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Effect of Quantity, Quality, and Length of Alfalfa Hay on Selective Consumption by Dairy Cows

Department of Dairy Science, University of Wisconsin, Madison 53706

Corresponding author:
L. E. Armentano; e-mail:
learment{at}facstaff.wisc.edu.

	ABSTRACT

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

 
Twenty-four lactating Holstein cows were used in a replicated 6 x 6 Latin square design. Experimental periods were 6 or 7 d. Cows were housed in tie-stalls, and diets were fed ad libitum twice daily at 1100 and 1600 h. Diets contained 60% concentrate and either 40% alfalfa hay or 20% alfalfa hay and 20% alfalfa silage (dry matter basis). The effect of quantity, quality, and length of hay on sorting behavior was determined. Treatments consisted of 20% lower or higher quality long alfalfa hay, 20% lower or higher quality chopped alfalfa hay, and 40% lower or higher quality chopped alfalfa hay. Variation of sorting among cows was also determined. Particle size distribution of samples of as-fed total mixed rations and orts were determined using the Wisconsin particle size separator. Screens have square holes with diagonals of 26.9, 18, 8.98, 5.61, and 1.65 mm (screens Y₁ to Y₅, respectively). Sorting was calculated as the actual intake of each fraction expressed as a percentage of the predicted intake. Increasing the proportion of dry hay increased sorting. Quality of alfalfa hays that were offered did not affect sorting activity. Feeding long alfalfa hay increased selective consumption of fine particles. However, feeding long alfalfa hay also increased intake of longer particles because a higher percentage of long particles was offered. Across treatments, animals consistently sorted against longer particles in favor of finer particles. In particular, intake of Y₁ as a percentage of the predicted intake was the most variable. Average Y₁ intake, across the six treatments for each cow, was between 60 and 70% of predicted intake for four cows, 71 to 80% for 11 cows, 81 to 90% for five cows, 91 to 100% for two cows, and 101 to 110% for two cows. On one diet a cow failed to consume any of the Y₁ portion of the total mixed ration. This variation among animals in sorting of very long feed particles may have practical significance.

Key Words: sorting • selection • alfalfa hay

Abbreviation key: AM = a.m. sampling 21 h after feeding, 20HQC = 20% higher quality chopped alfalfa hay, 40HQC = 40% higher quality chopped alfalfa hay, 20HQL = 20% higher quality long alfalfa hay, 20LQC = 20% lower quality chopped alfalfa hay, 40LQC = 40% lower quality chopped alfalfa hay, 20LQL = 20% lower quality long alfalfa hay, NFC = nonfibrous carbohydrate, PAN = bottom pan, PM = p.m. sampling 4 h after feeding

	INTRODUCTION

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

 
Various chemical and physical dietary factors such as NDF concentration and particle size can affect rumen fermentation, and consequently milk production and composition. The NRC (2001) recommends feeding dairy cattle a minimum of 25% dietary NDF with 19% of dietary DM from forage NDF to avoid milk fat depression. The NRC (2001) also suggests increasing dietary NDF concentration when < 19% of dietary DM is forage NDF or when forage mean particle size is < 3 mm. Many studies have shown that a reduction in dietary particle size decreases milk fat concentration (Grant et al., 1990; Beauchemin et al., 1994; LeLiboux and Peyraud, 1999), chewing activity (Grant et al., 1990; Beauchemin et al., 1994; Leliboux and Peyraud, 1999), and rumen pH (Beauchemin et al., 1994; LeLiboux and Peyraud, 1999). Therefore, it is important to consider both NDF and particle size in diet formulation.

A further complication exists when cows sort, and therefore, do not ingest feeds in proportion to dietary concentration. In particular, when diets are formulated close to minimum recommendations, sorting could reduce intake of long particles and thereby possibly decrease chewing activity, rumen pH, and milk fat test.

No data are available on sorting activity of lactating dairy cattle fed a TMR, containing either corn silage or alfalfa silage. However, several studies have shown that cattle are capable of selecting among different anatomical portions present in grain stovers (Osafo et al., 1997; Methu et al., 2001). Increasing the amount of unchopped corn stover offered to dairy cattle increased the intake of more palatable plant parts such as leaf, sheath, and husk without changing the intake of the less palatable stems even though feed refusals were always at least 10% for all diets (Methu et al., 2001).

Physical processing can also affect sorting by dairy cattle. Osafo et al. (1997) fed chopped or unchopped sorghum stover to steers. Chopping decreased stem DMI, without affecting leaf plus sheath DMI. Therefore, chopping the sorghum stovers increased the stover leaf plus sheath intake expressed as a fraction of total intake, compared to feeding unchopped plants.

We hypothesized that dairy cattle could sort TMR diets resulting in reduced intake of long particles in the diet consumed relative to the abundance of these particles in the TMR offered. In most cases, the longer particles contain higher NDF concentration than the TMR. Therefore, sorting against long particles also reduces NDF concentration of the consumed diet compared to the diet offered. The net effect would be a reduction in both long fiber and total NDF intake. We also hypothesized that cows would sort more with diets containing lower quality hay and containing more hay and less silage. Therefore, the primary objective of this study was to investigate the effects of feeding different quantity, quality, and length of alfalfa hay as a TMR on sorting behavior of lactating dairy cattle.

Simultaneously, we wanted to determine how a sudden dietary change would impact sorting. In farms, cows often change diet during their lactation. This usually takes place by moving the animal from one pen to another; therefore, dietary changes happen quite rapidly. Also within a day, dairy cattle show different eating patterns (Beauchemin, 1991; Tolkamp et al., 2000). Therefore, a secondary objective was to measure sorting that occurred during the first day that a new diet was fed, after a period of adaptation, and at different times within the day.

We also hypothesized that animals could behave differently from each other in both a qualitative and quantitative manner. For example, a diet that is not sorted at all by any animal would likely perform differently than one for which half of the animals selectively consumes long particles, while the other half rejects long particles for an average of no sorting. An estimate of cow variability in sorting could help us understand why in some farms where all recommendations are followed, some cows may still have health problems associated with finely ground diets. Therefore, an additional objective of this study was to measure variability in feed sorting among animals.

	MATERIALS AND METHODS

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

 
Animals
Twelve multiparous and 12 primiparous lactating Holstein cows were utilized in a replicated 6 x 6 Latin square design. At the beginning of the study, multiparous cows averaged (± SD) 153 ± 7 DIM and produced (± SD) 42.1 ± 2.0 kg of milk daily; primiparous cows averaged 160 ± 19 DIM and produced 34.2 ± 3.6 kg of milk daily. Two squares consisted of multiparous cows, and two squares of primiparous cows. Cows were randomly assigned to squares within parity. Treatment sequences were ordered to minimize carryover effects of any treatment in the succeeding period. Cows were housed individually in tie-stall facilities and had free access to water. The Animal Care Committee of the College of Agriculture and Life Sciences of the University of Wisconsin-Madison approved all procedures involving animals.

Experimental Diets
Diets were fed for ad libitum intake twice daily at 1100 and 1500 h. The amount of feed offered was adjusted daily to obtain approximately 10% of orts (as-fed basis). Approximately 40% of the diet was offered at 1100 h and the remaining 60% at 1500 h. Cows were fed at 1100 h to follow barn schedule and at 1500 h, because at 1500 h animals were milked. Therefore, at 1500 h, refusals samples could be taken without disturbing the cows’ eating pattern. After the morning milking, cows were allowed to exercise daily from 0800 until 1100 h. Therefore, cows had access to feed for approximately 19 h. Cows were milked twice daily, but milk production is not reported due to short experimental periods. Diets contained 40% forage and 60% concentrate (DM basis). Diets were formulated to be isonitrogenous, isoenergetic, and have similar NDF concentrations. Forage was either alfalfa hay or a mixture of 50% alfalfa hay and 50% alfalfa silage (Table 1). Treatments consisted of different quantity, quality, and length of alfalfa hay: 20% higher quality long alfalfa hay (20HQL), 20% lower quality long alfalfa hay (20LQL), 20% higher quality chopped alfalfa hay (20HQC), 20% lower quality chopped alfalfa hay (20LQC), 40% higher quality chopped alfalfa hay (40HQC), and 40% lower quality chopped alfalfa hay (40LQC).

Orts and diets were sampled on the first and last 2 d of each experimental period. Day 1 was sampled to study feeding behavior immediately following a diet change. Orts samples were collected twice daily, at 1500 (PM) and 0800 h (AM), 4 and 21 h after the morning feeding, respectively. Sorting activity was determined 4 and 21 h after feeding, in order to better understand sorting activity across the day, especially because eating patterns vary during the day (Beauchemin, 1991; Tolkamp et al., 2000). However, our major interest was to determine how sorting affects total consumption. Data collected 21 h after morning feeding represent the entire day, and these data include sorting of the first 4 h as well as sorting from 4 through 21 h. During the PM sampling, orts were weighed, sampled, and returned to the manger; while at the AM sampling, orts were weighed, sampled, and discarded. Sorting and DMI at 21 h were calculated taking in consideration orts samples amounts collected during the previous PM sampling. Samples of orts were taken while the cows were either in the milking parlor or outside, to avoid interference of the sampling with the eating behavior. Particle size distribution of diets and orts were determined using the Wisconsin particle size separator, according to the ASAE S424.1 protocol (ANSI, 1998), and geometric mean particle length was calculated assuming a mean length of 48 mm for the material retained on the top screen. The separator has five square-hole screens (Y₁ to Y₅) with nominal diagonal openings of Y₁ = 26.90 mm, Y₂ = 18.00 mm, Y₃ = 8.98 mm, Y₄ = 5.61 mm, Y₅ = 1.65 mm, and a bottom pan (PAN).

Diets were adjusted weekly to account for forage DM fluctuation. Feed samples were collected during the last day of each experimental period, dried at 60°C for 48 h, ground to pass through a 1-mm screen (Wiley mill, Arthur H. Thomas, Philadelphia, PA), and analyzed for DM, CP, NDF, ADF, ash, and fatty acids. The CP concentration was determined by micro-Kjeldahl analysis (AOAC, 1990). Neutral detergent fiber was determined using -amylase (Sigma no. A3306: Sigma Chemical Co., St. Louis, MO), sodium sulfite and corrected for ash concentration according to Van Soest et al. (1991), adapted for Ankom²⁰⁰ Fiber Analyzer (Ankom Technology, Fairport, NY). Acid detergent fiber was determined using the method described by Goering and Van Soest (1970), adapted for Ankom²⁰⁰ Fiber Analyzer (Ankom Technology, Fairport, NY). Fatty acids were determined following the procedure described by Sukhija and Palmquist (1988) and represented the sum of C₁₄ to C₁₈. The nonfibrous carbohydrate (NFC) component was calculated as 100 - (NDF + ether extract + CP + ash), where ether extract was calculated as fatty acids plus one (NRC, 2001).

Calculations and Statistical Analysis
Sorting was calculated as the actual intake of each fraction (Y₁ to PAN) expressed as a percentage of the predicted intake, where predicted intake of Y_i equals the product of as-fed intake and as-fed fraction of Y_i in the TMR. Values <100% indicate selective refusals, >100% is preferential consumption, and =100% is no sorting. Data from the last 2 d of the sampling period were averaged prior to analysis and are labeled as d 6. All analyses were performed using the mixed procedure of SAS (SAS, 1998).

Data were originally analyzed as a single dataset (d 1 and 6, and 4 and 21 h). There was a significant (P < 0.05) day x hour x treatment interaction for Y₂, Y₃, Y₅, and PAN. Therefore, least squares means of d 1 at 4 h and at 21 h, and d 6 at 4 h and at 21 h are reported in Table 3. For simplicity, significance of treatment effects for sorting and intake are only reported at 21 h during d 6, which are probably most indicative of long-term behavior. Treatment effects were tested, including in the final model: period, treatment, parity, and parity x treatment interaction. Square within parity and cow within square x parity were included in the random statement. Parity x treatment, period x treatment, and period x parity interactions were tested in the initial model and were not significant (P > 0.25); therefore, they were dropped from the analysis. Orthogonal contrasts were built to test the effect of different quantity (40HQC and 40LQC vs. 20HQC and 20LQC), quality (40HQC, 20HQC, and 20HQL vs. 40LQC, 20LQC, and 20LQL), and length (20HQL and 20LQL vs. 20HQC and 20LQC) of alfalfa hay on feeding behavior. The interactions between quantity and quality (40HQC and 20LQC vs. 40LQC and 20HQC), and quality and length (20HQC and 20LQL vs. 20LQC and 20HQL) were also tested.

	RESULTS AND DISCUSSION

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

 
Diet Composition
Dietary chemical composition is reported in Table 2. The four diets with 20% alfalfa hay had similar DM concentration (69.3%), while the 40% alfalfa hay diets had higher DM concentration (89.9%). Ash, CP, ADF, and NFC were similar across all diets. Diets were balanced to have similar NDF concentration; however, 40LQC had a numerically higher NDF concentration compared to the remaining diets. Dietary geometric mean length was 4.70 mm for 20HQL, 4.59 mm for 20LQL, 4.03 mm for 20HQC, 3.88 mm for 20LQC, 3.29 mm for 40HQC, and 3.35 mm for 40LQC. Distribution of forages particles, as percentage of total mass, on the five screens and the pan, was 5.1, 18.6, 38.3, 13.0, 17.3, and 7.7 for alfalfa silage; 15.3, 13.4, 17.8, 11.2, 16.9, and 25.4 for LQC alfalfa hay; 17.5, 10.9, 14.3, 10.1, 18.6, and 28.6 for HQC alfalfa hay; 56.1, 6.7, 9.8, 8.5, 11.7, and 7.2 for LQL alfalfa hay; and 49.3, 5.4, 11.5, 9.9, 14.8, and 9.1 for HQL alfalfa hay. Dietary particles distribution is a result of forages and grain particles distribution; therefore, diets with 20% long hay had more material retained on Y₁ compared to 20% chopped hay (Figure 1). Doubling the amount of chopped hay in the diet (40 vs. 20% alfalfa hay) increased the amount of material retained on Y₁, even though the geometric mean length of 20% chopped hay diets was greater than the 40% chopped hay diets. There were no general differences in particle size distribution for diets with different alfalfa hay quality.

View larger version (40K): [in this window] [in a new window]   Figure 1. Dietary particles retained on each screen (as-fed basis). Screens are labeled from left (long material) to right (fine material) as Y1, Y2, Y3, Y4, Y5, and PAN, respectively. Treatments consisted of 20HQL = 20% higher quality long hay, 20LQL = 20% lower quality long hay, 20HQC = 20% higher quality chopped hay, 20LQC = 20% lower quality chopped hay, 40HQC = 40% higher quality chopped hay, and 40LQC = 40% lower quality chopped hay. Standard deviations for Y1,Y2, Y3, Y4, Y5, and PAN were: 3.5, 0.8, 1.0, 1.3, 2.6, 3.2 for 20HQL; 3.2, 1.5, 1.5, 0.7, 2.9 for 20LQL; 1.7, 0.4, 1.1, 1.1, 1.6, 1.9 for 20HQC; 1.9, 1.4, 1.3, 0.8, 2.5, 2.5 for 20LQC; 2.8, 1.2, 1.4, 1.8, 1.1, 6.5 for 40HQC; and 3.3, 1.2, 1.3, 0.9, 2.4, 3.6 for 40LQC.

View larger version (25K): [in this window] [in a new window]   Figure 2. Cow variability for sorting (as-fed basis) 21 h after morning feeding. Data are averaged across d 1 and 6 and also across diets, by cow. Screens are labeled from the top (long material) to the bottom (fine material) as Y1 (), Y2 (), Y3 (), Y4 (•), Y5 (), and PAN (), respectively.

Although the 4-h data provides an interesting insight into cow behavior, daily consumption measured at 21 h is more likely to impact rumen function and animal performance. In contrast to the 4-h data, the 21-h data show a day effect only for screen Y₄ (P < 0.05), with a slight increase in sorting against this screen or less preferential consumption following adaptation. The impact of this change is probably minor given that consumption for this screen was always very close to predicted intake. Day by treatment interactions at 21 h were significant (P < 0.05) only for screens Y₂ and Y₃. For the 40% chopped hay diets that had the most sorting against longer particles, screens Y₂ and Y₃ were less extensively sorted on d 6 compared to d 1. These moderately long particles seemed less prone to sorting than the longest particles, and this difference was magnified as cows adapted to the diets.

Dietary effects.
Day-6 data are the best indication of chronic sorting activity. There were no significant quantity x quality or quality x length interactions in these data.

Quantity.
Across treatments, cows sorted against longer particles and in favor of finer particles (Figure 2). This behavior was most evident when cows were fed 40% chopped hay. Cows fed 40% chopped hay reduced Y₁ intake by 40.2 percentage units and increased PAN intake by 10.0 percentage units compared to their predicted intake (Figure 3). Feeding 20% chopped hay and 20% alfalfa silage reduced the extent of sorting compared to 40% hay (P < 0.0001). It is not possible to distinguish if this was due to the change in particle size distribution offered or if it was the result of the lower moisture content. Methu et al. (2001) reported increased sorting due to increasing the amount of corn stover offered above requirements. Therefore, the increased sorting activity could have resulted from an increased percentage of long particles offered. No data are available regarding sorting when feeding diets with different DM contents. When dry feeds are mixed, the feeds generally tend to separate into fine, high-density particles at the bottom of the manger and longer, lower density particles on top. Cows have little ability to nibble; therefore, they utilize their tongues and noses to gather and sort their feed (Beauchemin, 1991). Therefore, if dry diets are fed, cows can use their tongues to selectively eat the fine particles and their noses to push away the longer particles.

View larger version (13K): [in this window] [in a new window]   Figure 3. Least squares means for sorting (as-fed basis) of cows fed 40% () vs. 20% () alfalfa hay measured on d 6 at 21 h. Screens are labeled from left (long material) to right (fine material) as Y1, Y2, Y3, Y4, Y5, and PAN, respectively. Replacing alfalfa silage with chopped alfalfa hay increased sorting with significant changes occurring on each screen (Y1 to PAN, P < 0.05).

In this experiment, diets were not balanced for forage NDF but for total NDF. As a result, increasing the quality of alfalfa hay corresponded to replacing forage NDF with nonforage NDF (Tables 1 and 2). Because preferential consumption of the finer screens must accompany relative rejection of the coarser screens, it is very possible that the composition of the finer screens affected sorting behavior. Small differences in particle size distributions between the two qualities of hay resulted in significantly different intake (as-fed basis) of feed retained on individual screens but similar total DMI (Table 4).

Length.
Contrary to the Osafo et al. (1997) study, where chopping increased animal’s capability to selectively refuse stems, in this experiment feeding long alfalfa hay significantly increased selective consumption of Y₅ (P = 0.01) and PAN (P = 0.02), although the increase was small (Figure 3). In the Osafo et al. (1997) experiment, the difference between treatments was chopped vs. intact plant, but in our experiment, forages were mixed with grains, and all diets underwent some mixing and particle size reduction in the TMR mixing wagon. The present results are probably more applicable to TMR feeding system.

Dry matter intake was not different feeding chopped or long alfalfa hay. Y₁ as-fed intake was greater for the long material because more long material was offered. Feeding 20% chopped hay increased intake (as-fed basis) of feed retained on the finest screens (Y₄, Y₅, and PAN). Although feeding long hay increased preferential consumption of the finer particles, a higher amount of Y₅ and PAN was offered feeding 20% alfalfa hay diet, resulting in overall higher intakes.

	CONCLUSIONS

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

 
In each of the six TMR fed in this study, cows sorted most against the longest particles in the diet. Consumption of particles relative to amount offered increased progressively as particle size decreased. Sorting of each screen was similar for long and chopped hay; therefore, feeding long hay increased intake of long particles. However, diets based on long hay are likely to have a larger difference between the TMR offered and that consumed due to the presence of more long particles. In addition, sorting increased when feeding 40 vs. 20% chopped alfalfa hay. This resulted in less absolute intake of long particles on the 40% diet even though the 40% diet had more long particles in the TMR. Hay quality did not affect sorting activity per se, but in practice, reduced hay quality may amplify the impact of sorting by concentrating dietary NDF into the longest, most easily sorted feed particles. It is important to note that cows behave differently and sorted to a different degree. This was true with individually fed animals where a sorting animal has a progressively coarser diet as the day progresses. In a free-stall barn, where sorting cows are free to move to minimally sorted TMR, this sorting behavior could be enhanced.

	ACKNOWLEDGEMENTS

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

 
The authors thank the barn crew of the University of Wisconsin Emmons Blaine Dairy Cattle Research Center located in Arlington, for their help chopping hay, feeding cows, and collecting samples. This project was supported by USDA formula funding as part of Regional project NC-185.

Received for publication May 10, 2002. Accepted for publication August 27, 2002.

	REFERENCES

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

 


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Beauchemin, K. A. 1991. Ingestion and mastication of feed by dairy cattle. Pages 439–463 in Vet. Clin. North Am. Food Anim. Pract. Vol. 7, No. 2.

Beauchemin, K. A., B. I. Farr, L. M. Rode, and G. B. Schaalje. 1994. Effects of alfalfa silage chop length and supplementation of long hay on chewing activity and milk production of dairy cows. J. Dairy Sci. 77:1326–1339.[Abstract]

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Grant, R. J., V. F. Colenbrander, and D. R. Mertens. 1990. Milk fat depression in dairy cows: Role of particle size of alfalfa hay. J. Dairy Sci. 73:1823–1833.[Abstract]

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Osafo, E. L. K., E. Owen, A. N. Said, M. Gill, and J. Sherington. 1997. Effects of amount offered and chopping on intake and selection of sorghum stover by Ethiopian sheep and cattle. Anim. Sci. 65:55–62.

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