Production performance and nutrient digestibility of lactating dairy cows fed low-forage diets with and without the addition of a live-yeast supplement.

We aimed to evaluate the use of a live-yeast product as a means to attenuate plausible nutritional disturbances when feeding relatively low-forage diets containing rapidly fermentable carbohydrates (i.e., wheat) to high-producing cows in early to mid lactation. Eight primiparous [mean ± SD; 569 ± 35 kg of body weight (BW) and 80 ± 29 d in milk (DIM) at the beginning of the experiment] and 16 multiparous (665 ± 67 kg of BW and 64 ± 10 DIM at the beginning of the experiment) Holstein cows were blocked by parity and DIM, and randomly assigned to 1 of 2 diets (control vs. yeast) for a 12-wk-long period according to randomized complete block design. The formulated diets contained 36.7% corn silage, 8.3% alfalfa hay, and 55% concentrate. The yeast diet was formulated to provide approximately 5.4 × 1011 cfu/d of Saccharomyces cerevisiae (BeneSacc; Global Nutritech Biotechnology LLC, Richmond, VA). Total-tract nutrient digestibility was estimated using 240-h undigested neutral detergent fiber (NDF) as an internal marker. Dry matter intake, milk yield, and milk component concentrations and yields were analyzed using repeated measures. The statistical model for these variables included the effects of block, treatment, the block by treatment interaction, week, the treatment by week interaction, and the random residual error. The statistical model for analyzing BW gain, body condition score gain, and dry matter and nutrient digestibilities included the effects of block, treatment, and the random residual error. Supplementing live yeast to lactating dairy cows did not affect dry matter intake (26.0 kg/d), milk yield (48.1 kg/d), milk fat concentration (3.61%), milk fat yield (1.72 kg/d), milk protein concentration (2.96%), milk protein yield (1.43 kg/d), milk lactose concentration (4.84%), milk lactose yield (2.35 kg/d), milk urea nitrogen (7.99 mg/dL), body weight gain (0.62 kg/d), and body condition score gain (0.02 units; all averages of the 2 treatments). The digestibilities of dry matter (70.2%), crude protein (71.4%), NDF (36.4%), and starch (99.8%) were not affected by treatments. In conclusion, the supplementation of the live yeast did not affect production performance and nutrient digestibility of high-producing dairy cows. A potential interaction between live-yeast supplementation and NDF passage rate, which may have hindered the beneficial effects of live-yeast supplementation on production performance and nutrient utilization, deserves further research.

Short communication: Effect of corn planting population on phosphorus concentration and uptake in corn silage.

Greater utilization of nutrients reduces the potential runoff of nutrients to bodies of water. The objective of this study was to determine the concentration of P in corn biomass to estimate the removal of P from the soil when planting corn at different population levels. Whole-plant corn samples were collected during an on-farm research project conducted previously. The study included 7 different growing and harvesting conditions. In each cornfield, corn was planted in plots at a theoretical seeding rate of 55,000, 70,000, 85,000, and 100,000 seeds/ha. Each seeding rate had 4 replicates within each field. At harvesting time, 5 consecutive plants from the 2 center rows and at 2 randomly selected spots within each plot were cut by hand at 15 cm above ground. Whole plants were weighed and chopped. After mixing thoroughly, a sample of the chopped material was placed in a bag, immediately placed in a cooler with dry ice, and transferred to the laboratory for storage. After thawing and drying, samples were ground and analyzed for P concentration. Single plant biomass and the number of standing plants at harvesting were used to determine dry matter yield. Total extraction of P was estimated as the product between plant biomass and P concentration. All variables were analyzed using a statistical model that included the effects of field, planting population, planting population nested within field, and random residual error. The concentration of P in the corn plant was greatest for 55,000 and 70,000 plants/ha (0.250% dry matter) and least for 85,000 and 100,000 plants/ha (0.235% dry matter), whereas the uptake of P through the harvested biomass increased when corn planting population increased. In conclusion, increasing the planting population of corn for silage can increase P uptake from the soil, therefore reducing the potential runoff of P to bodies of water.

Technical note: In situ ruminal starch disappearance kinetics of hull-less barley, hulled barley, and corn grains.

The objective of this study was to compare ruminal starch disappearance rates of hull-less barley, hulled barley, and corn grains. Five different genotypes were used for each of the 2 barley types. In addition, each of these genotypes was grown in 2 different locations and years, resulting 10 independent barley samples for each of the 2 barley grain types. Five different genotypes of corn grain were obtained from a commercial seed company. After being ground to pass through a 4-mm screen of a cutter mill, 3.6 g of each grain was placed into a porous bag, which was then incubated in the rumen of 2 ruminally cannulated cows for 0, 4, 8, 12, 24, and 48 h. Corn grains had greater instant ruminal starch disappearances than barley grains (22.4 and 8.2%, respectively). Instant ruminal starch disappearances did not differ between hulled and hull-less barley grains. Ruminal starch fractional disappearance rates were greatest for hulled barley grains, moderate for hull-less barley grains, and lowest for corn grains (15.3, 13.9, and 7.1%/h, respectively). Ruminal starch half-life was shortest for hulled and hull-less barley grains (4.4 h) and longest for corn grains (6.6 h). Ruminal starch half-life did not differ between hulled barley and hull-less barley grains. In conclusion, using a holistic experimental design and statistical analysis, this study showed that starch from hull-less barley grains has a ruminal half-life similar to that of hulled barley grains and shorter than that of corn grains.

Effects of feeding hulled and hull-less barley with low- and high-forage diets on lactation performance, nutrient digestibility, and milk fatty acid composition of lactating dairy cows.

The objective of this study was to evaluate lactation performance, nutrient digestibility, and milk fatty acid composition of high-producing dairy cows consuming diets containing hulled or hull-less barley as the grain source when feeding low-forage (LF) or high-forage (HF) diets. Eight primiparous (610 ± 40 kg of body weight and 72 ± 14 d in milk) and 16 multiparous (650 ± 58 kg of body weight and 58 ± 16 d in milk) Holstein cows were randomly assigned to 1 of 4 diets in a replicated 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments and 21-d periods. Cows were assigned to squares based on parity (1, 2, and ≥3) and days in milk. Diets were formulated to contain on a dry matter basis (1) 45% forage and hulled barley as the sole grain source, (2) 65% forage and hulled barley as the sole grain source, (3) 45% forage and hull-less barley as the sole grain source, and (4) 65% forage and hull-less barley as the sole grain source. Dry matter intake tended to be lower for the diet with 65% forage and hulled barley than for the rest of the diets (24.4 vs. 26.6 kg/d). Neither the type of barley nor the forage-to-concentrate ratio affected milk yield (41.7 kg/d). Barley type did not affect milk fat or protein concentrations. Feeding LF diets decreased milk fat concentration from 3.91% to 3.50%. This decrease was less than anticipated and resulted in a 7% decrease in milk fat yield relative to cows consuming HF diets (1.60 and 1.49 kg/d for HF and LF diets, respectively). Feeding LF diets increased the concentration of C18:1 trans-10 in milk fat, suggesting that feeding LF diets may have marginally altered rumen function. In conclusion, LF diets containing barley grains can marginally decrease milk fat concentration. Overall, and based on the conditions of this study, there is limited evidence to anticipate a dramatic or acute milk fat depression when feeding hull-less barley as the grain source in diets for high-producing dairy cows.

Nutritional composition and in vitro digestibility of grass and legume winter (cover) crops.

In dairy farming systems, growing winter crops for forage is frequently limited to annual grasses grown in monoculture. The objectives of this study were to determine how cropping grasses alone or in mixtures with legumes affects the yield, nutritional composition, and in vitro digestibility of fresh and ensiled winter crops and the yield, nutritional composition, and in vitro digestibility of the subsequent summer crops. Experimental plots were planted with 15 different winter crops at 3 locations in Virginia. At each site, 4 plots of each treatment were planted in a randomized complete block design. The 15 treatments included 5 winter annual grasses [barley (BA), ryegrass (RG), rye (RY), triticale (TR), and wheat (WT)] in monoculture [i.e., no legumes (NO)] or with 1 of 2 winter annual legumes [crimson clover (CC) and hairy vetch (HV)]. After harvesting the winter crops, corn and forage sorghum were planted within the same plots perpendicular to the winter crop plantings. The nutritional composition and the in vitro digestibility of winter and summer crops were determined for fresh and ensiled samples. Growing grasses in mixtures with CC increased forage dry matter (DM) yield (2.84 Mg/ha), but the yield of mixtures with HV (2.47 Mg/ha) was similar to that of grasses grown in monoculture (2.40 Mg/ha). Growing grasses in mixtures with legumes increased the crude protein concentration of the fresh forage from 13.0% to 15.5% for CC and to 17.3% for HV. For neutral detergent fiber (NDF) concentrations, the interaction between grasses and legumes was significant for both fresh and ensiled forages. Growing BA, RY, and TR in mixtures with legumes decreased NDF concentrations, whereas growing RG and WT with legumes did not affect the NDF concentrations of either the fresh or the ensiled forages. Growing grasses in mixtures with legumes decreased the concentration of sugars of fresh forages relative to grasses grown in monoculture. Primarily, this decrease can be attributed to low concentrations of sugars of mixtures with HV (10.5%). Growing grasses in mixtures with legumes reduced the fiber digestibility of both winter crops (75.7% to 72.8% NDF). Growing grasses in mixtures with legumes did not affect estimated DM yield, nutritional composition, or digestibility of the succeeding summer crops. In conclusion, growing grasses in mixtures with legumes as winter forage crops can increase forage estimated DM yields and its nutritional quality in dairy farming sytems.

Effects of feeding hull-less barley on production performance, milk fatty acid composition, and nutrient digestibility of lactating dairy cows.

The objectives of this study were to evaluate production performance, milk fatty acid composition, and nutrient digestibility in high-producing dairy cows consuming diets containing corn and hull-less barley (cultivar Amaze 10) in different proportions as the grain source. Eight primiparous and 16 multiparous Holstein cows were assigned to 1 of 4 diets in a replicated 4 × 4 Latin square design with 21-d periods. Cows were fed once daily (1200 h) by means of a Calan gate system (American Calan Inc., Northwood, NH). All diets contained ∼20% grain (dry matter basis). Treatments consisted of 100% corn (0B), 67% corn and 33% hull-less barley (33B), 33% corn and 67% hull-less barley (67B), and 100% hull-less barley (100B) as the grain sources. Total-tract nutrient digestibility was estimated using lanthanum chloride (LaCl3) as an external marker. Dry matter intake differed quadratically among treatments, being lowest for 67B and highest for 0B and 100B. Feeding hull-less barley did not affect milk yield, and milk fat concentration differed cubically among treatments. The cubic response was attributed to the higher milk fat concentration observed for the diet containing 67B. Neither the concentrations in milk of protein and lactose nor the yields of protein and lactose differed among treatments. The proportion of de novo synthesized fatty acids in milk did not differ among treatments. The apparent total-tract digestibility of dry matter, crude protein, and neutral detergent fiber did not differ among treatments. Although a quadratic effect was observed, starch digestibility was minimally affected by treatments. In conclusion, this study indicates that hull-less barley grain is as good as corn grain as an energy source when formulating diets for high-producing dairy cows.