| Abstrakt: |
Alternative forage crops (AFC) include cool and warm season grasses and legumes that could be used to overcome periods of limited pasture production. Rumen bacteria and protozoa cell membranes consist of varying proportions of fatty acids (FA) that contribute to milk FA. The objective of this study was to compare the rumen bacterial and protozoal membrane FA compositions from lactating Jersey cows fed pasture strip-tilled with AFC vs. a traditional grass-legume pasture mix. In spring (SPR) and summer (SUM), two separate, 21-d experiments were conducted using 16 lactating Jersey cows (SPR, 85 ± 46 DIM; SUM, 143 ± 58 DIM). Cows were divided into control (CON, n= 8) and treatment (TRT, n= 8) groups, matched by parity, DIM, and milk production, and offered (DM basis) 40% pasture as AFC or traditional and 60% TMR. On a DM basis, SPR TRT pasture consisted of AFC (barley, hairy vetch, triticale, rye, and wheat) representing 2.4% of total diet DM, while the SUM TRT pasture consisted of AFC (buckwheat, chickling vetch, and oats), representing 10% of total diet DM. Individual whole ruminal digesta samples (500 mL) were collected via esophageal intubation on d 20 and 21 of each experiment. Bacterial and protozoal fractions were isolated by differential centrifugation. Microbial FA were analyzed by GLC. Student's ttests (JMP Pro 12) were used to determine if least-squares means differed between groups. Total protozoal and bacterial branched-chain FA, PUFA, as well as trans18:1 isomers and 18:0, the products of rumen bacterial biohydrogenation, did not differ by group in either experiment. In the SPR, bacterial cis-11 18:1 (CON, 0.57 g/100 g FA; TRT, 0.50 g/100 g FA), cis-13 18:1 (CON, 0.44 g/100 g FA; TRT, 0.37 g/100 g FA), and cis-15 18:1 (CON, 0.76 g/100 g FA; TRT = 0.68 g/100 g FA) were less abundant in the TRT than CON group (P< 0.05). Protozoal levels of CLA from SPR TRT (1.13 g/100 g FA) cows were higher than SPR CON (0.85 g/100 g FA). In the SUM, bacterial 17:0 was lower in cows grazing TRT pasture (0.67 g/100 g FA) than CON pasture (0.71 g/100 g FA; P< 0.01). In the SUM, no differences in the protozoal FA compositions were observed. In conclusion, few differences were identified in the microbial FA compositions in cows consuming pasture with or without AFC. |
