Effects of adding beta-carotene to rations of lactating cows consuming different forages

Thirty-six Holstein cows fed a corn silage-based ration and 34 fed an alfalfa-grass silage-based ration were assigned according to calving date to receive either 300 mg/head per day of synthetic beta-carotene in a gelatin capsule or an empty gelatin capsule daily for the first 100 days postpartum. Supplemental vitamin A was provided at 3919 IU/kg of ration dry matter. Cervix diameters for cows supplemented with beta-carotene were smaller at 21 days and 28 days postpartum. Days from parturition to first observed estrus were less when beta-carotene was added and less when corn silage was fed. Means of other reproductive traits were more favorable for cows treated with beta-carotene (fewer services per conception and shorter intervals between parturition and conception). Milk progesterone at 21 and 28 days postpartum was not affected by either roughage or beta-carotene treatment. Milk from cows receiving alfalfa-grass silage contained lower somatic cell concentrations than that produced by cows fed corn silage. Milk somatic cell concentrations were lower in both roughage treatment groups for cows supplemented with beta-carotene. No effects of roughage or beta-carotene on milk production or milk fat percentages were significant.     

Sodium bicarbonate for early lactation cows fed corn silage or hay crop silage-based diets

To compare the effects of NaHCO3 in diets based on different forage sources, 16 Holstein cows, in a split-plot design, were assigned at 2 d postpartum to a total mixed diet of either 30% hay crop silage: 70% concentrate or 40% corn silage: 60% concentrate (dry basis) that contained 0 or 1.25% NaHCO3. Over the first 6 wk postpartum, NaHCO3 increased milk fat percentage in cows fed the corn silage-based diet. During wk 2 through 6 postpartum, NaHCO3 increased milk yield with the hay crop silage-based diet and tended to decrease milk yield with the corn silage-based diet. Sodium bicarbonate increased digestion of NDF with both forages and increased excretion of urinary nitrogen with the corn silage-based diet. Responses to NaHCO3 by cows in early lactation may depend on the nature of the dietary forage component.     

Effect of alfalfa forage preservation method and particle length on performance of dairy cows fed corn silage-based diets and tallow

A study was conducted to evaluate the effect of including alfalfa preserved either as silage or long-stem or chopped hay on DMI and milk fat production of dairy cows fed corn silage-based diets with supplemental tallow (T). Fifteen Holstein cows that averaged 117 DIM were used in a replicated 5 x 5 Latin square design with 21-d periods. Treatments (DM basis) were: 1) 50% corn silage:50% concentrate without T (CS); 2) 50% corn silage:50% concentrate with 2% T (CST); 3) 25% corn silage:25% short-cut alfalfa hay:50% concentrate with 2% T (SAHT); 4) 25% corn silage:25% long-cut alfalfa hay:50% concentrate with 2% T (LAHT); and 5) 25% corn silage:25% alfalfa silage:50% concentrate with 2% T (AST). Cows were allowed ad libitum consumption of a TMR fed 4 times daily. Diets averaged 16.4% CP and 30.3% NDF. Including 2% T in diets with corn silage as the sole forage source decreased DMI and milk fat percentage and yield. Replacing part of corn silage with alfalfa in diets with 2% T increased milk fat percentage and yield. The milk fat of cows fed CST was higher in trans-10 C18:1 than that of cows fed diets with alfalfa. No effect of alfalfa preservation method or hay particle length was observed on DMI and milk production. The milk fat percentage and yield were lower, and the proportion of trans-10 C18:1 in milk fat was higher for cows fed LAHT than for cows fed SAHT. Alfalfa preservation method had no effect on milk fat yield. Ruminal pH was higher for cows fed alfalfa in the diets, and it was higher for cows fed LAHT than SAHT. Feeding alfalfa silage or chopped hay appears to be more beneficial than long hay in sustaining milk fat production when 2% T is fed with diets high in corn silage. These results support the role of trans fatty acids in milk fat depression.     

Effect of peripartum energy concentration on production performance of Holstein cows

Ninety multiparous Holstein cows were used to measure the effect of energy during the prepartum and postpartum periods. During the prepartum period (63 d) half of the cows were fed grass silage ad libitum and a concentrate (16% protein) was offered daily at .25% of BW. The other half of the cows were offered the silage ad libitum but concentrate at .75% of BW. At calving each of the two prepartum groups was subdivided into three subgroups and fed corn silage for ad libitum consumption, 4.5 kg of hay/d and concentrate (20% protein) at .25 or .75% of BW daily, or ad libitum. After 112 d of lactation, all cows were switched to a diet consisting of corn silage fed ad libitum and 1 kg of concentrate (20% protein)/4 kg of milk. Roughage intake was reduced with an increase of concentrate consumption. Body measurements, calf weight, milk yield, feed efficiency, services per conception, and incidence of diseases were not influenced by the prepartum regimen. However, the interval from parturition to conception was 24 d longer for cows on the higher prepartum energy concentration (.75% of BW). None of the cows was able to meet its nutrient requirement in early lactation. Milk yield increased with each increment of concentrate in the postpartum diet. Reproduction and health were not affected by the postpartum regimen.     

Effects of differences in starch content of diets with whole cottonseed or rice bran on milk casein

Forty lactating Holstein cows in early to midlactation were used in a randomized complete block design to measure the effects of the following diets on milk casein. Treatments were four complete rations fed for ad libitum intake consisting of 1) 60% concentrate, 10% alfalfa hay, and 30% corn silage; 2) 45% concentrate, 10% alfalfa hay, 30% corn silage, and 15% whole cottonseed; 3) 60% concentrate, 5% alfalfa hay, 20% corn silage, and 15% whole cottonseed; and 4) 45% concentrate, 10% alfalfa hay, 30% corn silage, and 15% rice bran. Least squares means for daily DM intake all were significantly different and were 3.51, 3.90, 3.28, and 3.74% BW, respectively. Cows fed diet 3 had higher arterial glucose and insulin and venous insulin. Least squares means were significantly different for milk yield, 30.1, 31.4, 28.4, and 31.6 kg/d; for milk protein, 3.30, 3.13, 3.48, and 3.12%; and for casein N, .376, .358, 3.73, and .330, respectively. However, milk protein and casein N yields were similar for all cows. The diet that contained the highest percentage of starch did not result in a significantly higher percentage of casein N in the milk but had the lowest milk production. Both whole cottonseed and rice bran, substituted for concentrate, depressed milk protein percentage.     

Influence of formaldehyde-treated soybean meal on milk production

Forty-eight Holstein cows were fed one of four diets containing 12.5% crude protein (negative control); 15.5% crude protein with untreated soybean meal; 15.5% crude protein with formaldehyde (.3%)-treated soybean meal; or 18% crude protein (positive control). Diets were 60% concentrate, 22% corn silage, 14% alfalfa hay, and 4% beet pulp (dry matter). Data were collected during the first 200 d of lactation. Dry matter intake, milk, and milk component yields did not differ among cows fed the untreated soybean meal, treated soybean meal, and positive control diets. Cows fed negative control diet consumed less dry matter and produced less milk than cows fed the other diets. Milk protein yield was lower for cows fed the negative control diet compared with the other diets. Nonprotein nitrogen content of milk increased as dietary protein increased.     

Effect of feeding a corn hybrid selected for leafiness as silage or grain to lactating dairy cattle

A leafy corn hybrid was compared to a grain corn hybrid as silage and high moisture grain to evaluate dry matter intake, milk yield, and milk composition. Sixteen multiparous Holstein cows averaging 97 DIM were used in a feeding trial based on 4 x 4 Latin squares with 21-d periods. Each of four diets contained (dry basis) 8% chopped hay, 42% corn silage, 11% high moisture corn grain, 10% whole, fuzzy cottonseed, and 29% protein concentrate. One diet used leafy corn as both high moisture grain and silage. A second diet contained grain corn hybrid (control) as both high moisture grain and silage. A third diet contained leafy corn for high moisture grain and control corn for silage and the fourth diet used control corn for high moisture grain and leafy corn for silage. Cows fed diets containing leafy silage produced more milk and milk protein and ate more DM than cows fed control silage. The corn hybrid used for high moisture grain did not influence milk yield or composition. Dry matter intake was greater for cows fed the diet containing both leafy high moisture grain and leafy silage than for cows fed both control high moisture grain and control silage, but milk yield and composition were not different. When fed as silage, the leafy corn hybrid used in this experiment supported greater DMI as well as higher milk and protein yields when compared to the grain corn hybrid.     

Milk production and composition from cows fed wet corn distillers grains

Twelve lactating Holstein cows were utilized in a repeated switchback design to evaluate milk production and milk fat composition responses to wet corn distillers grains. Total mixed diets consisted of 31.4% corn silage, 18.4% alfalfa hay, and either 50.2% of a concentrate mix that contained mostly corn and soybean meal or 19.4% of a concentrate mix that contained mostly corn and 31.2% wet corn distillers grains. The first 4 wk of each 6-wk period were for adaptation to diets; data were collected during wk 5 and 6 of each period. Although dry matter intake (22.1 vs. 19.7 kg/d) was lower when cows were fed the wet corn distillers grains diet, milk production (30.7 vs. 30.8 kg/d) was similar for cows fed both diets. Milk fat (3.60 vs. 3.85%) was slightly higher, and protein (3.06 vs. 2.84%) was lower, when cows were fed the wet corn distillers grains diet. Milk fat from cows fed wet corn distillers grains contained lower concentrations of saturated fatty acids and higher concentrations of long-chain and unsaturated fatty acids. The feeding of wet corn distillers grains increased the proportion of unsaturated fatty acids in milk fat without changing milk production.     

Responses of primiparous and multiparous Holstein cows to additional energy from fat or concentrate during summer

Supplemental fat has been advocated for use during hot weather and often increases milk yield of cows past peak production when energy intake should not be limiting. Relative responses of primiparous and multiparous cows to supplemental fat or isocaloric addition of concentrates under hot weather conditions have not been determined. Nine multiparous and nine primiparous Holstein cows (154 and 167 d in milk, respectively) were used in a replicated 3 x 3 Latin square design with 28-d periods. Diets were 1) control (35% alfalfa silage, 25% corn silage, and 40% concentrate, dry matter [DM] basis); 2) control plus 3% fat (HF); and 3) high concentrate ([HC] 15% alfalfa silage, 25% corn silage, and 60% concentrate). Diets were isonitrogenous; diets HF and HC were isocaloric (1.60 Mcal of net energy for lactation [NE(L)] per kilogram DM) and higher energy than the control (1.52 Mcal/kg). No parity x diet interactions approached significance. DM intake (DMI) was greater when cows were fed HC than when they were fed HF (21.0, 20.1, and 21.3 kg/d for control, HF, and HC, respectively); intake of NE(L) tended to be increased only for HC. Milk yield was increased by higher-energy diets, but milk fat content was decreased. Milk total protein content was decreased by HF and increased by HC. Yield of solids-corrected milk (SCM) was not different among diets. Efficiency of milk production, expressed either as total milk solids yield per kilogram of DMI or as kilograms of SCM per megacalorie of NE(L) intake, was greater for HF than for HC. Plasma glucose was higher after feeding for cows fed HC; plasma nonesterified fatty acids were greater for HF. Respiration rate and rectal temperature were greater for HC than for HF. Regardless of parity, increased energy density from either fat or concentrate increased milk yield in midlactation cows, but diets caused energy to be partitioned differently among milk components and body storage. Supplemental rumen-active fat had modest advantages over additional starch-based concentrate during summer heat conditions.     

Supplementation of dairy cow diets with ammonium salts of volatile fatty acids

The objective was to determine the efficacy of a blend of ammonium salts of the volatile fatty acids, isobutyric, 2-methylbutyric, isovaleric, and valeric as a supplement to diets for dairy cows. Treatments of 0 (control) or 120 (supplemented) g/cow of the blend were fed daily from approximately 3 wk prepartum through a complete lactation. Five trials were conducted concurrently with a total of 116 multiparous Holstein cows. Dietary ingredients or combinations of ingredients differed in each of the trials. Diets contained either 1) corn gluten meal and urea, 2) soybean meal, or 3) cottonseed meal as the primary grain source of crude protein. The forage portion of the diets contained corn silage in combination with one or more of the following: alfalfa hay, alfalfa haylage, or wheat silage. Cows fed the supplement produced more milk and fat-corrected milk than the control cows for the 305-d lactation on four of the five diets, resulting in an average increase of 1.7 kg/d or 7%. Feed intake of cows on the supplemented diet was generally similar or lower than intake of the control cows throughout lactation, indicating that increased milk yield was associated with improved feed utilization. Percent milk fat was similar for cows on the supplemented diet, but fat yield was higher. Percent milk protein was lower for supplemented cows, but protein yield was about the same for both treatments because of higher milk yield. Health and reproduction were similar for all cows.     

Influence of particle size on the effectiveness of the fiber in corn silage

This experiment evaluated the influence of particle size on the effectiveness of fiber in corn silage relative to that in hay crop, which consisted of mostly alfalfa silage. Fifteen multiparous Holstein cows were assigned to five treatments in each of 2 yr. The design was replicated but truncated 5 x 5 Latin squares with three 21-d periods in 1994 and four 21-d periods in 1995. The five diets (2-yr average, dry basis) were a basal, low fiber control with 12% neutral detergent fiber (NDF) from hay crop forage (60% of total diet NDF); a high fiber control with 22% NDF from hay crop forage (82% of total diet NDF); and three diets each containing 12% NDF from hay crop forage and 9% NDF from coarse corn silage, fine corn silage, or an equal mixture of the two. An increase in the forage content above the basal amount with either hay crop or corn silage increased rumination and total chewing time. No detectable differences in rumination, total chewing time, or milk fat concentration were detected among the corn silage diets. In yr 1, yield of milk components and dry matter intake were greater for cows fed the four low alfalfa diets, but there was no effect due to particle size of the corn silage. In yr 2, linear increases in milk, fat, and protein yields were observed as the mean particle size of the corn silage decreased. Reduction of corn silage particle size did not affect chewing behavior.     

Impact of feeding a raw soybean hull-condensed corn steep liquor pellet on induced subacute ruminal acidosis in lactating cows

We used four ruminally cannulated, multiparous Holstein cows (690 kg; 21 kg/d milk) in a 2-period crossover design to determine the impact of feeding a raw soybean hull-corn steep liquor pellet (SHSL) on induced subacute ruminal acidosis (SARA) in lactating cows. Cows were fed control [30% alfalfa hay, 15% corn silage, 34% corn, 9% whole cottonseed, 5% soybean meal (SBM)] or SHSL (20% of diet DM) diets as TMR. SHSL replaced 6.2% alfalfa hay, 3.7% corn silage, 6.6% corn, and 3.3% SBM. Periods were 15 d (10 d adaptation, 2 d for prechallenge measures, and 3 d of SARA challenge). Cows were fed once daily at a common DMI dictated by the cow consuming the least. Cows were fasted 12 h before the first SARA challenge. For each of the three SARA challenges, cows were offered 75% of their daily diet at 0600 h. The remaining 25% of diet DM was replaced by ground corn, which was mixed with the orts that remained 2 h after feeding and placed into the rumen. Ruminal pH declined linearly with time after feeding, and this decrease was greater during the SARA challenges. Ruminal lactate increased linearly with repeated SARA challenges. Concentrations of total ruminal VFA increased linearly after feeding, and increases were greater when cows were challenged. No differences were observed due to SHSL inclusion. The model induced SARA, but partial replacement of alfalfa, corn silage, corn, and SBM by SHSL did not influence responses to SARA challenges.     

Corn silage hybrid effects on intake, digestion, and milk production by dairy cows

Three corn hybrids harvested as whole-plant silage were evaluated in three separate feeding trials with lactating dairy cows. In trial 1, 24 multiparous Holstein cows were used in a replicated 4 x 4 Latin square with 28-d periods. Treatments were conventional (Pioneer 3563) and leafy (Mycogen TMF 106) corn silage hybrids, each planted at low (59,000 plants/ha) and high (79,000 plants/ha) plant populations. There were no milk production differences between treatments. Total-tract digestibility of dietary starch was higher for leafy compared with conventional corn hybrids. In trial 2, 26 multiparous Holstein cows were assigned randomly to diets containing either conventional (48% forage diet) or brown-midrib (60% forage diet) corn silage in a crossover design with 8-wk periods. Milk yield was lower, but milk fat percentage and yield were higher, for the high-forage diet containing brown-midrib corn silage. In trial 3, 24 multiparous Holstein cows were used in a replicated 4 x 4 Latin square with 28-d periods. Treatments were corn silage at two concentrations of neutral detergent fiber (Garst 8751, 39.2% NDF; Cargill 3677, 32.8% NDF) each fed in normal- (53% of dry matter) and high- (61 to 67% of dry matter) forage diets. Milk production was not different between corn hybrids. Increased concentrate supplementation increased DMI and milk production. There were minimal benefits to the feeding of leafy or low-fiber corn silage hybrids. Feeding brown-midrib corn silage in a high-forage diet increased milk fat percentage and yield compared with conventional corn silage fed in a normal-forage diet.     

Effects of diet nitrogen and forage nitrogen insolubility on performance of cows in early lactation

Thirty-six Holsteins were allotted at parturition to six treatments to measure effects of diet nitrogen and increased insolubility of silage nitrogen on performance and ruminal, plasma, and milk constituents during the first 100 d of lactation. Diets contained 40% concentrate and 60% silage in dry matter. The six silage treatments were untreated corn silage (low nitrogen); untreated corn silage and untreated alfalfa silage (1:1); untreated corn silage and formaldehyde and formic acid-treated alfalfa silage (1:1); ammonia-treated corn silage (low nitrogen); treated corn silage and untreated alfalfa silage (1:1); or treated corn silage and treated alfalfa silage (1:1). Diets containing ammonia-treated corn silage had higher hot water-insoluble nitrogen and diets containing formaldehyde and formic acid-treated alfalfa had higher autoclaved rumen fluid-insoluble and hot water-insoluble nitrogen that their respective untreated silage diets. Dry matter intake, daily yields of milk and its constituents, ruminal NH3 nitrogen, and plasma urea nitrogen were lower for cows consuming low nitrogen diets containing only corn silage compared with cows consuming high nitrogen diets containing alfalfa. Dry matter intake and milk protein yields were greater for cows consuming treated alfalfa compared with untreated alfalfa in the diet. Daily 4% fat-corrected milk yields tended to be higher for diets containing treated alfalfa than untreated alfalfa. Cows fed diets containing NH3-treated corn silage had similar milk, fat, and protein yields compared with diets containing untreated corn silage and urea in the concentrate.     

Effects of corn processing and supplemental hay on rumen environment and lactation performance of dairy cows grazing grass-legume pasture

The effect of corn processing (9 kg of dry matter/d of ground dry shelled or 9 kg of dry matter/d of steam rolled) and supplemental hay (0 or 3.2 kg of dry matter/d of alfalfa hay) on milk yield and composition, rumen environment, and starch utilization by lactating cows grazing grass-legume pasture was studied. Twelve rumen cannulated, multiparous Holstein cows in early lactation (95 d in milk), were assigned to a 4 x 4 Latin square design replicated three times. Treatments were ground shelled corn-based concentrate, ground shelled corn-based concentrate plus alfalfa hay, steam-rolled, corn-based concentrate, or steam-rolled, corn-based concentrate plus alfalfa hay. Supplements were fed in equal proportions twice daily. Cows fed steam-rolled corn tended to have higher percentage of milk protein and lower milk urea nitrogen concentrations than cows fed shelled corn. Milk yield was not affected by corn processing or hay supplementation. Intake of pasture forage but not total dry matter intake was reduced by hay supplementation. Starch plus free glucose digestibility in the total tract was not affected by grain processing; however, starch plus free glucose digestibility tended to increase with hay supplementation. Supplemental hay increased starch plus free glucose digestibility through changes in rumen digestion kinetics. Hay supplementation reduced the liquid rate of passage, and tended to reduce particulate turnover. Rumen degradability of pasture forage organic matter tended to be higher for cows fed supplemental hay. Supplemental hay in these diets had a greater impact on starch utilization than corn processing.     

Eating and resting salivation in early lactation dairy cows

Salivation rates were measured by cardial collection in four ruminally fistulated, early lactation cows. Complete diets of 70% concentrate: 30% hay crop silage (dry matter) or an isonitrogenous, isocaloric mixture of 60% concentrate: 40% corn silage were fed ad libitum once daily in a replicated 2 X 2 Latin square design. Thirty-day periods, beginning 2 d postpartum, consisted of 22 d adaptation and 8 d for determination of eating behavior, eating and resting salivation rates, and rumen liquid turnover rate. Diet did not affect eating behavior, salivation rates, saliva volumes produced while eating or resting, or saliva composition, but degree of feed ensalivation (fresh basis) and volume of saliva per bolus were higher for the hay crop silage diet due to its higher dry matter content. Resting salivation rate and volume produced while resting were greater at wk 8 than wk 4 of lactation even when corrected to constant dry matter intake, indicating that adaptation to diet postpartum involved increased basal resting salivation rate. Rumen pH was lower for the hay crop silage diet, but rumen fluid kinetic measurements did not differ with diet or week of lactation.     

Influence of addition of yeast culture supplement to diets of lactating cows on ruminal fermentation and microbial populations

Six ruminally fistulated Holstein cows were utilized in a randomized block design to examine effects of yeast culture supplement on ruminal metabolism and apparent digestibility. Cows were fed a diet of 40% corn silage and 60% concentrate (DM basis). Treatments were control (supplement without yeast cells) and yeast culture supplement. Treatment periods were 6 wk. Ruminal pH, ammonia, molar proportions of acetate and isovalerate, and acetate: propionate ratio were lower and molar proportions of propionate and valerate higher in cows receiving yeast. The concentration of anaerobic bacteria tended to be higher and cellulolytic bacteria concentrations were greater in cows fed yeast than in cows receiving control diet. Supplemental yeast did not affect molar proportions of isobutyrate or butyrate, total VFA, or viable yeast concentrations in ruminal fluid. Ruminal liquid dilution rate and total tract apparent digestibilities were not different between treatments. Rate of disappearance of cellulose in vitro was lower in cows receiving yeast. Less variation in ammonia concentrations and microbial numbers suggest that ruminal fermentation was more stable in cows receiving yeast culture supplement.     

Response of lactating dairy cows to diets containing wet corn gluten feed or a raw soybean hull-corn steep liquor pellet

We evaluated effects of wet corn gluten feed (WCGF) and a novel product (SHSL) containing raw soybean hulls and corn steep liquor on performance and digestion in lactating dairy cows. In Experiment 1, 46 multiparous Holstein cows were assigned to control (C), WCGF (20% of diet DM), or SHSL (20% of diet DM). Diets were fed as a total mixed ration beginning after calving. The C diet contained (dry matter [DM] basis) 30% alfalfa hay, 15% corn silage, 32% corn, 9.3% whole cottonseed, 4.4% solvent soybean meal (SBM), and 3.3% expeller SBM. The WCGF replaced 10% alfalfa hay, 5% corn silage, and 5% corn grain, while expeller SBM replaced solvent SBM to maintain diet rumen undegradable protein. The SHSL replaced 10% alfalfa hay, 5% corn silage, 3% solvent SBM, and 2% corn. Dietary crude protein averaged 18.4%. Milk, energy-corrected milk (ECM), DM intake (DMI), and ECM/DMI were similar among diets during the first 13 wk of lactation. During wk 14 through 30 postpartum, WCGF and SHSL improved milk, ECM, milk component yield, and ECM/DMI. In Experiment 2, 6 cows were used to evaluate digestibility and rumen traits. Dry matter intake and total tract digestibilities of DM, fiber, and crude protein were not different among diets. Diets did not affect ruminal liquid dilution rate, pH, or concentrations of total volatile fatty acids or ammonia, but acetate:propionate was higher for C (3.38) than for WCGF (2.79) or SHSL (2.89). The WCGF and SHSL products can serve as alternative feedstuffs in diets fed to lactating dairy cattle.     

Effects of moisture content of complete diets on feed intake and milk production by cows

In two trials, 47 and 54 Holstein cows were fed diets containing ensiled forages, ensiled and dry forages, or diets of different moisture contents. In trial 1, diets were fed during a preliminary dry period, early lactation, late lactation, a second dry period, and a second early lactation. In trial 2, four diets identical except for moisture content (78, 64, 52, and 40% dry matter) were fed for the first 200 days of lactation. Substitution of dry hay for alfalfa silage increased dry matter intake during the first early lactation, whereas partial substitution of corn silage with straw did not affect intake during dry periods. Dry matter intake increased linearly as dry matter content of diet increased in trial 2. Neither milk production nor body weight were affected by treatment in either trial. Percentage total solids increased linearly as dry matter content of diet decreased in trial 2. Volatile fatty acids differed slightly, but no trends were consistent. No differences of daily chewing time were observed. From these trials, diets of less than 60 to 65% dry matter may reduce intake by lactating dairy cows.     

Effect of dietary acid detergent fiber on responses to high environmental temperature.

Twenty-seven multiparous Holstein cows averaging 120.7 DIM, 9 per diet, were assigned at random to 20, 17, or 14% ADF diets of corn, corn silage, and soybean meal, following a covariant period when all cows received the 14% ADF diet. An 18-d period (period 1) of cool weather preceded the onset of high environmental temperature from June 1988 to the end of July 1988 (period 2). Mean daily maximum air temperatures were 35.2, 36.8, and 34.7 degrees C for the covariant period and for periods 1 and 2, respectively. Minimum temperatures were 14.5, 16.0, and 21.5 degrees C. Milk production during both periods was higher, and the decrease in milk production associated with the onset of hot weather was lower, in cows fed the 14% ADF diet. Intake was not affected by diet during period 1 but was lower in cows fed the 17 and 14% ADF diets in period 2 relative to period 1. At any given environmental temperature, DMI was higher in cows fed lower ADF diets. Although DMI declined more rapidly with increasing daily minimum temperature with lower ADF diets, milk production was less sensitive to daily minimum temperature in cows fed the 14% ADF diet.