**RESEARCH FEATURE**

Forage NDF Digestibility and Animal Performance -- A Brief Summary of Results

Oba, M., and M. S. Allen. 1999. Evaluation of the importance of the digestibility of neutral detergent fiber from forage: Effects on dry matter intake and milk yield of dairy cows. J. Dairy Sci. 82:589-596.

Approach: Research papers from published studies were used as a database. These papers reported either in vivo, in vitro, or in situ forage NDF digestibility. Variations did exist between papers in the actual digestibility methods used. Thirteen sets of forage comparisons were used. Papers comparing legume and grass forages were excluded from the database.

Results:

If the cow response to changes in in vitro or in situ forage NDF digestibility is assumed to be linear, a one unit increase of in vitro forage NDF digestibility is associated with a 0.37 lb/day increase in dry matter intake, a 0.50 lb/day increase in milk yield, and a 0.55 lb/day increase in 4% fat-corrected milk.

Limitations:

1. In vitro and in situ methods were not standardized across papers utilized for this summary.
2. The relationship between increased NDF digestibility and animal performance may not be linear (i.e., a one unit change in digestibility from 30 to 31 may influence performance differently than a one unit change from 60 to 61).

3. The results of this summary should not be used in comparing legumes with grasses.

Overall Conclusion:

Increased NDF digestibility is linked to improved animal performance. This paper strengthens the need to consider digestibility measurements of forages in some situations. The most logical time to consider this is when the observed animal response is not matching the predicted response. However, the digestibility measurement should be done only after other nutritional and managerial factors have been carefully examined and eliminated as the source of the “problem”.

L. E. Chase

Protein supply to closeup cows revisited

A couple of months ago, we emphasized the need to evaluate protein sufficiency for cows in terms of metabolizable protein and not crude protein in the context of a discussion on the protein requirements for closeup dry cows. Recent reviews have emphasized that the NRC-specified requirement of 12% CP is sufficient for dry cows; however, changes (or lack thereof) in crude protein supply often mean little in terms of metabolizable protein supply to the cow. This is illustrated nicely by evaluation of diets using CPM Dairy from two recent experiments designed to test the effect of prepartum protein supply on transition cow metabolism and performance (Putnam and Varga, 1998; Putnam et al., 1999) and one experiment designed to test the effects of nonfiber carbohydrate supply prepartum on transition cow performance (Minor et al., 1998). All three papers were published in the Journal of Dairy Science.

The experiments designed to test the effects of prepartum protein supply on postpartum performance (Putnam and Varga, 1998; Putnam et al., 1999) delivered substantially more CP (40.4 and 39.0% more than the basal diet) when CP percentage of the rations fed was increased. However, metabolizable protein supply increased only 11.8 and 13.8%, respectively, when the CP content of the rations was increased. Conversely, a small change in CP supply combined with a large change in nonfiber carbohydrate supply resulted in a large change in metabolizable protein supply (Minor et al., 1998). We recommend delivering 1100 to 1200 g/d of metabolizable protein to typical Holstein cows during the closeup period.

T. R. Overton

How Does the CNCPS Model Work on “Real” Farms?

The CNCPS v3.0 model has been used in the field since 1994. A group from the United Kingdom recently reported the results of using this model on 10 dairy herds. The project leaders were Rosemary Mansbridge, Jonathan Blake and Ivor Bending. Rosemary and Jonathan are associated with the ADAS Bridgets Dairy Research Centre. Ivor is a private dairy consultant.

Ten dairy herds with a minimum milk production of 7,500 litres (16,500 lbs) were used. These herds had not previously used the CNCPS model. The herds were monitored for two 28 day periods in late 1997 and early 1998. The UK metabolizable energy (ME) and metabolizable protein (MP) system was also compared. Results were:

1. The CNCPS model predicted DMI across the 10 farms to within 2% of actual.
2. The CNCPS model predicted ME milk within 3% of actual daily production. The CNCPS predicted milk was 70 lbs/day and the actual was 71.7. The UK system overpredicted ME milk by 17%.
4. The CNCPS overpredicted MP milk by 5% while the UK system overpredicted MP milk by 46%.
5. None of the CNCPS predicted values were statistically different from the observed values.
6. The authors want to expand their effort to include more herds and a wider variety of feeding practices.

L. E. Chase

Advanced Dairy Nutrition Course

A limited number of seats are still available for the 1999 Advanced Dairy Nutrition Course at Cornell University from August 16 to 20.

Contact Dee Brothers (dab2@cornell.edu) or Charlie Elrod (cce1@cornell.edu) for reservation information. Our FAX number is 607-255-1335. Make your reservations soon!

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