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Corn Grain Endosperm Type and Brown Midrib 3 Corn Silage: Feeding Behavior and Milk Yield of Lactating Cows

Department of Animal Science, Michigan State University, East Lansing 48824-1225

Corresponding author: Michael S. Allen; e-mail: allenm{at}msu.edu.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Interactions of endosperm type of corn grain and the brown midrib 3 mutation (bm3) in corn silage on feeding behavior, productivity, energy balance, and plasma metabolites of lactating dairy cows were evaluated. Eight ruminally and duodenally cannulated cows (72 ± 8 d in milk; mean ± SD) were used in a duplicated 4 x 4 Latin square design experiment with a 2 x 2 factorial arrangement of treatments. Treatments were corn grain endosperm type (floury or vitreous), and corn silage type (bm3 or isogenic control). Diets contained 26% neutral detergent fiber (NDF) and 30% starch. Floury endosperm grain decreased dry matter intake (DMI) 1.9 kg/ d compared with vitreous grain when combined with control corn silage but did not affect DMI when combined with bm3 corn silage. This interaction of treatments occurred because of changes in meal size; floury endosperm grain decreased meal size in control silage diets but increased meal size in bm3 corn silage diets. Ruminal pool sizes reflected DMI differences among diets, suggesting that ruminal fill was not the primary limitation on intake. Brown midrib 3 corn silage reduced rumination time per day and number of rumination bouts per day. Floury endosperm grain decreased 3.5% fat-corrected milk by 1.2 kg/d when combined with control silage but increased 3.5% fat-corrected milk by 2.1 kg/d when combined with bm3 corn silage. Starch and fiber digestibility interact to affect feeding behavior and milk production and production response to bm3 corn silage depends on the grain source that is fed.

Key Words: endosperm • brown midrib • feeding behavior

Abbreviation key: bm3 = brown midrib 3 mutation, iNDF = indigestible NDF, NE_M = net energy for maintenance, pdNDF = potentially digestible NDF

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
Energy intake often limits milk yield for high-producing dairy cattle, and strategies to maximize energy intake are critical to maximize production. Although diets are often formulated based on nutrient concentration alone, an analysis of the literature indicated that forage NDF digestibility measured in vitro or in situ was positively related to feed intake and milk yield; a mean increase in NDF digestibility of 8.4 units across forage comparisons was associated with a 1.4-kg/d greater DMI, resulting in a 2.1-kg/d greater 4% FCM yield (Oba and Allen, 1999). The brown midrib mutation decreases lignin content and increases in vitro NDF digestibility of forages (Cherney et al., 1991). Feeding brown midrib sorghum (Grant et al., 1995) and corn (Oba and Allen, 2000a) silages have improved DMI and milk production in dairy cows; increases in DMI are a result of changes in meal patterns (Oba and Allen, 2000a). Brown midrib corn silage can affect DMI by changing meal patterns but how brown midrib corn silage interacts with other dietary components to affect feeding behavior is unknown.

Variation in starch digestibility is often not considered in diet formulation but ruminal starch digestibility for a variety of feedstuffs ranged from 42 to 96% (Nocek and Tamminga, 1991). Starch digestibility is dependent on several factors, including grain type, processing methods, and physical characteristics of the grain. Starch granules in vitreous or flinty endosperm are surrounded by an insoluble protein matrix that resists digestion; in contrast, floury or opaque endosperm has a soluble protein matrix that is easily digested by ruminal microorganisms (Kotarski et al., 1992). Grain vitreousness is dependent on both hybrid and maturity (Philippeau and Michalet-Doreau, 1997) and is negatively correlated with in situ ruminal starch disappearance across hybrids (Philippeau et al., 1999a). Flint endosperm decreased ruminal starch digestibility 26 percentage units (34.8 vs. 60.8, P < 0.001) compared with a dent genotype when fed to steers (Philippeau et al., 1999b).

Increased ruminal starch degradability has significantly depressed DMI in some experiments but not others (Allen, 2000). Feed intake is a function of both meal size and meal frequency, determined by satiety and hunger, respectively, so meal patterns are likely influenced by ruminal starch digestion. Diets high in ruminally degraded starch decreased DMI by decreasing meal size (Oba and Allen, 2003a), and linear addition of refined cornstarch to the diet linearly decreased meal length but tended to increase the number of meals consumed in a day (Krause et al., 2003). Because endosperm type can dramatically change ruminal starch digestibility, research is needed to specifically examine the effect of corn endosperm type on feeding behavior of lactating dairy cows.

Although meal patterns and DMI are affected by changes in ruminal starch and fiber digestibility, potential interactions between varying digestibility of fiber source and endosperm type of corn grain on intake and production of dairy cows have not been investigated. We hypothesized that highly fermentable grain with floury endosperm would have greater effect at reducing meal size and possibly DMI when combined with brown midrib 3 (bm3) corn silage than control silage. The objective of this experiment was to evaluate effects of the bm3 mutation in corn silage and corn grain endosperm type on feeding behavior, DMI, milk yield, and energy balance of lactating dairy cows.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
This article is the second of 3 articles in a series from one experiment that evaluated effects of corn grain endosperm type and the bm3 mutation in corn silage. This article discusses treatment effects on feeding behavior and milk production, and the companion articles focus on ruminal fermentation and microbial N efficiency (Taylor and Allen, 2005a) and site of digestion and ruminal kinetics (Taylor and Allen, 2005b). Experimental procedures were approved by the All University Committee on Animal Use and Care at Michigan State University.

Cows and Treatments
Eight multiparous Holstein cows (72 ± 8 DIM; mean ± SD) from the Michigan State University Dairy Cattle Teaching and Research Center were assigned randomly to treatment sequence within duplicate 4 x 4 Latin squares balanced for carryover effects. A 2 x 2 factorial arrangement of treatments was used with main effects of corn grain endosperm type (floury or vitreous) and bm3 mutation in corn silage (present or absent). Treatment periods were 21 d, consisting of an 11-d diet adaptation period followed by 10 d of collection. Surgical preparation of ruminally and duodenally cannulated cows is reported in Taylor and Allen (2005b). At the beginning of the experiment, empty body weight (ruminal digesta removed) of cows was 531.8 ± 43.9 kg (mean ± SD).

Two corn hybrids, 6208FQ and 657 (Cargill Hybrid Seeds, Minneapolis, MN), were planted for silage in the spring of 2001 at the Michigan State University Research Farm. The hybrids are isogenic except that Cargill 657 contains the bm3 mutation. Harvesting conditions of both silages were reported previously (Taylor and Allen, 2005b). Nutrient compositions and physical characteristics of treatment corn silages used in the experiment are reported in Table 1 of Taylor and Allen (2005b).

Feeding behavior was monitored from d 15 through d 18 (96 h) of each period by a computerized data acquisition system (Dado and Allen, 1993). Data of chewing activities, feed disappearance, and water consumption were recorded for each cow every 5 s. When chewing equipment malfunctioned for an individual cow during a 24-h period (1100 to 1100 h), chewing behavior data were deleted for that cow during that 24-h period. The system successfully collected 79.0% of the total chewing behavior data (average 3.1 d/cow per period).

Blood was collected from a coccygeal vessel into 2 evacuated tubes (Vacutainer, Becton Dickinson, Franklin Lakes, NJ), one containing sodium heparin and one containing potassium oxalate and sodium fluoride. Samples were collected every 9 h from d 12 to 14, starting at 1400 h on d 12, so that samples represented 3-h intervals of a 24-h period to account for diurnal variation. Blood was centrifuged at 2000 x g for 15 min immediately after sample collection; plasma was harvested and frozen at –20°C until analysis.

Ruminal contents were evacuated manually through the ruminal cannula at 1500 h (4 h after feeding) on d 20 and at 0900 h (2 h before feeding) on d 21 of each period. Total ruminal content mass and volume were determined. During evacuation, 10% aliquots of digesta were separated to allow accurate sampling. Aliquots were squeezed through a nylon screen (1-mm pore size) to separate into primarily solid and liquid phases. Samples were taken from both phases for determination of nutrient pool size and an additional liquid sample was taken to measure VFA concentration. All samples were frozen immediately at –20°C.

Sample and Statistical Analyses
Diet ingredients and orts were dried and ground as described in a companion article (Taylor and Allen, 2005b). Rumen liquid and solid subsamples were lyophilized (TriPhilizer MP, FTS Systems, Stone Ridge, NY), ground, and recombined according to the original ratio of solid and liquid DM. All dried samples were analyzed for DM, ash, NDF, indigestible NDF (iNDF), potentially digestible NDF (pdNDF; 1 – iNDF), CP, and starch as described in Taylor and Allen (2005b).

Commercial kits were used to determine plasma concentration of insulin (Coat-A-Count, Diagnostic Products Corp., Los Angeles, CA), pancreatic glucagon (Linco Research, Inc., St. Charles, MO), glucose (glucose kit #510; Sigma Chemical Co., St. Louis, MO), NEFA (NEFA C-kit; Wako Chemicals USA, Richmond, VA), and ß-hydroxybutyrate (procedure no. 2440; Stanbio Laboratory, Boerne, TX). Milk samples were analyzed for fat, true protein, and lactose with infrared spectroscopy, and for urea nitrogen by chemical methodology based on a modified Berthelot reaction (ChemSpec 150 Analyzer, Bentley Instruments, Chaska, MN) by Michigan DHIA (East Lansing).

For analysis of feeding and chewing behavior data, daily means were calculated for number of meal bouts per day, interval between meals, meal size, eating time, ruminating time, and total chewing time. Daily means for each response variable were averaged over the number of successful collection days for each period and for statistical analysis were weighted according to the number of successful collection days.

Energy values for NE_L and net energy for maintenance (NE_M) were calculated as follows:

Ruminal pool sizes (kg) of OM, NDF, iNDF, and starch were determined by multiplying the concentration of each component in DM by the ruminal digesta DM weight (kg).

All data were analyzed using the fit model procedure of JMP (Version 4, SAS Institute, Cary, NC) according to the following model:

where µ = overall mean, C_i = random effect of cow (i = 1 to 8), P_j = fixed effect of period (j = 1 to 4), T_k = fixed effect of treatment (k = 1 to 4), PT_jk =interaction of period and treatment, and e_ijk = residual.

A reduced model without period x treatment interactions was used when this effect was not significant (P> 0.15). Orthogonal contrasts were used to determine main effect of corn silage type, main effect of corn grain type, and the interaction of corn silage type and endosperm type of corn grain. Pearson correlation coefficients were determined between cow-period observations for some parameters. Main treatment effects and correlations were declared significant at P < 0.05 and tendencies were declared at P < 0.10. Interactions between treatments were declared significant at P < 0.10 and tendencies were declared at P < 0.15.

Data for one cow were removed from all statistical analysis due to clinical mastitis during the first period. This cow was replaced with a spare animal for the remaining 3 periods. Another cow developed pneumonia during the diet adaptation subperiod of period 2 and was recovering during the first day of the collection period. Data for this cow were omitted from the digestibility subperiod of period 2 but were used from the feeding behavior subperiod as it had recovered sufficiently.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
DMI and Meal Patterns
A significant interaction of main effects was detected for DMI (P < 0.07; Table 1). Specifically, endosperm type had no effect on DMI within bm3 corn silage diets, but floury endosperm grain decreased intake by 1.9 kg/d compared with vitreous grain within control corn silage diets. This interaction of treatments was caused by changes in meal intake patterns; floury endosperm grain decreased DM meal size by 0.29 kg compared with vitreous corn grain when combined with control corn silage, but had the opposite effect (increasing DM meal size 0.20 kg compared with vitreous grain) for diets containing bm3 corn silage. Diets containing vitreous corn grain and bm3 silage did not reduce DMI despite a smaller meal size because cows consuming bm3 silage tended to eat a greater number of meals per day (10.6 vs. 11.7, P < 0.10). Control of meal size and frequency can be affected by numerous factors related to physical distension, metabolism of fuels, or hormonal effects. Because diets were relatively low in NDF and ruminal pool size responded in a similar fashion to DMI, physical factors were probably not limiting DMI. Therefore, the focus of this discussion will be on metabolic and hormonal factors limiting DMI.

Increased ruminal starch degradability has been shown to decrease DMI in some but not all cases (Allen, 2000). Inconsistent effects of ruminal starch fermentation on DMI might be the result of temporal pattern of fuel supply relative to the rate of use for milk yield and body tissues. Hypophagic effects of propionate are well documented and the mechanism might be related to its oxidation in the liver (Allen, 2000). Oxidation of a variety of metabolic fuels in the liver has been shown to depress feed intake for nonruminants (Langhans, 1996). Infusions of propionate into the rumen linearly decreased DMI and meal size in lactating cows, and extent of hypophagia induced by propionate infusion was positively related to plasma glucose concentration (Oba and Allen, 2003b). Oba and Allen (2003b) speculated that propionate from rapid ruminal fermentation is oxidized in the liver, causing satiety in animals when flux to the liver exceeds its flux through the gluconeogenic pathway. Increased glucose demand as milk yield increases creates a draw for metabolites to be used for gluconeogenesis rather than oxidation and might reduce the hypophagic effects of propionate. In support of this, plasma glucose was negatively correlated with DM meal size across cow period means (r = –0.37; P < 0.04) in the present experiment. Oxidation of metabolic fuels may explain the interaction of treatments observed for meal size. Floury endosperm increased ruminal propionate concentration (P < 0.001; Taylor and Allen, 2005a) and more rapid fermentation of starch from floury endosperm grain (Taylor and Allen, 2005b) likely increased absorption of propionate and other VFA during meals compared with vitreous endosperm corn grain. Because milk production (and glucose demand) was not increased in diets containing floury corn grain and control corn silage, these metabolic fuels might have been oxidized in the liver, thus reducing meal size. Conversely, in floury corn grain and bm3 corn silage diets, milk production and glucose demand were increased and fuels were likely directed toward gluconeogenesis, thus reducing oxidation of fuels and increasing meal size.

Although vitreous grain with bm3 silage reduced DM meal size, meal frequency tended to increase to compensate. Oba and Allen (2000a) reported that cows consuming bm3 corn silage ate smaller meals more frequently when compared with control corn silage in low (29%) NDF diets and speculated that more rapid VFA absorption decreased meal size but increased rate of VFA utilization, which resulted in hunger sooner and increased feeding frequency. In diets containing vitreous corn grain, greater oxidation of fuels within meals with bm3 vs. control corn silage might explain the smaller meal size. Although valerate absorption rate (a measure of VFA absorption rate) was not different among treatments, propionate concentration of rumen fluid was numerically higher and acetate:propionate ratio and ruminal pH were numerically lower in vitreous grain diets containing bm3 vs. control silage (Taylor and Allen, 2005a), consistent with greater propionate production. Additionally, plasma insulin:glucagon ratio tended to be higher for vitreous grain (P < 0.07), primarily because the diet containing vitreous corn grain and bm3 silage increased plasma insulin and reduced glucagon concentrations compared with other treatments. Higher plasma insulin:glucagon ratio is expected to result in increased oxidation of fuels in the liver (Watford and Goodridge, 2000), contributing to satiety. Hepatic oxidation of fuels varies over time and a reduction in meal size can be compensated for by an increase in meal frequency, which occurred for diets containing vitreous corn grain and bm3 corn silage.

In addition to oxidation of metabolic fuels, gut peptides could have influenced meal patterns because of the significant changes in site of starch digestion (Taylor and Allen, 2005b). Intraduodenal glucose infusion strongly elicited increases in plasma insulin, glucose-dependent insulinotropic polypeptide, and glucagon-like peptide-1 in humans (Lavin et al., 1998). Although glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 appear to play a role in signaling satiety (Havel, 2001), this has not been definitively established and little work has been conducted on the role of gut peptides in regulation of DMI for ruminants.

Chewing Activity
Chewing time (total and eating) was similar between endosperm types in control corn silage diets but floury endosperm grain tended to increase chewing time (total and eating) vs. vitreous grain in bm3 silage diets (interaction P < 0.12 and P < 0.03, respectively; Table 2). These interactions occurred because of the interaction of main treatment effects for DMI and for chewing per kilogram of DMI. Both floury corn grain and control silage increased chewing per kilogram of DMI but floury corn grain increased chewing to a greater extent when combined with control than with bm3 corn silage. Although rate of starch digestion was highest in this diet (Taylor and Allen, 2005b), cause and effect is not apparent. Ruminating time per day was positively related to rate of starch digestion across cow period means (r = 0.37; P < 0.05). Greater mastication increased starch digestion rate of several cereals (Beauchemin et al., 1994) and rate of starch digestion increases as corn particle size decreases (Callison et al., 2001). Greatest rate of starch digestion in the diet containing floury endosperm grain and control silage could be related to greater chewing per kilogram of DMI; however, the cause of greater chewing is unknown.

Total ruminating time per day, rumination bout length, and ruminating chews per bout and per day were greater for diets containing control vs. bm3 corn silage (Table 2). These results suggest that bm3 silage may not be as effective as control corn silage in stimulating rumination. In contrast, Oba and Allen (2000b) reported that ruminating time per day was not different between bm3 and control corn silages and concluded that bm3 corn silage was as effective as normal corn silage in stimulating chewing activity. Similar to results in the current experiment, brown midrib sorghum silage tended to decrease chewing per kilogram of NDF intake when compared with normal sorghum silage (Grant et al., 1995). Enhanced fiber degradability and increased particle fragility of brown midrib hybrids could cause brown midrib silages to be slightly less effective at stimulating chewing than normal corn silages. Differences in the ability of bm3 corn silage to stimulate chewing compared with control corn silage between the current experiment and that of Oba and Allen (2000b) might be because of differences in environmental and management effects on the in vitro NDF digestibility of the hybrids; 30-h in vitro NDF digestibility of the bm3 hybrid used in this experiment was greater than the bm3 hybrid used in the experiment by Oba and Allen (2000a). Corn hybrids with the bm3 mutation might be a less effective fiber source compared with normal corn silage and might require higher minimum forage NDF concentrations in diets.

Ruminal Nutrient Pools
Significant interactions of main treatment effects were detected for ruminal pools of DM (P < 0.03) and OM (P < 0.03; Table 3). Similar to DMI, floury endosperm decreased DM and OM pool size when combined with control silage but increased pool sizes when in bm3 silage diets. Significant interactions of treatments for ruminal pools of NDF (P < 0.03), pdNDF (P < 0.08), and iNDF (P < 0.02) were also detected. These pools reflected DMI differences among diets but also indicated greater pool size of pdNDF and smaller iNDF pool size in diets containing bm3 silage. The ability of the pool size to reflect changes in DMI indicated that intake was not likely limited by ruminal fill in these animals. Starch ruminal pool size tended (P < 0.07) to be greater for vitreous vs. floury corn grain because ruminal turnover rate of starch was numerically greater for floury vs. vitreous corn grain (Taylor and Allen, 2005b). Wet weight, volume, and density of ruminal contents did not differ among treatments.

Milk Yield and Composition
In control corn silage diets, floury corn grain decreased 3.5% FCM by 1.2 kg/d, but increased FCM by 2.1 kg/d when combined with bm3 corn silage (P < 0.10; Table 4). A similar trend occurred for milk yield (P < 0.22) and milk fat percentage (P < 0.11). Milk fat percentage was similar between diets containing floury grain regardless of silage type, but compared with floury grain, corn grain with vitreous endosperm tended to increase milk fat percentage in control silage diets but not in bm3 silage diets. Milk fat percentage was positively correlated with ruminal pH (r = 0.58; P < 0.001) and ruminal pH was greater for vitreous corn grain compared with floury corn grain when fed with the control corn silage (6.23 vs. 6.01; Taylor and Allen, 2005a). The increase in milk fat concentration by vitreous corn grain with control corn silage might be because of increased ruminal biohydrogenation and lower flux of trans C_18:1 fatty acids from the rumen with higher ruminal pH. Many studies have shown a negative relationship between milk trans C_18:1 fatty acids and milk fat concentration (Bauman and Griinari, 2003), and higher ruminal pH might result in more complete bio-hydrogenation of C_18:1 fatty acids in the rumen. Protein, lactose, and SNF composition of milk were not affected by any treatment. Although a significant main effect of silage (P < 0.005) was detected for MUN, differences were small (<1.5 mg/dL).

Energy Balance and Plasma Metabolites
An interaction of treatments was detected (P < 0.08) for NE_L intake (Table 5); floury corn grain decreased NE_L intake by 0.8 Mcal/d in control silage diets but increased NE_L intake by 4.3 Mcal/d in bm3 silage diets. This interaction reflects the changes in DMI observed but also accounts for greater digestibility of corn grain with floury endosperm. Milk NE_L (Mcal/kg) was increased for vitreous vs. floury corn grain combined with control silage but was decreased when combined with bm3 corn silage (interaction P < 0.05) because of the similar treatment effects on milk fat yield. A tendency for an interaction of treatments was detected for NE_L balance (P < 0.15). Energy balance was similar between endosperm types in control silage diets but was greater for floury grain than vitreous within bm3 silage diets.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

	ACKNOWLEDGEMENTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 
We wish to acknowledge Purina Mills, Inc., and Syngenta Seeds, Inc., for their financial support of this research. The authors thank N. K. Ames for performing duodenal and ruminal cannulations, and thank D. G. Main, Y. Ying, R. A. Longuski, C. S. Mooney, J. A. Voelker, K. J. Harvatine, B. J. Bradford, and R. E. Kreft for technical assistance and support.

Received for publication September 8, 2004. Accepted for publication December 10, 2004.

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TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS ACKNOWLEDGEMENTS REFERENCES

 


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