Department of Dairy Science, Virginia Tech, Blacksburg, VA 24061-0315 U.S.A.

Nutritionists, veterinarians, and dairy farmers have been attempting to relate manure consistency with changes in rations for many years. Feeding different levels and types of fiber, protein, and fat have been suggested as causing changes in manure. Also moisture content of the ration may cause changes in manure of cattle. Mineral content of feeds and rations may have an impact. However, there are few published reports that have compared manure of lactating cows fed different diets. In addition visual observation is usually the way comparisons are made in the field. To address some of these questions, we conducted a study comparing manure from lactating cows fed the following diets (Table 1).

Also we wanted to test the effect of including alfalfa for part of the corn silage. These diets are in Table 2.

In addition to ADF and protein, diets also varied in dry matter content (45 to 59%), neutral detergent fiber (32 to 40% of dry matter), and soluble nitrogen (20 to 63% of total nitrogen), as well as other components not measured.

In Experiment 1, 12 multiparous (101 days in milk and 583 kg body weight) and 18 primiparous Holstein cows (55 days in milk and 468 kg body weight) were blocked and assigned randomly to experimental diets. A total of four 21 day periods were used with a 7 day adjustment and 14 day experimental period for sample collection. Corn silage diets were fed during periods 1 and 4 and alfalfa/corn silage during 2 and 3. In Experiment 2, 6 primiparous Holstein cows (80 days in milk and 1056 lbs. body weight) were randomly assigned to diets in a 6 by 6 Latin square design. The first Latin square evaluated corn silage based diets and a second Latin square was conducted to evaluate alfalfa/ corn silage diets. The Latin squares had 10 day periods with 5 days for adjustment to diets and 5 day collection.

Fecal samples were collected manually by rectal evacuation on 2 days of the experimental period. Samples were scored for visual consistency by each member of a three person panel during sampling. Defecation was simulated by dropping fresh feces from a consistent height of approximately 1 meter to a clean floor for visual observation. To have fresh sample for accurate appraisal, cows were sampled and scored in blocks of five. The following scale was developed for visual scoring:

1 = runny; liquid consistency, splatters on impact, spreads readily

2 = loose; may pile slightly and spreads and splatter moderately on impact and settling

3 = soft; firm but not hard, piles but spreads slightly on impact and settling

4 = dry; hard, dry appearance, original form not distorted on impact and settling

Table 3 contains observations on intake, production, and fecal characteristics from cows fed in Experiment 1.

Notice that lower dietary ADF resulted in more dry matter intake and milk production, but less milk fat. These are all expected responses to a more digestible diet. Fecal score was less for cows fed the 17% ADF diet, however, fecal dry matter was greater. This was unexpected because visually the manure appeared to be more liquid. Fecal NDF, ADF, and pH were less on the 17% ADF rations. Fecal starch was greater on the 17% diet.

Corn silage based diets did result in more intake and milk production. Fat test was not different, but protein test was less on corn silage relative to alfalfa/corn silage mixtures. Fecal dry matter was less on corn silage diets as was fecal ADF and starch. Fecal NDF was greater, however.

 Table 4 shows that only fecal NDF was different when the 15% protein diet was fed compared with the 22% diet. Source of protein, however, did result in fecal score, dry matter, and NDF being different. The 22% protein diet with soybean meal had a lower fecal score and dry matter, but greater NDF. These observations indicated a positive relationship between fecal score and dry matter unlike what was observed when comparing manure from cows fed either 17 or 25% ADF. In Experiment 1 water intake was not monitored. Therefore, Experiment 2 was conducted to determine if intake of water had an impact on fecal score.

Results are similar to Experiment 1 with greater dry matter intake and milk for cows fed 17% ADF, and reduced milk fat. Water intake, free or total, did not differ by fiber level of the diet and can not be used to explain differences in fecal score. Feces from cows fed 17% ADF had a lower visual score, but greater dry matter content, similar to Experiment 1. Also NDF, ADF, and pH were less in feces from cows fed the low fiber diets.

No differences were detected in dry matter intake, milk production, or protein when corn silage based diets were compared to alfalfa/corn silage combinations, unlike Experiment 1. Experiment 2 was of shorter duration, which might explain these observations. Also there were no differences in water intake between forage sources. Manure from cows fed corn silage based diets did have greater NDF and pH, but lower ADF. These fiber relationships were observed in Experiment 1, however, pH was not different in Experiment 1.

Results from Experiment 2 are shown in Table 5.

Table 6 contains information that helps explain why 22% protein diets with soybean meal results in lower fecal scores than 22% with corn gluten meal and 15% with soybean meal. Higher protein diets caused increased water intake, probably in an attempt to dilute excess nitrogen. Also soybean meal supplementation at a high level caused more water consumption than corn gluten meal. This may be related to greater rumen degradability of protein from soybean meal which results in more rumen and blood nitrogen that must be excreted. Fecal score and dry matter appeared to be related in a positive manner similar to comparisons of protein levels and source in Experiment 1.

A digestibility trial was conducted on cows fed diets in Experiment 2. No differences in dry matter, ADF or NDF digestibilities were detected when comparing the 17% to the 25% fiber diet. The 22% protein diets did have greater dry matter digestibilities than the 15% protein diet, but ADF and NDF were not different. Also disappearance of whole corn kernels was measured and results are in Table 7.

Results indicate that between 4097 to 7620 whole corn kernels are consumed per day on corn silage based diets and 3532 to 4873 on alfalfa/corn silage combinations. No statistics were possible on this data. In corn silage based diets 9.5% of the dry matter was whole corn kernels compared with 6.5% on alfalfa/corn silage combinations. Fecal kernel dry matter excreted ranged from 199 to 408 grams/day compared with 55, 162, or 480 grams/day in three experiments by Miller et al. (1969). Whole corn kernels excreted in the feces with corn silage based diets were 18 to 23% of that which was ingested and there did not appear to be an effect of fiber or protein amount or source. Alfalfa/corn silage combinations resulted in 29 to 36% of the diet whole kernels being in the feces. Therefore, there did appear to be greater whole kernel passage on alfalfa/corn silage combinations when expressed as a % of whole kernels ingested. Miller et al. (1969) found only 10% of whole diet kernels in the manure. The size of kernels ingested were .27 to .30 grams of dry matter per kernel compared to .21 to .24 for kernels in the feces. This indicates that smaller kernels were more likely to pass out of the rumen and not be chewed and/or some digestion occurred to the whole kernel during movement through the gastrointestinal tract. Miller et al. (1969) analyzed fecal kernels and found loss of ash and protein.

Results indicate that cows producing more milk and consuming more feed will tend to have feces with lower score. This observation is supported by work of Shellenberger and Kesler (1961). This would be likely because these cows would be consuming a more digestible diet (lower in fiber). More dry matter intake results in greater water intake according to various reports (Holter and Urban, 1992; Murphy et al., 1983), which is similar to our observations of greater free and total water intake. We also observed that cows with lower fecal score had feces with lower pH and fiber. Allen and Beede (1996) speculate that ruminal acidosis can cause increased fluidity of feces because lactic acid in the lumen of the intestine causes an influx of water from the blood. There was no indication that our 17% ADF diet caused acidosis, however. Dry matter intake was not reduced and milk fat was not depressed.

Cows consuming 17% ADF diets had feces that visually appeared to be of more liquid consistency but actually had greater dry matter content. These feces were composed of more nonfibrous components such as starch, and perhaps greater microbial matter because of lower GI tract fermentation. Cows fed the 25% ADF diet had feces with greater visual score, lower dry matter content, and greater fiber. It may be that fibrous material in the feces absorb large quantities of water, but contribute bulkiness and structural appearance of feces. Visual appearance indicates a dryer feces even though dry matter is less because the water is associated with fiber. Feces from cows fed low fiber diets have less fiber. Water intake was similar for cows fed 17 and 25% ADF diets and would not explain the differences seen between the two diets.

Increasing protein in the diet with soybean meal resulted in feces with a lower score and dry matter than using corn gluten meal. Soybean meal is more degradable and would result in more rumen ammonia than corn gluten meal. As a result water might be needed to excrete excess nitrogen via the urine. In Experiment 1, cows consuming the 22% protein diet with soybean meal had 29% of cows with a fecal score of 1, 52% with a score of 2, and 19% with a score of 3 indicating cow variation in fecal score. No fecal score of 4 was recorded for any cow on any diet. Dry cows fed no grain and receiving mostly hay might be expected to have a fecal score of 4.