Production performance of Holstein cows at 4 stages of lactation fed 4 dietary crude protein concentrations

Authors: LETELIER, PAULINA - University Of Wisconsin; Zanton, Geoffrey; WATTIAUX, MICHEL - University Of Wisconsin

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2022
Publication Date: 10/26/2022
Citation: Letelier, P., Zanton, G.I., Wattiaux, M.A. 2022. Production performance of Holstein cows at 4 stages of lactation fed 4 dietary crude protein concentrations. Journal of Dairy Science. 105(12):9581-9596. https://doi.org/10.3168/jds.2022-22146.
DOI: https://doi.org/10.3168/jds.2022-22146

Interpretive Summary: Production performance was evaluated in Holstein cows when fed four crude protein (CP) levels and categorized into four days in milk (DIM) groups. Dry matter intake, milk and component yield, and measures of efficiency were decreased by lower CP and greater DIM. Quadratic responses to CP resulted in the highest intake and production at 16.7% CP. Treatment interactions were observed due to cows responding to dietary CP differently with increasing DIM resulting in different recommended ranges of CP across stages of lactation. Regression analysis indicated that CP ranging from 16.2 to 17.4% would maintain production across most DIM. However, CP could be reduced to between 15.4 and 17.1% when cows progressed to late lactation. By feeding diets formulated using the CP ranges identified in this research, dairy farmers and nutritionist will be able to more precisely meet CP needs of their cows while limiting N excretion into the environment.

Technical Abstract: Dairy cow responses to level of dietary crude protein (CP) may depend on stage of lactation. The primary objective of this study was to evaluate the effects of four levels of CP on dry matter intake (DMI), production performance, net energy for lactation output (NEL), feed efficiency (FE: NEL/DMI), and nitrogen use efficiency (NUE: 100 x milk protein N/N intake) when fed to cows grouped as early, mid-early, mid-late, and late lactation. Our secondary objective was to determine the range of CP at which production responses were not negatively affected across days in milk (DIM). Multiparous Holstein cows (n = 64) were stratified by DIM (initial average ± SD: 86 ± 14.9 (early), 119 ± 10.0 (mid-early), 167 ± 22.2 (mid-late), and 239 ± 11.1 (late)) and then randomly assigned within DIM group to receive one out of four diets containing 13.6, 15.2, 16.7, and 18.3% CP (dry matter basis) according to a 4x4 factorial arrangement of treatments. For 14 d, cows were individually fed a covariate diet followed by 56 d of treatment diets. DMI and milk yield recorded daily and milk components were analyzed for two consecutive days at all three daily milkings for each week of the study. To meet our first objective, data from weeks four and eight of the treatment period were analyzed using a categorical, mixed-effect model to evaluate the main effects of CP, DIM, and their interaction through the use of linear, quadratic, and cubic contrasts. To meet the second objective, a mixed-effect, cubic regression model was fit with DIM and dietary CP levels as continuous independent variables. The optimal range of dietary CP across DIM was determined as the range of CP in which the dependent responses did not differ from the predicted maximum. Treatment differences, regression parameters, and the range responses were considered significant when P < 0.05. With advancing stage of lactation, DMI, NEL, and FE decreased linearly (from 30.4 to 28.4 kg/d for DMI, from 33.2 to 23.3 for NEL, and from 1.09 to 0.82 Mcal NEL/kg DMI for FE for early and late lactation cows, respectively). The responses to dietary CP were linear, quadratic, and cubic with the greatest values observed when cows were fed the 16.7% CP diet (30.8 kg/d, 31.0 Mcal/d, and 1.01 Mcal/kg for DMI, NEL, and FE, respectively). There was a significant interaction between dietary CP and stage of lactation for DMI; NEL; milk fat, protein, and lactose yield; and FE. When feeding the 13.6% CP diet, early lactation cows produced 7.0 Mcal/d more than cows in late lactation (30.4 vs. 23.4 Mcal/d), but when fed 18.3% CP diet early lactation cows produced 14.7 Mcal/d more than cows in late lactation (35.3 vs. 20.6 Mcal/d). Additionally, feeding 18.3% CP diets in late lactation, decreased 7.0 Mcal compared to 16.7% CP diets, indicating that overfeeding dietary CP in late lactation had a negative effect on cow performance. NUE declined linearly with increasing CP and DIM. Regression analysis indicated that CP ranging from 16.2 to 17.4% would maintain production across most DIM. However, CP could be reduced to between 15.4 and 17.1% when cows progressed to late lactation. This research suggested that there are opportunities to reduce CP while still maintaining cow performance.