Abstract #W332

Section: Ruminant Nutrition
Session: Ruminant Nutrition: Dairy III
Format: Poster
Day/Time: Wednesday 7:30 AM–9:30 AM
Location: Gatlin Ballroom

# W332
~~Effect of the starch level in diets with soybean or canola meal on the performance of lactating dairy cows.
Juan I. Sanchez-Durte^*1, Kenneth F. Kalscheur², David P. Casper¹, ¹Dairy Science Department, South Dakota State University, Brookings, SD, ²US Dairy Forage Research Center, USDA, ARS, Madison, WI.

This study was designed to test the impact of reducing corn grain starch with nonforage fiber sources in diets using either soybean meal or canola meal as the primary protein source. Sixteen Holstein cows were assigned to a 4 × 4 Latin square design with 4 periods of 28 d. Treatments were arranged as a 2 × 2 factorial with 2 protein sources [soybean meal (SBM) and canola meal (CM)] and 2 starch levels (21 and 27% of DM). Diets were formulated to contain 16.5% CP and the starch levels were achieved by replacing corn grain with soybean hulls and beet pulp. Protein source × starch interactions (P < 0.05) were observed for DMI, feed efficiency (ECM/DMI), fat %, protein %, protein yield, and MUN. Cows fed the 27% starch diet consumed more DMI than cows fed the CM-21% diet. However, there was no interaction for milk yield, as cows fed 27% starch produced 2.5 kg/d more than cows fed 21% starch. Milk fat percentage was the least for cows fed CM-27% and greatest for cows fed SBM-27% and CM-21%. Milk protein percentage and yield was least for CM-21% compared with the other 3 diets. Milk urea nitrogen was least for cows fed CM-27% compared with the other 3 diets. Cows fed 27% starch produced 1.9 kg/d more energy-corrected milk (ECM) than cows fed 21% starch. Feed efficiency was the greatest for cows fed CM-21% and least for cows fed CM-27%. Overall, lower starch % in SBM or CM diets negatively affected DMI, milk yield, ECM, and milk protein percentage and yield, but not feed efficiency and milk fat percentage and yield. Increasing starch level in canola meal diets decreased milk fat percentage, but potentially improved protein balance because less MUN was observed. Table 1.

Item	SBM			CM		SEM	P > F¹
21%	27%	21%	27%
DMI, kg/d	26.2^ab	26.8^a		24.7^b	27.7^a	0.90	I
Milk, kg/d	36.5	38.5		36.6	39.7	1.30	S
ECM, kg/d	39.8	41.8		40.0	41.8	1.23	S
ECM/DMI	1.53^ab	1.57^ab		1.66^a	1.53^b	0.06	I
Fat, %	4.08^ab	4.14^a		4.21^a	3.86^b	0.16	I
Fat, kg/d	1.49	1.57		1.53	1.51	0.06	NS
Protein, %	3.28^a	3.26^a		3.15^b	3.26^a	0.06	I
Protein, kg/d	1.20^ab	1.24^a		1.15^b	1.28^a	0.04	I
MUN, mg/dL	12.8^a	12.4^a		12.6^a	11.2^b	0.53	I

^abMeans with different letters differ (P < 0.05). ¹S = starch effect; I = protein source by starch effect; NS = no significant.

Key Words: protein, starch, milk production