Feeding Lactating Dairy Cows Proteins Resistant to Ruminal Degradation I

Sixty multiprious Holstein cows were fed treatment diets from 11 to 40 d postpartum with corn silage as the forage. Treatment diets each contained a different supplemental protein: 1) solvent soybean meal; 2) extruded soy product; 3) combination of corn gluten meal and distillers dried grains with solubles; and 4) a combination of protein sources from diets 2 and 3. Covariate adjusted means for milk (kg/d) and milk fat (%) for treatments 1 through 4 were 37.5, 3.14; 38.5, 3.19; 31.8, 3.45; and 35.2, 3.08. Milk protein content and DM intake were greatest for cows fed diet 1. In a second trial, 105 multiparous Holstein cows 13 d postpartum were placed on 7 t reatment diets for 60 d. Treatments 1 to 5 contained equal amounts of corn silage and alfalfa silage as forage sources and contained either: 1) solvent soybean meal; 2) roasted soybean meal; 3) roasted soybeans; 4) roasted soybeans and urea; or 5) a mixture of corn distillers dried grains and corn gluten meal. Treatments 6 and 7 had alfalfa silage as the forage source and either 6) solvent soybean meal or 7) roasted soybeans as the supplemental protein. Feeding roasted Received June 1, 1987. Accepted March 14, 1988. a Trade names are used in this paper solely to provide specific information. Mention of a trade name does not constitute a warranty of the product by the US Department of Agriculture or an endorsement o f the product to the exclusion of other products n o t mentioned. 2 River Valley Veterinary Clinic, E 5721 County Highway B, Plain, WI 53577. aMiddleton Veterinary Hospital, 2705 West Beltline Highway, Middleton, Wl 53562. soybeans with the alfalfa silage-based diets increased milk 2.0 kg/d, 4% FCM 4.6 kg/d, and fat .23 kg/d when compared with solvent soybean meal. Milk protein production was depressed by feeding a combination of distillers dried grains and corn gluten meal when compared with feeding diets containing soybean sources with the corn silage-alfalfa silage diets. Resistant protein sources may have greater value with diets containing alfalfa silage than with diets containing corn silage. I N T R O D U C T I O N Milk product ion response to feeding of proteins that are relatively resistant to degradation in the rumen has been inconsistent. Mielke and Schingoethe (15) found no difference in milk product ion when soybean meal or extruded soybeans were fed, and Grummer and Clark (11) observed similar milk product ion with feeding soybean meal or heated soybean meal. However, in both studies, CP content of the diet was 13% and corn silage was the forage. This amount of dietary protein in combination with a resistant protein source may have resulted in inadequate ammonia in the rumen. Milk product ion has been increased with feeding of roasted soybeans (19) and heated soybean meal (13). Protein content of these diets was 18 and 17%, respectively. There are several reasons for the variable milk production response to feeding of protected proteins, including stage of lactation, extent of heating of the protein source, forage fed in the diet, protein content of the diet, and protein quality or amino acid content of dietary protein. Dietary protein requirements are greatest during the first 8 wk of lactation; therefore, the greatest response to resistant proteins would be expected during this time. 1988 J Dairy Sci 71:2428-2439 2428 RESISTANT PROTEINS FOR DAIRY COWS 2429 The length of t ime a protein source is heated affects its resistance to microbial breakdown in the rumen. Tagari et al. (26) found dry heating of cottonseeds caused a linear decrease of ammonia concentration as measured in vitro when temperatures increased from 120 to 180°C and as the length of heating increased from 20 to 120 min. Their work further suggests that dry heating for 20 rain at 120°C may enhance protein breakdown. Temperatures above 120°C and times of 40 min or greater reduced ammonia product ion from that of the control. The effectiveness of heat t reatment is influenced by both temperature and duration of heat exposure. Degradation in the rumen of protein in alfalfa silage may be greater than with protein in corn silage (21). Most published work with resistant proteins has been with diets containing corn silage as the only forage. The response to resistant proteins may be different with alfalfa silage. Distillers dried grains (DDG) and corn gluten meal (CGM) are two protein sources that are normally quite resistant to microbial degradation. Forster et al. (9) reported an increase in milk production with feeding of CGM. In contrast, Vandersall and Erdman (27) found a depression in milk production when feeding a combination of DDG and CGM. Lysine may become limiting for synthesis of milk protein when a large port ion of the dietary protein is derived from corn. The objective of this study was to determine the response in yield and composit ion of milk to several resistant supplemental proteins during the first 70 d of lactation. Heated soybean meal and soybeans and a combination of DDG and CGM were the resistant proteins used. Presumably, heated soy products would be good sources of lysine, and corn by-products would be good sources of methionine, the two amino acids most frequently cited as first limiting for 4 The extruded mixture of soybean meal and whole soybeans was supplied by Triple "F", Inc. of Des Moines, IA. This product contained, on an as-is basis, 60% of 44% CP soybean meal, 32% ground whole soybeans, 5% sodium bentonite, 1.5% lignin sulfonate, and 1.5% hemicellulose extract. The product was extruded at 149°C and held following extrusion at approximately 100°C for 90 min in insulated containers. milk production. Two forage sources were included in trial 2 because of potential ly large differences in the quant i ty of lysine and methionine supplied by the forage component of the diet. M A T E R I A L S A N D METHODS