The effect of corn silage particle size on eating behavior, chewing activities, and rumen fermentation in lactating dairy cows

The objective of this experiment was to evaluate effects of reducing corn silage particle size on eating behavior, chewing activity, and rumen fermentation in lactating dairy cows. Four cannulated, multiparous cows averaging 110 +/- 4 d in milk and weighing 675 +/- 70 kg were randomly assigned to a 4 x 4 Latin square. During each of four 14-d periods, animals were offered one of four diets that were chemically similar but varied in corn silage particle size: short (SH), mostly short (MSH), mostly long (MLG), and long (LG), with a geometric mean particle length of 7.4, 7.8, 8.3, and 8.8 mm, respectively. Reducing particle size increased dry matter intake (DMI) linearly (28.0, 26.8, 26.8, and 25.7 kg/d for SH, MSH, MLG, and LG respectively). At 8, 16, and 24 h postfeeding, the neutral detergent fiber (NDF) concentration of feed remaining in the bunk decreased linearly with reduced particle size. Time spent eating or ruminating was not different across treatments; however, total chewing activity (TC; sum of time spent eating and ruminating) exhibited a quadratic response with highest chewing activities observed for diets with shortest and longest particle size. Eating or ruminating time per kilogram of DMI was not affected by corn silage particle size, but TC per kilogram of DMI decreased linearly with decreasing particle size. In comparison, when expressed as minutes per unit of NDF intake (NDFI), ruminating, and TC were linearly reduced as particle size decreased. Rumen pH was not affected by corn silage particle size even though total concentration of volatile fatty acids increased linearly from 89.1 mM/L to 93.6 mM/L as diet particle size decreased. A quadratic effect was observed in molar proportion of acetate and propionate with the highest concentration observed in animals consuming diets of intermediate particle size. Results of this experiment suggest that reducing corn silage particle size may increase DMI, positively affect rumen fermentation, and reduce sorting behavior. Because both chewing activity and sorting tendencies increased when proportion of TMR particles > 19.0 mm increased, results suggest that particle size measurement as estimated by the PSPS is useful in understanding some factors that affect feeding behavior.     

Eating behavior,milk production,rumination, and digestibility characteristics of high- and low-efficiency lactating cows fed a low-roughage diet

This study aimed to identify individual characteristics differing among high-efficiency (HEf; upper 20%, n = 31), low-efficiency (LEf; lower 20%, n = 31), and mid-efficiency (MEf, 60% n = 93) lactating cows. Primiparous (37) and multiparous (118) high-producing milking cows at 30 to 180 d in milk were fed individually a low-roughage diet [31.6% of dry matter (DM)] for 4 wk. Daily average DM intake, rate of eating, visit duration, meal size, and daily rumination time were higher in LEf compared with HEf cows. On the other hand, HEf cows exhibited higher digestibility of DM, crude protein, and neutral detergent fiber than the LEf cows. Daily eating time was similar in the HEf and LEf groups and higher than that of the MEf cows. Visit and meal frequency, average visit and meal duration, daily lying time, and pedometer activity were similar in the HEf, LEf, and MEf groups. The HEf cows produced 1.75% more milk, but similar energy-corrected milk compared with the LEf cows. Milk fat and protein content were lower by 1.8 and 3.8%, respectively, in the HEf cows than in the LEf group. Body weight (BW) and BW gain were similar in the 3 efficiency groups. Diurnal distribution of DM intake showed 6 distinct major meals, each composed of 1.1 to 1.6 visits. Higher intake peaks (greater meal size) were found in the LEf cows compared with the HEf group. Daily DM intake was highly correlated (affected) with energy-corrected milk production (r = 0.61), BW (r = 0.4), eating rate (r = 0.57), and visit size (r = 0.54). Energy balance showed that the lower efficiency of the LEf cows was attributed to their excess heat production and energy loss.     

Whole-plant flint corn silage inclusion in total mixed rations for pre- and postweaning dairy calves

Assuming that acetic acid plays a minor role in the development of ruminal epithelium of preweaning dairy calves, the fiber supply for growing calves has been neglected. More research has been done on including starch and nonfibrous carbohydrates in solid feed for preweaning calves. Accordingly, the fiber requirement of these calves is not well known, as diet recommendations vary greatly. Hence, elucidating the effects of including fiber from long particle sizes in the diet may be essential for helping calves overcome the transition challenge during weaning. Forty-five Holstein calves were used in a randomized block design, considering sex, birth date, and weight at 28 d of age, when the supply of the total mixed ration (TMR) with the inclusion of corn silage started. Three TMR with increasing whole-plant flint corn silage content (0, 10, or 20% on a dry matter basis) were compared: 0CS, 10CS, or 20CS, respectively. During the first 28 d of life, the calves were managed homogeneously and were fed 6 L/d of whole milk, a commercial calf starter pelleted, and water ad libitum. Next, the solid diet was changed to the respective solid feed treatment. Calves were gradually weaned from 52 to 56 d of age but were evaluated for an additional 14 d postweaning. Feed intake was measured daily, while body weight and metabolic indicators of intermediate metabolism were evaluated weekly. Ruminal fluid was collected at 6, 8, and 10 wk of age. Behavioral analysis was conducted on wk 7 (preweaning) and 10 (postweaning). There was a quadratic effect for dry matter intake from wk 7 to 10, with higher intake for the 10CS diet than the 0CS and 20CS diets. Consequently, the 10CS diet also promoted greater average daily gain at wk 8 and 9 compared with the 0CS and 20CS diets. However, the final body weight was not affected by the different solid diets. Silage inclusion in calves' diet positively affected time spent ruminating and chewing pre- and postweaning. Including 10% of whole-plant flint corn silage in the diets of young dairy calves is a strategy to increase total solid intake and decrease acidosis risk by increasing pH and ruminating activity around weaning.     

Effect of feeding cows in early lactation with diets differing in roughage-neutral detergent fiber content on intake behavior, rumination, and milk production

This study measured the effects of including soyhulls as partial roughage replacement in total mixed rations (TMR) fed to 25 pairs of cows during early lactation, on the dry matter (DM) intake, particle kinetics, rumination, in vivo DM and NDF digestibility, milk and FCM yields, and BW changes. The 2 diets used in this study differed in the content of roughage and roughage NDF [23.5 vs. 35.0%, and 12.8 vs. 18.7% in the experimental (EXP) and control (CON) TMR, respectively]. The EXP TMR contained 20.5% less physically effective NDF than the CON TMR (11.7 vs. 14.1% of DM, respectively). These differences were expressed in a greater intake per meal (by 13.3%), a higher rate of meal intake (by 23.2%), a similar number of meals per day, a shorter daily eating duration (by 13%), and a higher total daily DMI (by 7.2%) in the EXP cows as compared with the CON cows. The in vivo DM and NDF digestibility was higher by 4.9 and 22.7%, respectively, in the EXP cows than in the CON cows. The rumination time for the TMR in the EXP cows was 12.7% (54.3 min/d) shorter than in the CON cows, and this was probably related to the difference of 12.4% in physically effective NDF intake between the 2 groups. Patterns of daily rumination and feed consumption throughout an average day showed a delay of approximately 1 to 2 h between the eating and rumination peaks. Particle flow from the rumen of the EXP cows was characterized by a longer rumen mean retention time (by 17.8%) and longer rumination time per kilogram of roughage ingested (by 23.5%) as compared with the CON cows. Thus, favorable conditions for NDF digestion were created in the rumen of the EXP cows, as reflected in their rumen pH values (6.67). The advantage of the EXP cows in intake and digestibility was reflected in a concomitant increase of 7.4% in milk production and of 9.2% in FCM yield as compared with the CON cows. No difference was found between the 2 groups with respect to efficiency of feed utilization for milk production and BW changes.     

Effects of short-term variation in forage quality and forage to concentrate ratio on lactating dairy cows

Within-farm variation in forage composition can be substantial and potentially costly, and it presents challenges for sampling the forage accurately. We hypothesized that day-to-day variation in forage neutral detergent fiber (FNDF) concentrations and diet variation caused by sampling error would have negative effects on production measures in lactating dairy cows. Twenty-four Holstein cows (73 d in milk) were used in 8 replicated 3 × 3 Latin squares with 21-d periods. Treatments were (1) control (CON), (2) variable (VAR), and (3) overreacting (ORR). On average, over the 21-d period, all 3 treatments were the same [24.7% FNDF and 48.2% forage dry matter (DM) composed of 67% alfalfa silage and 33% grass silage]. The CON treatment was essentially consistent day-to-day in total forage and FNDF concentrations and proportion of alfalfa and grass silages. The VAR treatment changed daily (in a random pattern) in proportion of alfalfa and grass silages fed, which resulted in day-to-day changes in FNDF (range was 21.5 to 28%). The ORR treatment varied in a 5-d cyclic pattern in total forage and FNDF concentrations (26, 24, 28, and 21.5% FNDF). Over the 21 d, ORR (25.1 kg/d) had higher DM intake compared with CON (24.5 kg/d) and VAR (24.3 kg/d). Milk production (42.8 kg/d), milk fat (3.5%), and milk protein (2.8%) were not affected by treatment; however, a treatment × day interaction was observed for milk production. Lower daily milk yields for VAR and ORR compared with CON were rare; they only followed sustained 4- and 5-d periods of feeding higher FNDF diets compared with CON. In contrast, increased daily milk yields for VAR and ORR versus CON were more frequent and followed sustained diet changes of only 2 or 3 d. Lipolytic and lipogenic-related enzyme mRNA abundances in subcutaneous adipose tissue were not affected by treatment. Treatment × day interactions were observed for milk fatty acid markers of cellulolytic bacteria (iso-14:0, iso-15:0, iso-16:0) and lipolysis (18:0) and generally followed the expected response to changes in daily rations. Overall, extreme daily fluctuations in FNDF had no cumulative negative effect on production measures over a 21-d period, and daily responses to transient increases in FNDF were less than expected.     

Physical effectiveness of corn silage fractions stratified with the Penn State Particle Separator for lactating dairy cows

This study evaluated the physical effectiveness of whole-plant corn silage (CS) particles stratified with the Penn State Particle Separator, composed of 19- and 8-mm-diameter sieves and a pan, for lactating dairy cows. Eight Holstein cows (27.6 ± 2.8 kg/d of milk, 611 ± 74 kg body weight; 152 ± 83 d in milk) were assigned to two 4 × 4 Latin squares (22-d periods, 16-d adaptation), where one square was formed with rumen-cannulated cows. Three CS particle fractions were manually isolated using the 8- and 19-mm diameter sieves and re-ensiled in 200-L drums. The 4 experimental diets were (% dry matter): (1) CON (control): 17% forage neutral detergent fiber (NDF) from CS (basal roughage), 31.5% starch, and 31.9% NDF; (2) PSPan: 17% forage NDF from CS + 9% NDF from CS particles <8 mm, 25.9% starch, and 37.9% NDF; (3) PS8: 17% forage NDF from CS + 9% NDF from CS particles 8 to 19 mm, 25.5% starch, and 38.3% NDF; and (4) PS19: 17% forage NDF from CS + 9% NDF from CS particles >19 mm, 24.9% starch, and 38.8% NDF. Cows fed PS8 had greater dry matter intake and energy-corrected milk yield (22.4 and 26.9 kg/d, respectively) than cows fed CON (20.8 and 24.7 kg/d) and PS19 (21.2 and 24.8 kg/d), but no difference was detected between PSPan (21.6 and 25.8 kg/d) and other treatments. Milk fat concentration was greater for PS8 than CON, with intermediate values for PSPan and PS19. Milk fat yield was greater for cows fed PS8 than CON and PS19, and cows fed PSPan secreted more fat than CON cows but were not different from cows fed the other 2 diets. Cows fed CON had a lower meal frequency than cows fed PSPan, shorter meal and rumination times than PS8, and greater meal size and lower rates of rumination and chewing than the other 3 diets. Total chewing per unit of NDF was higher for PS8 than PSPan, although neither treatment differed from CON or PS19. Cows fed PS19 had higher refusal of feed particles >19 mm than cows fed CON and PSPan. The refusal of dietary NDF and undigested NDF in favor of starch were all greater for PS19 than on the other treatments. Cows fed PS19 had a greater proportion of the swallowed bolus and rumen digesta with particles >19 mm than the other 3 diets. Cows fed CON had the lowest ruminal pH and greatest lactate concentration relative to the other 3 diets. Plasma lipopolysaccharide was higher for cows fed CON and PSPan than for cows fed PS8 and PS19, and serum d-lactate tended to be lower on PSPan than for CON and PS8. In summary, the inclusion of CS fractions in a low-forage fiber diet (CON) reduced signs of ruminal acidosis. Compared with CS NDF <8 and >19 mm, CS NDF with 8- to 19-mm length promoted better rumen health and performance of dairy cows. These results highlight the importance of adjusting CS harvest and formulating dairy diets based on the proportion of particles retained between the 8- and 19-mm sieves.     

The effects of forage proportion and rapidly degradable dry matter from concentrate on ruminal digestion in dairy cows fed corn silage-based diets with fixed neutral detergent fiber and starch contents

This study investigated the effects of the forage-to-concentrate (F:C) ratio and the rate of ruminal degradation of carbohydrates from the concentrate on digestion in dairy cows fed corn silage-based diets. Six cows with ruminal cannulas were assigned to 6 treatments in a 6 × 6 Latin square. Treatments were arranged in a 3 × 2 factorial design. Three proportions of neutral detergent fiber from forage [FNDF; 7.6, 13.2, and 18.9% of dry matter (DM)] were obtained by modifying F:C (20:80, 35:65, and 50:50). These F:C were combined with concentrates with either high or low content of rapidly degradable carbohydrates. The dietary content of rapidly degradable carbohydrates from the concentrate was estimated from the DM disappearance of concentrate after 4 h of in sacco incubation (CRDM). Thus, 2 proportions of CRDM were tested (20 and 30% of DM). Wheat and corn grain were used as rapidly and slowly degradable starch sources, respectively. Soybean hulls and citrus pulp were used as slowly and rapidly degradable fiber sources, respectively. Concentrate composition was adjusted to maintain dietary starch and neutral detergent fiber contents at 35.9 and 28.9% of DM, respectively. There was no effect of the interaction between F:C and CRDM on DM intake (DMI), ruminal fermentation, chewing activity, and fibrolytic activity. When F:C decreased, DMI increased, the mean ruminal pH linearly decreased, and the pH range linearly increased from 0.95 to 1.27 pH unit. At the same time, the acetate-to-propionate ratio decreased linearly. Decreasing F:C linearly decreased the average time spent chewing per kilogram of DMI from 35.2 to 19.5 min/kg of DMI and decreased ruminal liquid outflow from 11.6 to 9.2 L/kg of DMI, suggesting a decrease in the salivary flow. Increasing CRDM decreased DMI and increased the time during which pH was below 6.0 (3.1 vs. 4.8 h), the pH range (0.90 vs. 1.33), and the initial rate of pH drop. It also increased the volatile fatty acid range (35 vs. 59 mM), thus suggesting an increased rate of fermentation. It also decreased the acetate-to-propionate ratio (2.9 vs. 1.8). Increasing CRDM barely affected the average time spent chewing per kilogram of DMI and the ruminal liquid outflow. These results suggest that rumen pH is controlled by different mechanisms when F:C is decreased or when CRDM is increased. Consequently, FNDF is a good predictor of the chewing time, whereas CRDM is a good predictor of the pH range and volatile fatty acid profiles. Finally, considering both FNDF and CRDM improves the prediction of mean pH.     

Interactions between forage and wet corn gluten feed as sources of fiber in diets for lactating dairy cows

Twelve early lactation Holstein cows (4 fistulated) were used in replicated 4x4 Latin squares with 4-wk periods to determine the effective neutral detergent fiber (NDF) content of wet corn gluten feed and to measure the effect of forage particle size on ruminal mat consistency and passage rate of wet corn gluten feed. Diets were 1) 23.3% NDF (17.4 percentage units of NDF from alfalfa silage), 2) diet 1 plus 11.1 additional percentage units of NDF from alfalfa silage, 3) diet 1 plus 10.7 percentage units of NDF from wet corn gluten feed, and 4) 8.6 percentage units of NDF from alfalfa silage plus 8.9 percentage units of NDF from coarsely chopped alfalfa hay and 10.7 percentage units of NDF from wet corn gluten feed. The calculated effective NDF factor for wet corn gluten feed, using change in milk fat concentration per unit change in NDF, was 0.74 compared with an assumed 1.0 for alfalfa silage. Rumination activity was measured to calculate a physically effective NDF factor for wet corn gluten feed, which was only 0.11 compared with 1.0 for alfalfa silage. Physically effective NDF also was determined for wet corn gluten feed by wet sieving; 22% of the particles were retained on the 3.35-mm screen or greater. Ruminal mat consistency increased and passage rate of wet corn gluten feed decreased with added hay. The inclusion of chopped alfalfa hay to a diet containing wet corn gluten feed increased ruminal mat consistency, rumination activity, and slowed passage rate, resulting in greater ruminal digestion of NDF from wet corn gluten feed. Depending on the response variable, the effectiveness of NDF from wet corn gluten feed varied from 0.11 to 0.74.     

Short communication: Effect of a citrus extract in lactating dairy cows

Dry matter intake is a main driver of energy balance in lactating dairy cows, and some plant extracts have been commercially fed to dairy cows to stimulate feed intake. Citrus extracts contain several bioactive components and have been shown to modify metabolism in other animal models. Our hypothesis was that a citrus extract would increase dry matter intake. Two experiments were conducted to determine the effect of a citrus extract on intake and milk production in lactating dairy cows. In experiment one, 11 early-lactation dairy cows (experiment 1; 77 ± 15 d in milk, mean ± standard deviation) were used in a switchback design, and in experiment two, 15 mid-lactation Holstein cows (experiment 2; 157 ± 44 d in milk, mean ± standard deviation) were used in a crossover design. In both experiments, treatments were control (no supplement) or a citrus extract (4 g/d in experiment 1 and 4.5 g/d in experiment 2). Treatment periods were 21 and 14 d in experiment 1 and experiment 2, respectively, with the final 7 d used for sample and data collection. No effect was observed for treatment on dry matter intake, feeding behavior, milk yield, milk fat yield, milk protein yield, or milk composition in either experiment. Treatment also had no effect on milk trans fatty acid profile, but the extract increased total 16 carbon fatty acids 0.9 and 0.6 percentage points in experiment 1 and experiment 2, respectively. Plasma nonesterified fatty acids were decreased 6 h after feeding in both experiments (11.1 and 16.0 μEq/L in experiment 1 and experiment 2, respectively). Plasma insulin was increased 1 h before feeding compared with the control in experiment 1 (3.36 vs. 2.13 µIU/mL) and tended to increase 1.79 units 1 h before feeding in experiment 2. The citrus extract had no effect on feed intake or milk production at the dose investigated, but changed plasma insulin and nonesterified fatty acids, indicating some metabolic effects requiring further investigation.     

Effects of fatty acid supplements on feed intake, and feeding and chewing behavior of lactating dairy cows

Saturated and unsaturated fatty acid supplements (FS) were evaluated for effects on feed intake, meal patterns, and chewing behavior. Eight ruminally and duodenally cannulated cows were used in a replicated 4 × 4 Latin square design experiment with 21-d periods. Treatments were control and a linear substitution of 2.5% fatty acids from supplemented saturated FS (SAT; prilled, hydrogenated free fatty acids) for partially unsaturated FS (UNS; calcium soaps of long-chain fatty acids). All rations contained identical forage and concentrate components including 37.2% forage and 13.5% cottonseed. Dry matter intake for SAT was not different from control, whereas increasing unsaturated FS linearly decreased dry matter intake by 3.2 kg. Wet weight of ruminal digesta decreased linearly up to 11.3 kg (13%) with increasing unsaturated FS. Adding supplementary fatty acids did not change meal number, meal length, or time between meals compared with control, but increasing unsaturated FS decreased meal size 0.22 kg (9%) within FS. The SAT treatment increased time spent ruminating by 56 (10%) and 42 (7%) min/d compared with control and UNS, respectively. Increasing saturated FS did not affect frequency of rumination bouts or interval between bouts, but increased rumination bout length by 5.6 min. Water intake was not affected by treatment, but increasing saturated FS linearly decreased the number of drinking bouts per day by up to 2.9 bouts (23%). Increased unsaturated fatty acid flow to the duodenum decreased feed intake by decreasing meal size, and increased saturated fatty acid flow to the duodenum increased rumination time per day by increasing rumination bout length.     

Maximal replacement of forage and concentrate with a new wet corn milling product for lactating dairy cows

Three experiments were conducted to determine the maximal amount of concentrate and forage that could be replaced with a new wet corn milling product. The corn milling product contained 23.1% crude protein, 9.9% ruminally undegradable protein, 13.7% acid detergent fiber, 40.3% neutral detergent fiber, and 2.6% ether extract (% of dry matter; DM). In experiment 1, 16 Holstein cows were assigned to one of four diets in a replicated 4 x 4 Latin square design with 28-d periods. The four diets contained 54.3% forage (alfalfa:corn silages, 1:1 DM basis) with the wet corn milling product replacing 0, 50, 75, or 100% of the concentrate portion (corn and soybean meal) of the diet (DM basis). The diets containing wet corn milling product resulted in 7.8% lower DM intake, equivalent milk production (28.5 kg/d), and 13.6% greater efficiency of 4% fat-corrected milk (FCM) production than the control diet. There was no effect of diet on ruminal pH. In experiment 2, 16 Holstein cows were assigned to one of four diets in a replicated 4 x 4 Latin square design with 28-d periods. The 100% concentrate replacement diet from experiment 1 was used as control diet. For the test diets, forage was replaced with 15, 30, or 45% of the corn milling product (DM basis). Efficiency of FCM production (1.16) was not affected by diet. Rumination time was reduced for the 30 and 45% forage replacement diets, but ruminal pH was unaffected. In experiment 3, 30 Holstein cows were assigned at parturition to either a control diet (no corn milling product) or a diet containing 40% corn milling feed in place of both forage and concentrate (optimal levels from experiments 1 and 2) for 9 wk. The diet containing corn milling feed resulted in 21% greater efficiency of FCM production than the control diet. These results indicate that a new feed product based on wet corn milling ingredients has the potential to effectively replace all of the concentrate and up to 45% of the forage in the diet for lactating dairy cows.     

Effect of exogenous amylase on lactation performance of dairy cows fed a high-starch diet

Exogenous amylase supplementation can increase starch and fiber digestibility in lactating dairy cows. We evaluated the effect of exogenous amylase supplementation on diets with high starch concentration (32% of dry matter). Twenty-eight Holstein cows (171 ± 80 d in milk, 4 primiparous) received a standard diet for 14 d and then a treatment for 63 d, in a covariate-adjusted randomized block design with repeated measures over time. Treatments were amylase [0.5 g of Ronozyme RumiStar (DSM Nutritional Products, Basel, Switzerland) per kg of total mixed ration dry matter] or control. The diets contained (% of dry matter): 39.4% corn silage, 11.2% rehydrated and ensiled mature corn grain, and 11.7% finely ground mature corn. Amylase increased milk yield (32.3 vs. 33.0 kg/d) and reduced dry matter intake (20.7 vs. 19.7 kg/d), increasing feed efficiency (1.52 vs. 1.63). Amylase also increased milk lactose synthesis (1.49 vs. 1.56 kg/d) and plasma glucose concentration (59.3 vs. 68.6 mg/dL). Secretions of milk fat and protein did not differ. Although milk urea N did not differ, amylase reduced the concentration of urea N in blood, suggesting an increase in ruminal starch degradation. However, the total-tract apparent digestibility of starch (96.3% of intake) and neutral detergent fiber (44.4% of intake), ruminal fermentation profile, and microbial yield estimated by urinary allantoin excretion did not differ. Cows fed amylase sorted in favor of long feed particles and against short particles, had shorter chewing activity (780 vs. 699 min/d), and had fewer meals per day (11.5 vs. 9.7). Amylase improved the feed efficiency of lactating cows fed a high-starch diet; the enzyme increased milk yield and reduced intake.     

Digestibility and clover proportion determine milk production when silages of different grass and clover species are fed to dairy cows

This study examined how silages of different grass and clover species affect dry matter (DM) intake, milk production, and eating behavior in dairy cows. The primary growth of perennial ryegrass (early and late harvested), festulolium, tall fescue, red clover, and white clover swards were cut, wilted, and ensiled without additives. Thirty-six Danish Holstein cows were fed ad libitum with total mixed rations containing 70% forage on DM basis in an incomplete Latin square design. The forage source was either 1 of the 6 pure silages or late perennial ryegrass silage mixed (50:50 on DM basis) with either red clover or white clover silage. Intake of DM, milk yield, and milk lactose concentration were higher, whereas milk fat and protein concentrations were lower when cows were fed clover compared with grass. No differences in DM intake and milk composition were detected between cows fed red clover and white clover, but white clover resulted in higher milk yield than red clover. Lower body weight, probably caused by lower rumen fill, in cows fed pure white clover compared with the other treatments indicated that intake was regulated physiologically instead of physically. Cows fed early perennial ryegrass, which had the highest silage organic matter digestibility (OMD), did not produce the expected amount of energy-corrected milk (ECM) compared with the other treatments based on the amount of OM digested in the gastrointestinal tract, but the reason was unclear. Across all other grass species, ECM was related to OMD. Inclusion of 50% clover in the diet increased ECM with 2.3 kg/d, and the response to OMD was comparable to the response for the grass silages. In situ fiber degradation profile parameters indicated that fiber in festulolium differed compared with fiber in the other grass species and resembled fiber in clover. Drinking and eating behavior differed markedly in cows fed pure white clover compared with the other treatments. Water intake per drinking bout was comparable among treatments, but cows fed pure white clover had higher drinking bout duration and reduced drinking rate. Additionally, meal size was smaller for cows fed pure white clover compared with the other treatments, for which meal size was similar. In conclusion, differences in ECM between different grass species can be explained by differences in OMD, and at a given OMD level inclusion of clover in the diet increased ECM.     

Polyethylene glycol as an indigestible marker to estimate fecal output in dairy cows

The objective of this study was to evaluate the accuracy of fecal output measurements using polyethylene glycol (PEG) as an external marker determined by near-infrared reflectance spectroscopy. In addition, the accuracy of dry matter intake predictions based on fecal output and digestibility estimated using an internal marker [indigestible neutral detergent fiber (iNDF)] was assessed. The experiment was conducted using 6 lactating dairy cows fed 2 different diets. Polyethylene glycol was administered twice daily into the rumen and the diurnal pattern of fecal concentrations and recovery in feces were determined. To evaluate the effects of alternative marker administration and sampling schemes on fecal output estimates, the passage kinetics of PEG in the digestive tract of dairy cows was determined and used for simulation models. The results indicate that PEG was completely recovered in feces and, thus, fecal output was accurately estimated using PEG. Good agreement between measured and predicted dry matter intake (standard error of prediction = 0.86 kg/d, R² = 0.81) indicates good potential to determine feed intake using PEG in combination with iNDF. The precision of cow-specific digestibility estimates based on iNDF was unsatisfactory, but for a group of cows iNDF provided an accurate estimate of dry matter digestibility. The current study indicated that, to overcome inherent day-to-day variation in feed intake and fecal output, the minimum of 4 fecal spot samples should be collected over 4 d. Preferably, these samples should be distributed evenly over the 12-h marker administration interval to compensate for the circadian variation in fecal PEG concentrations.     

Short communication: Effects of dietary fat supplements and forage:concentrate ratio on feed intake, feeding, and chewing behavior of Holstein dairy cows

Feed intake and feeding behavior of dairy cows fed diets that varied in fat supplementation and forage:concentrate (F:C) ratio were investigated. Eight multiparous Holstein dairy cows were used in a replicated 4 × 4 Latin square experiment with 21-d periods. Treatments were 1) no supplemental fat and 34:66 F:C ratio; 2) 2% hydrogenated palm oil and 34:66 F:C ratio; 3) 2% yellow grease and 34:66 F:C ratio; and 4) 2% yellow grease and 45:55 F:C ratio. Cows were fed ad libitum twice daily as total mixed ration with free access to water. Dry matter intake (DMI) was not affected by fat supplementation regardless of fat source, whereas increased F:C ratio (from 34:66 to 45:55) lowered DMI by 7.5%. Meal interval, eating rate, and meal size were lower for cows fed yellow grease, and eating rate was less for cows fed the 45:55 F:C ratio diet. Chewing activity was not affected by fat supplementation, but was greater for cows fed the 45:55 F:C ratio diet. Results suggest that supplementation of 2% hydrogenated palm oil or 2% yellow grease had little effect on DMI and chewing behavior of Holstein dairy cows fed a 34:66 F:C ratio diet. The 2 fat sources can replace each other, depending on the availability or cost. Results also showed that DMI and chewing activity can be effectively manipulated by changing the F:C ratio of diet.     

The value of different fat supplements as sources of digestible energy for lactating dairy cows

The effects of fat supplements that differed in fatty acid composition (chain length and degree of saturation) and chemical form (free fatty acids, Ca salts of fatty acids, and triacylglyceride) on digestible energy (DE) concentration of the diet and DE intake by lactating cows were measured. Holstein cows were fed a control diet [2.9% of dry matter (DM) as long-chain fatty acids] or 1 of 3 diets with 3% added fatty acids (that mainly replaced starch). The 3 fat supplements were (1) mostly saturated (C18:0) free fatty acids (SFA), (2) Ca-salts of fatty acids (CaFA), and (3) triacylglyceride high in C16:0 fatty acids (TAG). Cows fed CaFA (22.8 kg/d) consumed less DM than cows fed the control (23.6 kg/d) and TAG (23.8 kg/d) diets but similar to cows fed SFA (23.2 kg/d). Cows fed fat produced more fat-corrected milk than cows fed the control diet (38.2 vs. 41.1 kg/d), mostly because of increased milk fat percentage. No differences in yields of milk or milk components were observed among the fat-supplemented diets. Digestibility of DM, energy, carbohydrate fractions, and protein did not differ between diets. Digestibility of long-chain fatty acids was greatest for the CaFA diet (76.3%), intermediate for the control and SFA diets (70.3%), and least for the TAG diet (63.3%). Fat-supplemented diets had more DE (2.93 Mcal/kg) than the control diet (2.83 Mcal/kg), and DE intake by cows fed supplemented diets was 1.6 Mcal/d greater than by cows fed the control, but no differences were observed among the supplements. Because the inclusion rate of supplemental fats is typically low, large differences in fatty acid digestibility may not translate into altered DE intake because of small differences in DM intake or digestibility of other nutrients.     

A meta-analysis of feed digestion in dairy cows. 1. The effects of forage and concentrate factors on total diet digestibility

A meta-analysis based on published experiments with lactating dairy cows was conducted to study the effects of dietary forage and concentrate factors on apparent total diet digestibility. A data set was collected that included a total of 497 dietary treatment means from 92 studies. The diets were based on grass silage or on legume or whole-crop cereal silages partly or completely substituted for grass silage. The silages were supplemented with concentrates given at a flat rate within a dietary comparison. For the statistical evaluation, the data were divided into 5 subsets to quantify silage (digestibility, 42 diets in 17 studies; fermentation characteristics, 108 diets in 39 studies) and concentrate (amount of supplementation, 142 diets in 59 studies; concentration of crude protein, 215 diets in 82 studies; carbohydrate composition, 66 diets in 23 studies) factors on total diet digestibility. The diet digestibility of dairy cows was determined by total fecal collection or by using acid-insoluble ash as an internal marker. Diet organic matter digestibility (OMD) at a maintenance level of feeding (OMD_m) was estimated using sheep in vivo or corresponding in vitro digestibility values for the forage and reported ingredient and chemical composition values, with tabulated digestibility coefficients for the concentrate components of the diet. A mixed model regression analysis was used to detect the responses of different dietary factors on apparent total diet digestibility. Improved silage OMD_m resulting from earlier harvest was translated into improved production-level OMD in cows (OMD_p). The effects of silage fermentation characteristics on OMD_p were quantitatively small, although sometimes significant. Concentrate supplementation improved total diet OMD_m, but this was not realized in lactating dairy cows because of linearly decreased neutral detergent fiber (NDF) digestibility as concentrate intake increased. Increasing the concentrate crude protein amount quadratically improved OMD_p in cows, with the response being mostly due to improved NDF digestibility. Replacement of starchy concentrates with fibrous by-products slightly decreased OMD_p but tended to improve NDF digestibility. The true digestibility of cell solubles (OM - NDF) estimated by the Lucas test both from all data and from the data subsets was not significantly different from 1.00, suggesting that responses in OMD_p of dairy cows are mediated through changes in the concentration and digestibility of NDF.     

Short-term effects of regrouping on behavior of prepartum dairy cows

The objectives were to determine the effect of regrouping during the dry period on feeding, social, rumination, and lying behavior for cows that were moved to a new pen and cows that remained in their home pen but had new cows introduced. Forty-eight prepartum Holstein dairy cows were housed in groups of 6 and regrouped in groups of 3 (16 triads) with 1 triad moving to another pen and 1 triad staying in the same pen; the triad was considered the experimental unit. For 7 d before and 8 d after regrouping, cows were continuously monitored for feeding, rumination, and lying behavior by means of an electronic feeding system, a rumination logger on each cow's neck, and a data logger attached to 1 of the hind legs, respectively. Video recording was used to monitor displacements at the feeder for 3 h following the afternoon fresh feed delivery before regrouping and for the 2 subsequent afternoon feed deliveries after regrouping. Cows that were moved to a new pen after regrouping decreased DMI by approximately 9% on the day of regrouping compared with baseline values, but cows that remained in their home pen showed no significant decrease in intake after regrouping. Feeding rate decreased in both treatments by 10% after regrouping. Rumination times also decreased by approximately 9% in both treatments, reaching the lowest values on the day of regrouping for cows that stayed in the home pen and on the day after regrouping for the moved cows. Cows that were moved to a new pen displaced other cows at the feeder twice as frequently after regrouping, but no such effect of regrouping on cows that stayed in the home pen was observed. These results indicate that regrouping can affect behavior of prepartum dairy cows, especially those cows that are moved to a new pen.     

Feeding behaviors of transition dairy cows fed glycerol as a replacement for corn

Feed sorting is a natural behavior of dairy cows that can result in inconsistencies in the nutritive value of a total mixed ration (TMR). The objective of this study was to determine the effects of replacing high-moisture corn with glycerol on feed sorting and the feed intake pattern of transition dairy cows. Multiparous Holstein cows (n = 26) were paired by expected calving date, housed in individual tie stalls, and fed diets containing either glycerol or high-moisture corn once daily from d −28 to +56 relative to calving. Glycerol was included at 11.5 and 10.8% of the ration dry matter for the pre- and postpartum diets, respectively. The feed consumption pattern was determined by measuring TMR disappearance during the intervals from 0 to 4 h, 4 to 8 h, 8 to 12 h, and 12 to 24 h relative to feed delivery. Feed sorting was determined on d −16, −9, 9, 16, and 51 relative to calving at 4, 8, 12 and 24 h after feeding. The TMR particle size profile was determined at feed delivery and at 4, 8, 12, and 24 after feed delivery by using the Penn State Particle Separator (Nasco, Fort Atkinson, WI) to yield long (> 19 mm), medium (< 19 mm, > 8 mm), short (<8 mm, > 1.18 mm), and fine (< 1.18 mm) particles. Overall feed intake did not differ between diets and was 14.7 ± 0.4 and 20.2 ± 0.5 kg/d for the pre- and postpartum intervals, respectively. During the prepartum period, glycerol decreased the amount of feed consumed during the first 4 h after feed delivery (7.22 vs. 5.59 ± 0.35 kg; control vs. glycerol, respectively) but increased feed consumed from 12 through 24 h after feed delivery (2.22 vs. 3.82 ± 0.35 kg; control vs. glycerol, respectively). Similar effects on the feed consumption pattern were observed after calving. During the prepartum period, cows fed the control diet sorted against long particles, whereas cows fed glycerol did not sort against long particles (77.2 vs. 101.5 ± 3.50% of expected intake for control vs. glycerol; significant treatment effect). The data indicate that addition of glycerol to the TMR alters the feed consumption pattern to increase feed consumption late in the day at the expense of feed consumed immediately after feeding, and it reduces sorting behavior against long particles. Together, these may reduce diurnal variations in the rumen environment to promote greater rumen health in transition cows.     

Comparison of brown midrib-6 and -18 forage sorghum with conventional sorghum and corn silage in diets of lactating dairy cows

Total mixed rations containing conventional forage sorghum, brown midrib (bmr)-6 forage sorghum, bmr-18 forage sorghum, or corn silage were fed to Holstein dairy cows to determine the effect on lactation, ruminal fermentation, and total tract nutrient digestion. Sixteen multiparous cows (4 ruminally fistulated; 124 d in milk) were assigned to 1 of 4 diets in a replicated Latin square design with 4-wk periods (21-d adaptation and 7 d of collection). Diets consisted of 40% test silage, 10% alfalfa silage, and 50% concentrate mix (dry basis). Acid detergent lignin concentration was reduced by 21 and 13%, respectively, for the bmr-6 and bmr-18 sorghum silages when compared with the conventional sorghum. Dry matter intake was not affected by diet. Production of 4% fat-corrected milk was greatest for cows fed bmr-6 (33.7 kg/d) and corn silage (33.3 kg/d), was least for cows fed the conventional sorghum (29.1 kg/d), and was intermediate for cows fed the bmr-18 sorghum (31.2 kg/d), which did not differ from any other diet. Total tract neutral detergent fiber (NDF) digestibility was greatest for the bmr-6 sorghum (54.4%) and corn silage (54.1%) diets and was lower for the conventional (40.8%) and bmr-18 sorghum (47.9%) diets. In situ extent of NDF digestion was greatest for the bmr-6 sorghum (76.4%) and corn silage (79.0%) diets, least for the conventional sorghum diet (70.4%), and intermediate for the bmr-18 sorghum silage diet (73.1%), which was not different from the other diets. Results of this study indicate that the bmr-6 sorghum hybrid outperformed the conventional sorghum hybrid; the bmr-18 sorghum was intermediate between conventional and bmr-6 in most cases. Additionally, the bmr-6 hybrid resulted in lactational performance equivalent to the corn hybrid used in this study. There are important compositional differences among bmr forage sorghum hybrids that need to be characterized to predict animal response accurately.