Start Date: Jul 01, 2010
End Date: Mar 31, 2013
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.