期刊
JOURNAL OF DAIRY SCIENCE
卷 99, 期 8, 页码 6334-6341出版社
ELSEVIER SCIENCE INC
DOI: 10.3168/jds.2016-11032
关键词
lipid; biohydrogenation; starch degradability; continuous cultures
Excessive levels of starch in diets for lactating dairy cattle is a known risk factor for milk fat depression, but little is known about how this risk is affected by differences in rates of starch degradability (K-d) in the rumen. The objective of this study was to compare accumulation of biohydrogenation intermediates causing milk fat depression, including conjugated linoleic acid (CLA), when corn with low or high K-d were fed to continuous cultures. Diets contained (dry matter basis) 50% forage (alfalfa pellets and grass hay) and 50% concentrate, with either no added fat (LF) or 3.3% added soybean oil (HF). Within both the LF and HF diets, 3 starch degradability treatments were obtained by varying the ratio of processed (heat and pressure treatments) and unprocessed corn sources, giving a total of 6 dietary treatments. Each diet was fed to dual-flow continuous fermenters 3 times a day at 0800, 1600, and 2400 h. Diets were fed for four 10-d periods, with 7 d for adaptation and 3 d for sample collection. Orthogonal contrasts were used in the GLIMMIX procedure of SAS to test the effects of fat, starch degradability, and their interaction. Acetate and acetate: propionate were lower for HF than for LF but daily production of trans-10 18:1 and trans-10, cis-12 CLA were higher for HF than for LF. Increasing starch K-d from low to high increased culture pH, acetate, and valerate but decreased butyrate and isobutyrate. Changes in biohydrogenation intermediates (expressed as % of total isomers) from low to high starch K-d included reductions in trans-11 18:1 and cis-9, trans-11 CLA but increases in trans-10 18:1 and trans-10, cis-12 CLA. The results show that increasing the starch K-d in continuous cultures while holding starch level constant causes elevation of biohydrogenation intermediates linked to milk fat depression.
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