Impacts of increasing levels of salt on intake, digestion, and rumen fermentation with beef cattle consuming low-quality forages

Abstract

The objectives of this study were to evaluate the levels of supplemental salt on low-quality forage intake, water intake, dry matter digestibility, and rumen fermentation. Six ruminally cannulated, Angus crossbred heifers (14 mo of age; 449 kg ± 24 kg BW) were used in a dual 3 × 3 Latin square design. The heifers were housed in individual stalls with two animals assigned to each treatment per period. Salt treatments were mixed into a protein supplement of 50% cracked corn and 50% soybean meal and fed at 0.3% of shrunk BW. Salt treatments consisted of: 1) control, no salt (CON), 2) 0.05% of BW salt (LOW), and 3) 0.1% of BW salt (HIGH). Chopped, low-quality (CP = 7.4%; NDF = 64.2%), grass hay was used as the base ration and was provided daily at 120% of the average daily intake of the previous 3 days. Each period included a 14-day diet adaptation, 6 days of sample collection, 1 day collection of rumen fluid samples for ruminal and microbial profiles. Individual forage dry matter intake, water intake, and dry matter digestibility were measured during the 6-day collection period. Rumen pH, ammonia levels, and VFA concentrations were measured during the 1-day ruminal profile. Rumen DM and liquid fill were determined with a 5-hour post feeding rumen evacuation. Supplemental salt had no influence on forage intake (P = 0.19) expressed on a kg/day basis yet tended to decrease linearly (P = 0.06) with increasing levels of salt when expressed on a grams/kg body weight basis. Dry matter digestibility was not influenced by salt levels (P > 0.05), but DM fill tended to increase linearly with increasing salt levels (P = 0.06). Water intake and liquid fill, however, increased linearly with increasing level of salt (P < 0.01) with an 18.9% increase in water intake and 17.0% increase in liquid fill compared to control animals. Ruminal pH and ammonia levels both decreased linearly with increasing salt (P < 0.01). Acetate concentration and acetate: propionate ratio increased linearly with increasing levels of salt (P < 0.01). In contrast, isobutyrate and butyrate concentrations decreased linearly with increasing levels of salt (P < 0.01). Our research suggests that increasing levels of salt tends to influence dry matter intake, DM fill, liquid kinetics, and rumen fermentation characteristics. Results from this research provides additional information on how salt-limited supplements may impact beef cattle consuming low-quality forage diets.