Progress 10/01/01 to 09/30/07
Studies under this project concerned N and P excretion in dairy cows. The excretion of N was reduced when dietary protein was reduced from 19.2 to 15.7% for cows producing 38 kg/d of milk. Likewise, P excretion was reduced when dietary P was reduced from 0.42-0.44 to 0.0.33-0.37% (18% average reduction). Adjusting dietary P did not appear to be necessary when the forage portion of the diet was varied from 48 to 58% based on milk production and P excretion. However, substitution of soyhulls for alfalfa hay in the diet reduced fecal P excretion, partially through increased P apparent digestibility, suggesting that using readily digestible fiber sources in the diet may allow further reductions in dietary P. A study also was conducted to look at the partitioning of P and N when dairy manure was separated into liquids and solids, and results showed that the majority of the manure P and N were associated with separated liquids.
Protein at 17% of the diet based on alfalfa and corn silage as the forage source appeared to be sufficient for medium to high producing cows. Dietary P at 0.37% can meet the requirement for most of the cows. Formulating diets with these levels of protein and phosphorus can contribute to the control of the excretion of these nutrients and their environmental impact. Manure management to remove phosphorus and nitrogen should be focused on the liquid portion in manure separation systems.
- No publications reported this period
Progress 01/01/05 to 12/31/05
A study was conducted to evaluate the partitioning of P and N when dairy manure was processed with a screw press manure separator. An eight hundred cow dairy was selected to conduct the study. All dairy manure was processed through the separator. The mass balance was calculated by measuring displaced volume in the influent pit over a set time of separation, weighing the separated solids over that same time period and using the difference between these two to calculate effluent volume. Samples of manure for all three fractions, influent manure, separated solids and effluent liquid were collected on 7 different occasions. Preliminary data show that the majority of the P (85%) and N (75%) in manure was associated with the liquid portion of the manure. Spot evaluation of the settled sludge on the bottom of the lagoon showed higher P content than that of the liquid effluent (1.43% vs 1.08%). Future plans are to evaluate the amount of soluble P contained within each
Liquid manure is low in total solids and presents difficulties in transporting and applying as fertilizer. By removing the coarse solids, liquid manure can be more readily adapted to spray irrigation thus eliminating considerable machinery cost. Since fine solids contain a large portion of the P in manures, allowing them to settle after separation would result in more of the P being removed from the liquid portion. The realization that most of the nutrients follow the liquid stream allows for researchers to concentrate on methods to extract excessive P from the liquid or develop a method to extract more of the P into the separated solids during the separation process. Either of these possible processes would make the liquid manure a more balanced fertilizer. This information will be useful for farmers who may be planning to install manure separation equipment.
- Tallam, S.K., Ealy, A.D., Bryan, K.A. and Wu, Z. 2005. Ovarian activity and reproductive performance of dairy cows fed different amounts of phosphorus. Journal of Dairy Science. 88:3609-3618.
- Wu, Z. 2005. Utilization of phosphorus in lactating cows fed varying amounts of phosphorus and sources of fiber. Journal of Dairy Science 88:2850-2859.
Progress 01/01/04 to 12/31/04
A study was conducted to determine the effect of dietary P content and forage source on fecal P excretion. Four dietary treatments were formed in a 2 x 2 factorial arrangement. The P content was 0.33 or 0.44%, and the forage source was varied by substituting 10% soyhulls for 6% alfalfa hay (dry matter basis). Diets also contained approximately 50% corn silage and alfalfa silage for all treatments. The diets were fed to 32 early to mid lactation Holsteins for 10 weeks. Milk yield of the cows was high, averaging 43 kg/d during treatment. However, cows fed the low P diets produced 1.8 kg/d less milk than those fed the high P diets on average, associated with 1.5 kg/d less dry matter intake. Milk fat content was also lower for cows fed the low-P diets (3.72 vs. 4.20%). The P intake averaged 84 and 125 g/d for cows fed the low and high P diets, respectively, compared to the estimated requirement of 97 g/d based on the 2001 NRC for this level of production. The substitution
of soyhulls for alfalfa hay did not affect feed intake, milk production, or milk composition.
A previous study showed that dietary P can be reduced to the 2001 NRC levels without being adjusted according to the forage proportion of the diet. When the analysis of P excretion is completed, this study will provide information on whether the dietary P needs to be adjusted when the forage source is changed. The information will be useful for farmers as they make strategic nutrient management plans.
- Lopez, H., Wu, Z., Satter, L. D. and Wiltbank, M. C. 2004. Effect of dietary phosphorus concentration on estrous behavior of lactating dairy cows. Theriogenology. 61:437-445.
Progress 01/01/03 to 12/31/03
A fourth experiment was completed as the final trial of a study designed to determine the response of lactating dairy cows to the protein content of the diet using various proportions of alfalfa and corn silage. Alfalfa silage and corn silage were used at a ratio of 75 : 25 in this trial. The three trials completed earlier used alfalfa to corn silage ratios of 100 : 0, 50 : 50, and 25 : 75. In all experiments, the two forage sources contributed 50% of the diet. Diets used in all experiments were formulated to contain 15.00, 16.25, 17.50, or 18.75% CP, obtained by varying the amount of soybean products in the diets. Each of the experiments used 16 Holsteins in mid lactation in a replicated 4 x 4 Latin square design with 3-wk periods (2-wk adjustment followed by 1-wk collection). Results showed similar trends in milk production and N excretion in response to the protein content of the diet for all experiments. Averaged from all experiments, N intake was 636, 692, 733,
and 733 g/d, milk yield 35.5, 35.6, 35.7, 36.3 kg/d, and N excretion 492, 558, 610, and 678 g/d for the 15.00, 16.25, 17.50, and 18.75% CP dietary treatments, respectively. Overall, increasing the protein content of the diet from 15.00 to 18.75% resulted in a 38% increase in N excretion. Among trials, milk yield was higher when corn silage constituted a larger proportion of the forage, averaging 32.7, 35.9, 36.1, and 38.7 kg/d for 100:0, 75:25, 50:50, and 25:75 alfalfa to corn silage ratios, respectively.
Reducing the protein content of the diet and adjusting the alfalfa and corn silage mix can result in reductions in N excretions.
- Groff, E. B. and Wu, Z. 2003. Lactation performance of dairy cows fed different amounts of protein. J. Dairy Sci. 86(Suppl. 1):277.(Abstr.)
Progress 01/01/02 to 12/31/02
The response of lactating dairy cows to dietary protein amount under various alfalfa to corn silage programs was determined. Three trials were conducted using 100 : 0, 50 : 50, or 25 : 75 alfalfa to corn silage ratios. Each trial used 16 Holsteins (117 plus or minus 33 DIM) in a replicated 4 x 4 Latin square design with 3-wk periods (2-wk adjustment followed by 1-wk collection). All diets consisted of 50 : 50 forage : concentrate and were formulated to contain 15.00, 16.25, 17.50, or 18.75% CP. The difference in protein was obtained by varying the amount of soybean products in the diets. Increasing dietary protein did not affect milk yield, but increased fecal N and urinary N concentrations. The efficiency of N utilization was reduced . The averages for the three trials ranged from 2.88 to 3.01% for fecal N, from 6.04 to 7.14 g/l for urinary N, and from 0.30 to 0.24 for the conversion of intake N to milk N, as dietary protein was increased from 15.00 to 18.75%. Across
trials, cows yielded more milk when corn silage constituted more of the forage (averaging 32.0, 36.5, and 39.1 kg/d for 100:0, 50:50, and 25:75 alfalfa to corn silage ratios, respectively).
Reducing the protein content of the diet and adjusting the alfalfa and corn silage mix can result in reductions in N excretions. Such management practices should also result in the optimum economical returns
- Groff, E.B, and Wu, Z. 2002. Minimum dietary protein required for lactating dairy cows fed different amounts of alfalfa and corn silage. J. Dairy Sci. 85(Suppl. 1):73.(Abstr.).