Effects of dietary n-3 polyunsaturated fatty acids and ... - FINS

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1 st WorkshopXIII International Feed Technology Symposiumeffective fiber-peNDF in diet and proper physical form of forages stimulate increasing ofchewing activity, provide proper ruminal function and feed conversion, and eliminateappearance of milk fat depression and metabolic diseases (Stojanović et al. 2002).EFFECTS OF FORAGE CHEMICAL QUALITY IN DAIRY COWSNUTRITIONMeeting the energy and protein requirements of high-yielding lactating cows, depends ofquantity and feed efficiency of consumed dietary dry matter and organic matter. Besideschemical composition, main parameter that influence on nutritional value and quality offorages is digestibility of DM, OM and some nutrients (Grubić et al. 1996).The most important fact for nutritive value of grasses and legumes is stage of maturity atthe moment of cutting (Đorđević and Dinić, 2007). With the maturing, the proportion oflives is being reduced, and proportion of steams with greater structural fiber content isbeing increased in the total yield. This causes decreasing of energy and protein content,increasing of fiber content and percentage of lignin, which is indigestible andinaccessible for animals (Grubić et al. 1995). Grasses is characterized with higherproportion of cell walls, and slower ruminal digestion of this material, than legumes,where is found that structural polysaccharides in cell walls have higher rate of digestionin rumen. Although with slower digestion, fiber from grass is more digestible andutilizable for dairy cows, according to lesser degree of lignification. Legumes arecharacterized with higher proportion of cell content (Van Soest, 1994).It is found decreasing yield of 4 % FCM, with using first cutting grass-legume or alfalfahay in diets for lactating dairy cows, with lesser quality because of cutting in later stageof maturity. There were no effects of second cutting alfalfa hay with different quality onyield of 4 % FCM (Waldern and Baird, 1967). The largest differences in dry matterdigestibility of hay cut in different stages of plant maturity appear for first cutting hay,and are less for later cutting. Different nutritional value of grass hay cut at differentstages of plant maturity did not have effect on milk production of dairy cows in earlylactation, fed diets with high proportion of concentrate (Steacy et al. 1983). There wereno effects of rations for dairy cows in early lactation with two different quality of alfalfahay: early cut alfalfa (21 days interval, prebloom stage) and normal cut alfalfa (30 daysinterval, 10 % bloom stage) on DM intake and daily milk production, until the content ofmilk protein was higher (3.2 and 3.1 %) for cows fed ration with early cut alfalfa hay,and percentage of milk fat was higher (3.5 and 3.9 %) for cows on ration with later cutalfalfa hay (DePeters and Smith, 1986). Miller et al.(1991) report decreasing of DMintake (9.1 %), average daily gain (9.5-20.9 %), and content of NE for maintains (10.2%), in diets for young fattening cattle with alfalfa hay (chopped and pelleted) preparedafter cut of alfalfa in full bloom stage (36 days of vegetation), compared with alfalfa hayafter cut at prebloom stage (25 days of vegetation). Using an alfalfa hay prepared afterearly cut (21 days of vegetation), instead of later cut alfalfa hay (30 days of vegetation),in diets for dairy cows in 2. phase of lactation, and dried cows, increases digestibility of:DM (67.4 and 61.5 %), energy (67.5 and 60.4 %), N (74.6 and 71.6 %), NDF (45.1 and30.5 %), and ADF (44.1 and 31.0 %), (Llano and DePeters, 1985).Merchen and Satter (1983) report increasing of lactic acid proportion and decreasing ofacetic acid proportion in total acid content, as the least expressed decreasing (increasing219
1 st WorkshopXIII International Feed Technology Symposiumwas found) of DM amino acids content, decreasing of soluble N, increasing ofpercentage of N insoluble in acid detergent (ADIN) in total N content, for ensiling wiltedalfalfa (40 and 66 % of DM content), comparing with ensiling a fresh material with 29 %of DM. Better intake and total digestibility of OM is also found, as increasing ofproportion of total digestible OM that is digested in the intestine, and decreasing of partof digestible OM that is fermented in rumen (probably as a result of depression ofprotein digestibility), for dairy cows in early lactation. In this study, increasing contentof ruminally undegraded N, decreasing concentration of ammonium N in rumen, andincreasing of flow of nonammonium N in duodenum is determined.Table 1. Ruminal characteristics of some nutrients for lactating dairy cows fed alfalfahaylage or hay (Merchen and Satter 1983)ItemDry matter, %29 40 66HayIntake of OM, kg/day 16.3 18.5 17.6 16.5NH 3 - N in rumen, mg/100 ml 21.2 22.7 10.0 15.0Digestibility of OM, % 69.8 73.6 71.5 68.7Proportion of digestible OM (%), that is digested in:Rumen 70.9 69.7 57.9 65.2Intestines 23.2 23.4 32.1 27.9Colon 5.8 6.8 9.9 6.9Flow of nonammonium N in duodenum, g/day 326 393 463 324Flow of bacterial N in duodenum, g/day 257 314 287 229Flow of dietary and endogen N in duodenum, g/day 69 80 176 95Significant increasing of daily milk and milk protein yield as a result of using feeds thatare sources of ruminally undegraded protein in the diets for lactating cows based onalfalfa haylage, points to limited duodenal flow of protein, with this kind of rations. Thisis more distinct for rations with alfalfa haylage as main forage compared with rationsbased on alfalfa hay (Broderick et al. 2002). Higher proportion of alfalfa haylage in dietsfor lactating dairy cows often is connected with increased concentration of dietary crudeprotein and increased content of rumen degradable protein. Comprehensive conversionof protein into NPN, during the ensiling process results with intensive releasing of NH 3in rumen. Increased content of ruminally available energy in diet is significant forgreater efficiency of utilizing of rumen degradable protein from alfalfa haylage, andsynthesis of microbial protein (Đorđević et al. 2001). Greater content of ground highmoisture corn grain in diets for lactating cows, increases synthesis and duodenal flow ofmicrobial protein, as also a milk protein yield, to a greater extent for cows fed diets withalfalfa haylage (170 and 337 g/day, respective) then for cows on diets with alfalfa hay(100 and 100 g/day, respective), (Vagnoni and Broderick, 1997). Amount of protein,more accurate protein absorbed in intestine, and not energy, is main limiting factor indiets for dairy cows in the first half of lactation, based on high level of alfalfa haylage(Dhiman et al. 1993). There were no effects of replacing chopped alfalfa hay with alfalfahaylage in diets for dairy cows in late lactation, on DM intake, ruminal pH, ruminalconcentration of volatile fatty acids, milk fat and protein, serum concentration of lactate,220
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