the Michaelis-Menten inhibitor in vitro procedure to estimate protein degradation rates and RUP. Degradability of canola meals fed in the in vivo trials will be determined to confirm that the meals have similar degradability. A feeding study will assess canola meal (CM) value, relative to solvent soybean meal (SSBM), as a protein supplement for dairy cows. Five protein sources and amounts will be fed: 2 supplemental proteins (SSBM and CM), at 2 CP levels (15 and 17% CP), with all added CP from SSBM (15 and 17% CP), CM (15 and 17% CP), or half from SSBM and half from CM (17% CP). Additional diets with the same CP sources, but with supplemental rumen-protected Met + Lys, will also be fed. We hypothesize that if canola meal supplies greater amounts of absorbed His, then that effect will only be apparent after any Met + Lys deficiency is corrected. Basal diets will be composed of alfalfa and corn silages plus high-moisture corn. These dietary treatments will be fed as 2 parallel sets of 5x5 Latin squares; the study will have five 3-wk periods. Forty cows will be grouped by parity and days-in-milk into 8 blocks of 5. Ten ruminally cannulated cows, fed the same diets, will also be used in 2 replicated 5x5 Latin squares for omasal and ruminal sampling. Production data from the last week of each period will be analyzed using mixed procedures of SAS. Cows will be fed individually for ad libitum intake; intake and milk yield data will be collected daily. Milk samples will be taken mid-week at 4 milkings during week 3 of each period and analyzed for fat, protein, lactose, SNF, and urea. Cows will be weighed 3 consecutive days at start and end of each period. Blood samples and spot samples of feces and urine will be collected at the end of each period. Blood plasma will be deproteinized and analyzed for urea and free AA. Internal markers in urine (creatinine) and feces (indigestible ADF) will be used to estimate urinary excretion of urea and total N, apparent nutrient digestibility, and fecal N excretion. Omasal sampling will quantify ruminal flows of RDP, RUP, microbial protein and AA. Ruminal samples will be analyzed for metabolite concentrations. Samples of all feeds and TMR will be analyzed for DM, ash, NDF, ADF, CP, ADIN, NDIN, indigestible ADF, and ether extract. Silage extracts will be analyzed for pH, NPN and fermentation products. Results of the initial production-omasal sampling trial will dictate the subsequent experiments to be conducted.
3. Progress Report:
This project is related to Objective 1 of the parent project: Maximize nitrogen (N) use efficiency and animal performance by determining the optimal levels and qualities of dietary protein appropriate for differing base forages in dairy cattle diets, and determining the influence of polyphenol (o-quinones, tannins) or other feed additives on feed N use efficiency. In vitro incubations were used to assess the rumen degradability of protein in canola meal samples collected from 12 different processing plants over two production years. These 12 processing plants account for nearly all of the canola meal produced in North America. A range of values was observed. Canola meal varied by as much as 25% more in rumen-undegraded protein among processing plants. This would result in 25% more value as a protein supplement for lactating dairy cows. The overall averages for rumen-undegraded protein were 41% for canola meal versus 33% for soybean meal. These differences confirmed in vivo observations of lower rumen concentrations of protein degradation products when canola meal replaced soybean meal in the diet of lactating dairy cows. The value of canola meal, relative to soybean meal, as a protein source for lactating dairy cows was assessed in four lactation trials. Equal amounts of crude protein were fed in each diet as either solvent-extracted soybean meal or canola meal to supplement diets containing forage from alfalfa silage-corn silage plus corn-based concentrate. In three reversal trials, replacing soybean meal protein with that from canola meal increased feed intake by an average 0.4 kg/day, and yield of milk and protein by averages of 0.8 kg/day and 25 g/day. These differences were statistically significant in two of the three trials. Milk urea concentration was lower when feeding canola meal in all three trials, indicating more efficient protein utilization. Forage source did not affect results in one trial whereby different ratios of alfalfa silage to corn silage were fed, indicating canola meal was more effective than soybean meal, regardless of the proportion of dietary forage from alfalfa silage or corn silage. A final lactation trial assessed relative energy value of soybean and canola meals in a non-reversal experiment. Cows produced 2.8 kg/day more milk, 80 g/day more fat, 90 g/day more protein, and 150 g/day more lactose when canola meal replaced soybean meal. However, cows also ate 4.8 kg/day more feed dry matter on canola meal. Thus, feed efficiency (milk/dry matter intake) was reduced, indicating lower energy content in canola meal. Estimated digestible energy contents of canola meal and soybean meal were 3.12 and 3.21 Mcal/kg dry matter, respectively.