Bulgarian Journal of Agricultural Science
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COMPARISON OF DIFFERENT DIETARY PROTEIN SOURCES FOR DAIRY COWS
E. Yildiz, N. Todorov, K. Nedelkov
Abstract: The aim of the experiment is to compare sunflower meal (SFM), as a protein source in rations of lactating dairy cows to rape seed meal, canola type (RSM), dry distillers grain with solubles (DDGS) from maize, and soybean meal (SBM). Twenty four multiparous Holstein cows averaging 51±19 days in milk at the start of the experiment and 603±48 kg body weight were randomly assigned in 4x4 Latin square design trials. Each period lasted 21 days. Weeks 1 and 2 were used for adjustment and week 3 for data collection. Diets for each period and treatment group consisted of 4.3 kg alfalfa hay and 22 kg maize silage (31% DM), and 12.2 kg compound feed. All ingredients were mixed and provided to the cows as total mixed rations (TMR). TMR contained 17.1% crude protein in dry matter, with 47 to 58% coming from 4 tested supplementary protein sources. During each period, the
cows were offered 1 of 4 compound feeds containing: 1) 39% SFM, 2) 46.6% RSM, 3) 62% DDGS, and 4) 32% SBM. By adding sunflower hulls to diets with SBM, RSM and DDGS, and maize germ as source of fat to those with SFM, RSM and SBM all rations were equalized by net energy concentration, crude fiber and fat in dry matter. Therefore, the different protein source was the only main difference between the 4 diets. Dry matter intake tended to increase for diets with DDGS and SBM as protein supplement. Milk production was significantly lower for cows receiving SFM with diet (30.1 kg/day), compared to diets with SBM (33.2 kg/day) (P<0.05) and tended to be lower than in cows fed rations with RSM and DDGS. There were no significant differences (P>0.05) between SBM, RSM and DDGS as a protein sources. Milk protein yield per day was 1.08, 1.05, 1.04 and 0.96 for cows receiving diets with SBM, RSM, DDGS and SFM respectively, and respective percentages of milk protein were 3.24, 3.22, 3.19 and 3.18 (P>0.05). Fractions of true protein, casein and whey protein from total protein did not differ significantly. There was a tendency for lower true protein and casein content in milk of cows receiving diet with SFM. Non-protein nitrogen in milk from SFM diet was significantly higher, than in other diets. There were no significant differences in yield of fat, and milk fat percentage in cows receiving diets with 4 different protein feeds. Production of energy corrected milk from intake of one kilogram dry matter was the lowest in cows fed SFM diet (1.54 kg) (P<0.05), followed by DDGS (1.63 kg), RSM diets (1.67 kg), and SBM (1.69 kg). Less true protein in milk (P<0.05) was produced from 1 kg crude protein in ration with SFM compared to other rations. However, utilization of protein digestible in intestine for milk true protein production did not differ significantly between
the four rations. Milk produced from cows fed ration with SBM had a farm gate price which was by 15 to 23% higher than those of milk produced by the other three rations. The cheapest milk was from the DDGS diet, followed by RSM and SFM.
Keywords: dairy cows; dry distillers grain; milk composition; milk yield; protein sources; rape seed meal; soybean meal; sunflower meal
Date published: 2017-09-11
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