Effects of dietary crude protein levels during a twelve-week period on late-lactation dairy cow performance

Monday, July 21, 2014
Exhibit Hall AB (Kansas City Convention Center)
Margaret A. Quaassdorff , University of Wisconsin-Madison, Madison, WI
Tiago Barros , University of Wisconsin-Madison, Madison, WI
Jesus J. Olmos Colmenero , University of Guadalajara, Tepatilan, Mexico
Matias J Aguerre , University of Wisconsin-Madison, Madison, WI
Sandra J. Bertics , University of Wisconsin-Madison, Madison, WI
Michel A. Wattiaux , University of Wisconsin-Madison, Madison, WI
Abstract Text:

The objectives were to determine the effects of feeding four dietary CP levels on late-lactation dairy cow performance, and whether there were any treatment by week interactions.  One hundred twenty-eight late-lactation Holstein cows (736 ± 18 kg BW; 224 ± 54 DIM) were used in a 16-pen study with 8 cows per pen, and fed a TMR once per day for 12 weeks (pen = experimental unit).  Treatments which included diets characterized by 11.8, 13.1, 14.6, or 16.2% CP (DM basis) were randomly allocated to pen for the entirety of the experiment.  Rations consisted of approximately 67% forage (half corn silage; half alfalfa silage); and soy hulls (SH) replaced soybean meal (SBM) to achieve the desired dietary CP levels for each treatment.  Pen-level data presented were covariate-adjusted and included DMI, milk yield (MY) and composition (biweekly), BW (final minus initial), and body condition score (BCS); (every 3 wk).  There was no treatment by week interaction for any variables except MY (P<0.01) and true protein % (P<0.01), but there was a linear effect on DMI, MY, true protein %, fat yield (FY) and true protein yield (PY).  No measured variables differed between treatments 14.6 and 16.2% CP except for true protein %.  DMI, MY, FY and PY were lower on treatment 11.8% than other treatments.  There was a quadratic effect (P<0.01) for BW change, with the highest BW gain observed on the 14.6% CP treatment, but there was no difference in BCS.  Results suggest that there was essentially no difference in late-lactation cow performance when diets of 14.6 or 16.2% CP were fed.

                                                        Dietary CP% (DM basis)                                   P-value1

Item 11.8 13.1 14.6 16.2 SEM    L  Q
DM intake, kg/d 22.7b 24.0a 24.0a 24.4a  0.28 <0.01 0.09
Milk, kg/d 25.2c 28.6b 31.0a 31.3a  0.76 <0.01 0.06
Milk composition
  Fat, %   4.35   4.32   4.11   4.27  0.07   0.23 0.24
  True protein, %   3.34c   3.51ab   3.45b   3.57a  0.03 <0.01 0.22
Milk components yield
  Fat, kg/d   1.09b   1.24a   1.28a   1.31a  0.04 <0.01 0.17
  True protein, kg/d   0.82c   0.98b   1.06a   1.12a  0.02 <0.01 0.07
BW change, kg/d   0.07cb   0.37ab   0.44a   0.27ab  0.08   0.10 0.01
BCS2   3.17   3.31   3.28   3.27  0.05   0.15 0.07
a-cLeast squares means within the same row with different superscripts differ (P≤0.05).
1Linear (L) or quadratic (Q) effect of CP% level in the diet.
2BCS on scale of 1 (emaciated) to 5 (obese).

Keywords: soy hulls, soybean meal, protein nutrition