Chemical Composition and Nutritive Value of Almond Hulls from Two Almond Varieties and Influence of Including Almond Hulls in the Diet on In Vitro Ruminal Fermentation and Methane Production

Simple Summary Almond hull (AH) is a by-product of almond production that can be used in ruminant feeding, but their composition is variable and needs further characterization. We observed that there were significant differences in chemical composition and nutritional value of samples of AH from two varieties, with AH from Guara variety having more energy and protein than those from Soleta variety in samples collected in two different almond campaigns in the South of Spain. Moreover, harvesting year affected the chemical composition and nutritive value of AH, making necessary their chemical analysis before being used as feed in the practice. In addition, we conducted in vitro trials to investigate the effects of including increasing amounts of AH in diets for dairy ruminants on diet degradability and methane production. Methane is a greenhouse gas with high warming potential that is produced during feed fermentation in the rumen. The results indicate that dried AH can replace up to 16% of conventional feed ingredients in diets for dairy ruminants, but methane production was not reduced. In conclusion, the tested AH can be used as alternative feed for ruminants, although this by-product does not contain antimethanogenic compounds.Abstract Almond hulls (AH) are frequently used in dairy ruminant feeding, but information on variability of their nutritive value and their potential effects on CH4 production is still scarce. The influence of almond variety (Guara vs. Soleta) on chemical composition and energy value of AH was investigated using 10 samples per variety collected in 2 consecutive years. Guara-AH had greater (p <= 0.015) ash, protein, and fat content, but lower (p <= 0.001) fiber than Soleta-AH. The metabolizable energy content estimated from chemical composition and in vitro gas production was 8.5% greater for Guara than for Soleta samples. Harvesting year significantly affected most of the chemical fractions. The in vitro ruminal fermentation of diets for dairy ruminants including increasing amounts of dried AH (8, 16 and 24% of the total diet; fresh matter basis) indicated that AH can be included up to 16% of the diet, partially substituting corn, wheat bran and sugar beet pulp without detrimental effects on in vitro volatile fatty acid (VFA) production. In contrast, when AH replaced alfalfa hay and corn, VFA production was reduced at all levels of AH inclusion. No antimethanogenic effects of AH were detected in the in vitro incubations.