Whole citrus fruits as an alternative to wheat grain or citrus pulp in sheep diet: Effect on the evolution of ruminal parameters

Abstract

Five ruminally fistulated Manchega ewes were fed twice daily (0900 and 1500 h) with five experimental diets in a 5 × 5 Latin square design to determine the effect of the diets on ruminal parameters. The diets were control based on wheat grain (0WCF), three diets in which whole citrus fruits (WCF) replaced wheat grain at 13% (13WCF), 26% (26WCF) and 39% (39WCF), and one diet with 26% of citrus pulp (26CP) replacing wheat grain. After 10 days of adaptation, the rumen pH, volatile fatty acids (VFA) and NH 3-N of the experimental animal were measured at 0, 2, 4, 6, 8, 10 and 12 h after the first feeding. The 39WCF diet ingestion was significantly lower than that of the other four diets. Ruminal pH increased linearly with the inclusion of WCF (+0.05 per 10%), although it was similar 2 h after meals, while VFA concentration decreased (−2.31 mmol/l per 10%), especially 4 h after the meals. Ruminal NH 3-N concentration decreased with the inclusion of WCF (−0.61 mmol/l per 10%), especially during the first 5 h as of the first meal. The acetate proportion increased from 0.61 to 0.66 mmol/mmol, while propionate proportion reduced from 0.20 to 0.18 mmol/mol when dietary WCF was increased from 0% to 39%. Also acetate:propionate ratio increased linearly from 3.2 to 4.1, while butyrate proportion decreased linearly from 0.15 to 0.11 mmol/mmol. The concentration of i-butyrate and i-valerate also decreased while that of valerate and caproate increased. Main ruminal parameters for 26WCF and 26CP diets were similar. However, ruminal concentrations of NH 3-N and molar proportion of butyrate and caproate were significantly lower when the animals received the 26CP diet (−1.1, −0.021 and −0.003 mmol/l, respectively). Highly degradable citrus carbohydrates could be used as an alternative to cereal starch to cover the energy requirements of ewes, and did not seem to suppose a risk, as even a higher ruminal pH was maintained throughout the day. The fermentative behaviour of WCF was similar to that of CP, although higher butyrate and NH 3-N production was observed.