D. I. Harvatine, J. E. Winkler, J. L. Firkins1, and M. L. Eastridge
The Ohio State University Department of Animal Sciences
By-product feeds are becoming increasingly popular as non-forage fiber sources (NFFS) in lactating dairy-cattle diets when forage quality or quantity is limiting. To evaluate the fiber value of one of these by-product feeds, a study was conducted to determine the effectiveness of whole linted cottonseed (WCS) when fed with corn differing in ruminal starch digestibility. Six mid-lactation Holstein cows, fitted with ruminal and duodenal cannulas, were used in a 6 x 6 Latin Square digestibility trial. Cows were fed six different alfalfa-silage based total mixed ration (TMR) diets. Diets were: forage control with ground corn (21% forage NDF [fNDF]), 5% WCS with ground corn or steam-flaked corn (18% fNDF), 10% WCS with ground or steam-flaked corn (15% fNDF), and 15% WCS with ground corn (12% fNDF). Dry matter intake increased quadratically with increasing substitution of alfalfa silage neutral detergent fiber (NDF) with NDF from WCS. Milk production did not differ across treatments, although milk fat percentage was affected quadratically, and milk protein percentage increased linearly with increasing substitution with WCS. The WCS are as effective as alfalfa silage at maintaining milk fat percentage in diets containing ground corn and at least 12% fNDF. Ruminal pH and acetate: propionate decreased linearly with increasing WCS level. Ruminating and total chewing activity, expressed as minutes per day, did not differ across diets, indicating that NDF from WCS is as effective as NDF from alfalfa silage in maintaining chewing activity in low forage diets. However, total chewing time, expressed as minutes of chewing per pound of fNDF, increased quadratically with increasing WCS addition. This suggests that cows may possess an adaptive mechanism that maximizes the efficiency of rumination when fNDF intake is limited. No interactions between corn source and WCS were detected for chewing measures, suggesting that WCS is equally effective in lactating dairy cattle diets that contain moderate or high ruminal starch digestibility.
Ruminants have a need for dietary fiber. Dietary fiber of good quality, provided in the proper quantity and physical form, helps to maintain DM intake, rumen function, and milk fat percentage, and therefore, aids in the prevention of metabolic disorders. The NRC (1989) recommended that lactating cow diets contain a minimum of 25 to 28% dietary NDF with 75% of the dietary NDF provided as forage, resulting in 21% dietary fNDF. In addition to the level of dietary NDF, the effectiveness of the dietary fiber source must also be considered. Effectiveness is defined as the ability of a dietary fiber source to stimulate chewing, the ability to maintain normal milk fat percentage and fat corrected milk production, or both (Grant, 1997). Chewing stimulates saliva production, which serves as a buffer for the acid end products of ruminal fermentation. However, as increasing levels of milk production necessitate feeding energy-dense diets that contain large amounts of highly fermentable feeds, such as starch from grains, it becomes a challenge to provide enough energy from the grains while providing enough buffering capacity from fiber sources. Increasing dietary fiber from traditional fiber sources (i.e., forages) to compensate for increased production of fermentation acids is not always successful because of the limitations imposed by gut fill. As a result, recent attention has been focused on increasing the physical effectiveness of dietary fiber sources by using NFFS, such as WCS. The NFFS are often used when forage quality or quantity is limiting. The NFFS may provide the needed physically effective fiber without causing gut fill to be a limitation. Many factors need to be considered by researchers and dairy producers before NFFS, such as WCS, can optimally be used in rations. These factors include the physical effectiveness of the WCS, the ability of WCS to dilute dietary starch, the ruminal digestibility of the starch, and the potential interaction that may occur between WCS and the forage components of the ration. Thus, the purpose of this study was to evaluate the effectiveness of WCS as a NFFS when fed in diets varying in starch availability.
Six first-lactation Holstein cows (average body weight = 1,139 lbs) fitted with ruminal and duodenal cannulas were arranged in a 6 x 6 Latin square design. Experimental feeding periods were 21 days, with the first nine days used to allow cows to adjust to the treatment diet and the last 12 days for sample collection. At the start of the experiment, cows averaged 122 days in milk. Cows were injected with Posilac® (Monsanto, St. Louis, Mo.), a synthetic bovine somatotropin, every two weeks. Cows were housed in a tie-stall barn and milked twice daily.
All experimental diets were alfalfa-silage based TMR and were fed twice daily. Diets were balanced to be equivalent in nutrient composition (Table 1). The forage control diet (FCG) with no WCS addition contained the NRC recommendation of 21% fNDF. The WCS diets contained WCS at low (L), medium (M), or high (H) concentrations (5, 10, and 15% of dietary DM, respectively). In diets with ground (G) corn, alfalfa silage was replaced with WCS on an NDF basis to achieve diets with 18% fNDF (LG), 15% fNDF (MG) and 12% fNDF (HG). To evaluate the potential interaction of starch availability and level of forage substitution, the ground corn in the LG and MG diets was replaced with steam-flaked (SF) corn (LSF and MSF diets).
Table 1. Ingredient and Chemical Composition of the Forage Control Diet and Diets in Which Whole Cottonseed, Fed with Ground Corn or Steam-Flaked Corn, Replaced Alfalfa Silage on an NDF Basis. |
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|---|---|---|---|---|---|---|
| Diets1 | ||||||
| Ingredients2 | FCG | LG | MG | HG | LSF | MSF |
| (% os DM) | ||||||
| Alfalfa silage | 53.0 | 44.7 | 38.0 | 30.3 | 44.7 | 38.0 |
| Whole linted cottinseed | .... | 5.00 | 10.0 | 15.0 | 5.0 | 10.0 |
| Cottonseed hulls | .... | 0.65 | 0.93 | 1.43 | 0.65 | 0.93 |
| Corn, ground shelled | 27.7 | 30.4 | 32.6 | 35.2 | .... | .... |
| Corn, steam-flaked | .... | .... | .... | .... | 30.4 | 32.6 |
| Soybean meal, 48% CP | .... | 3.63 | 7.36 | 11.16 | 3.63 | 7.36 |
| Roasted soybeans, cracked | 14.41 | 9.89 | 4.94 | .... | 9.89 | 4.94 |
| Remaining Ingredients3 | 4.87 | 5.69 | 6.18 | 6.95 | 5.69 | 6.18 |
| Chemical Composition: | ||||||
| NDF | 30.9 | 31.3 | 31. | 31.4 | 31.1 | 31.6 |
| Forage NDF | 21.5 | 18.3 | 15.4 | 12.3 | 18.1 | 15.4 |
| ADF | 21.5 | 21.4 | 21.7 | 21.5 | 21.6 | 21.8 |
| 1 FCG = forage
control with groune corn; LG = low cottonseed with ground corn; MG = medium
cottonseed with ground corn; HG = high cottonseed with ground corn; LSF
= low cottonseed with steam-flaked corn; and MSF = medium cottonseed with
steam-flaked corn. 2 NDF = neutral detergent fiber; forage NDF = NDF from forage; and ADF = acid detergent fiber. 3 Contained soybean hulls, chromic oxide (a digesta marker), minerals and vitamins. |
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Individual feed intakes were measured daily. Milk samples were taken at a.m. and p.m. milkings on three consecutive days during the third week of the feeding period. Ruminal fluid samples were taken at 3, 6, 9, and 12 hours after the a.m. feeding on one day during the third week to measure ruminal pH and to quantify volatile fatty acid concentrations. Cows were monitored for chewing activity every five minutes for a continuous 24-hour period during the second week to determine the amount of time spent chewing while eating or ruminating.
The chemical composition of the diets is shown in Table 1. Total NDF values were higher than the formulated values of 28% for each diet because of variations in NDF for whole cottonseed and the grain mix. Forage NDF concentrations were very similar to the formulated values for each diet. Cottonseed hulls were added to the diets in slightly different amounts during each period to balance NDF and enable the replacement of alfalfa silage NDF with cotton (WCS plus cottonseed hulls) NDF on a one-to-one basis as alfalfa silage NDF varied.
Dry-matter intake (DMI), expressed as pounds per day and as a percentage of body weight, increased quadratically as the proportion of WCS in the diet increased (Table 2). This supports the findings of others (Mooney and Allen, 1997; Clark and Armentano, 1993) that showed increased DMI when WCS replaced a portion of the dietary forage. The reduction of dietary forage content and the reduced feed particle size associated with the addition of WCS may have been responsible for the increased DMI due to decreased gut fill effects or increased rate of passage. Similarly, NDF intake increased quadratically as the proportion of WCS in the diet increased. Dry matter and NDF intakes were decreased when cows were fed steam-flaked corn diets compared with cows fed similar diets (low and medium WCS) with ground corn.
Table 2. Least Squares Means for Response by Cows Fed the Control Diet or Diets in Which Whole Cottonseed, Fed with Ground Corn or Steam-Flaked Corn, Replaced Alfalfa Silage on an NDF Basis. |
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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Diets1 | SE2 | P3 | |||||||||||
| Item4 | FCG | LG | MG | HG | LSF | MSF | n=5 | n=6 | L | Q | C | Corn | Intx |
| DMI, lb/day | 39.2 | 43.4 | 45.1 | 44.7 | 42.4 | 41.4 | 1.0 | 0.9 | <0.01 | 0.02 | NS | 0.02 | 0.17 |
| NDF intake, lb/day | 12.2 | 13.7 | 14.4 | 14.2 | 13.3 | 13.1 | 0.4 | 0.3 | <0.01 | 0.04 | NS | 0.03 | NS |
| BW, lb | 1,205 | 1,242 | 1,250 | 1,248 | 1,241 | 1,243 | 13 | 11 | 0.01 | 0.10 | NS | NS | NS |
| DMI % of BW | 3.25 | 3.50 | 3.61 | 3.59 | 3.43 | 3.40 | 0.07 | 0.07 | <0.01 | 0.05 | NS | 0.04 | NS |
| Milk, lb/day | 58.5 | 58.8 | 61.5 | 60.2 | 64.3 | 61.6 | 2.8 | 3.2 | NS | NS | NS | NS | NS |
| Milk protein, % | 3.04 | 3.16 | 3.14 | 3.26 | 3.10 | 3.19 | 0.05 | 0.04 | <0.01 | NS | 0.16 | NS | 0.18 |
| Milk fat, % | 3.45 | 3.70 | 3.58 | 3.41 | 3.08 | 3.19 | 0.11 | 0.09 | NS | 0.04 | NS | <0.01 | NS |
| Ruminal pH | 6.28 | 6.13 | 6.12 | 5.93 | 6.07 | 6.02 | 0.08 | 0.07 | <0.01 | NS | NS | NS | NS |
| Total VFA, mM | 102.4 | 106.7 | 108.2 | 110.3 | 107.6 | 107.8 | 4.8 | 4.3 | 0.2 | NS | NS | NS | NS |
| Acetate: propionate | 3.98 | 3.59 | 3.21 | 3.01 | 2.98 | 2.77 | 0.22 | 0.21 | <0.01 | NS | NS | <0.01 | NS |
| 1 FCG = forage
control with groune corn; LG = low cottonseed with ground corn; MG = medium
cottonseed with ground corn; HG = high cottonseed with ground corn; LSF
= low cottonseed with steam-flaked corn; and MSF = medium cottonseed with
steam-flaked corn. 2 SE = standard error. For the LG treatment, n=5; for all other treatments, n=6. 3 Probability (P) of a treatment response; NS = not significant (P>0.20). Contrasts compared the linear (L), quadratic (Q) and cubic (C) effects of increasing level of whole cottonseed in the diet when ground corn was used aas the corn source. Contrast (Corn) compared the effect of corn source (ground vs. steam-flaked) when low or medium levels of cottonseed were fed. Contrast (Intx) evaluated the interaction of corn source (ground vs. steam-flaked) and level of cottonseed (low vs. medium). 4 DMI = dry matter intake, NDF = neutral detergent fiber, BW = body weight, and VFA = volatile fatty acids. |
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No differences were observed for milk production, although milk fat percentage responded quadratically with increasing substitution of forage with WCS. Milk fat percentage was similar or higher in the WCS diets with ground corn when compared to the forage control diet, indicating that WCS was as effective as alfalfa silage in maintaining milk fat percentage. Milk protein percentage increased linearly with increasing level of WCS in the diet.
As the level of WCS substitution increased, the average ruminal pH decreased linearly from 6.28 for cows fed the FC diet to 5.93 for cows fed the HG diet. Although there were no differences across diets in total VFA concentration, the acetate:propionate decreased linearly with increasing level of whole cottonseed substitution. This may be related to the source of non-fiber carbohydrates (NFC) in the diets. Although diets were balanced to be equivalent in NFC, the source of NFC varied, with the higher cottonseed diets having more NFC from corn as compared with the lower cottonseed and control diets, which had more NFC from alfalfa. Cows fed the diets with ground corn had higher acetate:propionate than cows fed the diets with steam-flaked corn. This is a result of a decrease in acetate concentration and an increase in propionate concentration when steam-flaked corn, the source higher in ruminal available starch, replaced ground corn in the low and medium cottonseed diets.
Ruminating and total chewing activity, expressed as minutes per day, did not differ across diets (Table 3). Similarly, no differences existed among treatments for chewing activity per pound of DMI, per pound of NDF intake, or per pound of intake from fNDF plus cotton NDF, suggesting that NDF from WCS was as effective as NDF from alfalfa silage in maintaining chewing activity in low forage diets. However, total chewing time, expressed as minutes of chewing per pound of fNDF, increased quadratically as the level of cottonseed substitution increased. As fNDF levels decreased below 15% fNDF, cows responded by chewing more efficiently per pound of fNDF intake. This supports the observations by Grant (1997) and suggests that cows may possess an adaptive mechanism that maximizes the efficiency of rumination when NDF is limited (cows chew more per pound of fNDF intake) in order to provide the needed salivary buffers to the rumen. The substitution of steam-flaked corn for ground corn had no significant effect on chewing activity, which suggests that chewing activity is a response that is independent of dietary starch source. Additionally, no corn source times WCS interaction was detected in this study. The NDF from WCS stimulated sufficient chewing activity to produce enough salivary buffers to compensate for the increased acid production associated with ruminal degradation of diets high in starch availability. Consequently, ruminal pH was not affected by the substitution of steam-flaked corn for ground corn in the low and medium WCS diets (Table 2). Cows probably reduced their feed intake in response to the higher ruminal degradability from steam-flaking of corn. Either low pH or increased concentration of protonated fermentative acids can regulate DMI.
Table 3. Least Squares Means for Chewing Response by Cows Fed Control Diet or Diets in Which Whole Cottonseed, Fed with Ground Corn or Steam-Flaked Corn, Replaced Alfalfa Silage on an NDF Basis. |
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|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Diets1 | SE2 | P3 | |||||||||||
| Item | FCG | LG | MG | HG | LSF | MSF | n=5 | n=6 | L | Q | C | Corn | Intx |
| Ruminating | |||||||||||||
| min/d | 514 | 505 | 434 | 520 | 461 | 455 | 44 | 39 | NS | NS | NS | NS | NS |
| min/lb DM intake | 13.3 | 11.9 | 10.0 | 11.7 | 10.9 | 11.1 | 1.1 | 1.0 | 0.14 | 0.14 | NS | NS | NS |
| min/lb NDF intake | 42.9 | 37.4 | 31.4 | 36.9 | 34.9 | 35.2 | 3.7 | 3.3 | 0.12 | 0.12 | NS | NS | NS |
| min/lb fNDF intake4 | 62.1 | 64.9 | 65.1 | 95.4 | 60.0 | 72.3 | 6.7 | 5.9 | <0.01 | 0.04 | NS | NS | NS |
| min/lb fNDF+cNDF intake5 | 62.1 | 56.0 | 47.7 | 56.4 | 51.6 | 52.9 | 5.2 | 4.6 | NS | 0.14 | NS | NS | NS |
| Total chewing | |||||||||||||
| min/d | 785 | 799 | 734 | 805 | 714 | 722 | 53 | 46 | NS | NS | NS | NS | NS |
| min/lb DM intake | 20.3 | 18.8 | 16.8 | 18.0 | 17.0 | 17.6 | 1.3 | 1.1 | 0.10 | NS | NS | NS | NS |
| min/lb NDF intake | 65.4 | 59.2 | 52.7 | 56.8 | 54.2 | 55.8 | 4.5 | 3.9 | 0.09 | NS | NS | NS | NS |
| min/lb fNDF intake4 | 94.7 | 103.1 | 109.0 | 147.1 | 93.4 | 14.4 | 7.8 | 6.9 | <0.01 | 0.05 | NS | NS | NS |
| min/lb fNDF+cNDF intake5 | 94.7 | 88.6 | 80.0 | 86.9 | 80.3 | 83.7 | 6.0 | 5.3 | 0.19 | NS | NS | NS | NS |
| 1 FCG = forage
control with groune corn; LG = low cottonseed with ground corn; MG = medium
cottonseed with ground corn; HG = high cottonseed with ground corn; LSF
= low cottonseed with steam-flaked corn; and MSF = medium cottonseed with
steam-flaked corn. 2 SE = standard error. For the LG treatment, n=5; for all other treatments, n=6. 3 Probability (P) of a treatment response; NS = not significant (P>0.20). Contrasts compared the linear (L), quadratic (Q) and cubic (C) effects of increasing level of whole cottonseed in the diet when ground corn was used aas the corn source. Contrast (Corn) compared the effect of corn source (ground vs. steam-flaked) when low or medium levels of cottonseed were fed. Contrast (Intx) evaluated the interaction of corn source (ground vs. steam-flaked) and level of cottonseed (low vs. medium). 4 fNDF = NDF from forage 5 cNDF = NDF from cotton products (whole cottonseed and cottonseed hulls). |
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Replacing a portion of the dietary fNDF with NDF from WCS did not decrease total chewing activity, expressed as minutes per day, indicating that WCS may be as effective as alfalfa silage at stimulating chewing activity. However, increasing levels of WCS substitution resulted in increased rumination and total chewing activity per pound of fNDF. Therefore, cows appeared to possess an adaptive mechanism that maximizes the efficiency of rumination when fNDF intake is limited. Increasing levels of WCS substitution for alfalfa silage resulted in a quadratic response in milk fat percentage in diets with low starch availability (ground corn). This indicates that WCS was as effective as alfalfa silage at maintaining milk fat percentage in diets containing ground corn and at least 12% fNDF. A WCS times corn source interaction was not detected for any of the criteria evaluated in this study. Even though factors such as the dietary source of NFC may alter apparent effectiveness of WCS, WCS appears to be equally effective in diets for lactating dairy cows that contain moderate or high ruminal starch digestibility. Dietary forage NDF levels may be lower than the NRC guideline of 21% forage NDF when whole cottonseed is used to replace alfalfa silage in diets for lactating dairy cattle. Ruminal fermentability of starch needs to be monitored carefully, and diets with steam-flaked corn probably should have reduced concentrations of starch to prevent reductions in DMI.
Clark, P. W. and L. E. Armentano. 1993. Effectiveness of neutral detergent fiber in whole cottonseed and dried distillers grains compared with alfalfa haylage. J Dairy Sci. 76:2644-2650.
Grant, R. J. 1997. Interactions among forages and nonforage fiber sources. J. Dairy Sci. 80:1438-1446.
Mooney, C. S. and M. S. Allen. 1997. Physical effectiveness of the neutral detergent fiber of whole linted cottonseed relative to that of alfalfa silage at two lengths of cut. J. Dairy Sci. 80:2052-2061.
National Research Council. 1989. Nutrient Requirements of Dairy Cattle. 6th Rev. Ed. Natl. Acad. Sci., Washington, D.C.
1 For more information, contact at: The Ohio State University, 223 Animal Science Building, 2029 Fyffe Road, Columbus, OH 43210; (614) 688-3089, Fax (614) 292-1515; email:firkins.1@osu.edu