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

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